text:
This action might not be possible to undo. Are you sure you want to continue?
Improving Motor and Drive System Performance:
A Sourcebook for Industry
Improving Motor and Drive System Performance: A Sourcebook for Industry was developed for the U.S. Department of Energy's (DOE) Industrial Technologies Program (ITP). This project is one in a series of sourcebooks on industrial systems. Other publications in this series cover fan, compressed air, process heating, pumping, and steam systems. For more information about DOE and ITP, please see Section 4, "Where to Find Help." This sourcebook was prepared for ITP by technical staff at Lawrence Berkeley National Laboratory and Resource Dynamics Corporation. They wish to thank the many organizations that so generously assisted in data collection and to acknowledge the helpful reviews and other contributions provided by the following individuals: Dale Basso, Rockwell Automation Thomas Bishop, Electrical Apparatus Service Association Austin Bonnett, Electrical Apparatus Service Association Rob Boteler, U.S. Electrical Motors Dennis Bowns, Bowns & Co. Don Casada, Diagnostic Solutions Jasper Fischer, Industrial Motor Repair John Kueck, Oak Ridge National Laboratory John Machelor, Motor-Vations, LLC John Malinowski, Baldor Electric Co. Ilene Mason, Consortium for Energy Efficiency Gil McCoy, Washington State Energy Office Sally McInerney, University of Alabama Cynthia Nyberg, Electrical Apparatus Service Association Howard W. Penrose, Ph.D., SUCCESS by Design Reliability Services Charles Straub, P.E., Marathon Electric Edward J. Swann, Rockwell Automation John Tolbert, Bristol Compressor Chuck Yung, Electrical Apparatus Service Association September 2008 Prepared for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Industrial Technologies Program By Lawrence Berkeley National Laboratory Berkeley, California Resource Dynamics Corporation McLean, Virginia Produced by the National Renewable Energy Laboratory Golden, Colorado
Table of Contents
i 1 3 3 3 4 4 8 10 11 14 15 16 17 17 17 39 39 39 39 40 40 44 45 49 50 60 61 63 67 99 105 111
Acknowledgements Quick Start Guide Section 1: Motor and Drive System Basics Overview A System Approach Indications of Poor System Design Types of Electric Motors Motor Operating Characteristics Load Characteristics Matching Motors and Drives to Their Applications Load Duty Cycles Common Motor Selection Problems Summary Section 2: Performance Opportunity Roadmap Overview Efficiency Opportunities Section 3: Motor System Economics Overview Understanding Corporate Policies Measuring the Dollar Impact of Efficiency Presenting the Finances of Efficiency Relating Efficiency to Corporate Priorities Summary Section 4: Where to Find Help Directory of Contacts Resources and Tools Training Courses Appendices Appendix A: Glossary of Basic Motor System Terms Appendix B: Motor Tip Sheets Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Appendix D: Motor Repair Service Center Checklist Appendix E: Guidelines for Comments
Continued >
Figure 15. Figure 5. Figure 7. Figure 16. Figure 9. Figure 11.List of Figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 10. 23 27 29 43 . Figure 17. Figure 18. Figure 8. Figure 14. Table 2. Figure 12. Table 4. 4 6 6 8 10 11 11 12 13 15 15 18 26 27 27 34 45 46 List of Tables Table 1. Figure 6. Table 3. Figure 13.
A systems approach is emphasized. It also describes key factors involved in motor and drive selection and system design. Guidance is provided in a set of efficiency opportunities. It is not meant to be a comprehensive technical text on motor and drive systems. This is one of several important benefits of efficiency improvements. and others whose work involves motor and drive systems will find this sourcebook helpful in assessing the efficiency of their motor and drive applications. and provides an overview of the different types of motors and drives and their applications. Plant engineers. a plant project that increases the overall efficiency of a motor and drive system often reduces plant downtime. and controlling their operation might want to skip this section and go on to the next one. this section briefly describes important terms. rather than a focus on individual components. Improving Motor and Drive System Performance: A Sourcebook for Industry 1 . as well. designing systems. including life-cycle costs and payback periods. facility managers. relationships. as outlined below. Discussions of improvement opportunities in this sourcebook emphasize the connection between operating efficiency and system reliability. software. This sourcebook is divided into four main sections. and training opportunities. and clarifying the financial aspects of efficiency improvements. and system design considerations. Readers who are already familiar with key terms and parameters used in selecting motors and drives. rather.Quick Start Guide Quick Start Guide This sourcebook is designed to provide those who use motor and drive systems with a reference that outlines opportunities to improve system performance. Topics include understanding and identifying corporate priorities. videos. tools. This section also lists helpful resources for more information. For example. n Section 2: Performance Opportunity Roadmap This section describes the key components of a motor and drive system as well as opportunities for performance improvements. relating those priorities to efficiency. n Section 4: Where to Find Help Section 4 provides a directory of associations and other organizations associated with motors and drives and their markets. n Section 1: Motor and Drive System Basics For readers who are unfamiliar with the basics of motor and drive systems or would like a refresher. it provides practical guidelines and information to make readers aware of potential performance improvements. operations personnel. which cover the following topics in separate subsections for easy reference: • • • • • • • Assessing Motor and Drive System Operating Conditions Establishing a Motor Management Program Providing Basic Maintenance Selecting the Right Motor Using Variable Frequency Drives Addressing In-Plant Electrical Distribution and Power Quality Issues Using the Service Center Evaluation Guide n Section 3: Motor System Economics This section provides recommendations on how to propose projects like those described in Section 2 by highlighting for management the favorable economics of motor and drive system improvements. Guidance on how to find more information and assistance is also included.
• Appendix D includes a checklist for motor repair facilities. Department of Energy (DOE). . Developed by the U. along with National Electrical Manufacturers Association (NEMA) Premium® motor efficiency levels. but in less detail than the efficiency opportunities described in Section 2. these tip sheets discuss opportunities for improving the efficiency and performance of motor systems.S. • Appendix E provides guidelines for submitting suggested changes and improvements to the sourcebook. • Appendix B contains a series of motor and drive system tip sheets. • Appendix C provides Energy Policy Act (EPAct) efficiency levels for motors up to 200 horsepower (hp) in size. these terms appear in bold type when they are first mentioned in the text.n Appendices This sourcebook contains five appendices: • Appendix A is a glossary of terms used in discussing motor and drive systems.
an inefficient motor and drive system often increases maintenance costs. reliable. in the process industries.15. and valves. Industrial plants can avoid unnecessary increases in energy consumption. from looking for one piece of Improving Motor and Drive System Performance: A Sourcebook for Industry 3 . and costs. The pump was specified according to the requirements of this flow condition. Despite these advantages. Other avoidable losses include waste heat and flow energy that dissipates without performing useful work. To optimize system performance. electric motors account for roughly 60% of electricity consumption. and the production rate. sizing a motor so that it is larger than necessary—essentially giving it a safety factor—ensures that the motor is strong enough to meet the needs of the application. equipment that can meet worst-case needs to evaluating whether components can be configured to maintain high performance over the entire range of operating conditions. For example. For example. To handle the need for variable flow rates. Focusing on systems means expanding possibilities. by selecting motors that are well suited to their applications and making sure that they are well maintained. In industrial applications. suppose that a motor-driven pump supplies water to several heat exchangers and has a flow requirement that the system piping and heat exchangers were designed to handle. For example. Operators can sometimes be so focused on the immediate demands of their equipment that they overlook the ways in which the system's parameters are affecting that equipment. structures. An advantage of this approach is that it simplifies problems. in a pumping system. make up the single largest end use of electricity in the United States. many fan systems have variable air delivery requirements. an oversized motor can compromise the reliability of both the components and the entire system. taken together. When systems do not operate efficiently. the system is equipped with valves and bypass lines. In certain circumstances. excess flow energy must be dissipated across throttle valves or through bypass valves. such as torque) above full load at which a motor can operate without causing a failure under certain conditions. the lack of a drive to control the motor's speed (and thus airflow) can cause system operating costs to be significantly higher than necessary. actual operating conditions can vary according to the season. A common practice is to size the fan so that it meets the highest expected load and use dampers to restrict airflow during periods of low demand. Similarly. A common engineering approach is to break a system down into its basic components or modules. In a systems approach. A systems approach analyzes both the supply and demand sides of the system and how they interact. one of the least efficient methods of controlling flow is to use dampers. dampers. but wasteful if it is not. Common service factor values are 1. environmental conditions. the engineer evaluates the entire system to determine how end-use requirements can be provided most effectively and efficiently. In a component approach. the time of day. However. long-lasting service. Motor and drive system loads often vary according to cyclical production demands. and so on. especially in turbomachinery such as fans or pumps. and then assemble the system. This equipment can be useful if it is properly applied. and most require comparatively little maintenance. changes in customer requirements. essentially shifting the focus from individual components to total system performance. Electric motors provide efficient. the engineer must configure the system to avoid inefficiencies and energy losses. Additional system stresses can accelerate wear and create loads for which the system was not originally designed. optimize the selection or design of those components. A disadvantage is that this approach ignores the interaction of the components. In addition to increasing energy costs.10 and 1. The service factor is a multiplier that indicates the percentage of horsepower (or other nameplate rating. or it must be absorbed A System Approach Cost-effective operation and maintenance of a motor and drive system requires attention not just to individual pieces of equipment but to the system as a whole. Consequently. For example. However. electric motors account for more than 70% of electricity use. maintenance. however. an oversized motor can create performance problems with the driven equipment. motors that typically run at more than one-half to full load usually operate much more efficiently than they do at less than one-half load or into their service factor. the stress on the system caused by energy losses must be dissipated by piping. although the system provides adequate airflow.Section 1: Motor and Drive System Basics Section 1: Motor and Drive System Basics Overview Electric motors. However. the engineer employs a particular design condition to specify a component. they can be inefficient and costly to operate if they are not properly selected and maintained. A basic premise of a systems approach is that industrial systems usually do not operate under one condition all the time.
In addition. Common indications include abrupt or frequent system starts and stops.Section 1: Motor and Drive System Basics by the piping and support structure. Since energy losses in fluid flow often dissipate as noise. several operating constraints on these motors limit their widespread use in industrial applications. Repairing or replacing this equipment can be costly. all of this equipment can degrade more easily. Types of motors DC Motors Series Wound Shunt Wound Compound Wound Specialty Motors Switched Reluctance Permanent Magnet 4 Improving Motor and Drive System Performance: A Sourcebook for Industry . As a result. system designers often specify oversized motor and drive and end-use equipment in order to improve AC Motors reliability. The most common types of industrial motors are shown in Figure 1. An oversized motor might be more reliable. In many material handling systems. and air-conditioning (HVAC) system. or simply operating the equipment. Alternating current (ac) motors can be single-phase or polyphase. systems with large flow losses tend to be loud. single-phase motors are the most common type. This added heat usually must be removed by the facility's heating. High noise levels can be the result of flow noise. the need for frequent maintenance. In terms of quantity. structural vibrations. further increasing total operating costs. Throttle and bypass valves can require seat repair. In addition. Electric motors fall into two classes. and poor system performance—can be corrected. it is essential to understand the various types of motors and their operating characteristics. The banging that often accompanies sudden accelerations and decelerations is symptomatic of stress on the motor and drive system. However. In addition. inefficient equipment operation often greatly increases the temperature of the workspace. The primary causes of increased maintenance requirements are the added stresses on the system and the increased heat that accompanies inefficient operation. High noise levels are common in inefficient fluid systems. Integral single-phase High Energy Costs High energy costs can be the result of inefficient system design as well as inefficient motor operation. such as voltage sags. Figure 1. mainly because many small motors are used for residential and commercial applications in which single-phase power is readily available. n Poor System Performance Operating a motor and drive system that was not properly selected for its application can result in poor overall system performance. A more effective way Introduction Synchronous of ensuring high reliability is to design a system and specify system Wound Rotor components so that the system's operating efficiency is high over the Squirrel Cage full range of operating conditions. The consequences of this stress can be more frequent maintenance and poor operating efficiency. ventilating. Ironically. high noise levels. inefficient system operation in an industrial plant can create poor working conditions. especially if the added heat load was not included in the design specifications for the HVAC system. Poor system performance is a major cause of increases in maintenance and decreases in reliability. such as high levels of noise and excessive heat. Indications of Poor System Design Taking a component-based approach to industrial system design and operation tends to increase facility costs and maintenance requirements and reduce reliability. inefficient systems often add heat to the workplace. Excessive noise can fatigue workers more quickly and thus reduce productivity. Not selecting or designing a proper motor and drive system for the application can also lead to power quality problems. and low power factor. but it might Single Phases Polyphase also make other parts of the system less reliable. the work-in-process moves roughly from one work station to the next. harmonics. based on the power supply: alternating current (ac) or direct current (dc). n Frequent Maintenance Equipment that is not properly matched to the requirements of the application tends to need more maintenance. However. the problems associated with a poorly designed system—high energy costs. and piping and support structures can develop cracks and leak as a result of fatigue loads. and hot work environments. as indicated below. n Types of Electric Motors To ensure that motors are applied properly.
using PM motors Direct Current Motors Direct current (dc) power was central to Thomas Edison's vision of how electricity should be supplied. and this permits relatively accurate control of the motor speed. This relationship is true until the magnetic strength of the motor is reached. And they use electromagnetic force (EMF) sensing to determine rotor position and perform the commutation function. dc power has advantages in certain industrial applications and is still widely used. In terms of energy consumption and efficiency improvement opportunities. The advantages of dc motors include excellent speed control and the ability to provide high torque at low speeds. Compound Motor. dc motors have an advantage in applications in which the motor is supplied by a dc bus as part of an uninterruptible power system.Section 1: Motor and Drive System Basics induction motors tend to pull large starting currents relative to the motor's size. PM motors can maintain relatively high efficiencies at low motor loads and. they can also increase maintenance requirements. As brushes wear. a condition known as saturation. Despite the predominance of three-phase ac motors. A compound motor is a combination of a series and a shunt wound motor. Improving Motor and Drive System Performance: A Sourcebook for Industry 5 . one circuit wraps around the stator. Series wound. In contrast. torque increases in proportion to the square of the increase in current. PM motors can be up to 600 hp in size. they create a housekeeping problem by generating carbon dust. Brush assemblies not only require a larger motor. The differences between these motors are based on how the stator (field frame) and the rotor (armature) are connected. especially in applications with wide variations in load and speed. the rotor and the stator circuits are connected in parallel. Therefore. such as motor generator sets or rectifier systems. polyphase motors are used widely in industrial applications. A key operating characteristic of this type of motor is that it can handle sudden increases in loads without a great change in speed. shunt wound. ECMs do not exhibit the brush wear and noise associated with typical dc motors. In general. It has two basic circuit branches. shunt wound. Brushes are also sensitive to contamination. They can be constructed in several different ways. Series Motor. However. Although these applications are somewhat specialized. and the other is a series circuit that includes both the stator and the rotor. additional equipment that generates dc power. The torque and speed of these motors is relatively independent of the load. is needed to run dc machines. they operate less efficiently than three-phase motors of comparable size. however. any load increase is directly proportional to an increase in current. they can provide high torque at low motor speeds. Permanent magnet (PM) motors rely on inherently magnetic materials—such as alloys of cobalt. as the name implies. adjusting the stator circuit resistance controls the strength of the magnetic field. Because of their competitive advantages. and titanium—to create a magnetic field. the stator and the rotor are connected in series and the same current passes through both. Because of their design. PM motors have certain performance advantages over ac induction motors. They consume more than half of all the electricity used in industry. and permanent magnet. iron. However. like other dc motors. a majority of dc motors use brushes to transfer electrical power to the motor armature. ac power and ac motors soon became the industry favorite. n There are four principal classes of dc motors: series wound. nickel. and compound wound motors all require brushes to supply current to the stator. Since they do not require brushes. Beyond saturation. Permanent Magnet. In a series motor. In this configuration. Polyphase motors can be found in almost every industrial process. most industrial PM motors are brushless dc types. compound wound. and they must be replaced periodically. Shunt Motor. they are the main focus of this sourcebook. An electronically commutated motor (ECM) is a type of brushless dc motor having speed and torque control. they could increase as industry becomes more sensitive to power quality problems and more aware of the high cost of interruptions in production. Consequently. In a shunt motor. ECMs can use single-phase ac input power and convert it into three-phase operation. Since electric power is supplied as alternating current. three-phase motor systems predominate. Because batteries supply dc current. The effectiveness and low cost of three-phase motors are major reasons why three-phase power is used so widely in industry. These motors can achieve high efficiencies with favorable torque and current characteristics. especially in machines that contain silicone materials. and they often operate continuously to support production processes. and are not available in larger sizes. and some versions operate with ac power.
Advances in PM motor technology have made this type competitive with the more commonly used induction motor/variable frequency drive combination. forming a circuit with very little resistance. the rotors of induction motors are not physically connected to any external circuits. the slip also increases. Synchronous motors operate without slip at synchronous speed. A typical induction motor is shown in Figure 2. With the exception of wound rotor motors that have slip rings. Squirrel cage rotor 6 Improving Motor and Drive System Performance: A Sourcebook for Industry . Induction motor Courtesy of Leeson Electric Corporation Squirrel Cage Motors. the field in a four-pole motor rotates at 1800 rpm. have some useful advantages and are used in more specialized applications. Fan Cover (Hood) Fan Frame Stator (Windings) Bearings Bracket (End Bell) Alternating current (ac) motors are the most widely used in industry. in a 60 Hz system. in many applications. An important operating difference between induction motors and synchronous motors is that induction motors operate at somewhat less than synchronous speed. Industry's preference for ac motors springs from their simplicity. and efficiency. The most common type of industrial motor is the squirrel cage induction motor. Synchronous motors. The difference between the actual speed and synchronous speed is known as slip. End Rings Rotor Bars Figure 3.Section 1: Motor and Drive System Basics avoids many of the operating and maintenance problems normally associated with dc motors. Induction motors rely on a magnetic field to transfer electromagnetic energy to the rotor. low cost. instead. Induction motors are used widely because of their simple design. even when the motor is idle. the stator field in a two-pole motor rotates at 3600 rpm. The name derives from the similarity between the rotor and the type of wire wheel commonly found in pet cages at the time this motor was first developed (see Figure 3). and characteristically long operating life. and it is determined by the following equation: Synchronous speed = 120 x frequency (Hz) number of poles For example. The induced currents in the rotor create a magnetic field that Conduit Box Cover Conduit Box Rotor Motor Shaft Seal Figure 2. As the load on the motor increases. the stator circuit creates a magnetic field that rotates at a synchronous speed. The speed of the rotor's magnetic field is slightly less than that of the stator (this difference is the slip). This speed depends on the number of poles and the frequency of the electricity supply. and the field in a six-pole motor rotates at 1200 rpm. There are two primary types of ac motors: induction (also referred to as asynchronous) and synchronous. In both types of motors. Rotor bars are either welded or cast to two circular end rings. A drawback of PM motors is their tendency to accumulate magnetic contaminants. Induction motors include squirrel cage and wound rotor types. the excitation current is induced by a magnetic field. rugged construction. on the other hand. n Alternating Current Motors interacts with the stator field. the excitation current is fed directly to the rotor by means of brushes or slip rings. relatively low cost. Induction Motors. In synchronous rotors.
Selecting the Right Motor. Despite the many advantages of these motor systems. the performance of SR motors is largely a function of the power electronics that control the sequencing of pole energizations. which makes them attractive to many industrial facilities. For more on these motor classifications. the cost of the power modules often offsets the lower cost of the SR motor itself. the disadvantages of SR motors included torque ripple (pole-to-pole variations in torque) and higher operating noise. Characteristics of this type of motor include the following: • • • • • • Excellent speed control High starting torque Low starting current Ability to handle high-inertia loads (induction motor slip losses would be too large and could overheat rotors) Ability to handle frequent starts and stops Ability to operate at reduced speeds for long periods. 4. Important advantages of SR motors include exceptional feedback and flexibility in speed and torque control. operate at the same speed as the rotating magnetic field. the rotor needs a separate squirrel cage winding during starts. however. just to increase a facility's power factor. However. In wound rotors. often generating four-phase power. In newer models. increasing their applicability. efficiency. SR motors do not have magnets or rotor windings. They can also add a leading power factor component to a distribution system. Adopting better operating practices or incorporating better controls into existing induction motor systems incurs less risk and can result in the same levels of efficiency and performance that new motor technologies exhibit. and slip rates. Later developments in power electronics improved their performance and lowered their costs. In the past. Another type of induction motor is the wound rotor. the most common type of industrial motor is still the squirrel cage induction type. These classifications help engineers and designers select the right motors for applications that require certain starting torques. SR motors operate much like an electromagnetic coil. Consequently. operating torques. SR motors have characteristically high power-to-weight ratios and are well suited for vehicle applications. as their name implies. In this type. either bars are inserted into the rotor or wires are wound into slots in the rotor. brushless excitation systems and permanent magnet generators are built into the rotor. These motors. Their torque and speed control characteristics also make them suitable for pump and fan applications in which power is highly sensitive to operating speed. and cost advantages that should encourage their use in an increasing number of applications. the squirrel cage winding becomes inoperative. see Efficiency Opportunity No. they can be 1% to 2% more efficient—depending on motor size—than induction motors. But Improving Motor and Drive System Performance: A Sourcebook for Industry 7 . create a magnetic field that pulls the nearest pole on the rotor toward it. but limitations in power electronics technology made this type of motor impractical. Since motors are indispensable to plant operations. Improvements in power electronics have made both PM and SR motors and similar systems much more suitable for many applications. when energized. current is induced in the rotor and the resistance of the rotor circuit is varied by adding or removing external resistance to control torque and speed. improvements have been made in these areas. Although they are more expensive to purchase and maintain. SR motor technology was initially developed in the 19th century. in Section 2 of this sourcebook. Since the dc current does not change the polarity. Switched Reluctance Motors. In fact. Since squirrel cage induction motors can be designed and built to have a relatively wide range of torque and slip characteristics. as synchronous condensers. an external supply of dc power is usually supplied to the rotor by a set of slip rings or brushes. as the dc current is applied. The modules are relatively specialized. The stator contains poles that. NEMA has developed a set of classifications for these motors. synchronous motors are occasionally operated without a load. Wound Rotor Motors. facilities tend to resist using a new motor technology if the current system is performing adequately.Section 1: Motor and Drive System Basics Advantages of this type of motor include the following: • Low cost • Low maintenance • High reliability • A fairly wide range of torque and slip characteristics. the rotor speed is pulled into synchronicity with the rotating magnetic field created by the stator. Their simple. In industrial synchronous motors. An important operating characteristic of these motors is the ability to adjust speed and torque characteristics by controlling the amount of resistance in the rotor circuit. rugged design also provides higher reliability. once the rotor approaches operating speed. Synchronous Motors. Switched reluctance (SR) motors have several performance.
the motor's horsepower should ensure that the motor not operate below 40% of full load for long periods (see Figure 4). cost-effective operation. hydraulic couplings. Addressing InPlant Electrical Distribution and Power Quality Issues. and over or undervoltage. These devices include gears. 4. 36:1. The speed of an electric motor is an important element that depends on many factors.252 Percent Efficiency 100 95 100 hp 50 hp 90 Motor performance depends on how well these operating characteristics match the load. the strength of the magnetic field. and operating costs (including costs for power factor correction). however. Bonnet. and torque. Jan. in some cases. The responsiveness of the motor in starting and operating is critical and should be considered concurrently with its horsepower. Common synchronous speeds are 3600. this type of problem is not common. For more on this. the facility's distribution system should be reviewed. in Section 2 of this sourcebook. Many applications require speeds different from these. Fig. operating speed (measured in revolutions per minute [rpm]). A mismatch between the motor voltage and the system voltage can result in severe operating problems and. and 600 rpm. including poor motor operation. See Efficiency Opportunity No. Synchronous ac motors operate at the speed of the rotating magnetic field. A facility that experiences wide swings in voltage will probably have an abundance of power quality problems. The operating speed of an ac motor depends on the rotor type. n 70 0 Percent Rated Load 25 50 75 100 Figure 4. depending on the motor's slip characteristics. 2000) Engineers should be careful not to oversize a motor just to satisfy a speed or torque requirement. etc. most induction motors operate within 1% to 3% of this speed. 1800. problems like these are often the result of a distribution system problem. immediate failure. IEEE Trans. The load on a motor is not always constant. 900. Motor torque and speed are important additional considerations in determining a motor's ability to operate effectively and efficiently. And. However. n 85 80 Voltages 75 The motor voltage must match the rated system supply voltage. the frequency of the power supply. n Speed Horsepower The horsepower rating of the motor should be able to support the power requirements of the load without being oversized. variable frequency drives (VFDs). such as three-phase voltage unbalance. Selecting the Right Motor. voltage outages. These are related by the following equation: Hp = torque (ft-lb) x rpm 5. eddy-current couplings.Section 1: Motor and Drive System Basics Motor Operating Characteristics The most important motor operating characteristics are horsepower. In other words. and the load. If that is the case. 6. and slip characteristics. sags. and the response of the motor to changes in load is a fundamental factor in selecting the right motor for an application. Operating a motor when the system voltage varies significantly from its rated level is a more critical concern. Typical motor part load efficiency curve (Adapted from A. in Section 2 of this sourcebook. The operating speed of a dc motor depends on the type of motor. surges. maintenance. 1200. A systems approach to motor selection is an effective way of ensuring adequate. so motors are usually combined with various types of speed adjustment devices. Motors can also operate at multiple speeds by using separate 8 Improving Motor and Drive System Performance: A Sourcebook for Industry . see Efficiency Opportunity No. Motor performance is significantly affected when a motor operates at voltages +/–10% or more from its rated voltage. belts. the number of poles. 26. Oversized motors tend to incur higher purchase.
An important consideration is whether the speed must be constant or variable. and a fundamental factor in motor performance. 5. Variable speed applications can be served by multiple-speed motors or drive systems with adjustable speed ratios. Another speed control option is to use an ac motor with an intermediate drive device that allows adjustable speed ratios. Motors with different sets of windings are used in many cooling system applications so they can operate at different speeds. and require additional maintenance. Floor space is valuable. lines are controlled by energizing and de-energizing a series of motors. In general. In eddy current couplings. and high maintenance costs. speed control is often a more efficient and cost-effective option for many systems. Multiple-speed motors are another speed control option. Eddy current and hydraulic couplings allow varying degrees of slip between the driver and the driven equipment to achieve the desired output speed. Drawbacks to these devices include relatively low efficiency compared to that of other speed control devices. but they can be built to run at three or four speeds. The torque capacity of a motor depends on many design characteristics. high-torque applications. the slip is controlled by adjusting the strength of the magnetic field in the coupling. Misapplying VFDs to inservice motors can quickly cause motor failures. and multiplespeed motors are space savers. one for each speed. not all in-service induction motors can be combined with a VFD. gears or belts can provide fixed speed ratios between the motor and the driven equipment. a pump similar to the one used in automobile transmissions allows fluid to recirculate rather than perform mechanical work. in Section 2 of the sourcebook. These motors are usually two-speed. Using Variable Frequency Drives. and low maintenance requirements. Some ac motors can also be used in speed adjustment situations. Although dc motors still have some operating advantages in low-speed. See Efficiency Opportunity No. Many applications that are currently served by constant speed motors are well suited for variable speed motors. the added complexity associated with operating and maintaining a dc motor system is an important factor behind the increasing numbers of induction motor/VFD systems. in many multiple-speed motors. First. However. In hydraulic couplings. Moreover. in many material handling systems. Wound rotor motors can have speed ratios of as much as 20:1 by changing the resistance in the rotor circuit. The speed adjustments of dc motors can be as much as 20:1. These frequent starts and shutdowns are tough on motors and line components because of repeated stresses from starting currents and acceleration and deceleration of mechanical components. these motors are less efficient because of the effects of the additional windings. For example. or bypass methods. such as throttle valves or dampers. reliability. engineers should evaluate motors case-by-case to see if such combinations are feasible. and these must be considered in any assessment associated with changes in speed. dc motors have excellent speed and torque control characteristics and are often used when high torque at low speeds is required. Multiple-Speed Motors. Induction motors are widely used in industrial applications because of their inherent advantages in terms of cost. For example. availability. Similarly. in many conveyor systems. some motor-driven machines have speed-dependent lubrication systems. and they can operate at 5% to 7% of the motor's base speed (some can even operate at 0 rpm). Another common method of controlling speed is to use induction motors combined with VFDs.Section 1: Motor and Drive System Basics windings within the same motor or by using a single winding with an external switch that changes the number of poles. in many pumping system and fan system applications. adjustable speed drives can increase system efficiency and improve system reliability. In constant speed applications. a single winding can be controlled with a starter that allows the winding to be reconfigured into different speeds (with a ratio of only 2:1). For example. Using variable speed drives can smooth out line motion for more efficient and effective operation. Improving Motor and Drive System Performance: A Sourcebook for Industry 9 . flow is controlled by using restrictive devices. discrete speeds using two principal approaches. Some motors have inherent speed control capabilities. Ac motors can be built to operate at different. they can be constructed with multiple windings. Although these flow control methods have advantages. Combining an in-service motor with a VFD provides facilities with an effective speed control technology that does not require the use of a different type of motor. Mechanics and operators are usually familiar with these motors. Induction motors with VFDs are increasingly being used in applications that once featured dc motors. Second. Adjustable Speed Motors. which facilitate repair and maintenance tasks. A principal advantage of multiple-speed motors is their ability to operate at different speeds using a compact motor/ drive assembly. n Torque Torque is the rotational force that a motor applies to its driven equipment. Alternative speed control options often take up space savers.
the torque is independent of speed. the torque increases with decreasing speed and vice versa. For example. rpm Pressurefinal = pressureinitial Powerfinal = powerinitial rpmfinal rpmfinal rpmfinal 10 Improving Motor and Drive System Performance: A Sourcebook for Industry . This torque value is important because. For example. A good example of this type of load is a winding machine in which the torque increases as the roll thickness builds up but the rotational speed slows down. Load inertia refers to the resistance of the load to changes in speed. Common applications include conveyor systems. even if a motor has sufficient horsepower. in centrifugal pumps and fans. If the load exceeds this torque. torque is constant. however. conveying a 500-pound load along an assembly line requires the same amount of torque whether it is moving at a constant speed of 5 feet per minute or 10 feet per minute. Full Load Torque Percent of Full Load Torque 250 Breakdown Torque 200 Locked Rotor Torque (also Startup Torque) 150 Pull-Up Torque 100 50 0 25 50 75 100 Percent of Synchronous Speed A cyclic load is one in which the torque changes significantly within a cycle or over a series of cycles. the motor will stall.Section 1: Motor and Drive System Basics Figure 5 shows a torque curve for a typical induction motor. and cranes. Full-load torque is the torque produced by the motor at rated horsepower. and it is the same torque generated during locked rotor and stall conditions. Affinity Laws Flowfinal = flowinitial rpmfinal rpmfinal rpmfinal Load Characteristics There are four basic types of loads: • • • • Variable torque Constant torque Constant horsepower Cyclic loads. Figure 5. some air compressors and refrigeration system compressors have cyclic load characteristics. Although horsepower varies according to speed. Load inertia is commonly referred to by the term Wk2. the downstroke of the pump piston requires much less force than the upstroke. Typical motor speed torque curve Pull-up torque is the minimum torque that the electric motor develops when it runs from zero to full-load speed (before it reaches the breakdown torque point). An example is an oil well pump. Motors sometimes exceed full-load torque during changes in the load. The most common type of load has variable torque characteristics. causing it to rapidly overheat and risking insulation failure if it is not properly protected. it could overheat before reaching operating speed if it cannot accelerate the load from rest. Applications that have high load inertia tend to require high starting torques. hoists. they tend to shut down and start up in response to system pressures. In a constant torque load. In a constant horsepower load. torque varies according to the square of speed. such as punch presses. Starting torque is the instantaneous torque developed by the motor when it is first energized. Examples of loads with high inertia are large fans and machines with flywheels. Breakdown torque is the maximum torque that the motor can generate without an abrupt drop in speed. sustained operation above full load can reduce the operating life of a motor. Machine tools such as lathes and cutting machines display these operating characteristics. in which horsepower and torque are proportional to speed. in this application. Also. The ratio of load inertia to motor torque has a strong effect on the responsiveness of the motor system to changes in the load.
so maintenance requirements. doubling the speed of the machine requires eight times more power. the importance of operating flexibility. environmental conditions. and reliability requirements. Opening the throttle valve drops the pressure. For example. and power. centrifugal pumps and fans share some common relationships between speed (commonly measured in rpm). Additional examples of this relationship are shown in Figures 7 and 8. and compressors. About 60% of the energy consumed by industrial motor-driven applications is used to drive pumps. Energy losses in a pump system when a throttle valve controls flow Improving Motor and Drive System Performance: A Sourcebook for Industry 11 . the engineer needs to consider the basic requirements of the service. The throttle valve increases the pressure in the pipe and takes pump performance to point A on the original performance curve. these are known as affinity laws (see sidebar on page 10). Reducing the pump's speed with an adjustable speed Total Head (ft) 200 Original Performance Curve 160 Point A 120 Performance Curve After Reducing Pump Speed Throttled System Curve Original System Curve 0 50 100 150 200 Significant Distance in Power Point B 80 40 Desired Flow Rate 250 300 Flow (gpm) Figure 6. These include the load profile. it does so with much less horsepower. the pump operates much more efficiently. The pump performance curve shown in Figure 6 illustrates the relationship between power and speed. There is no longer a large pressure drop across the throttle valve. pressure. Note how the amount of power that the pump uses is dramatically reduced by slowing its rotational speed. assume a 19 energy unit loss) 80 61 34 100 99 93 Remaining Energy Units Begin with 100 Energy Units End with 34 Energy Units Figure 7. decreasing the speed of a fan or pump removes a significant load from the motor. Energy Losses 19 1 13 13 61 Transformer Motor Pump Throttle Valve (partially closed. To achieve the desired operating flow with a fixed-speed pump. Within these applications. At point B. a throttle valve is used to control flow. Effect of speed reduction on the power used by a pump drive (ASD) takes the pump to operating point B. fans. and system vibration are reduced.Section 1: Motor and Drive System Basics Matching Motor and Drives to Their Applications To select the proper motor for a particular application. The operating point is the intersection between the system curve and the pump's performance curve. thus saving energy. One important implication of these laws is that power consumption is highly sensitive to operating speed. Increasing the speed of a fan or a pump requires a relatively large increase in the power required to drive it. Similarly. flow. system noise. Although operating point B provides the same desired flow rate.
In addition. System designers and engineers need to understand specific system operating conditions to size a centrifugal pump correctly. they are not suitable for all applications. and pumps coupled to ASDs. Oversizing can increase operating costs as a result of increased energy and maintenance requirements and reduce system reliability because of added stresses on the system. VFDs are by far the most commonly used adjustable speed option. the system does the same work with only 80 energy units. A useful tool for evaluating potential pumping system improvements is the Pumping System Assessment Tool (PSAT). the PSAT software helps the user evaluate pumping systems in order to determine the best improvement opportunities. 100 energy units are supplied to the system. primarily because they are low in cost. these methods provide adequate and efficient flow control. n drawbacks. In pumping systems. When they are incorporated properly into a system. Energy losses in a pump system when an adjustable speed drive controls flow Replacing a control valve with an ASD can increase system efficiency and provide significant energy savings. in Figure 8. however.gov/industry/bestpractices. particularly those in which pumps operate against high static (or elevation) head. much less energy is lost across the throttle valve because the pump generates less flow. potential capacity expansions. Pumps Centrifugal pumps are the type most commonly used. multiple-speed pumps. Each flow control method has advantages and 12 Improving Motor and Drive System Performance: A Sourcebook for Industry . eere. A screening process identifies pump applications that are worth investigating further. Flow control options include throttle valves. However. and easy to maintain. improper design or use can increase system costs significantly. Many engineers tend to be conservative in estimating system requirements. Although installing VFDs can result in substantial energy savings. and system fouling. Pumping systems also frequently operate inefficiently because of poor flow control practices. and they often increase the size of the centrifugal pump and motor to accommodate design uncertainties. ASDs help to match the flow energy delivered to the system to the system's actual need. bypass valves. and PSAT prompts the user to acquire data for further analysis. With the ASD. depending on the particular application. simple to operate.S. For more information on the PSAT and on properly matching pumps to system requirements. Reducing the pump speed proportionally reduces the flow while exponentially reducing the power requirement.Section 1: Motor and Drive System Basics Energy Losses 0 1 3 6 10 27 Transformer VFD Motor Pump Throttle Valve (Full open. reliable. see Improving Pumping System Performance: A Sourcebook for Industry. However.energy. Developed with the support of the U. which is available on the ITP Web site at www. this approach often leads to oversized pump/motor assemblies. Note that in Figure 7. Department of Energy Industrial Technologies Program (ITP) and available at no charge to users. multiple pump configurations. assume no losses) 61 61 34 80 79 77 71 Remaining Energy Units Begin with 80 Energy Units End with 34 Energy Units Figure 8. they have relatively long operating lives.
oversized fans increase operating costs and can cause problems that are similar to those caused by oversized pumps. Although alternative flow control measures. Some energy-saving measures that are useful with certain centrifugal pump and fan systems. this is true only in certain applications. and positive displacement blowers—the relationship between flow and power is different from that of pumps and fans. often specifying a larger fan than the system requires. in some cases. motors with a higher service factor are used. These differences have several implications with respect to motors. much like a propeller. efficient. and then prompts the user to acquire data for additional analysis. in some cases. There are two principal types of air compressors: positive displacement and dynamic.energy. Centrifugal fans use a rotating impeller to accelerate air outward. Developed with the support of ITP and available for download on the ITP Web site. such as dampers and inlet vanes. applying paints and coatings. An important exception to this guideline is vaneaxial fans. A useful tool for evaluating potential fan system improvements is the Fan System Assessment Tool (FSAT). Axial fans move air along the axis of a fan. Most compressors make use of standard polyphase induction motors. and cleaning and drying parts.Section 1: Motor and Drive System Basics Because required airflow rates often change according to the temperature. such as a VFD.000 18. and they provide power to compressors economically. However.000 Fan Curve System Curve Flow Rate (cfm) Figure 9. based on the way that they impart flow energy to the airstream: axial fans and centrifugal fans. A screening process identifies fan applications that are worth investigating further. such as rotary screw compressors with variable loads. and they often have high load inertia. often the most efficient option is to use a speed-control mechanism. reliably. Axial fans usually operate at higher speeds and. Since these motor speeds are usually too high for direct drives. More information on FSAT and fan systems can be found in Improving Fan System Performance: A Sourcebook for Industry. however. particularly with respect to compressed air systems. can also save energy with these other systems. and they also require more maintenance. belt drives are usually used to establish the desired fan speed. Electric motors are widely available. and usually equipped with small fan blades to minimize the stresses caused by high rotating speeds. which translates into an increase in pressure.000 14. many large fans can be equipped with suitable soft-start devices that avoid the stresses of across-the-line starts. These fans are compact. and boiler load. can be effective. fans frequently experience varying demand. It is used for such applications as driving hand tools. In certain cases. Fans can be grouped into two fundamental classifications. many common design and operating practices tend to reduce system efficiencies. and efficiently. VFDs often have inherent softstart capabilities that can limit starting currents. Centrifugal fans tend to be heavier. to adjust the fan's output. Positive displacement compressors are more commonly used than dynamic ones. occupancy. FSAT software helps the user evaluate fan systems in order to determine the best improvement opportunities. Most fans are driven by induction motors that operate at 3600. This high load inertia can affect a plant's electrical distribution system. Oversized fans are often noisier than they should be. and 1200 rpm. n Static Pressure (wg) 28 24 20 16 12 8 4 0 2000 6000 10. Fan system designers also tend to be conservative. Typical fan and system curves n Fans Fan performance curves (Figure 9) show that flow varies with pressure.eere.gov/ industry/bestpractices. such as ASDs. More information on fan systems can be found in Improving Fan System Performance: A Sourcebook for Industry. This acceleration increases the kinetic energy of the airstream. production level. Air Compressors Compressed air is important to most industrial facilities. they are directly coupled to the motor. positive displacement pumps. especially when the fans are started. supplying pneumatic control systems. However. In other types of equipment—such as air compressors. 1800. However. In addition. which is available on the ITP Web site at www. the engineer can specify an energy-efficient or premium efficiency motor when a plant is purchasing a Improving Motor and Drive System Performance: A Sourcebook for Industry 13 .
can create highly variable load duty cycles. By evaluating different operating schedules and control strategies. applications in which normal operating loads are much smaller than the worstcase load often force the motor to operate at part-load much of the time. and evaluating the savings and effectiveness of energy efficiency measures. as well as downtime on nights and weekends. and modifying motor and drive systems tends to reduce operating costs and increase system reliability. Accommodating these wide fluctuations in demand is a principal challenge of compressed air system design. When replacing a drive motor in a compressor that uses a VFD as part of the control system. can lead to power factor penalties.gov/industry/bestpractices. Using VFD options to control output is becoming more common. AIRMaster+ can help you determine how best to improve a compressed air system. These applications often have unique load characteristics. it is important to pay careful attention to performance parameters such as full-load speed and torque. however. throttling the input.eere. This software tool was developed to help users simulate existing system operation and test potential modifications. One place to start is to evaluate the load duty cycle of system components. including modeling existing and future system upgrades. using a load/unload mechanism. A useful tool for assessing improvement opportunities in compressed air systems is AIRMaster+. Changes in shifts and production levels. The incremental cost of a premium efficiency motor is usually recovered in a very short time because of the resulting energy savings. The load duty cycles for such motors would show a peak number of operating hours at low load levels. Also. so they are somewhat difficult to describe in general terms. part-load operation of a motor usually results in a low power factor. if not corrected. AIRMaster+ is available for download on the ITP Web site. which is available on the ITP Web site at www. see Improving Compressed Air System Performance: A Sourcebook for Industry. The consequences of operating a motor at these load levels include poor power factor and low efficiency. The rotary screw air compressor is the type most widely used. make sure the motor is designed to be used with inverters. sponsored by ITP. mixed. using a systems approach in designing. which. A variable displacement control strategy changes the output of the compressor by controlling the displacement volume. A load/unload control strategy uses a valve or some other pressure-relieving device to reduce the load on the compressor so that it continues to operate. Despite all of these differences. 14 Improving Motor and Drive System Performance: A Sourcebook for Industry . most control systems still change flow demand by either starting and stopping the air compressor. material processing loads largely depend on the nature of the material being moved. The replacement motor's performance should be as close as possible to that of the original motor. Since motors are often specified according to worst-case operating conditions. or sifted. employing a variable displacement device. Load Duty Cycles The term load duty cycle refers to the amount of time that equipment operates at various loads relative to its rated capacity. AirMaster+ provides comprehensive information on assessing compressed air systems. This approach stresses the importance of evaluating how different system components interact and how different control or sizing options can keep the components operating efficiently. operating. Frequently starting and stopping large ac motors can result in power quality problems for the electrical distribution system and can cause motors to run at high temperatures. and operating priorities vary widely in each of those two categories.energy. found that more than 40% of the motors in industrial applications operate at or below 40% of their load rating. The United States Industrial Electric Motor Systems Market Opportunities Assessment. This problem is actually relatively common. In addition. For more information on compressed air applications. An example of a load duty cycle is shown in Figure 10. or using some other means of operating the compressor at partload. For most compressed air systems.Section 1: Motor and Drive System Basics compressor or replacement motor. When replacing a standard motor with a premium efficiency one. For example. demand varies widely from day to day. chopped. These output control options for motor and drive systems can result in frequent starts and shutdowns and motors operating at low loads. n Other Applications Motors and drives are also used in a wide range of material handling and material processing services. these applications may be either batch-type or continuous.
the motor described in Figure 10 operates near full load about 15% of the time. creating a time difference between the motor's peak voltage and its peak current. Common Motor Selection Problems Electric motors are relatively inefficient when they are operated at very light loads. n Percent of Operating Hours 45 40 35 30 25 20 15 10 5 0 20 40 60 80 100 Poor Power Factor Percent of Motor Full Load Figure 10. This practice and the tendency of engineers who assemble the system to be conservative can lead to the selection of a motor that operates far below its rated capacity. save energy. The vector difference between real power and the product of volts and amps is known as reactive power. Improvement opportunities can include replacing the motor with one of a more appropriate size or type. In many applications. problems such as voltage unbalance that require motor derating. n Oversized Motors Engineers frequently specify motors that are larger than needed to meet system requirements in order to ensure that the existing motor/drive assembly can support anticipated increases in capacity. there are often many excellent opportunities to optimize the entire system. This is especially applicable in seasonal industries that experience peak loads only a few times each year. Real Power (kW) Real Power (kW) Power Factor App are nt Pow er ( kVA ) Figure 11. In many motors. and improve reliability by making various improvements. For example.Section 1: Motor and Drive System Basics When motors operate frequently at low loads and over a wide range of conditions. or installing a speed-adjusting device (or both). This relationship is shown in Figure 11. the consequences of oversizing motors include the following: • Lower efficiency • Higher motor/controller costs • Higher installation costs • Lower power factor • Increased operating costs. Vector representation of power factor Improving Motor and Drive System Performance: A Sourcebook for Industry 15 . Motor operation at low load factor can result when the driven load is smaller than anticipated. In that case. Power factor is the ratio of real power—the power used to perform mechanical work—to apparent power. When current and voltage are out of phase. below 40% of the rated load. and any errors in the calculation of the motor load. Another consequence of improper motor selection is low power factor. so speed control could be a better solution. Load duty cycle – Example 1 In considering whether to downsize a motor. A good rule of thumb is to size motors to operate at about 75% load. some of the electrical energy is stored in the magnetic field. the amount of real power is less than the amount of electric power available (the scalar product of volts and amps) in the line. original equipment manufacturers will overstate the horsepower needs of their equipment to avoid liability in specifying a motor that cannot meet service requirements. that is. They are usually most efficient at about 70% to 80% load. it is important to check the load duty cycle to avoid overloading the motor during peak-load conditions. downsizing the motor could cause overheating. This will also take into account occasional operational changes that require a higher load. However.
The principal consequence of operating a motor above its rated load is a higher winding temperature. which shortens the operating life of the motor. significant performance improvement opportunities can often be found in systems with poorly sized.0. the motor lifetime may be only a few months if it is operated above rated load or if it is operated at rated load when there is a power quality problem. therefore.Section 1: Motor and Drive System Basics Reactive power creates additional I2R losses in the distribution system and creates additional stress on transformers. Often. configured. However. However. and maintained properly. As a rule of thumb. and operators can provide their plants with an important competitive advantage by using a systems approach—one that includes all the benefits of greater system efficiency—to assess their motor and drive applications. the increase in energy cost is usually not as severe as the cost associated with shorter intervals between repairs or replacements. utilities often assess fees for reactive power to recover the costs associated with stress on the distribution equipment. Plants that have large motor systems often face substantial power factor penalties. or inadequately maintained motors.. because of the close relationship between motor efficiency. These systems tend to feature large motors that run much of the time. 16 Improving Motor and Drive System Performance: A Sourcebook for Industry . every 10ºC rise in winding temperature reduces insulation life by half. power lost because of current flow is the product of voltage drop and current. Motors should be sized to operate from 75% to 100% of rated load. illconfigured. many facilities invest in capacitors to increase their overall power factor and thus minimize these costs. Undersized Motors Another type of motor selection problem is undersizing the motor for the intended application. because then they would have to be shut down for a time for repairs or replacement. voltage drop in a resistive circuit is the product of current and resistance. performance. So.e. it can be beneficial to implement energy efficiency projects that involve these systems.) Consequently. managers. the most important benefit of an energy efficiency project is the increased level of motor reliability (i. Often. most of the energy used by the motor systems in an industrial facility is concentrated in a few systems. Energy-intensive motor and drive systems tend to be critically important to production. and reliability. uninterrupted service) that can result. they might not often be evaluated for efficiency improvements. engineers. Although motor efficiency drops off slightly at higher-than-rated loads. n Summary Motor and drive systems can be highly efficient and reliable if they are specified. Consequently. (I refers to current and R refers to resistance. If the motor has a service factor of 1.
Using the Service Center Evaluation Guide Plant Profile Motor Size and Hours of Operation Screen with Data Acquisition and Analysis Keep Records Improving Motor and Drive System Performance: A Sourcebook for Industry 17 . Effective motor and drive system management can reduce operating costs. Industry Profile Efficiency Opportunities The rest of this section describes seven efficiency opportunities that address both component and system issues. plant engineers and managers can usually determine the most cost-effective motor improvement projects by first screening all their motors to identify those that are essential and that consume the most energy. The following sequence of steps can help plants identify the best opportunities for motor system improvements. and these few systems are often essential to production. which includes the ways in which system parameters affect all the equipment. An important first step is to determine current operating conditions. Addressing In-Plant Electrical Distribution and Power Quality Issues 7. In this task. most of the energy used by motors is consumed by just a few systems. so it is usually not practical to evaluate every motor system in a plant individually. operators must pay attention to the entire system as well as to its individual components. essentially shifting the focus from individual components to total system performance. 1 Assessing Motor and Drive System Operating Conditions A large industrial facility can contain thousands of motors. operators are so focused on the immediate demands of this equipment that they overlook the bigger picture. which include helping to prioritize performance improvement opportunities and providing a useful baseline for determining whether system efficiency is declining and remedial actions need to be taken. the engineer analyzes the system itself and how its components interact. Therefore. Assessing Motor and Drive System Operating Conditions 2. operators evaluate how effectively and efficiently the motors and the driven equipment are meeting the needs of the system. In many facilities. Establishing a Motor Management Program 3. Often. Selecting the Right Motor 5. In this approach. improve performance. however. In addition. Providing Basic Maintenance 4. This has several benefits. energy projects involving essential motor systems typically provide the shortest paybacks. taking all subsystems into consideration Implement the best option Assess energy consumption with respect to performance Continue to monitor and optimize the system Continue to operate and maintain the system for peak performance. and increase reliability. This big-picture view is embodied in the systems approach.Section 2: Performance Opportunity Roadmap Section 2: Performance Opportunity Roadmap Overview For cost-effective operation and maintenance of a motor and drive system. Efficiency Opportunity No. Each one details a specific opportunity for improving motor system performance: 1. Using Variable Frequency Drives 6. A systems approach usually involves the following types of interrelated actions: • • • • • • • • • Establish current conditions and operating parameters Determine present process production needs and estimate future ones Gather and analyze operating data and develop load duty cycles Assess alternative system designs and improvements Determine the most technically and economically sound options.
Energy Footprints. However. provides motor use profiles for many manufacturing industries. it can be difficult to justify making efficiency and performance improvements to small motors or motors that run infrequently. seasons.gov/industry/bestpractices. then the motor load corresponding to these pressure data can be determined. including tuning the in-plant distribution system. depending on the weather. loads must be measured electrically. Percent of Motor Full Load Figure 12. staff in each facility should review plant processes to identify the most energy-intensive motor systems. an electrician can access the motor control center and. which was developed by ITP and is available on the ITP Web site. A load duty cycle is helpful in evaluating motor system improvement opportunities. This publication can help users identify the systems in their plants that use the most energy. This can be done in any of several ways. n Plant Profile Even within a particular industry. and some other systems do not usually have the instrumentation needed to estimate motor loads.energy. while others normally n Different industries have different motor system requirements.eere. some motors normally operate near their full-load rating. a helpful resource developed by ITP.Section 2: Performance Opportunity Roadmap Industry Profile When pressure and flow rate data are available. Large motors that operate for long periods of time are usually the best candidates for improvements.gov/industry/bestpractices. n Data Acquisition and Analysis After identifying the most energy-intensive motor systems. For more information on some of the electrical problems that impair the performance of motor systems. see Efficiency Opportunity No. Often. These publications identify the sources and end uses of energy to help pinpoint areas of energy intensity and characterize the unique energy needs of individual industries. paying particular attention to how their operation is controlled. But in general. and product mix. by measuring the fluid power generated by a pump or fan. In many applications. 6. Load duty cycle – Example 2 18 Improving Motor and Drive System Performance: A Sourcebook for Industry . A walk-through inspection of the larger motor systems. manufacturing industries. In many systems. The United States Industrial Electric Motor Systems Market Opportunities Assessment. energy. Addressing In-Plant Electrical Distribution and Power Quality Issues. A series of documents development by ITP. the largest motor system energy consumers can be found in industries that make frequent use of pumps.S. The data can be acquired by measuring the electrical power supplied to the motor and. by using a power meter. In fact. can directly measure voltage. compressed air. motor requirements can vary widely and depend on each plant's level of integration.eere. as discussed in Section 3 in this sourcebook on motor and drive system economics. In these cases. in some fluid systems. n Motor Size and Hours of Operation Percent of Operating Hours 35 30 25 20 15 10 5 0 20 40 60 80 100 Screening a plant's motors by motor size and annual operating hours can make it easier to identify the best opportunities for improvements. Find Energy Footprints on the ITP Website at www. the user can start collecting operating data on the motors and the systems slated for improvements. motor loads can often be estimated by measuring the pressure developed by the fan or pump. Similarly. loads vary significantly. map the flow of energy supply and demand in U. these measurements can be helpful in evaluating other aspects of motor systems. fans. production demand. the methods used to calculate annual motor energy use are the same. current. Consequently. If performance curves for the fan or pump are available. and can be found on the ITP Web site at www. can help staff get started. Electrical measurements are also useful in determining system economics. can be helpful in creating a profile of a plant's motor use. material handling systems. and power factor. The MotorMaster+ software tool. Material handling. depending on how the motor and the motor controller are configured. and air compressors.
especially if the motor is essential or critical to a production process. these systems are often overlooked as manageable assets. Assessing Motor and Drive System Operating Conditions. Examples of system demand are fluid power (especially in pumping and fan systems) and the combination of torque and speed (in material handling systems). in production facilities. or the 1-2-3 Approach to Motor Management tool offered by the Motor Decisions Matter national awareness campaign (www. The benefits of implementing a motor management program include greater motor reliability. see Efficiency Opportunity No. it may be feasible to develop separate load duty cycles for different seasons and product types. However. An industrial user has two options when dealing with an electric motor failure: (1) replace the existing motor with a new motor. One or more of these strategies can be used. For more information on how different load duty cycles can impact motor selection. System energy demand is an important data component that should be acquired. as appropriate. although a formal repair/ replace policy can reduce inconsistencies in motor replace/ repair decisions. Several factors need to be taken into consideration when deciding between these two options. Additional information on establishing a motor management plan. motor system management is often reactive. n Recordkeeping Creating an inventory record of energy-intensive (more than 50 hp) or production-critical motors can be valuable in developing maintenance schedules and in tracking motor life and performance. and they should be developed for large motor systems. if possible. HorsePower Bulletin. such as a guidebook titled Energy Management for Motor-Driven Systems. The MotorMaster+ program is a useful tool for developing and maintaining these records.org). These strategies include instituting repair/replace and purchasing policies. product redesigns. n Efficiency Opportunity No. systemsbased approach is a good first step toward realizing the many benefits of an effective motor management program. or (2) repair the motor at a qualified service shop. motor requirements also change. creating a spares inventory. establishing a motor inventory. in some cases. Consequently. a motor failure can be an opportunity to purchase a replacement motor of a more appropriate type or size. see Efficiency Opportunity No.Section 2: Performance Opportunity Roadmap operate at small portions of their full-load rating. improved overall system performance.eere. and establishing a schedule for required maintenance. advances in technology. improve performance. Thus. systems often change as a result of capacity expansions.gov/industry/bestpractices. as shown in Figure 12. Establishing a Motor Management Program. and so on. Adopting a proactive. Load duty cycles plot the load on a motor over time. Maintaining a history of motors and their load duty cycles facilitates the identification of improvement opportunities and performance trends. cost-effective planning. Improving Motor and Drive System Performance: A Sourcebook for Industry 19 . Although motor systems account for a large portion of the energy used at many industrial facilities. in that improvements are made only in response to obvious problems or motor failures. can be found on the ITP Web site at www. One factor is whether a motor is meeting the plant's current needs. in a motor management program. For example. Correlating the system demand to a motor's power use provides a helpful indication of motor system efficiency. developed by the Industrial Electrotechnology Laboratory (now Advanced Energy) with support from ITP. Depending on the factors that drive the system load. Selecting the Right Motor. by defining strategies that support proactive. General guidelines on motor replacement and repair options can be found in several resources. energy. 2 Establishing a Motor Management Program Although most industrial facilities rely heavily on motor systems to maintain or support production. For example. and increase reliability. Another useful n Summary Determining motor system operating conditions is a good place to start in order to identify opportunities that reduce motor-related costs. and lower energy costs. A formal motor management program expands on the assessment activities described in Efficiency Opportunity No. sm Instituting a Repair/Replace Policy When a motor fails. is a motor management policy guide covering general motor repair and specific information for NEMA Designs A and B up to 200 hp. These records can also be used to determine whether maintenance schedule adjustments are required. 2. 4. getting it back in service is often a priority. 1. For more information on motor management.motorsmatter. many facilities do not have one. tracking motor life.
org under "Standards." provides more information about these publications. Assurance of this result can be obtained by researching prospective motor service centers. Using the Service Center Evaluation Guide. which was developed by the Bonneville Power Administration. Guidelines for Maintaining Motor Efficiency during Rebuilding. The recommended practice is to evaluate repair facilities in advance. evaluating a facility after a motor failure can ITP helped to develop the MotorMaster+ motor system management software to assist industry in managing electric motor systems. cost-effective motor is chosen for each application • Streamlines the approval process for purchasing NEMA Premium motors. NEMA's General Specification for Consultants. Several sample policies are available.Section 2: Performance Opportunity Roadmap resource is an Electrical Apparatus Service Association (EASA) booklet. Section 4. see Efficiency Opportunity No. which was developed by the Electrical Apparatus Service Association (EASA). for example. instead of making a decision based solely on the initial cost. Other sources of motor repair information include the EASA's Recommended Practice for the Repair of Electrical Apparatus and EASA-Q." was developed by Washington State University to provide detailed repair specifications. The tip sheet in Appendix B titled "Model Repair Specifications for Low-Voltage Induction Motors.300 hours per year for 18 years at a cost of $0. "Where to Find Help. users can examine both options more thoroughly by means of a life-cycle cost analysis." n Evaluating Motor Repair Facilities Using MotorMaster+ for Motor System Management The cost benefits of repairing an existing motor usually can be realized only if the repair results in a slight deviation. 94.gov/industry/bestpractices. maintaining a plant's electric motor inventory. Several other resources also discuss motor repair specifications. and Electric Motor Repair Specifications. EASA standards contain guidelines for motor repair service shops. and it provides a checklist to help the user perform the evaluation. For example. The condensed version is available free of charge at www. motor repair quality is an important consideration. The guide can be accessed from the ITP Web site at www. the policy must be supported by management and disseminated to all those who regularly make motor-related decisions. However. from the motor's original specifications." for more information on these publications When the initial costs of motor repair versus replacement are compared.5% efficient motor operates 6. EASA-Q is a service shop evaluation program that parallels ISO 9000 standards for management practices with respect to motor repair quality assurance. 7. In that case. This can benefit both the motor user and the motor service center.eere. n Instituting a Purchasing Policy A motor purchasing policy accomplishes several key objectives: • Ensures consistency in procurement • Helps to ensure that the most appropriate. MotorMaster+ can access performance data from nearly 30. Industrial and Municipal: NEMA Premium Efficiency Electric Motors (600 Volts or Less) covers many design criteria as well as material and mechanical considerations. This guide discusses the attributes that a motor user should look for in a motor repair service center. Along with analyzing cost issues in order to make a motor replacement/repair decision. "Where to Find Help. keeping a historical record of motor maintenance. "Where to Find Help. and the recommended practice discusses in some detail the minimum practices that motor service shops should follow. when appropriate • Demonstrates management support for decisions based on life-cycle costs. See Section 4. The Motor Decisions Matter campaign is also a good resource. See. nema. This analysis takes into consideration two important factors— hours of operation and electricity costs—as well as purchase and repair costs. or none at all.energy. To be effective. suppose a hypothetical 100hp. See Section 4." for more information. The motor user can ensure the quality of the motor repairs and the motor service center can benefit from knowing what its customers expect. However.000 industrial electric motors and perform several tasks to help motor users with system management. the repair option is usually the less expensive one. 20 Improving Motor and Drive System Performance: A Sourcebook for Industry . These tasks include performing a comparative benefits analysis of existing motors with possible alternatives. Evaluating repair facilities (service centers) provides quality control advantages similar to those gained when facilities evaluate vendors and suppliers of their parts and materials. The Service Center Evaluation Guide provides useful information on service center quality. and calculating the life-cycle costs of a motor project. A Guide To AC Motor Repair And Replacement. electricity costs represent approximately 95% of the motor's lifetime operating costs. n result in a costly loss of production time.075 per kilowatt-hour (kWh).
The need to replace one or several motors is also an opportunity to improve the efficiency of a plant's motor systems. 1200. MotorMaster+ can help motor users understand how motor efficiency affects the life-cycle cost of an electric motor. along with different interest and tax rates. as well as compare the cost of a new motor with that of a repaired motor to find the most cost-effective option. Track Motor Lifetimes and Life-Cycle Costs. Although many economic decisions are based on initial capital costs. electric motor efficiency data are based on an industry standard for measuring full. and French. sorted by motor efficiency. Purchasing electric motors is a common and recurring procurement activity in most large industrial plants. This program includes many of the capabilities and features of MotorMaster+ but allows users to evaluate repair/ replacement options on a broader range of motors. In addition. MotorMaster+ can also compare an existing motor economically with other motors available in the market. Spanish.000 hp that operate at speeds of 900. MotorMaster+ will perform a life-cycle analysis on all motor and rewind options. including electricity and demand charges. End-users can choose between the straight line. and the expected lifetime of the project. n MotorMaster+ International Some users might want to use the MotorMaster+ International software rather than MotorMaster+. Like a typical life-cycle analysis. The electric motor database includes all NEMA and some International Electrotechnical Commission (IEC) metric motor types from 1 to 4. MotorMaster+ was developed to achieve four basic objectives: • Increase awareness of electric motor system efficiencies • Emphasize a life-cycle cost approach to motor replacement decisions • Assist motor users in selecting the proper motor for an application • Assist users in establishing an effective motor system management program. These factors include frequent cycling or starting. considering capital depreciation. operation and maintenance. sum-of-year-digits. This allows the user to view all possible motors. users can create a list of motors that includes performance and cost specifications to match specific operating requirements. MotorMaster+ also allows the user to input details about the plant's electricity service. and doubledeclining balance methods to account for depreciating assets. Two methods can be used to perform a comparative analysis.and part-load efficiencies. MotorMaster+ minimizes some uncertainties by incorporating the expected operating life of the motor and other operational variables. All of these parameters are integrated into the life-cycle cost analysis according to the lifetimes of the proposed projects. Users have the flexibility to define the operating conditions related to electrical power to reflect realistic rate schedules. Although motor repair costs vary considerably. the life-cycle module depreciates capital equipment using several methods to incorporate these benefits into the final analysis. Using MotorMaster+. Although low lifecycle costs are an important factor in selecting a motor replacement option. a life-cycle analysis presents a more realistic view of the investment value. for an application. For example. associated costs. the depreciation life. and fuel costs.Section 2: Performance Opportunity Roadmap MotorMaster+ helps users to find the most energy-efficient motors that meet the requirements of the application and to compare the life-cycle costs of potential replacements with the cost of a typical repair. along with the equipment life expectancy. To ensure consistency among various manufacturers. 1800. and specific load profiles. and/or payback periods. financing details. MotorMaster+ accounts for associated costs and financing details such as capital. The program calculates life-cycle costs using various userestablished scenarios. The first method is a simple payback analysis to compare two motors at a time. edit and modify motor rewind efficiency loss defaults. Increase Awareness of Motor Efficiency. installation. The user can conduct analyses in different currencies. The life-cycle module in MotorMaster+ enables users to evaluate comprehensive costs and benefits. and the scrap value. hurdle rates. calculate efficiency benefits for utility rate schedules with demand charges. several other factors should be considered before making a final choice. and 3600 rpm at ratings up to 6600 volts (V). electricity use. MotorMaster+ allows the user to input different fuel cost escalation scenarios for the predicted lifetime of the project. If the user wants to perform a more indepth analysis. This tool can be operated in English. and determine "best available" motors. Improve Motor Selection Methods. required start-up Improving Motor and Drive System Performance: A Sourcebook for Industry 21 . MotorMaster+ calculates annual energy and demand costs and determines the simple payback period. the salvage value.
This test is performed by applying a voltage (typically 500 or 1000 V) to the motor windings and measuring the resistance from the insulation to ground. Motor systems are often essential to industrial facility operations. IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery. 22 Improving Motor and Drive System Performance: A Sourcebook for Industry . "Where to Find Help. Megohmmeter checks are commonly done on in-service motors. In some cases. these inspections can and should be combined with cleaning to remove contaminants from the motor. lower life-cycle costs. if the slip ring surface becomes pitted or out-of-round because the brushes are operating poorly. and so on. The most obvious benefit is the extended operating life of the equipment. environmental conditions. The causes of these problems include poor installation and maintenance practices as well as contamination. Customized programs might include stocking. accelerates motor wear by reducing the life of the insulation. Wet insulation is a common cause of low insulation resistance. See Section 4. This inventory helps to ensure that decisions are based on evaluation and planning rather than availability and first cost. the insulation resistance should be remeasured to see if moisture was the problem or if the insulation itself is weak. repairs can be costly and time intensive. Brush problems include poor contact. n Establishing a Spares Inventory Once replacement requirements are understood. use of variable speed drives. effective maintenance programs can help plants avoid costly disruptions in production. and/or tracking agreements. a low resistance reading should be investigated further. such as a "hi-pot" (highpotential) test. See IEEE Standard 43-2000. dc motors tend to require more frequent inspection and maintenance. 3 Providing Basic Maintenance Proper maintenance of motor and drive systems provides several economic benefits. Therefore. Motor sales and service providers are stepping up efforts to work with customers in this area. Energizing motors with weak or wet insulation can lead to catastrophic failure of the motor. or both. and better use of assets. and motors that might be wet. Others include increased reliability. Contamination is particularly problematic in brush assemblies in which silicone-based insulation is used. These problems can lead to quick deterioration of the brushes and damage to the slip ring surface on the motor shaft. an even greater consequence. Efficiency Opportunity No. an insulation resistance check can indicate whether such a measurement will cause insulation damage. consequences of failure. motors that have been idle for awhile. relatively frequent brush problems should be investigated to see whether the cause is exposure to silicone materials. Inspections of motor and drive system components should be based on such factors as run time. Moisture directly reduces the dielectric strength of insulation.org. Since hi-pot tests expose the insulation to much higher voltages. storage. Insulation Resistance Checks. negating the benefits of low life-cycle costs. Therefore. Contaminated oil also degrades the dielectric strength and encourages the accumulation of contaminants. increasing the risk of sudden failure. etc.org. The off-gassing that occurs from the insulation as it is heated during operation can cause the brushes to deteriorate quickly. Since windings shift around in reaction to thermal and magnetic forces. contaminants on the winding insulation create abrasive wear that can lead to early insulation failure. maintaining a spares inventory will guarantee that the proper motor is available when needed. Because of potential problems with the brush assemblies.Section 2: Performance Opportunity Roadmap torques. Although the brushes themselves are relatively inexpensive. Table 1 contains a list of basic inspection and maintenance tasks and the recommended intervals for performing them. It may also help to minimize downtime associated with unexpected motor failure. maintenance. Then. The insulation should be checked before more extreme measurement methods are used. so a motor failure can cause costly production delays. Moisture or contaminated oil on motor windings. insulation class. an insulation resistance check can indicate the need to dry the equipment before conducting additional tests. Measuring the motor winding insulation resistance can indicate cleanliness and moisture levels and help to determine the potential for insulation failure. these factors may diminish a motor's reliability. and sparking. Often. n Preventative Maintenance Inspections." for more on how to obtain MotorMaster+ and MotorMaster+ International. on the IEEE Web site at www.ieee. Expected resistances should be on the order of megohms as outlined in Institute of Electrical and Electronics Engineers (IEEE) Standard 43-2000 available on the IEEE Web site at www. By minimizing the risk of unplanned downtime. misalignment. When the insulation has been exposed to moisture. A megohmmeter is used to measure the insulating resistance of electrical materials.ieee. a motors service factor.
motors can be seriously affected by dynamic unbalances. Like most rotating machinery. poor alignment between the motor and the driven equipment. seating contact. A motor might be correctly aligned to a pump before the system piping is connected to the pump flange. Balance and Alignment Checks. For example. the manufacturer's guidelines should be carefully followed. installing mechanics often "force-fit" the connection. switches. so it is important to design the motor/driven-load assembly properly in overhung load applications in order to prevent the development of balance and alignment problems. Alignment problems can result from a poorly done installation. Remarks Look for sparking. Similarly. overhung loads create significant radial load conditions on motor bearings. Improving Motor and Drive System Performance: A Sourcebook for Industry 23 . However. but it may be recommended for motors that have been idle for long periods. and 60% of this calculated value for used motors. The causes of balance problems include overhung loads. many initial alignment problems can be attributed to the installation sequence. or bearing system wear. verify proper position and pressure Look for signs of grout degradation or loosening of shims A hi-pot test measures the dielectric strength of winding insulation and can determine whether the insulation has a weakness that may cause failure when the motor is operating. and a weight imbalance on the motor fan or the motor shaft. when the piping does not line up exactly with the pump flanges. Unless the welding process is sequenced to limit this distortion. A high-pot test typically applies more than 1000 V to the windings for new motors. Large.Section 2: Performance Opportunity Roadmap Table 1. foundation movement. Generally. evidence of contamination* Blow out dirt (25-30 psig air). any machinery alignments should be checked after all the welding is completed. this test is used on new motors. Common Inspection Tasks Interval Weekly Action Inspect commutator and brushes Check oil level in bearings Check oil rings Inspect the shaft for signs of oil leakage Inspect starter. The pull exerted by severe force-fits can cause severe misalignment with the motor/pump shaft system. welding tends to distort foundations. and fuses Check the start-up time for the motor Every 6 months Clean the motor thoroughly Check brushes Inspect brush holders Check oil quality in sleeve bearings Check grease in antifriction bearings Check operating speed Verify end-play Check electrical connections Check enclosure Check foundation connections Check insulation resistance Annually Regrease antifriction bearings Check air gap Check bearing clearances Clean undercut slots in the commutator * Never use silicone-based insulation or leads in a motor with brushes. wipe down commutator and brushes Inspect for wear. an imbalance in the driven equipment that transfers to the motor. shaft deflection. Since the test itself can damage the insulation.
Misaligned or unbalanced couplings will also show up as hot during an IR scan. rotating imbalances can be caused by the driven equipment. It is often the result of material loss around the mounting hardware that allows movement of the motor or drive assembly under load. In addition. provides information about the winding and ground insulation system and the motor rotor when equipment is de-energized. etc. Rotor bars that become loose will display vibration characteristics of a certain frequency. especially intermittent ones. IR scanning should be performed by someone trained in thermography. the motor fan itself can degrade. FFT is a mathematical technique for efficiently calculating the frequency response of sampled time signals. IR scanning evaluates the thermal image of a body to determine its temperature characteristics. insulation resistance measurement (see also the section on insulation resistance in this efficiency opportunity). The most effective predictive maintenance tools for motors include vibration analysis. This property is useful in detecting problems. Like vibration analysis. or ESA. Vibration analyzers are also useful in evaluating the condition of rotor bars in squirrel cage induction motors. In pumps. Vibration Analysis.Section 2: Performance Opportunity Roadmap Shaft deflection is an operating problem usually associated with pumps. Soft foot refers to the gaps that develop between a motor's mounting foot and the foundation. the condition of the mounting feet should be periodically inspected. a bearing problem that develops under specific but infrequent operating conditions may not be detected by conventional methods unless that load condition happens to occur during the measurement. Predictive Maintenance Predictive maintenance programs are designed to increase the reliability of motor and drive systems. Early identification of a developing problem improves the engineer's ability to plan the repair effectively. As the motor or drive "flexes" on its soft foot. n couplings. measuring the temperature of a motor at successive intervals helps to identify trends. Vibration analyzers can also detect unbalances and misalignments in the shaft system due to loose 24 Improving Motor and Drive System Performance: A Sourcebook for Industry . It can influence the performance of the motor as a result of the added bearing loads. There are several EMD methods. How To Get The Most From Your Electric Motors. Motor current signature analysis.easa. Commercial vibration analyzers read and evaluate the vibration signature of a motor or other rotating machinery. Motor circuit analysis. Recording the vibration characteristics at different points in a motor's operating life can reveal trends that indicate developing problems.com. a ventilation fan that operates in a corrosive environment can become unbalanced as the materials in the fan blade degrade. Lubricant Analysis. If the grout is damaged or if the shims or mounting bolts have come loose. Infrared Scanning. An electrical signature analysis. severe shaft deflection usually occurs when the pump operates below its minimum flow requirement . Infrared (IR) scanning (thermography) is an effective method of determining the condition of insulation and the integrity of a connection. For example. air-gap. causing a damaging imbalance condition. Motor/foundation interfaces that develop soft-foot problems can also have balance and alignment problems. Electrical motor diagnostics (EMD) is effective in evaluating the condition of the electric motor circuit. motor fan problems. These devices are particularly useful in determining emerging bearing problems. or MCSA. and electrical motor diagnostics. Further information on electric motor maintenance can be found in the EASA publication. the resulting misalignment can produce bearing problems. infrared (IR) scanning. weakened insulation may show up as a high-temperature area on the motor stator. lubricant analysis. provides a fast Fourier transform (FFT) spectra and demodulated spectra of current in order to detect rotor. To avoid false positives. or MCA. In some applications. and load-related faults while equipment is energized. the problem should be corrected and the motor/drive alignment rechecked. Lubricants are usually changed permanently by heat. These methods are intended to identify problems that are developing but have not yet created a failure. Bearings that begin to run hot or connections that become weak and create more resistance will show up as hot spots on an IR scan. A lubricant analysis can indicate the existence or the development of a bearing problem as well as determine whether the lubricant should be replaced. In motors. provides an FFT spectra of both the voltage and current of the motor circuit in order to detect current-related faults and supply faults while equipment is energized. For example. To avoid this problem. Lubricant analysis can also indicate the presence of hightemperature bearing problems. Electrical Motor Diagnostics. which can be ordered from the EASA online catalog at www.
design letter. and undervoltage. To prevent brinelling during storage. Relying on the service factor rating of the motor under continuous-duty conditions is usually not recommended." Motor life is also reduced by power quality problems such as voltage imbalance. and the strength of the magnetic field depends on the strength of the current and the magnetic properties of the material in the field. Operating a motor above its rated horsepower can shorten the life of its insulation. Horsepower. As a guideline. Efficiency Opportunity No.1 and 1.Section 2: Performance Opportunity Roadmap Maintenance of Stored or Idle Motors of operating conditions. The principal operating characteristics are horsepower. the motor should be operated periodically. see Section 4. Operating a motor at 1. A properly specified motor will match the power requirements of the load over the expected range Improving Motor and Drive System Performance: A Sourcebook for Industry 25 .15 rated load increases the winding temperature by about 20ºC (depending on factors such as the enclosure type. The additional heat in the windings also translates to higher bearing temperatures and can impact lubricant life as well. This requires an understanding of a motor's operating characteristics and the basic components of a motor system. such as wound rotor motors. the service factor rating applies to short-term or occasional overloads. and a motor's insulation life is halved for every 10ºC increase in the heat at which the motor runs. slip.. To prevent brinelling during shipment. motor life is reduced by one-half if the motor is operated continuously at the service factor level. Direct current motors are frequently selected for applications that require high torque at low speeds. The speed and torque requirements of the driven equipment and the ability of the motor to respond to load changes are important factors in determining how well a motor performs. overvoltage. the speed range adjustments of dc motors can be up to 20:1. and some can operate even at 0 rpm. power supply. More information on the service factor is available from EASA. such as those in backup applications. speed. Some ac motors. and elevation).15. the shaft should be rotated periodically as part of a preventive maintenance program. However. To prevent brinelling after installation. To adjust the resistance of the rotor circuits. motor enclosure. Other important considerations include efficiency. speed. power factor. In general. Among the more important principles are that an electric current passing through a conductor generates a magnetic field. it is usually not sufficient just to match the motor horsepower to the load horsepower. The indentations are usually small. This often occurs in motor bearings that remain idle for long periods but that are still subjected to external vibrations. roller bearings).g. Motors are fairly simple devices that rely on some basic principles of electricity and magnetism. Keeping a bearing in a static position for a long time results in a loss of the lubrication film that separates the bearing surfaces. The horsepower of a motor is the product of its torque and speed. The speed ratios of these motors can also be up to 20:1. There are several different ways to configure motor systems to provide effective speed control. and operating temperature. False brinelling refers to the indentation of the races or rotating elements (or both) of an antifriction bearing (e. They can operate as low as 5%-7% of the base speed of the motor. n Motors that operate infrequently. the motor shaft should be securely locked. n Motor Characteristics and Considerations Several basic operating characteristics are important in properly specifying and operating a motor and drive system. 4 Selecting the Right Motor An essential component of cost-effective system performance is properly matching a motor type to its application. The service factor is a multiplier that indicates the percentage of horsepower (or other nameplate rating like torque) at which a motor can operate above full load without causing failure under certain conditions. ball bearings. a good rule of thumb is to size motors so that they operate at about 75% of rated load. common service factor values are 1. these motors are usually equipped with slip rings that connect to external resistance banks. These magnetic fields create torque that turns the motor shaft. to correctly specify a motor/drive system. these surface imperfections can lead to poor bearing performance and shorten the motor's operating life. Because of potential problems with power quality and the uncertainties associated with determining an actual service load. However. The vibrations common to machinery areas promote a brinelling effect at these points of contact. when a motor is operating and the bearings are placed under a load. and torque. should be activated periodically to keep the bearing surfaces lubricated and to prevent problems such as false brinelling. Speed. "Where to Find Help. This also usually provides optimum efficiency. also offer effective speed control by controlling the resistance of the rotor circuits.
Torque is the rotational force exerted by the motor shaft. full-load. Breakdown torque is the highest torque a motor can generate before stalling. this is several times greater than the full-load torque. The enactment of EPAct has had several effects on the design and performance of motors. which went into effect in October 1997 and pertains to the most common types and sizes of motors. In many systems. U. LDCs plot the load on a motor over time. To achieve the required efficiency levels. with assistance from DOE. they also increase the complexity. Torque. A system with a constant load can probably use a standard motor without a control system. More advanced system designs allow wound rotor motors to regenerate power extracted from the rotor circuit. improvements in the efficiency of motors for high-run-time applications have resulted in very favorable payback periods. Although the initial costs of motors have increased 10% to 20%. n Percent of Operating Hours 45 40 35 30 25 20 15 10 5 0 20 40 60 80 100 Percent of Motor Full Load Figure 13. and maintenance requirements of the system. Full-load torque is that developed by a motor at its rated horsepower. however. These changes have at times included reducing the resistance of the rotor and stator circuits. Energy-Efficient Electric Motor Selection Handbook. largely as a result of the 26 Improving Motor and Drive System Performance: A Sourcebook for Industry . Other changes have included designing motors with a smaller slip (higher Efficiency and Losses The efficiency of general purpose motors has significantly improved in the last 20 years. pull-up (usually the lowest point on the curve).Section 2: Performance Opportunity Roadmap Large wound rotor applications can require the use of relatively large resistance banks. These options increase the efficiency of the speed adjustment process. This regenerated power can be used to drive another motor or can be sent back into the power line. Motors have four principal torque characteristics: starting or locked-rotor. production demand. a standard motor with another speed control device (such as an eddy current clutch). using electrical grade steel with improved magnetic characteristics for the stator and rotor laminations to reduce core losses. and redesigning the cooling fan to decrease fan windage losses. (See. while others operate normally at small portions of their full-load rating. this has resulted in slight changes in motor operating characteristics. A system load duty cycle (LDC) is helpful in choosing the right motor and motor control system (if required). More recent motor efficiency improvements have been spurred by the Energy Policy Act (EPAct).pdf). and product mix. the losses associated with operation at slow speeds can increase a plant's energy costs. Load Duty Cycle. cost. Unless the energy pulled from the rotor circuit is recaptured. 1993 at www. motor manufacturers have had to change the designs of many of their Design A and B models. Load duty cycle – Example 3 efforts of motor manufacturers. and the most common VFD is the pulse width modulation (PWM) type. motor manufacturers have had to modify the design of motors and use better materials. wbdg. To improve efficiency. Alternating current induction motors can be used in many applications with adjustable speed drives.org/ccb/DOE/TECH/ce0384.S. such as salt water rheostats that rely on plates immersed in salt water to provide electric resistance and heat dissipation. Locked-rotor torque is that developed by the motor at zero speed. Department of Energy. These drives are commercially available at from 0 to 120 Hz and can be used to operate motors over a wide range of characteristics. loads vary significantly according to the weather. as shown in Figure 13. or a multiple-speed motor. Often. some motors operate normally near their full-load rating. Therefore. EPAct efficiency levels for a range of motor types are included in Appendix D of this sourcebook. for example. A varying load may be served best by a motor designed to be used with a VFD. and breakdown. The most commonly used ASD is the variable frequency drive (VFD). seasons.
motor efficiency for many EPAct Design A and B motors is often relatively constant between 70% and 80% of rated load and drops slightly at full load. Motor efficiency may also drop slightly between 50% and 70% of rated full load. Percent of Full Load Torque 300 Percent Efficiency 100 95 90 85 80 75 70 0 Design D 5000 hp 1000 hp 500 hp 100 hp 250 Design C 200 Design A 50 hp 10 hp 5 hp 25 50 75 100 150 Design B 100 50 0 Locked Rotor Torque (also Startup Torque) Breakdown Torque 25 50 75 100 Percent Rated Load Percent Rated Load Figure 14. Table 2 shows some typical ranges. Torque and speed characteristics of various types of motors Improving Motor and Drive System Performance: A Sourcebook for Industry 27 . The NEMA Premium® efficiency motors program of the National Electrical Manufacturers Association defines "premium efficiency" motors as those with higher levels of efficiency than the ones established by EPAct. As a rough rule of thumb. load (1800 rpm) Figure 15. In addition to higher breakdown torques. size. but grossly oversizing a motor can lead Design Classifications NEMA has established several different motor classifications that reflect the speed and torque characteristics of induction motors. Design A. Additional factors include type of enclosure (open enclosures tend to be more efficient) and design classification (lower slip motors tend to be more efficient). crushers. and air compressors. The NEMA Premium efficiency electric motors program covers continuous rated. This motor is usually selected for applications requiring high. Figure 14 shows some of these differences. 4-. These include not only the energy losses associated with inefficient operation but also the reduced power factor. Sources of Motor Losses Friction and Windage Core (Iron) Losses Stator (I R) 2 to substantial efficiency losses. Design A motors usually have higher starting currents and less slip than Design B motors. 2-. transient increases in load. The primary factors affecting efficiency are speed (high-speed motors tend to be more efficient) and the size of the motor (larger motors tend to be more efficient).Section 2: Performance Opportunity Roadmap speed) and using lower loss core iron. At loads below 40% of full load. and speed. These characteristics are shown in Figure 15. motor efficiency begins to decline dramatically. but generally range from 85% to 97% at full load. This type of motor is used primarily in special applications for which a comparable Design B motor would not have a high enough breakdown torque. NEMA Premium® Efficiency Motors. Typical motor efficiency vs. Losses vary among motors of different sizes and designs. 1 to 500 hp. It can be a manufacturer's most efficient motor solution and is often selected because of its efficiency advantages. Slightly oversizing a motor (up to 25%) can actually increase efficiency. single-speed. Appendix C in this sourcebook shows efficiency levels for each motor type. polyphase. n 5% – 15% 15% – 25% 25% – 40% 15% – 25% 10% – 20% Rotor (I R) 2 Stray Load Motor efficiencies vary according to several factors. and 6-pole NEMA Design A or B squirrel cage induction motors. Typical applications are injection molding machines. Table 2.
The voltage is usually determined by the power available in the plant's distribution system. Depending on the design of the motor. Because motors are sensitive to temperature. Decreasing the line voltage usually increases the current required by a motor to meet a particular load. Line voltage that is higher than a motor's rating can also affect the motor's life and performance. Design D. 230. Because of their high slip characteristics. Motors are also subject to transient voltage events. Line voltages can vary according to the 28 Improving Motor and Drive System Performance: A Sourcebook for Industry . cyclical load applications such as punch presses. In fact. Table 3 contains a list of enclosure types. some motors are equipped with an undervoltage relay that de-energizes the motor in response to low voltage conditions. Also. plants that experience frequent voltage sags often experience problems caused by the activation of these undervoltage relays. 460. Major Specification Characteristics It is important to determine the voltage and enclosure needed when specifying an industrial motor. and moderate slip characteristics. These motors are slightly less efficient than comparable Design B motors. However. positive displacement pumps and refrigeration compressors often start against high backpressures and therefore require high starting torques. start-up and maximum running torques can increase more than 20%. A high-slip motor operates evenly within this load cycle. In industrial motor applications. Since different bearing designs have different lubrication requirements. overvoltage conditions can cause magnetic saturation of the iron core that can lead to overheating of the motor. These motors are generally used in high transient. Bearings. the full-load efficiency of the motor might actually increase up to 1% as a result of the lower current required. the operating characteristics of Design B motors are often compared with those of other motor designs in order to provide a practical perspective. The enclosure refers to the motor's level of protection from its environment. and there is a relatively large difference between the highest and the lowest torques in the cycle. it is important to ensure that the bearings are compatible with the load. except in cases of light loads. Voltage. but the motor voltage often does not precisely match the voltage rating of the power supply because of unanticipated voltage drops in the distribution system. Oil well pumps are often powered by Design D motors because the load is cyclic. Design C. This type has very high starting torques and high slip characteristics. These events can be triggered by utility switching or in-plant activities such as the energization of large loads. The voltage rating of a motor should match the power supply. exposure to moisture. Design B motors have normal starting torques. at 110% of a motor's rated voltage. For example. a relatively large Design B motor would be required. such as surges and sags. such as hoists and punch presses. 575. Typical applications are material handling systems such as conveyors. Typical applications are pumps. consequently. Motors are relatively sensitive to the power supply voltage. efficiency losses are balanced by the reduced electrical stress on the system resulting from lower current surges. and so on. For centrifugal loads such as pumps and fans. the most common bearing types are journal (sleeve) bearings and antifriction bearings. It is important to understand the effects of these variables on the operation of a motor. Enclosure Type. plant loads. Applications include systems with sudden load changes. fans. power factor effects. normal breakdown torques.Section 2: Performance Opportunity Roadmap Design B. 2300. and environmental conditions. Operation at high voltage can also decrease the power factor and increase the operating speed. In fact. This higher current level generates more heat and losses in the motor windings and decreases a motor's operating efficiency. and air compressors. Common motor voltages are 115. To meet this starting torque. Bearings are essential to the operation of a motor. but a more properly sized Design C motor would be more costeffective. the result can be an increase in energy use. 200. To protect against potential damage caused by operating a motor at low voltages. This type of motor is similar to a Design A motor and is the most common type—a true industry workhorse. When selecting a motor. and the performance of the transformer. for voltages up to 110% of the motor's rating. Prolonged operation at low voltages will shorten a motor's operating life. This type is characterized by high torques and is often used in high-inertia applications. temperature. the proper enclosure must be selected in order for the motor to operate properly. moisture. Antifriction bearings rely on the action of rolling elements such as balls or rollers to minimize friction while supporting the load. ranging from 5% to 13%. n utility supply. Journal bearings usually use a lubricant film to separate the metal surfaces and thus reduce friction. they are somewhat less efficient than the other classes. Design C motors are often selected for applications requiring high starting torques. and contaminants. Consequently. The enclosure type is usually determined by environmental conditions such as air quality. any harmful vapors present. and 4000 V.
improved system reliability. In severe cases. and more effective process control. Insulation and winding placement are also improved. Faults can occur between windings of different phases or between different winding turns on the same phase or coil. An insulation failure usually results in a fault. Common Types of Enclosures Enclosure Type Open Drip-proof Splash-proof Characteristics Can withstand dripping liquids up to 15º off vertical Can withstand splashing liquids up to 100º off vertical Ventilation openings are less than ¾ in. motor windings are exposed to short-duration. high-voltage spikes that can shorten their life. speed. a recent trend in industry is to use VFDs with ac motors. They are highly efficient. users should carefully consider the service and lubrication requirements of bearings when selecting a motor. Under normal operating conditions. dc motors have been used in these applications because of their effective speed control characteristics. reliable. The induced bearing currents associated with PWM drives can also degrade bearings. 5 Using Variable Frequency Drives The advantages and benefits of motor speed control include lower system energy costs. wide Ventilation is provided by a separate motor-driven fan Does not contain a means of external cooling Contains an integral fan Will not ignite an external gas Excludes leakage Guarded Externally ventilated Totally Enclosed Unventilated Fan-cooled Explosion-proof Waterproof it is important to follow the manufacturer's guidelines on lubrication procedures. most insulation classes are rated for a certain operating temperature (which varies according to the insulation class) and a certain operating life (typically 20. Common Problems Motors can experience both mechanical and electrical damage. Mechanical damage includes bearing failure. Some competing ASD technologies. such as a ground or a short. In VFD applications. motor surfaces. however. as a result of improvements in power semiconductor technology. Insulated bearings may be required for VFD applications to protect against bearing damage from the shaft voltage. Grounding problems occur when a winding directly contacts a ground path. offer similar advantages in terms of speed control. Selecting the proper bearings depends on the load. fewer maintenance requirements. This issue is discussed further in the Efficiency Opportunity No.000 hours). and more than half of all motor failures involve bearings. winding insulation ages over time. Compatibility with Inverter Drives. Because bearing failure usually results from the breakdown of lubrication. Many manufacturers also offer inverter-friendly insulation in their premium efficiency motors. Inverter-duty motors are specifically designed to handle the stresses of service with PWM inverters. The causes of insulation failure include the high temperatures caused by a current overload and voltages that exceed the dielectric strength of the insulation. Conditions that impair the dissipation of heat—such as the contaminants that can build up on windings. such as hydraulic couplings and eddy current drives. temperature. Table 3. and the frequency of motor starts and stops.Section 2: Performance Opportunity Roadmap Electrical damage has many causes and is evident in an insulation failure. and flexible. especially those that use PWM controls. But they are not recommended for all motor/drive applications. Using Variable Frequency Drives. However. n Efficiency Opportunity No. including low voltage conditions and high motor loads. heat accelerates this breakdown rate. bearings can seize as a result of a loss of lubrication or entrainment of solid contaminants. 5. VFDs have substantial advantages in comparison to other speed control options. and fan blades—can also increase winding temperatures by reducing the amount of heat transferred away from the motor. coupling method. Even under normal conditions. Several conditions can cause high winding temperatures. Improving Motor and Drive System Performance: A Sourcebook for Industry 29 . and motor users can bypass them for maintenance or repairs without having to take the motor out of service. Many applications require accurate control of a motor's operating speed. environmental conditions. Historically. However. These pulses are caused by switching in the power electronics. lubricant method. so understanding their performance and application is essential in deciding whether to use them. and most motor manufacturers offer them.
In many machining operations. that dissipate energy after it is added to the system fluid. the key drawback of gear systems is their lack of flexibility. then started. material handling systems. VFDs allow the speed of a process or a feedstream to be slowed or accelerated according to an automated feedback signal. which makes this upgrade relatively nondisruptive. Most machining and fabrication applications use constant speed ac motors. including fluid (gas and liquid) systems. and their speed adjustment ratios are similar to those of other speed control systems. on-off methods tend to impose stresses on the system as material is abruptly stopped. These components increase the risk of failure and other problems. Wound rotor motors add resistance to the rotor circuit for speed control. however. Thus. Because they can save a significant amount of energy. Using a signal that directly measures line speed. This also reduces stress on the piping system and support structures. In contrast. And. these devices have limited flexibility. In material handling applications. Fluid Systems. In this regard. Machining and Fabrication. Since many fluid systems have varying flow requirements. Using an intermediate speed adjustment device. and machining and fabrication processes. VFDs can provide substantial flow control improvements and reduce the stress on the entire system. however. even if the motor must be changed. Gear systems allow different speed ratios between the motor and the driven equipment. Conventional speed control options use gears or pulleys to maintain the cutting speed within a certain range. The operating life of tools and cutting bits is highly sensitive to how well and constantly the cutting speed and pressure are maintained during machining operations. If they are used in place of mechanical drive options. VFDs offer several advantages. In contrast. however. VFDs can improve the process control and the speed of production. all existing motors should be evaluated for compatibility with this modification. Although each type has advantages. In fan systems and systems served by centrifugal pumps. need more maintenance. For example. VFDs can often be retrofitted to existing pump and fan motors. Usually. Material Handling Systems. Historically. a VFD controls the rotation of the winder to maintain a constant process speed. VFDs allow better control of transport. there is a cube power relationship between flow and power (see the discussion of affinity laws in Section 1). the speed ratio is usually fixed. dc motors are relatively expensive. VFDs can control the cutting speed continuously during the machine operation and can shift to different speeds without requiring the machine to be reconfigured. VFDs are often used to control the speed of the winding machines in aluminum mills and paper plants. Unlike other flow control measures. these systems are limited to discrete speed changes that often interrupt a machine's operation. But. The principal advantage of VFDs is improved operating efficiency. VFDs can be incorporated into closed-loop control systems. adds another component to the motor/drive system. 30 Improving Motor and Drive System Performance: A Sourcebook for Industry . VFDs can also improve system reliability by removing potential failure modes and requiring less maintenance because they have fewer components. For example. using a brake to control the Alternatives There are two principal ways to adjust the speed of a motor/ drive system: • Adjust the speed of the motor directly • Use a constant speed motor with an intermediate device between the motor and the driven equipment that can change the speed ratio. In contrast. and packaging processes. Although clutch devices can allow shifting between different gears to achieve different speed ratios. designers had to use dc motors or wound rotor ac motors. Using a brake also requires the use of a motor with large slip characteristics and increases system maintenance requirements. such as throttle and bypass valves. speeds must be selected when the machine is being set up for the task. VFDs reduce the amount of energy imparted to the system. which is inefficient unless a comparatively complex recovery system is used. which means substantial cost savings in many motor systems. Conventional control processes use bypass or on-off controls to modulate the movement of work-in-process. a VFD can adjust the output of a pump or a fan to meet these requirements automatically. other system components can be left intact. they also have drawbacks in terms of maintenance and efficiency. However. and require a means of generating dc power. Mechanical. mixing. when direct control of the motor speed was required. such as a gearing system or an adjustable pitch pulley system. bypass methods similar to those used in fluid systems tend to be wasteful. n n VFDs are used in a wide range of applications. demonstrating that energy savings are not the only benefit of this technology. This can improve the quality of the finished product.Section 2: Performance Opportunity Roadmap Common Applications winding speed results in a loss of energy. VFDs are well suited for fluid systems.
such as throttling and bypass. Bearing Currents. These advantages are discussed in more detail in Improving Pumping System Improving Motor and Drive System Performance: A Sourcebook for Industry 31 . Electrical. such as positive displacement pumps. they have been replaced by VFDs. The energy lost because of increases in the amount of hydraulic slip is essentially unrecoverable. it can cause pitting on the bearing races and rolling elements.Section 2: Performance Opportunity Roadmap Belt systems are similar to gear systems in that various combinations of pulleys can be used to achieve different speed ratios. In some VFD applications. However. However. VFDs have many benefits and provide numerous advantages over other control methods. in applications in which the torque increases at low speeds. using VFDs in pumping and fan systems provides far greater energy savings than other flow control options. These systems work well in plants in which air demand varies. these systems tend to require a lot of maintenance and are subject to reliability problems. creating degradation problems. In applications in which torque decreases with speed. In these cases. A rotor assembly containing permanent magnets is mounted on the load shaft. they are inherently inefficient. such as insufficient torque or poor cooling. In such cases. for the most part. In applications in which the shaft is connected to a ground source (for example. and a conductor assembly with copper rings is connected to the motor shaft. although doing so requires securing the system and replacing one or more pulleys. the integral motor fan may not provide sufficient cooling at lower speeds. Hydraulic couplings work like a centrifugal pump. n Performance: A Sourcebook for Industry and Improving Fan System Performance: A Sourcebook for Industry. they consist of two components that do not come in physical contact with one another. For example. the harmonics could contribute to the induced shaft voltage. the induced voltage discharges through the bearings. The pulleys in these systems have a varying pitch angle that changes the speed ratio when the pulley is moved in or out. Although this current is relatively small. allowing speed to be adjusted continuously by controlling the amount of slippage. n Misapplications VFDs are not recommended for applications in which slowing down the machine speed causes operating problems. this concern is not as important because the windings generate less heat. Similarly. Air compressors using VFDs are becoming more common. Eddy current couplings allow speed to be adjusted continuously by controlling the strength of the magnetic field between the driver and driven component. Since VFDs tend to generate harmonics in the power supply to the motor. additional cooling may be required to prevent the motor from overheating. such as certain mixing processes. this allows greater slip between the two. In pumping systems that have high static head characteristics. Strengthening the field transfers more torque from the driver to the driven element while decreasing the field strength. and this can result in increased wear rates under load. power.gov/ industry/bestpractices.energy. often do not favor the use of VFDs.eere. in some constant horsepower applications. Magnetic ASDs use rare-earth magnets to transmit torque from a motor to a load. the linear relationship between output. The relative motion between the magnets and the copper rings creates a magnetic field that transmits torque through the air gap. however. The load characteristics of other machinery. Both are available on the ITP Web site at www. Eddy current couplings provide effective speed control. and equipment speed tends to favor other control technologies. Eddy current clutches can also be maintenance intensive. Most belt systems use fixed pulleys that can be changed. slowing down the pump speed too much can force the pump to operate in a virtual shutoff head condition. the pump can experience damaging vibrations and could fail to provide adequate flow to the system. producing an infinitely variable output speed. bearing currents are generally not a problem. Although these systems adjust speeds during system operation. In other applications. Competitive Advantages Depending on the application. Making use of the principle of magnetic induction. Varying the width of the gap changes the coupling force. they result in comparatively high heat loss and are typically less efficient than VFDs. because of sidewear on the belts. the power requirements of the motor will not drop significantly at lower speeds. Some belt systems allow speed ratios to be continuously adjusted. a pumping system) that provides a better discharge path for the voltage. This tends to be highly disruptive to the operation of the equipment. The cause of these problems is the induction of a slight voltage in the shaft of a motor or its driven equipment. In these applications. a cooling fan powered by its own motor is used. motors experience bearing problems caused by current that travels through the bearing. Under these conditions.
Newer technologies are always being evaluated. It can take several minutes for a ballast to bring these lights up to normal intensity. The most harmful effect occurs when the motor feeder cable is relatively long. can be placed on the output of the drive. Power Quality Effects. When the voltage changes from zero to its full value. there can be an overshoot at the motor terminals of more than twice the normal value. For example. Consequently. and they can cause equipment operation problems or even failure. Normally. There are several solutions to this problem. While effective at reducing bearing currents. this discharge can cause winding damage and premature failure of the motor. the issue of power quality merits attention. Efficiency Opportunity No. 6 Addressing In-Plant Electrical Distribution and Power Quality Issues Motor system performance can be adversely affected by poorly designed and maintained in-plant electrical distribution systems as well as power quality issues. inverter-duty motors should be used in PWM applications. or frequency. The pulses have a very steep leading edge. Insulated bearings on the motor could move bearing current issues downstream to the driven equipment. or inductor. current. The turn-to-turn insulation is designed for only a few volts. or an L-C filter can be placed at the drive output. Almost half of that overshoot can be dropped across the first turn of the first coil of the motor stator winding. although many manufacturers offer "inverterfriendly" insulation in their premium efficiency motors. and stepper motors along with programmable logic controllers (PLCs). Although this is not yet a proven technology for industrial motors. in plastics extrusion processes there is a risk that plastics or resins might solidify in production equipment during a process interruption. Some VFDs. it could eventually be used to eliminate drag and require minimal maintenance. Today's sophisticated motor systems employ newer technologies such as soft-starters. HID lighting systems must be supplemented by other lights to ensure safety. A voltage with a high rate of change is unevenly distributed along the motor's windings. One of the latest in the motor industry is the microfiber brush. Finally. This grease provides a ground path that can remove enough current to protect the bearing. drives. or rapid change of voltage with time. these motor systems and others nearby are often sensitive to and affected by poor power quality. It is important to note that motor manufacturers have developed an insulation classification known as inverterduty. which has been used on copying machines for years. a common trend in many energy efficiency programs is to upgrade interior lights to high-intensity discharge lighting (HID). Another option involves equipping the shaft with a grounding brush to provide an alternate path for the shaft voltage discharge. the grounding brush must be maintained. Since digital equipment often must be reset or resynchronized after a power disturbance. a capacitor can be placed in parallel with the motor. in emergency lighting applications. a momentary loss of power can result in a lengthy delay in restoring adequate light. and the overshoot voltage causes a discharge between the turns of the winding. the use of electrochemical grease is recommended for some applications. expensive batches can be lost if a power quality problem strikes at the wrong time. especially pulse width modulation (PWM) types. In fact. which often means replacing the element every three months. Motor users should always consult the drive manual when using longer motor feeder cables to ensure that the cables do not exceed the maximum recommended length. In pharmaceutical and other mixing or time-sensitive processes. An L-C filter is a low pass filter that consists of an inductance (L) and a capacitance (C). 32 Improving Motor and Drive System Performance: A Sourcebook for Industry . In addition. The inductance of a long motor feeder cable may create a resonance in the drive-cable-motor circuit. create rapid-rise-time pulses (spikes) in the voltage waveform. A reflected voltage wave may appear at motor terminals.Section 2: Performance Opportunity Roadmap One of the most common ways to avoid bearing current problems is to select or retrofit motors with insulated bearings. which is much more resistant to voltage pulses. Power quality is a growing concern in industry as more processes are being automated and more computers are being used to control and monitor equipment. Over time. Clearing the equipment of solidified plastics can be costly and time-consuming. Power quality issues are usually expressed in deviations in voltage. power problems can be quite costly. A choke. For some processes.
such as a damaged power line or the catastrophic failure of a transformer or switchgear component. and equipment contact with trees or vehicles. Outages. drives can be specified to have an adequate ride-through capability if the duration and magnitude of the expected sag are known. wind might cause a power line to contact a ground source. n Motors with large starting currents can create voltage sags. including outages. Voltage sags can be caused by utility system events such as faults created by equipment failure. many motors are equipped with an undervoltage relay that deenergizes the motor under low voltage conditions to prevent damage from the high current draw. For example. Voltage sags are most often caused by in-plant events or activities at a neighboring facility that pull large currents. Faults that cause momentary power losses are usually cleared quickly. and other signal distortions • Poor power factor • Electromagnetic interference. efficiency. Sags. once the fault is cleared. such as its torque. Since motor failure may interrupt a process. increasing the motor's voltage by 10% improves some operating characteristics of the motor. requiring replacement of the motor and restarting and perhaps resynchronizing the entire system. and power factor. Ideally. the most noticeable problem. Voltage Problems Voltage problems—which include outages. However. can be momentary power losses caused by faults from either internal or external events. transients and surges. Another consequence of low voltages is the increased current draw that the motor requires to meet the power requirement. The motor's efficiency can increase when the line voltage is up to 10% higher than the rated voltage. Motors are designed to operate with +/– 10% of their rated voltage. Outages. some utilities use rolling brownouts to manage their capacity. To prevent one area from losing power for an extended period. However. Long-term outages are usually the result of a line problem. reduce fire hazards.Section 2: Performance Opportunity Roadmap These are the primary problems associated with in-plant electric distribution systems and power quality: • Voltage problems. The consequences of voltage problems range from reduced performance characteristics to motor damage to complete motor failure. However. sags. and reduce downtime. Improving Motor and Drive System Performance: A Sourcebook for Industry 33 . Motor and drive systems that are intelligently configured and well-maintained are less likely to cause distribution system problems. a 10% decrease in the voltage supplied to a Design B induction motor decreases its torque by almost 20% while increasing its rated slip by more than 20%. Understanding the impact that motors have on the performance of a facility's electrical distribution system (and vice-versa) can help improve an industrial plant's overall operation. and unbalances—are basically any deviations in a normal waveform. lightning. and seasonal operation • Improperly sized transformers • Undersized conductors • Poor connections • Sources of low power factor in the distribution system. the switchgear can realign to provide power. Outages can also be part of a utility's strategy to manage loads during high demand periods. increase equipment life. sags. Voltage sags can cause protective devices such as relays to de-energize. especially if the motor is large relative to the capacity of the distribution system. harmonics. deviations in the voltage supplied to a motor system should be less than +/– 2%. Changes in the voltage supplied to induction motors can affect their performance significantly. causing an overcurrent condition that activates protective switchgear. and they can also create problems with process control equipment. even within this range. Voltage sags often cause problems with PWM types of VFDs. understanding common causes of outages and sags can prevent costly production problems. but at part load the efficiency could decrease. the effect of overvoltage on motor efficiency depends on the motor's load. Facilities with low power factors often experience voltage sags caused by the high current levels in the distribution system. A voltage sag is a decrease in the magnitude of voltage from 10% to 90% that lasts anywhere from half a cycle up to five minutes. nighttime. In fact. Voltage deviations can be caused by any of the following factors: • Changes in loads associated with daytime. surges. changes in the voltage supplied can affect a motor's performance. However. Finding solutions to these problems and correcting them can lower a plant's energy bills. Conversely. For example. Overvoltage and Undervoltage. Sizing motors to operate at 80% voltage is a major cause of oversizing. Power quality monitors can be installed to record troublesome sags and to identify their source and duration.
Dedicated transient voltage surge suppression (TVSS) devices are recommended for highly sensitive equipment. Seasonal changes also affect the power supply. each one of equal magnitude and out of phase by 120°. sensitive equipment such as computers and automated control systems usually require additional protection. Although facilities can sometimes be affected by power disturbances caused by neighboring customers. and so on. Unbalances. A nonsymmetrical—or unbalanced—system is so called because of differences between any two of the three phases. and life of a motor due are negative. This type of power supply unbalance can quickly lead to motor damage or failure. improve voltage. corrective action should be taken. When a voltage unbalance reaches 5%.Section 2: Performance Opportunity Roadmap These problems can be caused by sources within the plant or by the power supplier. in which a disproportionate share of single-phase loads is placed on one of the three phases • An open circuit on one phase • Different-sized cables carrying the three phases • Selection of the wrong taps on the distribution transformer • Single phase loads that create low power factors. installing automatic tap changing equipment. Transients and surges are often the result of a large switching activity. utilities usually increase voltage levels to handle anticipated increases in cooling loads from air-conditioners. A voltage unbalance results in a current unbalance. The derating factors require the motors to be operated at greatly reduced loads. Time Methods for correcting unbalanced voltages include redistributing single-phase loads or having the utility correct the supply voltage unbalance. Current Figure 16. these increases should remain within the tolerances specified by the utility in its power supply agreement. and reduce the system stresses that accompany large reactive loads. the phase currents can differ by as much as 40%. phase voltages in a plant should be monitored. System voltages can sometimes be corrected by adjusting transformer tap settings. An unbalance will also reduce the life of the motor because of the excess heat generated in the stator and rotor assembly. Transients and Surges. Voltage unbalance can be caused by factors like these: • The power supplier • A nonsymmetrical distribution of single-phase loads. In hot weather. In areas with large inductive loads. which can significantly reduce the efficiency of a motor. and if the unbalance exceeds 1%. a utility will often monitor the power supplied to the plant. or installing power factor correction capacitors. The enormous amount of energy in a lightning strike can destroy controllers and equipment. When a customer questions whether these standards are being met. Lightning is another common cause of transients. Unfortunately. The overall effects of voltage unbalance on the performance. energizing these capacitor banks can create transient voltage surges that affect sensitive equipment. NEMA Standard MG1 provides specific guidance on the motor derating factors used for various levels of voltage unbalance. utilities will energize capacitor banks to increase the power factor. however. a typical voltage standard is +/– 5%. chillers. efficiency. Three-phase electrical systems should have three vectors. such as energizing capacitor banks. Proper system grounding is essential to minimize the risk of equipment damage. Waveform distorted by harmonic effects 34 Improving Motor and Drive System Performance: A Sourcebook for Industry . Most utilities have standards for the power supplied to a customer's facility. plants that experience voltage problems should first perform an internal review to determine if an internal source is responsible. Therefore. However.
Harmonics can also interfere with the accuracy of sensitive control equipment. The increased current flow causes resistive losses. As plants become increasingly automated. However. The noise can cause failures in electronic circuits such as computers. Another is to enclose the entire motor feeder in metal conduit. compared to that of older. To minimize the effect of harmonics. Since a typical induction motor operates at around 85% power factor. one is to use a common choke mode or filter on the output of the drive. A low power factor can be corrected by installing capacitors at a particular motor. capacitors should never be installed directly at the motor terminals. many facilities install filtering devices and isolation transformers with VFDs. and so on should perform a power quality review. The reactance of the line between the drive and the motor can contribute to a resonance that increases harmonic distortion. many facilities with large motor systems and low power factors face stiff penalties as to power factor if it is not corrected. Therefore. noise couples easily into grounding conductors. such as transformers and induction motors. premium efficiency motors have actually increased the frequency of starting current problems. frequent sags. the line length between a VFD and a motor should be as short as possible. There are several ways to mitigate this noise. control circuits.Section 2: Performance Opportunity Roadmap Harmonics. Figure 16 shows a wave with about 8% fifth harmonic. where the capacitors are switched on and off with the motor contactor. Reactive power loads also reduce the in-plant electric distribution system's capacity by creating an additional voltage drop that can cause equipment to perform poorly. Soft-Starting Devices. Thus.90. controllers that operate poorly. or noise. Improving Motor and Drive System Performance: A Sourcebook for Industry 35 . Many electric utility companies charge additional fees (power factor penalties) if the power factor of the plant falls below 0. which waste energy. In fact. the starting torques of the new motors are lower and the starting currents are higher. motors are typically much less sensitive to harmonics than computers or communication systems. there is also an increase in the amount of equipment subject to power quality problems. as defined by IEEE Standard 519. Energizing large motors with "across-the-line" starting usually creates a large in-rush current. Start-up currents like those can cause voltage sags and other power quality problems. they create a jagged appearance to the sine wave. at a motor control center for a series of motors. n Electromagnetic Interference PWM types of VFDs can generate significant levels of electromagnetic interference (EMI). as a rule of thumb. whichever is more appropriate. or 300 Hz. large synchronous motors are used to add a leading power factor component to the distribution system. In some facilities. Harmonics negatively affect the performance of inductive machines. VFDs generate harmonic signals that affect both the incoming power supply and the power signal sent to the motors. which is defined in NEMA MG1. This can help plants locate the causes of problems and find cost-effective resolutions. that is both radiated from the drive and conducted in conduit. Because the switching is so rapid. and ground wires. this practice can lead to surges that damage the motor windings. At these high frequencies. The efficiency gains obtained with newer motors derive largely from a reduction in the rotor circuit resistance. Low power factor can also be caused by idling or lightly loaded motors and by operating equipment at above the Facilities that have problems with equipment overheating. Electrical equipment is often rated to handle a certain amount of THD (a common value is 5%). from the drive to the motor. This noise is generated by high-frequency switching of the voltage. Low power factor problems result mainly from the high line currents required to meet the real power demand. methods that help prevent such problems are worth considering. A sine wave with a fifth harmonic has a stair-step pattern. Harmonics increase the amount of heat generated in motor windings for a particular load. Consequently. the noise can be in the megahertz range. Harmonics are created by large nonlinear loads such as welders and variable frequency drives. However. cable tray. Many hand-held devices can record voltage and current waveforms that can be played back later on a personal computer for further analysis. A common multiple is the fifth harmonic. Harmonics are a form of signal distortion in which whole-number multiples of the main frequency are superimposed on the 60 Hz waveform. often six to eight times that of the normal operating current. n Solutions Power Factor Power factor is the ratio of real (working) power to apparent (total) power. NEMA has developed a special measure of harmonic distortion for motors called the harmonic voltage factor. conventional motors. When multiples of the fundamental are added in. and communications. n rated voltage. The harmonic content in a power signal is usually measured in terms of total harmonic distortion (THD). or at the utility point of delivery. Hand-held power quality monitoring devices are becoming quite inexpensive.
Filters. On-site power systems consist of generators that are powered by engines or turbines. And. number of times the system is expected to operate. but they are also often used with smaller VFD applications. These devices are almost always used with VFDs of more than 1. output power. and harmonics to prevent them from reaching sensitive equipment. controllers. adding single-phase loads to one phase of the distribution system can create a voltage unbalance among the phases that leads to poor motor performance. noise. time required for the system to operate. they can be grouped into two principal types: static and dynamic. consider using output filters to reduce potential overvoltage transients • Separate input power. several factors can degrade a system's ability to maintain proper voltage and current during internal or external events. check with the manufacturer to determine if the trip settings bandwidth can be increased • Consider automatic restart (flying restart) to mitigate trips caused by overvoltage or undervoltage. and controls in separate metal conduit or use metal shielding between them if they are in adjacent cable trays • If there are trips due to momentary high or low voltage. or oil. The drawbacks of these devices include slight efficiency losses. they have a finite life. and speed of start-up.000 hp.Section 2: Performance Opportunity Roadmap The electrical system stresses caused by starting large motors have prompted a demand for equipment that "softens" motor start-ups. Static systems rely on batteries to provide power when the incoming power either sags or stops completely. The purpose of soft-starting equipment is to limit the starting current. Typically. Uninterruptible power supply (UPS) systems should be considered for plants in which voltage sags or power interruptions can be particularly costly. These devices usually contain metal oxide varistors (MOVs) configured to provide a path for current to flow away from the equipment during a transient event. the introduction of another possible failure mode. Fuels cells are a promising alternative technology. In some cases. and the additional maintenance required for the transformer. the filters are used to comply with Federal Communication Commission (FCC) regulations regarding the transmission of signals that interfere with communication channels. Degradation of the grounding system can also interfere with equipment operation or prevent fault-clearing devices from working properly. On-Site Power Generation. Key considerations in selecting on-site generation systems are maximum load. if an automatic restart is appropriate for the end-use and can be done safely. and instrumentation. Isolation Transformers. TVSSs should indicate visually that all elements are still working. Dynamic systems rely on the inertia of a rotating mass—usually a flywheel—to supply rotating force to a generator long enough for an engine to start and take over as the prime mover. Types of soft-starters include special motor controllers and most VFDs. such as microwave heating and radio frequency drying equipment. The following actions can improve power quality in facilities using VFDs: • Install input line reactors (typically. increase the cumulative wear on the equipment. while they do not cause an immediate equipment failure. TVSSs afford protection from both highly damaging voltage surges and the less noticeable transients that. Install input. numerically controlled equipment. if a longer distance is required. A fundamental way to avoid many power quality problems is to review the capacity of the system before adding new loads. On-site power generation is used for cogeneration and to provide backup. and communication cables by at least 12 inches to minimize the EMI to control circuits. standby. 36 Improving Motor and Drive System Performance: A Sourcebook for Industry . These filters are also used with many electrotechnology applications. Although a properly designed system should not create power quality problems. output power. Capable electrical contractors or an electric utility can perform a site survey to determine whether the grounding system is adequate. Uninterruptible Power Supply Systems. 3% impedance) to reduce impacts from transients and mitigate harmonic currents • Keep the distance from the drive to the motor to within 50 feet. diesel fuel. Sophisticated filtering devices are often used with VFDs to prevent high-frequency harmonics from entering the power supply and disturbing other sensitive equipment in the distribution system. For example. shortening its operating life. Although UPS systems can be configured in many ways. Transient voltage surge suppressors (TVSSs) are designed to prevent sudden voltage surges from damaging sensitive equipment such as computers. these are in turn fueled by natural gas or stored fuels such as propane. Strategies for VFDs. Transient Voltage Surge Suppressors. which can usually limit starting currents to one and one-half to two times the motor's rated operating current. and emergency power. like any piece of electrical equipment. isolation transformers are used to filter damaging signal surges.
These include slot liners. However. This information allows the engineer or operator to make better decisions regarding the type of equipment required to correct the power quality problem. Improving Motor and Drive System Performance: A Sourcebook for Industry 37 . wire size(s). experienced. Tools and Facilities. Efficiency Opportunity No. To do this. practices. There are several ways to evaluate a service center. Next. Staff. These software systems allow the power quality of a facility to be evaluated continuously. It can also be helpful to inspect the service center and interview its staff. clean motor. a plant that uses small induction motors for the most part will want to avoid a service center whose "bread and butter" is locomotive motor-generator sets. such as electrical insulation materials. interruption). As large loads are added or dropped. and quality in regard to repairing low-voltage induction motors. An important first step is to assess whether the service center does a significant amount of repair work on motors of the type and size that your plant is likely to submit. the winding heads must be able to duplicate the original winding patterns. but these are not normally used in lowvoltage motors. an informal inventory of the facility and its capabilities and tools can be very helpful. The center's staff should be stable. Numerous computer-based monitoring systems are available to evaluate power quality. Most service centers stock only class F or class H insulating materials. Customers of motor repair service centers need to be knowledgeable about the service they are purchasing. but what does that mean? It certainly means more than ending up with a neat. and material for tying and restraining end turns. In such cases.g. Primary Market Niche. Errors and careless workmanship can reduce the efficiency and shorten the life of the repaired motor. Having a repaired motor tested at a lab certified by the National Volunteer Laboratory Accreditation Program can help to determine the motor's efficiency per IEEE 112-1996 method B and detect certain types of repair errors or shortcuts. Next. System Monitoring Software. qualified repair service centers. and it adds a slight thermal margin for motors that were originally insulated at a lower thermal class. but they can occur in plants that self-generate. it is helpful to check on whether the center houses a variety of materials needed for motor repairs. this alone cannot ensure quality work if the service center is not capable of it. It is important to specify the expected scope and quality of work.. the effect on the generator can be significant. number of effective turns. n Obtaining Information The following elements can indicate a service center's ability to perform high-quality motor repair work. this is usually impractical because of the time and expense involved. wire sleeves. For example. Plants that use a wide range of motor types can benefit from selecting two or more appropriate. A low turnover rate can indicate a high degree of employee satisfaction and a willingness on the part of management to invest in training and education. which often exceed original insulation heat ratings. This makes things simpler for the shop. A variety of predictive maintenance tests can be done to rule out certain flaws or rewinding errors that could reduce a rebuilt motor's service life rather than lower its efficiency. variations in frequency and current can be the result. 7 Using the Service Center Evaluation Guide Most users want to be sure that they are paying for a highquality repair. and cross-sectional area—unless proven better alternatives are agreed upon. Form-wound coils are often subcontracted. Repair Materials. Then.Section 2: Performance Opportunity Roadmap Current and frequency problems are not common in large utility systems. The repair should duplicate the original coils—the same dimensions. However. and well-trained. Work done outside a service center's primary market niche may be unacceptable in terms of quality and price. service centers should either carry a broad inventory of wires in various sizes or describe how they obtain the sizes needed quickly in order to meet your turnaround requirements. This also cannot reveal whether one repaired motor is typical of all those from the same service center. it can be helpful to inquire about the repair service center's staff. It is difficult to conduct thorough diagnostics and verify repairs without having equipment like surge testers and a well-regulated power supply. With on-site generation. This evaluation guide can assist industrial plants in evaluating a motor service center's capabilities. as needed. The service center must be able to handle the largest motors you expect to submit. the systems note the particular problem (e. special paper separators for coil groups. knowledgeable. voltage sag. If problems are encountered. For example. and it may not reveal whether a lowerthan-nameplate efficiency resulted from the recent repair or predated it. the electric power generator is sized to reflect individual end-use loads.
It is important to be familiar with motor construction. Tools and test equipment should be organized so they can be retrieved and used easily. but it does indicate the equipment and practices that are important for high-quality repairs. Determining satisfactory adherence to high-quality workmanship standards can be time-consuming. we associate cleanliness with good quality management. and calibration records. An elaborate computer system may be impressive. this includes a formal quality management system involving third-party inspections and certification. Examples are bearing fit standards. and important records. To maintain their calibration. See Section 4.Section 2: Performance Opportunity Roadmap Recordkeeping. and increasing awareness of ISO 9000 quality management standards. Places where bearings and lubricants are stored or installed must be clean. Advise the service center manager that this is part of a structured evaluation and that the manager might be asked to produce evidence of such things as employee training or equipment calibration practices. To ensure a comprehensive evaluation. Ideally. Avoid giving the impression of making judgments on the spot. Finally. So it is important to inquire about the repair center's recordkeeping system. be sure you are well informed. In spite of the rigorousness of the evaluation. Do not hesitate to diverge from the written checklist to better understand the service center's practices. because most of the materials and supplies used in a motor service center need to be protected from contamination. Standard Operating Procedures. it is important for the center to maintain high levels of quality. operating procedures. and related issues. This is more than a matter of aesthetics. "Where to Find Help. forms for recordkeeping. plan to reserve at least half a day. Two methods are available for evaluation: interviews and inspections." for more details about these publications. The checklist may not be necessary for infrequent customers of rewind services. These can be thorough and retained for many years. Advanced Energy's Proven Excellence certification program. testing procedures. Both should be used to an appropriate degree. Cleanliness. and commitment to quality. Finally. So. 38 Improving Motor and Drive System Performance: A Sourcebook for Industry . These are still rare. the next step is to observe the cleanliness of the center. It can be completed during the interview and annotated as necessary during a walk-through inspection. Read the Motor Repair Tech Brief and if possible. a Motor Repair Service Center Checklist is provided in Appendix D. because even a small particle can cause premature bearing failure. gauges and testing equipment should be put away or protected from damage when they are not in use. but many service centers keep good records on job cards. but they may become more commonplace as a result of EASA's promotion of the EASA-Q quality management system. try to make the service center manager feel comfortable. including how to obtain them. in that a record of past problems and remedies can be invaluable for diagnosing or preventing new problems and resolving warranty issues. more detailed sources such as Quality Electric Motor Repair: A Guidebook for Electric Utilities. Allow the manager to explain answers. repair methods. Motor management is like health care. Service center managers should be able to point to documents that provide standards. n Conducting the Evaluation The first step is to make an appointment with the service center. staff. Almost intuitively.
these officers favor the options that lead to both the largest and the quickest returns. a board of directors. Financial officers look for investments that will generate a favorable return on assets. And it allows financing department staff members to help prepare the kind of proposal that will persuade corporate officers of the monetary benefits of system upgrades. Fortunately. This kind of analysis often shows that electricity costs represent as much as 96% of the total LCC. The first step is to determine the total dollar impact of an energy efficiency measure. efficiency is often viewed as a luxury rather than a necessity. Measuring the Dollar Impact of Efficiency Motor system improvement projects can move to the top of the list of corporate priorities if the proposals reflect distinct corporate needs. The rate of return on assets is the annual earnings attributable to the sale of goods produced by those assets. Experience shows that corporate officials usually respond more readily to this approach than to a proposal that emphasizes the kilowatt-hours saved or efficiency ratios. such as product quality and downtime. The job of these officers is to create and grow the equity value of the firm. the LCC analysis for an efficiency measure includes projections of the following: • Search and selection costs for an engineering implementation firm • Initial capital costs. An economic approach also enables facility managers to relate energy efficiency improvements to broad corporate goals. A life-cycle cost (LCC) analysis provides an effective framework for this. by cutting corners in equipment maintenance and upkeep. As a comprehensive accounting of an investment option. the initial capital outlay only makes up 3% of the total. This rate of return is a key measure by which corporate decision-makers are held accountable. The corporation's industrial facilities do so by generating revenue that exceeds the cost of owning and operating the facility. including the purchase and installation of the equipment and the cost of borrowing money to finance the project • Maintenance costs • Supply and consumable costs • Energy costs over the economic life of the equipment • Depreciation and tax impacts • Scrap value or cost of disposal at the end of the equipment's economic life • Impacts on production. LCC analyses capture and total the expenses and benefits associated with an investment. and contributing to cost control today. As a result. Once the facility manager identifies one or more much-needed projects. and maintenance accounts for a mere 1%. avoiding unwanted surprises by sticking with familiar technologies and practices. This is information that the facility manager can use to make a more compelling case for an industrial efficiency project. The following sections describe the ways that industrial efficiency can save money and contribute to corporate goals while effectively reducing energy consumption and cutting noxious combustion emissions. This approach to making business decisions can impose several priorities on the facility manager. any measure Understanding Corporate Priorities Corporate officers are held accountable to a chief executive. The result—expressed as a net gain or loss—can be compared with other investment options or with the expected outcome of not making the investment.Section 3: Motor System Economics Section 3: Motor System Economics Overview Industrial facility managers often have to convince corporate management that energy efficiency improvements are worth the investment—which can be more of a challenge than the engineering behind the improvement. Clearly. The first step is to better understand the point of view and the priorities of corporate officers. and an owner or shareholders if the company is publicly held. Plant equipment—including system components— are assets that must generate an economic return. These include assuring reliability in production. divided by the value of the assets. This section contains some recommendations for proposing energy efficiency improvement projects to management. When faced with multiple investment opportunities. the next task is to prepare a proposal that reflects corporate priorities in dollars-and-cents language. sometimes Improving Motor and Drive System Performance: A Sourcebook for Industry 39 . There are usually many opportunities to improve the motor systems of an industrial plant. An effective way to begin the project proposal process is to analyze the economic ("dollars-and-cents") impacts of the efficiency improvement. the story does not end here.
" or for the net benefits of an investment to accrue to the point where they equal the cost of the initial outlay. The P/E ratio describes the corporation's stock value as the current stock price divided by the most recent annual earnings per share. There are five important factors to remember when calculating a simple payback: • It is an approximation. payback calculations do not always indicate the best choice among several project options • The payback calculation does not take into account the time value of money or tax consequences. LCC analyses should also include the "time value of money. tax impacts. This is the period of time required for a project to "break even. Establishing a Motor Management Program. The facility manager can strengthen the case for making improvements by relating a favorable LCC to determine corporate needs. But it might not be enough.Section 3: Motor System Economics that reduces electricity consumption without reducing reliability and productivity will have a positive financial impact on the company. not an exact economic analysis • All benefits are measured without considering their timing • All economic consequences beyond the payback are ignored • Because of the two previous factors. More sophisticated analyses take into account factors such as discount rates. 40 Improving Motor and Drive System Performance: A Sourcebook for Industry . and the cost of capital. One approach involves calculating the net present value of a project." A helpful tool in determining the LCC of motor improvement projects is the DOE MotorMaster+ software program. and the net present worth of the project must be positive in order for the project to be a "go. 2. it makes no distinction between a dollar earned today and one earned in the uncertain future. Another commonly used calculation for determining economic feasibility of a project is the internal rate of return. Staff in finance departments can determine which of the following suggestions for interpreting the benefits of electricity cost savings would work best in a specific company: n A New Source of Permanent Capital Lower electricity costs—a direct benefit of efficiency—can be regarded as a new source of capital for the company. the simple payback equals the initial investment divided by the annual benefit. This discount rate can be compared to the interest rate at which a corporation borrows capital." Presenting the Finances of Efficiency There are many ways to measure the financial impact of investments in efficiency. which is defined as follows: Net present value = present worth of benefits – present worth of costs Relating Efficiency to Corporate Priorities Future cost savings should be a strong incentive to improve the efficiency of a plant's motor systems. For a project that returns benefits in consistent. addition to earnings) that the proposal will generate. see Efficiency Opportunity No. A simple (and widely used) measure of project economics is the payback period. Regardless of how the efficiency investment is financed—through borrowing. Some analysis methods are more complex than others. The choice is up to the presenter and should take the audience into account. Still. retained earnings. For more information on this software tool. Many companies set a threshold (or hurdle) rate for projects. The investment that makes greater efficiency possible will yield annual savings each year over the economic life of the improved system. Multiplying that earnings increment by the P/E ratio yields the total new shareholder value attributable to the efficiency project. the simple payback period is easy to use and understand and many companies use it as the basis for a quick "go/no-go" decision. which is the minimum required internal rate of return for a project to be considered viable. annual increments. Future benefits are discounted at the threshold rate. the efficiency project proposal should first identify the annual savings (or rather. n Added Sharefolder Value Publicly held corporations usually take advantage of opportunities to enhance shareholder value. Shareholder value is the product of two variables: annual earnings and the price-to-earnings (P/E) ratio. and a proposal may be based on several of them. It does not take into account the time value of money. To take advantage of this measure. or third-party financing—the net annual cost savings will be a permanent source of funds as long as the efficiency savings continue. in other words. which is the discount rate that equates future net benefits (cash) to an initial investment outlay. and motor system efficiency can be an effective way to capture this value.
or to see if a project should be undertaken. With any of these methods. n A Better Bottom Line Each dollar saved on electricity goes directly to the bottom line. the facility manager can promise more reliable plant operations. Motor system economic analyses are driven largely by the amount of time and the percentage of its full capacity at which the motor system operates. Additional data needed include annual hours of operation (hours per year). In spite of this. Establishing a Motor Management Program. or how much money they could save by improving the performance of their motor systems. Nameplate Data Method. Performing a life-cycle cost analysis Improving Motor and Drive System Performance: A Sourcebook for Industry 41 . n Calculating Electricity Costs Electricity costs can be determined by using motor nameplate data or directly measuring current or power usage. based on a company's minimum threshold for return on the investment. Department of Energy's MotorMaster+ software program. n n Optimizing motor systems requires continual monitoring and maintenance. Routine system monitoring usually uncovers operational abnormalities before they present a danger to plant personnel. Further information on this tool is available in the Efficiency Opportunity No.S. A helpful tool in determining motor life-cycle costs is the U." These analyses are typically performed to compare one alternative with another. and property in the workplace. n A Call to Action A proposal for implementing an efficiency improvement can be attractive to corporate decision makers if it contains the following: • Specific opportunities for improving efficiency • The LCC associated with each proposed efficiency project • Identified project(s) that have the greatest net benefits • Connections to current corporate financial priorities— added shareholder value. its average load factor can be estimated. Efforts to achieve and maintain energy efficiency will also contribute to operating efficiency. 2. and these benefit workers in terms of enhanced safety and comfort. collecting data only once will not provide a true indication of the amount of energy that a motor system consumes.Section 3: Motor System Economics Greater Comfort and Safety on a system refers to an economic analysis that takes into account all of a project's costs. From a corporate perspective. For a corporation with a 10% profit margin. and improved capacity utilization • Ways in which the benefits of each project respond to current corporate needs. many facilities have no idea how much motor system operation costs on an annual basis. By ensuring the integrity of system assets. In systems with widely varying operating conditions. Life-cycle cost analyses should include the "time value of money. Eliminating or controlling these dangers reduces the threats to life. Life-cycle cost analysis is important when managing electric motor systems. which refers to the average percentage of full load electric power at which the motor operates. each dollar of electricity savings generates 10 times its equivalent in sales revenue. n Improved Reliability and Capacity Utilization Another benefit of greater efficiency is the more productive use of assets. including installation and the cost of borrowing money • Maintenance costs • Supply and consumable costs • Energy cost • Depreciation and tax impacts • Other annual or periodic costs • Scrap value or cost of disposal at the end of the project's or equipment's life • Effects on production. this also means a greater rate of return on a plant's assets. including: • Initial capital cost. health. and average load factor. unit cost of electricity ($/kWh)." Life-Cycle Costs Motor systems are critical to the operation of almost every plant and account for about 60%-70% of all the electricity used in an average plant. A quick way to determine energy costs is to use the motor nameplate data. such as product quality and downtime. the data must represent actual system operating conditions in order to be useful. To account for the fact that a motor usually does not operate at its rated full load all the time. reduction of environmental compliance costs. Annual electricity costs can be calculated by inserting this information into the simple calculation equation shown in the box on page 42 titled "Simple Calculation.
Line voltage is usually measured at the motor controller. Wattmeters require two simultaneous inputs—voltage and current. continuous operation) Case I. Taking hot measurements (at high power levels) of motor current pose safety risks for workers.760 hours) x ($0." Direct measurements of motor current are not always practical.746 kW/hp) x (1/motor efficiency) x (annual hours of operation) x (electricity cost in $/kWh) x load factor Assumptions: Cost of electricity = $0.356 Direct Measurement Most industrial motors have a service factor of 1.85 power factor (nameplate) 0. It can be convenient to take these readings at the motor controller.05/kWh) = $34. This calculation is for a motor with a constant load.732) x (power factor) ]/1000) x (annual hours of operation) x (electricity cost in $/kWh) Annual electricity costs = (77. line voltage drops with increases in power usage. which can significantly reduce insulation life.15. Direct Measurement Method. preferably at the same time that the current reading is taken. then calculations using direct measurement of amps and volts will not provide useful results.85)]/1000) x (8.05 $/kWh unit electricity cost Annual hours of operation = 8.Section 3: Motor System Economics A clamp-on type ammeter is used to measure current on each of the three power cables running to the motor.750 hours) x ($0. See the calculation for a motor with a constant load shown in Case II in the box titled "Direct Measurement. the measured kW value is multiplied by hours of operation and electricity costs. most industrial motors are three-phase. Assumptions: 3-phase motor 0. This means that a motor with a nominal nameplate rating of 100 hp could in fact be operated intermittently up to 115 hp. If a wattmeter is not available or if it is not practical to use one. however.05/kWh Load factor = 65% Motor efficiency = 95% Example: Motor full-load hp = 100 hp Annual hours of operation = 8. To calculate electricity consumption.111 42 Improving Motor and Drive System Performance: A Sourcebook for Industry . many motor installations do not provide convenient access to both. A more accurate way to determine electricity consumption is to take electrical measurements.111 Example: Average load amp measurement across all phases = 115 A Measured voltage = 460 V Annual electricity costs = [ (115 A) x (460 V) x (1.95) x (8.88 kWh) x (8.760 hours) x ($0. If there is a possibility the motor load is below 65% of the motor's rated capacity. The direct measurement method requires reading power (kW) with a wattmeter or reading amps and volts and calculating kW using the nameplate power factor.760 hours (3-shift.746 kW/hp) x (1/0. Simple Calculation Annual energy costs = (motor full-load brake horsepower) x (0. Using a Wattmeter Annual electricity costs = Wattmeter reading (using a 3-phase setting) x (annual hours of operation) x (electricity cost in $/kWh) Example: Wattmeter reading = 77. these measurements might not be feasible in an industrial environment where power connections are exposed to moisture or contaminants. motor efficiency can drop slightly when the motor is operated above the rated load. the connection box on the motor itself is sometimes more accessible.88 kWh Case II. continuous operation) Annual electricity costs = (100 hp) x (0. that is. one that does not vary over time. In some facilities. Using a Voltmeter and an Ammeter Separately Annual electricity costs = [ (load amps) x (volts) x (1. as shown in the calculation in Case I in the box titled "Direct Measurement" on this page.732) x (0.760 hours (3-shift.65 = $22. however. then amps and volts can be measured separately. An important implication of the service factor is that the load factor could be greater than one if the motor is operated continuously.05/kWh) x . However.05/kWh) = $34.
Paperboard Mills Blast Furnaces and Steel Mills Industrial Organic Chemicals. Electric utilities can answer questions about electrical tariffs. The study.7 million Motor Energy Costs / Total Operating Costs 6.4% 6. such as improved control over production processes.8 billion per year.000 $283.eere. Table 4 displays motor systems energy use and potential savings per establishment in the 10 four-digit SIC groups with the highest annual motor energy consumption.000 $492. Different rates depend on the level of consumption and the time of year.6% 6.5% 9. the use of lightly loaded induction motors can adversely affect the power factor of a plant and lead to higher bills. In these Table 4. power factor penalties.000 $946. Financial Impact of Motor Consumption and Savings for Selected Industries Industry Groups Paper Mills Petroleum Refining Industrial Inorganic Chemicals. Costs/ Estab. the marginal cost of the electricity must be considered.energy. or up to $5. and do not factor in other benefits likely to result from optimization. Repair involves both the parts and labor required to troubleshoot and fix equipment that is not performing A study commissioned by the U. n n The calculations shown earlier use electricity rates stated in terms of dollars per kilowatt-hour ($/kWh). can be affected by electric motor systems. Taking lifecycle costs into account during the initial system design phase or when planning system upgrades and modifications can both reduce operating costs and improve system reliability. proven. and improved environmental compliance.000 $219. and United States Industrial Electric Motor Systems Market Opportunities Assessment Improving Motor and Drive System Performance: A Sourcebook for Industry 43 .4% 10.0% 21. For example. effective design and equipment specification practices can help to minimize operating costs. 6. Addressing In-Plant Electrical Distribution and Power Quality Issues. in a probability-based sampling of the U. United States Industrial Motor Systems Market Opportunities Assessment.000 Savings as % of Operating Margin 5% 1% 6% 5% 2% 1% 13% 1% 4% 5% Sources: Manufacturers Energy Consumption Survey 1994. This takes into account energy and demand charges.5 million 2. This study is based upon on-site surveys of 265 industrial facilities in the United States.5% 1. Other components of industrial electricity bills. manufacturing sector. reduced maintenance.1 million 1.7% 1.000 $358. Department of Energy has estimated that optimizing industrial motor systems through the implementation of mature.gov/industry/bestpractices.7% Savings per Estab. Census of Manufacturers 1993. Similarly. can be downloaded from the ITP Web site at www. and help plants to avoid expensive failures.000 $116.000 $483. Bureau of Economic Analysis 1997. 4.1% 1. However.6 million 5.6 million 1. Demand charges are based on the peak demand for a given month or season and can have significant impacts on the electricity costs of some customers. A well-designed PPM schedule minimizes the need for repairs by detecting and resolving problems before they develop into more serious issues. see the Efficiency Opportunity No.000 $91. nec. electric utilities use more complicated rate structures to bill their industrial customers.S.3 million 1. reduce the risk of unplanned downtime. In general.S. such as power factor penalties. When the economic impacts of efficiency measures are calculated. or obtained through the EERE Information Center. and different rates for different levels of consumption. A PPM schedule can improve system reliability.4% 2. Industrial Gases Plastics Materials and Resins Cement. Hydraulic Pulp Mills Motor Sys.2 million 1. These typically include both energy ($/kWh) and demand charges ($/kW).0 million 1.Section 3: Motor System Economics Energy and Demand Charges—Understanding Your Utility Bill properly or has broken. seasonal rates. n Motor Systems Market Study Life Maintenance Considerations and Life Cycle Costs There are two principal types of maintenance: preventive or predictive maintenance (PPM) and repair. PPM is less costly than repair. nec. Per Year $659.6 million 3. For more information. These estimates include only the energy savings.0 million 6.000 $121. costeffective energy-saving techniques can reduce industrial energy consumption by 75 to 122 billion kWh per year.
the difference between revenues from sales and variable costs. Potential savings at the typical plant are also very large. For optimum motor system economics. motor system users should use a life-cycle cost analysis to select the best equipment and then carefully operate and maintain the equipment for peak performance. The right-hand column of Table 4 shows potential energy savings as a percentage of operating margin. operating margins for the 10 groups listed below ranged from 10% to 24%. and clustered around 16%.Section 3: Motor System Economics industries. overall system efficiency is the key to maximum cost savings. including labor. the energy cost is $6 million. Thus. the annual cost of motor system energy in a typical plant exceeds $1 million. in steel mills. and selling costs. Rather. ranging from $90. Summary A highly efficient motor system is not just one with an energy efficient motor. These figures suggest the potential impact of motor energy savings on the bottom line. materials. 44 Improving Motor and Drive System Performance: A Sourcebook for Industry . even relatively small increases in operating margin can have a significant impact on profitability.000 per year in the industrial organic chemicals sector to nearly $1 million per year in petroleum refineries. Many motor system users tend to be more concerned with initial costs and obtaining the lowest bids for components than with system efficiency. The process industries listed in Table 4 operate on very thin margins. that is. In 1996.
ITP helps industries identify and realize the best energy efficiency and pollution prevention options from a system and life-cycle cost perspective. ITP works with the nation's most energy. Three-Phase Input Power Process Mechanical and Electrical Feedback POWER CONTROLS MOTOR COUPLING LOAD PROCESS Motor/Drive Subsystem Mechanical Subsystem 1200 rpm Figure 17. MS EE-2F 1000 Independence Ave. DC 20585 Phone: 1-877-EERE-INF (1-877-337-3463) www. • The Directory of Contacts section contains a list of associations and other organizations that can provide additional information on improving the performance of motor and drive systems. and Resources and Tools. This collaborative process aligns industry goals with federal resources to accelerate research and development of advanced technologies identified as priorities by industry. ITP was established to assist industry in achieving significant energy process efficiency improvements.. The advancement of energy. software assessment tools. ITP is dedicated to improving the efficiency and performance of electric motor and other industrial systems nationwide.and resource-intensive industries to develop a vision of their future and roadmaps on how to achieve these visions over a 20-year timeframe. • Through its Technology Delivery strategy. training courses. Directory of Contacts. • Resources and Tools provides information on books and reports. SW Washington. and other resources that help industries improve the performance of industrial energy use. Electric Motor System Improving Motor and Drive System Performance: A Sourcebook for Industry 45 . government and commercial statistics and market forecasts.Section 4: Where to Find Help Section 4: Where to Find Help This portion of the sourcebook lists resources that can help end users increase the cost-effectiveness and performance of their motor and drive systems. renewable energy. ITP develops and delivers advanced energy efficiency.energy. other publications. software.and process-efficient technologies is complemented by ITP energy management best practices for immediate savings results. These resources are organized in three main subsections: DOE's Industrial Technologies Program (ITP) and Technology Delivery. and other sources of information These resources can help motor system users make informed decisions when designing and purchasing motor and drive systems. and pollution prevention technologies and practices for many industrial applications.eere. Department of Energy Industrial Technologies Program (ITP) Room 5F-065. training sessions.S. ITP and Technology Delivery U.gov/industry n Overview Industrial manufacturing facilities consume 36% of all the energy used in the United States. Resources include publications. Therefore.
Section 4: Where to Find Help In particular. minimizing distribution losses. Collectively. Potential energy savings 46 Improving Motor and Drive System Performance: A Sourcebook for Industry . System Optimization 65% Figure 18. and properly matching the motor and drive to each other as well as to the load. and boost productivity. and assessments for smallto mid-sized plants through university-based Industrial Assessment Centers (IAC). targeted industrial system assessments. The steps involved in accomplishing a system optimization involve characterizing the process load requirements.eere. and training. ITP delivers energy solutions to help industry save energy and costs. reduce waste. located at 26 universities around the country. n Emerging Technologies Energy-Efficient Motors 15% Motors Management 20% Emerging technologies are those that result from R&D and are ready for full-scale demonstration in actual applications. and save energy. ITP helps mitigate the risk associated with using new technologies that are supported by industry partnerships. This demonstrates that management decisions and technical actions reflecting a systems approach at the corporate and plant level are key to achieving large-scale energy efficiency improvements in industrial motor systems. considering all cycles of the process load. In addition. reduce emissions. Through activities such as energy assessments. energy expenditures can be 10% or more of total operating costs. However.gov/industry/bestpractices. third-party validation and verification of performance data.energy. implementation of emerging technologies. ITP offers ongoing. controlling the process load in the most optimal manner. These include software tools. components and control strategies are selected that best match the new. and enhance environmental performance. Visit ITP's Save Energy Now Web site at www. Shared implementation. matching the driven equipment to load requirements.energy. In a systems approach. and expert assessments of energy. ITP offers several resources to assist in motor and drive system energy management. ITP recognizes that companies may be reluctant to invest capital in new technologies even though they can provide significant energy and process improvements. technical resources. Teams composed of engineering faculty and students from the centers. Many of the recommendations made in these assessments have payback periods of less than 18 months and can still yield significant energy savings. Through its Save Energy Now strategy. these efforts assist industry in adopting near.and long-term energy-efficient practices and technologies. through its Technology Delivery strategy. This approach seeks to increase the efficiency of electric motor systems by shifting the focus from individual components and functions to total system performance (see Figure 17 on page 45). and environmental benefits enable new technologies to be accepted more rapidly. economic. reduced process load. reduce waste and pollution. n Energy Assessments Depending on the industry. and technical resources for industrial systems energy management. Save Energy Now energy assessments identify opportunities for implementing new technologies and system improvements to increase efficiency. conduct energy audits or industrial assessments and provide recommendations to manufacturers to help them improve productivity. small to medium-sized manufacturers can qualify for free assessments from IACs.gov/industry/saveenergynow for more information. eere. Figure 18 shows that two-thirds of the potential savings in manufacturing plants' motor systems are systems-related. ITP encourages the nation's largest energy-consuming plants to apply for energy assessments as an important first step in identifying energy efficiency opportunities. Learn more about IACs at www. Then. process system design and manufacturing best practices are used to optimize the performance of the entire process system. through technology implementation solicitations. energy assessments through ITP's Save Energy Now strategy. ITP encourages the use of a systems approach to motor system design and analysis.
energy.gov/industry/bestpractices.energy. The software features a number of what-if scenarios to determine which energy efficiency measures have the greatest savings potential for their facility. pumping. The BestPractices site offers case studies of companies that have successfully implemented energy-efficient technologies and practices. and identify the most energy-intensive equipment. training events.eere. or electricity. – The Steam System Assessment Tool (SSAT) estimates the impact of key steam system improvements. • The Steam System Tool Suite helps users identify and implement the most effective solutions for a facility's steam systems. steam. AIRMaster+ helps end users assess the potential for Improving Motor and Drive System Performance: A Sourcebook for Industry 47 . and emission savings of different improvements. Efficiency gains in compressed air. • The Fan System and Assessment Tool (FSAT) helps determine the efficiency of fan system operations by identifying savings opportunities. ITP offers software tools and training in a variety of system areas to help industry become more energy and process efficient. and solicitations for plant assessments. solicitations. and greater competitiveness. n Qualified Specialists A Qualified Specialist is an individual who has an extensive background in optimizing industrial systems. ITP and BestPractices Web Sites. ITP offers other software tools to help plant personnel identify and implement energy efficient practices in their manufacturing facilities. or to locate Qualified Specialists in your area.energy.gov/industry. The tool details the energy. n Software Tools In addition to MotorMaster + and MotorMaster+ International. Individuals become qualified by taking DOE-sponsored training on BestPractices assessment and analysis software tools. Compare performance of the furnace under various operating conditions and test "what-if" scenarios. • The Process Heating Assessment and Survey Tool (PHAST) provides an introduction to process heating methods and tools to improve thermal efficiency of heating equipment. tip sheets. go to www. and usually result in immediate energy and cost savings. n Technical Resources ITP offers a variety of resources to help industry achieve increased energy and process efficiency. and resources to assist manufacturers who are interested in increasing the efficiency of their industrial operations. and much more through the ITP site at www. and calculating energy savings.eere. and improve environmental performance.Section 4: Where to Find Help Energy Management efficiency and productivity improvements in compressed air systems. Users can also perform an energy (heat) balance on selected equipment (furnaces) to identify and reduce non-productive energy use. • AIRMaster+ is a software tool developed by ITP and jointly sponsored by the Compressed Air Challenge™. motor. fan.gov/ industry/bestpractices. process heating. cost. improved productivity. You can learn about upcoming events. – 3E-Plus® Insulation Appraisal Software was developed by the North American Insulation Manufacturers Association to increase awareness of the benefits of insulation and to assist plant personnel in assessing insulation opportunities. and steam systems can be significant. The ITP and BestPractices Web sites offer a large array of information. and passing a rigorous exam. as well as software tools. This includes: – The Steam System Scoping Tool (SSST) helps steam system energy managers and operations personnel for large industrial plants profile and grade steam system operations and management. You can see these and other resources at www. n ITP encourages manufacturers to adopt a comprehensive approach to energy use that includes assessing industrial systems and evaluating potential improvement opportunities. Use the tool to survey process heating equipment that uses fuel. rating system efficiency. and evaluate steam system operations against identified best practices. products. • The Pumping System and Assessment Tool (PSAT) assesses pumping system efficiency by using achievable pump performance data from Hydraulic Institute standards and motor performance data from the MotorMaster+ database to calculate potential energy and associated cost savings. reduce waste.eere. For more information on how to become a Qualified Specialist.
Contact the EERE Information Center at (877) 337-3463 or www. gov/industry/bestpractices/techpubs_motors. however. fans. gov/industry/bestpractices/case_studies. including those focused on industrial energy efficiency.energy.000 ac motors.html.energy. including MotorMaster+. The software also features motor inventory management tools.html. calculate efficiency benefits for utility rate schedules with demand charges. users can conduct analyses in different currencies. Educational and informative materials. and events related to motor systems and other industrial systems such as steam. motors. and repair documents can be found on the BestPractices Web site at www.eere. and determine "best available" motors. With this tool. technical issues. Since BestPractices continues to develop and identify energy improvement programs.energy. and steam. and French.gov/industry/bestpractices. new products and services. Web updates.gov/industry/ bestpractices/energymatters. MotorMaster+ International includes many of the capabilities and features of MotorMaster+. ITP has developed several motor tip sheets through its BestPractices program. market assessments. edit and modify motor rewind efficiency loss defaults. industrial plants.eere. They can also answer questions about industrial systems such as compressed air. These tip sheets provide concise descriptions of common improvement opportunities. Software. and compressed air.eere. Tip sheets can be found on the BestPractices Web site at www:eere. These projects and the accompanying savings can be replicated at similar plants owned by the same company and by other industrial plants. See motor system-specific case studies and performance spotlights on the BestPractices Web site at www. process heating. EERE Information Center The EERE Information Center fields questions on EERE products and services. including additional copies of this sourcebook. training and events.eere. and in Appendix B of this sourcebook. and further information on all aspects of the BestPractices Program are available by calling the EERE Information Center at (877) 337-3463. savings evaluation. gov/industry/bestpractices.Section 4: Where to Find Help Training n ITP offers training sessions in industrial systems improvements using DOE software tools. See the discussion on the MotorMaster+ tool in Efficiency Opportunity No.eere. additional tip sheets are expected. including those tested under the Institute of Electrical and Electronic Engineers (IEEE) standard. which includes a catalog of more than 20. go to www. gov/informationcenter.gov/industry/resources/ebulletin. new ITP and BestPractices products. and information on training is also available at the BestPractices Web site at www. process heating. Energy Matters is ITP's quarterly information source that informs the industrial audience of energy efficiency opportunities. Many case studies examine the bottomline benefits that successful applications of energy-efficient practices and technologies can yield. and environmental reporting capabilities. publications. users can evaluate repair/replacement options on a broader range of motors. The tool can be modified to operate in English. 2: Establishing a Motor Management Program in Section 2 of this sourcebook. energy accounting. These fact sheets. n Motor and Drive System Specific Resources Software: MotorMaster+ and MotorMaster+ International MotorMaster+ is an energy-efficient motor selection and management software tool.energy. and those tested using International Electrical Commission (IEC) methodology. Spanish.eere. maintenance log tracking. Subscribe online at www. 48 Improving Motor and Drive System Performance: A Sourcebook for Industry . n News E-Bulletin is a monthly online newsletter that spotlights technologies.S. ITP has also developed technical publications that provide an increased level of detail and guidance in identifying and implementing performance improvement opportunities. efficiency analysis. More information on motor systems training and other training offerings can be found on the BestPractices Web site at www. significant project developments.energy. To subscribe online.energy. and program activities. • Case Studies and Performance Spotlights Motor system case studies and performance spotlights describe successful energy and process improvement projects that are boosting productivity and saving energy at U.gov/industry/bestpractices.energy. Technical Publications • To increase industry awareness of several fundamental improvement opportunities. and solicitations.eere.energy. pumping.
epri. a nonprofit public benefits corporation. Fax: (212) 398-0023 www. Fax: (212) 752-4929 www. Electrical Apparatus Service Association. Founded in 1992. New York 10016 (212) 419-7900. The Institute's mission is to enhance both the global competitiveness of U. and control technology. with 700 under development. and safeguarding their integrity. Louis. EASA publishes a software product. 4th Floor New York.Section 4: Where to Find Help Directory of Contacts The following organizations can provide more information on improving the performance of motor and drive systems. The Consortium for Energy Efficiency. CEE is the only national organization for all ratepayer-funded efficiency program administrators.org The IEEE is a not-for-profit association and has more than 375. Motor Rewind Data.webstore.easa. develops national initiatives to promote the manufacturing and purchase of energy-efficient products and services.S. American National Standards Institute (ANSI) 25 West 43rd Street. and state-ofthe-art technology. Electric Power Research Institute (EPRI) 3420 Hillview Avenue Palo Alto.S.com EPRI is composed mainly of electric utility companies. (CEE) 98 North Washington Street. Fax: (617) 589-3948 www. CA 94304 (800) 313-3774 www. statewide and regional energy-efficiency administrators.ansi. and Canada use CEE national initiatives to increase the effectiveness of their local efforts. Inc.cee1. non-profit organization that administers and coordinates the U. business and the U. Through its engineering and educational programs. equipment.S. Suite 101 Boston. Improving Motor and Drive System Performance: A Sourcebook for Industry 49 .org To download standards: www. Fax: (314) 993-1269 www. Through its technical publishing. New York 10036 (212) 642-4900.S. the IEEE produces 30% of the world's published literature in electrical engineering and computers. 17th Floor New York. Inc. CEE members include administrators of energy-efficiency programs and their key public stakeholders.com EASA is an international trade organization of more than 2. that contains specifications for rewinding electric motors from numerous manufacturers. voluntary standardization and conformity assessment system. conferences.ansi. EPRI's charter is to discover.org ANSI is a private. develop. environmental groups. and deliver high value technological advances through networking and partnership with the electricity industry.ieee. Institute of Electrical and Electronics Engineers (IEEE) 3 Park Avenue. MA 02114 (617) 589-3949.000 individual members in 160 countries. Efficiency programs across the U. EASA provides members with a means of keeping up-to-date on materials. Missouri 63132 (314) 993-2220. research organizations and state energy offices. quality of life by promoting and facilitating voluntary consensus standards and conformity assessment systems. This includes utilities.org CEE. and consensus-based standards activities.100 electromechanical sales and service firms in 50 countries. and has more than 800 active standards. (EASA) 1331 Baur Boulevard St.
NEMA is a leading developer of voluntary standards for the electric component industry. better transmission hardware. and Policy Opportunities. U. Program. (CEE) 98 North Washington Street.nema. Michael Shepard.org Motor Decisions Matter is a national public awareness campaign that strives to educate corporate and plant decision-makers about the financial and productivity benefits of sound motor management policies. software designer. public and private sector sponsors include motor manufacturers. Inc.gov/informationcenter The Information Center is a one-stop-shop for resources and information on improving electric motor systems. Suite 801 Washington. chronicles experience with drivepower programs and policies. Resources and Tools A wide range of information is available on the application and use of drives and motors. regional efficiency organizations.Section 4: Where to Find Help Motor Decisions MatterSM Campaign The Consortium for Energy Efficiency. In understandable language to nonengineers.eere. Inclusion here does not constitute a recommendation or endorsement by the U. www.S. 2nd Edition Authors: Steven Nadel. and comprehensive monitoring and maintenance. DC 20036 (202) 429-0063 www. Neal Elliott. Note that the descriptions of these resources were taken from material developed by the publisher. and trade associations (including NEMA and EASA).org Energy Efficient Motor Systems: A Handbook on Technology. or author. addresses how motors and motor systems can achieve greater efficiency through motor management. Suite 1752 Roslyn. Suite 101 Boston. Fax: (703) 841-5900 www. R. This section focuses on the following resources and tools: • • • • • • Books Other Publications (reports.motorsmatter. provides an overview of existing motor stock. Fax: (617) 589-3948 www.aceee. Gail Katz. Managed as a special project by CEE. Department of Energy. manuals. and end-use of electricity. Steve Greenberg. standards) Software Periodicals Training Courses Materials available from the EERE Information Center. and offers recommendations for future efforts to increase motor system efficiency. 50 Improving Motor and Drive System Performance: A Sourcebook for Industry . optimized controls. guides.org NEMA is the largest trade association for manufacturers of products used in the generation. MA 02114 (617) 589-3949. de Almeida Description: Updates and revises the best-selling first edition. Department of Energy Office of Energy Efficiency and Renewable Energy EERE Information Center (877) 337-3463. utility and state efficiency program administrators. improved component sizing and repair. National Electrical Manufacturers Association (NEMA) 1300 North 17th Street.S. Books American Council for an Energy Efficient Economy 1001 Connecticut Avenue NW. distribution.energy. and Anibal T. VA 22209 (703) 841-3200. transmission.
L.cfm Energy Efficient Electric Motor Selection Handbook. Includes descriptions of how operating factors such as speed and design voltage effect performance.gov/corporate/contact/publicinfo.uk Energy-Efficient Electric Motors. Cambridge University Press 100 Brook Hill Drive West Nyack. Its audience includes plant managers. Suite 300 Boca Raton FL 33487 (800) 272-7737 www. W. and life-cycle cost.O. Completely revised and expanded. and advanced power electronic drivers. performance. and starting conditions.barks.org Power Electronics and Motor Control. NY 10994 (845) 353-7500 www. and D. windings. the book reflects the recent state of the field.co. 400 N. 4 Author: Washington State Energy Office Description: Compiled to help industry identify opportunities for cost-effective application of energy efficient motors. Liang Description: Includes a new chapter on the application of PWM techniques in induction motor speed control in this second edition of a comprehensive introduction to power electronics. Contains a discussion on the characteristics. Inc.crcpress. economics. plant engineers.cambridge. The middle portion considers motor application. such as insulation. including the finite element approach. Currently out of print. Bonneville Power Administration Public Information Office P. and others interested in energy management or preventive maintenance programs. as well as recent developments in control electronics. Chapters on electronic switching devices and adjustable speed drives are completely rewritten. Permanent Magnet Motor Technology Revised Authors: Jacek Gieras and Mitchell Wing Description: Demonstrates the construction of permanent magnet (PM) motor drives and supplies ready-to-implement solutions for common roadblocks. Hulley. 3rd Edition. explaining how motors are best matched to their power systems and operating environments. adjustable speed drives and their applications. advanced switched reluctance motor drives. IL 60611-4104 (312) 321-9440 www. power factor. and describes optional accessories and proper installation practices. Nailen Description: Covers standards and specifications. OR 97208 (503) 230-7334 www.Section 4: Where to Find Help Barks Publications. Suite 900 Chicago. the economics of energy-efficient motors and systems. Michigan Avenue. T. availability may be limited. CRC Press . The author presents fundamental equations and calculations to determine and evaluate system performance.USA 6000 Broken Sound Parkway NW. Improving Motor and Drive System Performance: A Sourcebook for Industry 51 . It covers the economic and operational factors to be considered when motor purchase decisions are being made.bpa. explores modern computer-aided design of PM motors. N. energy efficiency. and benefits of standard versus high-efficiency motors in the 1 to 500 hp range. efficiency. efficiency. Shepherd. Also looks at components.com Managing Motors Author: Richard L. and covers how to select PM motors to meet the specific requirements of electrical drives. 2nd Edition Authors: W. It includes five new chapters covering key topics such as the fundamentals of power electronics applicable to electric motor drives. Revised and Expanded Author: Ali Emadi Description: This detailed reference provides guidelines for the selection and utilization of electric motors for improved reliability. Box 3621 Portland. and reliability. and bearings. and permanent magnet and brushless DC motor drives. Rev.
Many circuits explained with step-by-step sequences that help students learn the concepts and applications of control logic. provides easy-to-follow instructions and essential information for controlling industrial motors. applications of motor control circuits in industry. commercial. and how to troubleshoot them. with discussion of installation issues. Fourth Floor Burlington MA 01803 (781) 313-4700 www. Bose Description: Power electronics is an area of extremely important and rapidly changing technology. Geitner Description: A four-volume series of books for machinery management at process plants. and troubleshooting motor controls. Electrician's Technical Reference: Variable Frequency Drives Author: Robert Carrow Description: Presents practical information on ac variable frequency drives.P. Volume 2: Machinery Failure Analysis and Troubleshooting (3rd Edition). Covers electric motors and drives in each volume. residential. Keljik Description: Provides extensive coverage of electric motors and motor controls. Both industrial and commercial variable frequency drive applications are addressed. This book is meant to help engineers operating in all these areas stay up-to-date on the most recent advances in the field. Volume 4: Major Process Equipment Maintenance and Repair (2nd Edition) 52 Improving Motor and Drive System Performance: A Sourcebook for Industry . Elsevier 30 Corporate Drive.com Electric Motor Control. NY 12065 (800) 648-7450 www. Herman Description: Provides explanations of motor control circuits.com Electric Motors and Drives: Fundamentals. Basic theory is explained when necessary. Types and Applications. explaining and comparing most of the types currently in use with many examples and applications. 7th Edition Authors: Walter N. and illustrations. as well as to be a vehicle for clarifying increasingly complex theories and mathematics. The book offers a practical approach with minimum theory. with little reliance on formulas. and shows how motors can be utilized in various types of electric circuits and products. sizing and selection. Each provides a thorough analysis of its respective title subject with field-proven techniques. military and aerospace environments.delmarlearning. 2nd Edition Author: Austin Hughes Description: For nonspecialist users of electric motors and drives. 3rd Edition Author: Michael Brumbach Description: Focuses on troubleshooting and maintenance.K. Bloch and F. Volume 1: Improving Machinery Reliability (3rd Edition). Electronic Variable Speed Drives. how to apply them. Herman and Walter N. Alerich Description: Newly revised. graphs. It also includes coverage of relay controls. Electric Motors and Motor Controls Author: Jeffrey J. troubleshooting. the hardware that makes up these circuits. 4th Edition Authors: Stephen L. Volume 3: Machinery Component Maintenance and Repair (2nd Edition). with applications proliferating in industrial. Industrial Motor Control. Power Electronics and Motor Drives: Advances and Trends Author: Bimal K. from basic principles of electrical motors and controls to more complex "real-world" applications. Alerich and Stephen L. and energy savings with variable frequency drives. taking their expertise into account. metering. Practical Machinery Management for Process Plants. Different types of drive circuits are explained and practical instruction is emphasized.elsevier. how they work. Covers most commonly used devices in contemporary industrial settings. Technological advancements in the area contribute to performance improvement and cost reduction. Volumes 1-4 Authors: H.Section 4: Where to Find Help Delmar Cengage Learning Executive Woods 5 Maxwell Drive Clifton Park. Practical Electric Motor Handbook Author: Irving Gottlieb Description: Shows engineers and designers how to incorporate electric motors into their products.
Section 4: Where to Find Help
Practical Variable Speed Drives and Power Electronics Author: Malcom Barnes Description: Provides a fundamental understanding of the installation, operation, and troubleshooting of variable speed drives, including coverage of control wiring, operating modes, braking types, automatic restart, harmonics, electrostatic discharge, and EMC/EMI issues. The Fairmont Press, Inc. 700 Indian Trail Lilburn, GA 30047 (770) 925-9388 www.fairmontpress.com Efficient Electric Motor Systems Handbook Author: Todd Litman Description: For engineers, designers, equipment specifiers, and equipment operators who want to optimize the efficiency and reliability of their electric motor systems. Included is a comprehensive overview of electric motor systems currently available, strategies for avoiding typical problems that cause inefficiency and failure, design considerations, selection criteria, and operation and maintenance factors. Variable Speed Drive Fundamentals, 3rd Edition Author: Clarence A. Phipps Description: Does not go into complex mathematical equations, but establishes basic relationships and rules of thumb helpful in applying relatively simple drive systems. Intended for technicians without a mathematical background. Institute of Electrical & Electronics Engineers 3 Park Avenue, 17th Floor New York, NY 10016 (212) 419-7900 www.ieee.org Variable Frequency AC Motor Drive Systems Author: David Finney Description: Covers various types of ac motors, along with their power switching devices, inverters, converters and slip energy recovery systems.
ISA 67 Alexander Drive Research Triangle Park, NC 27709 (919) 549-8411 www.isa.org Variable Speed Drives: Principles and Applications for Energy Cost Savings Author: David W. Spitzer Description: Many applications of variable speed drive technology fall in the cracks between traditional engineering disciplines. This new edition of a venerable classic incorporates the additional insights of the author over the past decade and helps practicing engineers learn about the technical and economic potential of this technology. It presents the electrical, hydraulic, chemical, and instrumentation information necessary to technically evaluate and economically justify variable speed drive applications. Jarsco Publishing 18901 State Street Corona, CA 92881 (909) 735-5239 www.jarscopublishing.com/guide.html Adjustable Speed Drives Applications Guide, 2nd Edition Authors: Arthur Wallace, Ralph Ferraro, and John Benz Description: The primary purpose of the EPRI ASD Applications Guide is to provide application and facility engineers with the basic information needed to use ASDs. But, the Guide is useful to anyone on the user side involved in evaluation, selection, specification and purchase of ASDs and motors. On the supplier side, engineers, sales and marketing professionals engaged in ASDs and motors would equally benefit from the publication. This electronic book is available on CD-ROM. McGraw-Hill 1221 Avenue of the Americas New York, NY 10020 (212) 904-2000 www.mcgraw-hill.com Electric Drives: Concepts and Applications Author: Vedam Subrahmanyam Description: Comprehensively covers the subject of electric drives and their industrial applications. The characteristics
Improving Motor and Drive System Performance: A Sourcebook for Industry
Section 4: Where to Find Help
and dynamics of electric drives are discussed, as well as aspects of control, rating, and heating. Special discussions feature working examples of converters, and microprocessors.
Electric Motor Handbook Authors: H. Wayne Beaty and James L. Kirtley, Jr. Description: Provides a full range of information on electric motors used in a variety of consumer, industrial, and commercial applications. It covers data on sizes, shapes, performance, electrical and mechanical parameters, protection, and other factors involved in motor selection and application. Electric Motor Maintenance and Troubleshooting Author: Augie Hand Description: Gives an overview of each motor type's components and operation, supplies troubleshooting procedures, which make concepts crystal-clear, and review questions at the end of each chapter to drive the concepts home. Covers essential safety issues. Motor Control Electronics Handbook Author: Richard Valentine Description: Describes reliable electronic controls for any motor application. This resource assists in the design of motor controls with microcontrollers and IGBT power devices and provides an introduction to digital motor speed controls. It also describes step-by-step practical methods for reducing EMI problems and provides information about control's reliability and insights into motor control diagnostics. Other topics include dc and ac motor control designs; automotive and appliance motor controls; digital controls; power semiconductors; microcontrollers; communication networks; and motor control test procedures. Oxford University Press 198 Madison Ave New York, NY 10016 (212) 726-6000 www.oup.com/us/ Electric Motors and Their Controls: An Introduction Author: Takashi Kenjo Description: A translation of the Japanese book ABC of Motors; describes the principles, construction, and use of different motor types and controllers in simple, nontechnical terms.
Pearson Education POD One Lake Street Upper Saddle River, NJ 07458 (201) 236-7000 www.pearsoned.com Modern Electric/Electronic Motors Author: Martin Clifford Description: Describes the history and growth of motors. The opening chapter describes the development of the electric motor and the fundamental principals of magnetism. The second chapter details the physical and electrical characteristics of motors in general. The remaining chapters look at the following technologies in detail: dc motors, ac motors, electronics for motors, brushless dc motors, stepping motors, and mechanical drives. This text is intended for the reader with a technical background who wants an understanding of the way motors work. The book is somewhat geared towards the reader who wishes to become involved in motor repair, as it contains sections on troubleshooting for each motor type. However, it is also a good general reference text on motors, although energy efficiency issues are not emphasized. This book can be purchased as an electronic facsimile at www.amazon.com. Modern Industrial Electrical Motor Controls: Operation, Installation, and Troubleshooting Authors: Thomas E. Kissell and Chris Hicks Description: Covers the theory of operation, installation, and troubleshooting of motor controls and motors. Includes hundreds of pictures and diagrams pertaining to the operation and interfacing of motor controls. This book can be purchased as an electronic facsimile at www.amazon.com. Prentice-Hall One Lake Street Upper Saddle River, NJ 07458 (201) 236-7000 www.prenticehall.com Complete Handbook of Electric Motor Controls Author: John E. Traister Description: Provides information on theory, design, and practical applications to help all concerned with electric and electronic motor controls. The complete spectrum of motor control applications is examined.
Improving Motor and Drive System Performance: A Sourcebook for Industry
Section 4: Where to Find Help
Electric Motor Drives: Modeling, Analysis, and Control Author: R. Krishnan Description: Emphasizes a systematic approach to motor drives based on physical insight and practical implementation aspects. System equations are derived and each of the motor drives is illustrated with an industrial application in detail at the end of chapters so readers can relate theory to practice. Springer 233 Spring Street New York, NY 10013 (212) 460-1500 www.springer.com Energy Efficiency Improvements in Electric Motors and Drives Authors: Anibal de Almeida, Paolo Bertoldi, and Werner Leonhard Description: This book covers the basics and the state of the art of energy-efficient motor technologies, which can be used now and in the near future to achieve significant and cost-effective energy savings. It describes recent developments in advanced motor technologies such as permanent magnet and reluctance motors. Energy-efficient motor technologies, though enabling a huge amount of electricity to be saved, still have not been widely adopted. The book presents barriers to the adoption of those technologies and features policies to promote the large scale penetration of energy-efficient technologies, describing the experiences carried out so far in different parts of the world. Energy Efficiency in Motor Driven Systems Authors: Francesco Parasiliti and Paolo Bertoldi Description: This book reports the state of the art of energyefficient electrical motor driven system technologies, which can be used now and in the near future to achieve significant and cost-effective energy savings. It includes the recent developments in advanced electrical motor end-use devices (pumps, fans and compressors) by some of the largest manufacturers. Policies and programs to promote the large scale penetration of energy-efficient technologies and the market transformation are featured in the book, describing the experiences carried out in different parts of the world. Energy Efficient Electric Motors and Their Applications, 2nd Edition Author: Howard E. Jordan Description: Evaluates the energy savings potential of different energy efficient motors. It examines all aspects of motor and ASD technology and provides a step-by-step description of the process of selecting and applying motors. Also included are chapters on efficiency verification, power factor, and ac motor control. TAB Books, a Division of McGraw-Hill, Inc. 1221 Avenue of the Americas New York, NY 10020 (212) 904-2000 www.mcgraw-hill.com Electric Motors and Control Techniques, 2nd Edition Author: Irving M. Gottlieb Description: Examines present and theoretical interfaces between motors and their control systems. The book's primary focus is on maximizing the efficiency of motors by carefully matching them with well-designed, state-of-the-art controls. Problems with electric vehicles are also discussed. Wiley-IEEE Press 10475 Crosspoint Boulevard Indianapolis, IN 46256 (317) 572-3000 www.wiley.com Power Electronics and Variable Frequency Drives: Technology and Applications Editor: Bimal K. Bose Description: A compendium of papers from eleven wellknown professionals to provide comprehensive coverage of power electronics and ac drive technology. Topics covered include power semiconductor devices, electrical machines, converter circuits, pulse-width modification techniques, ac machine drives, simulation techniques, estimation and identification, microprocessors, and artificial intelligence techniques.
Improving Motor and Drive System Performance: A Sourcebook for Industry
and maintenance of motors. principals of operation. DC 20009 (202) 467-2900 www. and Canada. and J.bpa. Edition is available from the American Public Power Association (APPA).epri. Bonneville Power Administration Public Information Office P.S.S. Motors Reference Guide. principals of operation. The Consortium for Energy Efficiency 98 North Washington Street. and Standards) Advanced Energy 909 Capability Drive. Ryan and Richard Okrasa Description: One of a series of product knowledge reference guides originally published by Ontario Hydro. Manuals. Small format (7" x 5") and contains chapters on how motors are classified. Guides. NC 27606 (919) 857-9000 www.gov Industrial Motor Repair in the United States Authors: V. and repair data. Suite 1200 Washington. Suite 2100 Raleigh.O. motor controls. Douglass Description: Characterizes the motor repair industry in the United States and summarizes current motor repair and testing practice. Electric Power Research Institute 3420 Hillview Avenue Palo Alto. Programs offer both financial and technical incentives. An interactive map is included to help locate programs throughout the U. and harmonic distortion. P. A small format (7" x 5") guide contains chapters on how ASDs are classified. The summary includes a general description of terms as well as specific details and contact information for many local programs. OR 97208 (503) 230-7334 or (800) 622-4520 www. Schueler.advancedenergy.org HorsePower Bulletin Author: Advanced Energy Description: Outlines a policy for cost-effective management of motor purchase and repair and is based on comments from industrial customers. Leistner. physical appearance.org National Summary of Energy-Efficiency Programs for Motors and Drives Author: Ilene Mason Description: Provides information about the incentive programs available to commercial and industrial customers for efficiency improvements through the installation of premium-efficiency motors. Uses nontechnical language and is intended for utility representatives or customers who want a short primer on motors. based on reviews of manufacturer. Failures typical in ac squirrel cage 56 Improving Motor and Drive System Performance: A Sourcebook for Industry . electric utilities. economics. Uses nontechnical language and is intended for utility representatives or customers who want a short primer on ASDs. It also identifies barriers to energy efficient motor repair practice and recommends strategies for overcoming those barriers. U.S. Edition Authors: Maura C. selection of motors. comparisons of ASDs. adjustable speed drives and motor system optimization projects from utilities and other administrators of publicly-funded benefit programs. The U. Suite 101 Boston MA 02114 (617) 589-3949 www.A. Oliver Description: A realistic maintenance schedule for the four types of electric motors commonly found in nuclear and fossil-fuel power plants. operator.appanet.cee1.org Adjustable Speed Drive Reference Guide. Box 3621 Portland. Edition Author: Ontario Hydro Description: One of a series of product knowledge reference guides published by Ontario Hydro. features of ASDs. U.Section 4: Where to Find Help Other Publications (Reports. motor suppliers and repair shops.com Electric Motor Predictive and Preventive Maintenance Guide Author: J. CA 94304 (800) 313-3774 www.S. American Public Power Association 1875 Connecticut Avenue NW.
construction.ieee.global. Motor Decisions Matter sm www. operation. Version 2. Motors and Generators Description: Provides practical information concerning ratings. Based on the international ISO 9002-1994 quality standard. CO 80112 (800) 624-3974. Electrical Apparatus Service Association 1331 Baur Boulevard St. Energy Management Guide for Selection and Use of Polyphase Motors Description: Provides practical information concerning the proper selection and application of polyphase induction and synchronous motors including installation. and highlights the importance of having an implementation plan ready before failures occur. brochure provides step-bystep guidelines. and an entire chapter on repair/replace considerations. information about best practice repair/rewind procedures. Kueck et al. Information about how to figure energy costs and why this is important when making repair/replacement decisions is also included.org A Comparison of Two Energy Efficient Motors Author: John D. Improving Motor and Drive System Performance: A Sourcebook for Industry 57 . Louis.2. this publication concludes that using best repair/rewind practices maintains motor efficiency. NEMA Standard MG 10-1994. as are tests that will reliably predict these failures.motorsmatter. MO 63132 (314) 993-2220 www. and dc motors are examined and described. testing. ac wound-rotor motors. 1950 www. No. Global Engineering Documents 15 Inverness Way East Englewood. Available in IEEE Transactions on Energy Conversion. performance. IEEE 3 Park Avenue 17th Floor New York. The preventive maintenance schedule outlined is less onerous than those prescribed by manufacturers.org Motor Planning Kit. NY 10016 (212) 419-7900 www. tools and resources for developing and implementing a customized plan that suits individual organizational needs.org EASA-Q: 2000 Quality Manual Author: Electrical Apparatus Service Association Description: EASA-Q was created to provide EASA members a practical means of developing a quality management system.com NEMA Standard MG 1-2003. Guide to AC Motor Repair and Replacement Author: Electrical Apparatus Service Association Description: This booklet provides help in making the best decision when deciding whether to repair or replace ac motors. June 1998. extensive background information about test procedures and methodology. should be sufficient to prevent breakdowns.0 Author: Sponsors of Motor Decisions Matter Description: A resource for those interested in developing a motor management plan. but. The Effect of Repair/Rewinding on Motor Efficiency Author: Electrical Apparatus Service Association Description: Based on a joint study by EASA and the Association of Electrical and Mechanical Trades (AEMT) of the United Kingdom. Volume 13. ext. resources for further reading.ihs. Description: Evaluates considerations that affect the selection of premium and EPAct motors.Section 4: Where to Find Help induction motors. EASA-Q is designed so that electrical apparatus service organizations can use it with minimal assistance. and manufacture of ac and dc motors and generators. and maintenance. Guidelines for Maintaining Motor Efficiency during Rebuilding Author: Electrical Apparatus Service Association Description: This pamphlet provides recommendations which contain safe values and correct procedures for repairing equipment properly and demonstrating that rewound motors retain their operating efficiency. ac synchronoustype motors. The report provides complete test data.easa. according to the authors.
University of Wyoming Electrical Engineering Department 1000 East University Avenue. Department 3295 Laramie. maintenance. Description: This document was prepared in a threeway cooperative effort between the Bonneville Power Administration. Compares empirical savings for more than 30 energy saving options and explores their numerous interactions. and recent articles on electric motors.Section 4: Where to Find Help Penton Media.org The 1-2-3 Approach to Motor Management Developers: Sponsors of Motor Decisions Matter Description: This Microsoft ExcelTM spreadsheet is a quick demonstration tool to showcase the benefits of proactive 58 Improving Motor and Drive System Performance: A Sourcebook for Industry . TEFC and ODP. full load and no load amperage. and the Western Area Power Administration.uwyo. including electrical supply. inventory management. Department of Energy Industrial Technologies Program www..gov/informationcenter Energy Management for Motor-Driven Systems Authors: Gilbert McCoy and John Douglass Description: Provides comprehensive information on electrical motor management. Assists engineers in identifying and evaluating energy conservation opportunities to reduce energy costs.eere. Lovins et al Description: Published by Competitek. and service center reporting capabilities. ID 83719-0921 (208) 322-6999 www. imbalance calculation. cooling.electricmotors. and increase productivity. Rocky Mountain Institute 2317 Snowmass Creek Road Snowmass.machinedesign. the documented cost and performance of the best equipment available. It includes sections on motors.eere.org/ The State of the Art: Drivepower Author: Amory B. improve the reliability and efficiency of motor-driven systems.em2solutions. and practices for providing unchanged or improved motor torque with less input energy. Inc. 1100 thru 3600 RPM. Motor Decisions Matter sm www. WY 82071 (307) 766-6268 www. Critically reviews diverse data on drivepower usage. picture/data file containers.energy. The report examines energy efficiency in systems that are driven by electric motors. as well as estimates of the combined effects of using a system approach in improving the efficiency of motor-driven equipment.penton. maintenance.edu Energy Efficient Drivepower: An Overview Author: Sadrul Ula et al.rmi. selection.com em2006 Developer: em2solutions with support from the Northwest Energy Efficiency Alliance Description: An introductory motor system survey and analysis software. electrical tune-ups. U. operation cost analysis and comparison. This report is largely a condensation of a report titled "The State of the Art: Drivepower" which is described elsewhere in this section. controls. an information service of the Rocky Mountain Institute. cleaning. and Machine Design Magazine 1300 East 9th Street Cleveland OH 44114 (216) 931-9458 www. includes average efficiency. information on suppliers. historical data. and management. Software em2solutions PO Box 190921 Boise.com Electric Motors Reference Center Author: Machine Design Magazine Description: Online reference center for information on electric motors – includes descriptions of different ac/dc motor types. new and rewind prices for motors 7½ thru 300 hp.S. Features intuitive motor management direction. CO 81654 (970) 927-3851 www. and repair.motorsmatter.energy. mechanical efficiency. motor systems totals. the DOE Denver Support Office.gov/industry EERE Information Center 877-337-3463 www.com www.
Section 4: Where to Find Help
motor management. By entering nameplate data from a few representative motors, the 1-2-3 Approach helps identify motor opportunities within a facility. The 1-2-3 Approach is an introductory tool designed as a gateway to more comprehensive motor management tools and strategies.
IEEE Control Systems Magazine Institute of Electrical and Electronics Engineers Control Systems Society (CSS) Indianapolis, IN www.ieee.org IEEE Industry Applications Magazine Institute of Electrical and Electronics Engineers Industry Applications Society, (IAS) Indianapolis, IN www.ieee.org IEEE Power Engineering Magazine Institute of Electrical and Electronics Engineers Power Engineering Society (PES) Los Angeles, CA www.ieee.org Industrial Maintenance & Plant Operation (IMPO) Cahners Publishing Company A Division of Reed Elsevier Properties, Inc. Des Plaines, IL www.impomag.com Machine Design Magazine Penton Media Inc. Cleveland, Ohio www.machinedesign.com Mechanical Engineering American Society of Mechanical Engineers (ASME) New York, NY www.memagazine.org Plant Engineering Cahners Publishing Company A Division of Reed Elsevier Properties, Inc. Des Plaines, IL www.plantengineering.com
U. S. Department of Energy Industrial Technologies Program www.eere.energy.gov/industry MotorMaster+ 4.0 Developer: U.S. Department of Energy Industrial Technologies Program Description: An energy-efficient motor selection and management software tool which includes a catalog of more than 20,000 ac motors. Features motor inventory management tools, maintenance log tracking, efficiency analysis, savings evaluation, energy accounting, and environmental reporting capabilities. MotorMaster+ International Description: Includes many of the capabilities and features of MotorMaster+ 4.0, but allows users to evaluate repair/ replacement options on a broader range of motors. The user can conduct analyses in different currencies, calculate efficiency benefits for utility rate schedules with demand charges, edit and modify motor rewind efficiency loss defaults, and determine "best available" motors. The tool can be modified to operate in English, Spanish, and French.
ASHRAE Journal American Society of Heating, Refrigerating, and AirConditioning Engineers Atlanta, GA www.ashrae.org Consulting-Specifying Engineer Cahners Publishing Company A Division of Reed Elsevier Properites, Inc. Des Plaines, IL www.csemag.com
Improving Motor and Drive System Performance: A Sourcebook for Industry
Section 4: Where to Find Help
Training Courses
Association of Energy Engineers 4025 Pleasantdale Road, Suite 420 Atlanta, GA 30340 (770) 447-5083 www.aeecenter.org
Area(s) covered: Seminars offered for various topics of interest, including motor systems, energy management, conservation, and economics.
Institute of Electrical and Electronics Engineering 3 Park Avenue, 17th Floor New York, NY 10016 (212) 419-7900 www.ieee.org
Area(s) covered: The IEEE provides learning opportunities within the engineering sciences, research and technology.
U.S. Department of Energy Industrial Technologies Program www.eere.energy.gov/industry/bestpractices/training
Area(s) covered: DOE offers a one-day workshop covering key elements of motor system management, such as applications, inventory tracking, maintenance, repair, replacement decisions, and the impact and maintenance of power quality. A rigorous overview shows attendees how the MotorMaster+ software can help form the structure of a motor management program, reduce the work involved, and facilitate decision-making.
Electric Power Research Institute 3420 Hillview Avenue Palo Alto, CA 94304 (800) 313-3774 www.epri.com
Area(s) covered: EPRI conducts hundreds of events throughout the year, including symposiums, workshops, conferences, and training courses.
Electrical Apparatus Service Association, Inc. 1331 Baur Blvd. St. Louis, MO 63132 (314) 993-2220 www.easa.com
Area(s) covered: EASA offers its members and others with a means of keeping up to date on materials, equipment, and state-of-the-art technology for motors, drives, and other electromechanical equipments and offers courses in topics such as motors, pumps, and industrial maintenance issues.
Improving Motor and Drive System Performance: A Sourcebook for Industry
This sourcebook contains the following five appendices:
Appendix A: A Glossary of Basic Motor System Terms
This appendix contains a glossary of the main terms associated with motor and drive systems.
n Appendix
B: Motor Tip Sheets
This appendix contains a series of tip sheets developed to increase users' awareness of potential performance benefits and energy savings that can be obtained by improving the efficiency of motor and drive systems. These brief tip sheets are less detailed than the efficiency opportunities in Section 2 of the sourcebook.
n Appendix
C: EPAct Efficiency Levels and Premium Efficiency Levels
This appendix provides EPAct efficiency ratings and NEMA premium efficiency motor ratings for a range of motor sizes and types.
n Appendix
D: Motor Repair Service Center Checklist
This contains a checklist for motor repair facilities.
Appendix E: Guidelines for Comments
This appendix provides a place for readers to suggest changes and improvements to this sourcebook.
Improving Motor and Drive System Performance: A Sourcebook for Industry
62 Improving Motor and Drive System Performance: A Sourcebook for Industry .
per minute. Note: Brushes are classified according to the types of material used. is not considered to have a breakdown torque. electrographite. burnout oven – Heat cleaning oven used for stripping windings from a core. as air capacitors. carbon-graphite. the term is commonly applied to the entire rotor. breakdown torque – The maximum shaft-output torque that an induction motor (or a synchronous motor operating as an induction motor) develops when the primary winding is connected for running operation. with rated voltage applied at rated frequency. Capacitors are usually classified. brake horsepower (BHP) – Mechanical energy consumed at a rate of 33.24 X 1018 electrons past any cross section in 1 second. alternating current series. bars – Axial conductors in a rotor cage. armature – The member of an electric machine in which an alternating voltage is generated by virtue of relative motion with respect to a magnetic flux field. bearing losses – The power losses resulting from friction in the bearings.000-ft. within a specified speed range. and repulsion-type machines. paper capacitors. mica capacitors. ANSI – American National Standards Institute. alternating current – A periodic current the average value of which over a period is zero. lbs. usually composed in part of some form of the element carbon. adjustable speed drive (ASD) – An electric drive designed to provide easily operable means for speed adjustment of the motor. They are distinguished from lower temperature baking ovens. the combination serving as a path for magnetic flux. which are used to cure varnish. ASHRAE – American Society of Heating. the term refers to a current which reverses at regular recurring intervals of time and which has alternately positive and negative values. cage – See "squirrel cage". 1984.) ambient – Immediate surroundings or vicinity. at normal operating temperature.085. In direct-current universal. capacitor – A device. the primary purpose of which is to introduce capacitance into an electric circuit. New York. required to raise the temperature of a volume of standard air a specific number of degrees is calculated by the formula: Btu/hr = (Temperature Rise) x (CFM) x 1. air gap – A separating space between two parts of magnetic material. according to their dielectrics. a consumption rating. brushes – A conductor. The Institute of Electrical and Electronics Engineers. Btu – British Thermal Unit.. (Unless distinctly specified otherwise. and metalgraphite. Inc. The Btu/hr. amps – A unit of electric current flow equivalent to the motion of 1 coulomb of charge or 6. Improving Motor and Drive System Performance: A Sourcebook for Industry 63 . For more. serving to maintain an electric connection between stationary and moving parts of a machine or apparatus. Refrigerating. etc. best efficiency point (BEP) – The operating condition at which a device operates most efficiently. These are sometimes called roasting ovens.Appendix A: Glossary of Terms Appendix A: Glossary of Basic Motor System Terms Here are some of the principal terms associated with motor and drive systems. They operate at temperatures up to 750°F and may have water spray systems to control temperature transients and secondary combustion to control emissions. Note: A motor with a continually increasing torque as the speed decreases to standstill. graphite. Note: This space is normally filled with air or hydrogen and represents clearance between rotor and stator of an electric machine. please see the IEEE Standard Dictionary of Electrical and Electronics Terms. heat required to raise the temperature of 1 pound of water by 1°F. as follows: carbon. and Air-Conditioning Engineers ASME – American Society of Mechanical Engineers ASTM – American Society for Testing and Materials balancing – The process of adding (or removing) weight on a rotating part in order to move the center of gravity toward the axis of rotation. breakaway torque – The torque that a motor is required to develop to break away its load from rest to rotation.
harmonics – A sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency.Appendix A: Glossary of Terms coil – One or more turns of wire that insert into a single pair of core slots. direct current – A unidirectional current in which the changes in value are either zero or so small that they may be neglected. hertz (Hz) – Unit of frequency. the term efficiency means efficiency with respect to power. shaft diameter. corrosion – The deterioration of a substance (usually a metal) because of a reaction with its environment. Note: Unless specifically stated otherwise. commutator – An assembly of conducting members insulated from one another. in the radial-axial plane. frequency – The number of periods per unit time. efficiency – The ratio of the useful output to the input (energy. quantity of electricity. Dimensions include. deducting that portion of the loss that results from: (1) Forcing the gas through any part of the ventilating system that is external to the machine and cooler (if used). Compressors are used to provide compressed air system to facilities and in mechanical vapor compression systems to provide cooling and refrigeration. demand – The load integrated over a specific interval of time. exciting current – Component of electric current used to induce a magnetic field. (2) The driving of direct-connected flywheels or other direct-connected apparatus. shaft height. demand charge – That portion of the charge for electric service based upon a customer's demand. including motor rewind facilities. used to enable current to flow from one part of the circuit to another by sliding contact. the term designates a practically non-pulsing current) EASA – Electrical Apparatus Service Association. it is customary to speak of the full-load speed under the (stated) conditions. a component the frequency of which is twice the fundamental frequency is called the second harmonic. It is comprised of stacked sheet iron. power.). 64 Improving Motor and Drive System Performance: A Sourcebook for Industry . against which brushes bear. one cycle per second. full load torque – The torque required to produce the rated horsepower at full load speed. compressor – A device that increases the pressure of a gas through mechanical action. performance – A graphic representation of pressure and flow for a pump or a fan. Note: For example. coil supports – Ring-like structures or individual blocking between coils to which a motor's end turns are tied to add rigidity. etc. consumption – The amount of energy used by a motor system. Sometimes called "surge rings". core losses – The power dissipated in a magnetic core subjected to a time-varying magnetizing force. and motor mounting footprint. a trade association that serves many areas of the electrical repair market. measured in kilowatt-hours (kWh) core – The magnetic iron structure of a motor's rotor or stator. (As ordinarily used. frame size – A set of physical dimensions of motors as established by National Electrical Manufacturers Association (NEMA) for interchangeability between manufacturers. curve. full load speed – The speed that the output shaft of the drive attains with rated load connected and with the drive adjusted to deliver rated output at rated speed. fan – The part that provides an air stream for ventilating the machine. curve. Note: In referring to the speed with full load connected and with the drive adjusted for a specified condition other than for rated output at rated speed. Note: Core loss includes hysteresis and eddy-current losses of the core. system – A graphic representation of the pressure versus flow characteristics of a given system. eddy current coupling – A type of adjustable speed drive that changes the strength of a magnetic field in a coupling to determine the amount of slip between the motor and the driven equipment. friction/windage losses – The power required to drive the unexcited machine at rated speed with the brushes in contact.
the laminated iron. device. Rewinding should replicate original resistance. the trade association establishing standards of dimensions. insulation. by far.000 watts. coupling and load to acceleration. with rated voltage applied at rated frequency. insulation – Resistance between points that are supposed to be electrically isolated. journal – Region on a shaft where a bearing is located. which are also known as variable speed drives or variable frequency drives. ratings. The number of poles is determined by the winding design and the motor speed is inversely related to the number of poles. low voltage – Voltage ratings not exceeding 600 VAC. nor salient (projecting) poles. and the squirrel cage. Changed resistance after rewinding may indicate altered winding pattern.34 hp.000 foot-lbs. to (B) the synchronous speed. poles – Poles are the total number of magnetic north/south poles produced in the rotating magnetic field of a motor. load factor – The ratio of the average load over a designated period of time to the peak load occurring in that period. induction motor – The simplest and. pound-foot (lb ft) – Torque rating or requirement. An inverter comprises the output stage of all electronic adjustable speed drives. externally excited electro-magnets. The induction motor rotor is simple. With sleeve bearings. or a turn miscount. when applied to the rated power. which is excited by magnetic induction from the stator without necessity of brushes or other direct contact. equivalent to the force required to move a one pound weight one foot in distance. inverter – A machine. 1. winding – Resistance of the winding measured between each pair of line connections. having neither permanent magnets. For motors. resistance. kilowatt – A measure of power equal to 1. resistance. enclosures. equal to 12 lb in. and other design criteria for electric equipment. service factor – A multiplier that. expressed as a ratio. Also called "hi pot test" horsepower (hp) – A measure of the amount of the work a motor can perform in a period of time. rpm – Revolutions per minute. locked rotor torque – The minimum torque of a motor which it will develop at rest for all angular positions of the rotor. slip – The quotient of (A) the difference between the synchronous speed and the actual speed of a rotor. rotor – The rotating part of an ac induction motor that includes the shaft. most commonplace ac motor design. The lost power manifests as heat in various parts of the motor structure. NEC – National Electrical Code.Appendix A: Glossary of Terms high potential test – Test of insulation integrity by application of a higher than nameplate rated ac or dc voltage between electrical winding or circuit elements and ground. The journal must be precisely machined for a correct fit to the bearing bore. 33. losses – Motor input power that is lost rather than being converted to shaft power. insulation – Material or a combination of suitable nonconducting materials that provide isolation of two parts at different voltages. inertia – Tendency of an object to remain in the state it is in. incorrect wire gauge. inverter duty – Intended for being powered by a dc to ac inverter. Part 31 of NEMA MG-1 provides recommended standards for Inverter Duty motors. or as a percentage. the journal is the actual bearing surface on the shaft. The rotor contains a conducting structure. per minute or 0. NEMA – The National Electrical Manufacturers Association.746 kW. rotor losses – The losses due to current flow in the rotor circuit (equal to I2R where I is the current in the rotor and R is the resistance of the rotor circuit). Improving Motor and Drive System Performance: A Sourcebook for Industry 65 . or system that changes directcurrent power to alternating current power. inertia generally refers to the resistance of the rotor. indicates a permissible power loading that may be carried under the conditions specified for the service multiplier.
commonly measured in lb. potential. National Electrical Manufacturers Association provides standards for temperature rise of fully loaded motors based upon insulation class and other motor parameters. and may readily be transferred from one conductor to another by means of electrostatic or electromagnetic coupling.-in. such as the opening of a disconnect. where I is the stator current and R is the resistance of the stator circuit). Sometimes called a rotor cage. or power in an electrical circuit. produced by or linking the primary winding.3 to 3. or by switching operation. these devices directly control motor rotation. not including that portion of the core loss associated with the resistance drop. damping factor.Appendix A: Glossary of Terms squirrel cage – This is the current conducting assembly used in most induction motor rotors. The concept eliminates torque pulsation and accommodates creation of rotating magnetic fields within motors to facilitate starting and running torque. and capacitance of the power and control circuits and the degree of coupling. synchronous speed – The speed of the rotation of the magnetic flux. Voltages as high as 10 kV in the frequency range of 0. or lb. (equal to I2R. separators – Insulating spacers used to separate coils of separate phases within a slot. Also called "slot sticks". watt – The unit of power in the International System of Units (SI). transients occurring in control circuits are a result of rapid changes in the power circuits to which they are coupled. stator losses – Losses due to the flow of current through the stator windings. Since motor speed is linearly related to electrical frequency. 66 Improving Motor and Drive System Performance: A Sourcebook for Industry .0 MHz have been observed where little or no protection was provided. and magnitude of the transients are determined by resistance. windings – An assembly of coils designed to act in consort to produce a magnetic flux field or to link a flux field. temperature rise – Temperature increase above ambient. stator – The stationary part of a motor's magnetic circuit. The watt is the power required to do work at the rate of 1 joule per second. three-phase – Commonplace ac electrical service involving three conductors offset in phase from each other. or both. The frequency. Transients may be caused by lightning stroke. Ensuring that temperature rise remains within these limits during noload running is a worthwhile safeguard though it does not prove that temperature rise will remain within limits at rated load. variable frequency drive – A type of adjustable speed drive that changes the frequency of the electric power supplied to a motor. produced by distortion of the magnetic flux by the load current.-ft. As used in this guide. torque – A force that produces rotation. transients – A change in the steady-state condition of voltage or current. a fault. inductance. In induction motors it is the outer annular iron structure containing the power windings. avoiding the need for an intermediate coupling between the motor and the driven equipment. It is typically cast aluminum in smaller motors and fabricated of copper alloy in larger motors. stray load losses – The losses due to eddy currents in copper and additional core losses in the iron. surge – A transient wave of current.
Is it Cost-Effective to Replace Old Eddy-Current Drives? 13.eere. Eliminate Excessive In-plant Distribution System Voltage Drops 9. energy. Turn Motors Off When Not in Use 11. The Importance of Motor Shaft Alignment 5. Replace V-Belts with Cogged or Synchronous Belts 6. When to Purchase NEMA Premium Efficiency Motors 2. Extend the Operating Life of Your Motor 4. Improving Motor and Drive System Performance: A Sourcebook for Industry 67 . Currently Available: 1. Improve Motor Operation at Off-design Voltages 10. Avoid Nuisance Tripping with Premium Efficiency Motors 7. When Should Inverter-Duty Motors be Specified? 15. Eliminate Voltage Unbalance 8. Minimize Adverse Motor and Adjustable Speed Drive Interactions These tip sheets discuss opportunities for improving the efficiency and performance of motor systems and can be downloaded from the ITP Web site at www.gov/industry/bestpractices.Appendix B: Motor Tip Sheets Appendix B: Motor Tip Sheets The Industrial Technologies Program has developed the following tip sheets through its BestPractices activities. Estimating Motor Efficiency in the Field 3. Magnetically Coupled Adjustable Speed Motor Drives 14. Adjustable Speed Drive Part-Load Efficiency 12.
Appendix B: Motor Tip Sheets 68 Improving Motor and Drive System Performance: A Sourcebook for Industry .
three-phase low. Department of Energy—Contact the EERE Information Center at 877337-3463 to obtain cited publications or to request additional information on motor and driven-equipment energy efficiency opportunities.05/kWh. • Adopt model motor repair specifications for low-voltage motors. Motors with speeds of 1200. Improving Motor and Drive System Performance: A Sourcebook for Industry 69 .200 1. NEMA Premium motors should also be considered when repairing or rewinding failed standardefficiency motors or as replacements for older. For example.energy. or where electric utility motor rebates or other conservation incentives are available. Examples of annual savings due to using NEMA Premium motors instead of motors that just meet the EPAct energyefficient motor standard are given in Table 1.820 4.5 95.000 volts or less. • Establish a motor repair/replace policy to achieve cost-effective and energy efficiency results.800 rpm totally enclosed fan-cooled motor with 8. 75% load.and medium-voltage induction motors rated from 1-500 horsepower (hp) and designed for service at 5. 25 to 500 hp standard efficiency motors used more than 2. Additional resources and information on training is also available at the BestPractices Web site at www. 1800. Resources U. operable lower-efficiency motors— particularly when the existing motor has been rewound or is oversized and underloaded. Table 1. Under this voluntary program.6 94.gov/industry/ bestpractices. NEMA Premium motors are particularly cost-effective when annual operation exceeds 2. NEMA Premium motor standards apply to NEMA Design A and B. replace immediately or upon failure with a NEMA Premium or Energy Efficient motor. and efficiency gain.553 3. Note: Based on purchase of a 1. and tag motors for appropriate action. a motor may be marketed as a NEMA Premium motor if it meets or exceeds a set of NEMA minimum full-load efficiency levels.4 93. and 3600 revolutions per minute (rpm) with open drip-proof (ODP). where utility rates are high. duty cycle. the National Electrical Manufacturers Association (NEMA) implemented a new NEMA Premium Energy Efficiency Motor Standard. kWh 1. NEMA Premium motors typically cost 10% to 15% more than their energyefficient counterparts.S. when motor repair costs are a significant fraction of the price of a replacement motor. rewind at failure with repair specifications and recommended guidelines.755 Dollar Savings $/year $60 78 191 223 588 Suggested Actions • Survey all critical motors in your plant.5 95.000 hours per year.0 NEMA Premium Efficiency Motor 91. These levels are higher than the minimum full-load efficiency standards for energyefficient motors under the Energy Policy Act of 1992 (EPAct).000 hours.4 96.2 Annual Savings from Use of a NEMA Premium Motor Annual Energy Savings.000 hours per year of operation.5 92.Appendix B: Tip Sheet Number 1 When to Purchase NEMA Premium™ Efficiency Motors NEMA Premium™ efficiency motors should be considered for new motor procurements and when specifying motor-driven equipment. explosion-proof. and an electrical rate of $0.0 94. Focus on general purpose. In August of 2001.7 93. Annual energy savings are dependent upon operating profile. and totally enclosed fan-cooled (TEFC) enclosures are included. Annual Savings from Specifying NEMA Premium Motors Full-load Motor Efficiency (%) Horsepower 10 25 50 100 200 Energy Efficient Motor 89.eere.470 11. Collect nameplate and application data and then measure the supply voltage and amperage for these inservice motors.
Appendix B: Tip Sheet Number 1 Example An old.000 x (100/91 – 100/95. the purchase price might represent just 2% of the total motor installation and operating costs.000 hours per year with an efficiency (ηstd) of 91.4% and electricity is priced at $0.746 x hours x (100/ηstd – 100/ηPE) = 75 x 0. The existing motor operates at a 75% load for 8.014 x $0.014 kWh/year Energy Cost Savings = 17. Even a small improvement in motor operating efficiency can produce significant energy and dollar savings and provide a rapid return on investment.746 x 8. Energy and maintenance costs account for the remaining 98%.05/kWh. Determine the annual energy savings if the replacement motor has an efficiency (ηPE) of 95.0%. DOE/GO-102005-2019 • September 2005 • Motor Systems Tip Sheet #1 70 Improving Motor and Drive System Performance: A Sourcebook for Industry . Energy Savings = hp x load x 0.75 x 0.05 = $851/year Over a 10-year operating period for a 75-hp motor.4) = 17. 75-hp standard efficiency boiler forced-draft fan motor is to be replaced with a NEMA Premium efficiency motor.
and cooling fan load) • Stator and rotor core losses • Stray load losses (miscellaneous other losses).4 93. then uncoupled and running unloaded. and ambient temperature. Resources U. Decreased efficiency may be due to: – Higher winding resistance compared to manufacturer specifications or an earlier measurement. and the availability of electrical power.gov/ industry/bestpractices.5 92.420 2. • Increase in no-load power or core losses. equipment. • Evidence of cage damage. What is an extra point of motor efficiency improvement worth? Full-load Motor Efficiency (%) Horsepower 10 25 50 100 200 Original Efficiency 89. The most direct and credible methods of measuring these losses involve considerable labor.05/kWh. yet most of the methods and devices attempt to assess losses to circumvent the difficult task of measuring shaft output power. Department of Energy—For additional information on motor and motor-driven system efficiency measures. Temperature corrections must be performed. but an inexpensive.5 96. wind resistance. Efficiency is output power divided by input power.Appendix B: Tip Sheet Number 2 Estimating Motor Efficiency in the Field Some utility companies and public agencies have rebate programs in place to encourage customers to upgrade their existing standard-efficiency motors to NEMA Premium™ efficiency motors. and an electrical rate of $0. Credible efficiency ratings are normally obtained in a laboratory. • Significant current unbalance when voltage is balanced. or learn more about training. 75% load.5 93.0 95. Table 1. kWh 605 1. Efficiency needs to be measured accurately because. • Stator electric power (I2R) losses • Rotor electric power (I2R) losses • Friction and windage losses (including bearing losses. visit the BestPractices Web site at www. following carefully controlled dynamometer testing procedures as described in IEEE Standard 112(b).0 Final Efficiency 90. power quality. to accurately estimate energy savings and determine annual dollar savings requires knowing the efficiency of the existing motor. A further complication is that motor efficiency is dependent upon loading.energy. Yet.S. to obtain the DOE's MotorMaster+ software. Core loss testing requires motor disassembly and is performed in a motor service center. Winding resistance must be measured. Power readings must be taken with the motor running under load.5 95.803 5. Motor losses fall into several categories that can be measured in various ways. as shown in Table 1.800 rpm totally enclosed fan-cooled motor with 8. Note: Based on purchase of a 1.4 94.eere.0 Annual Savings Annual Energy Savings. portable way to measure shaft output power of a coupled motor does not exist. A low resistance ohmmeter is often required for winding resistance tests. This may be caused by winding being at a higher temperature than that of the manufacturer's resistance specifications or by rewinding with smaller diameter wire. Field measurements for determining motor efficiency pose challenges that require developing various methods and devices.760 hours per year of operation. a single percentage point of improved efficiency is worth significant dollar savings—even for motors as small as 25 horsepower (hp).0 94. Improving Motor and Drive System Performance: A Sourcebook for Industry 71 . A good electric power meter can provide an accuracy of 1%.748 Dollar Savings $/year 30 71 140 272 537 Suggested Actions • Conduct predictive maintenance tests to reveal whether efficiency is below the original or nameplate level.431 10.
0. the marginal cost and labor of using these devices is small if they are already deployed for predictive maintenance uses. based upon electrical measurements of an operating motor. Slip is the difference between synchronous and shaft speed. The necessary instruments are costly and the process is very time and labor consumptive. thermometers. and/or operating speed. condition.0 software incorporates several methods for determining motor load. These methods have the potential of being accurate within 1% to 3% if carefully applied. While the accuracy of these devices has not been verified. for example. A number of sophisticated devices are marketed for analyzing motor condition. • Slip method. The slip method has largely been discredited as a viable technique for estimating motor efficiency. Power meters must be accurate at very low power factors that occur when motors operate unloaded. This method computes shaft output power as the rated horsepower multiplied by the ratio of measured slip to the slip implied by the nameplate. particularly current harmonics. These measure most of the above losses using either special dedicated "lab-in-a-box" devices or very accurate conventional instruments.Appendix B: Tip Sheet Number 2 Some of the available field motor-efficiency estimation methods include: • Loss accounting methods. With the percent load known. voltage. the software determines as-loaded efficiency from default tables based on the motor type. power meters. • MotorMaster+ 4. The MotorMaster+ 4. • Current signature predictive maintenance devices. These involve the use of motor nameplate data in conjunction with selected combinations of input power. current. and micro-ohmmeters. and horsepower. MotorMaster+ automatically chooses the best available method based upon the data it is given. DOE/GO-102005-2021 • September 2005 • Motor Systems Tip Sheet #2 72 Improving Motor and Drive System Performance: A Sourcebook for Industry .
Increasing the thermal rating during rewinding for example. such as those conforming to the Institute of Electrical and Electronic Engineers (IEEE) 841 specifications. When any components are degraded beyond the point of economical repair. In such cases. • Establish and follow a good predictive and preventive maintenance program. • Follow motor manufacturers' recommendations and user guides to protect out-of-service motors from humidity. energy. motor life can be extended by purchasing special motors." Motor life can range from less than two years to several decades under varying circumstances. Much of this progressive deteoriation can be detected by modern predictive maintenance techniques in time for life extending intervention. Still larger and more expensive motors may be refurbished and rewound to extend life indefinitely. For every 10°C rise in operating temperature. Depending upon type and replacement cost. and overload operation (even within the service factor). and quality of preventive maintenance determine how quickly motor parts degrade. How long do motors last? Answers vary. or other severe-duty or corrosion-resistant models. and still others saying "It depends.eere. and corrosion exposure. the motor is put out of service when a component such as a bearing fails. larger motors—up to 20 or 50 horsepower (hp)—may be refurbished and get new bearings. Wear is affected by dirt. Even with excellent selection and care.nema. poor ventilation. A competent motor service center can often pinpoint failure modes and indicate optional features or rebuild methods to strengthen new and rewound motors against critical stresses. over and undervoltage. voltage disturbances. Electrical Apparatus Service Association (EASA)—Provides guidelines on motor repair/rewind practices (www.energy. critical planning tips. the insulation life is cut in half. voltage unbalance. decision rules.000 hours.S.org). Refer to the Service Center Evaluation Guide (DOE/GO10099-937). The best safeguard against thermal damage is avoiding conditions that contribute to overheating. with some manufacturers stating 30. under and over-voltage. vibration." The useful answer is "probably a lot longer with a conscientious motor systems maintenance plan than without one. downloadable from the EERE BestPractices Web site at www. Suggested Actions • Evaluate and select a motor repair service center. An economic analysis should always be completed prior to a motor's failure to ensure that the appropriate repair/replace decision is made. and temperature. because new motors designed with higher insulation thermal ratings may actually operate at higher internal temperatures (as permitted by the higher thermal rating).Appendix B: Tip Sheet Number 3 Extend the Operating Life of Your Motor Why do motors fail? Certain components of motors degrade with time and operating stress. Department of Energy—Visit the BestPractices Web site at www. and corrosive fumes and is greatly accelerated when lubricant is misapplied. and motor replacement. abrasive. from Class B (130°C) to Class H (180°C). but are usually scrapped after a winding burnout. and/or electrically conductive. visit www. These include dirt. In some industries motors are exposed to contaminants that are severely corrosive. Contact between moving surfaces causes wear. harmonics. and a failure can occur if it is not detected. Electrical insulation weakens over time with exposure to voltage unbalance. Higher temperatures shorten motor life. the motor's economic life is ended.easa. U.eere. In the best circumstances. This can mislead one to think that purchasing new motors with higher insulation temperature ratings will significantly increase motor life.000 hours. Resources National Electrical Manufacturers Association (NEMA)—For information on NEMA Premium standards.gov/industry/best practices. Ask for causes of failure and confirm proper repair. others 40. motors can still suffer short lifetimes in unavoidably severe environments.gov/industry/bestpractices to access many industrial energy efficiency resources and training. Motor Decisions Matter—Download a motor management planning kit (www.org.org) that contains advice on building your in-plant motor inventory. high ambient temperature. Improving Motor and Drive System Performance: A Sourcebook for Industry 73 . The operating environment. does increase the winding life. moisture. or is not replaced at regular intervals. becomes overheated or contaminated. This is not always true. For the smallest and least expensive motors. degradation still proceeds. motorsmatter. conditions of use (or misuse).
Vibration trending is a good way to detect bearing problems in time to intervene. incorrect lubrication interval.Appendix B: Tip Sheet Number 3 Bearing failures account for nearly one-half of all motor failures. and frequency of starts. Always follow the manufacturer's lubrication instructions and intervals. Wrong replacement bearings. and even power quality problems can all destroy a bearing. the failing bearing can cause overheating and damage insulation. It does not follow that simply having a large L10 rating will significantly extend motor bearing life. voltage unbalance. The L10 rating is the number of shaft revolutions until 10% of a large batch of bearings fails under a very specific test regimen. or can fail drastically and do irreparable mechanical damage to the motor. contaminated lubricant. the L10h rating of a bearing may be cause for concern. incorrect lubricant. misaligned couplings. excessive belt tension. With bearings often implicated in motor failures. DOE/GO-102005-2018 • September 2005 • Motor Systems Tip Sheet #3 74 Improving Motor and Drive System Performance: A Sourcebook for Industry . excessive vibration. voltage variation. This NEMA standard defines limits for ambient temperature. excessive lubricant. Make sure motors are not exposed to loading or operating conditions in excess of limitations defined in manufacturer specifications and National Electrical Manufacturers Association (NEMA) standard MG1. If not detected in time.
can be used to distinguish between bearing wear.energy. efficient transmission of power from the motor to the driven equipment. as flexing of the coupling and of the shaft will impose forces on the motor and driven-equipment bearings. shaft misalignment. Department of Energy—For additional information on industrial energy efficiency measures and training. To achieve this goal. and premature bearing or coupling failure. • Monitor vibration as an indication of misalignment. however. Suggested Actions • Check shaft alignment of all production critical equipment annually. but not in the same line. Angular misalignment can cause severe damage to the driven equipment and the motor. or positioned at different elevations. or electrically caused vibrations. Parallel misalignment occurs when the two shaft centerlines are parallel. Effects of these forces include premature bearing. they would cross each other. correct shaft alignment ensures the smooth. Flexible couplings can also reduce vibration transmitted from one piece of equipment to another. and excessive radial and axial vibrations. Incorrect alignment occurs when the centerlines of the motor and the driven equipment shafts are not in line with each other. The angle or mismatch can be to the left or the right. U.org). noise. seal. Operating life is shortened whenever shafts are misaligned. or coupling faults.org.S. Misalignment produces excessive vibration. or above or below. • After 3-6 months of operation. They are offset horizontally or vertically (or both). Couplings Larger motors are usually directly coupled to their loads with rigid or flexible couplings. Improving Motor and Drive System Performance: A Sourcebook for Industry 75 . Types of Misalignment There are three types of motor misalignment: Ideal Alignment Angular Misalignment Parallel Misalignment Angular misalignment occurs when the motor is set at an angle to the driven equipment. While misalignment has no measurable effect on motor efficiency. If the centerlines of the motor and the driven equipment shafts were to be extended. eere. Resources Institute of Electrical Motor Diagnostics (IEMD)—For information on electrical motor diagnostic technologies and motor-system health. insufficient bolt tightening.easa. Rigid couplings do not compensate for any motor-to-driven-equipment misalignment while flexible couplings tolerate small amounts of misalignment. • Predictive maintenance techniques. Combination misalignment occurs when the motor shaft suffers from angular misalignment in addition to parallel misalignment. and loose or broken coupling bolts. Misalignment might be caused by foundation settling. It is a mistake. to take advantage of coupling flexibility for excessive misalignment. visit the BestPractices Web site at www. shaft breaking or cracking.gov/industry/bestpractices. defined in the instruction sheet for the coupling. including vibration tests and frequency spectrum analysis. visit www. and some can insulate the driven equipment shaft against stray electrical currents. Even flexible couplings require a minimal alignment. coupling and bearing temperature increases.iemd. rather than superimpose or run along a common centerline. Secondary effects include loosening of foundation bolts. recheck newly installed equipment for alignment changes due to foundation settling. or coupling failures. components that are the most likely to fail must be made to operate within their acceptable design limits. displaced to the left or right.Appendix B: Tip Sheet Number 4 The Importance of Motor Shaft Alignment The objective of optimized shaft alignment is to increase the operating life span of rotating machinery. Electrical Apparatus Service Association (EASA)—Provides information on motor maintenance topics (www.
Moving a pump.1. Alignment Tolerances Motor Speed. Many equipment manufacturers publish thermal offset values so the alignment professional can correct for thermal growth during the initial alignment process. After the equipment has operated long enough to become temperature stabilized.5 0.2 Acceptable 0. for instance.75 Angular Misalignment (mils) Excellent 0. DOE/GO-102005-2020 • September 2005 • Motor Systems Tip Sheet #4 76 Improving Motor and Drive System Performance: A Sourcebook for Industry .0. Then the motor should be moved into proper alignment and joined to the coupling.0 +/. and then install the coupling to the equipment.2. machines that are aligned in the "cold" pre-operating condition are almost always out of alignment when operating temperatures are attained.0.3 0. RPM 1200 1800 3600 Parallel Offset (mils) Excellent +/. shut it down and immediately recheck alignment.1.5 Acceptable +/. Typical alignment tolerances are summarized in Table 1.Appendix B: Tip Sheet Number 4 Alignment Tolerances Proper shaft alignment is especially critical when the motor is operated at high speeds. Due to thermal growth.8 0.1.25 +/.0 +/. would impose stress upon the connecting piping. The proper shaft alignment procedure is to secure the driven equipment first. Table 1.5 +/. proper alignment is difficult to achieve without using alignment equipment such as dial indicators or laser alignment tools to check and correct for misalignment.3 In practice.5 0.
Cogged belts have slots that run perpendicular to the belt's length. Photo Courtesy of Gates Rubber Company Suggested Actions • Conduct a survey of belt-driven equipment in your plant. and have an efficiency that is about 2% higher than that of standard V-belts. synchronous belts are noisy. Efficiency deteriorates by as much as 5% (to a nominal efficiency of 93%) over time if slippage occurs because the belt is not periodically re-tensioned. driven torque. and transfer vibrations. and run slip-free. V-belts have a sharp reduction in efficiency at high torque due to increasing slippage. Cogged belts can be used with the same pulleys as equivalently rated V-belts. under or over-belting. offering potential energy cost savings. However. requires no lubrication. Synchronous belts (also called timing. In contrast. Department of Energy—DOE's MotorMaster+ and MotorMaster+ International software tools help you make motor comparisons and selection on a broad range of motors. But. A properly designed belt transmission system provides high efficiency. Improving Motor and Drive System Performance: A Sourcebook for Industry 77 . Efficiency is also dependent on pulley size. Joined or multiple belts are specified for heavy loads. Synchronous belts require less maintenance and retensioning. positive-drive.gov/industry/bestpractices to access these and many other industrial energy efficiency resources and training.energy. operate in wet and oily environments. or high-torque drive belts) are toothed and require the installation of mating toothed-drive sprockets. Belt drives provide flexibility in the positioning of the motor relative to the load. eere. The slots reduce the bending resistance of the belt. V-belts use a trapezoidal cross section to create a wedging action on the pulleys to increase friction and improve the belt's power transfer capability. determine the cost effectiveness of replacing existing V-belts with synchronous belts and sprockets. Resources U. Visit the BestPractices Web site at www. They run cooler. • Install cogged belts where the retrofit of a synchronous belt is not cost effective. last longer. • Consider synchronous belts for all new installations as the price premium is small due to the avoidance of conventional pulley costs. Then. Pulleys (sheaves) of varying diameters allow the speed of the driven equipment to be increased or decreased. decreases noise. and V-belt design and construction. certain types of belts are more efficient than others. V-belt drives can have a peak efficiency of 95% to 98% at the time of installation. and presents low maintenance requirements.S. Synchronous belts offer an efficiency of about 98% and maintain that efficiency over a wide load range. Gather application and operating hour data.Appendix B: Tip Sheet Number 5 Replace V-Belts with Cogged or Synchronous Belt Drives About one-third of the electric motors in the industrial and commercial sectors use belt drives. The majority of belt drives use V-belts. unsuitable for shock loads.
000 kWh/year x (1 – 93/98) = 26. synchronous belt sprockets must be selected that take into account the absence of slippage. which exhibit a strong relationship between operating speed and power. Synchronous belts also make a whirring noise that might be objectionable in some applications. 100-hp. supply-air fan motor (93% efficient) operates at an average load of 75% while consuming 527. Energy Savings = Annual Energy Use x (1 – η1/η2 ) = 527. Operating costs could actually increase if slippage is reduced and a centrifugal load is driven at a slightly higher speed.05/kWh. What are the annual energy and dollar savings if a 93% efficient (η1) V-belt is replaced with a 98% efficient (η2) synchronous belt? Electricity is priced at $0. cogged belts may be a better choice when vibration damping is needed or shock loads cause abrupt torque changes that could shear a synchronous belt's teeth.05/kWh = $1.888 kWh x $0.345 Further Considerations For centrifugal fans and pumps.888 kWh/year Annual Cost Savings = 26.000 kWh annually. Synchronous belts are the most efficient choice. However.Appendix B: Tip Sheet Number 5 Example A continuously operating. DOE/GO-102005-2060 • September 2005 • Motor Systems Tip Sheet #5 78 Improving Motor and Drive System Performance: A Sourcebook for Industry .
0 F 5. U.3-7. Only small and non-NEMA Design B motors have Codes beyond L. instantaneous peak inrush and locked rotor current.0 software or deciphered from the locked-rotor code letter on the motor nameplate.org. 460-volt. • If adjusting the trip setting is not sufficient.energy.3% for each letter increment. The ratio of peak inrush to locked-rotor current tends to increase with higherefficiency motors due to their lower power factor under locked rotor conditions.S.0 M 10. kVA/hp designated as "Code.eere.1-8. Locked-rotor current is the root-mean-square or RMS current that establishes following the peak inrush. Locked-rotor current for specific new motor models can be looked up in the MotorMaster+ 4. Locked-rotor code B 3.5-5.0-5. most NEMA Premium motors are NEMA Design B and are subject to the same maximum allowable locked-rotor current as their standard-efficiency counterparts.0-10.0-11. the current remains near the locked-rotor value during acceleration until the motor approaches its operating speed.1 expresses current in kilovolt amperes (kVA) C 3. see the Motor Tip Sheet #1 (DOE/GO-102005-2019) on this topic or visit www. upgrading to NEMA Premium™ efficiency motors has no noticeable impact on the electrical system.46 kV)/ √3} 502 Amps The NEMA table actually continues all the way to letter V with current increasing about 12." is not the same as the A 0-3. However.55-4.0 kVA /hp / 0. Note that the Code can be quite complicated and exceptions do exist.0 J 7. The National Electrical Manufacturers Association (NEMA) recognizes and describes two components of starting current.3 motor design letter code.0 per horsepower (hp). • Refer to Section 430 of the latest National Electric Code for guidance on increasing the instantaneous trip level of your circuit protector. (Note: The terms inrush or starting current are often used to mean locked-rotor current. The Code has been modified to allow adjustments to a greater allowable trip setting when nuisance trips occur.nema. in rare cases nuisance trips can occur during startup.15-3. LR Current = = = Motor horsepower x (Maximum kVA/hp/Supply voltage in kV) / √3 100 hp x {(4.0 defined as follows: E 4. Resources National Electrical Manufacturers Association (NEMA)—For additional information on NEMA Premium standards.55 H 6. Don't hesitate to contact a licensed professional electrical engineer to resolve motor protection problems.2 Suggested Actions If nuisance tripping occurs: • Make sure power factor correction capacitors are installed ahead of the starter. usually just Locked-Rotor Code.6-6.gov/ industry/bestpractices to access additional resources and information on training. which is a momentary current transient that occurs immediately (within half an AC cycle) after contact closure.0-4. Nuisance tripping has been primarily associated with the instantaneous peak inrush. Department of Energy—For assistance in diagnosing nuisance motor trips and related information on industrial energy efficiency measures contact the EERE Information Center at (877) 337-3463. Visit the BestPractices Web site at www.) NEMA Premium motors have slightly higher locked-rotor currents and lockedrotor code letters than lower-efficiency motors of the same rating. However. the circuit protector can be replaced with a circuit protector with a mechanical delay that lets it ride through half a cycle of current above the nominal setting.6 Example The maximum locked-rotor current for a Code C. Improving Motor and Drive System Performance: A Sourcebook for Industry 79 . The code letters are D 4. Addressing this topic requires an understanding of starting current.0-9. L 9.15 G 5. This letter.Appendix B: Tip Sheet Number 6 Avoid Nuisance Tripping with Premium Efficiency Motors In most cases. 100-hp motor is determined as follows.5 K 8.
However. The exact peak-inrush current depends on the moment when contacts close in the AC voltage cycle. A motor may trip on peak-inrush current and start successfully on the next attempt. no standard limits the peak-inrush current.Appendix B: Tip Sheet Number 6 While NEMA Design B standards limit locked-rotor current. Nuisance trips are unlikely to occur in situations without instantaneous magneticonly circuit protectors when the replacement motor is a NEMA Premium Design B motor of the same speed and horsepower.8 times the RMS locked-rotor current and may exceed the circuit protector current setting. you may not have a problem with nuisance trips. and how close to simultaneously the three-phase contacts close. Fortunately. peak-inrush current is usually not a problem because it lasts only a few milliseconds. Many motor manufacturers offer NEMA Premium Design A motors that meet Design B torque requirements but exceed Design B locked-rotor current limits. That is because peak inrush can be as high as 2. Some of the most efficient motors are Design A. DOE/GO-102005-2022 • September 2005 • Motor Systems Tip Sheet #6 80 Improving Motor and Drive System Performance: A Sourcebook for Industry . so do not limit choices to Design B unless you have locked-rotor current concerns. it can be a problem when the motor controller uses instantaneous magnetic-only circuit protectors that react in less than a single AC cycle. Even if instantaneous magnetic-only circuit protectors are present.
Improving Motor and Drive System Performance: A Sourcebook for Industry 81 .nema. The general trend of efficiency reduction with increased voltage unbalance is observed for all motors at all load conditions. which results in a shorter winding insulation life. Voltage unbalance is defined by the National Electrical Manufacturers Association (NEMA) as 100 times the absolute value of the maximum deviation of the line voltage from the average voltage on a three-phase system. • Check your electrical system singleline diagrams to verify that singlephase loads are uniformly distributed. * Results vary depending upon motor design. Revision 1-2004. org for additional information on voltage imbalance.1 Suggested Actions • Regularly monitor voltages at the motor terminals to verify that voltage unbalance is maintained below 1%. eere. Another indicator that voltage unbalance may be a problem is 120 Hz vibration. • Unbalanced transformer bank supplying a three-phase load that is too large for the bank.1 1% 94. The voltage unbalance is: (460 . speed. If unbalanced voltages are detected. The efficiency of a rewound. • An open circuit on the distribution system primary. Energy and dollar savings occur when corrective actions are taken.4 95.0 93. • Unevenly distributed single-phase loads on the same power system.Appendix B: Tip Sheet Number 7 Eliminate Voltage Unbalance Voltage unbalance degrades the performance and shortens the life of a three-phase motor. increased vibrations and mechanical stresses. 463. Motor Efficiency* Under Conditions of Voltage Unbalance Motor Load % of Full 100 75 50 Motor Efficiency. 100-hp motor is given as a function of voltage unbalance and motor load in the table.5 2. U. Resources National Electrical Manufacturers Association (NEMA)—Visit www. if the measured line voltages are 462. • Unbalanced or unstable utility supply. For example. and 455 volts. divided by the average voltage. • Unidentified single-phase to ground faults.S. Typically. and will void most manufacturers' warranties. % Voltage Unbalance Nominal 94. a thorough investigation should be undertaken to determine the cause. but the above motor tested in the lab showed otherwise. electric motors have peak efficiency near 75% load.gov/industry/bestpractices to access these and many other industrial energy efficiency resources and training.1% 460 It is recommended that the voltage unbalances at the motor terminals not exceed 1%. full-load efficiency.455) x 100 = 1. 1800-RPM.4 95.2 96. A finding of 120 Hz vibration should prompt an immediate check of voltage balance.1 95. Visit the BestPractices Web site at www.9 94. increased losses.energy. Common causes of voltage unbalance include: • Faulty operation of power factor correction equipment. and horsepower rating. Unbalanced currents lead to torque pulsations. Department of Energy—DOE's MotorMaster+ and MotorMaster+ International software tools help you make motor comparisons and selection on a broad range of motors. • Install ground fault indicators as required and perform annual thermographic inspections. Voltage unbalance at the motor stator terminals causes phase current unbalance far out of proportion to the voltage unbalance.5% 93. and motor overheating. Unbalances over 1% require derating of the motor per Figure 20-2 of NEMA MG-1-2003. the average is 460 volts. Voltage unbalance is probably the leading power quality problem that results in motor overheating and premature motor failure.
000 hrs/yr x (100/93 – 100/94.000 hours per year. a motor with a 100°C temperature rise would experience a temperature increase of 8°C when operated under conditions of 2% voltage unbalance. The magnitude of current unbalance may be 6 to 10 times as large as the voltage unbalance. DOE/GO-102005-2061 • September 2005 • Motor Systems Tip Sheet #7 82 Improving Motor and Drive System Performance: A Sourcebook for Industry . after corrective actions are taken.5% voltage unbalance) were unbalanced by 27. Motors and Generators.Appendix B: Tip Sheet Number 7 Example Assume that the motor tested as shown in the above table was fully loaded and operated for 8. Further Considerations Voltage unbalance causes extremely high current unbalance. with an unbalanced voltage of 2. the annual energy and dollar savings.746 kW/hp x 8. For the 100-hp motor in this example. line currents (at full-load with 2. References Information in this tip sheet is extracted from NEMA Standards Publication MG1-2003.05/kWh.517 kWh x $0.05/kWh = $476 Overall savings may be much larger because an unbalanced supply voltage may power numerous motors.517 kWh Annual Dollar Savings = 9. 2003. For example. Winding insulation life is reduced by one-half for each 10°C increase in operating temperature.7%. are: Annual Energy Savings = 100 hp x 0. The additional temperature rise is estimated with the following equation: Percent additional temperature rise = 2 x (% voltage unbalance )2.5%. A motor will run hotter when operating on a power supply with voltage unbalance.4) = 9. With energy priced at $0.
eere. Compare the magnitude of the voltage drop for each phase with the voltage drop for the other phases supplying the load. The voltage drop is simply the voltage difference across the connection. Causes of poor connections include: • Loose cable terminals and bus bar connections • Corroded terminals and connections • Poor crimps • Loose. Resources U.gov/industry/ bestpractices.energy. undersized conductors. Losses due to poor connections represented one-third of these losses and accounted for 40% of the savings after corrective actions were taken. Terminations should be regularly inspected. The total energy loss in a three-phase component is determined by summing the losses for each phase. In a study at three industrial facilities. average electrical distribution system losses accounted for 2% of plant annual energy use. leakage to ground. dirty. The increased resistance converts electrical energy into heat and imposes additional loads on the distribution system. an excessive voltage drop indicates that component voltage drop testing should be initiated. Conducting a Voltage-Drop Survey A voltage-drop survey can usually be done in-house with existing equipment such as a hand-held voltmeter. Limit the load on each circuit or install larger-than-codeminimum conductors if the voltage drop exceeds 3%. Suggested Actions • Conduct a voltage drop survey. and poor connections—can account for less than 1% to over 4% of total plant electrical energy consumption. Termination maintenance is generally a cost-effective electrical distribution system energy savings measure. The cost of cleaning or replacement is low compared to the significant energy savings and secondary benefits. For a typical motor circuit.and under-voltage. worn or poorly adjusted contacts in motor controllers or circuit breakers • Loose.S. including reduced downtime due to unscheduled equipment outages and improved safety due to reduced fire hazards. Replacing fuse clips or cleaning breaker fingers can be very cost-effective. Voltage drop information can be used to determine energy losses and excess energy consumption due to loose and dirty connections. Voltagedrop measurements should be taken at each phase. These hot spots may be detected by infrared thermography or a voltage drop survey. Inexpensive handheld infrared thermometers can quickly and safely reveal hot spots. low power factor. Maintenance of connections is generally referred to as termination maintenance. Voltage drop measurements should be taken from the input of each panel to the panel output for each load. measure the voltage drop from the bus bar to the load side of the motor starter.Appendix B: Tip Sheets Number 8 Eliminate Excessive In-Plant Distribution System Voltage Drops Studies indicate that in-plant electrical distribution system losses—due to voltage unbalance. Improving Motor and Drive System Performance: A Sourcebook for Industry 83 . A voltage drop difference of over 15% indicates that testing should be initiated to identify poor circuit connections. Even with good balance. Poor connections or inadequate conductor sizes result in excessive energy losses. Department of Energy—Contact the EERE Information Center at 877337-3463 to obtain cited publications or to request additional information on motor and driven-equipment energy efficiency opportunities. Additional resources and information on training is also available at the BestPractices Web site at www. over. or corroded fuse clips on manual disconnect switches Distribution system losses due to poor electrical contacts appear as hot spots caused by increased resistance or electric power (I2R) losses.
Volts 8. 5. and 201.512 = $1.1 5.126 14.05/kWh = $331 + $1. Measured line currents are 199. The potential annual energy and electrical demand savings due to correcting the problem are: Table 1.1.7 1.7.6 5. potential savings are valued at: Savings = 3.8 Totals: Excess Power. Excess Energy Consumption at a MCC Breaker Circuit L1 L2 L3 Measured Voltage Excess Voltage Drop. kWh 9. DOE/GO-102005-2024 • September 2005 • Motor Systems Tip Sheet #8 84 Improving Motor and Drive System Performance: A Sourcebook for Industry .4 8. Volts Drop.6 volts on L1.45 Excess Energy Use.7 205. kW 1. and L3. respectively.7 201.318 30.843 per year (for a single breaker) References This tip sheet is extracted from two publications prepared for the Bonneville Power Administration: Industrial Electrical Distribution Systems Study Report and Keeping the Spark in Your Electrical System: An Industrial Electrical Distribution Maintenance Guidebook.240 Assuming a utility energy charge of $0.00/ kW per month.240 kWh/year x $0. Amps 199.1 Current.5 volts should be obtainable.Appendix B: Tip Sheets Number 8 Energy Savings Example Measurements at a motor control center (MCC) breaker indicate voltage drops of 8.9 10. and 10.63 3.9.796 6. L2.45 kW x $8. Voltage drop measurements for circuits serving similar loads indicate that a voltage drop of 2. 205.8 amps for L1. The driven equipment is continuously operated. L2.6 3. and L3.12 0.00/kW/month x 12 months/year + 30.05/kWh with a demand charge of $8.7.
Correcting power factor at the points of use will reduce system current and associated voltage drop. The 4% difference was established to allow for a reasonable line voltage drop between the transformer secondary and the point of use (see Table 1). Power factor improves with under-voltage. low power factor is usually corrected by installing capacitors attached to the load-side terminals of the motor starter. Replace existing conductors with larger ones or add parallel conductors. the synchronous speed for a 1750 RPM motor is 1800 and the slip is 50 RPM. • If voltage does not vary much. torque capability is reduced over the whole accelerating range from initial start to stabilization at running speed. For 1:1. Running speed stabilizes at only a fraction of a percent lower than normal but the breakdown torque is reduced. Higher currents lead to increased resistance and power losses (I2R). • If daily voltage variation occurs at the service entrance. These correspond to (but are about 4% lower than) standard service voltages.10% of their nameplate rated voltages. the drive can compensate for voltage discrepancies as long as the input voltage is within the operating range of the drive. motor efficiency and other performance parameters are degraded. Improving Motor and Drive System Performance: A Sourcebook for Industry 85 .or under-voltage and voltage unbalance. This can be provided by the customer or the utility. There is no difference in performance at the different voltage ratings because the different connection compensates to put exactly the same total current through each winding turn. There are certain standard utilization voltages for motors. • When using a motor with an adjustable speed drive (ASD). What Happens to Motor Performance when Voltage Varies? With reduced voltage. Standard Motor Operating Voltages (Volts) Service Voltage Utilization Voltage 208 200 240 230 480 460 600 575 2400 2300 4160 4000 Suggested Actions The best motor performance occurs when power supplied to the motor terminals is close to the nominal utilization voltage.73 like 2300/4000. This reduces a motor's ability to break loose a stuck load and increases acceleration times. For 1:2 ratios like 230/460. The different voltages are accommodated by making different connections in the motor terminal box. inefficient.Appendix B: Tip Sheets Number 9 Improve Motor Operation at Off-Design Voltages Motors are designed to operate within +/. When motors operate at conditions of over.g. 900 RPM (8-poles). they can evaluate the design for other possible ways to improve reliability and efficiency. 1200 (6-poles). and possible overheating. an "auto-tapchanger" transformer is recommended. Slip is the difference between a motor's actual speed and synchronous speed. This might be seen as a benefit except the reduction in reactive current is more than nullified by the increase in the total current necessary to deliver the real power at reduced voltage. or undersized transformers if they are the cause. • If voltage is constant at the service entrance. Synchronous speed is always 7200 RPM divided by the pole count. change to a different main service transformer tap setting. conductor and/or in-plant transformer losses are excessive. but is constantly too high or too low. Replace old. Running this motor at 10% over-voltage would increase the power draw for centrifugal fans and circulating pumps by around 1. Slip and starting torque vary as the square of the voltage deviation. meaning the motor has less ability to drive through a brief torque overload without stalling. 1800 (4-poles). the connections change coil groups from delta (for the lower voltage) to wye (for the higher voltage). The drive's capacitors correct for low power factor. the connections change coil groups from parallel to series. • Have your service center rewind motors for the actual utilization voltage. Adjust branch or secondary transformer tap settings as necessary.or under-voltage.5% because their power requirement is sensitive to speed. To ensure efficient motor performance. The actual synchronous speed is always the lowest possible synchronous speed above the nameplate full-load speed. etc. but will slip more and operate hotter at 208 volts than at 230 or 460 volts. Motors sometimes come in multivoltage ratings. • For a single motor attached to a conventional motor starter. For example. 3600 (2-poles). Low voltage caused by high system impedance is exacerbated during starting and acceleration when the current is four to eight times nameplate full-load levels. Tri-voltage motors (208230/460 V) are designed to produce rated torque at each voltage. e. reduced motor efficiency. At the same time. Table 1. but varies within the facility due to load variations and distance from the transformer. use the following tips to correct for over.
it may be practical to run medium voltage (>600 to 6600 volts) distribution lines to the remote areas. energy. Resources U. the voltage drop and power losses are usually held to well under 1%. Standard medium voltage motors are available as small as 100 hp.Appendix B: Tip Sheet Number 9 Full load efficiency is at maximum between nominal voltage and about 10% overvoltage. At medium voltage. Department of Energy For additional information on ways to improve motor efficiency by improving the voltage supplied to the motor terminals.eere. even with dramatically reduced conductor cross section.gov/industry/bestpractices. at reduced load the best efficiency point shifts considerably toward lower voltages. refer to the DOE Motor Tip Sheet # 7: Eliminate Voltage Unbalance. or where correction of severe voltage drop is necessary. DOE/GO-102008-2615 • June 2008 • Motor Systems Tip Sheet #9 86 Improving Motor and Drive System Performance: A Sourcebook for Industry . The medium voltage can be transformed down near the points of use.S. or the equipment can be driven by medium voltage motors. Find this tip sheet and additional information or resources on motor and motor-driven system efficiency improvement measures on the BestPractices Web site at www. Sometimes low voltage only occurs at remote areas of a facility where high loads are concentrated. or contact the EERE Information Center at (877) 337-3463. In new construction. However.
refer to NEMA MG 10-2001 "Energy Management Guide for Selection and Use of Fixed Frequency Medium AC Squirrel-Cage Polyphase Induction Motors. Repeated Motor Starts and Stops While it is true that starting stresses a motor. turning a motor off 10% of the time could reduce energy costs enough to purchase three new motors. motors are designed to be started. the belief that stopping and starting motors is harmful persists. While a typical NEMA Design B motor may draw from four to eight times the full-load current during starting. or contact the EERE Information Center at (877) 337-3463. Peak demand charges are generally based upon a facility's average energy use over a fixed or rolling average window of 15 to 60 minutes in duration.energy. Check with your utility to determine how they assess peak demand charges. Just 1 minute of additional running time consumes far more energy than a motor starting event. the excess starting demand is small due to the short duration of the motor starting interval. nema. Reducing motor operating time by just 10% usually saves more energy than replacing a standard efficiency motor with a NEMA Premium® efficiency motor. Resources National Electrical Manufacturers Association (NEMA) —Visit www. • Install automatic shutdown timers so motors will be turned off when they would otherwise be running idle or unloaded for intervals longer than the rest intervals identified in NEMA MG 10-2001. given that 97% of the life cycle cost of purchasing and operating a motor is energy-related. the power factor is low so the input power is not four to eight times rated load power. leading to cracks and failed end-ring connections. As long as the frequency of starts is not excessive. lunch breaks. • Shut down equipment that is energized but not in use for significant periods of time. Many users believe that repeated motor starts will use more energy than constant operation. When started. Consider times when motors can be shut down. soft starters. Improving Motor and Drive System Performance: A Sourcebook for Industry 87 . they do need to be put into proper perspective. Starting usually takes under 2 seconds and is rarely over 10 seconds. misapplication. shock. a motor accelerates and draws more power than when it is operating steadily at full load. Again.12. When making the decision to stop a motor. However.Appendix B: Tip Sheet Number 10 Turn Motors Off When Not in Use Motors use no energy when turned off. Overheating the stator winding and the rotor cage occurs if frequency of starts and duration of rest time between starts exceeds the NEMA design range. Suggested Actions • Keep track of your motors through a motor system management plan.gov/industry/bestpractices. Department of Energy For additional information or resources on motor and motor-driven system efficiency improvement measures. Starting Stresses Starting stresses a motor by: • Applying higher than rated full load torque to the shaft during acceleration • Applying high magnetic forces to the rotor cage and winding end turns • Heating the stator winding and the rotor cage. such as compressors or pumps. However. eere. even for large high inertia loads." For large induction motors.S. • Energy saving opportunities often exist when motors drive loads in parallel. In fact. and shorten motor life. most shaft failures are attributed to bearing failures. Frequent torque shocks to the shaft from starting could shorten shaft life through metal fatigue. including shift changes. Heat from exceeding these limits can degrade winding insulation and cause thermal stressing of the rotor cage. increase utility demand charges. while lasting for 15 years or more. wye-delta starting or autotransformers to reduce starting stresses on equipment that requires frequent starting and stopping. While these opinions are not totally without basis. or during process interruptions. visit the BestPractices Web site at www.org for more information. excessive belt tension. lifetime is not significantly affected. For example. refer to NEMA MG 1-2006 "Motors and Generators" Part 20. U. Evaluate sequencing of these motors. Another motor starting concern involves increased utility demand charges. or creep during storage (large motors). motors in applications like lift pumps or irrigation wells start and stop quite frequently. • Consider adjustable speed drives (ASDs).
Each start is one factor in the life expectancy and reliability of the motor and some reduction in life expectancy and reliability must be accepted when a motor is continuously applied at the upper range of its starting duty. and harmonic voltages • Do not overload the motor • Derate any motor used in severe ambient environments. under-voltage.Appendix B: Tip Sheet Number 10 NEMA provides standards for starting duty which consider inertia of the load an important factor in starting stress. You may find that you can substantially increase the time your motors are shut down without approaching the NEMA MG 10-2001 starting duty limits. When operating in the upper range of starting duty. even within NEMA limits. Frequent stopping and starting. • NEMA MG 10-2001 (Table 7) gives the maximum number of allowable starts per hour for motors of various horsepower and synchronous speed ratings. Motors driving loads that do not exceed these inertia limits can be started twice in immediate succession when the motor is initially at ambient temperature.000 feet altitude or above 40°C. Additional Information • NEMA MG 1-2006 provides a table on the maximum inertia load for starting induction motors of various ratings. take these steps to ensure that you are well within tolerances on other sources of thermal stress: • Keep the motor clean so air flow and heat transfer are not impeded • Keep supply voltage nominal. Multiple other factors also contribute to temperature rise. The greatest stress of pushing the limits on starting frequency is thermal. The table indicates how frequently motors can be started with a rest period between starts and provides a minimum length for that rest period. but there is no known relationship between number of motor starts and normal motor life expectancy. DOE/GO-102008-2616 • June 2008 • Motor Systems Tip Sheet #10 88 Improving Motor and Drive System Performance: A Sourcebook for Industry . avoiding voltage unbalance. such as over 3. does stress a motor due to mechanical flexing of the coils and rotor overheating during acceleration. NEMA also provides guidance relating to startrun-stop-rest cycles that are often employed in energy management programs.
Manufacturers can provide efficiency values for ASDs as a function of operating speed or load for both variable torque loads (centrifugal fans and pumps) and constant torque loads (cranes. you must determine the load duty cycle. use the values given in Table 1. • Use this information to accurately determine the energy savings due to the use of ASD versus throttle or damper flow control. in revolutions per minute (RPM) RPM2 = reduced speed of driven equipment. hp2 = hp1 x (RPM2 /RPM1)3 = hp1 x (Flow2 /Flow1)3 Where: hp1 = driven-equipment shaft horsepower requirement at original operating speed hp2 = driven-equipment shaft horsepower requirement at reduced speed RPM1 = original speed of driven equipment. Power requirement for centrifugal loads Determining Energy Savings To establish the energy savings that are possible when an ASD is applied to a variable torque load.eere. Department of Energy For additional information on motor and motor-driven system efficiency.energy. The load on the ASD is the actual power supplied by the device (shaft horsepower divided by the motor efficiency at its load point) divided by the rated output power. or percentage of time that the fan or pump operates at each system operating point. or pressure and then transmit a signal to a controller that adjusts the frequency and speed to match process requirements. A motor "load factor" is the load imposed upon the motor by the driven equipment divided by the motor's full output rating. the most common type of ASDs. For centrifugal fans or pumps with no static lift. The input power requirement varies as the cube or third power of the speed ratio (see Figure 1). Variable frequency drives (VFDs). and to download the MotorMaster+ software tool. Resources U. hoists.Appendix B: Tip Sheet Number 11 Adjustable Speed Drive Part-Load Efficiency An adjustable speed drive (ASD) is a device that controls the rotational speed of motor-driven equipment. External sensors monitor flow.nema. and conveyors).org for information on motor standards. When ASD partload performance values are not readily available. Pulse-width modulated (PWM) VFDs are most often used in variable torque applications in the 1 to 1. National Electrical Manufacturers Association (NEMA) —Visit the NEMA Web site at www.000 hp motor size range. Variable and constant torque loads are expressed in terms of the shaft horsepower supplied by the motor. For example. visit the BestPractices Web site at www. efficiently meet varying process requirements by adjusting the frequency and voltage of the power supplied to an AC motor to enable it to operate over a wide speed range.S. the fluid or air flow provided varies directly with the pump or fan rotational speed. Improving Motor and Drive System Performance: A Sourcebook for Industry 89 . Small decreases in equipment rotating speed or fluid flow yield significant reductions in energy use. or contact the EERE Information Center at (877) 337-3463. You must also know the efficiency of the variable speed drive and the drive motor when the motor is operating partially loaded and at a reduced speed to satisfy variable flow requirements. in RPM Flow1 = original flow provided by centrifugal fan or pump Flow2 = final flow provided by centrifugal fan or pump Suggested Actions • Contact your supplier to obtain drive efficiency as a function of motor operating speed or drive power output. reducing speed (flow) by 20% can reduce power requirements by approximately 50%.gov/industry/ bestpractices. application guides. liquid levels. and technical papers. Figure 1.
Percent of Drive Rated Power Output 1. At 1/4 of its rated operating speed. Table 1. with adjustable speed operation the power required by the fan and the VFD is only 0. the motor efficiency at its load point.Appendix B: Tip Sheet Number 11 When considering electronic PWM ASDs. Example Consider an adjustable speed drive coupled to a motor that delivers 20 hp to an exhaust fan when operated at its full rated speed. Efficiencies for integral horsepower NEMA Design A and B motors at full and part-load can readily be obtained from the U.6 31 35 41 47 50 46 51 47 55 61 61 12. DOE/GO-102008-2617 • June 2008 • Motor Systems Tip Sheet #11 90 Improving Motor and Drive System Performance: A Sourcebook for Industry . As shown in the following example. and the driven equipment efficiency (Esystem = EASD x Emotor x EEquipment ). Efficiencies for driven equipment must be extracted from the appropriate pump or fan performance curves. this reduction in efficiency is not as detrimental as it first seems.S. In addition. the fan delivers 25% of its rated airflow. The decline in efficiency is more pronounced with drives of smaller horsepower ratings. Even with the low drive efficiency of 47%. Note: This example does not account for the efficiency at each load point for the fan drive motor. Remember that the system efficiency is the product of the ASD efficiency. Inc.5 77 80 83 86 88 86 87 86 89 91 91 25 86 88 90 93 93 92 92 93 94 95 95 42 90 91 93 94 95 95 95 95 95 96 96 50 91 92 94 95 95 95 95 96 96 96 96 75 93 94 95 96 96 96 96 97 97 97 97 100 94 95 96 97 97 97 97 97 97 97 97 1.66 hp.0 software tool. PWM ASD Efficiency as a Function of Drive Power Rating1 Variable Speed Drive hp Rating 3 5 10 20 30 50 60 75 100 200 400 Efficiency.% Load.66 hp. Source: Safronics. there are many ways to set up an ASD that can affect the operating efficiency. These efficiency values may be considered representative of "typical" PWM ASD performance. Department of Energy's MotorMaster+ 4. ASD efficiency decreases with decreasing motor load. hp25% = (20 hp x (1/4)3 / (47/100)) = 0. There is no widely accepted test protocol that allows for efficiency comparisons between different drive models or brands. but requires only 1/64 of full-load power. you may use Table 1 to obtain efficiency values for drives of various ratings that supply power to motors connected to either variable or constant torque loads.
S.8 47. "Payback®" Magnetic-Coupled Variable Speed Drive Literature.org for information on motor standards.3 to 99. visit the BestPractices Web site at www. Department of Energy's Motor-Master+ 4.7 to 50.59 13. Use this information to determine the energy savings due to the use of a PWM ASD versus an eddy-current drive.05 Improving Motor and Drive System Performance: A Sourcebook for Industry 91 . Inc.13 6.6 EddyCurrent Drive Efficiency. • Efficiencies for integral horsepower NEMA Design A and B motors at full and part-load can readily be obtained from the U. Table 1. and 70% of rated flow for the remaining operating hours. the proposed replacement is a PWM ASD.nema. Torque is transmitted from the outer rotating drum to the rotor with an adjustable magnetic field.33 26.7 28. Department of Energy For additional information on motor and motor-driven system efficiency.9 Suggested Actions • Contact your drive supplier to obtain drive efficiency information as a function of motor operating speed or drive power output. % 90.% 91.9 to 59.5 56. An alternating current motor drives a constantspeed rotating drum that surrounds a cylinder (rotor).0 80. The eddy-current drive or clutch is a slip device consisting of two rotating elements that are coupled by a magnetic field with the slip and rotor speed based upon the magnetic field strength. The maximum efficiency of a slip-based adjustable speed controller is approximately equal to the amount of slip.6 90.6 17. and to download the MotorMaster+ software tool.3 21. 80% flow for 50% of the time.6 to 29. • When ASD part-load performance values are not readily available.1 to 80.gov/industry/ bestpractices. Source: Coyote Electronics. 1.9 to 90.2 Motor Efficiency.9 86.6 12. % of Full-Load Speed 100 90 80 70 60 50 40 30 Load % 100 72.5 6.7 Eddy-Current Drive Efficiency. Resources U.2 34.0 Total: Weighted Input Power (kW) 6. % 94. Efficiency Versus Speed for an Eddy-Current Coupled Centrifugal Load1 Drive Speed. Average Power Requirements for a Centrifugal Fan with Eddy-Current Drive Speed Control % of Rated Fan Speed/ Flow 90 80 70 Load Duty Cycle. The fan operates for 8.4 76.4 2.S. In Table 2. use the values given in the Motor Tip Sheet #11: Adjustable Speed Drive Part-Load Efficiency. Shaft hp 36. Energy Savings Example An eddy-current drive on a 50 hp boiler forced-draft fan has reached the end of its useful operating life.0 70. which is coupled to an output shaft.45 25.1 66.3 85.Appendix B: Tip Sheet Number 12 Is it Cost-Effective to Replace Old Eddy-Current Drives? Overview New pulse-width-modulated (PWM) adjustable speed drives (ASDs) may be costeffective replacements for aging or maintenance-intensive eddy-current drives.eere.9 to 70. and technical papers. ational Electrical Manufacturers N Association (NEMA) —Visit the NEMA Web site at www.2 39. % 20 50 30 Load.energy.000 hours per year while delivering 90% of rated flow for 20% of the time.9 51. or difference between full-load speed and the operating speed. or contact the EERE Information Center at (877) 337-3463.7 to 41. Table 1 indicates the efficiency of a magnetically coupled eddy-current drive when matched to a centrifugal load. Energy savings are obtained due to the improved efficiency of the PWM drive over the eddy-current drive. application guides. the existing system or baseline annual energy consumption is determined as follows: Table 2.0 software tool.
the fan power requirements decrease. are not subject to nuisance trips due to power disturbances. the cost effectiveness can be significantly improved if a utility efficiency incentive is available.480 kWh/year At an electrical rate of $0. and operate independently of the motor power supply voltage.99 As the eddy-current drive efficiency drops rapidly at loads below 70%. they do not transmit vibrations to the motor and provide inherent protection against load seizures.6 ASD Efficiency.624/year The above example illustrates that although early replacement of an older eddycurrent drive with an electronic ASD may not meet the two-year simple payback typically required by industry. Other factors that may favor replacement include predictive maintenance tests indicating an impending failure or when equipment fails and requires repair.05/kWh = $1. do not produce harmonic distortion.480 kWh x $0. Eddy-current drives can produce more torque at low speed than an induction motor and ASD. Average Power Requirements for a Centrifugal Fan with ASD Speed Control % of Rated Fan Speed/ Flow 90 80 70 Load Duty Cycle.9 86. energy savings are very sensitive to the load profile and duty cycle.% 91.000 hours/year = 32. % 96 95 93 Total: Weighted Input Power (kW) 6. the value of these savings is: 32. Load Considerations An ASD may not be a suitable replacement for high-torque repetitive-slip applications such as a punch press or a crusher. The annual energy savings for this application is: (26.Appendix B: Tip Sheet Number 12 Note that the input power is equal to 0. the motor and the drive may require oversizing by a factor of 150% to 200%. As eddy-current drives are not directly coupled to the load shaft.2 Motor Efficiency.05/kWh. In Table 3 when the ASD is installed.05 4.18 11.05 – 21.76 21. % 20 50 30 Load Shaft hp 36. Table 3. Installers must ensure that operational problems are not created through installation of an electronic ASD. The weighted input power value is the input power times the load duty cycle percentage divided by 100. Eddy-current drives can be used with standard efficiency motors. When switching to an ASD for a constant torque load.6 17.746 times the shaft horsepower divided by the product of the motor and drive efficiency values.99) kW x 8.6 90. DOE/GO-102008-2618 • June 2008 • Motor Systems Tip Sheet #12 92 Improving Motor and Drive System Performance: A Sourcebook for Industry .45 25.
Improving Motor and Drive System Performance: A Sourcebook for Industry 93 . a magnetically coupled ASD does not alter the power supplied to the motor. the motor is generally brought up to operating speed while unloaded. Suggested Actions • Complete a survey to identify constant speed motors in your plant that are used to drive centrifugal pumps with throttling valves or recirculation (bypass) lines or centrifugal fans equipped with inlet and/or discharge dampers. visit the BestPractices Web site at www. National Electrical Manufacturers Association (NEMA) —Visit the NEMA Web site at www. Electronic ASDs The current state-of-the-art speed control is the electronic ASD. and technical papers.S. eere.energy. The majority of ASD-equipped industrial motor systems are of 20 hp or less—with the ASD often installed for improved control over the production process rather than energy savings.Appendix B: Tip Sheet Number 13 Magnetically Coupled Adjustable Speed Motor Drives Adjustable Speed Drive Overview Alternating current electric motors rotate at a nearly constant speed that is determined by motor design and line frequency. The motor continues to operate at its rated design speed while the magnetic coupling controls the torque transferred and the speed of the driven equipment by varying the strength of the magnetic field between the motor shaft and the load shaft. vibrations that occur on the load side are isolated and not transmitted to the motor.2 However. or contact the EERE Information Center at (877) 337-3463.org for information on motor standards. For instance.gov/industry/bestpractices. a newsprint products plant recently installed a magnetically coupled ASD for a 250 hp/2300 V motor running a centrifugal pump with a by- Resources U. Although electronic ASDs have been available for more than 20 years.000 hours per year. Department of Energy For additional information or resources on motor and motor-driven system efficiency improvement measures. Depending on the situation. With a magnetically coupled ASD. ASD installations remain low (7%–13%). electronic ASD and motor combinations have replaced constant speed motors in virtually every type of industrial plant. an estimated 15% to 20% of industrial plants use medium voltage (>600 to 6600 volts) to supply power to motors rated as low as 250 hp. • Consider magnetically coupled ASDs for intermediate voltage motors. Market assessment studies indicate that in light and medium industry 26% of motors exhibit fluctuating loads. • Determine the load profile for systems that are in use for more than 2. when sensitive equipment cannot tolerate harmonic currents. The strength of the magnetic field is controlled by varying the width of an adjustable air gap or by varying the amount of current applied to an electromagnet. 22% of these are in process industries and 35% are in other heavy industries. they are not suited for all applications. Energy savings of 50% or more may be available when fixed speed systems are modified to allow the motor speed to match variable load requirements of a centrifugal fan or pump. other factors that can discourage electronic ASD use include: • Creation of harmonics (requiring installation of line reactors or harmonic filters) • Voltage spikes (leading to early motor failure) • Motor bearing failures due to currents induced in the motor's rotor that flow to ground through the bearing • Nuisance tripping • Limitations on the distance that ASDs may be installed from the motor. Magnetically Coupled ASDs In contrast to an electronic ASD. Semiconductors for medium voltage motor applications are particularly expensive. Because the load and motor shafts are not directly coupled in magnetically coupled ASDs. Because of their energy efficiency and control capabilities. For example. • Determine the energy savings and cost effectiveness of installing an electronic ASD or magnetically coupled ASD motor controller.1 Loads that vary over time by 30% of full load offer good opportunities for cost effective adjustable speed drive (ASD) retrofits. or where maintenance requirements are high due to load vibrations being transferred to the motor bearings. application guides.nema.
3 Magnetically coupled ASDs do not have to be housed in a controlled environment. No. avoidance of additional motor heating and the need for motor de-rating. "Product Testing: MagnaDrive. Usk. 1998.pdf Dan Greenberg. November. Disadvantages of magnetically coupled ASDs include space and weight constraints. 2000. www. "Case Study: Ponderay Newsprint. "Adjustable-Speed Drive Case Studies. December. They allow for multiple motor starts with no "cool-off period" and are desirable where harmonic distortion cannot be tolerated or where poor power quality would result in excessive nuisance trips.S." Prepared for the Northwest Energy Efficiency Alliance." ER-03-18. Oregon State University. 2002.org/resources/reports/00-048. Northwest Energy Efficiency Alliance.4 References 1. This project resulted in annual energy savings of 633..nwalliance. prepared for the U. Inc. "Market Progress Evaluation Report: MagnaDrive. Load seizure protection is also inherent with this design. United States Industrial Motor Systems Market Opportunities Assessment. 1994. Because magnetic coupled ASDs operate independent of motor power supply voltage. Savings decrease as the turndown increases. They are also maintenance-intensive and require repair by technicians with specialized training. they are often cost-effective in applications with medium voltage power supplies. March. Washington" 2000.pdf 4. www. 2003. 2. Long-term maintenance costs decreased as pump cavitation was eliminated and vibration was dramatically reduced. 1.000 kWh. May. Quantec. they capture only about 60% of the energy savings obtainable with conventional electronic ASDs. Report E02-099. Some are not compatible with vertical shaft motors or belt-driven loads. Other advantages include: compatibility with existing standard efficiency motors. Platts Research and Consulting." prepared for the Wisconsin Center for Demand-Side Management. 2. Xenergy. Report No.nwalliance. Field Testing the MagnaDrive Coupling Speed Control Technology on Northwest Industrial Applications. and accommodation of shaft thermal expansion. ADM Associates. "Magnetically Coupled Adjustable-Speed Drives: Going Where No VFD Has Gone Before. 3. DOE/GO-102008-2619 • June 2008 • Motor Systems Tip Sheet #13 94 Improving Motor and Drive System Performance: A Sourcebook for Industry . Motor Systems Resource Facility.6. Department of Energy's Office of Industrial Technologies." prepared for the Northwest Energy Efficiency Alliance.Appendix B: Tip Sheet Number 13 pass flow control valve. However.org/research/ documents/MagnaDriveCS_Pnderay2.. Inc. Magnetically coupled ASDs offer some operating advantages that are desirable for niche applications by providing speed control that can be up to 30% more efficient than damper fan control and 44% more efficient than throttled pump control.
visit the BestPractices Web site at www. application guides. Figure 1. Suggested Actions • Obtain information from drive and motor manufacturers about inverter rise times and cable length effects.org for information on motor standards. These effects can combine to damage a motor's insulation and severely shorten a motor's useful operating life. premature failures of motor insulation systems began to occur with the introduction of fast-switching pulse-width modulated (PWM) drives. • The potential for damaging reflected waves is especially high when multiple motors are run from a single ASD. or contact the EERE Information Center at (877) 337-3463. quantified in units of volts per microsecond). National Electrical Manufacturers Association (NEMA) Visit the NEMA Web site at www. eere. Improved insulation systems do not degrade as readily when subjected to transient voltage spikes. and use this information to evaluate the ability of existing motors to withstand drive-induced voltage stresses. resulting in premature failure of the motor. inverter-grade magnet wire to minimize adverse effects of ASD-produced waveforms." However. Steep-fronted waves with large dv/dt or very fast rise times lead to voltage overshoots and other power supply problems. magnetic noise.energy. When the motor impedance is larger than the conductor cable impedance. and a lower heat rise design results in improved resistance to voltage stresses. A greater thickness or build-up of premium varnish (through multiple dips and bakes) minimizes the potential for internal voids. These voltage spikes can rapidly damage a motor's insulation system. Department of Energy For additional information or resources on motor and motor-driven system efficiency improvement measures. PWM pulse with reflected voltage or ringing Inverter-Duty Motor Designs Solutions used to prevent motor failures due to voltage spikes include the use of power conditioning equipment (filters. creating a standing wave (see Figure 1). • Damaging reflected waves are generally not a problem when the distance between the motor and the drive is less than 15 feet. load reactors. Voltage spikes have been reported with peak values as high as 2150 volts in a 460 V system operating at 10% over-voltage. High voltage spikes can lead to insulation breakdown. and the creation of shaft currents. inadequate ventilation at lower speeds.gov/industry/bestpractices. Some drive installers also specify oversized motors or high-temperatureresistant Class H insulation. and isolation transformers) and placing restrictions on the distance or lead length between the drive and the motor. Inverter-duty motors are wound with voltage spike-resistant.Appendix B: Tip Sheet Number 14 When Should Inverter-Duty Motors Be Specified? Electronic adjustable speed drives (ASDs) used to be marketed as "usable with any standard motor. the voltage wave form will reflect at the motor terminals. The switching rates of modern power semiconductors can lead to voltage overshoots.S. Effects of ASDs on Induction Motors The non-sinusoidal variable frequency output of PWM drives results in increased motor losses. with subsequent over-current trips by the drive sensor. Quality manufacturing also Resources U. • Voltage overshoots are more likely to occur with smaller motors and drives with faster rise times.nema. Improving Motor and Drive System Performance: A Sourcebook for Industry 95 . resulting in phase-to-phase or turn-to-turn short circuits. increased dielectric stresses on motor windings. Longer motor cables favor the formation of higher amplitude standing waves. High switching rates of modern power semiconductors lead to rapid changes in voltage in relatively short periods of time (dv/dt. and technical papers.
The CIV is a measure of the ability of the motor's windings to withstand voltage stresses and is the voltage at which partial discharges begin to occur. Above the 500 frame size. Many manufacturers offer "inverter-friendly" insulation in their NEMA Premium® motors. The National Electrical Manufacturers Association (NEMA) specifies that insulation systems for low voltage (<= 600 V) inverter-duty motors be designed to withstand an upper limit of 3. voltage spikes produced by inverters on 208 V or 230 V systems are unlikely to cause insulation damage at any cable length or drive carrier frequency.426 peak volts at the motor terminals for a 460 V rated motor. or other voltage conditioning equipment may be required. Larger inverter-duty motors often have a constant speed auxiliary blower to provide adequate cooling at low motor operating speeds. Contact the motor manufacturer for guidance relating to motor/drive compatibility when peak voltages or rise times are expected to exceed these limits. When operated under usual service conditions. ensure that it is designed and manufactured to meet the most current specifications defined by NEMA MG 1 Section IV. and be equipped with a shaft grounding brush with a ground strap from the motor to the drive case." Part 31 "Definite-Purpose Inverter-Fed Polyphase Motors. These inverter-ready motors are suitable for variable torque loads over a wide speed range.1 microsecond. Thus. • When an inverter-duty motor is required. This is equivalent to an upper limit of 1. Motor Selection Guidelines • NEMA MG 1-2006 Part 30 provides performance standards for general-purpose motors used with ASDs. no significant reduction in service life should occur if the peak voltage at the motor terminals is limited to 1000 V and rise times equal or exceed 2 microseconds. chokes. inverter-duty motors should have both bearings insulated." DOE/GO-102008-2620 • June 2008 • Motor Systems Tip Sheet #14 96 Improving Motor and Drive System Performance: A Sourcebook for Industry . Rise times must equal or exceed 0. "Performance Standards Applying to All Machines. • Specify inverter-duty motors when operating at extremely low speeds or when operation over base speed is required. A definite-purpose inverter-duty motor and/or filters. The insulation system on a 208/230 volt motor is identical to that of a 460 V motor.1 times the motor's rated line-to-line voltage.Appendix B: Tip Sheet Number 14 affects the corona inception voltage (CIV) of a motor.
Resources U. As shown in Figure 2. and use an inverter to simulate an adjustable frequency and variable voltage AC output. To minimize switching losses and approximate sine waves.S. and technical papers. In Figure 2. National Electrical Manufacturers Association (NEMA) Visit the NEMA Web site at www.nema. Different types of transistors used in drives have different rise times.Appendix B: Tip Sheet Number 15 Minimize Adverse Motor and Adjustable Speed Drive Interactions Electronic adjustable speed drives (ASDs) are an extremely efficient and valuable asset to motor systems. there is a brief rise time.energy. but have very high losses when they create wave shapes other than square waves. the voltage increase is plotted against rise time in microseconds. Electronic Adjustable Speed Drive Characteristics All electronic adjustable speed drives rectify the 60 Hz fixed voltage alternating current (AC) to direct current (DC). consider locating the drive close to the motor.eere. or contact the EERE Information Center at (877) 337-3463. On new installations. ASDs can produce voltage overshoots or spikes with the increase over the normal peak voltage dependent upon both cable length and carrier frequency. application guides. Modern IGBT switches operate well down toward the left side of the graph so cable lengths of 50 feet or more almost always need mitigation. They allow precise process control and provide energy savings within systems that do not need to continuously operate at full output. ensure that no harm comes to motors by minimizing the cable length from the ASD to the motor." create the AC voltage output. usually between 2 carrier waves kHz and 20 kHz. The pulses do not turn on instantaneously. creating square waves of much higher frequency than the Figure 1. Sine wave overlaid on square fundamental. higher carrier frequencies and faster rise time transistors on PWM ASDs can produce voltage spikes or overshoots that can stress motor windings and bearings. visit the BestPractices Web site at www.gov/industry/ bestpractices. Improving Motor and Drive System Performance: A Sourcebook for Industry 97 . ASDs operate these switches full-on or full-off. Each on-portion of the carrier wave is called a pulse and the duration of on-time of each pulse is called the pulse width. Voltage spikes originate with fast rise time.org for information on motor standards. Transistors. and carrier frequencies above 5 kHz are likely to cause bearing damage unless protective measures are taken. These problems can be eliminated through proper design and equipment selection. Design Considerations Several design considerations should be taken into account when purchasing an ASD or fixing problems with an existing one. However. Eliminate problems of current flow across the rolling elements of the motor's bearings by isolating both bearings or using a shaft-grounding brush. The rise time is a characteristic of the power transistor switches and can be provided by the drive supplier. This is called a carrier wave (see Figure 1). The most common ASD design sold today is the pulse-width modulated (PWM) ASD with a fast rise-time insulated gate bipolar transistor (IGBT) to reduce switching losses and noise levels. Department of Energy For additional information or resources on motor and motor-driven system efficiency improvement measures. Suggested Actions To best avoid or mitigate voltage overshoots. consider installing filtering devices such as: • line inductors at the drive end of the cable • harmonic suppression filters at the motor end of the cable. or electronic "switches. Where this is not possible. Rise time is the time required for the voltage to increase from 10% to 90% of its steady state value.
80 1.5 2. Causes include common mode voltage problems and/or line voltage unbalance on the ASD input.0 4.60 1.Appendix B: Tip Sheet Number 15 Increase Over Normal Peak Voltage 2.0 3.5 3. usually within the first couple of turns.5 Figure 2.00 0. Eliminate these problems by isolating both bearings or using a shaft grounding brush.0 Rise Time (Ms) 0.00 1.5 5. Existing general purpose low-voltage motors may work fine with PWM ASDs if peak voltages due to ringing are held below 1000 volts. There are two commonly used filter arrangements—line inductors (sometimes called load reactors). which are placed at the motor end of the cable.40 1. With short cables. can cause bearing failure due to rapid voltage changes and a high frequency voltage potential on the shaft causing current flow across the rolling elements of the motor's bearings.5 4. If a short cable run is not possible. and harmonic suppression filters. This produces electrical resonance or "ringing" characterized by an oscillating voltage overshoot.1 500' Cable 200' Cable 100' Cable IGBT 50' Cable 1. which should be placed at the drive end of the cable. electrical stresses can cause a turn-to-turn short within a motor coil group. The fast rise time pulses from a PWM ASD can also create a potentially harmful current flow in bearings even when over-voltage is not significant. so keeping cables short is still the best alternative.20 1. Voltage overshoot is best avoided by locating the drive close to the motor. Sometimes ASD manufacturers provide a filter device along with the drive or even in the drive cabinet. DOE/GO-102008-2621 • June 2008 • Motor Systems Tip Sheet 15 98 Improving Motor and Drive System Performance: A Sourcebook for Industry . Effect of cable length on voltage increase Longer cables reflect the voltage rise so that the reflections reinforce the original pulse rise.0 1. resulting from irregular current waveforms and ground-mode currents. rapid rise time is not a problem. If high frequency voltage overshoots exceed 1000 volts. There are some losses associated with the filters. Capacitive coupling. Problems can also occur in driven-load bearings if insulated couplings are not used. a filtering device must be used.0 2.
general purpose motors of NEMA design "B" 201 to 500 horsepower should meet energy-efficient levels specified in NEMA Standards Publication MG-1 (2006). The Act applies to general purpose. The subject motors are designed to operate on 230/460 volts and 60 Hertz and have open and closed enclosures. Improving Motor and Drive System Performance: A Sourcebook for Industry 99 . Table 12-11). single-speed.e. integral-horsepower induction motors not currently covered under federal law. and 2 pole (3600 RPM) open and enclosed motors rated 1 through 200 horsepower. 4 pole (1800 RPM). Efficiency standards should be enacted for seven types of low voltage polyphase. those designed for use under unusual conditions or for use on a particular type of application which cannot be used in most general applications) or special purpose motors (i. Specifically. This level of efficiency is already required for new motors acquired for federal facilities by the purchasing guidelinesof the Federal Energy Management Program. Table 12-11. 3. the Energy Policy Act (EPAct) of 1992 required most general-purpose polyphase squirrel-cage induction motors manufactured for sale in the United States rated 1 through 200 horsepower to meet minimum efficiency standards. In addition to the standards below.. continuous rated.Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Starting in October 1997.e. 2. Table 12-12. the American Council for an Energy-Efficient Economy (ACEEE) and the National Electrical Manufacturers Association (NEMA) have agreed to a new set of proposed energy efficiency standards for industrial electric motors. ACEEE and NEMA have submitted letters containing these recommendations to the House Energy and Commerce Committee and the Senate Energy and Natural Resources Committee for their consideration in energy legislation now under development. Specifically: 1. The Act applies to 6 pole (1200 RPM). with the exception of "fire pumps" that will remain at the current Table 12-11 level as specified in EPAct 1992. seven motor modifications excluded from EPAct 1992 standards of electric motors sized from 1 to 200 horsepower should meet the efficiency standards currently applicable to general purpose motors of the same size (i. The agreement recommends that minimum energy efficiency standards be established or increased for three broad categories of electric motors by a date that is 36 months from the date of enactment.e. polyphase squirrel-cage induction motors of National Electrical Manufacturers Association (NEMA) Designs A and B.. foot-mounted. The Act does not apply to definite-purpose motors (i. The minimum efficiency standards of general purpose. those designed for a particular application with special operating characteristics or mechanical construction). T-Frame. integral-horsepower induction motors currently covered by federal efficiency standards should be increased to the "NEMA Premium" efficiency level specified in NEMA Standards Publication MG-1 (2006). In addition.. efficiency levels specified in NEMA Standards Publication MG-1 [2006].
0 1800 82.5 84.0 91.5 87.2 91.0 84.1 94.5 89.0 91.5 88.2 90.1 94.0 85.0 85.5 82.1 95.2 91.7 92.1 93.5 95.6 93.4 93.0 93. respectively.5 1200 80.0 93.6 94.6 94.5 87.5 89.3 93.0 93.0 93.7 91.2 90.0 91.5 87. NEMA Design A or B.5 94.4 92.5 91.5 89.7 93.5 2 3 5 7.5 87.5 89.0 91.5 90.0 92.6.5 94.6 93.0 3600 -82.0 93.7 92.0 93.0 86.1 94.5 89.0 93. 94.5 89.6 93.6 94.5 88.5 89.5 95.Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Electric Motor Efficiency Levels Prescribed in the Energy Policy Act of 1992 Nominal Full-Load Efficiency Open Motors Speed (RPM) Enclosed Motors Motor Horsepower 1 1.6 94. The NEMA Premium efficiency electric motor program scope is single-speed.0 91.5 86.5 10 15 20 25 30 40 50 60 75 100 125 150 200 1200 80. continuous rated. polyphase.0 The NEMA Motor and Generator Section established a NEMA Premium® energy efficiency motors program to provide highly energy efficient products that meet the needs and applications of users and original equipment manufacturers based on a consensus definition of "premium efficiency" and use of the NEMA Premium logo for premium products. and 6 pole.0 84.5 95. 100 Improving Motor and Drive System Performance: A Sourcebook for Industry .2003. squirrel cage induction motors.0 95.5 94.5 90.0 93.2 91.6 93.5 1800 82.4 93.0 91. in Tables 12-12 and 12-13.0 93.5 90.5 90. NEMA Premium energy efficiency motors are more efficient than equivalent rated motors that meet the EPAct efficiency levels.5 84.0 94. Products must meet or exceed the nominal energy efficiency levels presented below.2 91.0 3600 75.0 84.0 93.0 95.4 93.5 87.5 91. 4.0 91.7 92. The NEMA Premium efficiency levels are contained in NEMA Standards Publication MG 1.5 87.7 92.6 94. 1-500 horsepower.4 93. 2.2 90.0 93.5 87.5 86.4 93.0 84.5 88.0 85.0 95.0 91.1 94.0 85.5 84.5 88.5 84.0 87.
5 86.6 93.0 91.0 85.1 94.5 87.5 10 15 20 25 30 40 50 60 75 100 125 150 200 250 300 350 400 450 500 EPAct* 80.0 95.5 82.2 82.6 94.6 94.4 93.4 93.0 85.0 95.4 95.0 93.0 93.5 88.0 85.0 93.1 94.8 95.0 95.4 95.0 93.5 91.5 85.5 94.5 2 3 5 7.5 88.1 95.5 87.7 93.2 96.7 92.8 95.5 89.5 89.5 88.6 93.5 89.0 95.4 95.1 94.0 91.2 91.2 N/A 82.7 92.4 93.5 91.8 Improving Motor and Drive System Performance: A Sourcebook for Industry 101 .5 90.0 93.0 91.6 94.5 94.0 93.5 90.8 96.2 91.0 91.4 95.4 95.8 95.8 96.5 86.5 84.0 85.5 89.0 91.0 93.7 92.4 95.0 93.8 95.1 94.2 91.5 90.7 92.5 77.0 95.7 91.0 95.Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Nominal Efficiencies for NEMA Premium® Induction Motors Rated 600 Volts or Less (Random Wound) Open Drip-Proof 1200 RPM (6-pole) 1800 RPM (4-pole) EPAct* 3600 RPM (2-pole) EPAct* hp 1 1.2 96.2 91.1 94.5 88.5 95.0 93.4 95.0 91.7 92.5 87.0 86.0 84.0 91.6 94.6 93.0 93.6 94.1 94.5 86.5 90.6 93.5 88.0 95.6 94.5 89.0 84.5 86.5 89.4 95.4 93.2 90.7 91.5 86.4 95.0 84.8 95.5 84.8 95.4 93.1 94.8 95.1 94.5 95.5 95.1 94.0 93.0 84.5 87.
8 95.1 94.0 93.0 85.5 91.2 96.7 88.5 94.5 89.0 91.0 93.5 91.2 90.0 91.5 95.8 96.4 93.4 93.0 82.4 93.0 95.0 95.5 85.5 82.7 92.5 84.1 94.5 87.2 89.1 95.5 95.7 93.5 87.4 95.0 1.7 92.5 10 15 20 25 30 40 50 60 75 100 125 150 200 250 300 350 400 450 500 89.0 95.5 84.5 84.2 96.1 94.6 94.7 91.5 95.0 93.0 86.0 89.0 91.8 102 Improving Motor and Drive System Performance: A Sourcebook for Industry .5 94.Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Efficiencies for NEMA Premium® Induction Motors Rated 600 Volts or Less (Random Wound) Totally Enclosed Fan-Cooled 1200 RPM (6-pole) 1800 RPM (4-pole) 3600 RPM (2-pole) hp EPAct* EPAct* EPAct* 1 80.0 93.5 89.5 85.0 91.5 87.0 93.8 95.5 82.0 86.0 91.0 93.7 92.8 95.0 93.8 95.5 88.0 94.2 90.2 96.5 87.8 95.5 88.5 85.8 95.5 7.5 75.0 91.6 94.0 93.8 89.6 93.5 3 87.6 93.0 95.5 91.5 90.5 89.8 95.1 94.5 84.7 91.0 91.5 95.8 95.1 95.4 95.2 96.2 96.7 91.5 90.0 90.2 91.4 95.0 95.7 93.8 95.2 91.8 95.6 94.5 77.0 92.6 94.8 95.0 95.8 95.2 96.0 91.5 89.2 91.5 5 87.0 93.5 94.5 86.4 95.6 94.1 94.4 92.4 93.0 2 86.0 95.6 93.5 89.5 89.
0 Improving Motor and Drive System Performance: A Sourcebook for Industry 103 .0 95.5 Nominal Efficiencies for NEMA Premium® Induction Motors Rated Medium Volts — 5kV or Less (Form Wound) Totally Enclosed Fan-Cooled hp 6-pole 4-pole 2-pole 250-500 95.0 95.0 94.Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels Nominal Efficiencies for NEMA Premium® Induction Motors Rated Medium Volts — 5kV or Less (Form Wound) Open Drip-Proof hp 6-pole 4-pole 2-pole 250-500 95.0 95.
Appendix C: EPAct Efficiency Levels and Premium Efficiency Levels 104 Improving Motor and Drive System Performance: A Sourcebook for Industry .
Specific capability pertains mainly to the ability to do certain repairs that may not routinely be part of all motor rebuilds. list maximum capability of each) What is the largest motor for which the service center is fully equipped to rewind and test in-house? Rewind Capability Weight Length Diameter Horsepower Voltage ______ ______ ______ ______ ______ Testing ______ ______ ______ ______ ______ Record Keeping How long does service center keep records on each repaired motor?_____ (Obtain sample copy of filled-in job card or computer printout. Capacity pertains mainly to the size of motors that can be accommodated. These respectively assess capacity capability and specific capability.) Specific Repair Capability Check services offered: Random wound polyphase ac motor repair Form wound polyphase ac motor repair dc motor repair Single-phase motor repair Machine shop capability Improving Motor and Drive System Performance: A Sourcebook for Industry 105 . Limitations of these capabilities do not necessarily indicate efficiency or quality problems for repair jobs not requiring those capabilities.Appendix D: Motor Repair Service Center Checklist Appendix D: Motor Repair Service Center Checklist The first two parts of the checklist assess service center capability. Motor Repair Service Center Checklist Capacity Capability (for multiple devices.
$300 or more per employee desirable. workshops or seminars one or more days in length q Subsidized evening or part-time classes at college or trade school q Attendance at trade conferences or conventions q Other How much training or professional development do service center employees receive? _____ Percentage of employees receiving offsite training annually _____ Average days off-site per year per employee receiving offsite training _____ Annual training expenditure per employee receiving off-site training Desirable to have 20% or more with more than 4 years experience. Availability from in-house stock. or explanation of stranding to replicate original circular mills can all be acceptable. A training program culture involving formal internal or off-site training is desirable. Service center should have policies and technical guides to ensure original or better motor performance. 106 Improving Motor and Drive System Performance: A Sourcebook for Industry . At least 10% should receive annual off-site training. On random wound motors. Mechanical pulling at reduced temperature can flare laminations and increase stray loads. However.) q Chemical Stripping q Mechanical Pulling at temperature under 400°F q Other How does the service center ensure that the correct wire sizes and types are available for rewinding? What does the service center do if exact wire size is not in inventory? Burnout most common. Evidence of quick availability of all round wire sizes is important. explain circumstances. typical temperature ____F (If sometimes higher. Participation in job-related trainings is commendable. EASA offers many training courses and holds an annual convention. Monitoring for continuous improvement such as tracking scrap rate and completed motor test results contributes to a more competent and careful staff. It is best to replicate the original winding pattern.8 years _____ Less than 4 years What sort of supplemental training or professional development activity is offered to service center employees? (Obtain evidence if possible. is winding pattern ever revised for reasons other than customer ordered redesign? q Yes q No If yes. One or more days off-site desirable. it can be difficult to replicate some stator windings.) q In-house training or structured mentoring (Describe) q Off-site short courses. It is rare in United States. Best if core kept under 680°F. quick pipeline to supplier. what changes? q Lap to concentric q Concentric to lap q Other (explain) How many employees have the following years of experience? _____ More than 8 years _____ 4 .Appendix D: Motor Repair Service Center Checklist What primary methods of winding removal are used? q Controlled Burn-out. Wire should be inverter grade if inverter powered motors will be rewound.
Noting watts per pound and comparison to standard or before and after testing is commendable. It should also ensure that vibration and bearing temperature are not abnormally high. Test should verify rotation at nameplate speed in the correct direction and check for abnormal sounds. Equipment Calibration Item Normal interval Ammeters Wattmeters Core Loss Tester Burnout oven temp. This should be mandatory for operational motors. although very large service centers may have in-house capability to provide similar benefits. max kVA____ How often do they use it? ____ Are test records kept on permanent file? q Yes q No How are results used? Check all that apply: q Check for hot spots to be repaired q Note watts per pound and compare to a standard q Document impact of burnout/rewind to customer Is no-load testing done on all motors? q Yes q No Certainly check for hot spots. May be done in-house to certified clean dry standard blocks. If not. 6 months better.Appendix D: Motor Repair Service Center Checklist In what trade or professional associations does service center have membership? ___________ EASA membership is a definite plus. Using a tester on all motors is evidence that service center is conscientious about core losses. What temperature classes of insulation are stocked and used? ____ What (if any) kind of core loss testing does service center use? q Loop or ring test. F or H desirable. Micrometers & Calipers _____________ _____________ _____________ _____________ _____________ Date last calibrated or certified _____________ _____________ _____________ _____________ _____________ Annual Annual Annual Annual Annual OK. determine why not. max kVA____ q Commercial tester. Annual Annual Megohmmeter Voltmeter _____________ _____________ _____________ _____________ Improving Motor and Drive System Performance: A Sourcebook for Industry 107 .
amps.________ spec. to ensure no degradation from aging. Annual Annual to a certified standard resistance. 108 Improving Motor and Drive System Performance: A Sourcebook for Industry . Explain lower percentages.________ spec.________ Vibration Analysis Equipment Brand________ Model________ High Potential Tester (HiPot) Brand________ Model________ ac rating_______ dc rating_______ Annual Annual on volts.Appendix D: Motor Repair Service Center Checklist Surge Comparison Tester Brand _____ Model _____ ac Power Supply Voltage Range_____ kVA_____ Continuously variable voltage? _____ dc Power Supply Voltage Range _____ kW______ Continuously variable voltage? ______ What % of motor rewind jobs get core loss testing both before and after rewinding? _____% Varnish and resins spec. amps. Sample should have been taken and analyzed every 2-3 months.________ spec. Annual on volts. or watts unless these are monitored by the portable instruments above.________ spec. Manufacturer's material specs should be on file. and power factor or watts unless these are monitored by the portable instruments above. Ideally 100%.
The Bonneville Power printing is available for download at www. Reference: Quality Electric Motor Repair: A Guidebook for Electric Utilities. Quality Management and Quality Assurance. Original text authored by Johnny Douglass. 2004 q IEEE Std 432 Insulation Maintenance for Rotating Electric Machinery (5 HP to Less Than 10. 1995 q ISO 9001. 2001 (2) q EASA Warranty. 1995 and Electric Power Research Institute as EPRI TR-105730s. 2003 (1) q EASA Technical Manual. Nov.000 HP). 2003 q ISO 10816-1 Mechanical vibration – Evaluation of machine vibration by measurements on non-rotating parts – Part 1: General guidelines. 1996 q ISO 1940-1 Mechanical Vibration – Balance Quality Requirements of Rigid Rotors Part 1. The dates shown below are current as of this printing: q NEMA MG1-2003 Motors and Generators q ABMA Std 7 Shaft & Housing Fits for Metric Radial Ball & Roller Bearings. October 1999 (2) q ANSI/EASA AR100-2001 Recommended Practice for the Repair of Rotating Electrical Apparatus (1) Not applicable for service centers which do not serve this market (2) Non-EASA members should produce equivalent documents or file material.gov. 2000 q IEEE Std 43 Testing Insulation Resistance of Rotating Machines. June 1996. 2002 (2) q EASA Winding DATA on CD.Appendix D: Motor Repair Service Center Checklist Documents and Record Keeping Check whether current copies of all the following documents are present. prepared by Washington State Energy Office. Cylindrical Roller and Spherical Roller Types Metric Design. Washington State University Energy Program WSUEEP99004 Improving Motor and Drive System Performance: A Sourcebook for Industry 109 .osti. 1995 q ABMA Std 20 Radial Bearings of Ball. 2000 q IEEE Std 112 Test Procedures for Polyphase Induction Motors and Generators. 1992 q IEEE Std 1068 Recommended Practice for the Repair and Rewinding of Motors for the Petroleum & Chemical Industry. 1996 (2) q UL 674 Electric Motors and Generators for Use in Division 1 Hazardous (Classified) Locations. This document. was originally co-sponsored and printed by Bonneville Power Administration as DOE/BP-2747.
Appendix D: Motor Repair Service Center Checklist 110 Improving Motor and Drive System Performance: A Sourcebook for Industry .
O.Appendix E: Guidelines for Comments Appendix E: Guidelines for Comments Comments that can correct and improve this sourcebook are appreciated. Box 43165 Olympia. Improving Motor and Drive Performance: A Sourcebook for Industry Comment Form Page Number(s) Comments From: Contact: EERE Information Center P. WA 98504-3165 Phone: 877-EERE-INF (887-337-3463) Fax: 360-236-2023 Improving Motor and Drive System Performance: A Sourcebook for Industry 111 . Please copy this page and provide suggestions to the address listed below.
Department of Energy Energy Efficiency and Renewable Energy Washington. community. and university partners. renewable energy will mean a stronger economy.S. industry. Industrial Technologies Program U. and greater energy independence for America. Working with a wide array of state.About the Office of Energy Efficiency and Renewable Energy A Strong Energy Portfolio for a Strong America Energy efficiency and clean. DC 20585-0121 Improving Motor and Drive System Performance: A Sourcebook for Industry One in a series of industrial energy efficiency sourcebooks To order additional copies of this sourcebook. the U. please contact: EERE Information Center 1-877-EERE-INF (1-877-337-3463) www.S.gov September 2008 DOE/GO-102008-2317 .energy. a cleaner environment. Department of Energy's Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies.eere.
This action might not be possible to undo. Are you sure you want to continue?
We've moved you to where you read on your other device.
Get the full title to continue listening from where you left off, or restart the preview.