magnetic field in a dc generator is produced by
excitation
11448238
the shaft, such as the thyristor rectifiers and chopper interfaces . Excitation (magnetic) An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation,
Excitation (magnetic)
10997939
Ward Leonard drive unit consists of a motor and generator with shafts coupled together. The prime mover, which turns at a constant speed, may be AC or DC powered. The generator is a DC generator, with field windings and armature windings. The input to the amplifier is applied to the field windings, and the higher power output comes from the armature windings. (See Excitation (magnetic)#Amplifier principle for how a generator can act as an amplifier.) The amplifier output is usually connected to a second motor, which moves the load, such as an elevator. With this arrangement, small changes in current
Ward Leonard control
13243570
magnets. Other types of generator use electromagnets to produce a magnetic field in a rotor winding. The direct current in the rotor field winding is fed through a slip-ring assembly or provided by a brushless exciter on the same shaft. Permanent magnet generators (PMGs) or alternators (PMAs) do not require a DC supply for the excitation circuit, nor do they have slip rings and contact brushes. A key disadvantage in PMAs or PMGs is that the air gap flux is not controllable, so the voltage of the machine cannot be easily regulated. A persistent magnetic field imposes safety issues during
Permanent magnet synchronous generator
11448230
Excitation (magnetic) An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation, but at the expense of a flow of electric current. Hybrid
Excitation (magnetic)
11448238
the shaft, such as the thyristor rectifiers and chopper interfaces . Excitation (magnetic) An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation,
Excitation (magnetic)
12108523
is called a compound-wound dc generator. Shunt generator A shunt generator is a type of direct current electric generator in which field winding and armature winding are connected in parallel, and in which the armature supplies both the load current and the field current. A direct current (DC) generator, not using a permanent magnet, requires a DC field current for excitation. The field may be "separately excited" by a source of DC, such as a battery, or "self excited" by being connected to the armature of the generator so that the generator also provides the energy required for the field
Shunt generator
1734338
if it has a commutator. This method of excitation consists of a smaller direct-current (DC) generator fixed on the same shaft with the alternator. The DC generator generates a small amount of electricity just enough to "excite" the field coils of the connected alternator to generate electricity. A variation of this system is a type of alternator which uses direct current from the battery for initial excitation upon start-up, after which the alternator becomes self-excited. This method depends on residual magnetism retained in the iron core to generate weak magnetic field which would allow a weak voltage to be generated.
Alternator
12108520
Shunt generator A shunt generator is a type of direct current electric generator in which field winding and armature winding are connected in parallel, and in which the armature supplies both the load current and the field current. A direct current (DC) generator, not using a permanent magnet, requires a DC field current for excitation. The field may be "separately excited" by a source of DC, such as a battery, or "self excited" by being connected to the armature of the generator so that the generator also provides the energy required for the field current. A shunt field (and any
Shunt generator
9871453
allowing the development of compact, high-power motors without the extra real-estate of field coils and excitation means. But as these high performance permanent magnets become more applied in electric motor or generator systems, other problems are realized (see Permanent magnet synchronous generator). Traditionally, the field has been applied radially—in and away from the rotation axis of the motor. However some designs have the field flowing along the axis of the motor, with the rotor cutting the field lines as it rotates. This allows for much stronger magnetic fields, particularly if halbach arrays are employed. This, in turn, gives power to
Brushed DC electric motor
11448236
small portable generator sets may occasionally need field flashing to restart. The critical field resistance is the maximum field circuit resistance for a given speed with which the shunt generator would excite. The shunt generator will build up voltage only if field circuit resistance is less than critical field resistance. It is a tangent to the open circuit characteristics of the generator at a given speed. Brushless excitation creates the magnetic flux on the rotor of electrical machines without the need of carbon brushes. It is typically used for reducing the regular maintenance costs and to reduce the risk of
Excitation (magnetic)
13243563
Permanent magnet synchronous generator A permanent magnet synchronous generator is a generator where the excitation field is provided by a permanent magnet instead of a coil. The term synchronous refers here to the fact that the rotor and magnetic field rotate with the same speed, because the magnetic field is generated through a shaft mounted permanent magnet mechanism and current is induced into the stationary armature. Synchronous generators are the majority source of commercial electrical energy. They are commonly used to convert the mechanical power output of steam turbines, gas turbines, reciprocating engines and hydro turbines into electrical power for
Permanent magnet synchronous generator
8473229
speed. The motor speed is adjusted by adjusting the output voltage of the generator using a rheostat to adjust the excitation current in the field winding. The motor field current is usually not adjusted, but the motor field is sometimes reduced to increase the speed above the base speed. The prime mover is usually an alternating current (AC) motor, but a DC motor or an engine might be used instead. To provide the DC field excitation power supply, Ward Leonard systems usually include an exciter generator that is driven by the prime mover. Although only technical specialists are likely to
Harry Ward Leonard
13243571
assembly, field service or repair. High performance permanent magnets, themselves, have structural and thermal issues. Torque current MMF vectorially combines with the persistent flux of permanent magnets, which leads to higher air-gap flux density and eventually, core saturation. In this permanent magnet alternators the speed is directly proportional to the output voltage of the alternator. Permanent magnet synchronous generator A permanent magnet synchronous generator is a generator where the excitation field is provided by a permanent magnet instead of a coil. The term synchronous refers here to the fact that the rotor and magnetic field rotate with the same speed,
Permanent magnet synchronous generator
2608650
role of a generator by switching from a supply circuit to a receptor circuit while applying electric current to the field coils that generate the magnetic field (excitation). The amount of resistance applied to the rotating shaft (braking power) equals the rate of electrical power generation plus some efficiency loss. That is in turn proportional to the strength of the magnetic field, controlled by the current in the field coils, and the rate at which the armature and magnetic field rotate against each other, determined by the rotation of the wheels and the ratio of power shaft to wheel rotation.
Dynamic braking
1734337
method of excitation, number of phases, the type of rotation, cooling method, and their application. There are two main ways to produce the magnetic field used in the alternators, by using permanent magnets which create their own persistent magnetic field or by using field coils. The alternators that use permanent magnets are specifically called magnetos. In other alternators, wound field coils form an electromagnet to produce the rotating magnetic field. A device that uses permanent magnets to produce alternating current is called a permanent magnet alternator (PMA). A permanent magnet generator (PMG) may produce either alternating current, or direct current
Alternator
11448231
topologies exists, which encorporate both permanent magnets and field coils in the same configuration. The flexible excitation of a rotating electrical machine is employed by either brushless excitation techniques or by the injection of current by carbon brushes (static excitation). For a machine using field coils, as is the case in most large generators, the field must be established by a current in order for the generator to produce electricity. Although some of the generator's own output can be used to maintain the field once it starts up, an external source of current is needed for starting the generator. In
Excitation (magnetic)
6903116
completed an electric current will be produced. Homopolar generator A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder) with an electrical polarity that depends on the direction of rotation and the orientation of the field. It is also known as a unipolar generator, acyclic generator, disk dynamo, or Faraday disc. The voltage is typically low, on the order of a few volts in the
Homopolar generator
869871
of 1831–1832 by Michael Faraday. The principle, later called Faraday's law, is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux. He also built the first electromagnetic generator, called the Faraday disk; a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. It produced a small DC voltage. This design was inefficient, due to self-cancelling counterflows of current in regions of the disk that were not under the influence of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards
Electric generator
2864229
Engineering. The earliest commercial uses of electricity were electroplating and the telegraph. In the years of 1831–1832, Michael Faraday discovered the operating principle of electromagnetic generators. The principle, later called Faraday's law, is that an electromotive force is generated in an electrical conductor that is subjected to a varying magnetic flux, as for example, a wire moving through a magnetic field. He also built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. It produced a small DC voltage. Around 1832, Hippolyte Pixii improved
Electrification
711671
set of vibrator contacts on the transformer core, operated by its magnetic field, to repeatedly break the DC battery current to create a pulsing AC to power the transformer. Then a second set of rectifier contacts on the vibrator rectified the high AC voltage from the transformer secondary to DC. A "motor-generator set", or the similar "rotary converter", is not strictly a rectifier as it does not actually "rectify" current, but rather "generates" DC from an AC source. In an "M-G set", the shaft of an AC motor is mechanically coupled to that of a DC generator. The DC generator
Rectifier
3381572
of absorption/desorption of hydrogen by the metal, which regulates the pressure in the enclosure. The Penning source is a low gas pressure, cold cathode ion source which utilizes crossed electric and magnetic fields. The ion source anode is at a positive potential, either dc or pulsed, with respect to the source cathode. The ion source voltage is normally between 2 and 7 kilovolts. A magnetic field, oriented parallel to the source axis, is produced by a permanent magnet. A plasma is formed along the axis of the anode which traps electrons which, in turn, ionize gas in the source. The
Neutron generator
11040017
by building up electric charge. Early types were friction machines, later ones were influence machines that worked by electrostatic induction. The Van de Graaff generator is an electrostatic generator still used in research today. "Homopolar machines" are true DC machines where current is supplied to a spinning wheel through brushes. The wheel is inserted in a magnetic field, and torque is created as the current travels from the edge to the centre of the wheel through the magnetic field. For optimized or practical operation of electric machines, today's electric machine systems are complemented with electronic control. Electric machine In electrical
Electric machine
6903102
Homopolar generator A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder) with an electrical polarity that depends on the direction of rotation and the orientation of the field. It is also known as a unipolar generator, acyclic generator, disk dynamo, or Faraday disc. The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large
Homopolar generator
10051856
be able to build up voltage even if the residual field is present. The load acts as an energy sink and continuously drains away the small rotor current produced by the residual field, preventing magnetic field buildup in the field coil. The operating principle of electromagnetic generators was discovered in the years 1831–1832 by Michael Faraday. The principle, later called Faraday's law, is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux. He also built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc rotating
Dynamo
4056458
field coils. The basic construction of the rotary converter consists of a DC generator (dynamo) with a set of slip rings tapped into its rotor windings at evenly spaced intervals. When a dynamo is spun the electric currents in its rotor windings alternate as it rotates in the magnetic field of the stationary field windings. This alternating current is rectified by means of a commutator which allows DC current to be extracted from the rotor. This principle is taken advantage of by energizing the same rotor windings with AC power which causes the machine to act as a synchronous AC
Rotary converter
14151592
It is a Tangent to the Open Circuit Characteristics of the Generator(at a given speed). Critical field resistance Critical field resistance is a term that is associated with a shunt DC generator. In a DC Shunt Generator, the voltage induced across the Armature V is directly proportional to the Flux acting across it, The Flux in a DC Generator is directly proportional to the field current I. By Ohm's Law V = IR . The critical field resistance is defined as the maximum field circuit resistance (for a given speed) with which the shunt generator would excite. The shunt generator
Critical field resistance
14151591
Critical field resistance Critical field resistance is a term that is associated with a shunt DC generator. In a DC Shunt Generator, the voltage induced across the Armature V is directly proportional to the Flux acting across it, The Flux in a DC Generator is directly proportional to the field current I. By Ohm's Law V = IR . The critical field resistance is defined as the maximum field circuit resistance (for a given speed) with which the shunt generator would excite. The shunt generator will build up voltage only if field circuit resistance is less than critical field resistance.
Critical field resistance
3602442
first common electrical accessories. Early systems used 6 volts, but 12 volts became the standard because it provided greater power with less current. The original DC generator was replaced by an alternator controlled by a voltage regulator. Due to mechanical and electrical properties, it is more efficient to first produce alternating current and then immediately convert it to direct current. By regulating the current sent to the alternator's rotor and thus the strength of the magnetic field, a stable voltage can be produced over a wider range of engine speeds. Starting, lighting and ignition systems of most gasoline-powered vehicles remain
Automobile accessory power
11040011
behind the stator coils. The gap between rotor and stator is also made as small as possible. All this is done to minimize magnetic reluctance of the magnetic circuit which the magnetic field created by the rotor coils travels through, something which is important for optimizing these machines. Large brushed machines which are run with DC to the stator windings at synchronous speed are the most common generator in power plants, because they also supply reactive power to the grid, because they can be started by the turbine and because the machine in this system can generate power at constant
Electric machine
1794135
ring. The magnetic field lines are "pinched" closer together, so the (average) magnetic field intensity inside the ring increases by the ratio of the original area to the final area. The simple basic principle of flux compression can be applied in a variety of different ways. Soviet scientists at the VNIIEF in Sarov, pioneers in this domain, conceived of three different types of generators: Such generators can, if necessary, be utilised independently, or even assembled in a chain of successive stages: the energy produced by each generator is transferred to the next, which amplifies the pulse, and so on. For
Explosively pumped flux compression generator
5447043
Armature reaction drop is the effect of a magnetic field on the distribution of the flux under main poles of a generator. Since an armature is wound with coils of wire, a magnetic field is set up in the armature whenever a current flows in the coils. This field is at right angles to the generator field and is called cross magnetization of the armature. The effect of the armature field is to distort the generator field and shift the neutral plane. The neutral plane is the position where the armature windings are moving parallel to the magnetic flux lines,
Armature (electrical)
9811525
to aid stamping conductor slots to specific shapes and sizes. As currents travel through the wire coil a magnetic field is created around the core, which is referred to as field current. The field current strength controls the power level of the magnetic field. Direct current (DC) drives the field current in one direction, and is delivered to the wire coil by a set of brushes and slip rings. Like any magnet, the magnetic field produced has a north and a south pole. The normal clockwise direction of the motor that the rotor is powering can be manipulated by using
Rotor (electric)
872298
The sample's magnetization can be changed by applying a small ac magnetic field (or a rapidly changing dc field), as occurs in capacitor-driven pulsed magnets. These measurements require differentiating between the magnetic field produced by the sample and that from the external applied field. Often a special arrangement of cancellation coils is used. For example, half of the pickup coil is wound in one direction, and the other half in the other direction, and the sample is placed in only one half. The external uniform magnetic field is detected by both halves of the coil, and since they are counter-wound,
Magnetometer
8049605
that creates a circumferential traveling field to which the rotor's magnetic poles rapidly synchronize. Some stepping motors have a similar structure. AC motor An AC motor is an electric motor driven by an alternating current (AC). The AC motor commonly consists of two basic parts, an outside stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft producing a second rotating magnetic field. The rotor magnetic field may be produced by permanent magnets, reluctance saliency, or DC or AC electrical windings. Less common, AC linear motors operate on
AC motor
13252514
ultra-cold neutrons are stored in an electric and magnetic field. An AC magnetic field pulse is then applied to rotate the spins by formula_5. The signal generator used to apply the pulse is then gated off while the neutron spins precess about the magnetic field axis at the precession frequency; after a period of ~100s, another field pulse is applied to rotate the spins by formula_5. If the frequency of the applied signal is exactly equal to the precession frequency, the neutrons will all be synchronised with the signal generator, and they will all end up polarized in the opposite
CryoEDM
12431894
quantity produced by an ideal AC generator built with finely distributed stator and field windings that operate in a uniform magnetic field. Since neither the winding distribution nor the magnetic field are uniform in a working AC machine, voltage waveform distortions are created, and the voltage-time relationship deviates from the pure sine function. The distortion at the point of generation is very small (about 1% to 2%), but nonetheless it exists. Because this is a deviation from a pure sine wave, the deviation is in the form of a periodic function, and by definition, the voltage distortion contains harmonics. When
Harmonics (electrical power)
11040001
field component of an electrical machine. The armature can be on either the rotor or the stator. The magnetic field can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator. Generators are classified into two types, AC generators and DC generators. An AC generator converts mechanical energy into alternating current electricity. Because power transferred into the field circuit is much less than power transferred into the armature circuit, AC generators nearly always have the field winding on the rotor and the armature winding on the stator. AC generators are classified into several types.
Electric machine
13243569
the generator, and formula_10 and formula_11 are the voltage and the current in the load respectively and formula_12 is the angle between them. Here, we can see that the resistance, R, and the reactance, formula_13, play a role in determining the angle formula_14. This information can be used to determine the real and reactive power output from the generator. In this diagram, formula_15 is the terminal voltage. If we ignore the resistance as shown above, we find that the power can be calculated: formula_16 formula_17 In a permanent magnet generator, the magnetic field of the rotor is produced by permanent
Permanent magnet synchronous generator
1794136
example, it is foreseen that the DEMG generator will be supplied by a MK-2 type generator. In the spring of 1952, R.Z. Lyudaev, E.A. Feoktistova, G.A. Tsyrkov, and A.A. Chvileva undertook the first experiment with this type of generator, with the goal of obtaining a very high magnetic field. The MK-1 generator functions as follows: The first experiments were able to attain magnetic fields of millions of gauss (hundreds of teslas), given an initial field of 30 kG (3 T) which is in the free space "air" the same as H = B/μ = (3 V/m) / (4π × 10
Explosively pumped flux compression generator
19282821
first transistor-based audio devices in the 1950s. An important field of invention during this period was the tape recorder. Magnetic tape recording uses an amplified electrical audio signal to generate analogous variations of the magnetic field produced by a tape head, which impresses corresponding variations of magnetization on the moving tape. In playback mode, the signal path is reversed, the tape head acting as a miniature electric generator as the varyingly magnetized tape passes over it. Magnetic tape brought about sweeping changes in both radio and the recording industry. Sound could be recorded, erased and re-recorded on the same tape
Music technology (electric)
1734331
Alternator An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven
Alternator
1794132
magnetic field surrounded by a correspondingly large electric current. The purpose of the flux generator can be either the generation of an extremely strong magnetic field pulse, or an extremely strong electric current pulse; in the latter case the closed conductor is attached to an external electric circuit. This technique has been used to create the most intense manmade magnetic fields on Earth; fields up to about 1000 teslas (about 1000 times the strength of a typical permanent magnet) can be created for a few microseconds. An external magnetic field (blue lines) threads a closed ring made of a perfect
Explosively pumped flux compression generator
3381573
ions are extracted through the exit cathode. Under normal operation, the ion species produced by the Penning source are over 90% molecular ions. This disadvantage is however compensated for by the other advantages of the system. One of the cathodes is a cup made of soft iron, enclosing most of the discharge space. The bottom of the cup has a hole through which most of the generated ions are ejected by the magnetic field into the acceleration space. The soft iron shields the acceleration space from the magnetic field, to prevent a breakdown. Ions emerging from the exit cathode are
Neutron generator
12352341
Magnetic nozzles are used in electric propulsion to enhance the thrust produced by a stream of plasma. In magnetic nozzles, ionization instability is caused by ionization downstream of the nozzle, causing electrons born there to migrate upstream, counter to the direction of flow. This causes the plasma flow rate and energy through the nozzle to oscillate. An MHD generator is an apparatus through which hot gas flows, in which the gas is ionized and a magnetic field is used to extract flow energy as electrical energy. MHD generators were studied mostly in the 1960s and 1970s to increase the efficiency
Ionization instability
869882
remanent magnetism present in the iron core provides a magnetic field to get it started, generating a small current in the armature. This flows through the field coils, creating a larger magnetic field which generates a larger armature current. This "bootstrap" process continues until the magnetic field in the core levels off due to saturation and the generator reaches a steady state power output. Very large power station generators often utilize a separate smaller generator to excite the field coils of the larger. In the event of a severe widespread power outage where islanding of power stations has occurred, the
Electric generator
8049552
AC motor An AC motor is an electric motor driven by an alternating current (AC). The AC motor commonly consists of two basic parts, an outside stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft producing a second rotating magnetic field. The rotor magnetic field may be produced by permanent magnets, reluctance saliency, or DC or AC electrical windings. Less common, AC linear motors operate on similar principles as rotating motors but have their stationary and moving parts arranged in a straight line configuration, producing linear motion
AC motor
1794137
V/Am) = (approximately 2.4 MA/m). Helical generators were principally conceived to deliver an intense current to a load situated at a safe distance. They are frequently used as the first stage of a multi-stage generator, with the exit current used to generate a very intense magnetic field in a second generator. The MK-2 generators function as follows: The MK-2 generator is particularly interesting for the production of intense currents, up to 10 A (100 MA), as well as a very high energy magnetic field, as up to 20% of the explosive energy can be converted to magnetic energy, and the
Explosively pumped flux compression generator
869883
stations may need to perform a black start to excite the fields of their largest generators, in order to restore customer power service. An important class of direct-current generators are the dynamos - these are electrical machines with commutators to produce unidrectional (DC) current, and are self excited - their field electromagnets are powered by the machine's own output. Other types of DC generator use a separate source of direct current to energize their field magnets. A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static
Electric generator
20854577
the Lamor precession the neutron spin undergoes, while flying through static magnetic fields. Several other NSE schemes exist however, which employ resonant spin flips in a magnetic RF-field to achieve the same effect on the neutron, such as neutron resonant spin echo (NRSE) and modulation of intensity by zero effort (MIEZE). In NRSE, the static magnetic fields produced by large DC coils in NSE are replaced by two resonant flipper coils, producing a static magnetic field B and a thereto perpendicular radio frequency (RF) field of frequency ω (Figure 1. b). A neutron entering the first resonant flipper undergoes a
Neutron resonance spin echo
3342977
be connected in two arrangements: cumulatively or differentially. Cumulative compound motors connect the series field to aid the shunt field, which provides higher starting torque but less speed regulation. Differential compound DC motors have good speed regulation and are typically operated at constant speed. DC motor A DC motor is any of a class of rotary electrical machines that converts direct current electrical energy into mechanical energy. The most common types rely on the forces produced by magnetic fields. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current
DC motor
958413
Transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a form of neurostimulation. TMS is a non-invasive procedure in which a changing magnetic field is used to cause electric current to flow in a small targeted region of the brain via electromagnetic induction. During a TMS procedure, a magnetic field generator, or "coil", is placed on the scalp. The coil is connected to a pulse generator, or stimulator, that delivers a changing electric current to the coil. TMS is used diagnostically to measure the connection between the central nervous system and skeletal muscle to evaluate damage in a wide variety of
Transcranial magnetic stimulation
9279005
rotating magnetic field is produced inside a set of windings called the stator. While the rotating field winding consumes a fraction of a percent of the generator output, adjustment of the field current allows good control over the generator output voltage. Older style wind generators rotate at a constant speed, to match power line frequency, which allowed the use of less costly induction generators. Newer wind turbines often turn at whatever speed generates electricity most efficiently. The varying output frequency and voltage can be matched to the fixed values of the grid using multiple technologies such as doubly fed induction
Wind turbine design
1794133
conductor (with zero resistance). The total magnetic flux formula_1 through the ring is equal to the magnetic field formula_2 multiplied by the area formula_3 of the surface spanning the ring. The nine field lines represent the magnetic flux threading the ring. Suppose the ring is deformed, reducing its cross-sectional area. The magnetic flux threading the ring, represented by five field lines, is reduced by the same ratio as the area of the ring. The variation of the magnetic flux induces a current "(red arrows)" in the ring by Faraday's law of induction, which in turn creates a new magnetic field
Explosively pumped flux compression generator
19745087
pressure being confined by the magnetic field gives rise to a diamagnetic drift, which is proportional to the pressure of electrons and inversely proportional to the magnetic field strength. Together with the formula_1 drift, the diamagnetic drift is responsible of the formation of an "azimuthal electric current" formula_2 in the plasma domain. This azimuthal electric current generates an induced magnetic field which opposes the applied one, generating a repulsive magnetic force formula_3 that pushes the plasma downstream. The reaction to this force is felt on the magnetic generator of the magnetic nozzle and is called magnetic thrust. This is the
Magnetic nozzle
19403364
winding while rotor (also called armature) consists of armature winding. When both armature and field are excited by DC supply, current flows through windings and magnetic flux proportional to the current is produced. When the flux of field interacts with the flux of armature, it results in motion of the rotor.Armature control is the most common control technique for DC motors. In order to implement this control, the flux is required to be kept constant. . To this aim, either the stator voltage is constant or the stator coils are replaced by a permanent magnet. In the latter case, the
Armature Controlled DC Motor
6617331
Field coil A field coil is an electromagnet used to generate a magnetic field in an electro-magnetic machine, typically a rotating electrical machine such as a motor or generator. It consists of a coil of wire through which a current flows. In a rotating machine, the field coils are wound on an iron magnetic core which guides the magnetic field lines. The magnetic core is in two parts; a stator which is stationary, and a rotor, which rotates within it. The magnetic field lines pass in a continuous loop or magnetic circuit from the stator through the rotor and back
Field coil
3342960
The direction and magnitude of the magnetic field produced by the coil can be changed with the direction and magnitude of the current flowing through it. A simple DC motor has a stationary set of magnets in the stator and an armature with one or more windings of insulated wire wrapped around a soft iron core that concentrates the magnetic field. The windings usually have multiple turns around the core, and in large motors there can be several parallel current paths. The ends of the wire winding are connected to a commutator. The commutator allows each armature coil to be
DC motor
12789111
the voltage as the field is changed, which is very difficult in practice, or use a separate DC bias magnetic field parallel to the device to maintain a constant voltage and consequently constant magnetic flux through the loop. The strength of the field being measured will then be equal to the strength of the bias magnetic field passing through the SQUID. Although it is possible to read the DC voltage between the two terminals of the SQUID directly, because noise tends to be a problem in DC measurements, an alternating current technique is used. In addition to the DC bias
Scanning SQUID microscopy
3972434
Proper degaussing will ensure there is insufficient magnetic remanence to reconstruct the data. Erasure "via" degaussing may be accomplished in two ways: in AC erasure, the medium is degaussed by applying an alternating field that is reduced in amplitude over time from an initial high value (i.e., AC powered); in DC erasure, the medium is saturated by applying a unidirectional field (i.e., DC powered or by employing a permanent magnet). A degausser is a device that can generate a magnetic field for degaussing magnetic storage media. Many forms of generic magnetic storage media can be reused after degaussing, including reel-to-reel
Degaussing
9058514
Earth inductor compass The Earth inductor compass (or simply induction compass) is a compass that determines directions using the principle of electromagnetic induction, with the Earth's magnetic field acting as the induction field for an electric generator. The electrical output of the generator will vary depending on its orientation with respect to the Earth's magnetic field. This variation in the generated voltage is measured, allowing the Earth inductor compass to determine direction. The earth inductor compass was first patented by Donald M. Bliss in 1912 and further refined in the 1920s by Paul R. Heyl and Lyman James Briggs of
Earth inductor compass
869874
dynamo in 1861 (before Siemens and Wheatstone) but didn't patent it as he thought he wasn't the first to realize this. A coil of wire rotating in a magnetic field produces a current which changes direction with each 180° rotation, an alternating current (AC). However many early uses of electricity required direct current (DC). In the first practical electric generators, called "dynamos", the AC was converted into DC with a "commutator", a set of rotating switch contacts on the armature shaft. The commutator reversed the connection of the armature winding to the circuit every 180° rotation of the shaft, creating
Electric generator
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Electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and winding currents to generate force in the form of rotation. Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators. An electric generator is mechanically identical to an electric motor, but operates in the reverse direction, accepting mechanical energy (such as from flowing water) and converting this mechanical
Electric motor
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also works in reverse as a generator if driven. It is useful for generating very large currents at low voltage. It does not appear to comply with a simple interpretation of Maxwell's equations in the sense that the magnetic field does not at any point pass through any closed winding to generate an electromagnetic effect. A unipolar motor is also a type of small DC electric motor commonly found in small, portable cassette players. In this case, the 'unipolar' property refers to its winding that does not need to change current direction and therefore can be driven by a simple
Unipolar motor
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1.43 gigawatt motor generator and five 64-megawatt power supplies. The 1200-ton motor generator sits on a 4800-short ton (4350 t) inertia block which rests on 60 springs to minimize earth tremors and is the centerpiece of the Pulsed Field Laboratory. The facility's magnets include a 60 tesla long-pulse magnet that is the most powerful controlled-pulse magnet in the world. The University of Florida is home to user facilities in magnetic resonance imaging or (MRI) with an ultra-low temperature, ultra-quiet environment for experimental studies in the High B/T (high magnetic field/low temperature) Facility. Facilities are also available for the fabrication and
National High Magnetic Field Laboratory
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physics and are of great interest to the geophysics and astrophysics communities, since the magnetic fields of the earth and sun are produced by these natural dynamos. The Lorentz Force Law describes the effects of a charged particle moving in a constant magnetic field. The simplest form of this law is given by the vector equation. where The vector F is perpendicular to both v and B according to the right hand rule. Typically, for a large-scale power station to approach the operational efficiency of computer models, steps must be taken to increase the electrical conductivity of the conductive substance.
Magnetohydrodynamic generator
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used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo. The DC output from the armature is directly connected to the armature of the DC motor (sometimes but not always of identical construction). The shunt field windings of both DC machines are independently excited through variable resistors. Extremely good speed control from standstill to full speed, and consistent torque, can be obtained by varying the generator and/or motor field current. This method of control was the "de facto" method from its development until it was superseded by solid state thyristor systems. It found
Brushed DC electric motor
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This type of device is known as a single Galvanic cell, so an obsolete name for steady current was galvanic current. A "battery" consists of two or more cells, connected in either parallel or series pattern. A homopolar generator is an electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. AC generators can be used as sources of steady current with a rectifier and a good ripple
Constant current
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into a proton and electron with the emission of energy. When the time comes to actually try to make electricity from a tokamak-based reactor, some of the neutrons produced in the fusion process would be absorbed by a liquid metal blanket and their kinetic energy would be used in heat-transfer processes to ultimately turn a generator. Tokamak A tokamak () is a device which uses a powerful magnetic field to confine a hot plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. ,
Tokamak
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circling the wire "(green arrows)" by Ampere's circuital law. The new magnetic field opposes the field outside the ring but adds to the field inside, so that the total flux in the interior of the ring is maintained: four green field lines added to the five blue lines give the original nine field lines. By adding together the external magnetic field and the induced field, it can be shown that the net result is that the magnetic field lines originally threading the hole stay inside the hole, thus flux is conserved, and a current has been created in the conductive
Explosively pumped flux compression generator
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left in Britain". The rule for generators can be recalled by remembering that either the letters "g" and "r" is common to both "right" and "generator", or the phrase "Jenny is always right" ("Genny" being a common shortened version of Generator). When electrons, or any charged particles, flow in the same direction (for example, as an electric current in an electrical conductor, such as a metal wire) they generate a cylindrical magnetic field that wraps round the conductor (as discovered by Hans Christian Ørsted). The direction of the induced magnetic field is sometimes remembered by "Maxwell's corkscrew rule". That is,
Fleming's left-hand rule for motors
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on that charge to move it to the high potential terminal. The emf "ℰ" of the source is defined as the work "dW" done per charge "dq": . In the case of an electrical generator, a time-varying magnetic field inside the generator creates an electric field via electromagnetic induction, which in turn creates a voltage difference between the generator terminals. Charge separation takes place within the generator, with electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further charge separation impossible. Again, the emf is countered by
Electromotive force
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design is that the magnet is more efficient. First, it has simple parallel field lines. Second, because the fluid is processed in a disk, the magnet can be closer to the fluid, and magnetic field strengths increase as the 3rd power of distance. Finally, the generator is compact for its power, so the magnet is also smaller. The resulting magnet uses a much smaller percentage of the generated power. The efficiency of the direct energy conversion in MHD power generation increases with the magnetic field strength and the plasma conductivity, which depends directly on the plasma temperature, and more precisely
Magnetohydrodynamic generator
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magnetic nozzle is sufficiently long to minimize the amount of energy wasted in the radial and azimuthal directions. Additionally, an excessively weak magnetic field would fail to confine radially and guide axially the plasma, incurring in large radial losses. Other figures of merit of the system are the electric power, mass and volume of the required magnetic field generator (magnetic coils and/or permanent magnets). A low electric power consumption, mass and volume are desirable for space propulsion applications. Magnetic nozzle A magnetic nozzle is a convergent-divergent magnetic field that guides, expands and accelerates a plasma jet into vacuum for the
Magnetic nozzle
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approved by the FDA for this use. It is available in Australia. Transcranial magnetic stimulation (TMS) or deep transcranial magnetic stimulation is a noninvasive method used to stimulate small regions of the brain. During a TMS procedure, a magnetic field generator, or "coil" is placed near the head of the person receiving the treatment. The coil produces small electric currents in the region of the brain just under the coil via electromagnetic induction. The coil is connected to a pulse generator, or stimulator, that delivers electric current to the coil. TMS was approved by the FDA for treatment-resistant major depressive
Management of depression
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the ring, and Φ is the magnetic flux quantum. Hence, a DC SQUID can be used as a flux-to-voltage transducer. However, as noted by the figure, the voltage across the electrodes oscillates sinusoidally with respect to the amount of magnetic flux passing through the device. As a result, alone a SQUID can only be used to measure the change in magnetic field from some known value, unless the magnetic field or device size is very small such that Φ < Φ. To use the DC SQUID to measure standard magnetic fields, one must either count the number of oscillations in
Scanning SQUID microscopy
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and the magnetic field part on rotor. A basic design of revolving field single-phase generator is shown on the right. There are two magnetic poles, north and south, attached to a rotor and two coils which are connected in series and equally spaced on stator. The windings of the two coils are in reverse direction to have the current to flow in the same direction because the two coils always interact with opposing polarities. Since poles and coils are equally spaced and the locations of the poles match to the locations of the coils, the magnetic lines of force are
Single-phase generator
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that produces the field current for the larger generator. Modern generators with field coils are usually self-excited, i.e., some of the power output from the rotor is used to power the field coils. The rotor iron retains a degree of residual magnetism when the generator is turned off. The generator is started with no load connected; the initial weak field induces a weak current in the rotor coils, which in turn creates an initial field current, increasing the field strength, thus increasing the induced current in the rotor, and so on in a feedback process until the machine "builds up"
Excitation (magnetic)
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the magnetic field, and the opposing magnetic fields do not change polarity, no commutation is required for the conductor to keep turning. This simplicity is most readily achieved with single turn designs, which makes homopolar motors unsuitable for most practical applications. Like most electro-mechanical machines, a homopolar motor is reversible: if the conductor is turned mechanically, then it will operate as a homopolar generator, producing a direct current voltage between the two terminals of the conductor. The direct current produced is an effect of the homopolar nature of the design. Homopolar generators (HPGs) were extensively researched in the late 20th
Homopolar motor
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magnetic material to measure DC. Other current probes use Hall effect sensors to measure the magnetic field around a wire produced by an electric current through the wire without the need to interrupt the circuit to fit the probe. They are available for both voltmeters and oscilloscopes. Most current probes are self-contained, drawing power from a battery or the instrument, but a few require the use of an external amplifier unit. (See also: Clamp meter) More advanced current probes combine a Hall effect sensor with a current transformer. The Hall effect sensor measures the DC and low frequency components of
Test probe
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are relatively rare and the poloidal field is at maximum strength. During the next cycle, differential rotation converts magnetic energy back from the poloidal to the toroidal field, with a polarity that is opposite to the previous cycle. The process carries on continuously, and in an idealized, simplified scenario, each 11-year sunspot cycle corresponds to a change in the polarity of the Sun's large-scale magnetic field. Solar dynamo The solar dynamo is the physical process that generates the Sun's magnetic field. A dynamo, essentially a naturally occurring electric generator in the Sun's interior, produces electric currents and a magnetic field,
Solar dynamo
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purpose of an amplidyne is not to generate a steady voltage but to generate a voltage proportional to an input current, to amplify the input. The motor provides the power, turning the generator at a constant speed, and the signal to be amplified is applied to the generator's field winding. The higher the current applied to the winding, the stronger the magnetic field and thus the higher the output voltage of the generator. So the output voltage of the generator is an amplified copy of the current waveform applied to the field winding. In a typical generator the load brushes
Amplidyne
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surrounding the Gramme ring, the ring can be made to cut across more magnetic lines of force in one revolution than a basic two-pole generator. Consequently, a four-pole generator could output twice the voltage of a two-pole generator, a six-pole generator could output three times the voltage of a two-pole, and so forth. This allows output voltage to increase without also increasing the rotational rate. In a multipolar generator, the armature and field magnets are surrounded by a circular frame or "ring yoke" to which the field magnets are attached. This has the advantages of strength, simplicity, symmetrical appearance, and
Field coil
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to keep the current constant. The term back electromotive force is also commonly used to refer to the voltage that occurs in electric motors where there is relative motion between the armature and the magnetic field produced by the motor's field coils, thus also acting as a generator while running as a motor. This effect is "not" due to the motor's inductance but a separate phenomenon. This voltage is in series with and opposes the original applied voltage and is called "back-electromotive force" (by Lenz's law). With a lower overall voltage across motor's internal resistance as the motor turns faster,
Counter-electromotive force
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90-degree angle from the field. This ideal is useful as a starting point for understanding how the fields interact but it is not how a motor or generator functions in actual practice. In a real motor or generator, the field around the rotor is never perfectly uniform. Instead, the rotation of the rotor induces field effects which drag and distort the magnetic lines of the outer non-rotating stator. The faster the rotor spins, the further this degree of field distortion. Because a motor or generator operates most efficiently with the rotor field at right angles to the stator field, it
Commutator (electric)
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only periodic changes in its location in separate periods of time. Magnetic tracking has been implemented in Logitech Tracking. Pros: Cons: "Magnetic tracking" (or "electromagnetic tracking") is based on the same principle as a theremin. It relies on measuring the intensity of inhomogenous magnetic fields with electromagnetic sensors. A base station, often referred to as the system's "transmitter" or "field generator", generates an alternating or a static electromagnetic field, depending on the system's architecture. To cover all directions in the three dimensional space, three magnetic fields are generated sequentially. The magnetic fields are generated by three electromagnetic coils which are
Positional tracking
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between media is related to the permeability formula_15 of each medium: The two Maxwell equations, Faraday's Law and the Ampère-Maxwell Law, illustrate a very practical feature of the electromagnetic field. Faraday's Law may be stated roughly as 'a changing magnetic field creates an electric field'. This is the principle behind the electric generator. Ampere's Law roughly states that 'a changing electric field creates a magnetic field'. Thus, this law can be applied to generate a magnetic field and run an electric motor. Maxwell's equations take the form of an electromagnetic wave in a volume of space not containing charges or
Electromagnetic field
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Solar dynamo The solar dynamo is the physical process that generates the Sun's magnetic field. A dynamo, essentially a naturally occurring electric generator in the Sun's interior, produces electric currents and a magnetic field, following the laws of Ampère, Faraday and Ohm, as well as the laws of hydrodynamics, which together form the laws of magnetohydrodynamics. The detailed mechanism of the solar dynamo is not known and is the subject of current research. A dynamo converts kinetic energy into electric-magnetic energy. An electrically conducting fluid with shear or more complicated motion, such as turbulence, can temporarily amplify a magnetic field
Solar dynamo
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field is referred to as the Stark effect. Electric field NMR Electric field NMR (EFNMR) spectroscopy differs from conventional NMR in that a sample containing suitable nuclei is polarised by a strong dc electric field instead of a constant magnetic field. The nuclei are stimulated (perturbed) by means of an alternating magnetic field, generated by passing an alternating current through a set of coils. The resulting magnetic resonance signal is small, and as in conventional NMR is typically sensed using a second set of coils and an amplifier. The shifting and splitting of spectral lines of atoms and molecules due
Electric field NMR
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lift force. Using two opposed Halbach arrays increases the field even further. Halbach arrays are also well-suited to magnetic levitation and stabilisation of gyroscopes and electric motor and generator spindles. A conductor can be levitated above an electromagnet (or vice versa) with an alternating current flowing through it. This causes any regular conductor to behave like a diamagnet, due to the eddy currents generated in the conductor. Since the eddy currents create their own fields which oppose the magnetic field, the conductive object is repelled from the electromagnet, and most of the field lines of the magnetic field will no
Magnetic levitation
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and slowed by this process. MHD generators typically reduce the temperature of the conductive substance from plasma temperatures to just over 1000 °C. The main practical problem of a Faraday generator is that differential voltages and currents in the fluid short through the electrodes on the sides of the duct. The most powerful waste is from the Hall effect current. This makes the Faraday duct very inefficient. Most further refinements of MHD generators have tried to solve this problem. The optimal magnetic field on duct-shaped MHD generators is a sort of saddle shape. To get this field, a large generator
Magnetohydrodynamic generator
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some very large ones (thousands of horsepower) remain in service. The field currents are much lower than the armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly. For example, in one installation, a 300 amp thyristor unit controls the field of the generator. The generator output current is in excess of 15,000 amperes, which would be prohibitively expensive (and inefficient) to control directly with thyristors. A DC motor's speed and torque characteristics vary according to three different magnetization sources, separately excited field, self-excited field or permanent-field, which are used selectively
Brushed DC electric motor
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An electric generator is a machine that converts mechanical energy into electrical energy. An electric generator works based on the principle that whenever conductor cuts the magnetic field, an emf is induced which will cause the current to flow if conductor circuit is closed. Take the working of simple loop Generator as an example. An electric motor converts electrical energy into mechanical energy. The reverse process of electrical generators, most electric motors operate through interacting magnetic fields and current-carrying conductors to generate rotational force. Motors and generators have many similarities and many types of electric motors can be run as
Electric machine
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the winding is now connected so that current flows through it in the opposite of the initial direction. In a motor, the armature current causes the fixed magnetic field to exert a rotational force, or a torque, on the winding to make it turn. In a generator, the mechanical torque applied to the shaft maintains the motion of the armature winding through the stationary magnetic field, inducing a current in the winding. In both the motor and generator case, the commutator periodically reverses the direction of current flow through the winding so that current flow in the circuit external to
Commutator (electric)
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Electric field NMR Electric field NMR (EFNMR) spectroscopy differs from conventional NMR in that a sample containing suitable nuclei is polarised by a strong dc electric field instead of a constant magnetic field. The nuclei are stimulated (perturbed) by means of an alternating magnetic field, generated by passing an alternating current through a set of coils. The resulting magnetic resonance signal is small, and as in conventional NMR is typically sensed using a second set of coils and an amplifier. The shifting and splitting of spectral lines of atoms and molecules due to the presence of an external static electric
Electric field NMR
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the magnetic field of the Earth. The operation of the compass is based on the principle of electromagnetic induction with the Earth's magnetic field acting as the induction field for an electric generator. A variation generated voltage, thus allows the Earth inductor compass to determine direction. The earth inductor compass is an American invention. It was designed in 1924 by Morris Titterington at the Pioneer Instrument Company. Designed to compensate for the weaknesses of the magnetic compass, the Earth inductor compass provided pilots with a more stable and reliable reference instrument. 1924 Gas chamber execution 1924 Moviola 1924 Radio altimeter
Timeline of United States inventions (1890–1945)
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to supply make-up power during these events. Many generator designs use electric current flowing through windings to produce the magnetic field on which the motor or generator operates. This is in contrast to designs that use permanent magnets to generate this field instead. Such devices may have a minimum working voltage, below which the device does not work correctly, or does so at greatly reduced efficiency. Some will disconnect themselves from the circuit when these conditions apply. The effect is more pronounced in doubly-fed induction generators (DFIG), which have two sets of powered magnetic windings, than in squirrel-cage induction generators
Low voltage ride through
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magnetic flux law, similar to Ohm's law for closed electric circuits, is attributed to Henry Augustus Rowland in an 1873 paper. Rowland is also responsible for coining the term "magnetomotive force" in 1880, also coined, apparently independently, a bit later in 1883 by Bosanquet. Reluctance is usually represented by a cursive capital formula_3. In both AC and DC fields, the reluctance is the ratio of the magnetomotive force (MMF) in a magnetic circuit to the magnetic flux in this circuit. In a pulsating DC or AC field, the reluctance also pulsates (see phasors). The definition can be expressed as follows:
Magnetic reluctance
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that they had received real TMS, compared with those in sham rTMS groups. Depending on the research question asked and the experimental design, matching the discomfort of rTMS to distinguish true effects from placebo can be an important and challenging issue. Transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a form of neurostimulation. TMS is a non-invasive procedure in which a changing magnetic field is used to cause electric current to flow in a small targeted region of the brain via electromagnetic induction. During a TMS procedure, a magnetic field generator, or "coil", is placed on the scalp. The coil
Transcranial magnetic stimulation
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hence the output voltage of a DC generator. As the speed of a DC motor is dictated by the supplied voltage, this gives simple speed control. The DC generator could be driven by any means, provided that also supplied a voltage source for the field windings. This 'prime mover' could be an AC motor, or it could be an internal combustion engine (its application to vehicles was patented by H.W. Leonard in 1903). A Ward Leonard drive can be viewed as a high-power amplifier in the multi-kilowatt range, built from rotating electrical machinery. Where the 'prime mover' is electrical, a
Ward Leonard control
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(EFNMR) is typically stimulated by applying a relatively strong dc magnetic field pulse to the sample and, after the end of the pulse, analyzing the resulting low frequency alternating magnetic field that occurs in the Earth's magnetic field due to free induction decay (FID). These effects are exploited in some types of magnetometers, EFNMR spectrometers, and MRI imagers. Their inexpensive portable nature makes these instruments valuable for field use and for teaching the principles of NMR and MRI. An important feature of EFNMR spectrometry compared with high-field NMR is that some aspects of molecular structure can be observed more clearly
Nuclear magnetic resonance
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currents in the three conductors of the armature winding combine spatially in such a way as to resemble the magnetic field of a single, rotating magnet. This stator magnetic field or "stator field" appears as a steady rotating field and spins at the same frequency as the rotor when the rotor contains a single dipole magnetic field. The two fields move in "synchronicity" and maintain a fixed position relative to each other as they spin. They are known as synchronous generators because f, the frequency of the induced voltage in the stator (armature conductors) conventionally measured in hertz, is directly
Permanent magnet synchronous generator