text:
|Publication number
|Publication type
|Application number
|Publication date
|Feb 23, 1993
|Filing date
|Jul 17, 1989
|Priority date
|Jul 22, 1986
|Fee status
|Publication number
|Herbert H. Woodson, John S. Hsu
|Original Assignee
|Board Of Regents, The University Of Texas System
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (16), Non-Patent Citations (4), Referenced by (28), Classifications (10), Legal Events (4)
|External Links: USPTO, USPTO Assignment, Espacenet
This is a continuation of co-pending application Ser. No. 888,818 filed on Jul. 22, 1986, now abandoned.
The present invention relates generally to methods and apparatus for improving the performance of alternating current (AC) machines, and more specifically relates to methods and apparatus for improving the performance of polyphase AC machines through the injection of harmonic frequencies into the excitation current.
With conventional polyphase AC machines, both induction and synchronous, the machines are typically operated by a single frequency source. The machines have armature windings to which the single frequency sine waves are applied. The ideal performance of conventional polyphase AC machines would include a sinusoidal air-gap flux wave of constant amplitude rotating around the air-gap at synchronous speed. In this theoretical, ideal polyphase AC machine, the constant amplitude flux wave will produce a constant electromagnetic torque. The torque of the machine is monotonically dependent upon this constant amplitude flux wave. This ideal situation may be approximated in large scale machines.
In conventional AC machines the magnetic flux per pole of the machine is proportional to the area of 1/2 sine wave of the air-gap flux wave of the machine. Typically, a conventional AC machine is designed to operate with at least one of the magnetic members, the iron cores or teeth, of the machine in flux saturation. In conventional machines, the saturation flux densities of the iron, or other magnetic members, of the stator and rotor determine the maximum amplitude of the air-gap flux wave. In conventional machines, therefore, the amplitude of the fundamental flux sine wave determines the maximum power output of the machine. This is true even though maximum use is not made of all of the flux capability of the magnetic members.
In conventional AC machines, undesirable space harmonics are typically established in the air-gap flux waves. These naturally-arising space harmonics occur as a function of the particular machine design when excited by a fundamental frequency. Factors such as slots in the machines and core saturation contribute to the generation of these undesirable space harmonics. These space harmonic flux waves are undesirable because they typically rotate in the air-gap at speeds other than that at which the fundamental flux wave rotates. Additionally, the space harmonic flux waves can be travelling in either a forward or backward direction, as well as at different speeds, relative to the fundamental flux wave. For example, a naturally-arising fifth space harmonic flux wave will travel in a reverse direction relative to the fundamental flux wave and will travel at 1/5 the speed of the fundamental flux wave. Similarly, a naturally-arising seventh space harmonic flux wave will travel in the same direction as the fundamental flux wave, but at 1/7 the speed. These space harmonic flux waves can interact with the squirrel cage winding in an induction motor, or with the damper winding in a synchronous motor, to produce a braking torque which reduces the useful output of the machine. Additionally, these naturally-generated space harmonic flux waves can interact with each other, and with the fundamental flux wave, to cause pulsations in the torque of the machine, as well as unwanted mechanical vibrations.
Accordingly, the present invention provides a new method and apparatus for constructing and operating a polyphase AC machine whereby a harmonic flux wave will travel in the same direction, and at the same (synchronous) speed, as the fundamental flux wave and whereby the fundamental flux wave is augmented in response to the harmonic flux wave so as to achieve improved electromagnetic loading in the magnetic path of the machine; both achievements serving to improve the useful output of a given machine.
The methods and apparatus of the present invention improve the performance of polyphase AC machines through excitation of the machine with frequencies which are odd harmonics of the fundamental excitation frequency. This odd harmonic excitation serves to improve performance of the machine in two ways: (a) the flux distribution caused by the harmonic excitation enables a greater fundamental flux distribution and thereby yields an improved total flux distribution in the magnetic path of the machine, thereby causing improved magnetic loading of the material, and (b) if the other conductors on the machine (typically on the rotor) contain conductors or coils responsive to the harmonic frequencies applied to the armature, or if the pole shape of the rotor produces a permeance wave responsive to the harmonic frequencies, the harmonic flux distributions themselves will yield increased torque in the machine.
As will be discussed in more detail later herein, this odd harmonic excitation can be practiced in a variety of ways, including: separate coils for fundamental excitation and for each odd harmonic excitation; multiphase power supplies for both fundamental and harmonic frequencies coupled to a common winding; the use of a multiplicity of delta-connected windings coupled to one another through volt-amp balancers, with separate phases of the harmonic excitation current applied to each delta; and a common set of delta-connected windings actuated through use of a multiphase inverter, with a separate phase of the harmonic excitation current applied to each delta.
FIGS. 1A-D graphically depict the flux distribution in a section of the magnetic path of an AC machine. FIG. 1A depicts a sinusoidal flux distribution. FIG. 1B depicts a square wave flux distribution. FIG. 1C depicts a total flux distribution achieved by adding an increased level of fundamental flux distribution with a third harmonic flux distribution. FIG. 1D depicts a total flux distribution achieved by adding a further increased fundamental flux distribution with third and fifth harmonic flux distributions.
FIGS. 2A-C graphically depict the flux distributions in different portions of an AC machine. FIG. 2A depicts the flux distributions with the machine operated with neither of the magnetic members in saturation. FIG. 2B depicts how the flux distributions in a typical low speed machine can be adjusted through practice of the present invention to improve machine performance. FIG. 2C depicts how the flux distributions in a typical high speed machine can be adjusted through practice of the present invention to improve machine performance.
FIG. 3 graphically depicts the relationship between the ratio of the fundamental flux density to the maximum design flux density of a machine and the ratio of the third harmonic flux density to the maximum design flux density of the machine.
FIG. 4 schematically depicts the phase belts for a machine in accordance with the present invention having separate windings for fundamental, third harmonic and fifth harmonic frequencies and power supplies for exciting such machine.
FIG. 5 schematically depicts a single layer winding for a machine in accordance with the present invention to be excited through combined fundamental and third harmonic power sources.
FIG. 6 depicts the power source connections to the machine of FIG. 5.
FIG. 7 schematically depicts a machine in accordance with the present invention having double layer windings with a per-unit pitch of less than 1.
FIG. 8 depicts the connections and the back emf potential points for a machine when such machine is excited through use of volt-amp balancers.
FIG. 9 depicts the slot electrical connections for a machine to be excited as in FIG. 8.
FIG. 10 schematically depicts the connections for the machine of FIGS. 8-9.
FIG. 11 depicts the fundamental frequency back emf voltage differences between harmonic phases found in alternate slots in the machine of FIGS. 8-10.
FIG. 12 schematically depicts a machine with 60� phase belt connections for excitation through use of volt-amp balancers.
FIG. 13 schematically depicts the electrical connections for the machine of FIG. 12.
FIG. 14 schematically depicts the windings of an alternative embodiment of a machine to be excited through use of volt-amp balancers.
FIG. 15 schematically depicts the connections and the fundamental frequency back emf potential points for the machine of FIG. 14.
FIG. 16 schematically depicts the electrical connections for the machine of FIGS. 14 and 15.
FIG. 17 schematically depicts the winding configuration for the armature of a machine to be excited through use of a multiphase inverter.
FIG. 18 schematically depicts the windings of the machine of FIG. 17.
The present invention utilizes the injection of harmonic frequencies into the excitation current of a polyphase AC machine to optimize the flux densities in both the iron portions and the air-gap of the machine. Those skilled in the art will recognize that the resulting increase in total flux in the machine will yield improved performance of the machine.
Referring first to FIGS. 1A-D of the drawings, each Figure graphically depicts the total flux distribution in a section of the magnetic path of an AC machine under different conditions. The ordinate of each graph is the phase angle while the abscissa represents the ratio of the local flux distribution (B) to the maximum design flux density (BS) in the machine.
FIG. 1A depicts a sinusoidal flux distribution 10 in the magnetic path, resulting from a sinusoidal excitation current. Flux distribution 10 has a peak amplitude 12. FIG. 1B depicts a square wave flux distribution 14 having an amplitude 16 equal to the peak amplitude 12 of sinusoidal distribution 10 in FIG. 1A. The theoretical flux per pole of a machine actuated with the square wave flux distribution 14 of FIG. 1B is 1.57 times the flux per pole of a machine actuated by sinusoidal distribution 10 of FIG. 1A. Such a theoretical machine would make optimal usage of the flux capacity of the iron portions of the machine. Square waves, however, cannot be produced in practical machines because practical power supplies are not available.
A square wave can be synthesized by an infinite set of odd harmonics. Although such synthesization is impractical, a square wave can be approximated by a finite set of odd harmonics. FIG. 1C depicts a flux distribution 18 achieved by adding an increased fundamental flux distribution 19 to the flux distribution of the third harmonic 20. The flux per pole of flux distribution 18 is 1.23 times that of the sinusoidal flux distribution 10 resulting from only fundamental excitation.
FIG. 1D depicts a flux distribution 22 achieved by adding a further increased fundamental flux distribution 21 to an increased third harmonic flux distribution 23 and a fifth harmonic flux distribution 24. The flux per pole of flux distribution 22 is 1.31 times that of sinusoidal flux distribution 10.
Additional correlated odd harmonic flux distributions will allow further increases in the relative flux per pole relative to a sinusoidal flux distribution 10 resulting from fundamental excitation only. The further addition of these odd harmonic flux distributions will approach the flux per pole of square wave flux distribution 14. However, additional odd harmonic flux distributions will yield smaller incremental changes than those provided by the addition of the third and fifth harmonics as depicted in FIGS. 1C and 1D. The addition of the third harmonic flux distribution facilitates the greatest increase in the total flux distribution and will therefore be discussed here in the greatest detail.
Referring now to FIGS. 2A-C, graphically depicted in each figure are the core flux distributions 25a, 25b, and 25c in respective figures, and the teeth and gap flux distributions, 27a, 27b and 27c in respective figures, in a machine under three different conditions. Conventional practice in the design of polyphase AC machines is to design the flux densities in the stator core, the stator teeth, the rotor core and the rotor teeth in such a way as to avoid excessive flux saturation in any particular section. This practice serves to limit magnetization current and core loses to acceptable values. The air-gap flux distribution can be other than a sinusoidal wave form, distortion in the distribution being largely dependent upon the degree of saturation in the magnetic paths.
FIG. 2A depicts the core flux distribution 25a, and the teeth and gap flux distribution 27a of a machine wherein neither section of the machine is saturated. Each flux distribution is a sinusoid in response to the fundamental frequency excitation. Core flux distribution 25a is derived from integration of teeth and gap flux distribution 27a, and is therefore 90� apart in space from teeth and gap flux distribution 27a.
In reality, a machine will be operated with at least one section of the machine approaching saturation. Further, the degree of saturation in different magnetic paths cannot be totally equal. For example, in a low speed machine having a large number of poles, flux densities in the stator and rotor cores are much lower than the flux densities in the stator and rotor teeth. The reason is that the minimum dimension of each core is determined by mechanical requirements, such as rigidity, stress, and manufacturing requirements; but is not determined by electromagnetic requirements. Saturation of the teeth is therefore a determining factor for how much flux per pole can be produced in the machine. Conversely, for high speed machines, such as two pole machines, the core sections are typically more saturated than the teeth sections.
The performance, and therefore the rating, of an AC machine is dependent upon the total flux per pole that can be produced in the machine. The present invention facilitates the total flux per pole in a polyphase AC machine to be increased by maintaining or lowering flux density in one magnetic path while increasing the flux density in another magnetic path. This redistributing of the flux is accomplished by adjusting the phases of the harmonic excitation relative to the fundamental excitation. For example, FIG. 2B depicts exemplary flux distributions contemplated through use of the present invention in a low speed machine as discussed above. The density of the core flux 27b is increased through use of fundamental flux distribution 28 and third harmonic flux 20 distribution 29. At the same time, however, the density of teeth and gap flux 27b is decreased relative to fundamental flux distribution 28 and third harmonic flux distribution 29. The injection of third harmonic excitation current to establish third harmonic flux distribution 29, therefore, facilitates increasing the density of the core flux 25b while decreasing the density of teeth and gap flux distribution 27b, more evenly distributing the flux in the machine, and, most importantly, facilitating an increase in the total flux per pole in the machine.
FIG. 2C, depicts exemplary flux distributions contemplated through use of the present invention with a high speed machine as discussed above. In FIG. 2C, the phase angle of third harmonic flux distribution 29' has been changed relative to fundamental flux distribution 28'. This results in a decrease in the density of core flux 25c and facilitates an increase in teeth and gap flux 27c. This again promotes a more even flux within the machine and facilitates an increased total flux per pole in the machine.
Referring now to FIG. 3, therein is graphically depicted, by a curve 31, the relationship between the fundamental flux density and the third harmonic flux density in a machine. The abscissa of the graph of FIG. 3 represents the ratio of the fundamental flux density to the maximum design flux density of a machine, while the ordinate represents the ratio of the third harmonic flux density to the maximum design flux density of the machine. The relation expressed in curve 31 assumes that the total flux density in the machine remains unchanged.
In determining the relative amplitudes for the fundamental and third harmonic excitation voltages, the maximum third harmonic voltage should be applied which will facilitate the maximum fundamental voltage which can be applied which will improve machine performance without exceeding the thermal rating of the machine. In addition to this primary parameter, however, the actual ratio between the fundamental and third harmonic excitation voltages may be affected by secondary factors, such as changes in core losses due to the excitation by both fundamental and third harmonic frequencies, or changes in deleterious naturally-occurring space harmonics as discussed earlier herein, etc. The amplitude and the relative phases of all excitations will be in sync so as to produce optimal flux densities as discussed earlier herein.
Following is a discussion of increased performance of different types of AC machines through use of the present invention. With respect to any of the below discussed polyphase AC machines, because harmonic sinusoids of different frequencies are orthogonal, the fundamental and each harmonic of the stator-produced flux wave will interact to produce torque only with its counterpart in the rotor produced flux wave.
The benefits of the present invention may be achieved with different types of AC machines including, for example: squirrel cage induction motors, wound rotor induction motors, and both salient pole and round rotor synchronous machines. Different practical considerations with respect to the present invention will be found with these different machines, however. A squirrel cage induction motor will experience enhanced torque production from the increased fundamental component facilitated through harmonic injection, as depicted in FIGS. 1C and 1D. Additionally, a squirrel cage induction motor will experience enhanced torque production from each harmonic flux component provided that the conductors forming the squirrel cage on the rotor are finely enough divided to allow each space harmonic of induced current to flow. If the number of bars is so small that one or more space harmonic currents cannot flow, then no torque can be produced by those space harmonics in the stator flux wave.
In a wound rotor induction motor, the number of poles produced by rotor winding is determined by the winding configuration on the rotor. As a consequence, torque will be produced by each flux component in the armature for which there is a corresponding winding having a suitable number of poles on the rotor. For purposes of this discussion, the armature will have a fundamental winding and one or more harmonic windings. If the rotor has only a fundamental winding, the machine will experience enhanced torque from the higher armature fundamental flux density component as seen in FIGS. 1C and 1D. However, if the rotor includes windings having the correct number of poles to interact with the armature harmonic flux distributions, additional torque can be produced by each of these flux distributions also.
With respect to synchronous machines, torque is produced by the interaction of fields produced by the armature excitation with the steady fields produced by direct current in the field winding. The field winding is typically located on the rotor. Space harmonics in the flux wave produced by current in the field winding can be produced by properly shaping the poles in a salient pole machine, or by properly distributing the field winding in a round-rotor machine. If current in the field winding produces only a fundamental component of flux density, torque enhancement will result only from the increased armature fundamental flux component made possible by the harmonic components in the flux wave. However, for each harmonic component in the field-produced flux wave which matches a harmonic in the armature flux wave, further torque enhancement can occur. In a salient pole synchronous machine, if the salient poles are properly shaped, then additional torque can be produced by the harmonic components of the flux wave.
With respect to enhanced performance of any particular machine, any actual increase in the machine's rating must be determined through examination of the factors that initially set the rating, i.e., electrical heating of the armature winding, electrical heating of the rotor winding in an induction machine, electrical heating of the field winding in a synchronous machine, core loss heating of the magnetic members, and/or mechanical strength of machine components.
Flux distributions as depicted in FIGS. 1C or 1D, can be produced by providing separate sets of polyphase windings for the fundamental and for each desired harmonic. Each harmonic, thus, may be applied to a discrete set of windings. Alternatively, and preferably, however, the fundamental winding will be utilized also for harmonic excitation. This can be done in a variety of ways. For example, in one method of practicing the present invention, the outputs of two multiphase power supplies are coupled together in series to provide fundamental and harmonic excitation of the fundamental winding. Another method utilizes delta-connected windings coupled together through volt-amp balancers to balance the potential and currents of both fundamental and harmonic excitation in the windings. Yet another alternative method utilizes a single winding with a multiphase inverter, as often found with adjustable speed devices, to inject the harmonic excitations onto the fundamental winding.
Referring now to FIG. 4, therein is depicted in schematic form the cross section of phase belts for a machine 32 for excitation by fundamental, third harmonic, and fifth harmonic frequencies and the power supplies for exciting machine 32. Machine 32 is wound with a two-pole, three-phase fundamental winding 33 which will be excited by fundamental frequency supply 26. Third harmonic winding 34 is a six-pole, three-phase winding which will be excited by third harmonic frequency supply 38. Third harmonic frequency supply 38 will contain phase control circuitry as known in the art to assure that the third harmonic frequency is maintained in the desired phase relationship with the fundamental frequency. Fifth harmonic winding 35 is a ten-pole, three-phase winding which will be excited by fifth harmonic frequency supply 39 which also contains phase control circuitry.
A specific phase winding in machine 32 will extend between a pair of letters in a single winding ring, either 33, 34 or 35, indicated by that letter and its prime. For example, in the winding schematic the phase winding extending between a and a' in fundamental winding ring 33 is a single phase fundamental winding. Similarly, the third harmonic windings a to a' in winding ring 34 represent third harmonic phase belts. Pairs of third harmonic windings may be connected either in series or parallel or may be switched from one connection to the other for ease in starting.
As discussed above, in machine 32 each winding, fundamental winding 33, third harmonic winding 34 and fifth harmonic winding 35, will be excited by a separate three phase power supply, 26, 38 and 39, respectively. As determined above, the frequency of the third harmonic excitation current will be three times the fundamental frequency, and the frequency of the fifth harmonic excitation current will be five times that of the fundamental frequency. The three frequencies will be phase controlled to be in sync with one another as depicted, for example, in FIG. 1D.
Each harmonic winding must have a number of poles (Ph) equal to:
Ph =np (1)
n is the order of the harmonic (third, fifth, etc.); and
p is the number of poles in the fundamental winding.
For example, for an armature having a fundamental winding having four poles (p=4), the third harmonic winding must have 3�4=12 poles. The fundamental winding will be excited at the fundamental frequency: ω, and each harmonic winding will be excited at its harmonic of the fundamental, i.e., a third harmonic winding will be excited at the electrical frequency, 3ω. As will be discussed in more detail later herein, although the number of phases in the fundamental winding and in each harmonic winding must be two or more, the number of phases need not be the same for all windings.
This embodiment allows the greatest flexibility in choosing coil pitches and numbers of turns for the windings. This construction, however, requires that an armature slot be occupied by at least two different windings, thereby resulting in less efficient utilization of the slot area. Because of the less efficient utilization of the slot area by the multiple windings, this method typically results in less percentage improvement than do other methods as will be discussed later herein.
For two-phase systems, the displacement of the fundamental and third harmonic power supplies are 90 degrees. For three or more phase systems, displacements of the fundamental and the harmonic frequency supplies are 360/n electrical degrees for n number of phases.
Because the number of poles for the fundamental will automatically determine the required number of poles for the space harmonic windings, in a machine where separate windings are provided for the fundamental and for the harmonic excitation currents, the appropriate number of phases for the harmonic excitation is determined by the number of slots per pole available for the harmonic windings. Table 1 indicates the slot requirements of both fundamental and third harmonic windings for polyphase machines:
TABLE 1______________________________________PHf Spf SpPHf PH3 Sp3 SpPH3______________________________________2 6 3 2 2 13 6 2 2 2 16 6 1 2 2 13 9 3 3 3 l9 9 1 3 3 12 12 6 2 4 23 12 4 4 4 14 12 3 4 4 16 12 2 4 4 112 12 1 4 4 1______________________________________
PHf indicates the number of phases of the fundamental frequency;
Spf indicates the slots per pole required for the fundamental winding;
SpPHf indicates the number of slots per pole per phase for the fundamental winding;
PH3 indicates the number of phases of the third harmonic frequency;
Sp3 indicates the number of slots per pole required for the third harmonic winding; and
SpPH3 indicates the number of slots per pole per phase for the third harmonic winding.
Those skilled in the art will recognize that in addition to the integral slot per pole per phase distributions indicated in Table 1, fractional slots per pole per phase may be utilized.
As indicated earlier herein, harmonic frequencies may be injected through use of a single winding for both fundamental and harmonic excitation. FIG. 5 schematically depicts in winding ring 37 a single layer winding for a four-pole, full pitch machine 36 having 36 slots. Machine 36 will preferably be excited by balanced nine-phase fundamental current. Accordingly, as determined by equation 1, machine 36 will have three-phase, twelve-pole third harmonic excitation. Fundamental windings are indicated by the pair of a letter and its prime, with a subscript indicating the slot position of the winding. For example, the winding between, A, in slot 1, and A', in slot 10, is designated as A1 -A'10.
FIG. 6 depicts the power supply connections to the indicated windings of machine 36 of FIG. 5. Transformer secondaries A-I, indicated as 30a, 30b, . . . 30i, are the secondaries of one or more transformers coupled to an appropriate nine-phase fundamental frequency power supply. Those skilled in the art will recognize that a balanced nine-phase fundamental frequency supply may be obtained from a three-phase fundamental frequency supply through use of an appropriate number of transformers; typically, three transformers, each with four appropriately wound secondaries. Third harmonic frequency sources x-z, are preferably the secondaries of transformers 32x, 32y, and 32z, each coupled to one phase of a three-phase third harmonic frequency power supply. Alternatively, however, the three-phase third harmonic frequency power supply may coupled directly to secondaries 30a-30i in the manner indicated. In each arm of the star connection of FIG. 6, a secondary of the three-phase third harmonic frequency power supply 32 is coupled between ground and a nine-phase fundamental frequency supply secondary 30, and to a pair of fundamental windings. The fundamental windings are identified by the slot numbers of machine 36 as indicated in FIG. 5. For example, as shown in FIG. 6, three-phase secondary 32x is coupled in series between ground and nine-phase secondary 30a. The other side of nine-phase secondary 30a is then coupled to windings A1 -A'10 and to A19 -A'28. In machine 36 of FIGS. 5 and 6, the winding pairs A1 -A'10 and A19 -A28 are connected in parallel between nine-phase secondary 30A and ground. Alternatively, winding pairs A1 -A'10 and A19 -A'28 may be connected in series with one another between nine-phase secondary 30a and ground. Such series connection will approximately double the voltage required by machine 36 while halving the required current.
Ring 40 in FIG. 5 depicts the third harmonic phasers assigned to each slot of machine 36. The effective third harmonic excitations shown, (i.e., X1 -X'4, X7 -X'10 ; etc.) do not represent actual windings, but rather the third harmonic phaser distributions achieved through application of power as depicted in FIG. 6 to the fundamental windings arranged as in FIG. 5.
The present invention may also be employed with a multiple layer winding as opposed to the single layer winding utilized with machine 36 in FIGS. 5 and 6. The winding connections for a machine 42 with a double layer winding are schematically depicted in FIG. 7. Additionally, the principles of the present invention may be applied to a machine having less than a full pitch.
As indicated above, machine 36 of FIGS. 5 and 6 is a four-pole, thirty-six slot, full-pitch machine. A full-pitch machine is preferable for use with the present invention because an optimal increase in machine performance is realized through practice of the invention with a full pitch machine. However, those skilled in the art will realize that the fundamental excitation of some full pitch machines is more prone to generate undesirable fifth and seventh harmonics with such a phase relationship to the fundamental that machine performance is hindered, as discussed earlier herein. The coil pitch of a conventional machine is therefore often designed to be 0.83 so as to minimize these undesirable fifth and seventh space harmonics.
The fundamental coil pitch factor is determined by the relationship:
cos[(full pitch-actual pitch)/full pitch�180/2] (2)
The third harmonic coil pitch factor for a single winding is determined by the relationship:
cos[(full pitch-actual pitch)/full pitch�3�180/2](3)
Table 2 indicates the pitch factors for both the fundamental and the third harmonic for a double layer winding as determined through use of equations 2 and 3.
TABLE 2______________________________________ Per-Unit Fundamental Pitch 3rd HarmonicActual pitch Pitch Factor Pitch Factor______________________________________9 slots 1.00 1.00 1.008 slots 0.89 0.98 0.877 slots 0.78 0.94 0.506 slots 0.67 0.87 0.00______________________________________
FIG. 7 depicts a 36 slot machine 42 having a four-pole fundamental and a twelve-pole third harmonic, but with a 0.89 per unit pitch and a double layer winding. Windings are represented in FIG. 7 in the same manner as with FIG. 5, i.e., windings are represented by pairs A1 -A'9 ; B3 -B'11, etc. Phase windings in adjacent pairs of slots, for example A1 -A'9 and A2 -A'10 are connected in parallel. Inner ring 43 does not represent actual windings of machine 42, but rather the third harmonic phase distribution of machine 42. Machine 42 may be excited by power connections similar to those depicted in FIG. 6 for machine 36, with the addition of additional connections to the dual windings in each slot of machine 42.
A third method of practicing the present invention involves the use of volt-amp balancers. This method allows the use of three-phase power supplies to provide the fundamental and third harmonic excitation. With this method the machine windings are delta-connected. Coupled to each delta is one phase of the three phase third harmonic excitation current. Each leg of each delta preferably contains the secondary of a transformer (54a, 54b, 54c; 56a, 56b, 56c; 58a, 58b, 58c in FIG. 10) each of which has a primary coupled to one phase of the third harmonic frequency power supply. As previously discussed, the frequency of the third harmonic excitation current will be three times that of the fundamental excitation current.
Autotransformers used in the volt-amp balancers of the power connections for this method will yield variations of resistance and leakage-reactance between full load on the machine and no load. However, for purposes of illustration of this embodiment, ideal conditions are assumed, in which the excitation current, the leakage reactances, and the resistances of both the volt-amp balancers and the third harmonic transformers are neglected. Under this assumption, the terminal voltage of a winding is equal to the back emf produced by the fundamental air-gap flux. These ideal conditions assumed are generally representative of a no load condition of a large rating machine, whose no load currents are typically small compared to their full load currents.
FIG. 8 depicts the connections and the back emf potential points (A1, A2, and A3) for exciting a machine 45, as depicted in FIG. 9. Machine 45 is a four-pole, three-phase machine, having 36 slots and 120� phase belts. FIG. 10 schematically depicts the particular slot electrical connections for the connections depicted in FIG. 8. Inner ring 47 of FIG. 9 depicts the third harmonic phaser distribution of machine 45 when machine 45 is excited through the connections as shown in FIGS. 8 and 10.
With this volt-amp balancer method of harmonic injection, the number of phases of the third harmonic is determined by the number of slots per third harmonic pole by means of the relationship:
Nph3 =the smallest multiplier greater than 1 of [ns /(3�Pf)] (4)
Nph3 equals the number of third harmonic phases;
ns equals the number of slots in the machine; and
Pf equals the number of poles of the fundamental frequency.
In machine 45 coupled as depicted in FIGS. 8 and 10, 120� phase belt slots 1, 3 and 5, etc. correspond to the three discrete phases of third harmonic excitation. Each phase of the three-phase third harmonic current is a zero-sequence current with respect to a particular fundamental delta winding. The back emfs: emf 1, emf 2, and emf 3, of the fundamental frequency (in slots 1, 3 and 5, etc.) each have the same amplitude. Because the phases of these three currents are different, coils in slots 1, 3 and 5, etc. can not be directly connected, either in parallel or in series.
In the connections of FIG. 8, three volt-amp balancers 49a, 49b, and 49c are used, one for each phase of the fundamental frequency current. Each volt-amp balancer is formed of two autotransformers: T1, indicated as 50a, 50b and 50c, and T2, indicated as 52a, 52b and 52c. The turn ratio of transformers T1 (50a, 50b and 50c), is 1:1. The turn ratio of each transformer T2 (52a, 52b and 52c), is 2:1. The sides of each transformer T1 will be connected to a terminal potential point A1 or A3 of first delta 44 or third delta 48, respectively. Autotransformer T2 will be connected between terminal potential point A2 of second delta 46 and the center tap 53 of its respective transformer T1. Line current of phase A is coupled to the tap 54a, of autotransformer T2, 52a. Because the turn ratio of autotransformer T2 is 2:1 relative to tap 54a, the line current of phase A will convey one portion to terminal A2 of second delta 46 and two portions into center tap 53a of transformer T1, 50a. Similarly, because the turn ratio of each autotransformer (T1) 50a, 50b and 50c is 1:1, the current into the terminal potential point A3 of third delta 48 is the same as that going into the terminal potential point A1 of first delta 44. Accordingly, the line currents entering terminal potential points A1, A2 and A3 of first, second and third deltas 44, 46, and 48, respectively are identical. As a result, the phase current drive will be identical for each phase.
In operation of the embodiment depicted in FIGS. 8-10, the back emfs at terminal points A1 and A3 are balanced by transformers (T1) 50a, 50b and 50c. The potential at terminal potential point A2 and at the center tap of autotransformer T1 are balanced by each auto-transformer T2, 52a, 52b and 52c. As indicated above, each third harmonic current appears as a zero-sequence current relative to a particular fundamental current. Accordingly, the volt-amp balancers see only the fundamental frequency currents and voltages. The back emf voltages are therefore maintained in the same amplitudes, but in different phases, through operation of volt-amp balancers 49a, 49b, 49c. The net effect of this connection is that the flux wave produced is the same as that which would be produced with the coils of slots 1, 3 and 5 connected in series.
The fundamental frequency back emf voltage difference between the harmonic phases found in alternate slots, slots 1, 3 and 5, etc., are related as shown in the vector diagram of FIG. 11. As can be seen in FIG. 11, the back emfs in each delta 44, 46, 48 are of equal magnitude, but have a phase angle difference of 40�. The volt-amp balancers balance these phase differences, which occur between alternate slots in machine 45. As one skilled in the art can calculate, the total volt-ampere rating of volt-amp balancers 49a, 49b and 49c, is 0.37 that of the transformers required to provide the nine-phase fundamental frequency supply discussed in relation to the system of FIGS. 5 and 6. The results actually achieved with a machine excited through use of volt-amp balancers will depart somewhat from the ideal performance shown and described. This departure will be due in large part to winding resistance and leakage reactance in the volt-amp balancers and harmonic frequency transformers. Accordingly, in the design of components for any particular system, the transformers for the volt-amp balancers and third harmonic excitation should be designed with sufficiently low winding resistance and leakage reactance to minimize departure from the ideal.
FIG. 12 depicts another embodiment of this method of harmonic injection into a four-pole, thirty-six slot machine 60, with windings corresponding to a 60� phase belt connection. The actual connection diagram for machine 60 is depicted in FIG. 13. As can be seen in FIG. 13, the polarity of each third harmonic transformer 61a, 61b, 61c coupled to the delta in slot 2 is reversed relative to the polarity of third harmonic transformers 63a, 63b, 63c; 65a, 65b, 65c, coupled to the deltas in slots 1 and 3. The volt-ampere rating of the three volt-amp balancers 62a, 62b and 62c of FIG. 13 is 0.18 that of the transformers required to provide the nine-phase supply discussed in reference to the system of FIGS. 5 and 6. The volt-ampere rating of the balancers is therefore substantially less even than that of the system of FIGS. 8-10 having 120� phase belt connections.
Another example of the present invention can be illustrated through use of an ideal machine having two third harmonic phases. FIG. 14 schematically depicts a three-phase full-pitch, double layer winding six-pole fundamental, 36 slot machine 66. Referring to the number of slots per third harmonic pole is: 36/(3�6)=2. Referring to equation 4, because 2 is the smallest multiplier of 2 other than 1, the number of phases of the third harmonic excitation is 2. Ring 67 depicts the third harmonic phase distribution for machine 66.
Referring now also to FIGS. 15 and 16, the windings of machine 66 are connected in two deltas 69, 71. FIG. 15 depicts the winding fundamental frequency back emf potential points (A1 and A2), corresponding to the connection of the volt-amp balancers 68a, 68b and 68c of FIG. 17. In the machine of FIGS. 14-16, the total volt-amp rating of the three volt-amp balancers is 0.26 that of the transformers which would be needed to supply the fundamental frequency excitation through use of a three-phase fundamental frequency supply as discussed in reference to FIGS. 5 and 6. One phase of the third harmonic excitation will be applied to each leg of a delta through transformers as depicted at 70 and 72 in FIG. 16.
Because the third harmonic excitation of machine 66 is two phase, one autotransformer is used for each volt-amp balancer 68a, 68b, 68c. FIG. 16 schematically depicts a detailed connection diagram for exciting machine 66. Each third harmonic frequency supply transformer, 70 and 72, supplies one of the two phases of the third harmonic excitation current. Each transformer 70 and 72 preferably includes a single primary and three equivalent secondaries, coupled in the deltas as shown. As is well known in the art, because each secondary carries one phase of the fundamental frequency current, the mmfs of these fundamental frequency currents add to zero, and no fundamental frequency current is induced in the primary of the third harmonic transformers. This is true of all third harmonic transformers in all other embodiments described herein.
A fourth method of injection of third harmonic frequencies utilizes a single stator winding in conjunction with a multiphase inverter. Referring now to FIG. 17, therein is schematically depicted a machine 74 having six fundamental poles in thirty-six slots. The windings of machine 74 will be connected in two deltas, 78 and 80, displaced 30 electrical degrees from one another, each to be excited by a three-phase fundamental frequency supply. Windings indicated by letters enclosed in circles in FIG. 17 represent windings of the second delta as opposed to windings represented by the unencircled letters. For example winding pair A1 -A'7 is connected in delta 78, while winding A2 -A'8 is connected in delta 80. Ring 75 depicts the distribution of the third harmonic phases in machine 74.
FIG. 18 schematically depicts machine 74 and a multiphase inverter power supply 76 suitable for use therewith. In the method of this embodiment, neither the multiphase power transformers utilized with the apparatus of FIGS. 5 and 6, nor the volt-amp balancers of the various apparatus of FIGS. 7-16 are required. Multiphase inverter 76 provides two three-phase fundamental frequencies 82, 84 each displaced 30� from one another. The first fundamental frequency outputs 82 are coupled to first delta 78, while second fundamental frequency outputs 84 are coupled to second delta 80.
The third harmonic excitation is two phase. Each phase is injected into one of the fundamental delta windings 78, 80. Each leg of each delta, 78, 80, will include the secondary 86a, 86b, 86c; 88a, 88b, 88c, respectively, of a transformer having its primary coupled to a third harmonic frequency supply. Because this multiphase inverter method of the present invention is particularly suitable for use with adjustable frequency drives, it will be advantageous to generate the third harmonic frequency directly in response to the fundamental frequency. This may be done through conventional means. For example, the rectified power 90 may be applied to a third harmonic frequency generator 92 outputting two phases 94, 96. Third harmonic frequency generator 92 will preferably be responsive to one phase of a fundamental frequency output 98 to enable precise frequency and phase control of third harmonic frequency phases 94 and 96. Third harmonic frequency phases 94 and 96 will be coupled to primaries 86', 88' of transformer secondaries 86a, 86b, 86c: and 88a, 88b, 88c, respectively.
Each of the above-discussed methods and apparatus allows the optimizing of flux distribution in a polyphase AC machine. As discussed in reference to FIGS. 1-3, the optimal phase relationship will be selected between the harmonic excitation current and the fundamental excitation current to facilitate optimal distribution of the flux density and optional increases in the total flux per pole of the machine.
Many modifications and variations may be made in the techniques and structures described and illustrated herein without departing from the spirit and the scope of the present invention. Accordingly, it is to be readily understood that the embodiments described and illustrated herein are illustrative only and are not to be considered as limitations for the present invention.
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|Mechler, Robert Carl. "Increased Rating of Polyphase Induction Motors Using Third Harmonic Excitation," Thesis turned in to The Univ. of Texas at Austin, May 1985, catalogued Jul. 22, 1985.
|Mechler, Robert Carl. Increased Rating of Polyphase Induction Motors Using Third Harmonic Excitation, Thesis turned in to The Univ. of Texas at Austin, May 1985, catalogued Jul. 22, 1985.
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|Nissan Motor Co., Ltd.
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|Bulent Sarlioglu
|Method and system for providing single-phase excitation techniques to a start exciter in a starter/generator system
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|Dec 16, 2004
|Ingolf Groening
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|Edelson Jonathan S
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|Frederick William Klatt
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|Frederick William Klatt
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|Koninklijke Philips Electronics N.V.
|Driving a light-emitting diode
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|May 30, 2001
|Hitachi, Ltd.
|Very high speed permanent magnet type electric rotating machine system
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|Borealis Technical Limited
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|Rexroth Indramat Gmbh
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|U.S. Classification
|318/737, 318/807
|International Classification
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|Dec 14, 1993
|Certificate of correction
|Oct 1, 1996
|Maintenance fee reminder mailed
|Feb 23, 1997
|Lapse for failure to pay maintenance fees
|May 6, 1997
|Expired due to failure to pay maintenance fee
Effective date: 19970226


text:
- Key Largo Village
- Key Largo Yacht Club
- Lake Surprise Estates
- Landings of Largo
- Largo Gardens
- Largo Sound Village
- Lime Grove Estates
- Silver Shores
- Stillwright Point
- Sunrise Point
- Sunset Cove
- Tamarind Bay Club
- Tarpon Basin Villas
- Taylor Creek Village
- Twin Lakes
- Winston Waterways
- Wynken, Blynken & Nod
- Bay Haven
- Bowens Addition
- Buccaneer Point
- Buttonwood Bay
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This property allows you to book online with a credit card. After submitting a reservation request, the owner or manager has 24 hours to accept, at which time your card will be charged and you will receive an email confirmation
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Recent Key Largo reviews
"The condo community itself is beautifully landscaped and well kept, with PLENTY of things to do ON site. This particular condo is adorable. Light and airy and perfectly situated directly in front of the pool and the saltwater lagoon. Hallelujah -- no bored kids! The condo was well stocked with everything you could possibly need. We were so at home here. The owners, Gregory and Carolyn, were very accommodating and incredibly helpful. They thought of everything.I could not have been happier with this condo and this community. I want a do over!!"Guest: Becky Date of Stay: December 2015 Review Submitted: December 29, 2015View listing
"This house is exactly as the photos depict and a very nice base to explore the Keys, Miami, and the surrounding area. The owner is very cordial and helpful. When we arrived the cable wasn't working and the owner spent several hours of his time to correct the issue. You can't ask for better than that! The kayaks are a nice addition as well. There are a ton of places to eat within a couple minutes drive, grocery stores within a few miles as well. As for the house, it is exactly as pictured. Affordable, good location, very helpful owner....how can you go wrong?"Guest: Jonathan W. Date of Stay: May 2016 Review Submitted: May 27, 2016View listing
"Heading for our long weekend away we were a little nervous considering the serious drop in positive reviews. We have stayed in the keys many times. This trip was two couples(early 50's) enjoying a long holiday weekend. Dividing the cost between the two couples meant we paid less than a hotel room and had the plus of a full kitchen and laundry facilities and room to spread out. The a/c was plenty cold. The hot water was plenty hot. The cable tv was fine. The beds were comfy. We didn't encounter any issues with the house at all. The house was cleaned when we arrived, in fact the cleaners came back and asked if we wanted them to fold the laundry they had left in the dryer. Yes the house needs a deep cleaning like the berber carpeting is deeply stained. However, we go to the keys with kayaks in tow and after a day on the water, we come dragging into a house with sand and muck and wet, so we wouldn't like to stay in a place that we felt like we had to be totally tidy in. We also were able to bring our dog along, another plus. We couldn't have sat outside in July as we would have just been eaten alive by the mosquitos, but we were able to use the grill one night and it was fine. The dock is showing signs of aging, but the hole is intentionally part of the dock, to allow for mangroves growing there. We never felt unsafe walking on it. Yes the boat is old, but we weren't bothered by it. We go to the Keys to mostly kick back, relax, kayak, and fish. I can see how if you were going to stay at the house as a major part of your time there, that you could be disappointed, but clean and functional works fine for us as long as we aren't paying a premium price. The salt air is so hard on property in the keys, to keep a place in top shape requires expensive regular maintenance that probably would eat up most profit. So, I'm sure it's a balancing act for an owner to figure out what to invest in and what to let go. Also we did receive our security deposit back in the time stated. Would we stay there again? Yep."Guest: Beth W. Date of Stay: July 2016 Review Submitted: July 31, 2016View listing
"I hesitate writing this review because I fear Lime Time will become too difficult to book once others discover it! The place is fantastic with all the amenities that a boater (comes with it's own boat ramp!) or non-boater would ever want. Million dollar views off the dock, quiet, safe neighborhood, and all the nearby shopping and dining that one could ever want! Super clean, great wi-fi and a large screen TV with satellite to keep you connected if you need to...or not if you don't. The owner is a pleasure to deal with a super-responsive to communication. I'd give it 6 stars if I could!"Guest: Sniper Date of Stay: August 2016 Review Submitted: August 14, 2016View listing
Featured Destinations: Dauphin Island, Isle of Palms, Bald Head Island, Destin Condo Rentals

subset: commoncrawl


text:
I want to like Jeremy Lin, I really do. It's a pretty cool story when a player comes out of nowhere and rips off a dominating hot streak. In June 1995, Mike Benjamin of the San Francisco Giants, a utility infielder and career .229 hitter, collected a MLB record 14 hits over three straight games. It was an amazing story, ensuring countless baseball nerds like myself would never forget his name. For die-hard NBA fans, Lin has done the same. However, if the media continues to cover him this way, I'll do my damnedest to never hear it again.
Don't get me wrong: despite his propensity to turn the ball over like John Wall, the kid is incredibly exciting to watch. Standing at 6'3 and weighing only 200 pounds, he plays much bigger. The way Lin drives toward the basket shows no fear. I love watching players like that. What I hate is the way Lin's rise to fame is lazily portrayed by writers. For instance:
ESPN's Rick Reilly:
But the best part is that Lin is a hoop hopes machine now. He gives every kid at the end of every high school bench, every college scrub who never gets a minute, every 13th man in the NBA … faith. Faith that someday, if he can finally get his chance, he can Shu them How.
The New York Daily News:
Got Christ? The Huffington Post:
New York Knicks guard Jeremy Lin's underdog story and outspoken evangelical faith have some sportswriters dubbing him the "Taiwanese Tebow."
But while Lin and Denver Broncos quarterback Tim Tebow share similar Christian convictions, Lin's rise to stardom is even more miraculous.
The normally reliable Emma Carmichael:
He's looked positively at ease on the Garden floor, but we're reminded that none of this makes sense, really, every time he breaks character to smile disbelievingly at his own play. Last night, Lin received the ball wide-open on the perimeter after a freakish Chandler tip and drilled a three-pointer with that awkward, follow-through-free jumper of his, just as the shot clock's buzzer sounded. It was his 26th point of the game—breaking his two-day-old career high—and as he backpedaled down the court for Utah's next possession, he attempted a cool, winking nod in Chandler's direction. It lasted for about a second, and then he smiled like a kid and stuck out a Gatorade-stained tongue.
He didn't know how to react. Neither do we.
Had enough yet? There's a lot more, but I couldn't bring myself to read another story about the "underdog Asian kid" from California who "fought" his way into Harvard College and then into a few NBA training camps before being cut. I understand there's not much going on in sports right now, but seriously, how freaking lazy can you be?
Let me put this out there: anyone who plays professional sports is not an "underdog." Professional athletes are the 1%: they are the luckiest people on the face of the earth. Jeremy Lin isn't the scrappy Asian stereotype that Jason Whitlock or Floyd Mayweather so ignorantly portrayed. He's a talented freak of nature, a one-of-a-kind man-child who is either on an incredible hot streak or is enduring (yet another) miraculous stroke of luck, showcasing his talents in an ideal offensive system, with ideal offensive teammates, with an ideal coach, against ideal opponents. Hell, even Mike Benjamin had his day.
If you want to talk about "underdogs," how about the story of Thomas Robinson or Juan Dixon? Why are we idolizing a middle class kid with a seemingly-normal family who not only attended one of the best high schools in the country, but also went to Harvard? If Jeremy Lin never stepped foot on an NBA basketball court, his quality of life would likely still be superior to most of his fans. Lin is playing with house money: if he never hits another shot, he still can still catch the 2 train just outside MSG and ride it down to Wall Street and a $500K a year job in finance, no sweat. And now we want to make this a race and religion combo platter? Shoot me.
I like Lin. I hate the way he is covered. Please don't make me root against him.
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text: Add a Second Shower Rod for Extra Bathroom StorageAdam Dachis9/19/12 2:00pmFiled to: Clever UsesBathroomShowerHomeHouseholdStorageTop513EditPromoteDismissUndismissHideShare to KinjaToggle Conversation toolsGo to permalink Need somewhere to hang shampoo, soap, and other shower items? Redditor Teruterus solved this common storage problem by adding an extra shower rod. Of course, you have to purchase hangable baskets, but you can find those cheap and hook them on with shower curtain rings if they don't come with a hook already. If you really want to go crazy with shower rods, you can add one to dry towels and swimsuits, too. LPT: Add a 2nd shower rod in the back to hang poufs, kids toys, etc. | RedditGear from Kinja DealsYour Favorite Rolling Carry-On Is The Travelpro Maxlite3A Eulogy For The Bodum Bistro Automatic Pour-Over CoffeemakerSaturday's Best Deals: TriggerPoint Foot Massager, Grill Gauge, Keypad DeadboltReply51 repliesLeave a reply


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2 colors
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text:
Everton are banking on Barkley... and Ross is ready to repay the club's faith
Great expectations swirl around Goodison Park. With a new manager for a new season, it was inevitable optimism would abound on the opening day.
But the excitement Evertonians feel this summer runs deeper. While Roberto Martinez has been quickly embraced after succeeding David Moyes, it is the role Ross Barkley threatens to play in this campaign that provides an intriguing, exciting subplot.
Barkley's name has been well known on Merseyside for years. Moyes, after all, gave him his top-flight debut two years ago when he was 17. But this is set to be the campaign when he comes in from the periphery.
Central figure: Midfielder Ross Barkley (right) could become a key player for Everton this season
JACK BUTLAND (Stoke)
The keeper, 20, joined for £3.5m from Birmingham and is eyeing a World Cup squad place. Made his England debut last season.
TOM CARROLL (Tottenham)
The 21-year-old midfielder has excellent technique and vision — he just needs to bulk up. Andre Villas-Boas rates him highly.
NATHAN REDMOND (Norwich)
The winger, 19, is fast, tricky and confident and was man-of-the-match for the Under 21s against Scotland last Tuesday.
Midfielder Barkley, who had spells on loan at Sheffield Wednesday and Leeds last year, scored on his return to the England Under 21 squad on Tuesday and is set to be involved when the Martinez era begins on Saturday at Norwich.
'I'm looking forward to this season more than any other,' says Barkley. 'There will be more opportunities for me to play.
'People have opinions about me but not a lot know how I really play as I haven't had that many chances. Hopefully everyone will see what I can do now. It has been a massive change this summer.
'Every day I had been at Everton, David Moyes was there and everything I did was based around trying to impress people so they would tell him.'
His determination to succeed is beyond question. This is a young man who has battled back from a series of dreadful injuries, the worst being a triple leg fracture sustained playing for England's Under 19s when he was 16. He is aware time has arrived to push on.
'I owe (Moyes) everything,' adds Barkley. 'He brought me on as a player and looked after me when I had broken my leg. I was out for a while with a hernia and a broken foot, too.
International class: Barkley scores for England Under 21s against Scotland in midweek
'I had tough times but I got there in the end. Now Roberto Martinez has come in and, whatever chances I get, I must take them. These are exciting times for Everton and I want to play whatever role I can.'
Senior professionals at Everton tell of a player with enormous natural talent, one who is fearless and not afraid to try something out of the ordinary.
There were times Moyes used to be driven to distraction by that and Barkley perhaps didn't always get the chances he might have done for his previous manager, who placed a huge emphasis on discipline.
Martinez is set to accept the mistakes in order to find a way to get Barkley in his team.
'What I look for from players is how you react to a mistake: does it stop you getting on the ball again?' says Martinez. 'If Ross makes a mistake, he plays on in the same manner.
'When a player does that, I have no problems whatsoever. In every game I have seen Ross play, he has shown that bit of magic others do not have.'
Just go away and play: Roberto Martinez is prepared to let Barkley make mistakes
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I've played live chessfor a couple years here, now it no longer works, what's up with that?
Hi Dodger111,
Sorry to hear of your troubles with live chess :( Can you tell me what is happening that is causing you not to be able to play live chess?
It just sits and loads forever, no board comes up.
Can you try the suggestions found at the following link?
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text: Financial Diary Financial DiaryDiary of forthcoming financial events, including international and UK economic announcements, company interim and final results and trading announcements. Popular Articles Popular Latest Most commented Impressive potential in Nigeria By: Andrew Van Sickle Britain votes leave: don't panic – this is an opportunity By: John Stepek 23 Comments Japan: the only way is up By: Andrew Van Sickle What will you do when banking dies? By: Dan Denning Why a pension beats a buy-to-let flat hands down By: Merryn Somerset Webb Central bankers to governments: it's time to spend, spend, spend By: John Stepek 1 Comment The "Bank of Mum and Dad" is just like any other bank – it wants a return on its money By: Merryn Somerset Webb What to do about Britain's housing crisis? By: Simon Wilson Don't like "Brexit"? Vote here for a new word to describe the UK leaving the EU By: Merryn Somerset Webb 16 Comments What is financial martial law and how could it be imposed here in the UK? By: Tim Price 14 Comments Sorry Nicola Sturgeon, the revenue numbers do matter By: Merryn Somerset Webb 11 Comments Bankers and doom-mongers in retreat By: Dan Denning 10 Comments Video Tutorials The end of the death tax Behavioural finance: How psychology affects investors Equity crowdfunding: you can invest in start-ups more videos


text:
A new study calls into question the evolutionary stability of an ecological explanation of biodiversity.
The study, published in the journal PLOS ONE, brings together evolutionary theory and ecology to explore one of the big questions in ecology: How is biodiversity developed and maintained?
"This is a fundamental question if we want to protect biodiversity—what exactly do we need to protect?" says International Institute for Applied Systems Analysis (IIASA) Evolution and Ecology Program Director Ulf Dieckmann, who led the study together with Florian Hartig from the University of Freiburg, collaborating with colleagues from the Helmholtz Centre for Environmental Research in Leipzig and the French National Center for Scientific Research in Grenoble.
In introductory biology courses, students learn that two species cannot occupy the same niche, and that the world's biodiversity is thus closely related to the number of niches that exist. But in fact, in the real world this is often not true—it appears that organisms can and do occupy the same niche, meaning that they feed on the same resource, in the same place, at the same time.
"For example," says Dieckmann, "herring and sprat in the Baltic Sea occupy very similar ecological niches, feeding on the same kinds of plankton. How such species can robustly co-exist is a key question for modern ecology."
One theory, known as Relative Nonlinearity of Competition (RNC), suggests that such species can co-exist because they react differently to fluctuations in resources or other limiting factors—such as algal blooms for fish, or rainfall variations for mosquitoes—causing changes in the environment that temporarily benefit the other species. This leads to a dynamic relationship in which each species temporarily benefits from the other's influence on the environment, holding the two in balance.
"The idea has held up well in theory, but it's difficult to test in practice," says Dieckmann. So he and his colleagues decided to test RNC from another perspective, using three standard evolutionary models. "We wanted to find out what happens to the RNC mechanism when we allow the species to adapt."
Their results show that RNC is typically not stable if one considers evolution: in all three models, the species differences that supported their coexistence disappear through adaptation. This means that, evolutionarily, the two coexisting species are outcompeted and replaced by a single species. Dieckmann says, "We thus suggest that the potential of this mechanism for explaining the origin and maintenance of biodiversity might have been overestimated in the literature."
The scientists conclude that further research will be needed to understand what other mechanisms support biodiversity.
Dieckmann says that the study points to the importance of interdisciplinary research, such as that conducted at IIASA. "Because evolution and ecology research are most often done in isolation, nobody had yet thought to ask whether this mechanism was evolutionarily stable."
Hartig F, Münkemüller T, Johst K, Dieckmann U. 2014. On the sympatric evolution and evolutionary stability of coexistence by relative nonlinearity of competition. PLOS ONE. http://dx.plos.org/10.1371/journal.pone.0094454
For more information contact:
Ulf Dieckmann
Program Director
Evolution and Ecology
+43(0) 2236 807 386
Katherine Leitzell
IIASA Press Office
Tel: +43 2236 807 316
Mob: +43 676 83 807 316
About IIASA:
IIASA is an international scientific institute that conducts research into the critical issues of global environmental, economic, technological, and social change that we face in the twenty-first century. Our findings provide valuable options to policy makers to shape the future of our changing world. IIASA is independent and funded by scientific institutions in Africa, the Americas, Asia, Oceania, and Europe. www.iiasa.ac.at
Katherine Leitzell | idw - Informationsdienst Wissenschaft
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Fraunhofer HHI researchers have developed a camera system that films people with a perfect three-dimensional impression. The core of this system is a stereo...
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text:
The Cardiff Blues play their home matches at the Arms Park. They are coached by Danny Wilson, and star players include Sam Warburton and Alex Cuthbert
Hobbs has linked up with the Dragons after leaving the Blues last season
One of the stars of Super Rugby champs the Hurricanes has indicated that he will wear the red jersey on residency grounds if given the chance
It is understood the Blues want a two year option in a new lease to bring forward regeneration plans
Andy Howell watched impressive debuts from Nick Williams and Matthew Morgan, and was reminded of the class of Gavin Henson
The Blues had been beaten 38-28 at Newport Gwent Dragons in their opening friendly but coach Danny Wilson made wholesale changes for Bristol
Morgan faced his former side as Bristol made the journey across the Severn Bridge to the Welsh capital
The exciting back will make his Cardiff Blues debut against former side Bristol at the Cardiff Arms Park
The Wales international will make his first appearance for the Welsh region against the side he left at the end of last season
The Scarlets will kick off a testing Champions Cup campaign at home to Sale with the Cardiff Blues being the only Welsh region to go on the road on the opening weekend
He's one of the most powerful carriers and hardest hitters in the league, and he's about to make his bow for Cardiff Blues
The Cardiff Blues centre just failed to make the final 12-man Team GB squad for Rio after spending nine weeks as part of the wider training group
Have your say on how the Welsh regions will fare this season
The former Wales and New Zealand coach was there to film footage for a mini documentary on the All Blacks ahead of the autumn internationals
Rugby correspondent Andy Howell was there to take a look at how both teams are shaping up after the summer break
Kingsley Jones, who has taken over as Dragons coach from the departed Lyn Jones, fielded a near first-choice line-up in an attempt to build confidence before the start of the Guinness Pro12 campaign
Relive all the events at Rodney Parade as we brought you live coverage of the Dragons v Cardiff Blues
The 2013 Lions captain on how he's found being a parent and how excited he is about returning to action after having six weeks off
At times last season he cut a forlorn figure as things just didn't go his way with a World Cup quarter-final exit against South Africa and England repeatedly attacking his wing during the Six Nations
Wasps were crowned Singha Premiership Rugby 7s Series champions in extraordinary circumstances on home soil
Jenkins was left out of the original touring party but was rewarded for his fine form last season with a late call-up to face the All Blacks after Dan Lydiate was injured
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Paul has been editor of WalesOnline since March 2016. He was previously digital editor of Media Wales. He has been with the company since 2005 and started his career as a reporter on the Western Mail.


text:
Top Trending Hotels Near Botany Bay National Park
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Offering direct access to the beach, this Coogee motel is in the city center, 0.1 mi (0.2 km) from Coogee Beach, and 2.8 mi …
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Home › Forums › Gear Forums › Make Your Own Gear › Material Sourcing – Plastic Snaps
Hey gang – I'm looking to implement a new system on my tarps for closing off the ends and need to find a good source.
I need high quality, long lasting plastic snaps, but I don't want sew on kind. There's the trouble. It's easy to find sew on snaps…
My wife and I have used cloth diapers on our little one and these (Fuzzybunz) have amazing snaps that are rugged and work well in wet environments (think of the original application) – if you know what I'm talking about, that's the sort I'm in search of.
Any ideas?
@marshlaw303Locale: Minnesota
don't you have to buy a press to use this type of snap?
Yes, I believe so. A hand press is only about $40.00. I sell a lot of tarps so it'd be worth it.
Here's what my searching has come up with thus far – any more thoughts would be great.
@vickrhinesLocale: Central Texas
My only question is, what is the release strength of these snaps? Neither supplier seems to provide that information.
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
Hi Tim and all
> don't you have to buy a press to use this type of snap?
Yes, and no. You do need a tool of some sort to set the pin in the snaps, but you don't have to buy a whole press for this. A good drill-press with a clamped vice suffices.
The tooling needed is pretty simple. I made my own tooling out of 1/4" steel rod, as shown in my poncho article at
Alternately you could probably just buy the tool bits without the press.
The snaps are available from a variety of on-line sources such as
and I am sure many others.
Holding forces for plastic snaps – unknown, unspecified, and unspecifiable. For a start, it will depend hugely on the temperature of the plastic. Metal snaps can be specified.
@bfornshellLocale: Southern Texas
One of the members here offered a press and a bunch of snaps for sale about a week ago.
Don't look for it, I bought it.
This is the one I got:
Snap Press:
@richard295Locale: San Francisco Bay Area
Vertical release pressure on the (3/8" #15) Scovill snap sets, in nickel, average 1.5 lbs.
Patagonia Micropuff vest (1/2" #20) snaps, in plastic, average 2.2 lbs.
Standard size (5/8" #24) DOT snap sets, in nickel, average 3 lbs.
I used Rochford standard (5/8" #24) sized hard action snap sets, in nickel, on my most recent DIY project. The four component pieces weighed 4.1 g (.14 oz) combined and the vertical release pressure averaged 7.1 lbs.
@obxcolaLocale: Outer Banks of North Carolina
Richard the information you supply to this blog is really incredible. Thank you and no need to respond.
Thanks so much gang.
I also ran into one more, YKK snaps pointed me in their direction.
That large snap press looks nice. Once I get some samples and figure out what works for my application – I'll probably go ahead and get either that one or something similar. Thanks for the link.
Oh, and thanks very much for the tension numbers! Big help.
You must be logged in to reply to this topic.


text: Home Recipes Ingredients Chicken Recipes Slow Cooker Chicken Recipes Share: Slow Cooker Chicken Recipes Looking for slow cooker chicken recipes? Find slow cooker chicken recipes for a great menu item for main dishes, side dishes, and appetizers. Recipe Spotlight Pineapple Curry Chicken Curry has a moderate to strong flavor, so add it early in the cooking process for good balance with pineapple, coconut and ginger. —Robin Haas, Cranston, Rhode Island Get Recipe More Slow Cooker Chicken Recipes Previous Page ... 7 8 9 ... 25 Next Page Chicken with Stuffing Chicken with Stuffing In Stillman Valley, Illinois, Susan Kutz needs only five ingredients to create this comforting home-style meal of chicken topped with corn bread stuffing. "I sometimes add two cans of soup so there's more sauce," she notes. View Recipe Spicy Chicken Tomato Soup Spicy Chicken Tomato Soup Cumin, chili powder and cayenne pepper give Margaret Bailey's slow-cooked specialty its kick. "I serve bowls of it with crunchy tortilla strips that bake in no time," she writes from her Coffeeville, MIssissippi home. "Leftover soup freezes well for nights I don't feel like cooking." View Recipe Chicken with Vegetables Chicken with Vegetables "You'll be surprised at how easily this tender chicken entree comes together," says Norlene Razak of Tye, Texas. "It's simple, delicious and a great way to get your family to eat vegetables." View Recipe Advertise with us ADVERTISEMENT Mexican Chicken Soup Mexican Chicken Soup This zesty soup is loaded with chicken, corn and black beans in a mildly spicy red broth. As a busy mom of three young children, I'm always looking for dinner recipes that can be prepared in the morning. The kids love the taco-like taste of this easy soup. —Marlene Kane, Lainesburg, Michigan View Recipe Spicy Lemon Chicken Spicy Lemon Chicken "I took a favorite recipe and modified it to work in our slow cooker," writes Nancy Rambo of Riverside, California. "We enjoy this tender lemony chicken with rice or buttered noodles." View Recipe Lower Sodium Chicken Vegetable Soup Lower Sodium Chicken Vegetable Soup Not only is this recipe extremely low in fat, but it's as convenient as it is delicious. Chock-full of corn, lentils and tender chunks of chicken, the thick satisfying soup simmers to a heartwarming perfection in the slow cooker.—Connie Thomas, Jensen, Utah View Recipe Nostalgic Chicken and Dumplings Nostalgic Chicken and Dumplings Enjoy old-fashioned goodness without all the fuss when you fix this supper in your slow cooker. It features tender chicken, wonderfully light dumplings and a full-flavored sauce. —Brenda Edwards of Hereford, Arizona View Recipe Mushroom Chicken Cacciatore Mushroom Chicken Cacciatore Jane Bone from Cape Coral, Florida gives an Italian treatment to chicken by slow-cooking it in a zesty tomato sauce and serving it over spaghetti. "It's great for company because it frees up time to spend with guests. Toss a salad and you're ready to eat," she suggests. View Recipe Chicken Veggie Alfredo Chicken Veggie Alfredo "My family loves this dinner - it's easy to make and a great way to save time after a busy day," notes Jennifer Jordan, Hubbard, Ohio. "If you like, add other veggies to suit your family's tastes." View Recipe Chicken Stew Chicken Stew Rely on this slow cooker stew on busy weekends when you'd rather not be in the kitchen. Chicken, vegetables and seasonings give this stew great flavor. View Recipe Chicken Mushroom Stew Chicken Mushroom Stew Kim Marie Van Rheenan of Mendota, Illinois says, "The flavors blend beautifully in this pot of chicken, vegetables and herbs as it simmers slowly." More Chicken Mushroom Stew Recipes » View Recipe Previous Page ... 7 8 9 ... 25 Next Page Advertise with us ADVERTISEMENT Advertise with us ADVERTISEMENT