Background of the Invention 1. Field of the Invention This invention relates to the field of electrical motors, and more specifically to high efficiency polyphase induction motors.

2. Description of Related Technology Induction motors are well known in the electrical arts. The typical induction motor is comprised of 1) a series of electrically interconnected windings (one for each phase in a polyphase system), 2) a stator containing these windings and having a magnetically permeable core, and 3) a rotor having an electrically conductive structure ("cage").

Three phase windings are most often arranged in the well known"delta"or"wye"configurations, as shown in Figures 1 a and 1 b, respectively.

An induction motor works on the principle of inductive power transfer from the stator to the rotor. Power is transferred to the rotor by virtue of the electromotive force (emf) induced in the rotor conductors due to the relative motion of those conductors through a magnetic field. Since no torque on the rotor is generated when no relative motion exists, the rotor must necessarily turn slower or"slip"in relation to the stator field. This slip is typically on the order of 2-5%. Generally speaking, greater slip corresponds to greater rotor torque and greater current draw. A secondary magnetic field is generated due to the current flow within the rotor conductors.

The polyphase induction motor provides several advantages over other types of motors, including : a comparatively simple construction without a need for brushes or slip rings; good efficiency; high starting torque; and good reliability.

However, induction motors producing a high torque typically draw a very high starting current which may require limiting to protect the windings. This high inrush current can also place limitations on motor operation, possibly tripping distribution feeder protection (breakers), or requiring the operator to start multiple motors in staggered fashion rather than simultaneously.

The typical induction motor draws a high current when heavily loaded, as the rotor is slowed by the counter torque of the increased load, necessitating the use of a separate protective device or circuit. To compensate for these large currents and limit the possibility of winding damage during such high load conditions, the stator magnetic flux density must be maintained by design at comparatively low levels during normal operations. Accordingly, a larger motor than would otherwise be required to produce the same power output is typically needed.

Induction motors also experience electrical losses, related, for example, to 1) the AC resistance of the winding conductor (s) ; and 2) the properties of the magnetic stator core ("core losses"). Core losses are attributable to a variety of effects, notably including magnetic hysteresis and eddy (circulating) currents. The magnetization process includes alignment of magnetic dipoles of the core material under the influence of a magnetic"H"field caused by electrical current, and is represented by the hysteresis curve of Figure 2. So-called"hard"materials (such as those typically used in permanent magnets) have a comparatively high coercivity, and require a large external field and significant energy to

realign their dipoles."Soft"magnetic materials (such as those in motor stator cores) are more easily aligned with less external field. The area within the hysteresis curve of Figure 2 is related to the coercivity of the material ; a hard material has a greater bounded area than a soft material under the same conditions, and therefore greater hysteresis losses for the same ac frequency. The energy required to realign magnetic dipoles each cycle is lost as hysteresis losses. Another motor limitation is core saturation, when increasing the electrically induced magnetic (H) field fails to align more core domains to generate significantly more magnetic flux (B) within the core, which may lead to loss of inductance and excessive currents.

Eddy currents are localized circulating currents within a conductor or magnetic core which may arise due a variety of factors, including spatially and/or temporally non-uniform magnetic fields, and conductor material imperfections or inclusions. Eddy current magnitudes and corresponding losses may be reduced, for example, by using smaller diameter, layered, or segmented conductors or core elements. Another method of reducing eddy current losses is to control the magnetic flux density and uniformity.

Prior art designs have attempted to control stator core flux density to mitigate the effects of hysteresis and eddy current losses. For example, U. S. Patents 4,063, 135,4, 132,932, 4,152, 630, and 4,187, 457 to Wanlass generally disclose an alternative induction motor winding arrangement using one or more capacitors in series with the phase (stator) windings of the motor; see Figures 3a and 3b, which illustrate two exemplary prior art winding configurations. U. S. Patent 4,095, 149, also to Wanlass, describes maintaining the stator core in partial saturation as a function of motor load to reduce stator core energy storage capacity and associated losses.

Prior art efforts to enhance efficiency, and to reduce inrush and no load currents, reflect the great value of such improvements, but have not adequately effected such improvements. An improved motor connection and winding arrangement is accordingly needed which has a combination of one or more of the following characteristics: comparable size and weight to prior art induction motors for comparable mechanical performance; reduced AC core losses ; higher efficiency; reduced currents under some or all loading conditions; reduced inrush starting current; and reduced temperature rise. An ideal motor has a combination of all of the foregoing characteristics.

Summary of the Invention The present invention addresses the above goals by providing an improved polyphase induction motor and winding employing capacitance in parallel with one or more properly wound stator windings.

One aspect of the invention includes a method of connecting polyphase power to a polyphase induction motor having a primary winding including a plurality of first phase windings connected to each other. The method includes disposing a tap between a center and a first end of each of the first phase windings, and connecting a capacitive element in parallel to a portion of the phase winding between the tap and a second end of the phase winding opposite the first end of the phase winding, and connecting one phase of a polyphase alternating current power source to an end of each phase winding. The capacitive elements alternately charge and discharge during the application of a polyphase alternating current to the induction motor winding.

The method of connecting polyphase power to a polyphase induction motor may also include any combination of many other steps or acts, including: constructing the primary winding with three individual tapped phase windings,

and providing a three phase power source to the motor; making the tap connection at about 64% of the turns of each phase winding; and connecting another capacitive element between the tap and the first end of each phase winding. In any case, the alternating current may have a substantially sinusoidal waveform, and the tapped phase windings may be connected in either a delta or a wye configuration, and a neutral connection may be provided for the wye configuration. Moreover, the connection method may also include connecting a secondary winding having second phase windings parallel to the first phase windings, and the second phase windings may have capacitive elements connected in parallel, and may have taps disposed between a middle and a first end of the second phase windings (as do the first phase windings). The method may include controlling the tap connection so as to vary its location as a proportion of turns between the center and the first end of a phase winding, which may be effected with a switch.

Another aspect includes a polyphase induction motor having a motor casing, a rotor rotatably mounted to the casing, and a stator fixed to the casing and substantially surrounding the rotor. The stator generates a rotating magnetic field in the area of the rotor using a polyphase stator winding which includes a primary winding having a plurality of first phase windings electrically connected to at least one other of the first phase windings. Each phase winding has a corresponding first end, a corresponding second end, and a corresponding tap disposed between a center and the corresponding first end. At least one of the first phase windings has a corresponding capacitive element connected in parallel between the corresponding tap and the corresponding second end.

Each of the first phase windings may have a first corresponding capacitive element connected in parallel between the corresponding tap and the corresponding second end, and a second corresponding capacitive element may be connected in parallel between the corresponding tap and the corresponding first end of each phase winding which has a parallel first capacitive element. The rotor may, for example, be wound or have a squirrel cage configuration.

The first capacitive elements may be parallel to about 64% of the corresponding first phase windings. The capacitive elements may be about equal to each other in value, and the taps of each phase winding may be at about the same location, in turns, as the others. However, the tap location may also be made at a variable proportion of a distance in turns from the center to the first end of the phase winding. The motors may be, for example, delta or wye configured.

Yet another aspect includes a polyphase induction motor winding which has a tapped three-phase winding arranged in a predetermined configuration, with the taps being disposed in the vicinity of 64% of a turns distance from a second end toward a first end of each individual phase winding. At least a first capacitive element is connected in parallel between the tap and the second end of each phase of the tapped winding, and the first capacitive elements alternately charge and discharge during the application of a three-phase alternating current to the polyphase induction motor winding. The polyphase induction motor may also have at least a second capacitive element connected in parallel between the tap and the first end of each phase of said tapped winding.

A further aspect includes a three-phase induction motor having a rotor rotatably mounted within, a stator having a magnetically permeable core and substantially surrounding said rotor and including a three-phase stator winding having three phase windings arranged in a predetermined configuration, each winding being electrically connected to another, and being tapped at a tap point which is not centered on the winding. It includes at least a first

capacitive element connected in parallel between the tap point and an end of each of said tapped phase windings, and the at least one capacitive element alternately charges and discharges during the application of a three-phase alternating current to the stator winding. The three-phase induction motor may also have at least a second capacitive element connected in parallel between the tap point and an opposite end of each of the tapped phase windings.

Yet a further aspect includes a method of operating an induction motor including a polyphase stator winding having a plurality of individual phase windings and a rotor, the method including applying a polyphase alternating current to the (single) polyphase winding, and generating a rotating magnetic field, in the region of said rotor, rotating at a first speed. The rotor is allowed to rotate at a second speed in response to the rotating magnetic field. The method includes passively charging and discharging, during operation of the motor, at least a first capacitive element which is connected in parallel between an end and an off-center tap of a respective one of the individual phase windings.

The method may also include passively charging at least a second capacitive element during operation of the motor, the second capacitive element being connected in parallel between the off-center tap and an opposite end of the respective one of the individual phase windings. The first, or the first and second, capacitive elements may be passively charged and discharged in parallel with one or more portions of each of the individual phase windings. The capacitance of said at least one capacitive element may further be varied after connection to said phase winding to optimize a parameter associated with said motor, such as motor efficiency. The polyphase alternating current applied to the polyphase winding may, for example, be three-phase current. The at least one capacitive element may be connected using at least one switch element electrically in series with the at least one capacitive element.

Another aspect includes a polyphase induction motor having a rotor rotatably mounted within, and means for generating a rotating magnetic field in the vicinity of the rotor. The means for generating a rotating magnetic field includes a magnetically permeable stator core and a first winding arranged in a predetermined configuration. A second winding is also arranged in the predetermined configuration, and is tapped and electrically connected to said first winding. The taps of the second winding are disposed between a middle and a first end of each individual phase winding of the tapped second winding, and passive capacitive elements are connected between each tap and a second end of each individual phase winding, for storing energy. The motor may be configured in either a delta configuration or a wye configuration, for example.

Brief Description of the Drawings Figure 1 a is a schematic diagram of a prior art motor in a"delta"configuration.

Figure 1 b is a schematic diagram of a prior art motor in a"wye"configuration.

Figure 2 is an illustration of a hysteresis loop for a magnetically permeable material.

Figure 3a is a schematic diagram of a"wye"configured, controlled flux density motor.

Figure 3b is a schematic diagram of a"delta"configured, controlled flux density motor.

Figure 4 is a schematic diagram of a new"delta"induction motor winding.

Figure 5 is a schematic diagram of another new"delta"wound induction motor having both primary and secondary phase windings capacitively paralleled.

Figure 6 is a schematic diagram of a new"wye"configured induction motor.

Figure 7 is a schematic diagram of another"wye"configured induction motor with selectively tunable and switchable capacitive elements and variable winding taps.

Figure 8 is a side cross-sectional view of an exemplary new induction motor.

Detailed Description of the Invention Reference is made to the drawings, in which like numerals refer to like parts.

Figure 4 shows a first embodiment of an induction motor winding. The polyphase winding 100 includes a plurality of primary phase windings 102 arranged in a delta configuration and connected to a source via a plurality of line terminals 104. Three primary windings 102 or"phases"are shown, due to the widespread use of three-phase ac power (especially in larger industrial applications, due to the benefits of three-phase power for generation and transmission), although it should be appreciated that the skilled person may employ the present techniques successfully with other numbers of primary phase windings, as well. The phase windings 102 and 106 are typically metallic conductors (copper is a good choice, although other conductive materials may be substituted) which are ultimately wound around or within a magnetically permeable stator core using any one of a number of well known winding techniques, as described below in reference to Figure 8. The overall motor winding 100 is wound so as to generate a rotating magnetic field within the stator which acts upon the rotor conductors (not shown).

Figure 4 illustrates primary phase windings 102, which are shown without taps, as well as a set of tapped secondary phase windings 106, connected electrically in parallel with the primary phase windings. Capacitive couplings 110 are connected in parallel with portions of the secondary phase windings 106, for example from the winding node 121 at one end of the winding to the tap 116, or from the tap 116 to the winding node 121 at the other end of the winding 106. The capacitive couplings 110 typically include a pair of electrical conductors 112 connecting to one or more capacitive elements 114. Although capacitive couplings 110 are shown connected in parallel to both sides of the three illustrated tapped phase windings 106, for some purposes only a single capacitive coupling 110 is used with each tapped phase winding 106, and indeed capacitive couplings 110 need not be used on all tapped phase windings 106. The taps 116 may be physically constructed by looping the conductor (s) of the capacitive couplings <BR> <BR> 110 onto the windings 106 at the prescribed location (e. g. , number of turns) without separating the winding 106. The tap locations 116 are selected based primarily on the calculated density of ferrous material in the stator core, which varies for each individual core. Core density may be calculated using relationships well known in the art, such as: 1 T2 =Tl 3 (wye) or (delta) x f- H in Flux per pole<BR> Core Density = 2 x effective core area

where: T, = Number of turns on a given winding (tap point) En= Voltage HPnm Horsepower Fn-Electrical frequency CFn-Chord factor Nn= Circuits Pu number of poles A typical location for the tap points is 64% of the total number of turns of the given phase winding, although it will be recognized that other locations may be used. Also, while fixed in the present embodiment, the taps 116 may be variable or adjustable if desired, as described further below.

Figure 4 shows capacitive couplings 110 including a single capacitive element 114 in series with the respective conductors 112. It can be appreciated, however, that a number of alternate arrangements may be used to provide the desired electrical properties depending on the application, such as multiple capacitors in series or parallel, or one or more capacitors in conjunction with another electrical element (such as a resistor or inductor). Furthermore, while a discrete capacitor is typically used as the capacitive element 114 in this embodiment, other devices having capacitive properties may be substituted.

The energy stored by the capacitors 114 during charging, and released during discharging, is described generally by the relationship : E 2 CV2 Eqn. (1) Where: E = Energy (Joules) C-Capacitance (farads) V = Voltage across capacitor (volts) The capacitance values of the capacitive elements 114 of Figure 4 may be chosen according to the following guidelines: Capacitance (KVAR, per phase) = 0.12 x HP (per phase) Eqn. (2) and Capacitance (microfarad"OF,"per phase) = where: HP = Horsepower (1 HP approx. equals 746 Watts)

KVAR = Kilo-volt-amps (reactive) VR = Rated Voltage V= Line voltage For example, capacitance values of 8.85 OF would be used in a three-phase, 480 V motor rated at 3.73 KW (5 HP). If 8.85 OF capacitors are not available, the next nearest standardized increment (such as 10 OF) may be used with little impact on motor performance.

The capacitance for each phase may be chosen to be equal, thereby providing balance between the phases, and may be chosen (whether equal or not) such that the performance of the motor is optimized for the given line voltage and power rating. It will be recognized that the system may be operated in an unbalanced configuration if desired, particularly in conjunction with unbalanced power sources.

The winding 100 of Figure 4 operates in the following manner. When a polyphase alternating current is applied to the winding via the terminals 104, voltages are induced in each of the individual phase windings 102.

Current flow in the windings results from the induced voltages ; however, due to the inductive properties of the phase windings 102, the current and voltage typically peak at different times. As the current in a given phase winding 102, 106 increases, the resulting magnetic field (H) generated by the phase winding also increases. This magnetic field acts to align the magnetic domains within the local region of the stator core, and increase the internal magnetic flux density (B) of the core material. In tandem, the capacitive elements 114 associated with that phase are charged, thereby storing energy. Unlike prior art motors in which complete or near-complete saturation of the magnetic core is rapidly reached when the inductive energy storage capacity of the winding is exceeded, the present invention utilizes the capacitive elements 114 to limit the energy storage (and therefore saturation) within the stator core, thereby controlling the flux density within the core. As the voltage for a given phase winding decreases, the capacitor (s) act as an energy source and begin to discharge, thereby maintaining current flow through the phase windings 102, 106. In this fashion, the capacitive elements 114"buck"the field generated by the phase winding, alternatively storing energy during periods of energy storage within the core and inductance of the winding, and discharging when the phase voltage is reversing. This has the net effect of limiting the effective flux density and saturation of the core, and therefore of reducing the associated ac losses.

Figure 5 illustrates another delta configuration induction motor, but with two sets of capacitive couplings 110, one set connected to the primary windings 102, and another set connected to the secondary windings 106 for each phase. A similar effect may be obtained as with the configuration of FIG. 5, but smaller capacitors 114 may be used to maintain the same energy storage per phase. Again, though capacitors 114 are shown connected to each tap of each phase winding, in some instances the capacitance is not needed on both sides of a winding, and moreover for some power source and motor combinations capacitance will not be needed on all phases. The primary 102 and secondary 106 windings for each particular phase are typically connected together at a first end (connection 104 to a first phase, e. g., QA) and a second end (connection 104 to a second phase, e. g., OB). It should be noted that one (or both) capacitor (s) may be omitted from some phase windings. In some embodiments, one or more of the primary

windings 102 may have a capacitive coupling 110 only between its tap 116 and the first end which it shares with a corresponding secondary winding 106, while one or more of the secondary windings 106 has a capacitive coupling 110 only between its tap and the second end which it shares with a corresponding primary winding 102. If each phase winding set is thus arranged, then the capacitors for each phase set are opposite disposed such that they do not share a common connection point. Rather, the first capacitor for the phase winding set is connected from the first end (e. g., OC) of the phase winding set to the tap 116 of the primary winding 102 of the set, while the second capacitor for the phase winding set is connected from the second end (e. g., DA) of the phase winding set to the tap 116 of the secondary winding 106 of the set.

Figure 6 illustrates an induction motor winding in a"wye"configuration of the type well known in the electrical arts. Unlike the delta configuration, the line and phase currents in a balanced wye winding are equivalent, while the line voltage is-\/3 times the phase voltage. Similar to the delta configurations of Figures 4 and 5, the wye winding of Figure 6 may utilize one or more capacitive couplings 110 between taps 116 located on the individual phase windings 302,306 to effect energy storage and transfer within the windings and magnetic core. Figure 6 illustrates a set of primary phase windings 302 electrically connected at a primary common node 304, and set of secondary phase windings 306 which are electrically connected at a secondary common node 308. The primary and secondary windings 302,306 for each phase are also electrically connected to each other at the incoming conductor 310 for each phase. If a neutral connection is not provided to the common nodes 304 and 308, these connections may be left disconnected from each other.

Separate capacitive couplings 110 with capacitors 114 may be provided for each phase winding (either or both primary and secondary), and on one end may be electrically connected to their respective winding via taps 116.

The other end of each capacitive coupling 110 is connected to the winding conductor for that phase adjacent to the primary (or secondary) common node 304,308. Note also that neutral or ground wires connected to the primary and secondary winding node (s) 304,308 may be employed if the system is unbalanced. As shown, a capacitor 114 is connected in parallel to one of the two portions of each phase winding defined from the tap 116 to the first or second end of the phase winding (302,306). However, in other embodiments capacitors 114 may be provided on only some phase windings. Moreover, in yet other embodiments capacitors 114 may be provided in parallel to both portions of one or more phase windings. Capacitors 114 may also be oppositely disposed within each phase winding set, as described above with respect to Figure 5, wherein one capacitor 114 is connected from the common node 304 to the tap 116 of the primary phase winding 302 (as shown), while another capacitor 114 is connected from the tap 116 of the secondary winding 306 (typically for the same phase) to the phase connection point 310 (e. g., DA). The second capacitor is thus connected parallel to the opposite portion of the secondary winding from that which is shown.. The tap points 116 are typically not centered on the phase windings (in terms of turns), and may for example be at about 64% of the turns from the common node 304 or 308 to the phase conductor connection 310. Though typically located the same proportion of turns along the primary and secondary windings of a particular phase, the primary winding tap 116 may also be located at a different turn proportion than the secondary winding tap 116.

Figure 7 illustrates adjustment and modification features in the context of a polyphase induction motor having three phase windings in a wye configuration. Figure 7 illustrates the use of switch elements 360a in series with the capacitive couplings 110, switch elements 360b in phase windings, variable capacitors 114b, and variable location taps 116a. By means of the illustrated adjustment features, or equivalent means of varying the motor characteristics, the motor may be optimized for a wide range of conditions. In addition to providing adjustment for different operating conditions, the adjustability provided by features such as those shown in Figure 7 may be particularly useful for use with power sources whose electrical characteristics, such as voltage, waveform, balance between phases, and particularly frequency, varies from time to time. For example, in the case of variable frequency operation of a motor, the capacitance may be adjusted stepwise by switching a variety of different valued capacitors, under control of a program which recognizes the frequency at which the motor is driven, to approximately accord with the value explained above.

The switch elements 360a, 360b may be of any type having a current and voltage rating sufficient for the intended application. The use of the switch elements 360a in the primary and secondary winding capacitive couplings 110 permits the operator to selectively insert or remove capacitances 114a, 114b in order to obtain the desired level of performance for a specific operating condition. For example, a particular motor may operate most efficiently at low load with only the primary phase winding capacitive elements 114a in the circuit, in which case the secondary winding capacitors 114b may be switched out of the circuit when loads are low to increase overall motor efficiency.

Similarly, it may be desirable under certain circumstances to operate the motor without the secondary phase windings. In this case, the operator may simply open the switch elements 360b associated with the secondary windings. These switch elements 360b may be"ganged" (dotted line 366) such that the switches operate in tandem to simultaneously insert or remove all of the phase windings from the winding circuit. The switch elements 360a for the primary winding couplings 110 and the switch elements 360b for the secondary windings may all be opened, thereby electrically isolating the secondary windings for each phase from the capacitive couplings 110, such that the motor is configured as a"standard"motor, i. e. , without parallel capacitances.

Variable capacitors 114a, 114b permit variation or tuning of the capacitances both 1) between phases; and 2) between primary and secondary phase windings. This allows for optimization of motor efficiency due to factors including (i) variations in the impedance or other electrical properties of each of the individual phase windings, and (ii) spatial variations in the stator core iron density.

The capacitance may also be adjusted for variable frequency drive (VFD) operation. This may be accomplished by first determining optimal capacitance Co for a variable frequency motor operating at 60 Hz, for example in accordance with Eqn. 3, or to empirical testing. Then, C may be varied as C (f), a variable function of the operating frequency f in Hertz. Operating frequency f may be expressed as a frequency ratio, FR = f 160 ; K is a constant value generally between 1 and 2, depending upon motor construction parameters; whereupon C (f) = Co I FRK. Additionally, the present invention contemplates dynamic tuning of the variable capacitors 114a, 114b in response to parameters (such as phase or line current) sensed or measured from the motor during operation. Such

dynamic tuning can easily be accomplished using any number of control arrangements well understood in the electrical arts. As one example, the sensed line current for a motor operating at a constant may be input to a processor and control circuit which varies the capacitance value of one or more of the variable capacitors 114a, 114b through a program band. The control circuit would then maintain the variable capacitance at a value that minimizes line current (assuming constant load) until the load is again varied.

High current, high voltage variable capacitors are available, but may be bulky and/or expensive. Step-wise variable capacitance may be constructed from a plurality of capacitors, typically of different values, connected in parallel combinations of one or more capacitances. The switch 360a may be configured to provide connection to such a combination of capacitors. Continuous variability may be obtained, for example over a range of 2'capacitance units (the units may be any convenient value, such as 1 OF) by providing a variable capacitor having 0 to 1 unit of capacitance in the place of a capacitor 114a or 114b, and switchably providing fixed capacitors in parallel thereto with binary capacitance values of 1,2,..., 2 ("') capacitance units.

Variable winding taps 116a may be employed to allow adjustment of the tapping location (and resultant variation of the electrical performance of the winding 100) as desired. Such variable taps may be constructed using any number of techniques, including manually relocatable taps, motor driven load/no-load tap changers such as those used on large power and distribution transformers, or a plurality of discrete taps selectable manually or by means of a selector switch.

Although two windings are shown for each phase, for many purposes a single phase winding for each phase will suffice in many circumstances, obviating switch 360b. In other circumstances, a multiplicity of phase windings may be desired for each phase, in which event the switches 360b may have a plurality of connections by means of which any combination of a plurality of auxiliary phase windings may be connected.

The selectable and variable features described with respect to Figure 7 may equally be employed with other configurations, including the delta configurations illustrated in Figures 4 and 5. Moreover, the capacitor juxtaposition described with respect to Figures 5 and 6 is also applicable to motors configured according to Figure 7, such that a capacitance 114a connected to the tap 116a of a primary phase winding is connected to one end of the phase winding, e. g. a phase connection 310 such as OC (which is parallel to the other portion of the primary phase winding from that which is shown), while a capacitance 114b is connected from the tap 116a of the secondary phase winding to the common connection point, as shown. The windings and capacitances may be switchably connectable through switches 360a or 360b, as shown and described.

Figure 8 is a side cross-sectional view of an exemplary induction motor configuration for present purposes.

The motor 400 comprises 1) a housing 402 including a center portion 404 and end bells 406,408, 2) a stator 410 including magnetically permeable core 412 and windings 100, and 3) a rotor assembly 416 having a main shaft 420, a series of longitudinal conductors 422 and end plates 423 in the familiar"squirrel cage"arrangement, and a magnetically permeable rotor core 425. A wound rotor may also be used. Journal and thrust bearings 424 of the type well know in the mechanical arts are further included within each of the end bells 406,408 to provide longitudinal and

transverse support for the rotor assembly 416. It is noted that any of the aforementioned embodiments of windings <BR> <BR> 100 (e. g. , as depicted in Figures 4 through 7 herein) may be used within the motor 400 of Figure 8, depending on the desired properties of the motor.

The housing center portion 404 and end bells 406,408 of the motor 400 may be constructed of any material, for example steel, which provides sufficient rigidity for the rotor and stator assemblies. The skilled person will understand the many other issues, such as, for example, heat transfer and bearing support, which may influence the mechanical design of the motor. The magnetically permeable stator core 412 and rotor core 425 may be laminated to reduce eddy current loss, and are generally comprised of iron and a high grade silicon steel, in varying proportions.

Motors designed to operate at higher frequencies, or with substantial high frequency components in the voltage, may utilize ferrites or powdered iron composites to further reduce eddy currents. The stator core 412 is further constructed and sized so as to fit within the housing 402 and maintain a close tolerance (when wound) with the rotor <BR> <BR> assembly 416. The stator and rotor core material is chosen to be magnetically"soft", i. e. , to have comparatively low coercivity, so as to further mitigate ac core losses. The windings 100 are typically wound into"notches"or grooves within the stator core 412 using a random or"mush"winding technique, but it will be appreciated that any compatible winding method and physical configuration may be employed in conjunction with the present invention. Ideally, the gap 428 between the rotor assembly 416 and the stator 410 is minimized to obtain the maximum possible degree of flux coupling between the rotor and stator while still allowing for eccentricities andlor thermal expansion and contraction of rotor and stator components during operation. The motor 400 is typically provided with an electrical junction box 430 to permit termination of the individual phase leads (and ground lead, if required), commonly referred to as "pigtails." While the embodiment of Figure 8 illustrates an induction motor having magnetically permeable core material located within both the stator and rotor, the motor 400 may alternatively be constructed with the magnetic core located only in the stator.

The present invention may be embodied in many ways, as will be clear to the skilled person in view of the foregoing disclosure, which may result in a wide range of performance. However, performance data obtained from working prototypes of induction motors as disclosed herein indicate that motor efficiency is increased throughout the <BR> <BR> operating load range over standard prior art induction motors (i. e. , absent capacitive couplings). Compared to a conventional 480 V, three-phase induction motor, no load steady state operating current for either delta or wye wound capacitive motors is typically reduced by roughly 30 %, and both full load and inrush currents are typically reduced by about 20%. Operating temperatures also reflect measurable improvements.

While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art while remaining within the scope of the invention. This description is not intended to be limiting, but rather should be taken as illustrative of the general principles of the invention, such that the skilled person may utilize the invention over the wide range of embodiments which it encompasses. The scope of the invention should therefore be determined with reference to the claims.