Patent Publication Number: US-6713930-B2

Title: Power generator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/749,197, filed Dec. 27, 2000, now U.S. Pat. No. 6,608,419 the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates generally to a power generator, and in particular to a reduction of heat dissipation and undesirable voltage differentials in a power generator. 
     Thermal issues are critical to the design of a high power electrical generator and can serve as limiting factors in generator operation. A typical design of a high power electric generator includes a rotor having rotor windings rotatably disposed inside of a stator having stator windings. The rotation of the rotor induces an electromagnetic field in the stator, which electromagnetic field in turn induces a current in, and voltage drop across, the stator windings. However, the electromagnetic field also induces eddy currents in the stator, which is magnetically and electrically resistive. The eddy currents cause the dissipation of energy in the stator in the form of heat and impose a thermal constraint on the operation of the generator. 
     In order to improve generator efficiency and reduce generator size, generator manufacturers are constantly endeavoring to improve the thermal performance of the generator. For example, a prior art design of a high power electrical generator  100  is illustrated in FIGS. 1,  2 , and  3 . FIG. 1 is a cross-sectional view of generator  100  from an isometric perspective. FIG. 2 is a cut-away view of generator  100  along axis  2 — 2 . As shown in FIGS. 1 and 2, electrical generator  100  includes a substantially cylindrical stator  102  having a stator core  104  and housing a substantially cylindrical rotor  110 . Multiple circumferentially distributed and axially oriented keybars  118  are coupled together at each of a proximal end and a distal end by one of multiple flanges  204  (not shown in FIG.  1 ). Each keybar  118  is coupled to an outer surface of stator  102 . The multiple keybars  118 , together with the multiple flanges  204 , form a keybar cage around the stator  102 . 
     An inner surface of stator  102  includes multiple stator slots  106  that are circumferentially distributed around an inner surface of stator  102 . Each stator slot  106  is radially oriented and longitudinally extends approximately a full length of stator  102 . Each stator slot  106  receives an electrically conductive stator winding (not shown). 
     Rotor  110  is rotatably disposed inside of stator  102 . An outer surface of rotor  110  includes multiple rotor slots  114  that are circumferentially distributed around the outer surface of rotor  110 . Each rotor slot  114  is radially oriented and longitudinally extends approximately a full length of rotor  110 . An air gap exists between stator  102  and rotor  110  and allows for a peripheral rotation of rotor  110  about axis  130 . 
     Each rotor slot  114  receives an electrically conductive rotor winding (not shown). Each rotor winding typically extends from a proximal end of rotor  110  to a distal end of the rotor in a first rotor slot  114 , and then returns from the distal end to the proximal end in a second rotor slot  114 , thereby forming a loop around a portion of the rotor. When a direct current (DC) voltage differential is applied across a rotor winding at the proximal end of rotor  110 , an electrical DC current is induced in the winding. 
     Similar to the rotor windings, each stator winding typically extends from a proximal end of stator  102  to a distal end of the stator in a first stator slot  106 , and then returns from the distal end of the stator to the proximal end of the stator in a second stator slot  106 , thereby forming a stator winding loop. A rotation of rotor  110  inside of stator  102  when a DC current is flowing in the multiple windings of rotor  110  induces electromagnetic fields in, and a passage of magnetic flux through, stator  102  and the loops of stator windings. The passage of magnetic flux in turn induces an alternating current in each stator winding and eddy currents arid magnetic and resistive losses in stator  102 . 
     FIG. 3 is a side view of a cross-section of generator  100  and illustrates a coupling of magnetic flux  302  from rotor  110  to stator  102  as the rotor rotates inside of the stator. Magnetic flux  302  generated by a rotation of rotor  110  couples to and passes through the surrounding stator  102 . Magnetic flux  302  induces a flow of multiple eddy currents in the magnetically and electrically resistive stator  102 , which currents cause energy dissipation and heat generation in the stator that poses a thermal constraint on the operation and capacity of generator  100 . As a result, generator designers are always seeking improved methods of thermal management for power generator stators. 
     One known thermal management technique is the construction of stator core  104  from multiple ring-shaped laminations  402 . FIG. 4 is a partial perspective of generator of  100  and illustrates a typical technique of constructing stator core  104 . As shown in FIG. 4, the multiple ring-shaped laminations  402  are stacked one on top of another in order to build up stator core  104 . Each lamination  402  is divided into multiple lamination segments  404 . Each lamination segment  404  includes multiple slots  120  (not shown in FIG.  4 ), wherein at least one slot  120  of each segment  404  aligns with one of the multiple keybars  118 . Each keybar in turn includes an outer side  124  and an inner, or locking, side  122  that mechanically mates with one of the multiple slots  120 . Stator core  104  is then constructed by sliding each lamination segment  404 , via one of the multiple slots  120 , into the keybar cage formed by the multiple keybars  118 . The coupling of one of the multiple slots  120  of a lamination segment  404  with a locking side  122  of a keybar  118  affixes each lamination segment  404 , and thereby each lamination  402 , in position in stator  102 . By building stator core  104  from stacked laminations, as opposed to constructing a solid core, circulation of a current induced in stator  102  is limited to a lamination, thereby restricting current circulation and size and concomitantly reducing stator heating. 
     The above thermal management technique does not fully address thermal problems caused by a “fringing” of magnetic flux at each end of stator  102 . As illustrated in FIG. 3, the “fringing”  304  of magnetic flux at each end of stator  102  results in a number of flux lines  302  axially, or normally, impinging upon each end of stator core  104  and upon the multiple flanges  204 . A result of the fringing magnetic flux  304  is a greater flux density at each end of stator core  104  as compared to more centrally located portions of the stator core. The greater flux density at each end of stator core  104  results in increased eddy currents and greater heat dissipation in the laminations of stator core  104  near the ends of the stator, as opposed to more centrally located laminations. The fringing effect also results in increased eddy currents and greater heat dissipation in each flange  204 . 
     In order to combat a buildup of heat at each end of stator  102  due to fringing magnetic flux  304 , an inner surface of stator core  104 , at each end of the stator core, is radially stepped away  202  from rotor  110 , as shown in FIGS. 2 and 3. By increasing the distance between rotor  110  and stator core  104  at each end of the stator core, an amount of flux axially impinging upon each end of the stator core is reduced. However, the stepping of the ends of stator core  104  away from rotor  110  is only a partial solution to the stator core heat dissipation problem presented by “fringing” and does not address the problem of heat dissipation in the multiple flanges  204 . 
     A portion of the fringing magnetic flux  304  also impinges upon the ends of each of the multiple keybars  118 . The impinging of fringing magnetic flux upon an end of a keybar  118  can produce an uneven coupling of flux into each keybar, with a greater flux density at a keybar end than in more centrally located portions of the keybar. The uneven coupling of flux can produce keybar voltages and keybar currents in each keybar  118 . In “turn, the existence of keybar voltages in each keybar  118  can produce keybar voltage differentials between keybars, which voltage differentials can be transmitted to the lamination segments  404  coupled to the keybars. When a voltage differential is transmitted to adjacent lamination segments  404 , the voltage differential can cause arcing between the adjacent segments, overheating in stator core  104 , and reduced generator  100  performance. The arcing can also create localized heating in stator core  104 , causing lamination segments  404  and lamination rings  402  to fuse together. Such fusing can spread quickly in generator  100  as the lamination segments  404  and lamination rings  402  short circuit to each other, resulting in damage to the generator. 
     Therefore, a need exists for a method and apparatus for further reducing the heat dissipated in the ends of a stator core and in a flange and for providing for a more uniform coupling of flux into a keybar. 
     BRIEF SUMMARY OF THE INVENTION 
     Thus there is a particular need for a method and apparatus that reduces the heat dissipated in the ends of a stator core and in a flange and that provides for a more uniform coupling of flux into a keybar. Briefly, in accordance with an embodiment of the present invention, a flux shunt is provided for insertion adjacent to an inner surface of the stator and approximately at an end of the stator and wherein a permeability of the flux shunt is greater than a permeability of the stator core. The flux shunt reduces the amount of magnetic flux impinging in an axial direction upon the flanges and upon ends of the keybars and the stator core. By reducing the impinging flux, the flux shunt reduces the heat dissipated in the ends of stator and further provides for a more even coupling of flux into a keybar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric perspective of an end view of a cross-section of a power generator of the prior art. 
     FIG. 2 is a cut-away view of the prior art power generator of FIG. 1 along axis  2 — 2 . 
     FIG. 3 is side view of a cross-section of the prior art power generator of FIG.  1  and illustrates a coupling of magnetic flux, from a rotor of the power generator to a stator of the power generator as the rotor rotates inside of the stator. 
     FIG. 4 is a partial perspective of the prior art power generator of FIG.  1 . 
     FIG. 5 is an end view of a cross-section of an exemplary power generator from an isometric perspective in accordance with an embodiment of the present invention. 
     FIG. 6 is a cut-away view of the power generator of FIG. 5 along axis  7 — 7  as shown in FIG. 5 in accordance with an embodiment of the present invention. 
     FIG. 7 is a side view of a cross section of the power generator of FIG. 5 in accordance with an embodiment of the present invention. 
     FIG. 8 is atop view of an exemplary lamination segment in accordance with an embodiment of the present invention. 
     FIG. 9 is a cross-sectional side view of an end of the power generator of FIG. 5 in accordance with an embodiment of the present invention. 
     FIG. 10 is a logic flow diagram of steps executed in order to control flux in a power generator in accordance with an embodiment of the present invention. 
     FIG. 11 is a logic flow diagram of steps executed in order to reduce a keybar voltage of a power generator in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 5,  6 , and  7 , an exemplary power generator  500  that operates at a reduced stator temperature level and at reduced keybar voltage differentials is illustrated. FIG. 5 is an isometric perspective of an end view of a cross section of power generator  500 . FIG. 6 is a cut-away view of electrical generator  500  along axis  6 — 6  as shown in FIG.  5 . FIG. 7 is a cross-sectional side view of generator  500 . Generator  500  includes a substantially cylindrical stator  502  having a stator core  504  and housing a substantially cylindrical rotor  510  rotatably disposed inside of the stator. Multiple circumferentially distributed and axially oriented keybars  518  are coupled together at each of a proximal end and a distal end by one of multiple flanges  604  (not shown in FIG.  5 ). Each keybar  518  is coupled to an outer surface of stator  502 . The multiple keybars  518 , together with the multiple flanges  604 , form a keybar cage around the stator  502 . 
     An inner surface of stator  502  includes multiple stator slots  506  that are circumferentially distributed around the inner surface of the stator. Each stator slot  506  is axially oriented and extends approximately a full length of stator  502 . Each stator slot  506  receives an electrically conductive stator winding (not shown). Between each pair of adjacent stator slots  506  is a stator tooth  508  that, similarly, is circumferentially distributed around the inner surface of stator  102  and extends approximately a full length of stator  502 . Each stator tooth  508  is radially oriented and extends radially inward toward rotor  510  from stator  502 . 
     Similar to stator core  104  of the prior art, stator core  504  preferably includes multiple, stacked ring-shaped laminations that are each divided into multiple lamination segments. FIG. 8 is a top view of an exemplary lamination segment  800 . Lamination segment  800  includes a yoke  802  and one or more stator teeth  804 . Between each pair of stator teeth  804  is a stator slot  806 . Each lamination segment  800  further includes multiple dovetail-shaped slots  808  in an outer edge of the segment for mechanically coupling the lamination segment to one or more keybars  518 . In turn, each keybar  518  includes an outer side and an inner, locking side  810 . Locking side  810  includes a dovetail-shaped ridge that extends a length of the keybar and that is designed to mate with a dovetail-shaped slot  808  of a lamination segment  800 . Each ring-shaped lamination, and each lamination segment  800  associated with the lamination, is fixed in position in stator  502  by sliding each lamination segment  800  of the ring-shaped lamination onto a keybar  518  via the dovetail-shaped slots  808  and the corresponding dovetail-shaped ridge of the keybar. Multiple flanges  604  then hold the multiple keybars  518  and, in association with the keybars, the multiple ring shaped laminations in position in stator core  504 . 
     Rotor  510  is rotatably disposed inside of stator  502 . Similar to rotor  110  of the prior art, rotor  510  has an outer surface that includes multiple rotor slots  514 , which slots  514  are circumferentially distributed around the outer surface of rotor  510 . Each rotor slot  514  is radially oriented and extends approximately a full length of rotor  510 . Between each pair of adjacent rotor slots  514  is a rotor tooth  516  that similarly is circumferentially distributed around the inner surface of rotor  510  and extends approximately a full length of rotor  510 . Each rotor tooth  516  is radially oriented and extends radially outward toward stator  502  from rotor  510 . An air gap exists between stator  502  and rotor  510  that allows for a peripheral rotation of rotor  510  about axis  520 . 
     The multiple flanges  604  are each disposed adjacent to an end of stator core  504 . Disposed between each flange  604  and stator core  504  is an outside space block  606 . Each of the multiple flanges  604  is a ring-shaped metallic material that includes multiple keybar stud apertures (not shown) for receiving a keybar stud  608 . The apertures are circumferentially disposed around each flange  604  in positions that correspond to positions of keybars  518  around stator  502 . Each end of each keybar  518  includes a threaded keybar stud  608  that extends axially outward from the end of the keybar. Each flange  604  is placed on an end of stator  502  and over the keybar studs  608  such that each stud extends through the flange via a corresponding keybar stud aperture. Each flange  604  is then mechanically fastened onto an end of stator  502  and the multiple keybars  518  by multiple threaded nuts  610  that are each screwed onto a correspondingly threaded keybar stud  608 . 
     Similar to generator  100  of the prior art, each slot of the multiple rotor slots  514  receives an electrically conductive rotor winding (not shown) and each slot of the multiple stator slots  506  of generator  500  receives an electrically conductive stator winding (not shown). Each rotor winding typically extends from a proximal end of rotor  510  to a distal end of the rotor in a first rotor slot of the multiple rotor slots  514 , and then returns from the distal end to the proximal end in a second rotor slot of the multiple rotor slots  514 , thereby forming a loop around a portion of the rotor. Similar to the rotor windings, each stator winding typically extends from a proximal end of stator  502  to a distal end of the stator in a first stator slot of the multiple stator slots  506 , and then returns from the distal end of the stator to the proximal end of the stator in a second stator slot of the multiple stator slots  506 , thereby forming a stator winding loop. 
     A rotation of rotor  510  inside of stator  502  when a DC current is flowing in the multiple windings of rotor  510  induces magnetic fields in, and a passage of magnetic flux through, stator  502  and the loops formed by the stator windings. The passage of magnetic flux through the stator winding loops induces a current in the stator windings and a corresponding power generator output voltage. The rotation of rotor  510  also induces a “fringing” of the magnetic flux at each end of stator  502 . In order to combat a buildup of heat due to fringing, an inner surface of stator core  504  includes multiple steps  602  that radially step the stator core away from rotor  510  at each end of the stator core. However, the radial stepping  602  alone does not fully prevent an undesirable buildup of heat at each end of stator core  504 . Furthermore, the radial stepping  602  does not address the issue of “fringing” flux impinging upon each of the multiple flanges  604  or upon the ends of each of the multiple keybars  518 . In order to further reduce the heat buildup and to reduce the impinging of “fringing” flux upon the keybars  518  and flanges  604 , power generator  500  includes multiple flux shunts  522  that attract, and thereby redistribute, the fringing magnetic flux. 
     Each flux shunt  522  provides a low reluctance path for the fringing magnetic flux produced by a rotation of rotor  510 . By providing a low reluctance path, each flux shunt  522  attracts the fringing magnetic flux that would otherwise axially impinge upon a flange  604  and upon an end of each of stator core  504  and multiple keybars  518 . The fringing magnetic flux is thereby redirected from the flanges  604 , stator core  504 , and the multiple keybars  518  to the shunt  522 . By redirecting the fringing magnetic flux, each flux shunt  522  reduces the current induced in, and concomitantly the energy and heat dissipated in, stator core  504  and flanges  604  by the fringing flux. Furthermore, by redirecting the fringing magnetic flux, each flux shunt  522  reduces the fringing flux coupling into an end of each keybar  518  and provides for a more uniform coupling of magnetic flux into the keybar. A more uniform coupling of magnetic flux into each keybar  518  reduces a likelihood of an induction of keybar voltages and keybar currents in the keybar and reduces a development of keybar voltage differentials between each of the multiple keybars. 
     Preferably, each flux shunt  522  includes a magnetically isotropic material that is electrically highly resistive and thermally conductive and that has a higher axial permeability than stator core  504 . For example, a flux shunt  522  may include a powdered iron composition, wherein the powdered iron composition is electrically highly resistive and thermally conductive, has a high isotropic permeability, and, due the to powdered nature of the composition, will produce minimal current and low losses when a magnetic field is applied to the composition. Those who are of ordinary skill in the art realize that other high resistance, high isotropic permeability materials or compounds may be used in flux shunt  522  without departing from the spirit and scope of the present invention. 
     Each flux shunt  522  has a radially outer surface that is disposed adjacent to the inner surface, or teeth  508 , of stator  502  and a radially inner surface that is disposed opposite rotor  510 . Preferably, each flux shunt  522  is further disposed in a section of stator  502 , or stator core  504 , that is radially stepped away  602  from rotor  510 . In one embodiment of the present invention, a flux shunt of the multiple flux shunts  522  is disposed at a proximal end of stator  502 , or stator core  504 , and another flux shunt of the multiple flux shunts  522  is disposed at a distal end of the stator. However, in alternative embodiments of the present invention, flux shunt  522  may be inserted at either the proximal end of stator  502  or at the distal end of the stator. Furthermore, each flux shunt  522  is disposed in a manner such that the flux shunt does not obstruct the passage of the stator windings through stator core  504 . 
     In one embodiment of the present invention, a flux shunt  522  may be substantially cylindrically-shaped and disposed adjacent to the inner surface of stator  502  at approximately an end of the stator. Preferably, flux shunt  522  is radially stepped outward to mate with the multiple steps of a stepped region  602  of stator  502 . In another embodiment of the present invention, a flux shunt  522  may include multiple discrete rings that are each disposed adjacent to the inner surface of stator  502  and that each fits into one of the multiple steps included in each stepped region  602 . In yet another embodiment of the present invention, a flux shunt  522  may include multiple segments that are discretely disposed around the periphery of the inner surface of stator  502 , which segments may each mate with one or more steps of the multiple steps of a stepped region  602  of stator  502 . The multiple segments, in combination, may or may not completely encircle the interior of a stepped region  602  of stator  502 . In still another embodiment of the present invention, each ring or segment included in flux shunt  522  may include apertures that allow for the passage of gas through the shunt. 
     FIG. 9 is a partial side view of a cross-section of an end of stator  502  and rotor  510  in accordance with an embodiment of the present invention. Also shown in FIG. 9 is a retaining ring  902  and a centering ring  904  that fit over an end of the rotor windings (not shown) and that hold the windings in position as rotor  510  rotates inside of stator  502 . In one embodiment of the present invention, flux shunt  522  is retained in position relative to stator core  504  by a flux shunt retainer  906 . Flux shunt retainer  906  is disposed adjacent to the inner surface of flux shunt  522  and is affixed in position relative to stator core  504 . Those who are of ordinary skill in the art realize that there are many ways of either removably or permanently affixing flux shunt retainer  906  in position relative to stator  502  without departing from the spirit and scope of the present invention. For example, flux shunt retainer  906  may be fastened by bolts or screws onto outside space block  606  in order to hold flux shunt retainer  906 , and thereby flux shunt  522 , in position relative to stator core  504 . By way of another example, flux shunt retainer  906  can be welded to outside space block  606 , or outside space block  606  may be milled in such a manner that the outside space block includes an inner lip that functions as flux shunt retainer  906 . 
     Preferably, flux shunt retainer  906  is a substantially cylindrically-shaped ring that is disposed adjacent to the inner surface of flux shunt  522 . However, those who are of ordinary skill in the art realize that flux shunt retainer  906  may include any design intended to hold flux shunt  522  in position relative to stator core  504 , such as plates that are circumferentially disposed around the inner surface of flux shunt  522 , which plates may be individually axed to stator  502  or may be linked together to form a flux shunt retainer assembly that is affixed to stator  502 , without departing from the spirit and scope of the present invention. Preferably, each plate or the ring included in flux shunt retainer  906  is of a length ‘L’ that is sufficient to hold flux shunt  522  in position relative to stator core  504 , which length L may or may not be of a same length as flux shunt  522 . By axing flux shunt retainer  906  in position relative to stator  502 , flux shunt  522  is also affixed in position relative to the stator. 
     In another embodiment of the present invention, flux shunt  522  may be directly axed to outside space block  606  instead of using flux shunt retainer  906 . For example, flux shunt  522  may be attached to outside space block  606  by an adhesive or may be mechanically fastened to the outside space block by a fastener such as a bolt or a screw. In yet another embodiment of the present invention, flux shunt  522  instead may be axed to stator core  504 , preferably by an adhesive or alternatively by a mechanical fastener. The means used to affix flux shunt  522  in position relative to stator  502  is not critical to the present invention, and other means of affixing the flux shunt in position relative to the stator may occur to those of ordinary skill in the art without departing from the spirit and scope of the present invention. 
     By including multiple flux shunts  522  that are each disposed adjacent to an inner surface of stator  502 , power generator  500  is capable of operating at a lower temperature and at reduced keybar voltage differentials relative to the prior art. Each flux shunt  522  is disposed at either a proximal end of stator  502  or a distal end of the stator. Each flux shunt  522  has a high permeability and a low reluctance in all directions and attracts the fringing magnetic flux at the end of stator  502 , redirecting the flux away from a flange  604  and from the ends of each of stator core  504  and the multiple keybars  518 . By redirecting the fringing flux, each flux shunt  522  reduces eddy currents induced in, and energy and heat dissipated in, a flange  604  and ends of stator core  504  and multiple keybars  518  by the fringing flux, resulting in a more efficient power generator. Also, since stator core and flange temperatures can serve as operating constraints for power generators, a reduction of the operating temperatures of the stator core and flange for a given rotor  410  winding current can allow for the power generator to be operated at a higher rotor winding current and a higher output voltage. 
     In addition, by redistributing the fringing flux, each flux shunt  522  reduces the fringing flux impinging upon an end of each keybar  518  and causes a more uniform distribution of flux in the keybar. A more uniform distribution of flux in a keybar reduces the likelihood of keybar voltages and also reduces a likelihood of voltage differentials developing among the multiple keybars  518 . By reducing the likelihood of voltage differentials, power generator  500  reduces a possibility of arcing in the stator core due to voltage differentials among laminations coupled to the keybar. 
     Furthermore, the multiple flux shunts  522  in power generator  500  are positioned in areas where only air gaps existed in the prior art. The inclusion of a flux shunt  522  where only an air gap previously existed results in an induction of an increased amount of magnetic flux and an increased output voltage for a given level of operation of power generator  500 . Alternatively, the inclusion of a flux shunt  522  where only an air gap previously existed reduces the rotor winding current required to produce a given output voltage, resulting in a more efficient power generator. 
     FIG. 10 is a logic flow diagram  1000  of a method for controlling flux in a power generator in accordance with an embodiment of the present invention. Preferably, the power generator includes an approximately cylindrical stator having an inner surface, an outer surface, and a stator core, and a rotor rotatably disposed inside of the stator. The power generator further includes multiple axially oriented keybars that are circumferentially disposed around the outer surface of the stator and multiple flanges that are each disposed at an end of the stator. The logic flow begins ( 1001 ) when a flux shunt is positioned ( 1002 ) adjacent to the inner surface of the stator and at approximately an end of the stator. A rotating ( 1003 ) of the rotor induces ( 1004 ) a fringing magnetic flux at the end of the stator. The fringing magnetic flux is attracted ( 1005 ) to the flux shunt, and the logic flow ends ( 1006 ). The attraction of the fringing magnetic flux to the flux shunt results in a reduction of the amount of fringing magnetic flux that would otherwise axially, or normally, impinge upon the ends of the stator core and the multiple keybars and upon a flange of the multiple flanges. 
     By attracting ( 1005 ) the fringing flux to the flux shunt and redirecting fringing flux away from the stator core, flange, and keybars, the present invention reduces eddy currents and energy and heat dissipation in each of the stator core, flange, and keybars, resulting in a more efficient power generator. In addition, reduction of an amount of fringing magnetic flux impinging upon an end of each keybar causes a more uniform distribution of flux in the keybar, reduces the likelihood of keybar voltages, and reduces a likelihood of voltage differentials developing among the multiple keybars  518 . Furthermore, when a flux shunt is positioned ( 1002 ) in areas of a power generator where only air gaps existed in the prior art, an increased amount of magnetic flux may be induced for a given level of operation of the power generator. An increased amount of magnetic flux results in an increased voltage induced by the flux in the stator windings, which in turn reduces the rotor winding current required to produce a given voltage and produces a more efficient power generator. 
     FIG. 11 is a logic flow diagram  1100  of a method for reducing a power generator keybar voltage differential in accordance with another embodiment of the present invention. Preferably, the power generator comprises an approximately cylindrical stator having an inner surface, an outer surface, and a stator core. The power generator further comprises multiple keybars axially disposed adjacent to the outer surface of the stator and a rotor rotatably disposed inside of the stator. The logic flow begins ( 1101 ) when a flux shunt is positioned ( 1102 ) adjacent to the inner surface of the stator and approximately at an end of the stator. A rotating ( 1103 ) of the rotor induces ( 1104 ) a first keybar voltage in a first keybar of the multiple keybars and further induces ( 1105 ) a second, different keybar voltage in a second keybar of the multiple keybars, producing ( 1106 ) a voltage differential between the first keybar voltage and the second keybar voltage. The voltage differential is less than a voltage differential that would exist between keybar voltages induced in each of the first and second keybars by a rotation of the rotor in the absence of the flux shunt. The logic flow then ends ( 1107 ). 
     In sum, a power generator is provided that includes multiple flux shunts that each reduces an amount of flux coupling into a stator, flange and into multiple keybars of the power generator during operation of the generator. By reducing the amount of flux coupling into a stator or flange, the power generator is able to operate at a reduced temperature level, or alternatively can be driven harder in order to operate at the same temperature level. By reducing the amount of flux coupling into the multiple keybars, a voltage differential between keybar voltages induced by the flux in each of the multiple keybars is reduced, reducing the potential for arcing and localized heating in the stator. 
     While the present invention has been particularly shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed herein, but that the invention will include all embodiments falling within the scope of the appended claims.