U.S. patent application number 09/748911 was filed with the patent office on 2002-06-27 for power generator.
Invention is credited to Longwell, Ronald Irving, Salem, Sameh Ramadan, Shah, Manoj Ramprasad.
Application Number | 20020079756 09/748911 |
Document ID | / |
Family ID | 25011433 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020079756 |
Kind Code |
A1 |
Shah, Manoj Ramprasad ; et
al. |
June 27, 2002 |
Power generator
Abstract
A thermal control and keybar voltage differential reduction
mechanism is provided for use in a power generator having multiple
keybars that are each coupled to a flange. The mechanism includes
an electrically conductive coupler capable of being electrically
coupled to each of a first keybar and a second keybar of the
multiple keybars. The coupler facilitates a flow of a current from
the first keybar to the second keybar in response to a rotation of
a rotor of the power generator, shunting the current away from the
flange and producing a first magnetic field that opposes a second
magnetic field induced by the rotation of the rotor.
Inventors: |
Shah, Manoj Ramprasad;
(Latham, NY) ; Salem, Sameh Ramadan; (Rexford,
NY) ; Longwell, Ronald Irving; (Ballston Lake,
NY) |
Correspondence
Address: |
BANNER & WITCOFF, LTD.
ATTORNEYS FOR GENERAL ELECTRIC
1001 G. STREET, N.W.
ELEVENTH FLOOR
WASHINGTON
DC
20001-4597
US
|
Family ID: |
25011433 |
Appl. No.: |
09/748911 |
Filed: |
December 27, 2000 |
Current U.S.
Class: |
310/68C |
Current CPC
Class: |
H02K 11/40 20160101;
H02K 1/16 20130101; H02K 11/014 20200801; H02K 3/16 20130101 |
Class at
Publication: |
310/68.00C |
International
Class: |
H02K 009/00 |
Claims
What is claimed is:
1. A thermal control and keybar voltage differential reduction
mechanism for use in a power generator having a stator, a rotor
rotatably disposed in the stator, and a plurality of keybars, the
thermal control and keybar voltage differential reduction mechanism
comprising a keybar coupler capable of being electrically coupled
to each of a first keybar of the plurality of keybars and a second
keybar of the plurality of keybars, and wherein when the rotor
rotates in the stator, the coupler provides a low resistance
electrical path from the first keybar to the second keybar for a
current induced by the rotation of the rotor.
2. The thermal control and keybar voltage differential reduction
mechanism of claim 1, wherein the coupler comprises: a first
electrical conductor that is electrically coupled to the first
keybar; a second electrical conductor that is electrically coupled
to the second keybar; and an electrically conductive linking
apparatus coupled to each of the first electrical conductor and the
second electrical conductor.
3. The thermal control and keybar voltage differential reduction
mechanism of claim 2, wherein each of the first and second
electrical conductors is a ring that is affixed near a respective
end of the first keybar and the second keybar.
4. The thermal control and keybar voltage differential reduction
mechanism of claim 2, wherein each of the first and second
electrical conductors is a rod that is inserted in a respective
diametric aperture in the first keybar and the second keybar.
5. The thermal control and keybar voltage differential reduction
mechanism of claim 1, wherein the coupler comprises an electrically
conductive ring disposed between an end of the stator and a power
generator flange.
6. A keybar assembly comprising: a plurality of keybars; an
electrically conductive coupler that is electrically coupled to
each of a first keybar of the plurality of keybars and a second
keybar of the plurality of keybars; and wherein the electrically
conductive coupler provides a low electrical resistance path
between the first keybar and the second keybar.
7. The keybar assembly of claim 6, wherein the keybar coupler
comprises: a first electrical conductor that is electrically
coupled to the first keybar; a second electrical conductor that is
electrically coupled to the second keybar; and an electrically
conductive linking apparatus coupled to each of the first
electrical conductor and the second electrical conductor.
8. The keybar assembly of claim 7, wherein each of the first and
second electrical conductors is a ring that are affixed to an end
of each of the first and the second keybars.
9. The keybar assembly of claim 7, wherein each of the first and
second electrical conductors is a rod that is inserted in an
diametric aperture in each of the first and the second keybars.
10. The keybar assembly of claim 6, wherein the coupler comprises
an electrically conductive ring disposed between an end of the
stator and a power generator flange.
11. The keybar assembly of claim 6, wherein the keybar assembly
further comprises a flange coupled to an end of each keybar of the
plurality of keybars and wherein the coupler provides a shunt
whereby a current in a first keybar of the plurality of keybars can
flow to a second keybar of the plurality of keybars, bypassing the
flange.
12. A power generator comprising: an approximately
cylindrically-shaped stator comprising a stator core, an inner
surface, an outer surface, a proximal end, and a distal end; a
rotor rotatably disposed inside of the stator; a plurality of
keybars axially disposed adjacent to the outer surface of the
stator; a keybar coupler coupled to each of a first keybar of the
plurality of keybars and a second keybar of the plurality of
keybars; wherein a rotation of the rotor produces a keybar current
in the first keybar and wherein the keybar coupler permits the
keybar current to flow to the second keybar.
13. The power generator of claim 12, wherein the keybar coupler
comprises: a first electrical conductor that is electrically
coupled to the first keybar; a second electrical conductor that is
electrically coupled to the second keybar; and an electrically
conductive linking apparatus coupled to each of the first
electrical conductor and the second electrical conductor.
14. The power generator of claim 13, wherein each of the first and
second electrical conductors comprises a ring that is affixed near
a respective end of the first keybar and the second keybar.
15. The power generator of claim 14, wherein each of the first and
second electrical conductors comprises a rod that is inserted in a
respective diametric aperture in the first keybar and the second
keybar.
16. The power generator of claim 12, wherein the keybar coupler
comprises an electrically conductive ring disposed between an end
of the stator and a power generator flange.
17. The power generator of claim 12, wherein the keybar current
induces a first magnetic field in the power generator that opposes
a second magnetic field induced in the power generator by the
rotation of the rotor.
18. The power generator of claim 12, wherein the power generator
further comprises a flange coupled to an end of each of the first
keybar and the second keybar and wherein the keybar coupler
provides a shunt whereby the keybar current bypasses the
flange.
19. A method for reducing a temperature of, and a voltage
differential in, a power generator, wherein the power generator
comprises a stator having an outer surface, a rotor that is
rotatably disposed inside of the stator, and a plurality of axially
oriented keybars circumferentially disposed around the outer
surface of the stator, the method comprises steps of: electrically
coupling a first keybar of the plurality of keybars to a second
keybar of the plurality of keybars by a keybar coupler; allowing a
current to flow from the first keybar to the second keybar via the
keybar coupler in response to a rotation of the rotor to produce a
multiple keybar current; producing a first magnetic field based on
the multiple keybar current; and wherein the rotation of the rotor
induces a second magnetic field in the stator, which second
magnetic field is opposed by the first magnetic field produced by
the multiple keybar current.
20. A method for reducing an operating temperature of a power
generator that comprises a stator housing a rotor that is rotatably
disposed in the stator and that further comprises a plurality of
keybars that are adjacent to an outside surface of the stator and
that are coupled together at an end of each keybar of the plurality
of keybars by a flange, the method comprising steps of:
electrically coupling a first keybar of the plurality of keybars to
a second keybar of the plurality of keybars by a keybar coupler;
and shunting a current in the first keybar from the first keybar to
the second keybar via the keybar coupler, bypassing the flange.
21. The method of claim 20, further comprising steps of: rotating
the rotor; inducing a current in the first keybar in response to
the rotation of the rotor; and wherein the step of shunting a
current comprises a step of shunting the current induced in the
first keybar from the first keybar to the second keybar via the
keybar coupler, bypassing the flange.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates generally to a power generator, and in
particular to reduction of heat dissipation and undesirable voltage
differentials in a power generator.
[0002] In order to improve generator efficiency and reduce
generator size, high power electrical generator manufacturers are
constantly endeavoring to improve generator thermal performance and
efficiency. For example, a prior art design of a high power
electrical generator 100 is illustrated in FIGS. 1 and 2. FIG. 1 is
an end view of a cross-section of power generator 100 from an
isometric perspective. FIG. 2 is a cut-away view of power generator
100 along axis 2-2. As shown in FIGS. 1 and 2, power generator 100
includes a substantially cylindrical stator 102 housing a
substantially cylindrical rotor 110. Power generator 100 further
includes multiple axially oriented keybars 118 that are
circumferentially distributed around an outer surface of the stator
102. Each keybar 118 is mechanically coupled to the outer surface
of stator 102. Each keybar 118 is further mechanically coupled at
each of a proximal end and a distal end to one of multiple flanges
204 (not shown in FIG. 1). The multiple keybars 118, together with
the multiple flanges 204, form a keybar cage around the stator
102.
[0003] 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).
[0004] 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.
[0005] 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.
[0006] 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 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 through the stator
windings induces a current in the stator windings and a power
generator output voltage. The passage of magnetic flux through
stator 102 induces eddy currents in the magnetically and
electrically resistive stator. The eddy currents cause the
dissipation of energy in stator 102 in the form of heat and impose
a thermal constraint on the operation of generator 100.
[0007] FIG. 3 is a partial perspective of generator of 100 and
illustrates a typical technique of constructing stator core 104.
One known thermal management technique is the construction of
stator core 104 from multiple ring-shaped laminations 302. As shown
in FIG. 3, the multiple ring-shaped laminations 302 are stacked one
on top of another in order to build up stator core 104. Each
lamination 302 is divided into multiple lamination segments 304.
Each lamination segment 304 includes multiple slots 120 (not shown
in FIG. 3), wherein at least one slot 120 of each segment 304
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 304, 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 304 with a locking side 122 of a keybar 118
affixes each lamination segment 304, and thereby each lamination
302, in position in stator 102. By building stator core 104 from
stacked laminations 302, 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. However, the above thermal
management technique does not fully address the thermal problems
caused by the coupling of magnetic fields into stator 102.
[0008] Furthermore, induced magnetic flux also passes through, and
spills outside of, stator 102, coupling into each of the multiple
keybars 118. The coupling of magnetic flux into a keybar 118
induces keybar voltages and keybar currents in the keybar, which
current flows from the keybar to a flange 204 coupled to the
keybar. A mechanical joint by which a keybar 118 is coupled to a
flange 204 can be a poor electrical conductor that provides a high
resistance path for the current. As a result, the joint can be a
source of undesirable energy dissipation and heat generation in
power generator 100, and is also a potential source of arcing and
pitting in the power generator. Furthermore, the flow of keybar
current in a magnetically and electrically resistive flange 204
results in undesirable energy and heat dissipation in the flange.
To avoid overheating the joint and the flange 204 and potential
arcing and pitting, a power generator such as power generator 100
sometimes must be operated at backed off levels of magnetic flux
and output voltage, reducing the efficiency and rated power level
of the power generator 100.
[0009] In addition, the induction of keybar voltage in each of the
multiple keybars 118 can result in a voltage differential between
keybar voltages induced in two of the multiple keybars 118. When
adjacent keybars 118 are coupled to adjacent lamination segments
304, a keybar voltage differential appearing between the adjacent
keybars 118 may also appear across the adjacent lamination segments
304. The voltage differential between adjacent lamination segments
304 can cause arcing between the two segments, overheating in the
stator core 104, and reduced generator performance. The arcing can
also create localized heating in the core, causing lamination
segments 304, and lamination rings 302, to fuse together. Such
fusing can spread quickly in generator 100 as the lamination
segments 304, and lamination rings 302, short circuit to each
other, resulting in damage to the generator.
[0010] Therefore, a need exists for a method and apparatus for
further reducing the heat dissipated in the stator and for reducing
keybar voltage differentials that may appear between keybars.
BRIEF SUMMARY OF THE INVENTION
[0011] Thus there is a particular need for a method and apparatus
that reduces the heat dissipated in a generator stator and that
reduces keybar voltage differentials that may appear between
keybars. Briefly, in accordance with an embodiment of the present
invention, a thermal control and keybar voltage reduction mechanism
is provided for use in a power generator having multiple keybars.
The thermal control and keybar voltage reduction mechanism includes
a keybar coupler capable of being electrically coupled to each of a
first keybar of the multiple keybars and a second keybar of the
multiple keybars. When the rotor rotates in the stator, the keybar
coupler provides a low resistance electrical path from the first
keybar to the second keybar for a current induced in the first
keybar by the rotation of the rotor. By providing a low resistance
path, the thermal control and keybar voltage reduction mechanism
shunts the current away from a high resistance path and reduces the
heat dissipated by the power generator. In addition, by shunting
the current away from a high resistance path, a voltage
differential that can appear in the high resistance path is
reduced, which reduces the likelihood of arcing and pitting in a
power generator. Furthermore, by providing a low resistance path
between two coupled keybars, the voltage differential reduction
mechanism produces a larger current than would be produced in a
single uncoupled keybar. The current in turn produces a first
magnetic field that opposes a second magnetic field induced in the
stator by the rotation of the rotor. By opposing the second
magnetic field, the first magnetic field reduces the effective
magnetic field induced by the rotation of the rotor, thereby
reducing voltage differentials that can be induced by the effective
magnetic field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an isometric perspective of an end view of a
cross-section of a power generator of the prior art.
[0013] FIG. 2 is a cut-away view of the prior art power generator
of FIG. 1 along axis 2-2.
[0014] FIG. 3 is a partial perspective of the prior art power
generator of FIG. 1.
[0015] FIG. 4 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.
[0016] FIG. 5 is a cut-away side view of the power generator of
FIG. 4 along axis 5-5 in accordance with an embodiment of the
present invention.
[0017] FIG. 6 is an end view of a cross-section of the power
generator of FIG. 4 in accordance with an embodiment of the present
invention.
[0018] FIG. 7 is a side view of the power generator of FIG. 4 in
accordance with an embodiment of the present invention.
[0019] FIG. 8 is a magnified perspective view of an end of the
power generator of FIG. 7 in accordance with an embodiment of the
present invention.
[0020] FIG. 9 is a partial cross-section of an end of the power
generator of FIG. 7 in accordance with an embodiment of the present
invention.
[0021] FIG. 10 is a cut away side view of a power generator in
accordance with another embodiment of the present invention.
[0022] FIG. 11 is a side view of a cross section of the power
generator of FIG. 10 in accordance with another embodiment of the
present invention.
[0023] FIG. 12 is a ,partial cross-section of an end of the power
generator of FIG. 10 in accordance with another embodiment of the
present invention.
[0024] FIG. 13 is a logic flow diagram of steps executed in order
to reduce an operating temperature of, and voltage differentials
in, a power generator in accordance with an embodiment of the
present invention.
[0025] FIG. 14 is a logic flow diagram of steps executed in order
to reduce an operating temperature of a power generator in
accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Referring now to FIGS. 4 and 5, an exemplary power generator
400 with reduced stator heating and reduced keybar voltage
differentials is illustrated. FIG. 4 is an end view of a
cross-section of power generator 400 from an isometric perspective
in accordance with an embodiment the present invention. FIG. 5 is a
cut-away view of power generator 400 along axis 5-5 as shown in
FIG. 4. As shown in FIGS. 4 and 5, electrical generator 400
includes a substantially cylindrical stator 402 having a stator
core 404 and housing a substantially cylindrical rotor 410.
Multiple circumferentially distributed and axially oriented keybars
418 are coupled together at each of a proximal end and a distal end
by one of multiple flanges 504 (not shown in FIG. 4). Each keybar
418 is coupled to an outer surface of stator 102. The multiple
keybars 118, together with the multiple flanges 504, form a keybar
cage around the stator 402.
[0027] Similar to stator 102 of the prior art, an inner surface of
stator 402 includes multiple stator slots 406 that are
circumferentially distributed around the inner surface of the
stator. Each stator slot 406 is axially oriented and extends
approximately a full length of stator 402. Each stator slot 406
receives an electrically conductive stator winding (not shown).
Between each pair of adjacent stator slots 406 is a stator tooth
408 that similarly is circumferentially distributed around the
inner surface of stator 402 and extends approximately a full length
of stator 402. Each stator tooth 408 is radially oriented and
extends radially inward toward rotor 410 from stator 402.
[0028] Rotor 410 is rotatably disposed inside of stator 402.
Similar to rotor 110 of the prior art, rotor 410 includes an outer
surface that includes multiple rotor slots 414 that are
circumferentially distributed around the outer surface of rotor
410. Each rotor slot 414 is radially oriented and extends
approximately a full length of rotor 410. Between each pair of
adjacent rotor slots 414 is a rotor tooth 416 that similarly is
circumferentially distributed around the outer surface of rotor 410
and extends approximately a full length of rotor 410. Each rotor
tooth 416 is radially oriented and extends radially outward toward
stator 402 from rotor 410. An air gap exists between stator 402 and
rotor 410 that allows for a peripheral rotation of rotor 410 about
axis 420.
[0029] Similar to generator 100 of the prior art, each slot of the
multiple rotor slots 414 receives an electrically conductive rotor
winding (not shown) and each slot of the multiple stator slots 406
of generator 400 receives an electrically conductive stator winding
(not shown). Each rotor winding typically extends from a proximal
end of rotor 410 to a distal end of the rotor in a first rotor slot
of the multiple rotor slots 414, and then returns from the distal
end to the proximal end in a second rotor slot of the multiple
rotor slots 414, thereby forming a loop around a portion of the
rotor. Each stator winding typically extends from a proximal end of
stator 402 to a distal end of the stator in a first stator slot of
the multiple stator slots 406, 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 406, thereby forming a loop
inside of the stator.
[0030] The multiple flanges 504 are each disposed adjacent to an
end of stator core 404. Disposed between each flange 504 and stator
core 404 is an outside space block 506. Each of the multiple
flanges 504 is a ring-shaped metallic material that includes
multiple keybar stud apertures (not shown) for receiving a keybar
stud 508. The apertures are circumferentially disposed around each
flange 504 in positions that correspond to positions of keybars 418
around stator 402. Each end of each keybar 418 includes a threaded
keybar stud 508 that extends axially outward from the end of the
keybar. Each flange 504 is placed on an end of stator 402 and over
the keybar studs 508 such that each stud extends through the flange
via a corresponding keybar stud aperture. Each flange 504 is then
mechanically fastened onto an end of stator 402 and the multiple
keybars 418 by multiple threaded nuts 510 that are each screwed
onto a correspondingly threaded keybar stud 508. The mechanical
joint between each flange 504 and each of the multiple keybars 418
provides a poor electrical contact and a potentially high
resistance path for any current passing through.
[0031] Stator core 404 preferably includes multiple, stacked
ring-shaped laminations, similar to stator core 104 of the prior
art. Preferably, each ring-shaped lamination includes multiple
lamination segments, which segments each include multiple
dovetail-shaped slots in an outer edge of the segment for
mechanically coupling the segment to one or more keybars 418. In
turn, each keybar 418 includes an outer side and an inner, locking
side. The locking side includes a dovetail-shaped ridge that
extends a length of the keybar and that is designed to mate with a
dovetail-shaped slot of a lamination, thereby coupling the
ring-shaped laminations to the keybars. Multiple flanges 504 then
hold the multiple keybars 418 and, in association with the keybars,
the multiple lamination segments and associated ring-shaped
laminations in position in stator core 404.
[0032] FIG. 6 is an end view of a cross-section of generator 400.
As shown in FIG. 6, a rotation of rotor 410 inside of stator 402
when a DC current is flowing in the multiple windings of rotor 410
induces magnetic fields in, and a passage of magnetic flux 602
through, stator 402. The magnetic flux 602 induces eddy currents
and magnetic and resistive losses in stator 402, causing a
dissipation of energy and a concomitant temperature increase in the
stator. The magnetic flux passing through and spilling outside of
stator 402 couples into each of the multiple keybars 418, inducing
keybar voltages and keybar currents in each keybar. A flow of
keybar current through the joint by which a keybar 418 is coupled
to a flange 504 may result in resistive losses and undesirable heat
dissipation. Furthermore, a flow of keybar current in a
magnetically and electrically resistive flange 504 may result in
undesirable energy and heat dissipation in the flange. Therefore,
power generator 400 includes a thermal control and keybar voltage
differential reduction mechanism that shunts the keybar current
away from the joint and flange, reducing the need to operate power
generator 400 at backed off levels of magnetic flux and output
voltage.
[0033] Referring to FIGS. 7, 8, and 9, an exemplary thermal control
and keybar voltage differential reduction mechanism is illustrated
in accordance with an embodiment of the present invention. FIG. 7
is a side view of power generator 400 in accordance with an
embodiment of the present invention. FIG. 8 is a magnified
perspective view of an end of the power generator of FIG. 7 in
accordance with an embodiment of the present invention. FIG. 9 is a
partial cross-section of an end of the power generator of FIG. 7 in
accordance with an embodiment of the present invention. The thermal
control and keybar voltage differential reduction mechanism
includes multiple keybar couplers 702 that each provides a low
resistance electrical path between adjacent keybars 418. By
providing a low resistance path, each keybar coupler 702 provides a
low resistance shunt to the high resistance mechanical joint
coupling a keybar 418 to a flange 504. The low resistance shunt
detours a keybar current away from the flange 604 and the
mechanical joint.
[0034] Each keybar coupler 702 includes multiple, preferably two,
electrical conductors 704 that are linked to one another by a
flexible, electrically conductive linking apparatus 706. Each
electrical conductor of the multiple electrical conductors 704 is
electrically coupled to a keybar 418 and provides a conductive path
for a current in the keybar. For example, each electrical conductor
702 may be an electrically conductive, preferably copper, ring
coupled to an exterior of a keybar or an electrically conductive
rod disposed in a diametrical aperture in the keybar and affixed to
the keybar by a brazed joint. Preferably, each electrical conductor
702 is coupled to a respective keybar 418 near an end of the
keybar, such as at a position opposite the outside space block 506
in stator 402. Linking apparatus 706 is electrically coupled to
each of the multiple electrical conductors 704 and provides a
conductive path from one electrical conductor of the multiple
electrical conductors 704 to another electrical conductor of the
multiple electrical conductors 704, and thereby from one keybar 418
to another, different keybar 418. Preferably, each linking
apparatus 706 includes a flexible electrical conductor, such as
braided copper wires or a chain of copper links.
[0035] The operation of the thermal control and keybar voltage
differential reduction mechanism is as follows. When rotor 410
rotates in stator 402, rotor 410 induces magnetic fields in, and a
passage of magnetic flux through, stator 402. A portion of the
magnetic flux passes completely through stator 402 and spills
outside of the outer surface of stator 402, coupling into each of
the multiple keybars 418. The coupling of magnetic flux into each
keybar 418 induces keybar voltages and keybar currents in the
keybar. Each keybar coupler 702 then provides the keybar currents
induced in a keybar with a low resistance path to another, coupled
keybar of the multiple keybars 418. By providing a low resistance
path for the keybar currents, the keybar coupler 702 reduces a flow
of keybar currents to a flange 504 via the high resistance
mechanical joints. By reducing the flow of keybar currents in a
flange 504 and in the high resistance mechanical joints, the heat
and energy dissipated in each of the flange and the joints is
reduced.
[0036] Furthermore, the keybar currents in each keybar 418 induces
a first magnetic field in stator 402 that opposes a second magnetic
field induced in stator 402 by the rotation of rotor 410. By
opposing the second magnetic field, the keybar current induced
magnetic field reduces the effective magnetic fields in stator 402
and in each keybar 418. By electrically coupling multiple keybars
418, each keybar coupler 702 facilitates a flow of a keybar current
through multiple keybars, permitting a larger keybar current than
would flow in an uncoupled keybar. A larger keybar current
generates a larger opposing magnetic field, causing an additional
reduction of the effective magnetic fields. A result is smaller
eddy currents and less energy and heat dissipation in stator 402
and a reduction of the magnetic flux coupling into each of the
multiple keybars 418, thereby reducing the keybar voltage
differentials among the keybars.
[0037] Referring to FIGS. 10, 11, and 12, an exemplary thermal
control and keybar voltage differential reduction mechanism is
illustrated in accordance with another embodiment of the present
invention. FIG. 10 is a cut away side view of a power generator
1000 in accordance with another embodiment of the present
invention. FIG. 11 is a side view of a cross-section of the power
generator of FIG. 10 in accordance with another embodiment of the
present invention. FIG. 12 is a partial cross-section of an end of
the power generator of FIG. 10 in accordance with another
embodiment of the present invention. A difference between power
generator 1000 and power generator 400 is that power generator 1000
includes multiple keybar couplers 1002 that are each disposed
between stator core 404 and a flange 504 instead of the keybar
couplers 702 of power generator 400.
[0038] Preferably, each keybar coupler 1002 of FIGS. 10, 11, and 12
is an electrically conductive ring that includes a highly thermally
and electrically conductive material such as copper. Each keybar
coupler 1002 is disposed over an end of each of the multiple
keybars 418 and includes multiple apertures (not shown). Each
aperture of the multiple apertures is aligned with a keybar stud
508 of a keybar 418 and facilitates the disposition of the keybar
coupler 1002 over the ends of the keybars 418. Each keybar coupler
1002 is electrically coupled to each of the multiple keybars 418,
for example by brazing or by use of a mechanical fastener and
acceptable electrical contacts. In one embodiment of the present
invention, each keybar coupler 1002 can be disposed between an
outside space block 506 and a flange 504 at an end of stator 402
(which position is denoted as position `A` in each of FIGS. 11 and
12). In alternative embodiments of the present invention, each
keybar coupler 1002 may be disposed between an end of stator core
404 and a space block 506 at an end of stator 402 (which position
is denoted as position `B` in each of FIGS. 11 and 12), or may be
disposed adjacent to the space block and may be disposed between an
end of each keybar 418 from which a keybar stud 508 extends and a
flange 504 (which position is denoted as position `C` in FIG.
12).
[0039] Similar to keybar coupler 702, each keybar coupler 1002
provides a low resistance electrical path between multiple keybars
418 for keybar currents and functions as a low resistance shunt to
the high resistance path from a keybar 418 to a flange 504. Also,
by connecting multiple keybars 418, each keybar coupler 1002 allows
for a circulation of keybar currents through multiple keybars 418.
In addition, a keybar coupler 1002 may provide a thermal path from
a flange 504 to stator core 404 that facilitates a transfer of heat
from the flange to the core and helps reduce a flange operating
temperature.
[0040] By providing a keybar coupler 702, 1002 that couples the
multiple keybars 418 to each other and that provides a low
resistance shunt to the high resistance path between a keybar 418
and a flange 504, the thermal control and keybar voltage
differential reduction mechanism reduces undesirable thermal and
electrical effects of a magnetic field generated by a rotation of
rotor 410. Keybar coupler 702, 1002 provides a low resistance path
among multiple keybars 418 for keybar currents induced by the
magnetic field. The low resistance path shunts a high resistance
mechanical joint coupling a keybar 418 to a flange 504 and reduces
the flow of keybar current in the mechanical joint and the flange.
The reduced keybar current in turn results in reduced heat
dissipation in the mechanical joint and the flange. The reduced
keybar current also reduces a likelihood of a significant voltage
differential developing in the joint, due to the poor contact and
the high resistance of the joint, that could cause arcing and
pitting in the joint and the flange.
[0041] Furthermore, by providing a low resistance path among
multiple keybars 418, a keybar coupler 702, 1002 facilitates a flow
of a keybar current through multiple keybars, permitting a larger
keybar current than would flow in an uncoupled keybar. Larger
keybar currents generate larger magnetic fields in opposition to
the magnetic fields induced by the rotation of rotor 410, causing
an additional reduction in the effective magnetic fields. A result
is smaller eddy currents and less energy and heat dissipation in
stator 402 and a reduction of the magnetic flux coupling into each
of the multiple keybars 418, thereby reducing the likelihood of
voltage differentials among the keybars.
[0042] FIG. 13 is a logic flow diagram 1300 of a method for
reducing an operating temperature of, and voltage differentials in,
a power generator in accordance with an embodiment of the present
invention. Preferably, the power generator includes a stator having
an outer surface, a rotor that is rotatably disposed inside of the
stator, and multiple axially oriented keybars circumferentially
disposed around the outer surface of the stator. The logic flow
begins (1301) when a first keybar of the multiple keybars is
electrically coupled (1302) to a second keybar of the multiple
keybars by a keybar coupler. When the rotor rotates (1303), the
coupling of the first and second keybars allows (1304) a current to
flow from the first keybar to the second keybar via the keybar
coupler in response to the rotation to produce a multiple keybar
current. Based on the multiple keybar current, a first magnetic
field is produced (1305). The first magnetic field produced by the
multiple keybar current opposes a second magnetic field produced in
the stator by the rotation of the rotor, and the logic flow ends
(1306). By opposing the second magnetic field, the first magnetic
field reduces the magnetic flux coupling into each of the stator
and the multiple keybars. By reducing the coupling magnetic flux,
the second magnetic field reduces eddy currents in, and an
operating temperature of the stator and reduces keybar voltages and
thereby keybar voltage differentials.
[0043] FIG. 14 is a logic flow diagram 1400 of a method for
reducing an operating temperature of a power generator in
accordance with another embodiment of the present invention.
Preferably, the power generator includes a stator housing a rotor
that is rotatably disposed in the stator. The power generator f
further includes multiple circumferentially distributed and axially
oriented keybars that are coupled together at each of a proximal
end and a distal end by one of multiple flanges. Each keybar is
coupled to an outer surface of the stator and the multiple keybars,
together with the multiple flanges, form a keybar cage around the
stator. The logic flow begins (1401) when a first keybar of the
multiple keybars is electrically coupled (1402) to a second keybar
of the multiple keybars by a keybar coupler. In response to a
rotation of the rotor, the coupling of the first and second keybars
shunts (1403) a current in the first keybar from the first keybar
to the second keybar via the keybar coupler, bypassing a flange of
the multiple flanges, and the logic flow ends (1404). By bypassing
the flange, heat dissipation in the flange and in a mechanical
joint coupling the first keybar to the flange is reduced.
[0044] In sum, a power generator is provided that includes a keybar
coupler that electrically couples multiple keybars. When a rotor
rotates in a stator, the keybar coupler facilitates the induction
of a multiple keybar current, which multiple keybar current is
larger than a keybar current that would be induced in a single
isolated keybar. The multiple keybar current produces a first
magnetic field that opposes a second magnetic field induced in the
stator by the rotation of the rotor. By opposing the second
magnetic field, the first magnetic field reduces the amount of flux
coupling into the stator and into each of the multiple keybars,
thereby reducing the amount of energy and heat dissipated in the
stator and the keybar voltages and voltage differentials produced
in the keybars. The keybar couple also provides a low resistance
shunt to the high resistance mechanical joint coupling each keybar
to the flange, thereby reducing current flow in, and heat
dissipation in, the joint and flange.
[0045] 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.
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