U.S. patent application number 10/279908 was filed with the patent office on 2004-04-29 for keybar voltage and current reduction for a power generator assembly.
This patent application is currently assigned to General Electric Company. Invention is credited to Salem, Sameh R., Shah, Manoj R..
Application Number | 20040080230 10/279908 |
Document ID | / |
Family ID | 32042974 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040080230 |
Kind Code |
A1 |
Shah, Manoj R. ; et
al. |
April 29, 2004 |
KEYBAR VOLTAGE AND CURRENT REDUCTION FOR A POWER GENERATOR
ASSEMBLY
Abstract
A power generator that operates at a reduced keybar voltages and
currents, flange currents, and keybar voltage differentials
includes a keybar shield that reduces the amount of magnetic flux
coupling into a keybar of multiple keybars during operation of the
generator. By reducing the amount of coupled flux, the keybar
shield reduces a keybar voltage and a keybar current in a keybar,
reduces keybar current flowing into a flange, and reduces a voltage
differential between voltages induced by the flux in the multiple
keybars.
Inventors: |
Shah, Manoj R.; (Latham,
NY) ; Salem, Sameh R.; (Rexford, NY) |
Correspondence
Address: |
BANNER & WITCOFF, LTD.
ATTORNEYS FOR GENERAL ELECTRIC
1001 G. STREET, N.W.
ELEVENTH FLOOR
WASHINGTON
DC
20001-4597
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
32042974 |
Appl. No.: |
10/279908 |
Filed: |
October 25, 2002 |
Current U.S.
Class: |
310/179 |
Current CPC
Class: |
H02K 11/40 20160101;
H02K 1/16 20130101; H02K 11/014 20200801 |
Class at
Publication: |
310/179 |
International
Class: |
H02K 001/00 |
Claims
We claim:
1. A keybar voltage and current reduction apparatus for use in a
power generator comprising a stator having an outer surface and a
stator core, the keybar voltage and current reduction apparatus
comprising: a plurality of keybar shields for the coupling of a
magnetic field, each keybar shield being mechanically coupled to
the outer surface of the stator, each keybar shield being an
electrical conductor; and a keybar shunt electrically coupling at
least two of the keybar shields, the keybar shunt being flexible
for expanding and contracting during operation of the power
generator, the keybar shunt being an electrical conductor.
2. The keybar voltage and current reduction apparatus of claim 1,
wherein the stator core has stator slots formed in its outer
surface and each keybar shield of the plurality of keybar shields
is disposed in one of the stator slots.
3. The keybar voltage and current reduction apparatus of claim 2,
wherein each keybar shield of the plurality of keybar shields
comprises a dovetail shape and the corresponding stator slots
comprise an inverse dovetail shape for mating with the dovetail
shape of respective keybar shields.
4. The keybar voltage and current reduction apparatus of claim 1,
wherein each keybar shield of the plurality of keybar shields is
disposed between a keybar and the stator.
5. The keybar voltage and current reduction apparatus of claim 1,
wherein each keybar shield of the plurality of keybar shields is
affixed to an outer surface of the stator by a high temperature
adhesive.
6. The keybar voltage and current reduction apparatus of claim 1,
wherein a length of each keybar shield of the plurality of keybars
shields is approximately an axial length of the stator core.
7. The keybar voltage and current reduction apparatus of claim 6,
wherein the length of each keybar shield is shorter than the axial
length of the stator core.
8. The keybar voltage and current reduction apparatus of claim 1,
wherein the keybar shields are mechanically attached to the stator
core and one or more flexible keybar shunts, and the keybar shields
are mechanically isolated from other generator components.
9. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt further electrically couples a
keybar attached to the stator core.
10. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt couples the coupled keybar
shields at an axial end of each coupled keybar shield.
11. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises corrugated wire.
12. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises a flexible strip.
13. The keybar voltage and current reduction apparatus of claim 12,
wherein the flexible strip comprises a multi-contact strip.
14. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises a plurality of flexible
strips banded together.
15. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises a helical spring.
16. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises a chain.
17. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises a wire braid.
18. The keybar voltage and current reduction apparatus of claim 1,
wherein the flexible keybar shunt comprises wire fabric.
19. A power generator comprising: a stator having an outer surface
and a stator core; a rotor rotatably disposed inside of the stator;
a plurality of keybars mechanically coupled to the outer surface of
the stator; a plurality of keybar shields mechanically coupled to
an outer surface of the stator, each keybar shield being an
electrical conductor; and a keybar shunt electrically coupling at
least two of the keybar shields, the keybar shunt being flexible
for expanding and contracting during operation of the power
generator, the keybar shunt being an electrical conductor; wherein
a rotation of the rotor induces a magnetic field that is coupled
into the keybar shields, and wherein a magnetic field that is
coupled into a keybar of the plurality of keybars is less a
magnetic field that would be coupled into the keybar in the absence
of the keybar shields.
20. The power generator of claim 19, wherein the stator has stator
slots formed in its outer surface and at least some of the keybar
shields are each disposed within one of the stator slots.
21. The power generator of claim 19, wherein each keybar shield of
the plurality of keybar shields comprises a dovetail shape and the
corresponding stator slot for each keybar shield comprises an
inverse dovetail shape for mating with the dovetail shape.
22. The power generator of claim 19, wherein at least some of the
keybar shields are each disposed between one of the keybars and the
stator.
23. The power generator of claim 19, wherein at least some of the
keybar shields are each affixed to the outer surface of the stator
by a high temperature adhesive.
24. The power generator of claim 19, wherein a length of each
keybar shield of the plurality of keybars shields is approximately
an axial length of the stator core.
25. The power generator of claim 24, wherein the length of each
keybar shield of the plurality of keybar shields is shorter than
the axial length of the stator core.
26. The power generator of claim 19, wherein the keybar shunt
couples the coupled keybar shields at an axial end of each coupled
keybar shield.
27. The power generator of claim 19, wherein the keybar shunt is
disposed near an axial end of the stator core.
28. The power generator of claim 19, wherein the keybar shunt is
coupled to each coupled keybar shield via a brazed connection.
29. The power generator of claim 19, wherein the flexible keybar
shunt comprises a corrugated wire.
30. The power generator of claim 19, wherein the flexible keybar
shunt comprises a flexible strip.
31. The power generator of claim 30, wherein the flexible strip
comprises a multi-contact strip.
32. The power generator of claim 19, wherein the flexible keybar
shunt comprises a plurality of flexible strips banded together.
33. The power generator of claim 19, wherein the flexible keybar
shunt comprises a helical spring.
34. The power generator of claim 19, wherein the flexible keybar
shunt comprises a chain.
35. The power generator of claim 19, wherein the flexible keybar
shunt comprises a wire braid.
36. The power generator of claim 19, wherein the flexible keybar
shunt comprises wire fabric.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to a power generator, and in
particular to reduction of keybar voltages in a power
generator.
BACKGROUND OF THE INVENTION
[0002] 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 and 2. FIG. 1 is an end view of a
cross-section 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 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. The multiple keybars 118, together
with the multiple flanges 204, form a keybar cage around 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 established 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 of the stator in a second
stator slot 106, thereby forming a stator winding loop.
[0006] FIG. 3 is a partial perspective of generator of 100 and
illustrates a typical technique of constructing a stator core 104.
As shown in FIG. 3, stator core 104 includes multiple ring-shaped
lamination packets 302 that are stacked one on top of another in
order to build up the core. A gap 303 between adjacent packets
allows for ventilation to cool rotor 110 and stator core 104. One
design of stator core 104 further includes subdividing each
lamination packet 302 into multiple lamination segments 304. A
radially outer surface of each lamination segment 304 includes at
least one slot 120 (not shown in FIG. 3) that 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 each slot of the multiple slots 120 of
a lamination segment 304 with a locking side 122 of a keybar 118
affixes each lamination segment in position in stator 102.
[0007] A rotation of rotor 110 inside of stator 102 with a DC
current in the multiple windings of rotor 110 establishes a
magnetic flux in the generator. A portion of the magnetic flux that
passes through stator 102, spills outside of the outer surface of
stator 102 coupling into each of the multiple keybars 118. The
coupling of magnetic flux into each of multiple keybars 118 can
induce keybar voltages and thus setup keybar currents in each
keybar. One possible result is a development of a voltage
differential between keybar voltages produced in each of two
different keybars 118. When adjacent keybars 118 are coupled to
adjacent lamination segments, a voltage differential between the
adjacent keybars 118 may also appear across the adjacent lamination
segments. The voltage differential between adjacent lamination
segments can cause arcing between the two segments; overheating in
the stator core 104, and reduced generator performance.
[0008] Furthermore, the keybar currents induced in each keybar 118
flow from the keybar 118 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, a 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] Therefore, a need exists for a method and apparatus for
reducing keybar currents and keybar voltage differentials induced
in each of the multiple keybars.
BRIEF SUMMARY OF THE INVENTION
[0010] Thus there is a particular need for a method and apparatus
that reduces keybar currents and that reduces any voltage
differential that may appear between keybars. Briefly, in
accordance with an embodiment of the present invention, a keybar
shield is provided for insertion adjacent to an outer surface of a
stator and that extends approximately an axial length of the
stator. The keybar shield reduces the amount of flux coupling into
a keybar during operation of a power generator, reducing a keybar
voltage and a voltage differential that may appear between keybars.
Also, by reducing the amount of flux coupling into a keybar, the
keybar shield also reduces keybar currents and flange currents and
their associated energy losses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A more complete understanding of the present invention and
the advantages thereof may be acquired by referring to the
following description in consideration of the accompanying
drawings, in which like reference numbers indicate like features,
and wherein:
[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 power generator of FIG. 1
along axis 2-2.
[0014] FIG. 3 is a partial perspective of the 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 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 a top view of an exemplary lamination segment in
accordance with an embodiment of the present invention.
[0018] FIG. 7 is an end view of a cross section of the power
generator of FIG. 4 in accordance with an embodiment of the present
invention.
[0019] FIG. 8 is a partial end view of a cross section of the power
generator of FIG. 4 in accordance with an embodiment of the present
invention.
[0020] FIG. 9 is a side view of a cross section of the power
generator of FIG. 4 in accordance with an embodiment of the present
invention.
[0021] FIG. 10 is a partial end view of a cross section of a power
generator in accordance with another embodiment of the present
invention.
[0022] FIG. 11 is a partial end view of a cross section of a power
generator in accordance with another embodiment of the present
invention.
[0023] FIG. 12 is a partial end view of a cross section of a power
generator in accordance with a further embodiment of the present
invention.
[0024] FIG. 13 is a partial end view of a cross section of a power
generator in accordance with an additional embodiment of the
present invention.
[0025] FIG. 14 is a partial end view of a cross section of a power
generator in accordance with yet another embodiment of the present
invention.
[0026] FIG. 15 is a partial end view of a cross section of a power
generator in accordance with a further embodiment of the present
invention.
[0027] FIG. 16 is a side view of a cross section of a power
generator in accordance with an embodiment of the present
invention.
[0028] FIG. 17 a perspective view of an end portion of the power
generator of FIG. 16.
[0029] FIG. 18 is a logic flow diagram of steps executed in order
to reduce keybar voltages and currents, flange currents, and keybar
voltage differentials in a power generator in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Referring now to FIGS. 4 and 5, an exemplary power generator
400 with reduced stator heating 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, power generator 400
includes a substantially cylindrical stator 402 having a stator
core 404 and housing a substantially cylindrical rotor 410. The
stator core 404 includes multiple circumferentially distributed and
axially oriented dovetail slots 422. 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 402 and mates with a
respective dovetail slot 422 for coupling to outer surface 402. The
multiple keybars 418, together with the multiple flanges 504, form
a keybar cage around the stator 402.
[0031] 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.
[0032] 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 inner 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.
[0033] 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.
[0034] The multiple flanges 504 are each disposed adjacent to an
end of stator core 404. Disposed between each flange 504 and stator
core 404 are outside space blocks 506. Each outside space block 506
is a generally rectangular bar coupled to a respective one of
flanges 504 and sandwiched between the respective flange 504 and an
axial end of stator core 404. Multiple outside space blocks 506 are
radially oriented along each axial end of stator core 404 in a
spoke-like configuration. In such a configuration, outside space
blocks 506 form gaps between stator core 404 and flanges 504, which
allow ventilation at the ends of stator 402.
[0035] 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 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.
[0036] Stator core 404 preferably includes multiple, stacked
ring-shaped laminations, similar to stator core 104 of the prior
art. Preferably, each ring-shaped lamination is subdivided into
multiple lamination segments. FIG. 6 is an illustration of an
exemplary lamination segment 600 in accordance with an embodiment
of the present invention. As shown in FIG. 6, each lamination
segment 600 of the multiple lamination segments includes multiple
dovetail-shaped slots 602 in an outer edge of the segment for
mechanically coupling the lamination segment to one or more keybars
418. In turn, each keybar 418 includes an outer side 604 and an
inner, locking side 606. Locking side 606 includes a
dovetail-shaped ridge that extends a length of the keybar 418 and
that is designed to mate with a dovetail-shaped slot 602 of a
lamination segment 600, thereby coupling each lamination segment
600 to a keybar 418. Multiple flanges 504 then hold the multiple
keybars 418 and, in association with the keybars, the multiple
ring-shaped laminations and the associated lamination segments in
position in stator core 404.
[0037] FIG. 7 is an end view of a cross-section of generator 400.
As shown in FIG. 7, 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 702
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 of multiple keybars
418 can induce keybar voltages and keybar currents in the keybar
and a voltage differential between keybar voltages induced in each
of two different keybars 418. In addition, keybar currents induced
in each keybar 118 flow from the keybar 418 to a flange 504 coupled
to the keybar via a potentially high resistance mechanical joint.
In order to minimize undesirable effects of keybar voltage
differentials, keybar currents, and flange currents, power
generator 400 includes a keybar voltage and current reduction
apparatus that reduces keybar voltages and keybar currents induced
in a keybar 418 by a rotation of rotor 410.
[0038] Referring to FIGS. 8 and 9, a keybar voltage and current
reduction apparatus is illustrated in accordance with an embodiment
of the present invention. FIG. 8 is a partial end view of a cross
section of a power generator 400 in accordance with an embodiment
of the present invention. FIG. 9 is a side view of a cross section
of a power generator 400 in accordance with an embodiment of the
present invention. As shown in FIGS. 8 and 9, power generator 400
further includes multiple highly electrically conductive keybar
shields 802 that are each coupled to at least one of multiple
keybar shunts 804, thus forming a keybar shield cage. Each keybar
shield of the multiple keybar shields 802 is an electrical
conductor of a low electrical resistance, such as a strip of
copper, a bar of copper, or a copper braid. Those who are of
ordinary skill in the art realize that other materials of low
electrical resistance may be used herein without departing form the
spirit and scope of the present invention.
[0039] Each keybar shield 802 is axially oriented and is disposed
between a locking side 606 of a keybar and a slot 602 of stator
core 404. In addition, a preferable length of each keybar shield
802 is approximately a entire axial length of stator core 404;
however, those who are of ordinary skill in the art realize that
keybar shields of other lengths may be used herein, or that a
keybar shield may be divided into multiple discrete segments that
are each less than a full length of the stator core, without
departing from the spirit and scope of the present invention.
[0040] In power generator 400, magnetic flux generated by rotor and
stator windings that spills outside of stator 402 couples to one or
more keybar shields 802, which produces electric currents in keybar
shields 802. Because these currents are produced by the spilled
magnetic flux, they create their own secondary magnetic flux that
is substantially opposite in direction to the spilled magnetic
flux. Thus, de-magnetizing secondary flux created from induced
keybar shield currents reduces the amount of magnetic flux that
couples to a keybar 418, and thereby reduces voltages and currents
induced in the keybar by the flux. By reducing potential keybar
voltage differentials, the keybar shields 802 reduce the
possibility of arcing and localized heating in stator 402.
[0041] Each keybar shield 802 is electrically coupled to the other
keybar shields 802 at each of a proximal end and a distal end of
the keybar shield by one of the multiple keybar shunts 804. In one
embodiment, each keybar shunt 804 is an electrically conductive
ring that is affixed to an end of each keybar shield 802. For
example, a keybar shield 802 may be brazed to keybar shunt 804. By
way of another example, each keybar shield 802 may further include
a threaded keybar shield stud that extends axially outward from the
end of the shield. Each keybar shunt 804 may then include multiple
apertures that are each aligned with a keybar shield stud and that
facilitate a bolting of each keybar shield 804 to the keybar shunt
804. Alternatively, each keybar shunt 804 may be any kind of
electrically conductive link between the multiple keybar shields
802. Further, each keybar shunt 804 may be a flexible electrically
conductive link. As a flexible link, keybar shunts 804 are better
able to withstand operating stresses without significantly
affecting a resonant frequency of power generator 400 during
operation. As shown in FIG. 9, each keybar shunt 804 can be
disposed between each of the keybars 418 and an outside space block
506 and adjacent to a flange 540. In alternative embodiments of the
present invention, each keybar shunt 804 may be disposed between a
space block 506 and stator core 404 or between the space block and
a flange 506.
[0042] Referring now to FIG. 10, a keybar voltage and current
reduction apparatus is illustrated in accordance with another
embodiment of the present invention. As shown in FIG. 10, instead
of being disposed in a stator slot 602, each keybar shield 802 may
be disposed on an outer surface of the stator 402 outside of the
slots. Similar to the keybar reduction apparatus of FIGS. 8 and 9,
each keybar shield 802 is shorted at each of a proximal end and a
distal end of the keybar shield by being electrically coupled to
one of multiple keybar shunts 1004. Similar to multiple keybar
shunts 804, each keybar shunt of the multiple keybar shunts 1004
may be approximately ring-shaped and includes a low resistance
material in order to provide a low resistance electrical connection
among each of the multiple keybar shields 802. Further, like
multiple keybar shunts 804, each keybar shunt 1004 may be a
flexible electrically conductive link.
[0043] The multiple keybar shields 802, in conjunction with the
multiple keybar shunts 1004, may form a keybar shield cage that is
parallel to the keybar cage. In addition, each keybar shield may be
affixed to the outer surface of stator 402, for example by a high
temperature adhesive or by a mechanical fastener. The width of
keybar shield 802 may vary with the designer of power generator
400, and in yet another embodiment of the present invention, a
keybar shield may be of a width that spans most of the distance
along the outer surface of stator 402 between adjacent keybars 418.
Preferably, a wider keybar shield 1002, such as the keybar shield
that spans most the distance along the outer surface of stator 402
between adjacent keybars 418, will further include multiple
apertures that permit a gaseous flow through the keybar shield,
facilitating a temperature regulation of stator 402.
[0044] Referring now to FIG. 11, a keybar voltage and current
reduction apparatus is illustrated in accordance with still another
embodiment of the present invention. As shown in FIG. 11, each
keybar shield 1102 of multiple keybar shields may be of a shape,
preferably a dovetail shape, that mates with a shape of a slot 602
of stator 402. Each keybar shield 1102 is then disposed in one of
the slots 602 of stator 402 that is not used by one of the multiple
keybars 418. Similar to keybar shield 802, each keybar shield 1102
is an electrical conductor of a low electrical resistance, such as
a bar of copper or a copper braid. Further each keybar shield 1102
preferably extends approximately an entire axial length of stator
core 404 without extending beyond the ends of stator core 404 or
attaching to end flanges 504. In addition, and similar to the
multiple keybar shields 802, each keybar shield 1102 is shorted at
each of a proximal end and a distal end of the keybar shield by
being electrically coupled to one of multiple keybar shunts, such
as keybar shunt 1004.
[0045] By including multiple keybar shields that are each disposed
adjacent to an outer surface of a power generator stator and that
each extends approximately an entire axial length of the stator,
the keybar voltage and current reduction apparatus reduces keybar
voltages and currents, a keybar voltage differential, and an
operating temperature of the power generator. Magnetic flux
generated by a rotation of a power generator rotor is coupled to
the keybar shields, reducing the amount of magnetic flux coupled to
each of multiple keybars. By reducing the amount of flux coupled to
each keybar, the keybar shield reduces keybar voltages and currents
induced by the flux, thereby reducing potential voltage
differentials between the keybar voltages and reducing the
possibility of arcing and localized heating in the stator.
Furthermore, by reducing the amount of flux coupled to each keybar,
the keybar shield reduces the flow of keybar currents from the
multiple keybars to a flange thereby reducing flange currents. By
reducing keybar currents and flange currents, the keybar voltage
and current reduction apparatus reduces heat and energy dissipation
in the keybars, the flange, and the mechanical joints coupling the
keybars to the flange.
[0046] The keybar shields, such as keybar shields 1102 shown in
FIG. 11, are preferably mechanically isolated from all but stator
core 404 to decrease the possibility of affecting a resonant
frequency of power generator 400. During operation of power
generator 400, rotation of rotor 410 inside of stator 402 causes
vibrations throughout power generator 400. If some of these
vibrations match harmonics of a resonant frequency of generator 400
or a resonant frequency of components of generator 400, harmful
vibration effects may result. The frequencies of vibrations created
in generator 400 during operation depend on numerous factors, such
as the speed at which rotor 410 spins or the freedom of movement
between generator components.
[0047] Likewise, resonant frequencies of the generator and/or
components depend on numerous factors. For example, the generator
design, the type and orientation of generator mounts, and the
freedom of movement between generator components affect resonant
frequencies. Further, the mass and stiffness of various components,
as well as their material properties, affect resonant frequencies.
Additionally, attributes such as size, shape, and geometry of
components affect their resonant frequencies and the resonant
frequency of the system. When vibrations created during operation
match harmonics of one or more resonant frequencies, harmful
vibration effects may occur, such as operational instability,
increased wear, and accelerated fatigue of components.
[0048] To reduce negative vibration effects, generator 400 may be
tuned for operation at desired rotor speeds and in desired modes.
For example, rotor 410 may be balanced to reduce the creation of
vibrations or shock absorbers may be added to dampen undesirable
vibrations. The addition of a keybar voltage and current apparatus
to a tuned generator may change the resonant frequency of the
generator or its components. For example, adding keybar shields 802
and keybar shunts 1004 shown in FIG. 10 to a tuned generator 400
may change the resonant frequency of generator 400 or of its
components, such as stator core 404. Accordingly, it may be
important to reduce their vibration effects on the generator
system.
[0049] Mechanical isolation of keybar shields 802 from components
other than stator core 404 will reduce such vibration effects. This
may be accomplished by using stator-length keybar shields 802,
which do not extend beyond the distal and proximate ends of stator
core 404 and do not connect to end flanges 504. In such a
configuration, keybar shields 802 are only connected to stator core
404, and thereby do not limit the movement of the stator core 404
with respect to other components of generator 400. Consequently,
potential vibration effects to generator 400 from the addition of
keybar shields 802 and shunts 1004 are reduced.
[0050] Using flexible, rather than rigid, keybar shunts 1004 for
interconnecting keybar shields 802 will further diminish vibration
effects. This is because flexible keybar shunts 1004 have
negligible effects on the freedom of movement of the respective
keybar shields 802 and/or keybars 418 to which they are attached.
Also, because some of lamination segments 600 are connected to
keybar shields 802, flexible shunts 1004 between keybar shields 802
also have negligible effects on the freedom of movement of attached
lamination segments 600 and their corresponding ring-shaped
laminations. By reducing the effect on the freedom of movement of
generator components, the potential for creating negative vibration
effects is significantly reduced with the use of flexible
shunts.
[0051] Further, the use of flexible shunts, such as shunts 1004
shown in FIG. 10, provides a generally more robust design that is
able to respond to operating stresses and vibrations without
greatly stressing connections to shunts 1004. Flexible shunts 1004
are able to contract and expand as necessary to adapt to movement
of attached keybar shields 802 and/or keybars 418. Because of this
adaptability, movement and vibrations during operation are
generally not transmitted to the mechanical connections between
shunts 1004 and keybar shields 802, or in alternative
configurations, to the mechanical connections between shunts 1004
and keybars 418. Accordingly, these connections are less
susceptible to fatigue and are more durable than connections to
rigid shunts.
[0052] The keybar shields 802, 1102 and shunts 1004 shown in FIGS.
10 and 11 constitute a keybar voltage and current reduction
apparatus kit that may retrofit an existing system with little
modification. For instance, as shown in FIG. 11, keybar shields
1102 take advantage of existing dovetail-shaped slots 602 for
connecting to stator core 404 without requiring connection to
flanges 504. Further, as shown in FIG. 10, keybar shunts 1004 may
be mechanically and electrically connected to keybar shields 802
using techniques that are relatively simple and well known. As an
example, keybar shunts 1004 may be brazed to keybar shields 802
from the exterior of stator 402 after the keybar shields 802 are
connected to stator core 404.
[0053] Referring now to FIGS. 12-15, several keybar voltage and
current reduction apparatus, which are relatively easy to install
and have negligible vibration effects on power generator 400, are
illustrated in accordance with further embodiments of the present
invention. These embodiments are generally the same as the
embodiment of FIGS. 10 and 11, except for aspects and preferences
related to keybar shunts and their connection to keybar shields
and/or keybars. FIG. 12 shows a keybar shunt 1204 coupled to each
keybar shield 1102. The keybar shunt 1204 is coupled to keybar
shields 1102 via mechanical connections, such as brazed, bolted or
press-fit connections; however, the keybar shunts 1204 themselves
are flexible.
[0054] Keybar shunt 1204 includes multiple electrically conductive
strips 1205 banded together at certain locations using bands 1207.
Some of the bands 1207 are attached to keybar shields 1102. The
conductive strips 1205 are preferably made of copper or another
highly conductive metal. Optionally, keybar shunts 1204 may be
connected to both keybars 418 and keybar shields 1102, or may be
connected to selected ones of keybars 418 and keybar shunts 1204.
To provide reinforcement to shunt 1204 and help maintain a desired
shape, some of strips 1205 may be made of steel. Thus, shunt 1204
may have increased structural strength as provided by steel strips
and high conductivity as provided by copper strips. Shunt 1204 may
be reinforced in other ways, such as by guides (not shown) or other
structural members that do not interfere with the flexibility of
shunt 1204.
[0055] To provide an efficient connection with keybar shields 1102,
shunt 1204 may further be made from multi-contact strips or may use
multi-contact connectors for coupling with keybar shields 1102.
Multi-contact strips and multi-contact connectors as used herein
are electrical strips or connectors that include multiple outwardly
biased projections for making contact with a corresponding surface,
such as a surface on a keybar shield. Multiple contact points
between the corresponding surface via the projections provides good
electrical contact with low contact resistance. As an example,
shunt 1204 may include a multi-contact strip known in the art as a
MULTILAM strip, which can be press-fit into a slot (not shown) of
keybar shield 1102. In another example, shunt 1204 may include a
multi-contact connector (not shown) that is press-fit into a slot
(not shown) of keybar shield 1102.
[0056] FIG. 13 shows a keybar shunt 1304 coupled to keybar shields
1102 and keybars 418. The keybar shunt 1304 includes an
electrically conductive corrugated strip. Corrugated strip 1304 may
expand and contract in accordance with corrugations 1309 formed in
the strip. Corrugated strip 1304 is preferably made of copper or
another highly conductive metal. As shown, keybar shunts 1304 may
be connected to both keybar shields 1102 and keybars 418; however,
keybar shunts 1304 may be connected to any number of keybars 418
and/or keybar shields 1004 as desired. Corrugated strip 1304 may be
reinforced with a high strength strip (not shown) to add strength
and shape to the overall structure.
[0057] FIG. 14 shows a keybar shunt 1404 coupled to keybar shields
1102 and keybars 418. The keybar shunt 1404 includes an
electrically conductive cylindrical helical spring 1404. Helical
spring 1404 expands and contracts as necessary in accordance with
its coils. Helical spring 1404 may be made of copper or another
highly conductive metal. As shown in FIG. 14, bands 1411 placed
around spring 1404 may be used to mechanically attach spring 1404
to keybar shields 1004 (and optionally keybars 418) by brazing
bands 1411 to shields 1004. Helical spring 1404 may be reinforced
by a high strength structural member (not shown) if desired. For
example, a steel helical spring (not shown) may be coaxially
threaded through the center of spring 1404 to provide strength to
keybar shunt 1404.
[0058] FIG. 15 shows a keybar shunt 1504 coupled to keybar shields
1102 and keybars 418. The keybar shunt 1504 includes an
electrically conductive chain 1504. Chain 1504 includes
interconnected links 1513 made of copper or another highly
conductive metal. Chain 1504 includes rings 1515 that are attached
to keybars 418 and keybar shields 1102 via brazing or other
connection means. As shown, chain 1504 is preferably attached in a
slightly relaxed state to permit expansion and contraction as
necessary to respond to stresses and vibrations during operation of
generator 400. Shunt 1504 may be reinforced with a high strength
structural member, such as steel cable threaded through chain 1504,
to add strength to the structure.
[0059] FIGS. 16 and 17 show a keybar shunt 1604 coupled to keybar
shields 1102 and keybars 418. The keybar shunt 1604 includes an
electrically conductive braid 1604. Braid 1604 is made of
interwoven wire strands 1617 made of copper or another highly
conductive metal. In other embodiments, braid 1604 may include a
highly conductive fabric, such as a metal fabric made of copper.
Braid 1604 may also include strands of high strength materials,
such as steel, to reinforce the shunt. Braid 1604 is attached to
straps 1621 that are attached to keybars 418, and straps 1619 that
are attached to keybar shields 1102, via brazing or other
connection means. Straps 1619, 1621 are made from a highly
conductive material, such as copper or another metal, that aid
attachment of braid 1604 to keybars 418 and keybar shields 1102
respectively. As shown, braid 1604 is preferably attached in a
slightly relaxed state such that strands 1617 are loosely connected
to each other and segments of braid 1604 between straps 1619, 1621
are able to hang slightly. As such, braid 1604 may expand and
contract as necessary to respond to stresses and vibrations during
operation of generator 400.
[0060] As shown in FIGS. 16 and 17, keybar shunts 1604 are
preferably connected to keybar shields 1102 and keybars 418 at
their proximal and distal ends at a position inboard of the stator
ends. By placing keybar shunts 1604 inboard of the stator ends,
keybar shunts 1604 do not inhibit the flow of gases between space
blocks 506. Further, keybar shields 1602 preferably do not extend
beyond the proximal and distal ends of stator 402. As such, keybar
shields 1602 also do not inhibit the flow of gases between space
blocks 506. It is recognized, however, that keybar shunts 1604 may
be placed anywhere along the length of generator 400 as
desired.
[0061] FIG. 18 is a logic flow diagram 1800 of a method for
reducing keybar voltages and currents, flange currents, and keybar
voltage differentials in a power generator in accordance with an
embodiment of the present invention. Preferably, the power
generator comprises an approximately cylindrical stator having an
outer surface, a proximal end, a distal end, 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 diagram begins (1801)
when a keybar shield is positioned (1802) adjacent to the outer
surface of the stator. A rotating (1803) of the rotor induces
(1804) a magnetic field, which magnetic field is coupled (1805)
into the keybar shield and the logic flow ends (1806). By providing
for a coupling of the magnetic field into the keybar shield, the
keybar shield reduces the magnetic field coupled into a keybar,
thereby reducing voltages and currents induced in the multiple
keybars by the magnetic field and reducing a flow of keybar
currents into the flanges. In addition, by reducing keybar
voltages, potential keybar voltage differentials are reduced as
well. In an embodiment of the present invention, the method may
further include a step of coupling (1807) the keybar shield to a
keybar shunt.
[0062] In sum, a power generator is provided that includes multiple
keybar shields, which keybar shields reduce the amount of flux
coupling into each of multiple keybars during operation of a power
generator. By reducing the amount of flux coupling into the
keybars, the keybar shields permit the power generator to operate
at a reduced temperature level, or alternatively to be driven
harder in order to operate at the same temperature level. That is,
by reducing the amount of flux coupling into the multiple keybars,
the keybar shield reduces levels of keybar voltages and keybar
currents induced by the flux and also reduces a potential voltage
differential between voltages induced by the flux in each of the
multiple keybars.
[0063] 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. For example,
keybar shunts may be made from a copper alloy (e.g. beryllium
copper, brass, bronze, nickel silver) or other high conductivity
materials (e.g. nickel-Beryllium), and may be plated with a highly
conductive material (e.g. electroplated with gold or nickel). In
another example, keybar shunts may be made from a variety of
designs and configurations, such as a design that includes a copper
wire having slack between connections to provide flexibility, or
designs including electrical multi-contact elements, such as
electrical elements known in the art as MULTILAM. 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.
* * * * *