Note: Descriptions are shown in the official language in which they were submitted.
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AN APPARATUS FOR COOLING END
~EGIONS OF A STATOR CORE
BACKGROUND OF THE INVENTION
This invention relates generally to an apparatus
for cooling stator cores of large dynamoelectric machines,
and more particularly to an apparatus for cooling end
regions of such cores.
Dynamoelectric machines, such as large electric
generators are compactly built as a result of design
rec~uirements for high speed, small diameters, and a
relatively short length, and are sealingly enclosed for
containing a cooling medium. These design features make
it difficult to cool the electric wire windincJs and stator
of the generator. Even though such generators are very
efficient, they do have some heat losses, and it is
therefore necessary to force relatively large quantitieS
of the coolin~ gas, typically hydrogen, through the
generators to carry of khe heat~occasioned by the losses.
The heat losses are due, for example, to ohmic-
resis~ance losses in the stator windings as electric
;current flows through khe windings and to eddy currents
; generated in the stator core. With respect to the latter,
losses are reduced by the building of the core with very
thin laminations. Nevertheless, edcly currents do occur
;and the resulting heat loss must be dissipated to keep the
.
temperature rise in the stator within requirecl design
limits. To this end, cooling gas is circulated through
the generator including through passageways in the stator
core. To provide such passageways, the stator may be
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divided into distinct and separate packs of lam:inated
sheets. This separation between the stator packs is
accomplished by vent fingers or rectangular block struc-
tures positioned in the space between adjacent packs.
The passageways created between the vent fingers are
generally re~erred to as radial passageways. Other
independent passageways may be created for ~xample by
providing arcuate notches transversely through the
laminations of each stack generally referred to as axial
passageways.
The problem of cooling the stator core is
particularly difficult in the stator core end regions of
such electric generators. In large synchronous machines,
the electric currents in the end turn portions of the
rotor windings and in the end portions of the stator
windings generate magnetic fields which combine to produce
an axially directed magnetic flux. This axial flux enters
the end portions of the stator core in a direction
perpendicular to the core laminations and creates cir-
culating currents in the end region laminations. Thecorresponding heat losses may be quite large, causing
excessive temperature rises in the end regions of the
stator core. To allow passage of the cooling medium
through the stator core end regions, both radial and axial
passageways are formed therein; only axial passageways,
however, are normally formed in the central portion
of the stator core because the temperature rise therein is
less than in the end regions of the stator core.
The typical stator core has an annular, pipe-
like configuration extending substantially the entirelength of the generator~ The stator core includes an
inner peripheral inner surface forming an interior surface
and an outer peripheral exterior surface with the stator
core formed therebetween. In the typical generator
cooling system, axial passageways extend the entire length
o~ the stator core parallel to the inner and outer
; surfaces. Radial passageways extend through the stator
~ core from the outer peripheral surface to the inner
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peripheral surface, perpend:icular to the inner and outer
surface. The cooling gas (e.g., hydrogen) is circulated
through the axial and radial passageways. In a general
circulation sc:heme, a ~orced-convection device, such as a
fan, positioned at an end region of the rotor forces the
gas through the generator. The gas flows through the fan
and is cooled by a cooling device positioned adjacent
thereto. The gas circulation flow path then branches out
to cool different portions of the stator. one branch of
the gas (the radial flow) flows around the stator end
adjacent the fan and along the outer surface thereof and
then inwardly into the radial passageways located in the
stator end regions. The gas then flows through the
radial passageways to the inner surface and thereafter
axially along the inner surface, returning to the fan. A
second branch (i.e. the axial flow) allows the gas to
flow to the opposite end of the stator and then into the
axial passageways located in the stator core and then
axially through the stator. Finally, the gas exits at the
stator end region adjacent to the fan and returns to the
fan.
In the end regions of prior art stator cores,
the radial and axial passageways intersect allowing the
gas in the separate passageways to intermix. This
intermixing results in a less efficient cooling system
since gas flow direction is less~ predictable. Such gas
intermixing can result in an undesirable undercooling or
overcooling in the end regions of the stator and may
result in a shortened generator life or limited generator
operation.
Consequently, a problem in the art is to cool
the end regions of stator cores where two independent
passageways of the same cooling system intersect and avoid
the detrimental consequences of gas intermixing.
Therefore, there is a need for an improved
apparatus for cooling the end regions of stator cores
wherein two cooling passageways of the same cooling system
are kept independent of eaoh other at their ~ntersections.
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BRIEF DESCRIPTION OF THE DRAWINGS
While this specification concludes with claims
particularly pointing out and distinctl~ claiming the
subject matter of the invention, it is believed the
invention will be better understood from the following
description, taken in conjunction with the accompanying
drawings wherein:
Fig~re 1 is a view in vertical section of an
electric generator with parts removed for clarity;
Figure 2 is a perspective view in vertical
section of a portion of a stator end region illustrating
adjacent stator packs;
Figure 3 is a perspective view in vertical
section of two adjacent stator packs of Figure 2 showing a
means for isolating radial and axial passageways formed in
the stator packs in accordance with '~his invention;
Figure 4 is a perspect,lve view in vertical
section of two other adjacent stator packs of Figure 2
showing a means for isolating radi~.al and axial passageways
formed in the stator packs in accordance with this
invention and wherein pistoye slots transverse the packs;
Figure 5 is a perspective view partially in
vertical section of a portion of a stator,end region
illustrating stator teeth having pistoye slots;
Figure 6 is a perspective view in vert.ica]
section o~ an alternative embodiment of the invention
showing an alternative means for isolating radial and
axial passageways formed in the stator packs; and
' Figure 7 is a perspective view in vertical
section of still another embodiment showing still another
;means for isolating radial and axial passageways formed in
the stator packs.
SUMMA~Y
Disclosed herein is a generator stator core
in~luding an apparatus for cooling the end regions thereof
by employing radial and axial intersecting passageways in
the stator core for receiving a cooling m dium. I~he
stator core comprises a plurality of spaced-apart acl~acent
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56,889
packs, each formed from a plurality of laminated sheets,
as is well known in the art. l'he invenkion adds to the
existing art an apparatus that seals and isolates the
intersections of the axial and radial passageways in a
stator core to minimize coolant flow therebetwezn. In one
example, this is accomplished by pre-forming the arcuate
notches in the outer laminations of the packs such that
the preformed edge of the notch con-tacts the adjacent
pack, thereby isolating the axial passageways from the
radial passageways at the intersection thereof. In other
examples, such isolation is caused by placing conduits
along the axial passageways between adjacent laminations.
An object of the present invention is to provide
an improved stator for cooling the end regions of stator
cores.
A feature of the preferred embodiment of the
present invention is the provision of a laminated sheet
which is bent or curved toward at least one adjacent
laminated sheet for sealingly isolating the radial and
axial passageways.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like
reference numerals refer to like elements, Fig. 1 depicts
a typical construction of a large dynamoelectric machine,
such as an enclosed electric generator generally referred
to as 1, including a gas tight housing 10 with a laminated
stator core 20 disposed within housing 10. ~ousing 10
includes a generally circular, tubular-like housing body
30 enclosed on both ends with ~enerally circular sides 40
a and b. Stator core 20 r which is generally cylindrical r
has a generally annular transverse cross section and
extends substantially the length of housing 10. Stator
core 20 includes an inner peripheral surface 50, an outer
peripheral surface 60, and end surfaces 25a and 25b
extending between inner peripheral surface 50 and the
outer periphery 60~ Stator core 20 carries a plurality of
stator windlngs 70 of a type well known in the art which
are disposed in stator slots 172 (Fig. 2) in the stator
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core 20. Moreover, as shown in Fig. l, a generally
cylindrical rotor 80 is supported in bearings (not shown)
in housing lO, extends longitudinally th~ough stator core
20, and carries the usual field windings tnot shown).
Rotor 80 has a generally circular transverse cross section
and extends substantially the length of housing 10. Rotor
80 further includes a shaft portion 90 which is connected
at a turbine end lO0 to a turbine (not shown) and at an
exciter end 110 to an exciter (not shown). Attached to
rotor 80 on turbine end 100 is a fan 120. Fan 120
typically includes a plurality of blades 130 spaced
circumferentially around rotor shaft 90 and functions to
force a cooling medium, typically hydrogen, through
generator 1. Positioned adjacent rotor shaft 90 at
turbine end 100 are cooling means 140 for cooling the
circulating hydrogen. Cooling means 140 include a
suitable container (not shown) with a cooling medium
therein, such as water, that flows through the container.
The cooling water enters and exits generator 1 through
housing body 30 respectively via inlet piping 150 and
outlet piping 151 which pass through turbine end 100 of
housing body 30 and are connected to the container. A
plurality of separate axial passageways 160 extend the
entire length of stator core 20 for providing an axial
cooling passageway through stator core 20. Thusl axial
passageways 160 axial~ly extend through both ends and the
central region of stator core 20. A plurality of dis-
parate radial passageways 170 are positioned, in this
example, only in each of the end regions of stator core
~20.
Still referring to Fig. 1, fan 120 forces the
cooling gas ~rom exciter end llO of stator core 20
through stator core 20 and across and through fan 120
~ toward cooling means 140, which cools the hydrogen as it
flows in heat exchange relationship therewith. As
described more fully presently, the hydrogen branches out
to cool different portions of stator core 20 after passing
through heat exchanger 140. To begin such branching, the
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gas ~lows around the end 25b and back across outer
periphery 60 of stator core 20 and between surface 60 and
housing body 30. At the turbine end 100, the gas flow
branches out into two ~low paths. ~he first such flow
5~radial flow) enters radial passageway 170 at outer
sur~ace 60 and exits at inner sur~ace 50, where the gas is
~orced by fan 120 along inner surface 50 toward turbine
end 100. The second such flow path is along outer
surface 60 toward exciter end 110 where the gas further
10branches out in two separate directions ~or cooling the
core. The first direction (radial flow) flows :in and
through radial passageway 17Q and exits at inner surface
50 whera the hydrogan is forced by fan 120 along inner
surface 50 toward turbine end 100. The second direction
15(axial flow) flows along end surface 25a and into axial
passageway 160 and exits axial passageway 160 at turbine
end 100. At turbine end 100, all the gas returning from
the axial passageways 160 and the radial passageways 170,
and the portion flowing along inner surface 50, intermix
20at tur~ine end 100 of stator core 20. Fan 120 forces this
returning hydrogen across fan 120, after which the flow is
recirculated along the same path described above.
Referring now to Fig. 2, stator core 20 is
formed of stackad laminations 171 and includes end
25surfaces 25a/b ~(Fig. 1) previously mentioned. ~The
laminations 171, forming the stator core 20, when stacked
~form a plurality of generally rectangular, spaced-apart
hollow stator slots 172 which extend radially and axially
of the stator core 20 and open onto the inner surface 50
30of stator core 20; they terminate radially spaced from the
outer periphery 60 of stator 20. Each pair of adjacent
stator slots 172 defines a slot surface 173 therebetween
that is oriented parallel ~to and concentric with outer
surface 60. The~ portion of stator core 20 between
35adjacent stator slots 172 is generally r~ferred to as a
stator tooth 174, and the portion of stator core 20
extending from outer surface 60 radially to slot surface
173 is typically referred to as stator yoke 175~ Conven-
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tional wire windings (not shown) are typically inserted :in
stator slots 172 to provide electrical conductors wherein
an induced voltage may be created. Stator core 20 is
formed from a plurality of spaced-apart packs 176, with
each pack 176 comprising built-up laminated sheets 171
(Fig. 3). As best shown in Fig. 2, aligned arcuate
notches or openings, shown in this embodiment to be
circular in shape, extend transversely through all of the
laminations 171 for de~ining axial passageway 160. Thus,
axial passageways 160 extend longitudinally through both
stator teeth 174 and stator yoke 175. In both turbine and
exciter ends 100/110, a plurality of pairs of vent ~ingers
190 are matingly interposed between spaced apart packs
175 for defining a plurality of radial passageways 170.
Vent fingers 190 provide support means for supporting
packs 176 and also provide spacing means for maintaining
packs 176 in a predetermined spaced-apart relationship.
Thus, the spaced-apart relationship of packs 176 defines
the radial passageway 170 hetween adjacent packs 176.
Radial passageways 170 extend from inner surface 50 to
outer surface 60 of stator teeth 174 and are located
between vent fingers 190 and packs 17~.
Still referring to Fig. 2, in the typical stator
core 20, the outer sheet 171b of each pack 176 is slightly
larger and thicker than laminations 171a contained within
laminations 171b, and with inner lamination 171a compris-
ing a substantial portion of the volume of each pack 176.
The end portions of stator core 20, wherein axial and
radial passageways 160/170 intersect, is subdivided such
that a portion of stator core 20 contains a plurality of
pistoye slots 195 extending from end surfaces 25a/b
radially to some predetermined distance. It is to be
noted, however, that a substantial portion of stator core
~0 is without pistoye slots 195 which extend radially and
axially through a plurality of inner laminations 171a
only. Pistoye slots 195 open into inner surface 50 of
stator 80 and terminate radially spaced from outer
periphery 60 of stator ~core 20 to meet e1ectromagnetic
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requirements. Pistoye slots 195 are positioned along
stator core 20 spaced between adjacent vent ~ingers 190 or
between end surfaces 25a/b and an adjacent vent finger
190. A lamination 171 is positioned at both ends of
pistoye slots 195, laminations 171 being solid (except for
axial passageway 160) to prevent ga~ from esaaping into
the radial passageways. Pistoye slots 195 are sealingly
enclosed on inner surface 50 by sealing means such as an
epoxy material positioned in the hollow portion which
extends thereinto from inner surface ~0, a predetermined
distance above axial passageway 160 that is adjacent to
inner surface 50. ThP gas by the above described con-
struction includes any gas, that flows through axial
passageway 160 into and along each pistoye slots 195 so
that the hydrogen will not escape. Containing the gas
within pistoye slots 195 restricts any hydrogen loss to an
; insignificant amount.
As best seen in Fig. 3, at the end regions of
the stator core 20, where there are both axial 160 and
radial 170 passageways the gas will normally tend to
intermix at the intersections. According to the present
inven~ion, an outer laminated sheet 171b belonging to
least one of the packs 176 is~outwardly turned or dimpled
~to surround arcuate notch 200 of an adjacent outer
laminated sheet 171b. Before dimpling, outer laminations
171b need not contain any opening aligned with axial
passageway 160 and is normally formed by a generally
flat, contiguous sheet. outer lamination 171b may be
deformed or bent outwardly toward an adjacent stack 176 at
the area of outer lamination 171b, which covers axial
passageway 160, is~matingly positioned~a~ainst an adjacent
lamination, and may~ be cut in place, ~or pre-cut or
hollowed out in;~the~area covering axial passageway 160 to
allow an unobstructed conduit aligned with that axial
~ passageway 160. The dimpled portion of sheet 171b
completely surrounds and encloses arcuate notch 200 for
providing an essentially isolated, tunnel-liXe flow path
ext nding from one dimpled sheet 171b to arcuate notch 200
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of the adjacent sheet 171b. This dimpling or embossing
provides a barrier between radial 170 and axial 160
passageways for isolating the two passageways 170/160.
Now referring to Figures 2 ~nd 4, it will be
appreciated that pistoye slots 195 are provided and
extend generally one hundred eighty degrees ~180 degrees)
on each side of arcuate notches 200 through the packs 176,
as previously mentioned. Axial and radial passageways
160/170 in the region of each pistoye slot 195 are
sealingly separated and isolated from each other by the
same apparatus and process as in the portion not contain-
ing pistoye slots 195 (Fig~ 3).
Referring now to Fig. 5, stator core 20 includes
the previously mentioned stacks of laminations 171 a/b
which define stator teeth 174 with axial and radial
passageways 160/170 therethrough. As previously mentioned
and as best seen in Fig. 5, positioned at the end portions
of stator core 20 in stator teeth 174 are the hollow
pistoye slots 195 which extend radially and axially
through a plurality of inner laminations 171a only and
open onto inner surface 50 of stator core 20, but term-
inate radially spaced from outer periphery 60 of stator
core 20~ Pistoye slots 195 have sealing means such as an
epoxy material, as previously mentioned, to prevent gas
from flowing radially out of stator teeth 174 into
housing 3~ ~Fig. 1). Pistoye slots 195 terminate between
adjacent vent fingers 1~0 and between end surfaces 25a~b
and an adjacent vent finger 190, allowing laminations 171
at both ends of pistoye slot 195 to be solid for prevent-
ing hydrogen from escaping in the radial direction. Suchsealing allows the hydrogen loss through the pistoye
slots to be controlled to an insignificant amount.
Referring to Fig. 6, in another embodiment of
the present invention, tubing 220 may be inserted into
axial passageways 160, forming a tunnel-like annular
member spanning the intersection of axial 160 and radial
170 passageways to sealingly isolate the two passageways
160/170. Tubing 220 has inner periphery surface 230,
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outer periphery surface 2~0, and wall thickness 250
between inner 230 and outer 240 periphery surfaces and may
be made of for example an insulating material such as
a ceramic or glass. The end portions of tubing 220 outer
surface 240 ara firmly attached to and matingly positioned
against the periphery surface of axial passageway 160 of
adjacent stacks 176, forming a sealed passageway that
overlaps a plurality of outer and inner laminations 171a/b
and the inner periphery surface of the axial passageways
160. Tubing 220 likewise can be used in either the
pistoye slots 210 area of stator teeth 174 or the portion
of stator teeth 174 without pistoye slots 210.
Referring to Fig. 7, in still another embodiment
of the present invention, sleeve 260 with a tubular
configuration is there shown to sealingly isolate axial
160 and radial 170 passageways. Sleeve 260/ which
includes inner periphery surface 270, outer periphery
surface (not shown), and wall thickness (not shown)
between inner 270 and outer periphery surface, has a
length substantially equal to the space between outer
sheets 180 of adjacent stacks 176. Sleeve 260 may be made
of for example stainless steel and is inserted into axial
passageways 16Q; inner periphery surface 270 of the sleeve
260 is positioned and aligned to form a continuous surface
and passageway with the periphery surface of axial
passageway 160 extending through adjacent packs 176. The
walls of sleeve 260 are positioned firmly against outer
laminated sheet 171b of adjacent stacks 176, forming a
seal to isolate the two passageways 160/170 to prevent gas
intermixing. Sleeve 260 can also be used in either the
pistoye slot 210 area of stator teeth 174 or the portion
of stator teeth 174 without plstoye slots 210.
Although the invention is fully described
herein, it is not intended that the invention as il~
lustrated and described be limited to the details shown,
because various modifications may be obtained with respect
to the invention without departing from the spirit of the
lnvention or the scope of equivalents thereof. For
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example, the outer two or more laminated sheets, rather
than a single sheet, may be turned outwardly toward an
adjacent stack to sealingly isolate the axial 160 and
radial 170 passageways.
Therefore, what is provided is an apparatus ~or
cooling stator end regions of stator cores wherein two
independent passageways of the same cooling system
intersect.
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