CA2094093A1 - Apparatus for cooling end regions of a stator core - Google Patents

Abstract

56,889 ABSTRACT OF THE DISCLOSURE
Disclosed herein is a generator stator core including an apparatus for cooling the end regions thereof by employing radial and axial intersecting passageways in the stator core for receiving a cooling medium. The stator core comprises a plurality of spaced-apart adjacent packs formed from a plurality of laminated sheets, well known in the art. The invention adds to the existing art an apparatus that seals and isolates the intersections of the axial and radial passageways in a stator core. In one example, this is accomplished by pre-forming the outer lamination of a pack so that it is bent to form an opening that conforms with the axial passageway and firmly engages the adjacent pack, thereby isolating the axial passageways from the radial passageways at the intersec-tion thereof. In other examples, such isolation is caused by placing conduits along the axial passageways between adjacent laminations.

Description

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56, 889 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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2~940~3 2 5~,889 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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2 ~ 9 3 3 56,8~9 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.

',. ' 2 ~ 9 3 4 56,889 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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2 ~ 9 3 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 ~4~93 6 56,889 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 .'' ~ ' . ' - . . . . .. . . .

2~4~93 7 56,889 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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~ 8 56,889 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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2~9~0~3 9 56,~89 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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- , ~ , 2~3~93 56,889 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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21D9~ 093 11 56,889 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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2 ~ 3 12 56,889 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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Claims (6)

1. An elongated annular stator core including means for enhancing the cooling of the end regions thereof comprising:
(a) a plurality of spaced-apart packs having a plurality of laminated sheets forming said stator core, adjacent packs defining a radial cooling passageway therebetween, each of said packs defining an axial cooling passageway therethrough; which intersect with said radial passageways; and (b) a barrier interposed between said adjacent packs and disposed at each of the intersections of said radial and axial passageways for isolating said axial passageway from said radial passageway.

2. An apparatus as in claim 1, wherein said barrier is formed from at least one of said sheets of one of said packs, which is outwardly curved from one of said packs toward said adjacent pack to surround said axial passageway to isolate said intersecting radial and axial cooling passageways.

3. An apparatus as in claim 1, (a) wherein said barrier is a tube having end portions and outer surface, said tube spanning the intersection of said axial and radial passageway; and (b) wherein the end portions of said tube outer surface are attached to respective ones of said packs to isolate the radial and axial passageways.

4. An apparatus as in claim 1, wherein said barrier is a sleeve having ends, the length of said sleeve being substantially equal to the space between adjacent 14 56,889 packs, each end of said sleeve abutting its respective pack to isolate the radial and axial passageways.

5. An apparatus as in claim 1, further compris-ing vent fingers positioned in said radial passageway for supporting said packs.

6. An apparatus as in claim 1, wherein said radial passageways are positioned only in the end regions of the stator core.