GB2381389A

GB2381389A - Securing windings in a salient pole rotor

Info

Publication number: GB2381389A
Application number: GB0121158A
Authority: GB
Inventors: Lawrence Haydock; William Brian Turner; Philip David Bend
Original assignee: Newage International Ltd
Current assignee: Cummins Generator Technologies Ltd
Priority date: 2001-08-31
Filing date: 2001-08-31
Publication date: 2003-04-30
Anticipated expiration: 2021-08-31
Also published as: GB2381389B; GB0121158D0

Abstract

Mutually perpendicular windings 14,15 are fixed in an inter-polar space 11 of a four pole rotor 10 by a fixing arrangement which includes two clamping members 17,18, two wedge members 19 and an intermediate angle member 20. The two wedge members 19 are in face-to-face abutment with respective ramp surfaces 27,28 formed on the clamping members and are interconnected co-axially by a nut and bolt -mechanism so as to be operable as a wedge expander which acts directly on each of the clamping members 17,18 to clamp a respective one of the windings 14,15 in the space 11 and through the angle member 20 to force the clamping members 17,18 apart and to urge an edge 38 of each clamping member 17,18 against an inner surface of a respective cantilever portion 39,41 of a respective pole piece portion 12,13 adjacent the mouth of the inter-polar space 11.

Description

A FIXING ARRANGEMENT FOR USE IN AN ELECTRICAL MACHINE This invention relates to a fixing arrangement for fixing electrical conductors in an inter-polar space formed in a salient pole rotor of a wire wound electrical machine, the conductors being part of a winding of the electrical machine. The inter-polar spaces are formed between adjacent pole pieces which are part of the structure of the rotor. A mouth of each inter-polar space is formed between tip portions of the pole pieces on either side of that mouth.

Rotor windings of electrical machines are traditionally held in place by various methods. These may involve use of steel spring wedges, aluminium extrusions held apart by studs, small aluminium cast wedges also held apart by studs, special extrusions which interlock with the pole tip portions, or other devices which are fastened with studs which extend radially towards the centre of the rotor.

Rotor windings are usually formed of copper wire which may be round or rectangular in section. Rotation of the rotor gives rise to centrifugal forces which necessitate that the copper winding must be secured beneath the pole tip portions of the rotating pole pieces of the rotor. The copper winding also gets hot in service due to copper losses and since the adjacent magnetic circuit is

formed of steel, on which the copper is wound, there is differential thermal expansion between the copper and the steel. Such expansion needs to be constrained.

Some designs of machine offer little or no space for some of the designs of wedges referred to above to work effectively. Machine size and duty cycle and/or cost, may lead to some of those designs being impractical.

Where space is limited, the traditional method is to use the aluminium extrusions or cast wedges held apart by studs and nuts which are in compression. The pole tip portions are relied on entirely as the anchor to secure the winding in place. This method has the following limitations.

Although the studs and nuts are assembled so as to hold the windings in place by compression, there is angular distortion of the winding along its axis because of the effects of centrifugal forces and thermal expansion and that causes a substantial bending moment on the studs. However the studs are not strained beyond their elastic limit so that the distortion is only temporary.

The combination of the bending of the studs and of the pole tip portions due to the loading thereon leaves the copper free to move slightly. Such movement can lead to premature insulation stressing and eventual failure within the life of the equipment, causing downtime of the equipment as a major repair would be necessary.

Such studs need to be manufactured from very high quality steel

because of the high loading they must be designed to withstand.

The location of the studs does not prevent the angular distortion of the copper as the primary restraint against such distortion is the resistance to stud bending.

The stud diameter is restricted by the very nature of the fastening and the space constrictions involved. This has an unfortunate effect on the strength in bending of the stud as the diameter is proportional to its strength in bending.

An object of this invention is to provide a fixing arrangement for fixing electrical conductors in an inter-polar space formed in a salient pole rotor of a wire wound electrical machine which is suitable for use where space is limited but which does not use studs and nuts, which are loaded in compression, whilst acting to hold aluminium extrusions or cast wedges apart.

According to this invention there is provided a fixing arrangement for fixing electrical conductors in an inter-polar space formed in a salient pole rotor of a wire wound electrical machine. the conductor being part of a winding of the electrical machine and the inter-polar space having an internal surface and a mouth, the fixing arrangement including wedge means and two clamping members, each clamping member having a clamping surface which is adapted to abut conductors which are positioned in the inter-polar space and to apply a clamping load thereto, an abutment surface which is adapted to abut a cooperating portion of the internal surface of the inter-polar space adjacent the

mouth thereof and thereby to react a clamping load exerted by at least one of the clamping members to clamp conductors in position in the inter-polar space and a flat ramp surface which is in sliding interengagement with a respective surface of the wedge means, the two clamping members, their ramp surfaces and the wedge means being oriented such that translational movement of the wedge means over the two ramp surfaces with which said wedge means are in sliding interengagement forces the two clamping members apart to apply the clamping load and urges the abutment surfaces into abutment with said cooperating portion of the internal surface of the inter-polar space to react the applied clamping load.

Preferably the wedge means act between the flat ramp surface of each clamping member and an opposed surface of the other clamping member to force the clamping members apart. In a preferred embodiment there is an intermediate member between the wedge means and the opposed surfaces of the two clamping members. Preferably, in order to accommodate manufacturing tolerances, the wedge means and the intermediate member are arranged so that, during assembly of the fixing arrangement, they can be brought into face to face abutment for load transfer between the wedge means and the clamping members through the intermediate member when either the wedge means or the intermediate member is located anywhere within a laterally extending range of possible positions relative to the other.

Conveniently, the clamping surfaces of the clamping members are substantially normal one to the other, the abutment surface of each clamping member is substantially normal to the clamping surface of that clamping member and the flat ramp surfaces of the clamping members are adjacent and are substantially mutually perpendicular. The intermediate member may be an angle member.

Preferably the flat ramp surface of each clamping member is one of an opposed pair of such flat ramp surfaces which meet at a common apex and the wedge means include an opposed pair of wedge members which are each in sliding interengagement with the juxtaposed substantially mutually perpendicular pair of flat ramp surfaces of the two clamping members on the same side of the two apices and wherein means are provided which are operable to urge the two wedge members towards one another whereby to force the two clamping members apart. The means which are operable to urge the two wedge members towards one another may be a nut and bolt arrangement.

Conveniently each limb of the angle member has a recess formed in the end of each of its limbs, each recess receiving the common apex of the respective one of the clamping members which thereby serve to locate the angle member against lengthwise displacement relative to the clamping members.

In a preferred embodiment, the angle member forms a spaced pair of substantially co-planar surfaces, each at the end of a respective one of its side

limbs that is remote from its apex, the spaced pair of substantially co-planar surfaces being adapted for face to face contact with a corresponding pair of spaced substantially co-planar surfaces formed on said wedge means.

Conveniently there is clearance between structure of the wedge means and of the angle member between said spaced pairs of substantially co-planar surfaces when those surfaces of the angle members are in face to face contact with the respective spaced surfaces of the wedge means.

One form of fixing arrangement in which this invention is embodied is described now by way of example with reference to the accompanying drawings, of which :- Figure 1 is a side view of part of a four pole salient pole rotor of a wire wound electrical machine which forms two half poles separated by an interpolar space in which conductors which are part of the rotor windings are fixed by a fixing arrangement which embodies this invention; Figure 2 is a view in perspective of a clamping member of the fixing arrangement shown in Figure 1; Figure 3 is a view in perspective of a wedge member of the fixing arrangement shown in Figure 1 ; and Figure 4 is a view in perspective of the angle member of the fixing arrangement shown in Figure 1.

Figure 1 shows part of a rotor 10 in which an inter-polar space 11 is

formed between two pole pieces 12 and 13. Two windings 14 and 15 are positioned within the slot 11 and are fixed therein by a fixing arrangement 16. Each winding 14,15 comprises a solid mass of electrical conductors embedded in epoxy resin. The conductors are wires which may have a square or round cross-section.

The fixing arrangement 16 includes two clamping members 17 and 18, two wedge members of which only one, 19, is shown in Figure I and an angle member 20. The fixing arrangement 16 is held together by a nut and bolt mechanism, the bolt head 21 being shown in Figure I together with a washer 23.

Figure 2 shows the clamping member 17. The clamping member 18 is geometrically similar to the clamping member 17. The clamping members 17 and 18 are die-castings.

The underside of the clamping member 17 as seen in Figure 2 is a flat surface 24 and it serves as a clamping surface which abuts the winding 14.

The structure of the clamping member 17 opposite to the flat clamping surface 24 is formed as an array 25 of heat sink fins to one side of a flat surface 26 which is formed substantially at the centre of the clamping member 17. The flat surface 26 extends from side to side of the clamping member 17 and is substantially normal to the flat clamping surface 24. The remainder of the surface of the structure of the clamping member 17 that is opposite to the flat

clamping surface 24 forms two flat ramp surfaces 27 and 28 which are both inclined at a small angle to the plane of the flat clamping surface 24 and which meet at a common apex to form a ridge 29 which extends from the flat surface 26 towards the edge of the clamping member 17 that is remote from the array 25 of fins substantially midway between the two sides of the clamping member 17. Hence the portion of the clamping member 17 on the side of the flat surface 26 remote from the array 25 of fins tapers from the central ridge 29 to each side of the clamping member 17.

The edge of the clamping member 17 that is remote from the array 25 of fins is stepped so that the portion 31 of it to one side of the ridge 29 is further from the flat surface 26 than is the remaining portion 32 of that edge.

A chamfer 33,34 is formed on the side of the clamping member 17 that is remote from the flat clamping surface 24 and along each edge portion 31,32, the chamfer 33, 34 extending from the respective edge portion 31,32 to the end of the respective ramp surface 27,28 that is remote from the flat surface 26. An intervening flat surface 35 which is substantially normal to the flat clamping surface 24 and to the flat surface 26 is formed at the step between the two chamfers 33 and 34 and is in line with the ridge 29. The width of a part of the clamping member 17 which includes the two edge portions 31 and 32 is greater than the width of the remainder which includes the array 25 and a major portion of each of the ramp surfaces 27 and 28, there being a step 36,37

formed in each side of the clamping member 17 at the junction of that part and the remainder. This arrangement enables a greater surface area of the portion 9 1 of the clamping surface 24 that is formed by the wider part of the clamping member 17 to be applied to the respective winding 14,15 to retain it in position.

The arrangement of the chamfers 33 and 34 and the intervening flat surface 35 is such that, when the two similar clamping members 17 and 18 are first positioned in the inter-polar space 11 as shown in Figure I with their flat edges 38 that are remote from the respective stepped edge portions 31 and 32 in abutment with the inner surface of the portion of the inter-polar space 11 that is formed by the end of the respective cantilever portion 39, 41 of the respective pole piece portion 12, 13 that forms the respective edge of the mouth of the inter-polar space 11, the chamfer 33 of each of the clamping members 17 and 18 can be placed in face to face abutment with the chamfer 34 of the other of the clamping members 17 and 18 in which case the two clamping surfaces 24 will be substantially orthogonal as will the two flat surfaces 26. Also that portion of the clamping surface 24 of each of the clamping members 17 and 18 can be arranged to extend into the corner that is formed between the two windings 14 and 15, as can be seen in Figure 1, thereby providing support for the respective winding 14, 15 over the full extent of its surface that is abutted by that part of the clamping surface 24 of the

respective clamping member 17,18 that extends from the flat edge 38 to the edge portion 31. There would be a small gap between the adjacent edges of the flat surface$ 26 which are suitably chamfered as can be seen in Figure 2.

Figure 3 shows the wedge member 19. It has two mutually perpendicular faces 42 and 43 which are each to be in face to face abutment with the respective one of an opposed pair of the flat ramp surfaces 27 and 28 of the two clamping members 17 and 18 to one side of the ridges 29 of those two clamping members 17 and 18 when the two clamping members 17 and 18 are positioned in the inter-polar space 11 as described above. The wedge member 19 has a through bore 44 formed in it. The axis of the bore 44 is orientated within the wedge 19 such that it will be substantially parallel to the mutually perpendicular clamping surfaces 24 of the two clamping members 17 and 18 when the wedge member 19 is in face to face abutment with the respective opposed pair of flat ramp surfaces 27 and 28. Two arcuate grooves 45 and 46 are formed in the part of the surface of the wedge member 19 that extends between the two faces 42 and 43. The axes of the arcuate grooves 45 and 46 are substantially parallel to the axis of the through bore 44. The two grooves 45 and 46 are displaced substantially symmetrically on either side of the plane that includes the axis of the through bore 44 and the junction of the two faces 42 and 43. The structure 47 of the wedge member 19 between the two grooves 45 and 46 tapers to a ridge 48 which is substantially parallel to

the axis of the through bore 44. The structure 47 and the two arcuate grooves 45 and 46 separate two substantially co-planar flat surfaces 49 and 51. In addition to providing stress relief in the structure of the wedge member 19, the two arcuate grooves 45 and 46 enable the co-planar flat surfaces 49 and 51 to extend towards the structure 47 to a greater extent thus maximising the width of each of those flat surfaces 49 and 5 I.

The wedge member 19 is one of two similar wedge members which are die castings. The other wedge member (not shown) is placed in face to face abutment with the other opposed pair of the flat ramp surfaces 27 and 28 of the two clamping members 17, 18 on the opposite side of the ridges 29 from the wedge member 19. The shank of the bolt extends from the bolt head 21 through the through bore 44 of the wedge members and the nut is fitted to the bolt so that the two wedge members are between the nut and the bolt head 21.

Figure 4 shows the angle member 20. It has an apex 52 and two divergent side walls 53 and 54. The length of the angle member 20 along the ridge formed by the apex 52 is substantially equal to the width of the remainder part of each clamping member 17,18 that extends between the steps 36 and 37 and the flat edge 38. A bulbous protuberance 55,56 is formed along the inner edge of each side wall 53,54 at the end thereof remote from the apex 52. The end surface 57. 58 of each side wall 53,54 remote from the apex 52 is flat, the two flat surfaces 57 and 58 being substantially co-planar.

Provision of each of the bulbous protuberances 55 and 56 enables the width of the respective flat surfaces 57 and 58 to be maximised. A shallow recess 59, 1 is formed in each side of the angle member 20 at the junction of each side wall 53,54 and the respective flat end surface 57. 58. Each recess 57,58 is bounded by a pair of flat trapezium shaped surfaces which include an oblique angle between them. The angle member 20 is a loose fit on the two wedge members with each flat end, surface 57,58 of the angle member 20 being in face to face contact with a respective one of the two substantially co-planar flat surfaces 49,51 of each of the two wedge members. The surface area of the abutting flat end surfaces 57 and of the angle member 20 on the one hand and the coplanar flat surfaces 49 and 51 of the respective wedge member is maximised by the provision of the arcuate grooves 45 and 46 and by the bulbous protuberances 55 and 56. Figure 1 shows that there is a clearance between the tapered structure 47 of the two wedge members and the interior of the angle member 20 when the latter is loosely fitted on the wedge members.

Hence the position of the angle member 20 relative to the two clamping members 17 and 18 can be adjusted by sliding the angle member 20 laterally on the two clamping members to accommodate dimensional tolerances. The angle member 20 is a die casting.

When the fixing arrangement 16 is assembled as described above and as shown in Figure 1, the outer surface of each of the side walls 53 and 54 of the

angle member 20 is in face to face abutment with the flat surface 26 of a respective one of the clamping members 17 and 18. The nut and bolt is tightened up so as to draw the two wedge members towards one another and so that the mating flat surfaces of the wedge members and the clamping members 17 and 18 on one side and of the angle member 20 on the other side are loaded so that any load that is applied to the wedge members is evenly spread along those mating flat surfaces by which it is transferred to the clamping members 17 and 18 through the respective ramp surfaces 27 and 28 and to the angle member 20 through the mating spaced pairs of flat surfaces 49 and 51 and 57 and 58. Each of those wedge members slides along the respective flat ramp surface 27, 28 towards the ridge 29 and acts through the angle member 20 to force the two clamping members 17 and 18 apart so that each clamping member 17 and 18 applies a clamping load to the respective conductor 14, 15, the flat edge 38 of that clamping member 17, 18 being in abutment with the inner surface of the respective cantilever portion 39, 41 of the respective pole piece portion 12, 13.

The ridges 49 project into the respective shallow recesses 59 and 61 and thereby serve to retain the angle member 20 in position and to inhibit lengthwise displacement of it relative to the clamping members 17 and 18.

The interengaged flat casting faces of the ramp surfaces 27 and 28 and of the wedge members minimise the risk of relative angular movement between I

the parts of the fixing arrangement 16 and the electrical conductors 14 and 15.

The clearance between the tapered structure of 47 of each of the wedge members and the interior of angle member 20 facilitates accommodation of the manufacturing tolerance of the insulant covered multi-wired electrical conductors 14 and 15 without the stressed faces of the fixing arrangement 16 being affected significantly and ensures that all contact planes remain true to each other.

Claims

Claims 1. A fixing arrangement for fixing electrical conductors in an inter-polar space formed in a salient pole rotor of a wire wound electrical machine, the conductors being part of a winding of the electrical machine and the inter-polar space having an internal surface and a mouth, the fixing arrangement including wedge means and two clamping members, each clamping member having a clamping surface which is adapted to abut conductors which are positioned in the inter-polar space and to apply a clamping load thereto, an abutment surface which is adapted to abut a cooperating portion of the internal surface of the inter-polar space adjacent the mouth thereof and thereby to react a clamping load exerted by at least one of the clamping members to clamp conductors in

position in the inter-polar space and a flat ramp surface which is in sliding tn' interengagement with the respective surface of the wedge means, the two clamping members, the ramp surfaces and the wedge means being oriented such that translational movement of the wedge means over the two ramp surfaces with which the wedge means are in sliding interengagement forces the two clamping members apart to apple the clamping load and urges the abutment surfaces into abutment with said cooperating portion of the internal surface of the inter-polar space to react the applied clamping load.

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2. A fixing arrangement according to claim 1. wherein the wedge means act between the flat ramp surface of each clamping member and an opposed surface of the other clamping member to force the clamping members apart.
3. A fixing arrangement according to claim 2, wherein there is an intermediate member between the wedge means and the opposed surfaces of the two clamping members.
4. A fixing arrangement according to claim 3. wherein the wedge means 9 z : l and the intermediate member are arranged so that, during assembly ot the fixing arrangement, they can be brought into face to face abutment for load transfer between the wedge means and the clamping members through the intermediate member when either the wedge means or the intermediate member is located anywhere within a laterally-extending range of possible positions relative to the other.
5. A f'xin 5. A fixing arrangement according to any one of claims I to 4, wherein the clamping surfaces of the clamping members are substantially normal one to the other, the abutment surface of each clamping member is substantially normal to the clamping surface of that clamping member and the flat ramp surfaces of the clamping members are adjacent and substantially mutually

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perpendicular.
6. A fixing arrangement according to claim 3, claim 4, or claim 5 appended to claim 3, wherein the intermediate member is an angle member.
7. A fixing arrangement according to any one of claims 1 to 6, wherein the flat ramp surface of each clamping member is one of an opposed pair of such flat ramp surfaces which meet at a common apex and the wedge means include an opposed pair of wedge members which are each in sliding interengagement with the juxtaposed substantially mutually perpendicular pair of flat ramp surfaces of the two clamping members on the same side of the two apices and wherein means are provided which are operable to urge the two wedge members towards one another whereby to force the two clamping members apart.
8. A fixing arrangement according to claim 7, wherein said means which are operable to urge the two wedge members towards one another are a nut and bolt arrangement.
9. A fixing arrangement according to either of claims 7 and 8 when appended to claim 6, wherein each limb of the angle member has a recess

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formed in the end of each of its limbs, each recess receiving the common apex of the respective one of the clamping members which thereby serve to locate the angle member against lengthwise displacement relative to the clamping members.
10. A fixiNg arrangement according to claim 6 or claim 9 or either of claims 7 and 8 when appended to claim 6, wherein the angle member forms a spaced pair of substantially co-planar surfaces, each at the end of a respective one of its side limbs that is remote from its apex, the spaced pair of substantially co-planar surfaces being adapted for face to face contact with the corresponding pair of substantially co-planar surfaces formed on said wedge means.
11. A fixing arrangement according to claim 10 wherein there is a clearance between a structure of the wedge means and of the angle member between said spaced pairs of substantially co-planar surfaces when those surfaces of the angled member are in face to face contact with the respective spaced surfaces of the wedge means.
12. A fixing arrangement for fixing an electrical conductor in a semi-closed slot formed in a rotor of a wire wound electrical machine substantially as

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described hereinbefore with reference to and as shown in the accompanied drawings.