Abstract
A rotor for a rotating electrical machine, is disclosed, the rotor comprising a plurality of salient poles (14), rotor windings (16) on the salient poles, and a wedge (40; 60) for retaining the rotor windings of two adjacent poles, the wedge extending partway through the windings in an axial direction. The wedge comprises two legs (42, 44; 62, 64) arranged at an angle to each other. The wedge is configured to be slid axially in the rotor during assembly. This may maximize the space available for axial air flow between adjacent salient poles, while allowing the wedge to have sufficient strength to retain the windings, particularly in machines where higher forces may be developed.
Claims
1. A rotor of a rotating electrical machine, the rotor comprising: a plurality of salient poles; rotor windings on the salient poles; and a wedge configured to retain the rotor windings of two adjacent poles, wherein the wedge extends partway through the windings in an axial direction, the wedge comprises two legs arranged at an angle to each other, and the wedge is configured to be slid axially in the rotor during assembly.
2. The rotor of claim 1, wherein the wedge is a single piece.
3. The rotor of claim 1, wherein the wedge has an L-shaped cross-section.
4. The rotor of claim 1, wherein the wedge is configured to be inserted axially into the rotor.
5. The rotor of claim 1, wherein the wedge has a first leg which abuts rotor windings on a first salient pole and a second leg which abuts rotor windings on a second, adjacent salient pole, and wherein the first leg and the second leg are substantially planar.
6. (canceled)
7. The rotor of claim 5, wherein the wedge in its free state has an angle between the first leg and the second leg substantially equivalent to an angle between two adjacent salient poles.
8. (canceled)
9. The rotor of claim 8, wherein the wedge is arranged to have an angle between the first leg and the second leg which is substantially fixed in the free state, during assembly and/or in the assembled rotor.
10. The rotor of claim 9, wherein an axial cooling channel is defined between the first leg and the second leg.
11. The rotor of claim 5, wherein the wedge is of a design which does not include a bracing member between the first leg and the second leg.
12. The rotor of claim 1, wherein the wedge is not elastically deformable.
13. The rotor of claim 1, wherein the wedge is not subjected to a bending moment when the rotor is stationary.
14. The rotor of claim 1, wherein the salient poles comprise pole tips and the wedge is configured to slide beneath the pole tips of two adjacent poles.
15. The rotor of claim 1, wherein the wedge has insufficient elastic deformability for it to be inserted radially into the rotor between pole tips of adjacent salient poles.
16. The rotor of claim 14, wherein at least one of the pole tips has a recess which allows a wedge to be inserted radially into the rotor and then slid axially to a position under a pole tip without a recess.
17. The rotor of claim 1, further comprising a compressible sheet between the wedge and the windings, wherein the compressible sheet is arranged to absorb resin during an impregnation process.
18. (canceled)
19. The rotor of claim 1, wherein the salient poles comprise winding supports for supporting a radially inward side of the rotor windings; a gap is provided between the winding supports of two adjacent salient poles; the wedge comprises an extension which extends into the gap between the winding supports of two adjacent salient poles; and the extension engages with the winding supports to retain the wedge radially.
20. (canceled)
21. The rotor of claim 1, comprising a plurality of wedges at spaced locations in an axial direction for retaining the windings of two adjacent poles.
22. The rotor of claim 21, wherein at least one of the wedges is of a different type from at least one of the other wedges.
23. The rotor of claim 21, wherein at least one of the wedges is configured to be inserted radially into the rotor.
24. (canceled)
25. A method of assembling a rotor for a rotating electrical machine, the rotor comprising a plurality of salient poles, rotor windings on the salient poles and a wedge for retaining the windings of two adjacent poles, the method comprising: providing a wedge comprising two legs arranged at an angle to each other; and sliding the wedge axially in the rotor to a position where the wedge extends partway through the windings in an axial direction.
Description
[0049] FIG. 1 is a radial cross section through part of a rotating electrical machine;
[0050] FIG. 2 shows parts of a previously considered rotor;
[0051] FIG. 3 shows a known retaining wedge;
[0052] FIG. 4 shows parts of a rotor with another known wedge design;
[0053] FIGS. 5A to 5C illustrate how the wedge of FIG. 4 is inserted into the rotor;
[0054] FIGS. 6A and 6B show a side view and an end view of a wedge in an embodiment of the invention;
[0055] FIG. 7 shows part of a rotor in an embodiment of the invention;
[0056] FIG. 8 shows parts of a rotor in another embodiment of the invention;
[0057] FIG. 9 shows parts of a rotor in another embodiment of the invention;
[0058] FIG. 10 shows part of a rotor with a plurality of wedges in another embodiment of the invention;
[0059] FIG. 11 shows part of a rotor with a plurality of wedges in a further embodiment of the invention; and
[0060] FIG. 12 shows part of a rotor with a slide wedge in another embodiment.
[0061] FIG. 1 is a radial cross section through part of a rotating electrical machine. The machine comprises a rotor 2 located inside a stator 3 with an air gap 4 between the two. The rotor 2 is mounted on a shaft with an axis of rotation indicated by the dashed line 5. The rotor 2 is wound with rotor windings 6. The stator 3 comprises a stator core with slots on its inner circumference in which are wound stator windings 7. The stator 3 is contained within a stator frame 8. A shaft-driven fan 9 is located at the drive end of the machine.
[0062] In operation, the rotor 2 rotates inside the stator 3. An electrical current flowing in the rotor windings 6 causes a magnetic flux to flow radially across the air gap 4 between the rotor and the stator. The fan 9 is used to draw cooling air in an axial direction through the machine. If desired, an external, independently driven fan or fans or any other appropriate means of forcing air through the machine could be used instead of or as well as a shaft driven fan.
[0063] FIG. 2 shows parts of a previously considered rotor for a rotating electrical machine. Referring to FIG. 2, the rotor 10 comprises a rotor core 12 which is formed from a plurality of laminated sheets of metal stacked together to create a rotor of the required axial length. The rotor core 12 comprises a plurality of salient poles 14, each of which extends radially outwards from the centre of the rotor core. Each salient pole is wound with rotor windings 16. The windings 16 are in the form of a coil comprising a conductor such as copper wire which is wound around the pole 14. The windings 16 include side windings which run in a substantially axial direction along the length of the rotor, and end windings which run in a substantially tangential direction around the end of the rotor. Retaining wedges 18 are provided at spaced locations along the side windings. The retaining wedges 18 press against the side windings of two adjacent poles in order to hold the windings in place. The wedges 18 are designed to retain the rotor windings 16 against centrifugal and other forces while the machine is in operation. The salient poles 14 include pole tips 20 which extend circumferentially on either side of the pole at the radially outermost end. The pole tips 20 help to support the rotor windings 16 against the forces which are developed during operation of the machine. The retaining wedges 18 are held in place in part by the pole tips 20, and in part by frictional forces between the wedges and the windings. Rotor winding support bars 22 are also provided. The rotor winding support bars 22 run in an axial direction through the rotor and extend outwards at each end of the rotor in order to support the end windings. In this example the rotor has four poles, although other machines may have a different number of poles.
[0064] FIG. 3 shows in more detail a retaining wedge of the type used in the rotor of FIG. 2. Referring to FIG. 3, the wedge 18 comprises a first wedge member 24, a second wedge member 26, and a stud assembly 28. The first wedge member 24 and second wedge member 26 each has an outer surface which is designed to abut rotor side windings on a respective rotor pole. Wedge-shaped protrusions 25, 27 are provided on the inner surfaces of the wedge members (the surfaces which face each other). The wedge-shaped protrusions 25, 27 extend circumferentially inwards and engage with the stud assembly. The stud assembly 28 comprises a stud, nuts and washers. In the assembled rotor, the stud assembly 28 is in compression and pushes apart the first wedge member 24 and the second wedge member 26, causing them to press against their respective windings. The first wedge member and the second wedge member are typically formed from cast aluminium.
[0065] It has been found that the retaining wedge assembly of FIG. 3 can provide good mechanical retention of the rotor windings. However, due to the size and shape of the wedge members and the stud assembly, they may restrict axial air flow through the rotor. Reducing this restriction would increase air flow and improve cooling of the rotor windings. Inserting the wedge assemblies into the rotor also takes some time since each stud assembly needs to be tightened individually.
[0066] FIG. 4 shows parts of a rotor with another known wedge design. Referring to FIG. 4, the rotor comprises a rotor core 12 with a plurality of salient poles 14 and rotor windings 16, which may be substantially in the form described above. A plurality of wedges 30 are provided between the side windings of adjacent poles. Each wedge 30 comprises a single piece of material such as steel bent to form a first leg and a second leg. Each leg has an outer surface which is designed to abut rotor windings in a respective rotor pole. The wedges 30 are held in place in part by the pole tips 20, and in part by frictional forces between the wedges and the windings. In this arrangement, the wedges 30 are L-shaped spring wedges that are subjected to a bending moment during insertion and when in place. The wedge design of FIG. 4 may be used in smaller machines where lower forces are developed.
[0067] FIGS. 5A to 5C illustrate how the wedge 30 of FIG. 4 is inserted into the rotor. FIG. 5A shows the wedge 30 in its free state, before insertion. Referring to FIG. 5A, the wedge comprises a first leg 32 and a second leg 34 which are at an angle to each other. In this state, the angle between the first leg 32 and the second leg 34 of the wedge is greater than 90.
[0068] FIG. 5B shows the wedge 30 during insertion into the rotor. As the wedge 30 is inserted, the two legs 32, 34 of the wedge are pressed towards each other. The angle between the two legs reduces to less than 90 as the wedge passes radially through the smallest gap between the rotor windings and the opposite pole tip. At this point the wedge is subjected to high assembly stresses due to bending.
[0069] FIG. 5C shows the wedge 30 after insertion. The wedge retains sufficient elasticity to spring into its final fitted position. The angle of the wedge when fitted is approximately 90. The wedge 30 applies a small load to the rotor windings which prevents the wedge from moving axially during subsequent manufacturing processes. To ensure the wedge 30 does not crack during insertion and remains elastic, the thickness of the wedge is limited. The steel grade and hardness of the wedge are controlled so that the yield strength of the steel is sufficiently high.
[0070] The spring wedge design of FIGS. 4 and 5 is smaller in cross section than the cast aluminium wedges of FIGS. 2 and 3, and so provides less restriction to air flow. However, the spring wedge design is limited in mechanical performance since the wedge must be sufficiently ductile to compress when being fitted, but also sufficiently elastic to spring back against the rotor winding. With these mechanical constraints it has been found that the spring wedge is an option in smaller machines. However, larger or faster rotors may need a more robust wedge.
[0071] FIGS. 6A and 6B show respectively a side view and an end view of a wedge in an embodiment of the invention. The wedge in this embodiment is designed to have a small cross section, comparable to that of a spring wedge, but without its mechanical restrictions. The wedge is an L shape wedge similar in appearance to the spring wedge but is at a fixed 90 angle in its free state and when assembled to the rotor.
[0072] Referring to FIGS. 6A and 6B, the wedge 40 in this embodiment comprises an L shaped piece of material with a first leg 42 and a second leg 44. The legs 42, 44 are substantially planar, and are joined by a bend 45 with an inner radius r. Each leg 42, 44 has an outer surface which is designed to abut rotor windings in a respective rotor pole. The inner surfaces (the surfaces facing each other) are substantially flat. The wedge 40 has a length I.sub.1 in the direction of the first leg 42 and a length 12 in the direction of the second leg 44. The lengths I.sub.1 and 12 are roughly equal and correspond approximately to the distance between the outside of the windings on one pole and the inside of the pole tip on the adjacent pole. The legs 42, 44 are arranged at an angle to each other. The wedge is designed not to be elastically deformable, and thus the angle remains substantially constant when the wedge is in its free state, during insertion and in the assembled rotor. In this embodiment, the angle between the first leg 42 and the second leg 44 is 90 (within margins of tolerance) which corresponds to the angle between two adjacent salient poles in a four-pole machine. The wedge 40 has a thickness t which is substantially constant. The thickness t and the width w of the wedge, as well as the material and the manufacturing process, are chosen to give the wedge sufficient strength to retain the rotor windings, while allowing maximum air flow through the machine.
[0073] The wedge 40 may be manufactured from any suitable material such as hot rolled steel plate. In this case, the grain of the steel is in a radial direction (the direction of the legs 42, 44 away from the bend 45). This helps to provide the wedge with the necessary strength to retain the rotor windings.
[0074] To assemble the wedge 40 of FIGS. 6A and 6B, the wedge is inserted axially into the rotor from one end and then slid axially along the rotor, instead of being inserted radially between the pole tips. This wedge may therefore be referred to as a slide wedge. Since the wedge does not need to be elastically deformable, the thickness t of the wedge can be larger than would be the case for a spring wedge.
[0075] FIG. 7 shows part of a rotor with a slide wedge in one embodiment. Referring to FIG. 7, the rotor comprises a rotor core 12 with a plurality of salient poles 14 and rotor windings 16, which may be substantially in the form described above. A wedge 40 is provided between two adjacent salient poles 14, in order to retain the rotor windings 16. The wedge 40 comprises a first leg 42 and a second leg 44. The first leg 42 sits beneath (in a radial direction) a pole tip 20 of one pole and the second leg 44 sits beneath the pole tip 20 of an adjacent pole. The (radially outwards) ends of the legs 42, 44 abut, or are in close proximity to, the pole tips 20. The radially inwards sides of the pole tips are substantially flat and extend in a generally tangential direction.
[0076] Although for simplicity a single wedge is shown, a plurality of wedges 40 may be provided at spaced locations in an axial direction through the rotor, and between each pair of adjacent salient poles. If desired, insulation paper (not shown) may be provided between the wedge 40 and the windings 16.
[0077] During assembly, the wedge 40 is inserted into the rotor from one end, axially, and then slid axially along the rotor with each leg 42, 44 under a respective pole tip 20. During insertion, the rotor windings 16 may need to be held back against the poles 14 by tooling as the slide wedge 40 is inserted axially. This is because the windings may bulge out from the poles prior to the wedges being fitted.
[0078] When in place, the wedge 40 is retained radially by the pole tips 20. This is achieved by virtue of the fact that the gap between two adjacent pole tips decreases with increasing radial distance. Thus, the wedge 40 is retained without the need for grooves or other retaining means in the pole tips. The thickness of the wedge 40 corresponds substantially to the amount by which a pole tip 20 extends past the rotor windings 16.
[0079] When comparing the spring wedge of FIGS. 4 and 5 with the slide wedge of FIGS. 6 and 7, assuming a similar rotor design, the following differences can be noted: [0080] The slide wedge 40 has an angle between the two legs 42, 44 which is fixed in its free state, during assembly and when assembled to the rotor. [0081] The slide wedge 40 is not in bending moment against the rotor windings. [0082] The thickness t of the slide wedge 40 can be greater than that of the spring wedge. [0083] The lengths I.sub.1 and 12 of the legs 42, 44 in the slide wedge may be slightly less than those of the spring wedge, to provide clearance for the slide wedge to slide under the pole tips.
[0084] The slide wedge design of FIGS. 6 and 7 may provide the following features and advantages: [0085] Reduced restriction to air flow compared with standard rotor wedge assemblies. [0086] The thickness of the wedge can be increased compared to the spring wedge since the wedge is not compressed during insertion (zero assembly stress). [0087] The thicker wedge increases the mechanical retention of the rotor windings and allows the wedge to be used on larger rotor sizes. [0088] More readily available materials such as common steel grades may be used for manufacturing of the wedge, and it may be possible to avoid the need for controlled heat treatment. This may reduce part cost.
[0089] FIG. 8 shows parts of a rotor in another embodiment. Referring to FIG. 8, the rotor comprises a rotor core 12 with a plurality of salient poles 14 and rotor windings 16 which may be substantially in the form described above. In this embodiment each salient pole 14 has two support bars 22 to support the rotor end windings. A plurality of wedges 40 are provided between two adjacent rotor poles to retain the side windings. The wedges 40 are of the type described above with reference to FIGS. 6 and 7. The wedges 40 between two adjacent poles are located at spaced locations in an axial direction through the rotor. During assembly, each wedge is slid axially into place. The wedges 40 are located under the pole tips 20 of two adjacent salient poles 14.
[0090] In the arrangement of FIG. 8, the pole tips 20 on one side of a pole 14 have a plurality of recesses 46. The recesses may be formed by removing part of the pole tip from some of the rotor laminations prior to assembly. The recesses have a length in an axial direction which is slightly larger than the width w of a wedge. The recesses 46 allow a wedge 40 to be inserted radially into the rotor through the gap created by a recess. The wedge is then slid axially along the rotor so that it is under a part of the pole tip where there is no recess.
[0091] By providing a rotor with recesses 46 in the pole tip in the manner shown in FIG. 8, the distance that the wedges need to be slid along the core can be reduced, which may facilitate assembly and help avoid damage to the windings.
[0092] In the arrangement of FIG. 8, three recesses 46 are shown at spaced locations along the rotor in an axial direction. However, it will be appreciated that any appropriate number of recesses (for example, one, two, three, four or more) could be provided at any appropriate location. Recesses may be provided in either or both of the pole tips in adjacent poles.
[0093] FIG. 9 shows parts of a rotor in another embodiment. Referring to FIG. 9, the rotor comprises a rotor core 12 with a plurality of salient poles 14 and rotor windings 16 which may be in the form described above. Each salient pole 14 has two support bars 22 to support the rotor end windings. A plurality of wedges 30, 40 are provided between two adjacent rotor poles to retain the side windings. Each of the wedges 30, 40 is held in place by the pole tips 20.
[0094] In this embodiment, a combination of slide wedges 40 and spring wedges 30 is used. A slide wedge 40 is provided between two adjacent poles at each end of the rotor axially. A plurality of spring wedges 30 are provided between two adjacent poles at intermediate positions between the two ends. During assembly, each of the slide wedges 40 is inserted axially into the rotor from a respective end of the rotor, and slid axially into place. Each of the spring wedges 30 is inserted radially into the rotor, using the techniques described above with reference to FIGS. 5A to 5C.
[0095] Due to the movement of the rotor end windings, the wedges at the ends of the rotor core may be subjected to higher loads compared with the wedges in the centre of the rotor core. Having more robust slide wedges at the ends of the rotor core may allow less mechanically robust spring wedges to be used in the centre of the core. The spring wedges may be easier to insert in the centre of the core, with the slide wedges only needing to be slid a short distance from the core ends.
[0096] It will be appreciated that any appropriate combination of slide wedges and spring wedges could be used. For example, two slide wedges could be provided at each end of the rotor, or slide wedges could be alternated with spring wedges, or any other combination.
[0097] FIG. 10 shows part of a rotor with another embodiment of a slide wedge. Referring to FIG. 10, the rotor comprises a wedge 40 which is slid axially into place between two adjacent salient poles in a similar way to the slide wedges described above. However, in this embodiment, the slide wedge 40 has additional clearance between the wedge and the rotor windings 16 to help slide the wedge into position. A compressible sheet 48 is used between the wedge 40 and the windings 16 to fill the gap. The compressible sheet 48 may be made from a textile material, such as felt, or some other material such as a plastic. The compressible sheet 48 reduces the friction between the wedge 40 and the windings 16 and facilitates sliding of the wedge without damaging the windings. The compressible sheet 48 also helps to absorb any variations in the gap between the wedge 40 and the windings 16. However, the compressible sheet 48 preferably absorbs resin during a subsequent impregnation process. When the resin has hardened, this helps to lock the wedge in position.
[0098] In the embodiments described above, the wedge 40 may be manufactured from any suitable material such as hot rolled steel plate. For example, it has been found that common steel grade may be used without heat treatment, which may help to reduce part cost and complexity. The direction of the grain is preferably in a radial direction rather than an axial direction, to help the wedge retain its shape. If desired, a coating may be applied to the wedge to reduce friction and/or provide electrical insulation.
[0099] While the use of steel wedges may help to reduce cost and complexity, in some circumstances there may be a risk of flux leakage through the steel. In alternative embodiments, this may be prevented by using wedges manufactured from a material with a lower magnetic susceptibility such as aluminium. The aluminium wedges may be manufactured, for example, using a casting process.
[0100] FIG. 11 shows part of a rotor with another embodiment of a slide wedge. Referring to FIG. 11, the rotor comprises a wedge 50 which is slid axially into place between two adjacent salient poles in a similar way to the slide wedges described above. In this embodiment, the slide wedge 50 is made from aluminium, and may be manufactured using a casting process. The wedge 50 is L shaped with a first leg 52 and a second leg 54. Each leg 52, 54 has an outer surface which abuts the windings 16 on a respective rotor pole 14. The outer surfaces of the two legs 52, 54 have an angle between them of 90. However, each leg 52, 54 has a thickness which reduces from the centre of the wedge towards the ends. This allows the strength of the wedge to be increased at the point of maximum stress.
[0101] In this embodiment, a plurality of cooling fins are provided on the inner surfaces of each leg 52, 54. The fins may be formed during the casting process, or may be machined after the wedge has been cast. The cooling fins help with cooling of the rotor windings when the machine is in use.
[0102] Although in this embodiment the wedge 50 is cast from aluminium, any appropriate material, such as another metal or a plastic material may be used instead or as well, and any appropriate manufacturing process may be used.
[0103] FIG. 12 shows part of a rotor with a slide wedge in another embodiment. Referring to FIG. 12, the rotor comprises a rotor core 12 with a plurality of salient poles 14 and rotor windings 16, which may be substantially in the form described above. As in previous embodiments, the salient poles 14 include pole tips 20 which help to support the rotor windings 16 against centrifugal and other forces. However, in this embodiment, the salient poles 14 include winding supports 58 beneath the windings 16. The winding supports 58 are located on both sides of the salient poles 14 and extend from the salient poles into the interpolar space between two adjacent poles. Each winding support 58 is located directly beneath (radially inwards) of the rotor windings 16 of that pole, in order to support the windings in a radial direction. The radially inward sides of the winding supports 58 are open, and form axial channels through the rotor. The axial channels allow cooling air to pass beneath the winding supports. In this embodiment the winding supports 58 are integral with the salient poles and may be formed as part of a stamping process when the rotor laminations are manufactured.
[0104] In the arrangement of FIG. 12, the winding supports 58 extend across substantially the whole depth of the windings 16 in a generally circumferential direction. However, a gap is left between the end (circumferentially) of a winding support of one pole and that of the adjacent pole which extends into the same interpolar space. The gap is used to help retain rotor wedges.
[0105] Still referring to FIG. 12, a wedge 60 is provided between two adjacent salient poles 14, in order to retain the rotor windings 16 in a circumferential direction. The wedge 60 is L-shaped with a first leg 62 and a second leg 64 at an angle to each other. The legs 62, 64 are substantially planar, and are joined by a bend, in a similar way to the wedges described above. However, in this embodiment, the wedge includes an extension which extends radially inwards from the bend. The extension extends through the gap between the ends of the winding supports 58 of two adjacent poles. The extension comprises a neck 66 and a head 68. The neck 66 has a width (in a circumferential direction) which smaller than the gap between the ends of the winding supports 58. The neck 66 extends through this gap and into the axial channel beneath the winding supports. However, the head 68 has width which is larger than the gap. Thus, the head 68 is not able to pass through the gap in a radial direction. The head 68 is located in the axial channel beneath the winding supports 58. In this embodiment, the head 68 engages with the winding supports 58 in order to hold the wedge in place.
[0106] During assembly, the wedge 60 is inserted into the rotor from one end, axially, with the head 68 in the axial channel beneath the winding supports 58. The wedge is then slid axially along the rotor with each leg 62, 64 against a respective rotor winding 16. As the wedge is slid axially, the head 68 slides through the axial channel. Once the wedge is in position, the winding supports 58 and the head 68 retain the wedge radially. A plurality of wedges are provided at spaced locations axially through the rotor. Each of the wedges may be the same or different.
[0107] The arrangement of FIG. 12 can allow the wedge to be held in place without applying a force to the pole tips. This may allow the pole tips to be smaller than would otherwise be the case and/or additional space to be provided for rotor windings. This in turn may help to improve the power density and/or peak efficiency of the machine.
[0108] In the arrangement shown, the legs 62, 64 extend part way across the rotor windings 16 in a radial direction, but not as far as the pole tips 20. However, if desired, the legs 62, 64 could extend as far as the pole tips 20, or some other distance across the windings.
[0109] In an alternative embodiment, a tapped bar is provided in the axial channel beneath the winding supports, and a bolt passes through a hole in the wedge, through the gap between the ends of the winding supports 58 and into the tapped bar. The tapped bar and the wedge, and optionally the bolt, may be slid axially into position. When in position, the bolt may be tightened to draw the wedge towards the tapped bar and thus the winding supports. This arrangement can help to retain the wedge radially and may also help prevent axial movement once the bolt is tightened.
[0110] In a further embodiment, an arrangement comprising a tapped bar and bridging members as described in GB 2425663 A, the subject matter of which is incorporated herein by reference, is used to retain the wedge radially.
[0111] It will be appreciated that embodiments of the invention have been described above by way of example only. The various embodiments may be used on their own or in any appropriate combination. For example, a mixture of different wedges could be used in the same machine. Any of the wedges may be provided with a textile material between the wedge and the windings to help slide the wedge into place and/or retain the wedge after impregnation with resin. Furthermore, any of the wedges may be provided with cooling fins. The wedges may be made from any suitable material. The machine may have a different number of salient poles, in which case the angle between the two legs of a wedge may correspond to the angle between two adjacent poles. Other variations in detail will be apparent to the skilled person within the scope of the claims.
