GB2509735A

GB2509735A - Wedging arrangement for retaining windings in a rotating electrical machine

Info

Publication number: GB2509735A
Application number: GB1300479.1A
Authority: GB
Inventors: Radu Caplescu; Cristian D Emilian Chihaia
Original assignee: Cummins Generator Technologies Ltd
Current assignee: Cummins Generator Technologies Ltd
Priority date: 2013-01-11
Filing date: 2013-01-11
Publication date: 2014-07-16
Also published as: GB201300479D0

Abstract

A wedging arrangement for windings 16 in a salient pole rotor body comprises first and second outer wedge members (22, 24), and first and second inner wedge members (26, 28) located between the first and second outer wedge members. A bolt (30) urges the first and second inner wedge members apart, thereby to urge apart the first and second outer wedge members retaining the windings, a lock nut 40 being provided. The wedge members are provided with a tongue and groove arrangement allowing the inner wedges to slide against the outer wedges in a radial direction only. An even distribution of forces on the windings is achieved and loading of the pole tips is minimised. Cooling fins 42 may be provided on the outer wedge members.

Description

WEDGING ARRANGEMENT

The present invention relates to a wedging arrangement for retaining the windings on the rotor of a rotating electrical machine, such as a rotating electrical machine of a salient pole design.

Rotating electrical machines, such as motors and generators, generally comprise a rotor and a stator, which are arranged such that a magnetic flux is developed between the two. In a rotating machine of a salient pole design, the rotor has a plurality of poles which extend radially outwards, on which a conductor is wound.

An electrical current flowing in these windings causes a magnetic flux to flow across the air gap between the rotor and the stator. In the case of a generator, when the rotor is rotated by a prime mover, the rotating magnetic field causes an electrical current to flow in the stator windings, thereby generating the output power. In the case of a motor, an electrical current is supplied to the stator windings and the thus generated magnetic field causes the rotor to rotate.

In a salient pole machine, as the rotor rotates, centrifugal forces develop on the windings, which tends to force the windings outwards in a radial direction. For this reason many salient pole machines have pole shoes at the pole tip. The pole shoes overlap the rotor windings, and thus retain the windings against the centrifugal forces developed in a radial direction as the rotor rotates.

In a salient pole machine forces will also develop on the windings in a circumferential direction as the rotor rotates. In order to counteract such forces, as well as centrifugal forces, it is known to provide a wedge between the windings of adjacent poles. The wedge is bridged between the pole shoes, and presses against the windings on either side on a circumferential direction so as to retain the windings in place. Typically the wedge comprises two wedge pieces each of which abuts a respective winding, and a stud assembly between the two wedge pieces. The stud assembly forces the two wedge pieces against their respective windings.

A problem with the conventional wedge design is that it is relatively bulky, which may restrict its use in limited space environments. Furthermore the wedge stud assembly is in bending moment, which may place extra pressure on the pole shoes. The conventional design may also suffer from a lack of mechanical robustness.

US 3766417 discloses a wedging arrangement for retaining the windings in a rotating electrical machine. The wedging arrangement comprises two side blocks which overlay the windings on adjacent poles. A wedge is located between the two side blocks. A bolt passes through the wedge and engages with a nut which underlies the radially inner faces of the side blocks. Tightening the bolt pulls the wedge towards the bolt, which forces the side blocks apart.

A disadvantage of the arrangement disclosed in US 3766417 is that it tends to apply uneven pressure to the windings, which could potentially lead to movement of the windings. Furthermore the arrangement is relatively bulky, and may suffer from a lack of mechanical robustness.

GB 2381389 discloses a wedging arrangement for securing the windings in the rotor of a salient pole rotating electrical machine. The wedging arrangement comprises two clamping members, two wedge members, and an intermediate angle member. The two wedge members are in face-to-face abutment with respective ramp surfaces formed on the clamping members. The two wedge members are connected in an axial direction by a nut and bolt. Tightening the nut and bolt pulls the two wedge members together in an axial direction. This causes the wedge members to act as a wedge expander, urging the clamping members against the rotor windings.

While the design of GB 2381389 may function well in retaining the windings, it has been found that, in practice, manufacture of the machine can be rather cumbersome. This is due in part to the need to insert the entire wedging arrangement into the inter-polar space in an axial direction. Inserting the wedging arrangement axially may be difficult, particularly in larger machines or where a number of adjacent wedging arrangements are to be used. Furthermore, the design itself involves a number of parts which may be awkward to assemble. The need to tighten the bolt in an axial direction may also complicate manufacture of the machine. In addition, the design only allows for a limited expansion, which may make it difficult to compensate for variations in the windings.

GB 2425663 discloses a wedging arrangement for a salient pole machine, in which a bolt passes through a wedge and into a channel inside the rotor. A threaded end of the bolt engages with a tapped bar inside the channel. The bolt is tightened in order to urge the wedge against the windings.

The arrangement of GB 2425663 can reduce the stresses on the pole shoes while the rotor is rotating. However it has been found that connecting the bolt inside the rotor can be difficult due to limited visibility. Furthermore, tightening the bolt could cause the windings to be pulled inwards, leading to the risk that the windings may shift outwards again under centrifugal forces when the machine is in operation. It is therefore necessary to take measures during manufacture to counter this effect, which may make the process more cumbersome. In addition, the arrangement of GB 2425663 requires a special arrangement of laminations which may again complicate the manufacturing process.

It would therefore be desirable to provide a mechanically robust wedging arrangement which can operate under space restrictions. It would also be desirable to provide a wedging arrangement which distributes the force which is applied to the windings. In addition, it would be desirable to provide a wedging arrangement which is simple, lightweight, easy to manufacture, and does not require a special rotor design.

According to one aspect of the invention there is provided a wedging arrangement for retaining windings in a rotating electrical machine, the wedging arrangement comprising: first and second outer wedge members; first and second inner wedge members located between the first and second outer wedge members; and means for urging the first and second inner wedge members apart, thereby to urge apart the first and second outer wedge members.

The present invention may provide the advantage that a mechanically robust design can be achieved which can be used in a limited space environment. This can allow the design to be used in machines with high copper till (i.e. a large number ot windings). Furthermore the design may be relatively lightweight and simple to manufacture, and may avoid the need for a special rotor. The action ot urging apart the first and second inner wedge members, and thereby urging apart the first and second outer wedge members, can help to distribute the torce which is applied to the windings. In addition, pole tip loading may be reduced in comparison to conventional wedge designs.

Preferably the wedging arrangement is arranged such that, in use, the first and second inner wedge members lock against the tirst and second outer wedge members. This may help to provide a more robust arrangement that has an aversion to bending or collapse. The locking may be achieved, tor example, by providing appropriate tapers on the insides ot the outer wedge members and the outsides of the inner wedge members.

Preferably the first and/or the second inner wedge members are substantially wedge-shaped (for example, in the shape of a truncated wedge). Thus the first and/or second inner wedge members, in combination with the first and second outer wedge members, may act as a wedge expander to urge apart the first and second outer wedge members.

Preferably the first and/or the second inner wedge members have sides which narrow in a direction away from the centre of the wedging arrangement. This can allow the tirst and second outer wedge members to be urged apart as the first and second inner wedge members are urged apart.

Preferably the first and second outer wedge members each have a first inner surface which contacts a side of the first inner wedge member, and a second inner surtace which contacts a side of the second inner wedge member. The first inner surfaces may be inclined towards each other in a direction away from the centre ot the wedging arrangement. Similarly, the second inner surfaces may be inclined towards each other in a direction away from the centre of the wedging arrangement (which is preferably the opposite direction to that ot the tirst inner surfaces). Thus the first and/or second inner surfaces may provide ramp surfaces against which the first and/or second inner wedge members can act as wedge expanders.

Preferably the first and second outer wedge members are spaced apart circumferentially (that is, in a generally circumferential direction with respect to an axis of rotation of the machine). This can allow the first and second outer wedge members to be urged circumferentially outwards against the windings of adjacent poles.

Preferably the first and second inner wedge members are spaced apart radially.

This can help to reduce the width of the wedging arrangement, thereby facilitating its use in limited space environments. Furthermore this arrangement may allow the first and second inner wedge members to be in contact with a relatively large portion of the first and second outer wedge members, which can help to distribute the force which is applied.

For example, the first inner wedge member may be located radially outwards of the second inner wedge member. In this case the first inner wedge member may narrow in a radially outwards direction, while the second inner wedge member may narrow in a radially inwards direction. This can allow the first and second inner wedge members to act as wedge expanders as they are urged apart.

Preferably the first and second outer wedge members each have a first inner surface, and the first inner surfaces are inclined towards each other in a radially outwards direction. Furthermore, the first and second outer wedge members may each have a second inner surface, and the second inner surfaces may be inclined towards each other in a radially inwards direction. This can allow the first and/or second inner surfaces to act as ramp surfaces against which the first and/or second inner wedge members can act as wedge expanders.

The wedging arrangement may further comprise means for preventing movement of the first and/or second inner wedge member in an axial direction. This can help to prevent the inner wedges from translating axially out of the wedging arrangement during operation of the machine. The means for preventing movement may comprise, for example, a tongue-and-groove arrangement between contacting surfaces of the first and/or second inner wedge member and the first and/or second outer wedge member.

Alternatively or in addition the first and second outer wedge members may comprise lips for retaining the inner wedge members, or any other means for preventing axial drift of the first and/or second inner wedge members.

Preferably the first and second outer wedge members each have an outer surface arranged to abut a winding of the electrical machine. The outer surfaces may be in direct contact with the windings, or alternatively an intermediary such as a layer of cushioning material may be provided.

Preferably, when in use, the means for urging the first and second inner wedge members apart is in compression. The compressive force can then be translated into a force urging the first and second outer wedge members apart. This may help to achieve a mechanically robust wedging arrangement.

The means for urging the first and second inner wedge members apart may comprise a threaded member, such as a bolt or a threaded bar. The threaded member may be in threaded engagement with one of the first and second inner wedge members, and in rotational (but non-threaded) engagement with the other of the first and second inner wedge members.

The threaded member and the first and second inner wedge members may be arranged such that tightening the threaded member causes the first and second inner wedge members to be urged apart. For example, the threaded member may comprise a threaded shank which is in threaded engagement with an internally threaded hole through the first inner wedge member. In this case, the second inner wedge member may comprise a depression which receives an end of the threaded member. The end of the threaded member which is received in the depression is preferably non-threaded, to facilitate rotation of the threaded member in the depression.

Alternatively the threaded member may be in threaded engagement with the second inner wedge member and non-threaded engagement with the first inner wedge member, and means such as a flange may be provided for urging the first inner wedge member away from the second inner wedge member as the threaded member is unscrewed from the second inner wedge member.

Preferably the threaded member runs in a radial direction. This can help to reduce the centrifugal forces which act on the threaded member during operation of the machine, thereby contributing to mechanical robustness.

The threaded member may include a locking nut, which may be used to lock the threaded member in position once the desired pressure is applied to the windings.

The present invention extends to a rotating electrical machine incorporating the wedging arrangement. Thus, according to another aspect of the present invention, there is provided a rotating electrical machine comprising a plurality of poles, each of the poles carrying a winding, and a wedging arrangement in any of the forms described above for retaining the windings of two adjacent poles.

The rotating electrical machine may be a motor, or a generator, or operable as both a motor and a generator. The machine may be of a salient pole design, or any other suitable design.

According to another aspect of the invention there is provided a method of retaining windings in a rotating electrical machine, the method comprising: inserting a wedging arrangement between adjacent windings in the electrical machine, the wedging arrangement comprising first and second outer wedge members and first and second inner wedge members located between the first and second outer wedge members; and urging the first and second inner wedge members apart, thereby to urge apart the first and second outer wedge members.

Preferably the wedging arrangement is inserted in a radial direction into a space between the windings.

Features of one aspect of the invention may be applied to any other aspect. Any of the apparatus features may be provided as method features and vice versa.

In this specification the terms "axially", "radially", "circumferentially" and so forth are generally used with respect to the axis of rotation of the machine.

Preferred embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows parts of a rotor in a rotating electrical machine; Figure 2 is a cross section through part of the rotor of Figure 1, showing an embodiment of a wedging assembly; Figure 3 is a perspective view of the wedging assembly of Figure 2; and Figure 4 shows an alternative embodiment of a wedging assembly.

Figure 1 shows parts of a rotor in a rotating electrical machine. The rotor is designed to rotate inside a stator (not shown). The rotor comprises a rotor body located on a shaft 12, the centre of which defines the axis of rotation of the machine. The rotor body is formed from a plurality of metal laminations running axially through the machine. The rotor body includes a plurality of salient poles 14 which extend outwards in a radial direction. Each of the salient poles 14 carries rotor windings 16, which are usually in the form of coils of copper wires.

An electrical current flowing in these windings causes a magnetic flux to flow radially across the air gap between the rotor and the stator.

The rotor of Figure 1 includes a plurality of wedging assemblies 18 provided between the windings of adjacent poles. The wedging assemblies 18 are designed to retain the windings against centrifugal and other forces while the machine is in operation.

Figure 1 shows seven wedging assemblies spaced axially between two adjacent poles. However, in practice a single wedging assembly or any other number could be used between two adjacent poles, depending on the size and configuration of the machine. Furthermore, while Figure 1 shows a rotor with four salient poles, any number of salient poles could be provided.

Figure 2 shows a cross section through part of the rotor of Figure 1. Referring to Figure 2, the rotor comprises a rotor body 10 with a plurality of salient poles 14.

Each of the salient poles is wound with a rotor winding 16. The salient poles 14 include pole shoes 20 which extend circumferentially on either side of the pole at the radially outermost end. The pole shoes help to support the windings against the forces which are developed during operation of the machine. In addition, a wedging assembly 18 is provided between the windings of two adjacent poles.

The wedging assembly presses against the windings in order to provide further support. The wedging assembly is held in place in part by the pole shoes 20, and in part by frictional forces between the wedging assembly and the windings. A perspective view of the wedging assembly is shown in Figure 3.

Referring to Figures 2 and 3, the wedging assembly comprises a first outer wedge member 22, a second outer wedge member 24, a first inner wedge member 26, and a second inner wedge member 28. The first and second outer wedge members are spaced apart circurnferentially, and the first and second inner wedge members are located therebetween. The first and second inner wedge members are spaced apart radially, with the first inner wedge member 26 located radially outwards of the second inner wedge member 28.

The first outer wedge member 22 and second outer wedge member 24 each has an outer surface 32 and two inner surfaces 34, 36. The outer surfaces 32 are arranged to abut the windings 16 along most or all of their length. A layer of material 38 may be provided between the outer surfaces 32 and the windings 16 for electrical insulation and to help protect the copper.

The first inner surfaces 34 are angled inwards in a direction extending radially outwards from the centre of the machine. By contrast, the second inner surfaces 36 are angled inwards in a direction extending radially inwards towards the centre of the machine. The first inner wedge member 26 is wedge shaped, with a taper which narrows in a radially outwards direction. The second inner wedge member 28 is also wedge shaped, but has a taper which narrows in a radially inwards direction. The first inner wedge member 26 is arranged to abut the first inner surfaces 34, while the second inner wedge member 28 is arranged to abut the second inner surfaces 36.

A bolt 30 extends radially through the first inner wedge member 26. The bolt 30 has a threaded shank which engages with an internal thread on the inner wedge member. The end of the bolt 30 is non-threaded and is received in a hole in the second inner wedge member.

The first and second outer wedge members 22, 24 and the first and second inner wedge members 26, 28 are provided with a tongue and groove arrangement which allows the first and second inner wedge members to slide against the first and second outer wedge members in a radial direction, but not in an axial direction.

During assembly of the machine, the wedging assembly is inserted in a radial direction into the inter-polar space in a loosely assembled state. The bolt 30 is then tightened, such that the first inner wedge member 26 is urged radially outwards while the second inner wedge member 28 is urged radially inwards.

The actions of the first inner wedge member 26 against the first inner surfaces 34 and the second inner wedge member 28 against the second inner surfaces 36 cause the first and second outer wedge members to be urged against their respective windings. Thus the appropriate pressure can be applied to ensure that the windings are retained in place during operation of the machine. A locking nut 40 is used to secure the bolt 30 once it is sufficiently tightened.

In the assembled machine the wedging assemblies are held in place in part by the pressure of the wedging assemblies against the windings, which helps to minimise the loading on the tips of the pole shoes 20.

As can be soon from Figures 2 and 3, a relatively large contact area is provided between the first and second inner wedge members 26, 28 on the one hand, and the first and second inner surfaces 34, 36 on the other hand. Furthermore the first and second inner wedge members both apply pressure to the outer wedge members. This arrangement can help to ensure an even distribution of the force which is applied to the windings by the first and second outer wedge members.

The angles of inclination of the first and second inner surfaces, as well as the sizes and angles of the first and second inner wedge members, are chosen in order to help achieve an even distribution of the forces.

In the arrangement described above, since the first and second wedge members are spaced apart radially, a relatively slim design can be achieved. This can allow use of the wedging assembly in limited space environments, and allow a higher copper fill to be achieved.

In the arrangement described above the bolt is in compression and is not subject to a bending moment. Furthermore there are no parts which flex or deform under the action of centrifugal loading. This can help to achieve a mechanically robust design.

Thus attributes of the wedging assembly may include: * Even distribution of force over the width of the coil; * Rigid locking between adjacent wedge halves -no parts to flex or deform under the action of centrifugal loading; * Fixing bolt not subject to a bending moment -will not lose tension during operation; * Efficient space saving -more space for copper; * Design does not require a connection towards the shaft, thus allowing space for shaft increase (leading to improved rotor dynamics) and for cooling air flow; * Avoids an inwards clamping force, thus preventing the copper from being pulled away from the pole tip during tightening; * Ease of insulation as the locking mechanism does not pass between the coils; * High mechanical strength; * High resistance to copper movement under centrifugal load; * Low part count.

The wedging assembly described above can be made from any suitable material, such as machined metal or a resilient plastic material, and is preferably non-magnetic.

In an alternative arrangement, the second inner wedge member 28 is internally threaded rather than the first inner wedge member. In this arrangement the second inner wedge member engages with a screw thread on the bolt. A flange on the bolt engages with the radially inward face of the first inner wedge member.

The first and second inner wedge members are urged apart by unscrewing the bolt from the second inner wedge member.

Figure 4 shows an alternative embodiment of the wedging assembly in which fins 42 are provided on the outer surface of the first and second outer wedging members to assist with cooling of the machine.

While preferred features have been described with reference to specific embodiments, it will be appreciated that variations are possible within the scope of the invention. For example, it may be possible for just one of the inner wedge members to act as a wedge expander, with the other inner wedge member simply being trapped between the first and second outer wedge members. Also it will be appreciated that the wedging arrangement may be used with a rotor having any number of poles. Furthermore, the wedging arrangement may be used with any wound machine, and not necessarily just a salient pole machine. Various other modifications will be apparent to the skilled person.

Claims

CLAIMS1. A wedging arrangement for retaining windings in a rotating electrical machine, the wedging arrangement comprising: first and second outer wedge members; first and second inner wedge members located between the first and second outer wedge members; and means for urging the first and second inner wedge members apart, thereby to urge apart the first and second outer wedge members.
2. A wedging arrangement according to claim 1 arranged such that, in use, the first and second inner wedge members lock against the first and second outer wedge members.
3. A wedging arrangement according to claim 1 or 2, wherein the first and/or the second inner wedge members are substantially wedge-shaped.
4. A wedging arrangement according to any of the preceding claims, wherein the first and/or the second inner wedge members have sides which narrow in a direction away from the centre of the wedging arrangement.
5. A wedging arrangement according to claim 4, wherein the first and second outer wedge members each have a first inner surface which contacts a side of the first inner wedge member, and a second inner surface which contacts a side of the second inner wedge member.
6. A wedging arrangement according to claim 5, wherein the first inner surfaces are inclined towards each other in a direction away from the centre of the wedging arrangement.
7. A wedging arrangement according to claim 5 or 6, wherein the second inner surfaces are inclined towards each other in direction away from the centre of the wedging arrangement.
8. A wedging arrangement according to any of the preceding claims, wherein the first and second outer wedge members are spaced apart circumferentially.
9. A wedging arrangement according to any of the preceding claims, wherein the first and second inner wedge members are spaced apart radially.
10. A wedging arrangement according to any of the preceding claims, wherein the first inner wedge member is located radially outwards of the second inner wedge member.
11. A wedging arrangement according to any of the preceding claims, wherein the first and second outer wedge members each have a first inner surface and the first inner surfaces are inclined towards each other in a radially outwards direction.
12. A wedging arrangement according to any of the preceding claims, wherein the first and second outer wedge members each have a second inner surface and the second inner surfaces are inclined towards each other in a radially inwards direction.
13. A wedging arrangement according to any of the preceding claims, further comprising means for preventing movement of the first and/or second inner wedge member in an axial direction.
14. A wedging arrangement according to claim 13, wherein the means for preventing movement comprises a tongue-and-groove arrangement between contacting surfaces of the first and/or second inner wedge member and the first and/or second outer wedge member.
15. A wedging arrangement according to any of the preceding claims, wherein the first and second outer wedge members each have an outer surface arranged to abut a winding of the electrical machine.
16. A wedging arrangement according to any of the preceding claims, wherein in use the means for urging the first and second inner wedge members apart is in compression.
17. A wedging arrangement according to any of the preceding claims, wherein the means for urging the first and second inner wedge members apart comprises a threaded member.
18. A wedging arrangement according to claim 17, wherein the threaded member is in threaded engagement with one of the first and second inner wedge members, and in rotational engagement with the other of the first and second inner wedge members.
19. A wedging arrangement according to claim 17 or 18, wherein the threaded member and the first and second inner wedge members are arranged such that tightening the threaded member causes the first and second inner wedge members to be urged apart.
20. A wedging arrangement according to any of claims 17 to 19, wherein the threaded member comprises a threaded shank which is in threaded engagement with an internally threaded hole through the first inner wedge member.
21. A wedging arrangement according to claim 20, wherein the second inner wedge member comprises a depression which receives an end of the threaded member.
22. A wedging arrangement according to any of claims 17 to 21, wherein the threaded member runs in a radial direction.
23. A wedging arrangement according to any of claims 17 to 22, wherein the threaded member includes a locking nut.
24. A rotating electrical machine comprising a plurality of poles, each of the poles carrying a winding, and a wedging arrangement according to any of the preceding claims for retaining the windings of two adjacent poles.
25. A wedging arrangement or electrical machine according to any of the preceding claims, wherein the electrical machine is a salient pole machine.
26. A method of retaining windings in a rotating electrical machine, the method comprising: inserting a wedging arrangement between adjacent windings in the electrical machine, the wedging arrangement comprising first and second outer wedge members, and first and second inner wedge members located between the first and second outer wedge members; and urging the first and second inner wedge members apart, thereby to urge apart the first and second outer wedge members.
27. A method according to claim 26 wherein the wedging arrangement is inserted in a radial direction.
28. A wedging arrangement substantially as described herein with reference to and as illustrated in the accompanying drawings.
29. A method of retaining windings in a rotating electrical machine substantially as described herein with reference to the accompanying drawings.