WO2021176200A1

WO2021176200A1 - Stator assembly for reinforcing a rotating electrical machine

Info

Publication number: WO2021176200A1
Application number: PCT/GB2021/050508
Authority: WO
Inventors: Yang ZHIHUA; Wu Qiang; Hua Dong; Chen QIANYUN; Shen XIAOYAN
Original assignee: Cummins Generator Technologies Limited
Priority date: 2020-03-02
Filing date: 2021-03-01
Publication date: 2021-09-10
Also published as: CN218498894U

Abstract

A stator assembly for a rotating electrical machine comprising an inner rotor is disclosed. The stator assembly comprises a stator core (30) comprising slots (32) on the inner circumference, a plurality of landing bars (38) on the outer circumference of the stator core (30) and two end rings (40, 42) at both axial ends. Each end ring (40, 42) is connected to said landing bars (38) at its respective stator core end side. Thereby, landing bars (38) and end rings (40, 42) form the main reinforcing structure of the machine. This structure helps to maintain the machine's concentricity and allow the machine to be manufactured with fewer steps.

Description

STATOR ASSEMBLY FOR REINFORCING A ROTATING ELECTRICAL MACHINE

The present invention relates to a stator assembly for a rotating electrical machine, and in particular a stator assembly which can help to maintain concentricity and improve manufacturability of the machine.

Rotating electrical machines, such as motors and generators, generally comprise a rotor mounted on a shaft and arranged to rotate inside a stator. The rotor comprises a rotor core which holds rotor windings or permanent magnets. The rotor windings or permanent magnets produce a rotating magnetic field which crosses an air gap between the rotor and the stator. The stator comprises a stator core which holds stator windings which combine with the rotating magnetic field. The stator itself may be held within a stator frame.

In some known machine designs, the stator is located inside the stator frame using landing bars. The landing bars are bars which run along the outside of the stator core, parallel to the axis of rotation. The landing bars are usually welded to the outside of the stator. The stator frame can then be fitted around the landing bars, with the landing bars providing an air gap between the stator and the frame. Other non-rotating components, such as an adaptor for connecting the machine to a prime mover, can then be attached to the stator frame.

A problem which has been identified in some known machine designs is that it may be difficult to keep the stator frame concentric. For example, during manufacture it may be difficult to correctly locate the landing bars on the stator core with the required concentricity. Furthermore, the process of welding the landing bars to the outside of the stator may introduce deformities in the bars, which may impact the stator frame’s concentricity. This may affect the machine’s performance and add to manufacturing complexity.

Another problem in known machine designs is that the manufacturing process tends to involve a relatively large number of different stages, which adds to the time, cost and complexity of manufacture. It would therefore be desirable to provide a rotating electrical machine in which it is easier to maintain the machine’s concentricity, and/or with improved ease of manufacture.

According to a first aspect of the present invention there is provided a stator assembly for a rotating electrical machine, the stator assembly comprising: a stator core; a plurality of landing bars on the outside of the stator core; and two end rings, wherein an end ring is connected to the landing bars at each end of the stator core.

The present invention may provide the advantage that, by providing a plurality of landing bars on the outside of the stator core and an end ring connected to the landing bars at each end of the stator core, it may be easier to maintain the machine’s concentricity, in comparison to previous designs. Furthermore, it may be possible to manufacture the machine using a fewer number of stages, which may reduce the time and cost of manufacture.

In contrast to previous designs where the stator frame is the main structural component, in embodiments of the present invention the landing bars and end rings may form the main structural component of the machine. Thus, the landing bars and end rings may form a frame assembly. Preferably the landing bars and end ring are arranged to support the stator core. Preferably the landing bars and end rings function to hold the stator in concentricity with respect to other components of the machine. It has been found that such arrangements can help to ensure that concentricity is maintained.

The end rings may be arranged to engage with an end face of the stator core. This may help to retain the stator, to hold stator laminations together and/or to ensure concentricity of the stator core.

The landing bars are preferably bars which run axially along the length of the stator core, and are preferably connected at each end to an end ring. Any appropriate number of landing bars may be provided. For example, in one embodiment the stator assembly may have four landing bars. However, any other appropriate number of landing bars, such as 3, 5, 6, 8 or more, could be used instead. The landing bars are preferably spaced circumferentially around the outside of the stator core.

The stator core may comprise a plurality of cooling fins. The cooling fins may extend radially outwards from the stator core and may assist in the cooling of the machine when airflow is provided through the machine. In this case, the cooling fins may be located circumferentially between the landing bars. Thus, the landing may bars run through axial slots between adjacent fins.

In one embodiment, the cooling fins are arranged in groups, and the landing bars run between adjacent groups of fins. The cooling fins in a group may be connected by a peripheral connecting member. For example, the stator core, cooling fins and/or landing bars may be as described in co-pending UK patent application number 1916070.4, the subject matter of which is incorporated herein by reference, although of course other arrangements could be used instead.

The landing bars may be welded or otherwise secured to the outside of the stator core, in order to help prevent movement of the stator.

The end rings may be attached to the landing bars using bolts which pass axially through the end rings and into holes in the ends of the landing bars. Thus, the end rings may have a plurality of holes for attaching the end rings to the landing bars. The landing bars may have axial holes which receive bolts for securing the end rings to the landing bars. The holes may have an internal thread to receive a threaded bolt.

The end rings may be in the form of annular disc. Thus, the end rings may be in the shape of a disc bounded by two concentric circles and/or the end rings may have a central aperture. One side of the end ring may face an end face of the stator core, and the other side of the end ring may face away from the stator.

The stator core may be in the form of a hollow cylinder. In this case, the landing bars may run axially along its outside surface. Preferably the inside of the stator core comprises stator slots for stator windings. The stator windings may comprise side windings which run through the stator slots, and end windings at each end of the stator. The end windings may extend out of the stator slots and around the outside of the stator core. In this case each end ring is preferably located radially outwards of the corresponding end windings. For example, the end windings may pass axially through an aperture at the centre of the end ring.

At least one of the end rings may have an inner circumference with a radius which is greater than the radius of an inner circumference of the stator core. For example, where the stator core comprises a plurality of stator slots on its inner circumference, the inner circumference of the end ring may be radially outwards of the stator slots (preferably the radially outwards part of the stator slots). This may allow the end rings to engage with the stator core, while allowing stator end windings to extend through an aperture at the centre of the end ring.

Preferably the end rings extend radially outwards of the stator core. For example, the end rings may have an outer circumference with a radius which is greater than a radius of the outer circumference of the stator core. This can facilitate the attachment of another non-rotating component, such as a bracket, adaptor or lifting lug, to the end ring.

Furthermore, providing end rings which extend radially outwards of the stator core (and with an inner circumference which is radially outwards of the stator slots) may facilitate winding of the stator. In particular, it may be possible to use the end rings as tracing rings, that is, as rings for rotating the stator core during the winding process. Extending the end rings radially outwards of the stator core may allow the stator assembly to be easily rotated during the winding process, for example by mounting the end rings on rotating means such as rollers. Thus, the end rings may be arranged for use as tracing rings during winding of the stator.

In known machine designs, other non-rotating components, such as an adaptor or a bracket, may be attached to the stator frame. For example, in the case of a generator set, an adaptor may be used to connect the stator frame to the prime mover and/or a bracket may be attached to the stator frame and used to support a bearing for a rotor. In a preferred embodiment of the invention, at least one of the end rings is arranged to be attached to another non-rotating component such as a bracket or an adaptor. Thus, in this arrangement, the landing bars and end rings may form the main structural component of the machine and/or may be used to hold the stator core in concentricity with respect to other components of the machine.

This may help to ensure that concentricity is maintained. The end ring may have a mating face for mating with the adaptor or bracket, and the mating face may be located radially outwards of the stator core and/or facing away from the stator core. This may facilitate assembly of the bracket or adaptor to the end ring.

At least one of the end rings may comprise holes for attaching a bracket or an adaptor to the end ring. For example, the end ring may have bolt holes which allow a bracket or an adaptor to be bolted to the end ring. The holes may be spaced circumferentially about the end ring and/or may run axially through the end ring. The holes may be located radially outwards of holes which are used to connect the end ring to the landing bars. Preferably, the holes for attaching a bracket or adaptor are located radially outwards of the stator core. This can allow bolts for attaching the end ring to the bracket or adaptor to be inserted from the machine side, which may facilitate assembly.

In the case of a machine which is arranged to be driven by a prime mover, one of the end rings may be arranged to be attached to a drive end adaptor or a drive end bracket. In the case of an adaptor, the adaptor may be arranged to connect non-rotating parts of the machine to a prime mover. In the case of a bracket, the bracket may comprise a bearing support for supporting a rotor bearing. The bracket or adaptor may be arranged to house a fan for drawing cooling air through the machine.

One of the end rings may be arranged to be attached to a non-drive end bracket. The non-drive end bracket may comprise a bearing support for supporting a bearing for a rotor. Alternatively or in addition the non-drive end bracket may be arranged to support other components such as an exciter stator. At least one of the end rings may comprise means for attaching a terminal box. For example, one of the end rings (for example, at a non-drive end of the machine) may comprise bolt holes which can be used to attach one side of the terminal box to the end ring. The other side of the terminal box may be attached, for example, to a non-drive end bracket. This may provide a convenient way of attaching a terminal box to the machine.

At least one of the end rings may comprise means for attaching a lifting lug. For example, at least one of the end rings may comprise bolt holes for bolting the lifting lug to the end ring. The bolt holes may be located radially outwards of the stator core. This can allow a lifting lug to be easily attached to a structural component of the machine.

In operation, air may be drawn through the machine, for example using a fan which may be mounted on a machine shaft. This may cause air to flow axially along the outside of the stator core, for example through channels between cooling fins and/or through an air gap between the stator core and a stator cover.

In a preferred embodiment, at least one end ring comprises a plurality of air holes. The air holes may be, for example, axial holes. The air holes may be arranged to provide an entry or exit path for air flow along an outside of the stator core. This may facilitate the passage of cooling air through the machine, thereby assisting with cooling. The air holes may be at least partially aligned radially with the outside of the stator core and/or with cooling channels between cooling fins on the outside of the stator core. The air holes may be spaced circumferentially about the end ring, in order to provide exit paths for air flow at multiple locations around the machine.

In a preferred embodiment, an end ring is arranged to direct at least some air flow from outside of the stator core radially inwards towards stator end windings. For example, the end ring may be arranged with an air gap (in an axial direction) between the end ring and an end face of the stator core. This may allow the end ring to deflect at least some axial air flow radially inwards towards the stator end windings. Thus, in operation, air flow from the outside of the stator core may be directed radially inwards towards the stator end windings. This may further assist with the cooling of the machine.

In one embodiment, the end ring is arranged to provide a first air flow path in an axial direction and a second air flow path in a radial direction. The first air flow path may help to ensure that air flow through the machine is not overly impeded. The second air flow path may direct some air flow towards stator end windings. Thus, this arrangement may help to achieve a balance between cooling the end windings and cooling other parts of the stator.

Preferably at least one of the end rings comprises means, such as a plurality of claws, for locating the end ring on the stator core. The claws may extend axially outwards from the end ring. The claws may be arranged to locate the end ring concentrically on the stator core. For example, the claws may be arranged to engage with a radially outwards surface of the stator core and/or with an end face of the stator core. This may help to maintain concentricity during assembly of the stator assembly.

At least one of the end rings may comprise means, such as a spacer, for spacing the end ring axially away from an end face of the stator core. For example, where the end ring comprises a plurality of claws, the claws may be arranged to space the end ring axially away from an end face of the stator core. The claws may be substantially L-shaped, with a lip which engages with a radially outwards side of the stator core, and a spacer which spaces the end ring axially away from an end face of the stator core. This may allow an air gap to be provided between the end ring and an end face of the stator core, which may allow air flow to be directed radially inwards towards stator end windings.

Preferably at least some of the landing bars are arranged to receive a stator cover. For example, some or all of the landing bars may have radial holes arranged to receive bolts which can be used to bolt a stator cover to the stator assembly. Alternatively or in addition, a stator cover may be attached to one or more of the end rings. In one embodiment, the stator cover is provided in two or more parts. This can allow the stator cover to be fitted around the stator assembly after the stator assembly itself has been assembled. This may facilitate manufacture of the machine.

Where the stator cover is provided in two or more parts, it may be possible to attach a first part to the stator assembly, and then to attach a second part to the first part. Thus, some but not all of the landing bars may comprise holes for attaching part of a stator cover.

In one embodiment, at least one of the landing bars is arranged to secure a machine foot to the stator assembly. For example, one or more of the lower landing bars may have radial holes for attaching a machine foot. In this case, a part of a stator cover may be attached to the stator assembly by clamping it between the machine foot and a landing bar. Thus, at least some of the same holes in a landing bar may be used for attaching a part of a stator cover and a machine foot.

According to another aspect of the invention there is provided a rotating electrical machine comprising a rotor and a stator assembly according to any of the preceding claims. The rotor may be part of a rotor assembly comprising a rotor, a rotor shaft and a rotor bearing. The machine may be, for example, a synchronous generator arranged to be driven by a prime mover. The machine may further comprise a drive end adaptor or a drive end bracket attached to one of the end rings and/or a non-drive end bracket attached to the other end ring.

The drive end adaptor or bracket may be arranged to attach the machine to a prime mover and/or may house a fan. The non-drive end bracket may be arranged to support a rotor bearing.

The machine may further comprise a stator cover for safety and/or ingress protection. In this case, the stator cover may be bolted to at least one of the landing bars.

In a preferred embodiment, the landing bars and end rings are the main structural component of the machine, to which other components may be attached. Thus, the stator cover is preferably not the main structural component of the machine. This may allow the stator cover to be lighter and/or to use less material than would otherwise be the case.

The stator cover may comprise two or more parts which can be fitted around the stator core. In this case, a first part may be attached to one or more landing bars (for example using bolts passing through holes in the first part), and a second part may be attached to the first part (for example using a latching mechanism). This may facilitate assembly of the machine.

The machine may further comprise one or more machine feet attached to at least one of the landing bars. In this case, at least part of a stator cover may be clamped between the machine foot and a landing bar. This may be achieved, for example, using bolts which pass through the machine foot, through holes in the cover, and into radial bolt holes in at least one landing bar. Thus, the same bolts may be used to attach both a machine foot and a part of the stator cover to a landing bar.

The machine may further comprise one or more of: a terminal box attached to an end ring and/or a non-drive end bracket; a vents cover attached to a non-drive end bracket; a non-drive end cover attached to a non-drive end bracket; a screen attached to a drive end adaptor or a drive end bracket; and a non-drive end lug attached to an end ring.

Corresponding methods may also be provided. Thus, according to another aspect of the invention there is provided a method of assembling a stator for a rotating electrical machine, the method comprising: providing a plurality of landing bars on the outside of a stator core; and connecting an end ring to the landing bars at each end of the stator core.

The method may further comprise one of more of the following steps: stacking a first end ring, stator laminations and a second end ring on tooling; welding the stator laminations to form the stator core; attaching the landing bars to the end rings; welding the landing bars to the stator core; winding the stator core with stator windings, preferably using the end rings as tracing rings; and impregnating the wound stator with resin.

Preferably the steps are carried out in the above order, although some of the steps may be reordered where appropriate.

The step of welding the stator laminations may take place while they are on the tooling. The step of attaching the landing bars to the end rings may take place while on the tooling. The step of welding the landing bars to the stator core may take place while on the tooling. The step of welding the landing bars to the stator core may take place before the step of winding the stator core with stator windings. The step of winding the stator core may take place using the end rings as tracing rings (i.e. as rings for rotating the stator core during the winding process). The step of impregnating the wound stator with resin may take place after the landing bars have been welded to the stator core.

It has been found that at least some of the above steps may allow the stator to be assembled in a fewer number of stages and/or with a better concentricity than with previous techniques.

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, terms such as “axially”, “radially”, “circumferentially” and so forth are generally defined with reference to the axis of rotation of the electrical machine, unless the context implies otherwise.

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 known rotating electrical machine; Figure 2 shows parts of a stator assembly in an embodiment of the invention;

Figure 3 shows the stator assembly of Figure 2 in an assembled state;

Figures 4A and 4B show front and back views of an end ring;

Figure 5 shows the stator assembly of Figures 2 to 4 with a drive end adaptor, non-drive end bracket and generator feet attached;

Figure 6 is an exploded view of a rotating electrical machine including the stator assembly of Figures 2 to 5;

Figures 7A to 7I illustrate steps in the process of assembling the machine of Figure 6;

Figure 8 is a view of the assembled machine;

Figure 9 is a cross section through the machine;

Figure 10 is a cutaway view of part of the machine; and

Figure 11 is a cutaway view showing part of a stator core and end ring.

Figure 1 is an exploded view of parts of a known rotating electrical machine. In this example the electrical machine is a synchronous generator which is arranged to be driven by a prime mover such as a diesel engine. Referring to Figure 1 , the machine comprises a rotor assembly 10 and a stator assembly 20. The rotor assembly comprises main rotor 12 and an exciter rotor 13 both of which are mounted on a shaft 14. The main rotor 12 comprises a plurality of salient poles on which are wound rotor windings 15.

The stator assembly 20 comprises a stator core 16 which is in the shape of a hollow cylinder and is formed from a plurality of stacked stator laminations. The stator core has slots on its inner circumference in which are wound stator windings. Stator side windings run through the slots in a substantially axial direction. Stator end windings 18 extend out of the stator slots and around the outside of the stator core. A plurality of landing bars 22 are attached to the stator core 16 on its outer circumference. The landing bars 22 are arranged at spaced locations about the stator and run through the machine in an axial direction. The landing bars are used to locate the stator core 16 within a stator frame 24. The stator frame 24 has an inner surface which engages with the outside of the landing bars 22. The landing bars 22 create air gaps between the stator core 16 and the frame 24. The frame 24 is terminated with an end plate 25. In the assembled machine, the main rotor 12 is located inside the stator core 16 and arranged to rotate therein. An adaptor 26 is used to connect the generator to a non-rotating part of the prime mover such as a flywheel housing. The adaptor 26 is bolted to the end plate 25 of the frame 24. A shaft-mounted fan 27 is located inside the adaptor 26 and is used to draw cooling air through the machine. Also shown in Figure 1 are a coupling hub 28 and a coupling disc 29 which are used to couple the shaft 14 to a rotating component of the prime mover such as a flywheel.

In the arrangement of Figure 1 , generator feet 21 are attached to the bottom of the stator frame 24. The generator feet are used to mount the generator to a bed frame either directly or via a rubber mount. The generator also includes a terminal box 23 which is attached to the outside of the stator frame 24 and is used for making electrical connections to the generator.

The rotating electrical machine described above is of a single bearing design, with a bearing at the non-drive end of the shaft. The drive end of the shaft is supported by bearings on the prime mover using the coupling hub 28 and a coupling disc 29. In an alternative arrangement, the machine may be of a two- bearing design with a bearing at each end of the shaft. In this case the adaptor 26 or a separate drive end bracket may be provided with a bearing support for supporting the drive end bearing.

The process of assembling a stator such as that shown in Figure 1 typically involves the following stages.

1. The stator core is formed by stacking the stator laminations onto tooling and pressing the laminations together.

2. The stator core is welded together.

3. The stator core is wound with the stator windings using a winding machine. This typically involves needle winding, with a tracing ring to rotate the stator core as it is wound.

4. The wound stator is impregnated with resin using a dipping and baking process. 5. The landing bars are positioned on the stator. A welding fixture is used to keep the landing bars in place. A winding protection cover is added to protect the windings.

6. The landing bars are welded to the stator, and the tooling is removed.

7. Rust protection is applied to the stator, particularly to the areas which have been welded.

8. The stator is pressed into the stator frame.

It will be appreciated from the above that, in current generator designs, the stator frame is the main structural component of the machine. Landing bars are welded to the stator core to locate the stator core in the stator frame. The drive end adaptor and the non-drive end bracket are connected to the stator frame.

In such an arrangement, it is necessary for the stator frame to keep the drive end adaptor and non-drive end bracket in good concentricity, in order to ensure proper functioning of the machine. Since the stator core is connected to the stator frame by the landing bars, it is necessary for the length, shape, stiffness and flatness of the landing bars to be carefully controlled.

A problem which has been identified in machines of the type described above is that it may be difficult to correctly locate the landing bars relative to the stator frame and/or stator core with the required concentricity. Furthermore, although the quality of the landing bars can be controlled prior to assembly, the process of welding the bars to the stator may result in the bars becoming deformed. As a consequence, the landing bars may not keep the stator frame in the desired concentricity. This may impact the concentricity of the rotor and stator, which may affect the machine’s performance.

Another problem which has been identified is that the production process typically involves a relatively large number of different stages, each of which may need to be carried out by a different piece of equipment located at a different station.

This may result in relatively complex, time consuming and expensive production process. If there is a need to correct the machine’s concentricity, then this may further add to the production costs. Embodiments of the present invention provide a rotating electrical machine with a new frame structure and manufacturing techniques which may help to address some or all of the issues identified above.

Figure 2 is an exploded view of parts of a stator assembly for a rotating electrical machine in an embodiment of the invention. Referring to Figure 2, the stator assembly comprises a stator core 30, a plurality of landing bars 38, and two end rings 40, 42.

The stator core 30 is in the form of a hollow cylinder with slots 32 for stator windings on its inner side. The stator core 30 is formed from a plurality of stator laminations stacked together in an axial direction through the machine. The stator core includes a plurality of cooling fins 34 which extend radially outwards. Cooling channels for air flow extend in a generally axial direction between the cooling fins 34. In this embodiment, the cooling fins 34 are arranged in groups, with the fins in a group connected by a peripheral connecting member 36. The stator core 30, may be, for example, as described in co-pending UK patent application number 1916070.4, the subject matter of which is incorporated herein by reference, although of course other types of stator core could be used instead.

In the arrangement of Figure 2, four landing bars 38 are provided at spaced locations circumferentially around the stator core 30. The landing bars 38 run in an axial direction through channels between adjacent groups of cooling fins 34.

The first end ring 40 is located at one end axially of the stator core 30, and the second end ring 42 is located at the other end of the stator core. The end rings 40, 42 are attached to the landing bars 38 using bolts 44. The bolts 44 pass through holes 45 in the end rings, and into holes 46 which run in an axial direction in the ends of the landing bars 38. Each of the holes 46 has an internal thread which engages with a thread on the shaft of the corresponding bolt 44.

Figure 3 shows the stator assembly of Figure 2 in an assembled state. Referring to Figure 3, the end ring 42 is attached to the landing bars 38 using bolts 44 which pass through the holes 45 in the end ring 42 and into the holes 46 in the ends of the landing bars 38. Similarly, the end ring 40 is attached to the landing bars using bolts which pass through holes in the end ring 40 and into holes in the ends of the landing bars. This allows the stator 30 to be clamped axially between the two end rings 40, 42, and radially between the landing bars 38.

In this embodiment, the machine is a generator which is arranged to be driven by a prime mover. The end ring 40 is located the drive end of the stator core 30 and the end ring 42 is located at the non-drive end of the stator core. Also shown in Figure 3 are a drive end adaptor 46 and a non-drive end bracket 48. The drive end adaptor 46 is used to connect the machine to a non-rotating part of the prime mover, such as a flywheel housing. The drive end adaptor may be, for example, as described in WO 2019/243829, the subject matter of which is incorporated herein by reference, although other types of adaptor and/or drive end bracket could be used instead. The non-drive end bracket 48 is used to support non drive end bearings and an exciter stator. A bearing support 49 is provided at the centre of the bracket 48, which is used to support a bearing on the end of the generator shaft.

As can be seen from Figure 3, the drive end adaptor 46 can be attached directly to the end ring 40, rather than to the stator frame as in previous designs. The drive end adaptor 46 has a mating face 50 which is designed to interface with the axially outwards face of the end ring 40. Bolts 52 pass through holes in the end ring 40 and into corresponding holes in the adaptor 46. Similarly, the non-drive end bracket 48 can be attached directly to the end ring 42 using bolts 53 which pass through holes in the end ring 42 and into corresponding holes in the non drive end bracket 48.

Figure 3 also shows two generator feet 54. The generator feet 54 are arranged to be attached to the lower two landing bars 38, rather than to the stator frame as in previous designs. Bolts 56 are provided, which pass through holes in the generator feet 54 and into corresponding holes which run in a radial direction in the lower two landing bars 38.

As in previous designs, the landing bars 38 shown in Figures 2 and 3 are used to locate the stator core with respect to other components of the machine.

However, in this design, the end rings 40, 42 are used to hold the landing bars 38 in the required positions relative to the stator core. This can make it easier to control the machine’s concentricity. Furthermore, in this design, the end rings 40, 42 and the landing bars 38 are the main structural components of the machine.

As a consequence, deformations in the landing bars which may occur during the welding process will have less effect on the machine’s concentricity than in the previous design where the stator frame is the main structural component and is located on the outside surfaces of the landing bars.

Figures 4A and 4B show respectively a front and back view of the end ring 40. Referring to Figures 4A and 4B together with Figure 3, the ring 40 is essentially in the form of an annular disc with a central aperture 41 . The ring 40 has an inner circumference with a radius which is slightly greater than that of the slots 32 in the stator 30. This can allow the stator end windings to extend axially through the aperture 41 at the centre of the ring 40. The ring includes bolt holes 45 which pass through the ring 40 in an axial direction, and which are used to bolt the ring to the ends of the landing bars 38. Thus, the bolt holes 45 are co-located radially with the ends of the landing bars 38. Ring claws 58 are provided at various spaced locations around the stator side of the disc. The ring claws 58 extend outwards from the ring in an axial direction. The ring claws 58 are located radially at positions which correspond to the radially outwards side of the stator core 30 between the cooling fins 34. The ring claws 58 are arranged to engage with the outside of the stator core, in order to help maintain concentricity between the stator core and the ring. As will be explained below, the ring claws 58 also space the end ring 40 axially away from an end face of the stator core.

Referring in particular to Figure 3, it can be seen that the end ring 40 extends radially outwards of the stator core 30, including the cooling fins 34. Thus, the end ring 40 has an outer circumference with a radius which is greater than that of the stator core 30. The radially outwards part of the ring 40 has a mating face 60 on the side of the ring 40 facing away from the stator core. The mating face 60 is arranged to interface with the mating face 50 of the drive end adaptor 46. Bolt holes 62 pass through the ring in an axial direction and are used to bolt the adaptor 46 to the ring 40. The bolt holes 62 are located radially outwards of the stator core 30. This can allow the bolts 52 to be inserted through the bolt holes 62 from the machine side rather than the adaptor side, as shown in Figure 3. This can facilitate assembly and allow an adaptor of the appropriate size to the used. The radially outwards part of the end ring 40 may also include bolt holes (not shown) for attaching lifting lugs.

The ring 40 also includes a plurality of air holes 64 at circumferentially spaced locations around the ring. The air holes 64 are located radially at positions which correspond generally to the radially outwards side of the stator core 30 between the cooling fins 34. Thus, the air holes 64 are at least partially co-located radially with the axial cooling channels between the cooling fins 34 on the outside of the stator core. The air holes 64 allow air flow from the cooling channels between the cooling fins 34 to exit the machine.

The end ring also includes a number of grooves 65 at various locations on both sides of the ring. The grooves 65 are areas where the ring 40 has a reduced thickness. The grooves 65 are provided in locations where less strength is required, in order to reduce the weight of the end ring. At other locations, in particular locations around the various bolt holes and claws, the thickness of the ring is greater to ensure that it has sufficient mechanical strength.

The end ring 42 may be arranged in the same or similar way to the end ring 40, and may function in a similar way. However, changes in detail may be made to take into account different requirements at the drive and non-drive ends of the machine.

In one embodiment, the stator assembly of Figures 2 to 4 is assembled in the following steps.

1. The drive end ring, the stator laminations and non-drive end ring are stacked together on tooling.

2. The stator core pack is pressed and welded together while on the tooling.

3. The landing bars are attached to the end rings and welded to the stator core while on the tooling.

4. The stator is wound with stator windings using a winding machine. The end rings are used as tracing rings. 5. The wound stator is impregnated with resin using a dipping and baking process.

It has been found that this production process may provide one or more of the following advantages.

• The total number of stages involved is less than with the previous designs and involves less equipment. This also reduces the need to move the stator between different stations. This can improve the ease and speed of assembly and reduce the cost of production.

• The landing bars are held in place by the end rings as they are welded to the stator core. This helps to keep the bars concentric and avoids the need for separate welding fixtures, which simplifies the process.

• Any deformations which may occur in the landing bars during the welding process may have less effect on the machine’s concentricity than in the previous design.

• The landing bars can be welded to the stator core at the same location as where the stator laminations are welded together. This can reduce the amount of equipment required and speed up the production process.

• During the winding process, the end rings themselves can be used as tracing rings (i.e. as rings for rotating the stator core during the winding process). In the prior design, the tracing ring is a ring placed around the outside of the stator which is used to hold the stator and rotate it into a number of different indexed positions. By using the end rings as tracing rings, the need to use separate tracing rings around the stator can be avoided. Furthermore, by using end rings with a diameter which is greater than that of the stator core, the stator assembly including end rings and stator core can be easily rotated during the winding process by placing the end rings on rollers. This can reduce the amount of equipment required and speed up the production process.

• The stator can be wound after the landing bars have been welded. This avoids the need to take steps to protect the windings during welding and reduces the risk of damage to the windings.

• The impregnation process can take place after the welding, avoiding the need to add additional rust protection to areas affected by the welding. Thus, the process of producing the stator assembly described above may be more efficient, less time consuming and less expensive than the previous production process and may help to improve the machine’s concentricity.

Figure 5 shows the stator assembly of Figures 2 to 4 with the drive end adaptor, non-drive end bracket and generator feet attached. Referring to Figure 5, the stator core 30 is clamped axially between the two end rings 40, 42, and located radially between the landing bars 38. The drive end adaptor 46 is attached to the end ring 40 using bolts 52 which pass through holes in the end ring 40 and into corresponding holes in the adaptor 46. The non-drive end bracket 48 is attached to the end ring 42 using bolts which pass through holes in the end ring 42 and into corresponding holes in the non-drive end bracket 48. The generator foot 54 is attached to one of the two lower landing bars 38 using bolts 56 which pass through holes in the foot 54 and into corresponding holes in the landing bar. A second generator foot (not visible in Figure 5) is attached to the other of the two lower landing bars in a similar way.

From Figure 5 it can be seen that the fixture comprising the landing bars 38 and the end rings 40, 42 forms the main structural component of the machine, rather than the stator frame of the previous design. Thus, the adaptor 46, the bracket 48 and the feet 54 are attached to the fixture comprising the landing bars 38 and the end rings 40, 42, rather than to the stator frame. The landing bars 38 and end rings 40, 42 are used to hold the stator core in the required concentricity with the rest of the machine.

Figure 6 is an exploded view of a rotating electrical machine including the stator assembly of Figures 2 to 5. Referring to Figure 6, the machine comprises stator core 30, end rings 40, 42, drive end adaptor 46 and non-drive end bracket 48 substantially in the form described above. The machine also comprises a rotor assembly 66, which may be substantially in the form of the rotor assembly 10 described above with reference to Figure 1. The rotor assembly 66 comprises a main rotor 67, an exciter rotor 82, a fan 84 and a coupling disc 85, all of which are mounted on a shaft 78. Also shown in Figure 6 are a top cover 68, a bottom cover 70, a vents cover 72, a non-drive end cover 73, an adaptor screen 74, non-drive end lug 75 and a terminal box 76. The top cover 68, a bottom cover 70, vents cover 72, non-drive end cover 73 and an adaptor screen 74 may be provided for safety and for ingress protection. The non-drive end lug 75 may be provided to assist in lifting the assembled machine. The terminal box 76 may be provided for making electrical connections to the machine, in particular to the stator windings.

In the assembled machine, the rotor assembly 66 is located inside the stator assembly such that the bearing 80 is supported by the bearing support 49 on the bracket 48, the exciter rotor 82 is inside an exciter stator 83, the main rotor 67 is inside the stator core 30 and the fan 84 is inside the drive end adaptor 46.

Figures 7A to 7I illustrate various steps in the process of assembling the components of Figure 6 on the machine. Firstly, the bottom cover 70 is placed around the bottom half of the stator and clamped to the stator using the feet 54, as shown in Figure 7A. This is achieved by passing the bolts 56 through holes in the feet 54 and the bottom cover 70, and into corresponding holes in the bottom landing bars 38. Then the top cover 68 is placed around the top half of the stator and attached to the bottom cover 70 using a latch fastener 69 (rather than bolts) as shown in Figure 7B. The non-drive end bracket 48 is then bolted to the end ring 42 using bolts 53, as shown in Figure 7C. The drive end adaptor 46 is bolted to the end ring 40 using bolts 52, as shown in Figure 7D. The rotor assembly is then inserted into the stator assembly, as shown in Figure 7E. Figure 7E also shows that the non-drive end lug 75 is bolted to the end ring 42 using two bolts. The terminal box 76 is bolted to the end ring 42 on one side and to the non-drive end bracket 48 on the other side using four bolts, as shown in Figure 7F (see also Figure 8). The vents cover 72 is bolted to the non-drive end bracket 48 with eight bolts, as shown in Figure 7G. The adaptor screen 74 is bolted to the adaptor 46 using two bolts as shown in Figure 7H. The non-drive end cover 73 is bolted to the non-drive end bracket 48 using six bolts, as shown in Figure 7I.

It has been found that the process of assembling components such as the drive end adaptor, the non-drive end bracket, the generator feet, the covers, the terminal box and the lug is easier and involves fewer bolts than with the previous design, further improving manufacturability.

Figure 8 is a view of the assembled machine. Referring to Figure 8, the bottom cover 70 is secured to the bottom of the stator using the bolts 56 which pass through the feet 54 and the bottom cover 70. The top cover 68 is secured to the bottom cover 70 using a latching mechanism. The vents cover 72 and non-drive end cover 73 are bolted to the non-drive end bracket 48. The adaptor screen 74 is bolted to the drive end adaptor 46. The terminal box 76 is bolted on one side (axially) to the non-drive end bracket 48 using bolts 86, and on the other side to the end ring 42.

Figure 9 is a cross section through the machine of Figures 6 to 8. The machine includes a stator core 30 with stator slots in which are wound stator windings. Stator end windings 90 extend out of the stator slots and around the outside of the stator core. The stator end windings 90 extend axially through the apertures at the centres of the annular end rings 40, 42. A main rotor 67 is located inside the wound stator core. Other parts which are in common with the previous drawings are given the same reference numerals and are not described further.

It will be appreciated from the above that the stator is held in place by a fixture comprising the landing bars 38 and two end rings 40, 42. In contrast to previous designs, the drive end adaptor and non-drive end bracket are attached to this fixture, rather than to the stator frame. Thus, the landing bars 38 and the end rings 40, 42 provide the main structural components of the machine. It has been found that this arrangement can make it easier to control the properties of the landing bars and the machine’s concentricity than with previous designs. As a consequence, both ease of manufacture and the machine’s performance can be improved.

Figure 10 is a cutaway view of part of the machine, illustrating airflow in the machine. Referring to Figure 10, in operation of the machine the fan 84 rotates in order to draw air flow through the machine. Airflow is in a generally axial direction, principally through air gaps 88 between the stator 30 and the covers 68, 70, and through an airgap 89 between the rotor and the stator. As shown in Figure 10, airflow from the stator/cover airgap 88 (for example from axial air channels between the cooling fins) flows into the air holes 64 in the end ring 40. Some of the airflow continues in a generally axial direction towards the fan 84. However, some of the airflow from the stator/cover airgap 88 is diverted radially inwards by the end ring 40, towards the stator end windings 90. This is achieved by virtue of flow paths being provided in both an axial direction through the end ring 40, and in a radial direction between the end ring 40 and the end face of the stator 30. This air flow then passes along the outside of the stator end windings 90 and/or through the end windings towards the fan 84. This arrangement can assist with the cooling of the end windings 90, helping to improve the machine’s performance. However, allowing some air flow to continue in an axial direction through the end ring can help to ensure that there is sufficient air flow around the outside of the stator.

Figure 11 is a cutaway view showing part of the stator core 30 and end ring 40. Referring to Figure 11 , the end ring 40 is attached to landing bars 38 which run in an axial direction along the outside of the stator core 30. The end ring 40 includes ring claws 58 which locate the end ring 40 on the stator core 30. The rings claws 58 extend axially out of the main body of the end ring 40 and engage with the outside of the stator core 30. The ring claws have an L-shaped design with a lip part 92 and a spacer part 94. The lip parts 92 engage with the radially outwards part of the stator core 30, in order to ensure concentricity between the end ring 40 and the stator core. The spacer parts 94 space the main body of the end ring 40 away from the end face of the stator core 30. This creates air gaps 96 between the side of the end ring 40 which faces the stator core, and the end face of the stator core.

Also shown in Figure 11 are cooling fins 34 which extend radially outwards from the stator core 30. The cooling fins 34 are arranged in groups, with the fins in a group connected by a peripheral connecting member 36. As can be seen from Figure 11 , airflow from cooling channels between the cooling fins 34 can pass into the holes 64 in the end ring 40. Two exit paths are provided: one axially through the holes 64, and one radially through the gaps 96 between the end ring 40 and the end face of the stator core 30. The gaps 96 allow airflow to be directed towards the stator end windings 90, helping to improve the cooling. It will be appreciated that embodiments of the invention have been described above by way of example only, and variations in detail are possible. For example, while an embodiment has been described with reference to a single bearing generator, a two-bearing generator could be used instead. Furthermore, the principles of the invention may be applied to any appropriate type of rotating electrical machine, including generators and motors. Other variations in detail will be apparent to the skilled person within the scope of the appended claims.

Claims

1. A stator assembly for a rotating electrical machine, the stator assembly comprising: a stator core; a plurality of landing bars on the outside of the stator core; and two end rings, wherein an end ring is connected to the landing bars at each end of the stator core.

2. A stator assembly according to claim 1 , wherein the landing bars and end rings are arranged to support the stator core.

3. A stator assembly according to claim 1 or 2, wherein the landing bars and end rings function to hold the stator in concentricity with respect to other components of the machine.

4. A stator assembly according to any of the preceding claims, wherein the end rings are arranged to engage with an end face of the stator core.

5. A stator assembly according to any of the preceding claims, wherein the stator core comprises a plurality of cooling fins and the landing bars run through axial slots between adjacent fins.

6. A stator assembly according to any of the preceding claims, wherein the end rings are attached to the landing bars using bolts which pass axially through the end rings and into bolt holes in the ends of the landing bars.

7. A stator assembly according to any of the preceding claims, wherein the end rings are in the form of annular discs.

8. A stator assembly according to any of the preceding claims, wherein the stator core comprises a plurality of stator slots for stator windings, and at least one of the end rings has an inner circumference which is located radially outwards of the stator slots.

9. A stator assembly according to any of the preceding claims, wherein the end rings extend radially outwards of the stator core.

10. A stator assembly according to any of the preceding claims, wherein the end rings are arranged for use as tracing rings during winding of the stator.

11. A stator assembly according to any of the preceding claims, wherein at least one of the end rings is arranged to be attached to an adaptor or a bracket.

12. A stator according to any of the preceding claims, wherein at least one end ring comprises holes for attaching a bracket or an adaptor to the end ring, and the holes are located radially outwards of the stator core.

13. A stator assembly according to any of the preceding claims, wherein at least one end ring comprises means for attaching a terminal box.

14. A stator assembly according to any of the preceding claims, wherein at least one end ring comprises a plurality of air holes, and the air holes are arranged to provide an entry or exit path for air flow along an outside of the stator core.

15. A stator assembly according to any of the preceding claims, wherein at least one end ring is arranged to direct at least some air flow from outside of the stator core radially inwards towards stator end windings.

16. A stator assembly according to any of the preceding claims, wherein an air gap is provided between at least one of the end rings and an end face of the stator core.

17. A stator assembly according to any of the preceding claims, wherein at least one end ring is arranged to provide a first air flow path in an axial direction and a second air flow path in a radial direction.

18. A stator assembly according to any of the preceding claims, wherein at least one end ring comprises a plurality of claws for locating the end ring on the stator core.

19. A stator assembly according to claim 18, wherein the plurality of claws are arranged to space the end ring axially from an end face of the stator core.

20. A stator assembly according to any of the preceding claims, wherein at least some of the landing bars are arranged to receive a stator cover.

21 . A stator assembly according to any of the preceding claims, wherein at least some of the landing bars are arranged to secure a machine foot to the stator assembly.

22. A rotating electrical machine comprising a rotor and a stator assembly according to any of the preceding claims.

23. A rotating electrical machine according to claim 22, further comprising at least one of: a drive end adaptor or a drive end bracket attached to one of the end rings; a non-drive end bracket attached to one of the end rings; a stator cover bolted to at least one of the landing bars; and one or more machine feet attached to at least one of the landing bars.

24. A method of assembling a stator for a rotating electrical machine, the method comprising: providing a plurality of landing bars on the outside of the stator core; and connecting an end ring to the landing bars at each end of the stator core.

25. A method according to claim 24, further comprising one of more of the following steps: stacking a first end ring, stator laminations and a second end ring on tooling; welding the stator laminations to form the stator core; attaching the landing bars to the end rings; welding the landing bars to the stator core; winding the stator core with stator windings, preferably using the end rings as tracing rings; and impregnating the wound stator with resin.