GB2590610A

GB2590610A - Fan for a rotating electrical machine

Info

Publication number: GB2590610A
Application number: GB1917821.9A
Authority: GB
Inventors: Anpalahan Peethamparam; Bend Philip; Rolston Robert; David Green Shaun; Patrick Tobin Abhinav
Original assignee: Cummins Generator Technologies Ltd
Current assignee: Cummins Generator Technologies Ltd
Priority date: 2019-12-05
Filing date: 2019-12-05
Publication date: 2021-07-07
Anticipated expiration: 2039-12-05
Also published as: GB201917821D0; GB2590610B

Abstract

A fan 50 for a rotating electrical machine where the fan is mounted to a plurality of bars 20, such as field support bars, extending axially through the rotor 12. The bars are perhaps radially outwards of the rotor windings 18 and may have extensions 72. The fan 50 may be mounted to the bars using a mounting member (54, fig. 3), which may have a backplate (58, fig. 3) and a plurality of holes (65, fig. 3), perhaps in bosses (60, fig. 3), for bolts or the ends of the bars. The holes may have a restriction which provides a depth stop. The fan blades (52, fig. 3) may be connected to the mounting member, and perhaps an inlet ring (66, fig. 3), which may be angled with respect to the axis of rotation (96, fig. 6). The ring may be spaced axially from the mounting member and be arranged to face a vent. The fan may: be spaced away from the rotor; be arranged without any shaft mounting means; be partially non-metallic; include a load spreading and rotor balancing disc; be arranged to restrict radial displacement of the bars during rotation.

Description

FAN FOR A ROTATING ELECTRICAL MACHINE

The present invention relates to a fan for a rotating electrical machine, and in particular a fan which can simplify the manufacturing process and facilitate servicing 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 produces a rotating magnetic field which crosses an air gap between the rotor and the stator. In some cases, support bars may be provided to support the rotor windings during operation of the machine. 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.

When the machine is in operation, currents passing through the stator and/or rotor windings, as well as other factors such as friction and windage losses, may cause the machine to heat up. Therefore many machines, particularly those of a larger design, require some form of cooling. This may be achieved by providing a fan for forcing airflow through the machine. Typically, the fan is mounted on the shaft at one end of the machine. For example, European patent application number EP 3197027 Al, the subject matter of which is incorporated herein by reference, discloses a synchronous generator with a fan mounted on the shaft at the drive end of the machine.

In current rotating electrical machine designs, the cooling fan is normally mounted on a hub which is pressed onto the shaft. However, pressing a component onto the shaft is a time-consuming process which may add to the manufacturing cost. Furthermore, there is a possibility of the fan sliding on the shaft during operation due to a loose fit. In addition, it may be difficult to replace the fan in the field as it would involve removal of the hub from the shaft.

It would therefore be desirable to provide a more cost-effective and reliable technique for mounting a fan in a rotating electrical machine. It would also be desirable to provide a technique which can facilitate replacement of the fan in the field.

According to one aspect of the present invention there is provided a fan for a rotating electrical machine comprising a rotor and a stator, wherein the fan is arranged to be mounted to a plurality of bars extending axially through the rotor.

The present invention may provide the advantage that, by mounting the fan to a plurality of bars extending axially through the rotor, the number of components being pressed onto the shaft may be reduced. This may facilitate manufacturing and provide a more cost-effective way of mounting the fan onto the rotor. Furthermore, by mounting the fan to the bars, the likelihood of the fan sliding axially may be reduced. In addition, in the event of fan failure, it may be possible for the fan to be more easily replaced in the field.

The fan may be a centrifugal fan which may be arranged to dispel air radially outwards under centrifugal force as the fan rotates. Preferably the fan comprises a plurality of fan blades. The fan blades may be centrifugal blades, which may be arranged to dispel air radially outwards under centrifugal force. However, if desired, other types of fan (for example axial) could be used instead.

The bars may be any type of bar which extends axially through the rotor and which has sufficient strength to support the fan. However, in a preferred embodiment, the bars are rotor field support bars. Such bars may be provided in the rotor in order to support rotor windings (in particular, rotor end windings) against centrifugal forces during operation of the machine. Thus, by mounting the fan to rotor field support bars, use can be made of an existing component, which may reduce cost and complexity.

Alternatively, or in addition, one or more dedicated bars may be provided in the rotor, to which the fan may be mounted.

Preferably the fan comprises a mounting member for mounting the fan to the bars. The mounting member may comprise a plurality of holes for mounting the fan to the bars. The holes may be provided at spaced locations circumferentially about the fan, which locations may correspond to circumferential locations of the ends of the bars. The holes may be arranged to receive bolts which pass axially through the fan and into the bars. This may provide a convenient and low-cost way of attaching the fan to the rotor and may facilitate replacement of the fan.

Each hole may be arranged to receive an end of a bar. Thus at least part of each hole may have an internal diameter which corresponds to the external diameter of an end of a bar with which the fan is to be used (for example, a rotor field support bar). This may help to ensure that the fan is securely attached to the bars. A hole may have a restriction which prevents insertion of the bar beyond a certain point. Alternatively, or in addition, a bar or bar extension may have a shoulder which prevents insertion of the bar or extension beyond a certain point.

Preferably the mounting member comprises a plurality of bosses, and the holes run through the bosses. This may help to provide the mounting member with the necessary strength for attaching the fan to the bars. Furthermore, the bosses may extend in an axial direction which may help to achieve a desired spacing in an axial direction between the fan and the machine.

Preferably the fan comprises a plurality of fan blades connected to the mounting member. Thus, the mounting member may function to hold the blades in place and to mount the fan to the plurality of bars. This may help to provide a simple construction.

Preferably the mounting member comprises a backplate portion. This may help to direct airflow through the fan, for example from a substantially axial direction to a substantially radial direction, during operation of the machine.

By arranging the fan to be mounted to a plurality of bars extending axially through the rotor, it may be possible for the fan to be driven by the rotor, rather than the shaft. Thus, the fan may be arranged to be driven by the rotor. In this case it may be possible to omit means for connecting the fan to a shaft. Therefore, the fan may be arranged without any means for connecting the fan to a shaft.

The fan may further comprise an inlet ring connected to a plurality of fan blades. The inlet ring may help direct airflow towards the fan blades and/or help prevent exhaust air from re-entering the air intake during operation of the machine.

In one embodiment of the invention, the inlet ring is in the form of an annular disc which lies in a plane which is substantially perpendicular to the axis of rotation. This may allow the fan to have a similar construction to previously known types of fan, and thus produce similar airflow patterns.

In another embodiment of the invention, the inlet ring is angled (has a non-zero angle) with respect to the axis of rotation. For example, the inlet ring may be substantially frustoconical. This may allow the inlet ring to divert airflow from a substantially axial direction to a substantially radial direction. For example, the inlet ring may be arranged to divert airflow exiting the machine in a substantially axial direction to a more radial direction. This may help with cooling of the machine, for example, by diverting airflow more towards stator end windings.

The fan blades may comprise axial extensions, and the inlet ring may be located at the end of the axial extensions. Preferably each extension extends from a radially outwards part of a fan blade. Thus, the fan blades may be substantially L-shaped. This may help to position the inlet ring in a more desirable location such as facing an exit of a stator/frame airgap and/or radially outwards of stator end windings. This in turn may help to deflect airflow from a stator/frame airgap towards stator end windings. Furthermore, positioning the inlet ring closer to the stator/frame airgap may help to reduce eddy currents which may otherwise occur in the airflow at the exit of the stator/frame airgap. In addition, this may help to keep airflow from the stator/frame airgap separate from airflows from a rotor/stator airgap, and/or may allow the overall size of the machine to be reduced.

The inlet ring may be displaced axially with respect to the mounting member. For example, the axial extensions on the fan blades may position the inlet ring such that it is displaced axially with respect to the mounting member. This may allow the inlet ring to be positioned closer to the machine, which may help to deflect airflow towards stator end windings and/or help with airflow separation.

The inlet ring may be arranged to face an exit of a stator/frame airgap. This may help to deflect airflow from the stator/frame airgap towards stator end windings and/or towards the fan blades.

The inlet ring and/or fan blades may be, for example, as described in co-pending United Kingdom patent application number GB 1911175.6, the subject matter of which is incorporated herein by reference.

Preferably the fan is at least partially constructed from a non-metallic material, such as a plastic or a polyamide. This may allow the fan to be lighter and easier to manufacture than would otherwise be the case and may help to minimise the stress placed on the bars during operation of the machine.

If the fan is constructed from a light-weight material such as plastic, then it is possible that the material could be deformed when mounting the fan to the bars, for example using bolts. In one embodiment of the invention, a load spreading disc is provided which may help to spread the load which is applied to the fan by mounting the fan to the bars.

Thus, according to another aspect of the invention, there is provided a fan assembly comprising a fan in any of the forms described above and a load spreading disc arranged to spread a load applied to the fan when it is mounted to the bars. For example, if the fan is mounted to the bars using bolts, then the load spreading disc help to spread the load applied to the fan by the bolts. The load spreading disc may be made from metal or another suitable resilient material.

In one preferred embodiment, the load spreading disc functions as a balance plate. For example, the load spreading disc may comprise a pitch circle of holes to which weights may be attached in order to balance the machine. This can allow balancing to be achieved without having to provide a separate balance plate, thereby reducing cost and complexity.

A rotating electrical machine comprising a fan or fan assembly as described above may also be provided. Thus, according to another aspect of the invention there is provided a rotating electrical machine comprising: a stator; a rotor comprising a plurality of bars extending axially through the rotor; and a fan or fan assembly in any of the forms described above, wherein the fan is mounted to the plurality of bars.

The rotor may comprise a plurality of holes or slots through which the bars extend. Preferably the slots extend axially from one end of the rotor to the other. Preferably the bars extend out of the rotor at each end of the rotor. The rotor may comprise rotor windings, and the bars may extend axially out of the rotor at locations radially outwards of the rotor windings (for example, radially outwards of rotor end windings). Thus, the bars may be rotor field support bars for supporting rotor end windings. This may help to prevent radial displacement of the rotor windings due to centrifugal forces during operation of the machine.

Preferably the fan is connected to the ends of the bars. For example, the fan may be connected to the bars using bolts which extend through the fan and screw into threaded holes at the ends of the bars. The fan may also comprise holes for receiving the ends of the bars (such as holes in a mounting member). This may provide a convenient manner of mounting the fan and may facilitate its subsequent removal for servicing or replacement.

Preferably the fan is spaced axially away from the machine. For example, the fan may be spaced axially from end rotor windings and/or stator end windings. This may help to ensure that rotation of the fan is not impeded and/or that there is an airflow path between the machine and the fan.

Spacing the fan at an appropriate distance from the machine may be achieved by, for example, using longer rotor field support bars than would normally be the case, or by extending part of the fan to the bars, or both.

Alternatively, or in addition, the bars may be extended by bar extensions, and the fan may be connected to the bar extensions. For example, where the bars are rotor field support bars, the rotor field support bars may be extended by support bar extensions, and the fan may be connected to the support bar extensions.

Preferably means are provided for locating the fan at the required distance from the machine. For example, where the fan comprises a hole for receiving an end of a bar, the hole may comprise a restriction for preventing the insertion of the bar or bar extension beyond a certain point. Alternatively, or in addition, the bar or bar extension may comprise a shoulder preventing insertion of the bar or bar extension into the fan beyond a certain point. This may help to ensure that the fan is located at the appropriate distance from the machine.

The rotating electrical machine will typically comprise a shaft on which the rotor is mounted. However, the fan is preferably driven by the rotor, rather than by the shaft. Therefore, the machine may be arranged such that the fan is not connected to the shaft.

In operation of the machine, the bars may be subject to centrifugal forces which may tend to force the ends of the bars radially outwards. This is particularly the case where the bars are rotor field support bars for supporting rotor end windings, where the rotor windings may press against the bars.

Preferably the fan and/or fan assembly connects the ends of the bars or bar extensions. By connecting the bars or the bar extensions to the fan and/or load spreading disc, it may be possible to restrict radial displacement of the ends of the bars during operation of the machine. In particular, the fan and/or load spreading disc may connect the ends of opposing bars (for example bars which are diametrically opposed or evenly spaced circumferentially), thereby reducing or cancelling out the applied centrifugal forces.

Corresponding methods may also be provided. Thus, according to another aspect of the present invention there is provided a method of assembling a rotating electrical machine comprising a rotor and a stator, the method comprising mounting a fan to a plurality of bars extending axially through the rotor.

Features of one aspect of the invention may be provided with any other aspect. Apparatus features may be provided with method aspects and vice versa.

In the present disclosure, terms such as "radially", "axially' and "circumferentially" are generally defined with reference to the axis of rotation of the fan and/or rotating electrical machine unless the context implies otherwise.

Preferred embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a radial cross section through part of a known rotating electrical machine; Figure 2 is an axial cross section through part of the rotor of Figure 1; Figure 3 is a perspective view of a fan in an embodiment of the invention; Figure 4 shows parts of a rotating electrical machine with the fan of Figure 3; Figure 5 shows a fan assembly in another embodiment of the invention; Figure 6 shows a fan in another embodiment of the invention; Figure 7 shows parts of a rotating electrical machine with the fan of Figure 6; and Figure 8 shows another embodiment of a rotating electrical machine.

Figure 1 is a radial cross section through part of a known rotating electrical machine. In this example the electrical machine is a synchronous generator which is driven by a prime mover such as a diesel engine. Referring to Figure 1, the machine 10 comprises a rotor 12 located inside a stator 14 with an airgap 15 between the two. The rotor 12 is mounted on a shaft 22 which in this example is supported by a bearing 24. Alternatively. the bearing may be omitted, and the shaft may be supported by a bearing in the prime mover.

The rotor 12 is formed from a plurality of metal laminations stacked together to form a rotor core having the required axial length. The rotor core is wound with rotor windings 18. Rotor field support bars 20 run axially through the rotor and extend out of the rotor core, radially outwards of the rotor windings 18.

The stator 14 comprises a stator core with slots on its inner circumference in which are wound stator windings. The stator windings run through the slots in a substantially axial direction. Stator end windings 26 extend out of the stator slots and around the outside of the stator core in a substantially circumferential direction. The stator 14 is located inside a stator frame 28. Landing bars 30 are attached to the stator frame and run through the machine in an axial direction. The landing bars 30 engage with the stator 14 on its outer circumference in order to locate the stator within the stator frame. The landing bars create air gaps 32 between the stator core and the stator frame. The stator frame 28 is terminated with an end plate 34. An adaptor 36 is connected to the stator frame end plate 34. The adaptor 36 is used to connect the stator frame to a non-rotating part of the prime mover such as a flywheel housing.

In the arrangement shown, a shaft-mounted fan 38 is located inside the adaptor 36 at the drive end of the machine. The fan 38 comprises fan blades 40 and a mounting member 42. The mounting member 42 provides a connection point for mounting the fan 38 on the shaft 22 via a hub 44. An inlet rim 46 is provided at the front of the fan in the airflow direction.

Figure 2 is an axial cross section through part of the rotor of Figure 1. Referring to Figure 2, the rotor comprises a plurality of salient poles 16, each of which extends radially outwards from the centre of the rotor. The salient poles comprise pole shoes 17 on the leading and trailing edges. Each salient pole is wound with rotor windings 18. The windings 18 are in the form of a coil comprising a conductor such as copper wire which is wound around the salient pole 16, beneath the pole shoes 17. The windings 18 comprise side windings which run in a substantially axial direction along the length of the rotor beneath the pole shoes (perpendicular to the plane of the paper in Figure 2), and end windings which run in a substantially tangential direction around the end of the rotor (parallel to the plane of the paper in Figure 2). In this example the rotor has four poles, although of course different machines may have a different number of poles.

The rotor of Figure 2 includes damper bars 19, which are formed from a non-magnetic, electrically conductive material such as copper or aluminium. The damper bars are connected at each end by a damper ring. In addition, rotor field support bars 20 run axially through the rotor and extend out of the rotor core as shown in Figure 1.

In operation, the rotor 12 of Figures 1 and 2 rotates about the central shaft 22.

The pole shoes 17 assist in retaining the rotor side windings against centrifugal force as the rotor rotates. The support bars 20 support the rotor end windings in order to prevent movement or damage due to centrifugal loads.

Rotation of the shaft 22 also causes the fan 38 to rotate. Rotation of the fan produces airflow through the machine. This airflow is predominately in an axial direction through the rotor/stator airgap 15 and the stator/frame air gap 32. Airflow enters the fan 38 through the aperture in the inlet ring 44 and exits the machine through vents in the adaptor 36.

The fan design shown in Figure 1 has the hub 44 pressed onto the shaft. However, pressing the hub onto the shaft is a time-consuming process which adds to the manufacturing cost. There is also a possibility of the fan sliding on the shaft due to a loose fit. Furthermore, it has been found that it is difficult to replace the fan in the field as this involves removal of the hub. In addition, the fan is typically manufactured from aluminium which is a relatively expensive material.

Embodiments of the invention relate to a modified fan design which can make the need for a hub or machined rotor shaft surface redundant, thus reducing cost and complexity. This is achieved by mounting the fan directly to the rotor, rather than to the shaft.

Figure 3 is a perspective view of a fan in an embodiment of the invention. The fan is designed for use with a rotating electrical machine such as that illustrated in Figure 1. Referring to Figure 3, the fan 50 comprises a plurality of fan blades 52 spaced circumferentially around the fan. The fan blades 52 are centrifugal blades which are arranged to dispel air radially (and tangentially) outwards under centrifugal force as they rotate. The fan blades 52 are mounted on an annular mounting member 54 at the rear of the fan axially.

The annular mounting member 54 comprises a hub portion 56, backplate portion 58, and a plurality of mounting portions 60. The hub portion 56 is substantially cylindrical and is located at the centre of the mounting member 54 radially. The hub portion 56 extends axially from the front to the rear of the mounting member 54 and is co-axial with the axis of rotation of the fan. The backplate portion 58 is funnel-shaped, and curves from a substantially axial direction at the front of the hub portion 56 to a substantially radial direction at the rear of the mounting member 54, where it is radially outwards of the hub portion 56. This helps to direct airflow from a substantially axial direction as it enters the fan to a substantially radial direction as it exits the fan.

The mounting portions 60 are provided at spaced locations circumferentially about the fan 50 and are used to mount the fan to the rotor. The circumferential locations of the mounting portions 60 correspond generally to those of rotor field support bars in the machine with which the fan is to be used. In this example, four mounting portions 60 are provided with each mounting portion separated from an adjacent mounting portion by 90°. However, it will be appreciated that a different number of mounting portions and different spacings could be used if desired.

Each of the mounting portions 60 has a flat rear surface 61 which extends radially from the rear end of the hub portion 56 to the rear (and radially outwards) end of the backplate portion 58. The mounting portions 60 have interior walls 62 which connect the backplate portion 58 to the hub portion 56. The interior walls 62 act as braces to hold the backplate portion 58 and the hub portion 56 in place relative to each other. The mounting portions 60 also comprise cylindrical bosses 64 which extend axially into the interior of the fan. Holes 65 are provided which run axially through the mounting portions 60. The holes 65 run through the centres of the bosses 64 for mounting the fan. The fan 50 of Figure 3 is designed to be mounted on rotor field support bars, as will be explained below.

In the arrangement of Figure 3, the fan blades 52 are also connected to an inlet ring 66 at the front of the fan (in the direction of air flow). The inlet ring 66 is an annular disc which is located at the radially outwards end of the fan blades 52.

The inlet ring 66 is used to guide airflow into the fan and to help prevent exhaust air from re-entering the air intake.

Figure 4 shows parts of a rotating electrical machine with the fan of Figure 3 in place. Referring to Figure 4, the electrical machine comprises a rotor 12 and a stator 14 which may be substantially in the form described above with reference to Figure 1. A coupling plate 68 is connected to the shaft 22 by means of a hub 70. The coupling plate 68 is used to connect the rotating parts of the electrical machine to a rotating part of the prime mover, such as a flywheel. In this example, the shaft 22 is supported by bearings in the prime mover. Other parts of the machine which are in common with the machine of Figure 1 are given the same reference numerals and are not described further.

In the arrangement of Figure 4, the rotor field support bars 20 are extended in an axial direction by means of support bar extensions 72. Each support bar extension 72 has a collar 73 at one end which receives the end of the corresponding rotor support bar 20. The support bar extensions 72 extend the rotor support bars axially into the fan through the holes 65 in the mounting portions 60. The support bar extensions 72 have shoulders 74 which prevent their insertion into the holes 65 beyond a certain point. Each support bar extension 72 is hollow, with a hole running axially through its centre.

In Figure 4, the fan 50 is connected to the rotor 12 by means of bolts (not shown). Each of the bolts has a head which engages with the rear surface 61 of a mounting portion 60, and a shaft which extends through the middle of a support bar extension 72 and into a threaded hole at the end of a rotor field support bar 20. Thus, the bolts are used to clamp the fan to the support bars 20 via the support bar extensions 72. The shoulders 74 on the support bar extensions ensure that an appropriate spacing is provided in an axial direction between the fan and the electrical machine to achieve the desired airflow.

Although not shown in Figure 4, in the assembled machine the fan 50 is located inside an adaptor, such as the adaptor 36 shown in Figure 1. The adaptor includes vents which allow cooling air to exit the machine.

By extending the existing rotor field support bars and connecting the fan to the ends of the bars, the fan can be driven at normal synchronous speed without the need to connect it directly to the shaft. This removes the need for a hub or machined rotor shaft surface, thus reducing cost and complexity. Furthermore, in the event of a fan failure, the fan can be easily replaced in the field.

In an alternative arrangement, rather than using support bar extensions, the rotor field support bars themselves may be longer than would normally be the case. In this case, the fan may be connected directly to the ends of the rotor field support bars.

The fan of Figures 3 and 4 may be manufactured from any suitable material such as metal or plastic. However, in a preferred embodiment, the fan is manufactured from plastic. For example, the fan may be moulded from a high density, temperature resistant plastic. This can avoid the need to machine the part and reduce its weight, thereby making it easier to mount on the rotor.

Figure 5 shows a fan assembly in another embodiment of the invention. In this embodiment a load spreading disc is used to ensure the bolt load is distributed across the fan. This may be particularly desirable if the fan is made from plastic.

Referring to Figure 5 the fan assembly comprises fan 50 and load spreading disc 75. The fan may be essentially in the form described above with reference to Figures 3 and 4. The load spreading disc 75 is an annular disc which engages with the rear of the fan and rests against the flat rear surfaces 61 of the mounting portions 60. In this embodiment the fan 50 is made from plastic and the load spreading disc 75 is made from a metal such as steel, although other materials could be used instead. The load spreading disc may be provided as a separate component or may be integral with the fan. Also shown in Figure 5 are bolts 76 which are used to connect the fan 50 to the rotor 12. The bolts pass through the load spreading disc 75, through the support bar extensions 72 and into threaded holes in the rotor field support bars 20. Thus, the load spreading disc is used to clamp the fan to the rotor field support bars.

In the arrangement of Figure 4 the load spreading disc 75 may also function as a balance plate. In this case the load spreading disc is provided with a pitch circle of holes. During balancing, weights can be attached to the disc using these bolt holes as required. This can allow balancing of the rotor to carried out without the need to provide a separate balance plate.

A further benefit of the fan 50 and/or load spreading disc 75 is that they connect the ends of the rotor field support bars 20 or support bar extensions 72. This can reduce the effects of centrifugal loading on the rotor field support bars by supporting them in the radial direction. In particular, since the ends of opposing bars are connected together, the centrifugal forces applied to them tend to cancel out. Thus, the presence of the fan and/or load spreading disc can provide additional support for the rotor windings by helping to prevent displacement of the rotor field support bars.

Tests carried out by the present applicant have shown that there is no reduction in mass flow rate with the rotor mounted fan. Tests have also shown that the rotor mounted fan has no significant impact on the machine fluid flow split. Thus, it has been found that the benefits of a rotor mounted fan can be achieved without substantially impacting on the fan performance.

Figure 6 shows a fan in another embodiment of the invention. Referring to Figure 6, the fan 80 in this embodiment comprises a plurality of fan blades 82 spaced circumferentially around the fan. As in the previous embodiment, the fan blades 82 are centrifugal blades which are arranged to dispel air radially (and tangentially) outwards under centrifugal force as they rotate. The fan blades 82 are mounted on an annular mounting member 84 at the rear of the fan axially. The annular mounting member 84 comprises a backplate portion 86, a hub portion 88, and a plurality of mounting portions 90.

In the arrangement of Figure 6, four mounting portions 90 are provided at spaced locations circumferentially about the fan. The mounting portions 90 are in the form of bosses which extend axially out of the backplate 86 on the inner side of the fan. In the arrangement shown, the bosses are collocated with every third fan blade 82 circumferentially. Each of the bosses has a through hole 91 running in an axial direction for mounting the fan. As in the previous embodiment, the fan 80 is designed to be mounted on rotor field support bars.

In the arrangement of Figure 6, each fan blade 82 comprises a main blade portion 92 and an extension portion 94. The main blade portions 92 are spaced circumferentially around the fan and extend outwards from the hub portion 88 in a generally radial direction. The extension portions 94 extend from the radially outwards ends of the main blade portions 92 in an axial direction away from the backplate portion 86. Thus, the main blade portions 92 and the extension portions 94 together form L-shaped fan blades 82. An angled inlet ring 96 is located at the ends of the extension portions 94 axially. The extension portions 94 project the inlet ring 96 axially away from the backplate 86 and towards the electrical machine. The angled inlet ring 96 is substantially frustoconical in shape and has a radially inward surface which is angled with respect to the axial (and radial) direction.

Figure 7 shows parts of a rotating electrical machine with the fan of Figure 6 in place. Referring to Figure 7, the electrical machine comprises a rotor 12 mounted on a shaft 22 and wound with rotor windings 18. Rotor support bars 20 are provided to support the rotor windings. The rotor is arranged to rotate inside a stator (not shown in Figure 7). The electrical machine may be substantially in the form described above with reference to Figures 1 and 4.

In the arrangement of Figure 7, the fan 80 is connected directly to the ends of rotor field support bars 20. To achieve this, the lengths of the rotor field support bars 20 are increased, in comparison to those of the machine of Figure 1. The rotor field support bars 20 extend axially into the holes 91 in the mounting portions 90. Bolts (not shown) are used to connect the fan 80 to the support bars 20. The bolts extend through the holes 91 in the mounting portions 90 and into threaded holes at the ends of the rotor field support bars 20. The holes 91 include restrictions 93 which are points at which the diameters of the holes narrow. The restrictions present shoulders which prevent the bars 20 being inserted into the holes 91 beyond a certain point. This ensures that the appropriate spacing is provided in an axial direction between the fan and the electrical machine.

The fan 80 of Figure 7 comprises an angled inlet ring 96, which may be substantially in the form described above with reference to Figure 6. Referring to Figure 7, it can be seen that the fan extension portions 94 project the angled inlet ring 96 axially towards the end face of the machine. In the assembled machine, the angled inlet ring 96 is located in a void at the exit of an airgap between the stator and the frame. This locates the inlet ring 60 radially outwards of the stator end windings 26 and facing the exit of the stator/frame airgap 32 (see Figures 1 and 4). The angled inlet ring 96 presents an angled surface to airflow exiting the airgap 32. The profile of the fan blades is such that they follow the shape of the end part of the stator end windings with sufficient clearance to avoid any mechanical interference and to allow sufficient airflow.

In operation, the fan 80 is driven by the rotor 12. As the fan 80 rotates, the fan blades 82 force air radially (and tangentially) outwards under centrifugal force.

This causes air to be drawn through the machine in a substantially axial direction. Airflow is mainly through the stator/frame airgap 32 and the rotor/stator airgap 15. Airflow exiting the stator/frame airgap 32 is deflected downwards towards the stator end windings 26 by the rotating angled inlet ring 96. The airflow then passes along the end windings 26 in a substantially axial direction towards the fan 80. The airflow enters the fan 80 through the gap between the inlet ring 96 and the end windings 26. The main blade portions 92 together with the extension portions 94 of the fan blades cause the airflow to be expelled outwards through vents in the adaptor 36. On the other hand, airflow exiting the rotor/stator airgap 15 passes underneath the stator end windings 26 before entering the fan. This airflow is expelled outwards mainly by the main blade portions 94. As a consequence, the two airflows are kept largely separate and do not impede each other in the same way as in prior designs. In addition, a more even spread of air through the outlet vents is achieved.

The arrangement of the fan blades 82 and the angled inlet ring 96 may be substantially as described in co-pending United Kingdom patent application number GB 1911175.6, the subject matter of which is incorporated herein by reference.

Figure 8 shows another embodiment of a rotating electrical machine with a rotor mounted fan. Referring to Figure 8, the electrical machine comprises a rotor 12 mounted on a shaft 22 and wound with rotor windings 18. The rotor is arranged to rotate inside a stator (not shown). Rotor field support bars 20 are provided to support the rotor end windings. The electrical machine may be substantially in the form described above with reference to Figures 1 and 4.

In this embodiment, the fan includes struts 98 which extend axially out of the bosses 90 and connect with the rotor support bars 20. Bolts pass through the bosses 90 and struts 98 and screw into the ends of the support bars 20 in order to mount the fan 80 to the rotor 12. The length of the struts 98 is chosen to ensure the appropriate separation between the fan and the machine. The fan 80 includes an angled inlet ring 96, which may be substantially in the form described above with reference to Figure 6. Also shown in Figure 8 is part of an exciter 100 which is used to provide excitation to the rotor windings 18.

It has been found that use of the fan design with an angled inlet ring as described above may allow a reduction in overall machine length to be achieved by bringing part of the fan into the void above the stator end windings, while at the same time increasing machine performance. In particular, one or more of the following advantages may be provided, in comparison to prior designs: * improved airflow through the machine by reducing interaction between the stator/frame and rotor/stator airflows; * less turbulent airflow due to reduced voids and smoother airflow paths; * better heat transfer from the stator end windings due to cooling air being directed onto the end windings; * more even spread of air from the outlet of the drive end adaptor; * more compact design; * fewer parts; * lower manufacturing costs.

In the various embodiments described above, the fan is designed to be mounted on the rotor field support bars. The bars provide the drive or power input for rotating the fan. This makes the need for a hub or machined rotor shaft surface redundant, thus reducing cost and complexity. The fan can be moulded in plastic, negating the need to machine the part. Further benefits of the fan design may include: * helping to support the rotor end-windings preventing movement or damage due to centrifugal loads; * providing a balance plate for adding weights; and * bolt on design for easy service replacement with the hub or bearing in place. 10 It will be appreciated that embodiments of the present invention have been described above by way of example only, and variations in detail are possible. For example, although embodiments have been described with reference to rotor field support bars, the fan may be used with any type of rotor bars including specially provided rotor bars which may extend all or part way through the rotor.

Furthermore, although embodiments have been described with reference to a synchronous generator, the fan of the present invention may be used with any type of rotating electrical machine, including any type of motor or generator. Moreover, features of one embodiment may be used with any of the other embodiments. Other variations in detail will be apparent to the skilled person within the scope of the appended claims.

Claims

CLAIMS1. A fan for a rotating electrical machine comprising a rotor and a stator, wherein the fan is arranged to be mounted to a plurality of bars extending axially through the rotor.
2. A fan according to claim 1, wherein the bars are rotor field support bars.
3. A fan according to claim 1 or 2, wherein the fan comprises a mounting member for mounting the fan to the bars.
4. A fan according to claim 3, wherein the mounting member comprises a plurality of holes for mounting the fan to the bars.
5. A fan according to claim 4, wherein the holes are arranged to receive bolts which pass axially through the fan and into the bars.
6. A fan according to claim 4 or 5, wherein each hole is arranged to receive an end of a bar.
7. A fan according to claim 6, wherein a hole has a restriction which prevents insertion of the bar beyond a certain point.
8. A fan according to any of claims 4 to 7, wherein the mounting member comprises a plurality of bosses, and the holes run through the bosses.
9. A fan according to any of claims 3 to 8, comprising a plurality of fan blades connected to the mounting member.
10. A fan according to any of claims 3 to 9, the mounting member comprising a backplate portion.
11. A fan according to any of the preceding claims, wherein the fan is arranged without any means for connecting the fan to a shaft.
12. A fan according to any of the preceding claims, further comprising an inlet ring connected to a plurality of fan blades.
13. A fan according to claim 12, wherein the inlet ring is angled with respect to the axis of rotation.
14. A fan according to claim 12 or 13, wherein the fan blades comprise axial extensions, and the inlet ring is located at the end of the axial extensions.
15. A fan according to any of claims 12 to 14 when dependent on claim 3, wherein the inlet ring is displaced axially with respect to the mounting member.
16. A fan according to any of claims 12 to 15, wherein the inlet ring is arranged to face an exit of a stator/frame airgap.
17. A fan according to any of the preceding claims, wherein the fan is at least partially constructed from a non-metallic material.
18. A fan assembly comprising a fan according to any of the preceding claims and a load spreading disc arranged to spread a load applied to the fan when it is mounted to the bars.
19. A fan assembly according to claim 18, wherein the load spreading disc functions as a balance plate.
20. A rotating electrical machine comprising: a stator; a rotor comprising a plurality of bars extending axially through the rotor; and a fan or fan assembly according to any of the preceding claims; wherein the fan is mounted to the plurality of bars.
21. A machine according to claim 20, wherein the rotor comprises rotor windings, and the bars extend axially out of the rotor at locations radially outwards of the rotor windings.
22. A machine according to claim 20 or 21, wherein the fan is spaced axially away from the machine.
23. A machine according to any of claims 20 to 22, wherein the bars are extended by bar extensions, and the fan is connected to the bar extensions.
24. A machine according to any of claims 20 to 23, wherein the fan or fan assembly is arranged to restrict radial displacement of the ends of the bars during operation of the machine.
25. A method of assembling a rotating electrical machine comprising a rotor and a stator, the method comprising mounting a fan to a plurality of bars extending axially through the rotor.