The present invention relates to a fan for an electrical generator, and in particular a fan that can help to improve airflow through the machine.

Electrical 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. 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. Airflow through the machine is in a generally axial direction, with the main paths for the airflow being through the rotor/stator airgap and through the stator/frame airgap.

In current electrical generator designs, the cooling fan is typically mounted on the shaft, in front of the stator windings, with the fan inlet at the midpoint of the stator end windings. However, this can create a situation in which airflow from the stator/frame air gap collides with airflow from the rotor/stator air gap at the entry point to the fan, reducing the overall efficiency. Furthermore, the air flow from the stator/frame airgap tends to be the more dominant, resulting in less cooling towards the centre of the machine. Additionally, the air coming through the stator/frame airgap tends to avoid the stator end windings and gives less cooling than could be achieved by directing the flow onto the winding surface.

In order to improve the cooling of stator end windings, it has been proposed to provide deflectors which redirect airflow from the stator/frame air gap towards the end windings. For example, WO 2018/189523, the subject matter of which is incorporated herein by reference, discloses a plurality of deflectors which are provided at spaced locations circumferentially about the machine. Each deflector comprises a deflector plate which is presented to airflow from the stator/frame air gap at an angle so as to direct the airflow towards the stator end windings.

It has been found that the deflectors disclosed in WO 2018/189523 are effective in lowering the temperature of the stator end windings. However, a disadvantage of such deflectors is that they require additional parts in the machine to achieve the improvement, which adds to the cost of manufacture.

It would therefore be desirable to provide an arrangement which can improve the airflow through an electrical generator in a cost-effective manner.

According to one aspect of the present invention there is provided a fan for an electrical generator comprising a rotor, a stator, and a frame, the fan comprising: a plurality of fan blades; and an inlet ring at an inlet to the fan, wherein the fan is arranged to draw airflow through a stator/frame airgap and through a rotor/stator airgap, and the inlet ring is angled so as to direct airflow from the stator/frame airgap towards stator end windings.

The present invention may provide the advantage that, by providing a fan with an angled inlet ring, it may be possible to improve the cooling efficiency of the machine using fewer parts and/or a more compact machine design than with previous approaches. In particular, it may be possible to divert airflow from a stator/frame airgap towards stator end windings and/or reduce interaction between stator/frame and rotor/stator airflows, without requiring additional components such as deflectors.

The inlet ring is preferably a rotating ring which is preferably used to direct air towards the fan blades. The inlet ring is preferably angled (i.e. has a non-zero angle) with respect to an axial direction. For example, the inlet ring may be at an angle of at least 10°, 15°, 20° or 25° to the axial direction and/or less than 70°, 60°or 50°to the axial direction. This can allow the inlet ring 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 inlet ring may be annular. Preferably the inlet ring has an angled surface which is continuous circumferentially. For example, the inlet ring may be substantially frustoconical. This may help to ensure that airflow is diverted in a continuous manner circumferentially about the machine. The angled surface may be presented, for example, to airflow exiting a stator/frame airgap in order to divert it more towards stator end windings.

Preferably the inlet ring is arranged to divert airflow from a substantially axial direction to a substantially radial direction. This may help to direct airflow passing through the machine in a substantially axial direction towards stator end windings. By “substantially radial” it is preferably meant that the main component of the airflow is in a radial direction, although of course other components such as axial and/or circumferential components may also be present.

The fan may be arranged to be mounted on a rotating component of the electrical generator, such as a shaft of the generator. Preferably the fan is arranged such that, when it is mounted on a rotating component of the generator, the inlet ring directs airflow towards stator end windings. For example, airflow exiting a stator/frame airgap may be directed towards the stator end windings. Preferably airflow is directed towards a radially outwards surface of the end windings. This may help to improve the cooling of the generator by improving the heat transfer from the stator windings.

Preferably the inlet ring is integral with the fan. For example, the angled inlet ring may be connected to the fan blades. This may help to reduce the size of the machine and/or the number of components.

The fan blades are preferably centrifugal blades, which preferably extend in a substantially radial direction, in order to expel air radially outwards.

Preferably the fan blades comprise extensions which connect to the inlet ring.

The extensions preferably extend in an axial direction, for example, in a direction away from a fan back plate and/or towards the machine. The inlet ring may be located at the end of the extensions axially. This may help to position the inlet ring in a suitable location such as facing an exit of the stator/frame airgap and/or radially outwards of stator end windings. This in turn may help to deflect airflow from the stator/frame airgap towards stator end windings and/or may help to reduce eddy currents. Furthermore, extending the inlet ring axially may help to keep airflow from the stator/frame airgap separate from airflow from the rotor/stator airgap, and/or may allow the overall size of the generator to be reduced.

Each extension may extend from a radially outwards part of a fan blade. Thus, the fan blades may be L-shaped. This may help to position the inlet ring in a suitable location such as facing an exit of a stator/frame airgap, which may help to direct airflow towards stator end windings, help with separation of airflows, help to reduce eddy currents and/or help to reduce the size of the machine.

Preferably the inlet ring is arranged to face the stator/frame airgap. Thus, the inlet ring may present an angled surface to airflow exiting the stator/frame airgap.

Preferably the inlet ring is positioned such that it is displaced axially with respect to a mounting point of the fan (for example, a mounting point which is used to connect the fan to a rotating component such as a hub or shaft). For example, the extensions may position the inlet ring such that it is displaced axially with respect to a mounting point of the fan. 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 have a radially inner surface that curves from a substantially axial direction to a more radial direction in the direction of airflow. For example, the inlet ring may comprise a lip on its radially inwards edge. The lip may provide the inlet ring with a radially inner surface that curves from a substantially axial direction to a more radial direction in the direction of airflow. The lip may help to turn airflow entering the fan axially to a more radial direction, thereby reducing turbulence. The lip may also help to improve separation between stator/frame and rotor/stator airflows. The fan blades may include a curved tip, preferably at the radially outwards end. This may help to increase airflow and/or provide more even airflow through the fan.

The fan may be arranged to divert airflow from the rotor/stator airgap from a substantially axial direction to a substantially radial direction. For example, the fan may comprise a back plate portion for diverting airflow from the rotor/stator airgap radially outwards. The thus diverted airflow may exit the fan radially outwards through the fan blades.

Preferably the fan blades are mounted on a mounting member, for example, an annular mounting member. This may help to keep the fan blades in the correct position and provide a mounting point for the fan. The mounting member may comprise a back plate portion and a hub portion. The back plate portion may help to direct airflow in the fan, and the hub portion may provide a mounting point to connect the fan to a hub or to a shaft of the rotating electrical machine.

Preferably the inlet ring is spaced axially away from the back plate portion and/or the hub portion. This may help to position the inlet ring in a suitable location such as facing an exit of a stator/frame airgap and/or radially outwards of stator end windings.

According to another aspect of the present invention there is provided an electrical generator comprising a rotor, a stator, a frame, and a fan in any of the forms described above.

Preferably the angled inlet ring is arranged to face the stator/frame airgap (i.e. an airgap between the stator and the stator frame). Thus, the inlet ring may present an angled surface to airflow exiting the stator/frame airgap.

Preferably at least part of the inlet ring is axially aligned with the stator/frame airgap. For example, the angled inlet ring may be co-located radially with (and displaced axially from) the stator/frame airgap. Preferably the radially outwards part of the inlet ring is at least as far outwards as the radially outwards part of the stator/frame airgap, and the radially inwards part of the inlet ring is at least as far inwards as the radially inwards part of the stator/frame airgap. Thus, the inlet ring may have a face which extends across an exit of the stator/frame airgap (while being axially displaced therefrom). This may help to ensure that airflow from the stator/frame airgap is directed towards the stator end windings as smoothly as possible.

Preferably the inlet ring is arranged to deflect airflow from a stator/frame airgap towards stator end windings, for example towards a radially outwards surface of the end windings. This can allow more cooling air to come into contact with the end windings, thereby improving the cooling of the machine.

The stator may include stator end windings, and the inlet ring may be located radially outwards of (and axially aligned with) the end windings. This may help to ensure that airflow from the stator/frame airgap is directed towards the stator windings and may help to balance stator/frame and rotor/stator airflows.

Providing the inlet ring radially outwards of the end windings may also reduce the size of the void at the exit of the stator/frame airgap, thereby reducing eddy currents, which may also help to improve overall airflow. Furthermore, by providing the inlet ring radially outwards of the end windings, airflow from the stator/frame airgap may enter the fan from the radially outwards side of the end windings, which may help to keep the stator/frame airflow separate from the rotor/stator airflow. This may help to improve the overall flow of air through the machine. In addition, providing the inlet ring radially outwards of the end windings may allow the overall size of the machine to be reduced, resulting in further cost savings.

Preferably the fan blades have a profile which corresponds to an outer surface of at least part of the stator end windings. This can allow airflow from a stator/frame airgap to flow along at least part of the stator windings, enhancing their cooling. Preferably a clearance is provided between the fan blades and the stator windings to ensure sufficient electrical and/or mechanical separation and/or sufficient airflow. Preferably the fan is arranged such that at least some of the airflow from a stator/frame airgap enters the fan separately from airflow from a rotor/stator airgap. For example, the fan may be arranged such airflow from the stator/frame airgap enters the fan from a position radially outwards of the stator end windings and/or airflow from the rotor/stator airgap enters the fan from a position radially inwards of the stator end windings. This may help to avoid interference between the two airflows.

The inlet ring may be arranged to increase a proportion of airflow through the rotor/stator airgap, in comparison to the case that there is no inlet ring. For example, the angle of the inlet ring and/or the distance of the inlet ring from the stator end winding and/or the stator end face may be selected so as to increase the resistance to the stator/frame airflow. This may help to reduce the amount of airflow through the stator/frame airgap and thereby increase the amount of airflow through the rotor/stator airgap. This may help to balance the two airflows, thereby improving the cooling efficiency.

The machine may further comprise an adaptor for connecting the machine to a prime mover, and the fan may be located inside the adaptor. The adaptor may comprise vents to allow airflow to exit radially and/or tangentially. The fan is preferably mounted on a rotating component of the machine such as the machine shaft.

According to another aspect of the present invention there is provided a method of cooling a rotating electrical machine, the method comprising creating airflow through the machine with a fan, the fan comprising a plurality of fan blades and an angled inlet ring.

Preferably airflow is deflected from a stator/frame airgap towards stator end windings by the inlet ring. Preferably at least some airflow from a stator/frame airgap enters the fan separately from airflow from a rotor/stator airgap.

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 shows a plot of air flow through the machine 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 plot of air flow through the machine of Figure 4; and

Figure 6 shows a cutaway of a modified fan in an embodiment of the invention.

Figure 1 is a radial cross section through part of a known rotating electrical machine. Referring to Figure 1 , the machine 10 comprises a rotor 12 located inside a stator 14 with an air gap 16 between the two. The rotor comprises a rotor core on which are wound rotor windings 18. Rotor field support bars 20 run axially through the rotor and extend out of the rotor in order to support the rotor windings. The rotor 12 is mounted on a shaft 22 which is supported by a bearing 24.

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. 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. In this example the electrical machine is a synchronous generator which is driven by a prime mover such as a diesel engine. 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. 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 which are mounted on a mounting member 42. The mounting member 42 provides a connection point for mounting the fan 38 on the shaft 22 via a hub 43. An inlet rim 44 is provided at the front of the fan in the airflow direction.

In operation, the fan 38 rotates in order to provide airflow through the machine. This air flow is predominately in an axial direction through the rotor/stator air gap 16 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.

Figure 2 shows a plot of air flow through the machine of Figure 1 . Referring to Figure 2, it can be seen that air flow exiting the stator/frame air gap 32 encounters a void 33. This void creates a recirculatory region with slow moving eddy currents. This provides little cooling to the outer surface of the end windings and slows down the overall airflow rate. Airflow then passes between the inlet rim 44 and the end windings 26 in a radially inward direction and encounters air flow from the rotor/stator airgap 16. This causes an air knife effect on the rotor/stator airflow, slowing it down. The combined airflow then changes direction to a radially outward direction which results in further unwanted losses.

It can also be seen from Figure 2 that a greater proportion of the airflow mass is through the stator/frame airgap 32 rather than the rotor/stator airgap 16.

However, for optimum cooling, it would be desirable to increase the proportion of airflow through the rotor/stator airgap.

Various baffles and deflectors have been proposed in order to control the airflow exiting the stator/frame airgap. Such arrangements typically introduce complex airflow paths which give additional cooling but result in slower airflow through the machine due to increased flow resistance. Furthermore, such arrangements require additional parts which increases the cost of manufacture and may add to the overall length of the machine.

In embodiments of the present invention a modified fan design is proposed which helps to address at least some of the issues discussed above.

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 46 comprises a plurality of fan blades 48 spaced circumferentially around the fan. The fan blades 48 are mounted on an annular mounting member 50. The annular mounting member 50 comprises a backplate portion 52 at the rear of the fan axially (away from the machine) and a hub portion 54 at the centre of the fan radially. The backplate portion 52 is provided to help direct airflow through the fan radially outwards, while the hub portion 54 provides a mounting point to connect the fan to a hub or to the shaft of the rotating electrical machine. The inside surface of the annular mounting member 50 (on the side of the fan blades 48) is essentially funnel-shaped, that is, it curves from a substantially axial direction in the vicinity of the hub portion 54 to a substantially radial direction in the vicinity of the backplate portion 52. This helps to direct airflow entering the fan in a substantially axial direction to a substantially radial direction as it exits the fan. The fan blades 48 have a curved edge on the radially inwards and axially outwards side which is connected to the inside surface of the annular mounting member 50.

In the arrangement of Figure 3, the fan blades 48 are centrifugal blades which are arranged to dispel air radially (and tangentially) outwards under centrifugal force as they rotate. Each fan blade 48 comprises a main blade portion 56 and an extension portion 58. The main blade portions 56 are spaced circumferentially around the fan and extend outwards from the hub portion 54 in a generally radial direction. The extension portions 58 extend from the radially outwards ends of the main blade portions 56 in an axial direction away from the back plate portion 52. Thus the main blade portions 56 and the extension portions 58 together form L-shaped fan blades 48. An angled inlet ring 60 is located at the end of the extension portions 58 axially. The extension portions 58 project the inlet ring 60 axially away from the back plate portion 52 and towards the electrical machine. The angled inlet ring 60 is substantially frustoconical in shape and has a radially inward surface which is angled with respect to the axial (and radial) direction.

The fan of Figure 3 may be manufactured from any suitable material such as metal or plastic.

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 substantially in the form described above with reference to Figure 1 . 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 fan 46 is provided at the drive end of the machine. The fan 46 is mounted on a hub 62, which itself is mounted on the shaft 22. The hub 62 is also connected to a coupling plate 64 which is used to connect the rotating parts of the electrical machine to a rotating part of the prime mover, such as a flywheel. The fan 46 is located inside the adaptor 36. The adaptor includes vents 66 which allow cooling air to exit the machine.

The fan 46 of Figure 4 comprises fan blades 48, an annular mounting member 50 and angled inlet ring 60, which may be substantially in the form described above with reference to Figure 3. Referring to Figure 4, it can be seen that the blade extension portions 58 project axially into the void at the exit of the stator/frame airgap 32. This locates the inlet ring 60 radially outwards of the stator end windings 26 and facing the exit of the stator/frame airgap 32. The inlet ring 60 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 end windings with sufficient clearance to avoid any mechanical interference and to allow sufficient airflow.

In operation, as the fan 46 rotates, the fan blades 48 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 16. Airflow exiting the stator/frame airgap 32 is deflected downwards towards the stator end windings 26 by the rotating angled inlet ring 60. The airflow then passes along the end windings 26 in a substantially axial direction towards the fan 48. The airflow enters the fan 48 through the gap between the inlet ring 60 and the end windings 26. The main blade portions 56 together with the extension portions 58 of the fan blades cause the airflow to be expelled outwards through the vents 66 on the machine side of the adaptor. On the other hand, airflow exiting the rotor/stator airgap 16 passes underneath the stator end windings 26 before entering the fan. This airflow is expelled outwards mainly by the main blade portions 56. As a consequence, the two airflows are kept largely separate and do not impede each other in the same way as in the prior design. In addition, a more even spread of air through the outlet vents 66 is achieved.

Figure 5 shows a plot of air flow through the machine of Figure 4. Referring to Figure 5, it can be seen that the flow path of the air exiting the stator/frame airgap 32 is deflected by the angled inlet ring 60 towards the radially outwards surface of the stator end windings 26. As a consequence, an increased amount of cooling air comes into contact with the end windings. Furthermore, since the size of the void at the exit of the stator/frame airgap 32 is reduced by virtue of the inlet ring 60, there is less circulating air in the void, leading to lower losses.

From Figure 5 it can also be seen that there is greater separation between the airflows from the stator/frame airgap 32 and the rotor/stator airgap 16, in comparison to the previous design. In particular, airflow from the stator/frame airgap 32 tends to enter the fan from a position radially above the end windings 26, while airflow from the rotor/stator airgap 16 tends to enter the fan from a position radially beneath the end windings. As a consequence, the two airstreams do not impede each other’s flow path. Furthermore, the two airflows tend to exit the adaptor 36 at different locations, with the airflow from the stator/frame airgap 32 exiting the adaptor at a location which is closer to the machine axially than the airflow from the rotor/stator airgap 16. This helps to provide a more even spread of airflow out of the adaptor.

In addition, at the entry point to the fan, both airstreams move in a substantially axial direction. This can improve the overall amount of airflow through the machine. In the arrangement of Figures 3 and 4, the inside edge of the inlet ring 60 has a lip 68 which curves around from the angled direction to a substantially axial direction. This helps to turn the airflow entering the fan from the stator/frame airgap 32 from a predominantly axial direction into a more radially outward direction, thereby reducing turbulence. The lip 68 may also help to improve separation between the stator/frame and the rotor/stator airflows. If desired, the size, shape and/or location of the lip 68 can be changed to adjust the way that the airflows combine, or the lip can be dispensed with.

In the arrangement shown in Figures 3 and 4, the angle of the inlet ring 60 to the axial direction is approximately 35°. Altering the angle of the inlet ring changes the resistance shown to the stator/frame airflow. Generally, an angle of between about 20° and 70° is preferred.

In addition, the length of the extensions 58 can be adjusted to position the inlet ring 60 closer to or further from the end face of the stator. Moving the inlet ring axially towards the stator end face helps to increase flow separation as well as increasing the resistance to the stator/frame airflow. Therefore, the position of the inlet ring can also be adjusted to help achieve the required airflow separation and to help balance the two airflows.

Thus, the angle and/or position of the inlet ring can be adjusted in order to change the resistance/velocity profile of the airflow. In particular, by providing an inlet ring of the appropriate angle and at the appropriate distance to the end windings, the amount of airflow through the stator/frame airgap can be reduced in comparison to the case where there is no inlet ring. This can allow greater priority to be given to the airflow from the rotor/stator airgap than would otherwise be the case. This can help to balance the airflow more evenly between the stator/frame airgap and the rotor/stator airgap, resulting in more efficient cooling.

Thus, the fan design of Figures 3 and 4 can allow the flow split ratio of the machine to be changed by adjusting the geometry of the fan. In some applications, international standards may require that a certain clearance is provided between the fan and the stator windings. For example, in the case of a metal fan for marine applications the required clearance may be of the order of around 20mm, depending on the size of the machine. However, for other applications, particularly smaller machine, it may be possible to use plastic fan rather than a metallic fan. In this case the creepage and clearance allowances may change as the fan is electrically non-conductive. Thus the size of the clearance between the fan and the end windings may be adjusted in dependence on, amongst other things, the material used for the fan, the size of the electrical machine, the application in which the machine is to be used, and the desired resistance to stator/frame airflow.

Figure 6 shows a cutaway of a modified fan in an embodiment of the invention. Referring to Figure 6, the fan comprises fan blades 48, annular mounting member 50 and angled inlet ring 60. As in the previous embodiment, the angled inlet ring 60 is arranged to deflect airflow from the stator/frame airgap towards the stator end windings. The inside edge of the inlet ring 60 has a lip 68 which helps to turn the airflow towards the inside of the fan. In the arrangement of Figure 6, the fan blades 48 include a curved tip 70. It has been found that the curved tip can result in an increase to the total airflow mass through the machine when compared to a straight bladed fan. Use of the curved tip may also result in more even flow out though a louvred adaptor outlet screen.

It has been found that use of a fan design 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, the fan design described above may provide one or more of the following advantages, in comparison to the prior design:

• 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. It will be appreciated that embodiments of the present invention have been described above by way of example only, and variations in detail will be apparent to the skilled person. For example, although embodiments of the invention 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.