GB2627303A - Winding arrangement for an electrical machine - Google Patents

Abstract

A stator (Fig.1,105) for an electrical machine (Fig.1,100) comprises a stator core (Fig.1,110) and one or more windings (Fig.1,140) mounted on the stator core, wherein the windings each comprise a central region 610 and end winding regions 620. The central region of the windings comprises a heat pipe (Fig.2,250). An axial cross-sectional area of the central region is smaller than an axial cross-sectional area of the end winding regions. A conductor packing factor of the windings may be greater in the central region than in the end regions. The end winding regions may additionally comprise the heat pipe. The windings may include multiple turns alternately bent in opposite directions in the end winding regions (Fig.6, 625(1,2)). The end winding regions may be arranged to be cooled via an external fluid. The windings may be straight in the central region and extend in an axial direction of the electrical machine. The heat pipe may be a conductor having an internal sealed channel comprising a fluid. The channel may further comprise a wick (Fig.4B,430) arranged to provide for a capillary effect in the fluid. The turn that is closest to an air gap may at least partly define the air gap. The windings may be three-phase windings. The stator may be used with a rotor in an electric motor. The winding arrangement may improve temperature control for the stator, allowing operation at higher currents.

Description

Winding Arrangement for an Electrical Machine Field of the Invention The present invention relates to arrangements for windings for an electrical machine, more specifically to arrangements for windings incorporating a heat pipe.

Background

As the world transitions away from fossil fuels and to cleaner, renewable sources of power, electrical machines are becoming increasingly important. Electrical machines include electric generators to generate electricity in, for example, a wind turbine or for regenerative braking applications in vehicles. Alternatively, electric motors, such as induction motors, can use electrical energy to generate torque to power vehicles, aeroplanes and many other machines.

With the use of electrical machines becoming increasingly prevalent in the modern word, improving the performance and efficiency of these electrical machines is an area of intense research. However, there are a number of separate ways in which performance or efficiency might be improved.

The output of an electric motor can be increased by increasing the current density used to power the motor. However, this inevitably results in greater heating of the electrical machine and consequently performance losses, increased risk of component failure, and overall deterioration of the electric motor and its components over the motor's lifetime. Reliability is of the utmost concern for modern electrical machines, particularly in electrical vehicles and electrical aeroplanes, and as such further developments are required to improve upon existing techniques.

The present inventors have identified an arrangement which reduces the temperature in the core of electrical machines, thereby allowing a higher applied current density and improved efficiency (by minimising system losses). Moreover, AC losses within the electrical machine are reduced.

Summary of the Invention

Aspects of the invention are set out in the accompanying claims.

According to an aspect of the present invention, there is provided a stator for an electrical machine, the stator comprising: a stator core; and one or more windings mounted on the stator core, wherein the one or more windings each comprising a central region and one or more end winding regions, and wherein at least the central region of the one or more windings comprises a heat pipe; and wherein an axial cross-sectional area of the central region of the one or more windings is smaller than an axial cross-sectional area of the one or more end winding regions of the one or more windings.

As such, the resistance of the winding as a whole may be reduced by increasing the quantity of conductive material in the end winding, thereby reducing the DC resistance of the winding for each phase. In addition, the AC resistance is reduced through the use of heat pipes in the central region.

In some examples, a conductor packing factor of the one or more windings is greater in the central region than in the one or more end winding regions. The packing factor defines the fraction of the cross-sectional area of the heat pipe that is occupied by the channel, otherwise known as the vapour area (i.e. the area of the heat pipe occupied by the fluid/vapour). Accordingly, the size of the channel of the heat pipe may be not be increased in proportion to the cross section of the winding. Accordingly, the resistivity of the end winding can be significantly reduced, while still effectively cooling the winding.

Advantageously, the one or more end winding regions may additionally comprises the heat pipe. That is, the heat pipe may extend from the straight portion (i.e. central region) into the end winding. In this way, heat can be more effectively transferred away from the straight portions via the capillary effect.

In some examples, the one or more windings include multiple turns stacked in a radial direction and having a same circumferential position in central region of the one or more windings, and wherein the turns of the one or more windings are alternately bent in the one or more end winding regions in opposite circumferential directions. As such, the windings can be cooled from a greater number of sides, thereby increasing heat transfer away from the windings. Moreover, the alternate turning allows the straight portions of the windings to be located close to one another, while providing the advantageous effects of the greater cross-sectional area of the winding in the end winding region. The opposite circumferential directions may be, viewed from an axial direction, clockwise and anti-clockwise.

Advantageously, the end winding regions may be arranged to be cooled via an external fluid (i.e. liquid or gas). As such, heat transfer way from the windings (in particular the straight portions) is significantly improved. The end windings may be splashed with a liquid, submerged in a liquid, or cooled via a gas.

In some examples, the windings may be straight in the central region and extend in an axial direction of the electrical machine. As such, the windings may be easily wound into a slot of a stator.

The heat pipe described above may be a conductor (i.e. a conductive material such as copper or gold) having an internal sealed channel, the channel comprising a fluid. The channel may further comprise a wick, wherein the wick is arranged to provide for a capillary effect in the fluid.

In some examples, the turn that is closest to an air gap is arranged to at least partly define the air gap. In other words, a surface of this turn that is closest to the air gap is arranged to be radially level with the stator core. As such, a slot in which the windings are would does not include a gap between the windings and the air gap. Accordingly, the magnetic interaction between the stator and rotor may be increased, thereby increasing the output of the electrical machine. In conventional windings arrangements, the gap between the windings and the air gap is present to reduce AC resistance in the windings, as this is greatest closer to the air gap. However, as the present invention reduces AC resistance through the use of a heat pipe as a conductor in the central region, removing this gap can result in a greater number of turns, or allow the slot to be radially expanded.

In some example, the one or more windings include multiple turns arranged in a slot defined by a plurality of teeth, and wherein the circumferential width of the slot and/or the radial depth of the slot are arranged to accommodate a circumferential width and/or radial depth of the heat pipes of the one or more windings. In other words, the size of the slot may be made larger to accommodate the increased thickness of heat pipes, relative to solid conductors.

In some examples, the one or more windings are three-phase windings.

According to a second aspect of the invention, there is provided an electrical machine comprising: a stator as described above, and a rotor configured to rotate relative to the stator.

In some examples, the electrical machine is an electrical motor.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the following figures.

In accordance with one (or more) embodiments of the present invention the figures show the following: Figure 1 illustrates an example of an electrical machine.

Figure 2 illustrates a stator for an electrical machine according to an example of the present disclosure.

Figure 3 illustrates a rotor for an electrical machine according to an example of the present

disclosure.

Figure 4A illustrates a side-view of a heat pipe according to an example of the present disclosure.

Figure 4B illustrates a cross-sectional view of the heat pipe of Figure 4A along line A-A.

Figure 4C illustrates a cross-sectional view of the heat pipe of Figures 4A and 4B along line B-B.

Figure 5 illustrates a stator for an electrical machine according to an example of the present disclosure.

Figure 6 illustrates a winding arrangement for a stator according to an example of the present disclosure.

Figure 7 illustrates an alternative viewpoint of a winding arrangement for a stator according to

an example of the present disclosure.

Figure 8 illustrates an alternative viewpoint of a winding arrangement for a stator according to an example of the present disclosure.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field.

As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to". The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Detailed Description

Figure 1 illustrates an example of an electrical machine 100. The electrical machine 100 includes a stator 105 and a rotor 155, where the rotor 155 is arrange in use to rotate relative to the stator 105, and where an air gap 150 exists between the stator 150 and the rotor 155. This electrical machine 100 is an external stator 105 electrical machine 100, such that the stator 105 is arranged further from the axis of rotation than the rotor 155. The stator 105 includes a stator core 110 that extends in an axial direction of the electrical machine 100 (i.e. along the axis of rotation of the electrical machine, which in Figure 1 is into the page). The stator core 110 may be formed of a plurality of laminations, or may be formed of a solid core. The stator core may be formed of substantially any material, including ferromagnetic materials such as iron, or non-magnetic materials, such as a plastic or a ceramic material. The stator 105 further includes a plurality of slots 120 formed in the stator core 110. The slots 120 extend in a radial direction of the stator 105 (as shown in Figure 1) and also extend in an axial direction of the stator 105.

The plurality of slots 120 include stator windings 140. The stator windings 140 are solid conductors and are arranged in turns across the plurality of slots 120, and may be wound around teeth of the stator core 110 which define the slots 120. The slots 120 in Figure 1 include four turns of the windings 140, however any number of turns may be used e.g. based on the size of the slots 120 and the windings 140. The stator 105 shown in Figure 1 includes six slots 120 for ease of illustration, however the stator 105 may include substantially any number of slots 120, including a much greater number of slots.

Furthermore, as shown in Figure 1, the slots each include an empty region 130 that is arranged to be proximal to an air gap 150 of the electrical machine. In other words, the empty region is located between the radially innermost winding/turn 140 and the air gap 150 of the electrical machine. Slots 120 include empty region 130 in order to reduce the level of alternating current (AC) resistance in the windings 140. As magnetic flux in electrical machines is greater closer to the air gap, 150, the AC resistance is higher in windings 140 closer to the air gap 150. Therefore, in order to maintain the AC resistance in the windings 140 at manageable levels, the empty region 130 is provided.

The rotor 155 of the electrical machine 100 has a similar configuration to the stator 105. That is, the rotor 155 includes a rotor core 160 in which slots 170 are formed. Rotor windings 190 are arranged in turns in the slots 170 in the same way as the stator windings 140. Furthermore, the slots 170 also include an empty region 180 in a similar manner to the empty region 130 in the slots 120 of the stator 105. While both the stator 105 and rotor 155 of the electrical machine 100 are shown as having electrical windings 140, 190, it should be appreciated that this is just one example of an electrical machine configuration. For example, instead of windings the stator or rotor may include permanent magnets, such that only one of the stator and rotor includes electrical windings, depending on the particular type of electrical machine.

Electrical machines 100 including stators 105 and/or rotors 155 such as those shown in Figure 1 can be challenging to cool effectively. This is largely due to the central region of such windings (located in the slots 170) being comparatively far away from the end winding regions, which are typically externally cooled. As such, it is challenging to effectively cool the innermost portions of the electrical windings, as the thermal conductivity of conductor materials is generally not adequate to transfer enough heat away from the central region of the windings.

Therefore, the output of electrical machines such as this is generally limited to avoid hot spots and general damage to the electrical machine 100 through excess heating.

Figure 2 shows a stator 200 for an electrical machine according to an example teaching of the disclosure. The stator 200 includes a stator core 210 and slots 220 in a similar manner to the stator 105 of Figure 1. In particular, the stator core 210 extends in an axial direction of the stator 200 (i.e. along the axis of rotation of the electrical machine, which in Figure 2 is into the page). The stator core 210 may be formed of a plurality of laminations, or may be formed of a solid core, or may include only a scaffolding or support to which stator windings 240 are fixed. The stator core 210 may be formed of substantially any material, including ferromagnetic materials such as iron, or non-magnetic materials, such as a plastic or ceramic material. The slots 220 extend in a radial direction of the stator 200 (as shown in Figure 2) and also extend in an axial direction of the stator 200.

The slots 220 include stator windings 240 that are wound in a plurality of turns, where different turns of the stator winding 240 are arranged at different radial positions in the same slot, in a similar manner to the stator 105 of Figure 1. The stator windings 240 may be wound around teeth of the stator core 210 which define the slots 220. The slots 220 in Figure 2 include four turns of the windings 240, however any number of turns may be used e.g. based on the size of the slots 220 and the windings 240. The stator 200 shown in Figure 2 includes six slots 220 for ease of illustration, however the stator 200 may include substantially any number of slots 220, including a much greater number of slots.

As shown in Figure 2, at least some of the stator windings 240 (e.g. a subset of the stator windings 240) are heat pipes that include a sealed internal channel 250 comprising a fluid. In the example of Figure 2, two of the four windings per slot shown are heat pipes, however various arrangements of windings 240 may be utilised according to the present disclosure, including examples where all of the stator windings 240 are heat pipes. The structure of the heat pipes is discussed in more detail in relation to Figures 4A-4C.

Figure 3 shows a rotor 300 having a corresponding structure to the stator 200 of Figure 2. Rotor 300 includes a rotor core 310 and slots 320 formed in the rotor core 310. Rotor windings 340 are located in the slots 320 in the same manner as stator windings 240 are located in slots 220. Furthermore, the rotor windings 340 include heat pipes having a sealed internal channel 350, as shown in Figure 3. As such, all the techniques of this disclosure (unless explicitly stated) are equally as applicable to both stators and rotors. Furthermore, an electrical machine may include both a stator and rotor according to the example teachings of the present disclosure, or only the stator or rotor of the electrical machine may incorporate the teachings of the present disclosure. Furthermore, it should be appreciated that the techniques of the present disclosure are applicable to a variety of types of electrical machines, such as resonant electrical machines, conventional (i.e. non-resonant) electrical machines, ferromagnetic core (i.e. iron-core) electrical machines, non-magnetic core electrical machines, and coreless (i.e. air-core) electrical machines.

The use of heat pipes as windings 240 in the manner shown in Figure 2 and discussed above improves the cooling performance of the windings. In particular, windings generate heat due to the passing of current through the windings. Traditional electrical machines cool the windings by cooling an end portion (i.e. end winding) of the windings (e.g. with a coolant liquid), which allows the windings' heat to conductively dissipate away from the centre of the winding, to the end winding, to the coolant fluid. However, these techniques generally do not cool the centre of the windings as effectively (i.e. fast) as may be desired.

As mentioned above, a heat pipe is a conductive material (i.e. a conductor, such as copper) which includes a sealed internal channel which includes a working fluid. Figure 4A shows an external view of a heat pipe 400, such as the heat pipes shown in Figure 2. The heat pipe is shown extending from left to right in an axial direction (i.e. along the axis of rotation of the electrical machine). Figure 4B shows a cross-sectional view of the heat pipe 400 looking along line A-A. In other words, in Figure 4B the left-right direction is the radial direction, the up-down direction is the radial direction, and the in-out direction is the axial direction. As shown in Figure 4B, the heat pipe 400 includes a sealed internal channel 410 formed in a conductor 420, such as copper. The channel includes a fluid (which may be referred to as a working fluid). An example of the working fluid is water, however other fluids may be used.

The channel 410 also includes a wick 430 located on the internal surface of the channel 410. The wick 430 is a structure that facilitates (i.e. allows for) capillary action by the liquid phase of the fluid in the internal channel 410 (i.e. the wick 430 enables a capillary effect in the fluid, whereby the liquid is absorbed into the wick at a cool region of the heat pipe 400 and transferred to a warmer region of the heat pipe 400, where the liquid vaporises). The wick 430 may take on a variety of different structures, such as a sintered metal power or grooves formed in the conductor 420, or a hybrid wick which combines both types of wick.

Figure 4C shows a cross-sectional view of the heat pipe 400 looking along line B-B. That is, Figure 4C is shown from the same angle as Figure 4A, but depicts a cross-sectional view of the heat pipe 400. As can be seen, the channel 410 may extend along a majority of the heat pipe, with regions of solid conductor located at the extremities of the heat pipe in the length (axial) direction. The wick 430 is not shown in Figure 4C for ease of illustration. Furthermore, in some cases each winding may be formed of a single heat pipe (e.g. for each electrical phase).

As mentioned above, when in operation the heat pipe 400 may provide improved cooling performance as compared to solid conductors, as will be explained. Before being put into use, the working fluid located in the channel 410 may begin as a liquid. When the heat pipe 400 is heated, the working fluid evaporates to a vapour, thereby absorbing thermal energy. The vapour then migrates along the channel 410 to a cooler region of the channel, which may, for example, be externally cooled. At this cooler region, the vapour condenses to a liquid, releasing thermal energy. The liquid may be absorbed by the wick 430 and the thermal energy is transferred from the fluid to the conductive material 420 via the wick 430. The liquid then transfers to the warmer region of the heat pipe 400 via the wick 430 (due to the capillary effect), and then vaporises to a vapour at the warmer region.

In this manner, heat can be effectively transferred from a warm region of the heat pipe to a cooler region. The cooling performance of a heat pipe is significantly greater than a metal conductor of similar dimensions. The end winding region(s) of the heat pipes can be cooled to aid in the transfer of heat way from the heat pipe. That is, one or both axial ends of the heat pipe may be cooled (for example via a coolant liquid) to transfer heat away from the windings.

However, the cooling performance is dependent on the packing factor of the heat pipe 400.

The packing factor defines the fraction of the cross-sectional area of the heat pipe 400 that is occupied by the channel 410, otherwise known as the vapour area (i.e. the area of the heat pipe occupied by the fluid/vapour). In other words, the larger the area of the channel 410, the higher the packing factor. A packing factor of zero would mean that there is no internal channel 410. The cooling performance of the heat pipe depends on the packing factor/vapour area, as well as the pressure within the wick 430 area. Generally, the higher the packing factor the greater the cooling performance. However, when utilised as an electrical winding for an electrical machine (as in Figures 2 and 3), a higher packing factor increases the direct-current (DC) resistance of the conductor 420, as the total cross-sectional area through which current can flow is reduced, thereby generating more heat in the presence of a given current. Therefore, the packing factor may be chosen to optimise the performance of the electrical machine.

Figure 5 illustrates a stator 500 according to an example teaching of the present disclosure.

The stator 500 includes stator windings 600 and a stator core 510 through which the stator windings 600 pass, for example as discussed above in relation to Figures 1 and 2. The stator windings include end winding regions, which are visible in Figure 5, as well as a straight portion (i.e. central region) which passes through the stator core 510. In this example, some or all of the windings 600 may be formed of heat pipes, however the winding arrangement shown in Figures 5-8 may also be applied to windings formed of solid conductors (i.e. windings which do not comprise heat pipes).

The stator windings 600 are shown in more detail in Figure 6. As can be seen, the stator windings include a straight portion 610 in the central region of the windings 600, and an end winding portion 620 at the ends of the windings 600. In the straight portion 610, the windings 600 are stacked on top of one another in a radial direction so as to be mounted in a slot of the stator 500, in a similar manner to that shown in Figure 2. In the end winding region 620, the windings 600 are curved to allow the multiple turns of the windings 600 to be wound. The windings 600 include a first turn/winding 625(1) stacked above (i.e. arranged at a different radial position to) and adjacent to a second turn/winding 625(2). In Figure 6, the straight portion of the windings 600 includes eight windings stacked radially on top of one another, however other numbers of windings may be included within a slot.

As can be seen in Figure 6, the end winding portions 620 of the windings 600 are alternately rotated in different circumferential directions. That is, the first winding 625(1) is rotated (relative to the straight portion) in a first direction (in this case leftwards), while the second winding 625(2) arranged radially adjacent the first winding 625(1) rotated in the opposite direction (rightward). This pattern continues such that alternate windings rotate in different circumferential directions. This is illustrated in greater detail in Figure 7. In Figure 7, the windings 600 of Figure 6 are viewed from the top-down viewpoint, looking directly along the radial direction. Here, the first windings 6250) is located directly above the second winding 625(2), such that the straight portion 610 of the second winding 625(2) is blocked from view by the straight portion 610 of the first winding 6250). The first winding 625(1) includes two end winding regions 620a, 620b. The topmost end winding 620a of the first winding 6250) in Figure 7 bends leftwards (i.e. in a first circumferential direction), while the bottommost end winding 620b of the first winding 6250) in Figure 7 bends rightward (i.e. in a second circumferential direction). In other words, in examples where the windings 600 each include two end winding regions 620a-b, the two end winding regions 620a-b may turn or bend in opposite circumferential directions. Furthermore, the end winding region 620 of the second winding 625(2) may bend in opposite circumferential direction to the corresponding (i.e. the same) end winding regions 620 of the first winding 6250). In other words, in the topmost end winding region 620a of Figure 7, the first winding 6250) bends/turns leftwards, while the second winding 625(2) (shown by dashed lines) turns rightwards. Similarly, in the bottommost end winding region 620b of Figure 7, the first winding 6250) bends/turns rightwards, while the second winding 625(2) (shown by dashed lines) turns leftwards.

This alternating turning of the end winding regions of adjacent windings allows the end windings 620 to be cooled from four different sides, as opposed to just two. That is, the end windings 620 of windings 600 may be cooled by a fluid, i.e. a gas such as air or a coolant liquid (such as oil) to the end windings. For example, the end windings may be submerged in a liquid, or the coolant liquid may be splashed onto the end windings 620. The end windings 620 transfer heat to the coolant, thereby transferring heat away from the windings 600. If the end windings for adjacent windings are stacked on top of one another, only two sides of each winding can be directly cooled by the coolant fluid. However, in the winding arrangement shown in Figures 6 and 7, as the end winding regions of adjacent windings turn in opposite circumferential directions, all sides of the end windings 620 are exposed, meaning they can be cooled via a fluid. As such, the cooling performance of the windings 600 is improved.

Furthermore, the end windings 620 may also extend in the axial direction (e.g. towards the electrical machine's front/back yoke, or a region proximate the stator core area including with no slots). This further increases the surface area of the end windings 620, meaning the end windings can be more effectively cooled.

Figure 8 shows a view looking along the circumferential direction of an example implementation of the winding arrangement 600. The windings 600 each include straight portions 610 stacked on top of one another in the radial direction. While the straight portions 610 are shown as having a gap between each adjacent straight portion 610, the straight portions 610 may in fact abut one another such that there is no gap between adjacent straight portions 610.

The windings 600 in Figure 8 also include end windings 620 which turn alternately in the manner described above in relation to Figure 7. That is, the topmost end winding 620a of the first winding 625(1) turns into the page (shown by the dashed line), while the topmost end winding 620a of the second winding 625(2) turns out of the page. Similarly, the bottommost end winding 620b of the first winding 625(1) turns out of the page, while the bottommost end winding 620b of the second winding 625(2) turns into the page (shown by the dashed line). This pattern repeats with the end windings 620 for adjacent windings turning in different circumferential directions (with into the page being shown by dashed lines).

As can be seen in Figure 8, the end windings 620 are larger in size than the straight portions 610. That is, the cross-sectional area (shown in Figure 4B) of the winding is larger in the end winding region 620 than in the straight portion 610. As shown in Figure 8, the cross sectional area of the end windings 620 may gradually increase with distance from the central region 610. As such, the end windings 620 may slightly overlap one another (in the radial direction) close to the central region 610, before the end windings 620 have turned enough for the end windings to no longer overlap one another.

By increasing the cross-sectional area of the end winding 620, the quantity of conductor material in a given cross section of the winding may be greater in the end winding region 620 than in the straight portion 610. That is, when a winding comprises a heat pipe, there is more conductive material in the end winding 620 than in the straight portion 610. As such, electrical resistivity is reduced in the end winding region 620, as compared to the straight portion 610, thereby reducing overall resistance in the winding (and thus reducing the quantity of heat produced in the windings). In this way, the end winding regions 620 are able to compensate for the reduced quantity of conductive material in the central region 610 (which increases resistance), due to the winding being a heat pipe, by increasing the quantity of conductive material in the end winding 620.

The end winding region 620 may also comprise a heat pipe (i.e. the heat pipe extends from the central region 610 to the end winding region(s) 620), or the end winding region 620 may be formed of a solid conductor. As such, the quantity of conductive material may be increased in the end winding 620 by reducing the packing factor (e.g. by increasing the quantity of conductive material, without increasing the size of the channel of the heat pipe. Alternatively, the size of the channel of the heat pipe may also be increased in the end winding 620, in addition to providing a greater quantity of conductive material.

The alternate turning of the end windings 620 may allow the end windings 620 to be larger in size, whilst the straight portions 610 may be located close together (even abutting), such that the number of turns of the windings 600 in a slot may be maximised. As such, the magnetic flux of the stator (and thus the output of the stator) may be maximised, while controlling the temperature of the windings. That is, the alternate turning not only reduces resistance (and therefore heat generation) in the windings, but the alternate turning also allows for the end windings to be more effectively cooled by a coolant from more directions, as discussed above in relation to Figure 7. Moreover, the end windings 620 do not contribute to the magnetic circuit between the rotor and the stator, and as such the modification of the end windings in this manner does not negatively impact the performance of electrical machines. Furthermore, it should be appreciated that the alternate turning of the windings discussed above in relation to Figure 7 may be implemented in windings which do not include the increased cross-sectional area in the end windings discussed in relation to Figure 8.

The various features of the winding arrangement disclosed herein provide for greater temperature control in the windings and stator. Accordingly, the electrical machine can be operated at higher currents, thereby increasing the output of the electrical machine. The examples disclosed herein are applicable to substantially all types of electrical machine, including electrical motors and generators, and others. As such, there has been described a winding arrangement for a stator for an electrical machine, whereby the windings comprise heat pipes and whereby the cross-sectional area of the windings is greater in the end windings than in the straight portion of the windings. In addition, the end windings may alternately turn in opposite circumferential directions. The winding arrangement improves temperature control for the stator, thereby allowing the electrical machine to be operated at higher currents.

Claims (14)

1. CLAIMS1. A stator for an electrical machine, the stator comprising: a stator core; and one or more windings mounted on the stator core, wherein the one or more windings each comprising a central region and one or more end winding regions, and wherein at least the central region of the one or more windings comprises a heat pipe; and wherein an axial cross-sectional area of the central region of the one or more windings is smaller than an axial cross-sectional area of the one or more end winding regions of the one or more windings.
2. 2. The stator according to claim 1, wherein a conductor packing factor of the one or more windings is greater in the central region than in the one or more end winding regions.
3. 3. The stator according to claim 1 or claim 2, wherein the one or more end winding regions additionally comprises the heat pipe.
4. 4. The stator according to any preceding claim, wherein the one or more windings include multiple turns stacked in a radial direction and having a same circumferential position in central region of the one or more windings, and wherein the turns of the one or more windings are alternately bent in the one or more end winding regions in opposite circumferential directions.
5. 5. The stator according to claim 4, wherein the opposite circumferential directions are, viewed from an axial direction, clockwise and anti-clockwise.
6. 6. The stator according to any preceding claim, wherein the end winding regions are arranged to be cooled via an external fluid.
7. 7. The stator according to any preceding claim, wherein the one or more windings are straight in the central region and extend in an axial direction of the electrical machine.
8. 8. The stator according to any preceding claim, wherein the heat pipe is a conductor having an internal sealed channel, the channel comprising a fluid.
9. 9. The stator according to claim 9, wherein the channel further comprises a wick, wherein the wick is arranged to provide for a capillary effect in the fluid.
10. 10. The stator according to any preceding claim, wherein the turn that is closest to an air gap is arranged to at least partly define the air gap.
11. 11. The stator according to any preceding claim, wherein the one or more windings include multiple turns arranged in a slot defined by a plurality of teeth, and wherein the circumferential width of the slot and/or the radial depth of the slot are arranged to accommodate a circumferential width and/or radial depth of the heat pipes of the one or more windings.
12. 12. The stator according to any preceding claim, wherein the one or more windings are three-phase windings.
13. 13. An electrical machine comprising: a stator according to any preceding claim, and a rotor configured to rotate relative to the stator.
14. 14. The electrical machine according to claim 13, wherein the electrical machine is an electrical motor.