A winding system of an electric machine and a method for manufacturing the same

Abstract

A winding system comprises a hairpin winding made of hollow or tubular winding conductors (101). Said tubular winding conductors have, at a first end-winding region (102), first holes (105) extending to flow channels of the tubular winding conductors and, at the second end-winding region (103), second holes (106) extending to the flow channels of the tubular winding conductors. The winding system comprises a first casing structure (107) having a fluid inlet (108) for cooling fluid and s a second casing structure (109) having a fluid outlet (110) for the cooling fluid. Thus, the cooling fluid can flow between the first and second end-winding regions via a coil side region of the hairpin winding.

Description

[0001] A WINDING SYSTEM OF AN ELECTRIC MACHINE AND A METHOD FOR MANUFACTURING THE SAME

[0002] Field of the disclosure

[0003] The disclosure relates generally to cooling of electrical machines. More particularly, the disclosure relates to a winding system of an electrical machine. Furthermore, the disclosure relates to an electrical machine. Furthermore, the disclosure relates to a method for manufacturing a winding system of an electrical machine.

[0004] Background

[0005] Many electrical machines comprise one or more windings which generate magnetic fields and in which electromotive forces are generated based on the electromagnetic induction. An electrical machine can be for example a transformer, a reactor or a choke, or a rotating or linear electrical machine such as an electrical motor or a generator. In a rotating electrical machine, a magnetic flux is developed between electromagnetically active parts of a rotor and a stator of the electrical machine. In a linear electrical machine, a magnetic flux is developed between electromagnetically active parts of a mover and a stator of the electrical machine.

[0006] Hairpin technology is a winding technology for rotating electrical machines as well as for linear electric machines. In contrast to many conventional winding technologies, the hairpin technology is based on bars of electrically conductive material which are inserted into slots of a ferromagnetic core structure. These bars can be for example enameled copper bars bent into a U-shape, resembling the geometry of hairpins. The U-shaped bars are inserted in slots of a core structure so that the U-shape bent portions of the bars are at one end of the core structure leaving free ends of the bars at the other end of the core structure. These free ends of different ones of the U-shaped bars are galvanically connected to each other so that a desired winding, such as a three-phase winding, is formed.

[0007] In a radial flux rotating electrical machine, the maximum torque is proportional to an airgap radius, the area of an airgap surface, magnetic flux density in the airgap, and linear current density in the airgap surface of the stator. Thus, without increasing the mechanical size of the electrical machine, the maximum torque can be increased by increasing the above-mentioned linear current density because the magnetic flux density cannot be practically increased any more when the saturation point of iron has been reached. Increasing the linear current density increases, however, the resistive losses in the windings of the electrical machine. Therefore, cooling of the windings plays a significant role in the operation of rotating electrical machines as well as in the operation of linear electrical machines, too.

[0008] An effective method for cooling a winding of an electrical machine is liquid cooling where cooling liquid, e.g. water or oil, is in contact with, or at least in close vicinity of, winding conductors. The liquid cooling of a stator winding is traditionally used in conjunction with large turbogenerators in which winding conductors of stator coils can be hollow to allow the cooling liquid to flow inside the winding conductors. For example, the publication UA73661 discloses a liquid cooled stator of an electrical machine. The stator described in UA73661 comprises a magnetic core structure with hydrogen cooling and a liquid-cooled three-phase winding comprising hollow winding conductors configured to conduct cooling liquid.

[0009] Liquid-cooled windings are however not free from challenges. One of the challenges is related to cooling fluid connections which transfer cooling liquid between a tubular winding conductor, such as a tubular conductor bar of a hairpin winding, and an external cooling liquid circulation system. Depending on impregnation material and / or an impregnation method, another challenge can be how to guarantee that the tubular conductors remain open during winding impregnation and baking operations.

[0010] Summary

[0011] The following presents a simplified summary to provide basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention. In this document, the word “geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

[0012] In accordance with the invention, there is provided a new winding system for an electrical machine. The electrical machine can be a rotating or linear electrical machine such as an electrical motor or a generator.

[0013] A winding system according to the invention comprises winding conductors each comprising electrically conductive material and configured to constitute a hairpin winding having a first end-winding region, a second end-winding region, and a coil side region between the first and second end-winding regions, and wherein:

[0014] - the winding conductors are tubular to constitute flow channels to conduct cooling fluid in the longitudinal direction of the winding conductors,

[0015] - walls of at least some of the winding conductors have, at the first end-winding region, one or more first holes extending to the flow channels of the winding conductors and, at the second end-winding region, one or more second holes extending to the flow channels of the winding conductors, and wherein the winding system further comprises:

[0016] - a first casing structure having a first flow connection for the cooling fluid and configured to define a space containing the one or more first holes to enable the cooling fluid to flow via the one or more first holes, and

[0017] - a second casing structure having a second flow connection for the cooling fluid and configured to define a space containing the one or more second holes to enable the cooling fluid to flow via the one or more second holes so that the cooling fluid is enabled to flow between the first and second endwinding regions via the coil side region of the hairpin winding. As the winding conductors have the one or more first holes encompassed by the first casing structure at the first end-winding region and the one or more second holes encompassed by the second casing structure at the second end-winding region, there is no need to make e.g. joints between the tubular winding conductors and tubes which supply and draw cooling fluid to and from the tubular winding conductors. Furthermore, the end-winding regions can be effectively cooled since they are surrounded by the cooling fluid.

[0018] In accordance with the invention, there is also provided a new electrical machine that can be a rotating or linear electrical machine such as an electrical motor or a generator. An electrical machine according to the invention comprises a winding system according to the invention.

[0019] In accordance with the invention, there is also provided a new method for manufacturing a winding system of an electrical machine.

[0020] A method according to the invention comprises shaping and connecting winding conductors each comprising electrically conductive material to constitute a hairpin winding having a first end-winding region, a second end-winding region, and a coil side region between the first and second end-winding regions, wherein the winding conductors are tubular to constitute flow channels to conduct cooling fluid in the longitudinal direction of the winding conductors, and the method comprises the following actions in addition to the shaping and connecting winding conductors:

[0021] - making, to walls of at least some of the winding conductors at the first endwinding region, one or more first holes extending to the flow channels of the winding conductors and, at the second end-winding region, one or more second holes extending to the flow channels of the winding conductors,

[0022] - providing the winding system with a first casing structure having a first flow connection for the cooling fluid and defining a space containing the one or more first holes to enable the cooling fluid to flow via the one or more first holes, and providing the winding system with a second casing structure having a second flow connection for the cooling fluid and defining a space containing the one or more second holes to enable the cooling fluid to flow via the one or more second holes so that the cooling fluid is enabled to flow between the first and second end-winding regions via the coil side region of the hairpin winding.

[0023] Exemplifying and non-limiting embodiments are described in accompanied dependent claims.

[0024] Various exemplifying and non-limiting embodiments both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and nonlimiting embodiments when read in conjunction with the accompanying drawings.

[0025] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features.

[0026] The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

[0027] Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

[0028] Brief description of the figures

[0029] Exemplifying and non-limiting embodiments and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 illustrates a part of a winding system according to an exemplifying and nonlimiting embodiment, figures 2a, 2b, 2c, and 2d illustrate details of winding systems according to exemplifying and non-limiting embodiments, figure 3 illustrates an electrical machine according to an exemplifying and nonlimiting embodiment, figure 4 shows a flowchart of a method according to an exemplifying and non-limiting embodiment for manufacturing a winding system of an electrical machine, figure 5a illustrates a part of an electrical machine according to an exemplifying and non-limiting embodiment, and figure 5b illustrates a part of an electrical machine according to an exemplifying and non-limiting embodiment.

[0030] Description of the exemplifying embodiments

[0031] The specific examples provided in the description given below should not be construed as limiting the scope and / or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

[0032] Figure 1 illustrates a part of a winding system according to an exemplifying and nonlimiting embodiment. The winding system is presented so that an airgap surface of a ferromagnetic core structure 112 in on the figure plane. The winding system illustrated in figure 1 can be for example a winding system of a radial flux rotating electrical machine in which case the airgap surface is cylindrical but is presented in figure 1 as being spread on the figure plane. It is also possible that the winding system illustrated in figure 1 is a winding system of a linear electrical machine. In a case of a radial flux rotating electrical machine, the axial direction is parallel with the z-axis of a coordinate system 199. In a case of a linear electrical machine, a direction of movement is parallel with the x-axis of the coordinate system 199. It is also possible that a winding system according to an exemplifying and non-limiting embodiment is a winding system of an axial flux rotating electrical machine. The winding system can be for example a three-phase winding system of an alternating current “AC” linear or rotating electrical machine.

[0033] The winding system comprises winding conductors each comprising electrically conductive material such as for example copper or aluminum. The winding conductors are configured to constitute a hairpin winding having a first end-winding region 102, a second end-winding region 103, and a coil side region 104 between the first and second end-winding regions. In figure 1 , one of the winding conductors is denoted with a reference 101 . The winding conductors are bent to turn in total 180 degrees in the first end-winding region 102 and ends of different ones of the winding conductors are galvanically connected to each other in the second endwinding region 103. Joints between the ends of different ones of the winding conductors can be for example welded joints, soldered joints, or some other joints suitable for implementing galvanic contacts. In figure 1 , one of the joints is denoted with a reference 113.

[0034] The winding conductors are tubular to constitute flow channels to conduct cooling fluid in a longitudinal direction of the winding conductors. The cooling fluid can be for example oil or some other fluid that is advantageously electrically non- conductive. Walls of at least some of the winding conductors have, at the first endwinding region 102, first holes extending to the flow channels of the winding conductors and, at the second end-winding region 103, second holes extending to the flow channels of the winding conductors. In figure 1 , one of the first holes is denoted with a reference 105 and one of the second holes is denoted with a reference 106. In this exemplifying case, the first and second holes are round holes.

[0035] The winding system comprises a first casing structure 107 that has a first flow connection 108 for receiving the cooling fluid. The first casing structure 107 is configured to define a space containing the first holes to enable the cooling fluid received via the first flow connection 108 to flow via the first holes into the flow channels constituted by the tubular winding conductors. The winding system comprises a second casing structure 109 that has a second flow connection 110 for the cooling fluid. The second casing structure 109 is configured to define a space containing the second holes to enable the cooling fluid to flow from the second holes to the second flow connection 110. Therefore, the cooling fluid is enabled to flow from the first end-winding region 102 through the flow channels constituted by the tubular winding conductors in the coil side region 104 to the second end-winding region 103. The flow direction of the cooling fluid shown in figure 1 and described above is an example only. As well, the cooling fluid can be arranged to flow from the second end-winding region 103 to the first end-winding region 102 via the coil side region 104. The ends of different ones of the winding conductors at the second endwinding region 103 do no need to be galvanically connected to each other so that the cooling fluid can flow through the joints. Instead, the ends of different ones of the winding conductors can be galvanically connected to each other so that the flow channels of the tubular winding conductors are blocked at the ends of the winding conductors.

[0036] Figures 2a, 2b, 2c, and 2d illustrate details of winding systems according to exemplifying and non-limiting embodiments. Figure 2a shows a cross-section of a winding conductor 201 a of a winding system according to an exemplifying and nonlimiting embodiment. In this exemplifying case, the above-mentioned cross-section has a substantially rectangular shape and the flow channel 215 of the winding conductor 201 a has a substantially circular cross-sectional shape. The winding conductor 201 a has electrically conductive material 213 that can be for example copper or aluminum. The winding conductor 201 a further comprises an electrically insulating outer lining 214 that may comprise for example plastic, resin, enamel, and / or some other suitable electrically insulating material. Figure 2a shows a hole 205a for conducting cooling fluid between the flow channel 215 and an exterior space of the winding conductor 201a. The hole 205a can be merely on one side of the flow channel 215, or the hole 205a can be a through hole extending through the winding conductor 201 a, as illustrated with dashed lines in figure 2a. In some cases, a round hole can be manufactured by drilling after the winding has been impregnated. Especially, the outermost and innermost conductors of an endwinding can be drilled while a drill does not have access to conductors in the middle of the end winding.

[0037] Figure 2b shows a top view of a part of a winding conductor 201 b. The winding conductor 201 b has a hole 205b for conducting cooling fluid between a flow channel of the winding conductor 201 b and an exterior space of the winding conductor 201 b. In this exemplifying case, the hole 205b is a cut having a shape elongated in the longitudinal direction of the winding conductor 201 b. The hole 205b can be manufactured with for example laser engraving. In many cases, the laser engraving is advantageously made after the winding has been impregnated. Laser engraving often offers a possibility to also engrave conductors that cannot be accessed by a drill.

[0038] Figure 2c shows a top view of a part of a winding conductor 201 c, and figure 2c shows a side view of the part of the winding conductor 201 c. The winding conductor 201 c has a hole 205c for conducting cooling fluid between a flow channel of the winding conductor 201 c and an exterior space of the winding conductor 201 c. In this exemplifying case, the hole 205c is a cut having a shape elongated in the transverse direction of the winding conductor. The hole 205b can be manufactured with for example a hacksaw or a file. In many cases, the holes such as the hole 205b are advantageously made after the winding has been impregnated.

[0039] Figure 3 illustrates an electrical machine 300 according to an exemplifying and nonlimiting embodiment. In this exemplifying case, the electrical machine 300 is a radial flux rotating electrical machine that comprises a stator 316 and a rotor. An end of a shaft 317 of the rotor is shown in figure 3. The electrical machine 300 can be for example an induction machine, a permanent magnet synchronous machine, an electrically excited synchronous machine, a synchronous reluctance machine, a flux-switched permanent magnet machine, or some other rotating electrical machine. In this exemplifying case, the stator 316 of the electrical machine 300 comprises a three-phase winding system according to an embodiment of the invention. Coils of the winding system are galvanically connected to cables 318, 319, and 320. The winding system comprises a three-phase hairpin winding made of tubular winding conductors whose walls have holes in the end-winding regions of the three-phase hairpin winding. The end-winding regions are covered with a first casing structure 307 and with a second casing structure 309. The first casing structure 307 has a first flow connection 308 for cooling fluid e.g. oil, and the first casing structure 307 is configured to define a space containing the holes of the winding conductors at the respective end-winding region to enable the cooling fluid to flow via these holes of the winding conductors. Correspondingly, the second casing structure 309 has a second flow connection 310 for the cooling fluid, and the second casing structure 309 is configured to define a space containing the holes of the winding conductors at the respective end-winding region to enable the cooling fluid to flow via these holes of the winding conductors.

[0040] The exemplifying electrical machine illustrated in figure 3 comprises a pump 321 configured to transfer the cooling fluid between the first and second flow connections 308 and 310 of the winding system to maintain a circulation of the cooling fluid via the winding system. The exemplifying electrical machine illustrated in figure 3 comprises a cooler 322 on the flow path of the cooling fluid. Furthermore, the exemplifying electrical machine illustrated in figure 3 comprises a filter 323 on the flow path of the cooling fluid and configured to remove impurities from the cooling fluid.

[0041] Figure 4 shows a flowchart of a method according to an exemplifying and nonlimiting embodiment for manufacturing a winding system of an electrical machine. The method comprises the following actions:

[0042] - action 401 : shaping and connecting winding conductors each comprising electrically conductive material to constitute a hairpin winding having a first end-winding region, a second end-winding region, and a coil side region between the first and second end-winding regions, wherein the winding conductors are tubular to constitute flow channels to conduct cooling fluid in the longitudinal direction of the winding conductors,

[0043] - action 402: making, to walls of at least some of the winding conductors at the first end-winding region, one or more first holes extending to the flow channels of the winding conductors and, at the second end-winding region, one or more second holes extending to the flow channels of the winding conductors,

[0044] - action 403: providing the winding system with a first casing structure having a first flow connection for the cooling fluid and defining a space containing the one or more first holes to enable the cooling fluid to flow via the one or more first holes, and

[0045] - action 404: providing the winding system with a second casing structure having a second flow connection for the cooling fluid and defining a space containing the one or more second holes to enable the cooling fluid to flow via the one or more second holes so that the cooling fluid is enabled to flow between the first and second end-winding regions via the coil side region of the hairpin winding. The above-mentioned action 401 may comprise inserting mainwall insulations in slots of a core structure prior to inserting the shaped winding conductors in the slots of the core structure.

[0046] It is to be noted that the above-mentioned actions 401-404 do not necessarily need to be carried out in the above-presented order. For example, the above-mentioned first and second holes of the winding conductors can be made prior to the shaping the winding conductors or after the shaping but prior to the connecting the winding conductors to constitute the hairpin winding.

[0047] A method according to an exemplifying and non-limiting embodiment comprises impregnating the winding system with electrically insulating material in a fluent form and then solidifying the electrically insulating material. The electrically insulating material can be for example resin. The impregnating can be made prior to making the holes of the winding conductors, or the holes can be made prior to the impregnation if the holes are covered during the impregnation process to prevent the electrically insulating material in the fluent form from accessing to the flow channels of the winding conductors via the holes. Depending on impregnation material and / or an impregnation method e.g. the vacuum pressure impregnation “VPI” method, it may be however challenging to cover the holes in a reliable way so that the impregnation material does not access to the holes and the flow channels. In these cases, the holes are advantageously made after the impregnation, and it is advantageously ensured that the tubular winding conductors are hermetically sealed prior to the impregnation.

[0048] Figure 5a illustrates a part of an electrical machine 500a according to an exemplifying and non-limiting embodiment. In this exemplifying case, the electrical machine 500a is a radial flux rotating electrical machine that comprises a stator 516 and a rotor 524. In figure 5a, the stator 516 is presented as a section view so that a geometric section plane is parallel with the yz-plane of a coordinate system 599 whose z-axis is parallel with the axial direction of the electrical machine 500a. The electrical machine 500a can be for example an induction machine, a permanent magnet synchronous machine, an electrically excited synchronous machine, a synchronous reluctance machine, a flux-switched permanent magnet machine, or some other rotating electrical machine. The stator 516 of the electrical machine 500a comprises a winding system according to an embodiment of the invention. The winding system can be for example a three-phase winding system. Furthermore, the stator 516 comprises a stator core structure 525, a frame 526 surrounding the stator core structure 525, and end-shields attached to the frame 526 and configured to support bearings of the rotor. The stator core structure 525 comprises ferromagnetic material and has slots which contain coil-side portions of tubular winding conductors. In figure 5a, one of the tubular winding conductors is denoted with a reference 501 , one of the end-shields is denoted with a reference 527, and one of the bearings of the rotor is denoted with a reference 531 .

[0049] The above-mentioned winding system comprises a hairpin winding made of the tubular winding conductors whose walls have holes in end-winding regions of the hairpin winding. The holes are not shown in figure 5a. The end-winding regions of the hairpin winding are covered with casing structures configured to define, at each end of the ferromagnetic stator core structure 525, a space containing the holes of the tubular winding conductors. In figure 5a, one of the end-winding regions is denoted with a reference 502 and the casing structure covering this end-winding region 502 is denoted with a reference 507. Each casing structure has a flow connection for cooling fluid e.g. oil. In figure 5a, the flow connection of the casing structure 507 is denoted with a reference 508.

[0050] In the exemplifying electrical machine 500a illustrated in figure 5a, each casing structure is constituted by i) an axially facing end-surface of the stator core structure 525, ii) a surface of the end-shield facing towards the above-mentioned axially facing end-surface of the stator core structure 525, iii) an inner tubular part that is co-axial with the rotor 524, extends from the end-shield to the stator core structure 525, and is surrounded by the end-winding region, and by iv) an outer tubular part surrounding the end-winding region so that the end-winding region is radially between the inner and outer tubular parts. In figure 5a, the inner tubular part surrounded by the end-winding region 502 is denoted with a reference 528a and the outer tubular part surrounding the end-winding region 502 is denoted with a reference 529a. In this exemplifying case, the inner tubular part 528a is sealed to stator tooth tips and to ends of stator slot wedges. In figure 5a, one of the stator slot wedges is denoted with a reference 530. In this exemplifying case, the ends of the stator slot wedges are advantageously in flush with the end-surfaces of the stator core structure 525 to facilitate the sealing with the inner tubular part 528a. The inner tubular part 528a is advantageously made of electrically nonconductive material, e.g. plastic, to avoid energy losses caused by eddy currents. Depending on the wall thickness of the inner tubular part, the inner tubular part can be arranged to extend from one end-shield to the other end-shield via the airgap of the electrical machine. In a case where a joint between the frame 526 and an outer surface of the stator core structure 525 and joints between the frame 526 and the end-shields are tight enough, a tubular part 529b of the frame 526 can act as the above-mentioned outer tubular part and there is no need for the outer tubular part 529a. It is also possible that the outer tubular part is a portion of the end-shield. As the end-shield 527 is in contact with the cooling fluid, the bearing 531 is cooled by the cooling fluid indirectly via the end-shield 527.

[0051] Figure 5b illustrates a part of an electrical machine 500b according to an exemplifying and non-limiting embodiment. In the exemplifying electrical machine 500b, the inner tubular part 528b is arranged to extend from the end-shield 527 to the other end-shield, not shown, via the airgap of the electrical machine 500b, and a portion of the end-shield 527 acts as an outer tubular part 529c surrounding the end-winding region 502. Otherwise, the electrical machine 500b can be like the electrical machine 500a illustrated in figure 5a.

[0052] The specific examples provided in the description given above should not be construed as limiting the applicability and / or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

Claims

What is claimed is:1 . A winding system for an electrical machine, the winding system comprising:- winding conductors (101 , 201 a, 201 b, 201 c, 501 ) each comprising electrically conductive material and configured to constitute a hairpin winding having a first end-winding region (102, 502), a second end-winding region (103), and a coil side region (104) between the first and second end-winding regions, characterized in that:- the winding conductors are tubular to constitute flow channels (215) to conduct cooling fluid in a longitudinal direction of the winding conductors,- walls of at least some of the winding conductors have, at the first end-winding region, one or more first holes (105, 205a, 205b, 205c) extending to the flow channels of the winding conductors and, at the second end-winding region, one or more second holes (106) extending to the flow channels of the winding conductors,- the winding system comprises a first casing structure (107, 307, 507) having a first flow connection (108, 308) for the cooling fluid and configured to define a space containing the one or more first holes to enable the cooling fluid to flow via the one or more first holes, and- the winding system comprises a second casing structure (109, 309) having a second flow connection (110, 310) for the cooling fluid and configured to define a space containing the one or more second holes to enable the cooling fluid to flow via the one or more second holes so that the cooling fluid is enabled to flow between the first and second end-winding regions via the coil side region of the hairpin winding.

2. A winding system according to claim 1 , wherein ends of different ones of the winding conductors are galvanically connected to each other at the second endwinding region (103) so that the flow channels of the winding conductors are blocked at the ends of the winding conductors.

3. A winding system according to claims 1 or 2, wherein an outline of a crosssection of the winding conductors (201 a) has a substantially rectangular shape.

4. A winding system according to any one of claims 1 -3, wherein the flow channels (215) of the winding conductors have a substantially circular cross- sectional shape.

5. A winding system according to any one of claims 1 -4, wherein the one or more first holes (105) and the one or more second holes (106) are round holes.

6. A winding system according to any one of claims 1 -4, wherein the one or more first holes (205b) and the one or more second holes are cuts having a shape elongated in the longitudinal direction of the winding conductor.

7. A winding system according to any one of claims 1 -4, wherein the one or more first holes (205c) and the one or more second holes are cuts having a shape elongated in a transverse direction of the winding conductor.

8. A winding system according to any one of claims 1 -7, wherein the electrically conductive material of the winding conductors comprises copper or aluminum.

9. A winding system according to any one of claims 1 -8, wherein the winding system is a three-phase winding system of an alternating current electrical machine.

10. An electrical machine (300, 500a, 500b) comprising a winding system according to any one of claims 1 -9.

11. An electrical machine according to claim 10, wherein the electrical machine comprises a pump (321 ) configured to transfer the cooling fluid between the first and second flow connections (308, 310) of the winding system to maintain a circulation of the cooling fluid via the winding system.

12. An electrical machine according to claim 10 or 11 , wherein the electrical machine comprises a cooler (322) on a flow path of the cooling fluid.

13. An electrical machine according to any one of claims 10-12, wherein the electrical machine comprises a filter (323) on a flow path of the cooling fluid and configured to remove impurities from the cooling fluid.

14. An electrical machine according to any one of claims 10-13, wherein each of the first and second casing structures (507) is constituted by i) an axially facing endsurface of a stator core structure (525), ii) a surface of an end-shield (527) facing towards the axially facing end-surface of the stator core structure, iii) an inner tubular part (528a) that is co-axial with a rotor (524) of the electrical machine, extends from the end-shield to the stator core structure, and is surrounded by the respective endwinding region (502), and by iv) an outer tubular part (529a, 529b, 529c) surrounding the end-winding region (502) so that the end-winding region is radially between the inner and outer tubular parts.

15. An electrical machine according to any one of claims 10-13, wherein each of the first and second casing structures (507) is constituted by i) an axially facing endsurface of a stator core structure (525), ii) a surface of an end-shield (527) facing towards the axially facing end-surface of the stator core structure, iii) an inner tubular part (528b) that is co-axial with a rotor (524) of the electrical machine, extends from the end-shield to another end-shield via an airgap of the electrical machine, and is surrounded by the respective end-winding region, and by iv) an outer tubular part (529a, 529b, 529c) surrounding the end-winding region so that the end-winding region (502) is radially between the inner and outer tubular parts.

16. A method for manufacturing a winding system of an electrical machine, the method comprising:- shaping and connecting (401 ) winding conductors each comprising electrically conductive material to constitute a hairpin winding having a first end-winding region, a second end-winding region, and a coil side region between the first and second end-winding regions, characterized in that the winding conductors are tubular to constitute flow channels to conduct cooling fluid in a longitudinal direction of the winding conductors, and the method comprises:- making (402), to walls of at least some of the winding conductors at the first end-winding region, one or more first holes extending to the flow channels of the winding conductors and, at the second end-winding region, one or more second holes extending to the flow channels of the winding conductors,- providing (403) the winding system with a first casing structure having a first flow connection for the cooling fluid and defining a space containing the one or more first holes to enable the cooling fluid to flow via the one or more first holes, and- providing (404) the winding system with a second casing structure having a second flow connection for the cooling fluid and defining a space containing the one or more second holes to enable the cooling fluid to flow via the one or more second holes so that the cooling fluid is enabled to flow between the first and second end-winding regions via the coil side region of the hairpin winding.

17. A method according to claim 16, wherein the method comprises impregnating the winding system with electrically insulating material in a fluent form and then solidifying the electrically insulating material.

18. A method according to claim 17, wherein the winding system is impregnated with the electrically insulating material prior to making the one or more first holes and the one or more second holes.

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