WO2014120018A1

WO2014120018A1 - Electrical machine provided with a composite material cooling layer and method for producing such a cooling layer

Info

Publication number: WO2014120018A1
Application number: PCT/NO2014/050013
Authority: WO
Inventors: Jörg HÖYLAND
Original assignee: Smartmotor As
Priority date: 2013-02-01
Filing date: 2014-01-24
Publication date: 2014-08-07
Also published as: NO334942B1; NO20130166A1

Abstract

A method of cooling an electrical machine is disclosed, comprising a cooling layer that is water tight, non-corrosive, is self-supporting and has few connection points. The cooling layer comprises an impregnated cloth that can contain a cooling fluid flowing in a generally prescribed direction. The cooling layer may also include channels to ensure even cooling over a large cooling surface. Methods for producing a cooling layer are also disclosed.

Description

Electrical machine provided with a composite material cooling layer and method for producing such a cooling layer

The invention relates to cooling of electrical machines according to the preamble of claim 1, and manufacturing methods according to claims 15 and 18.

The invention relates especially to a cooling layer for electrical machines carrying a cooling fluid that is evenly distributed in the layer and moving in a certain prescribed direction. The cooling method can be applied to various types of electrical machines. Background

Efficient cooling of electrical machines has always been an issue. Because of losses in the machine, heat is generated that must be removed to avoid damaging temperatures within the machine. Cooling can be done by heat conduction or convection, where convection can be done by fluids flowing around the machine, through the air gap of the machine or through designated channels in the machine. Often a combination of the mentioned cooling methods is used.

A solution used for pressurized machines is the use of two cooling fluids. One is circulating inside the machine transferring the heat to the machine surface while the second cooling fluid flows on the outside transferring the heat away for the machine. Such a solution is described in EP 2,020,735 (A2) by Johann Neiszer. The invention described by Neiszer is a closed machine filled with oil that circulates inside the machine. Furthermore there are cooling channels in the stator where water or another fluid from the outside can flow through. The circulating oil inside the machine will then be heated by the electrical machine and be cooled by the cooling channels. This way heat is transferred from the inner parts of the machine to the cooling medium outside the machine. The flow direction of the oil inside the machine can be more or less random and the flow rate of the oil may not always be as fast as needed. Because of this cooling may not always be as good as desired. In addition, the oil inside the machine can lead to frictional losses in the machine.

Most of the heat in an electrical machine is generated in the conductor windings. Inventions have therefore been made that enable a cooling fluid to flow through the conductors. One such invention is described in WO 2007128275 (Al) by Friedrich Klinger. Although such cooling can be very effective, the conductors become much more complex to produce, more expensive to buy and much more vulnerable to faults. Bending and forming the conductors without breaking the cooling pipe, the outer conductor or the insulation in between has shown to be very challenging. In addition, since there are numerous cooling conductors in each coil, a lot of connections have to be made to make a closed circulating flow of cooling fluid in the machine.

An objective of a cooling system is to transfer as much heat as possible away from the heat source. The amount of heat that can be transferred to the cooling medium is proportional to the contact area between the heat source and the cooling medium. If efficient cooling is wanted, large cooling channels or many smaller cooling channels can be used. Large cooling channels are often not possible because of size restrictions while a large number of channels results in a large number of connection joints thus more expensive and less reliable. Cooling channels that have large contact area, few connections and uses as little space as possible are therefore desired.

Looking to casting industry, it is often important to keep the mold at a specific temperature for a given amount of time. Because of this, special cooling or heating arrangements are needed. An example of such an arrangement is a mold containing layers where a fluid can run through. The fluid temperature is then controlled with some means of external heat exchanger. By having a layer instead of channels where the fluid runs through, one avoids large temperature differences within a mold and thus giving a better control of mold surface temperature. Such layers have been described in for instance US

2009/0181208 (Al) by Ronald Clifford Sahr. A 3D-cloth is used to obtain the cooling layer, for instance like the one described in US 5,175,034 (A) by Gilles Andre De La Porte et al. Advantages mentioned by Sahr are less material, thus having a lighter mold, good strength-to-weight ratio and stiffness-to-weight ratio of the mold and providing of voids for cooling water in close proximity to molding surfaces of the mold.

Object

The object of this invention is to provide a method for even cooling of large surface areas in electrical machines.

It is also an object to reduce friction losses for circulation of the cooling fluids.

It is also an object to have the cooling channels water-tight and corrosion resistant.

Further objects will become apparent upon consideration of the claims and the following description.

The invention

An electrical machine according to the invention is described in claim 1. Preferable features of the electrical machine are described in the claims 2-14. Methods for producing cooling layers in an electrical machine are described in claims 15 and 18. Preferable features of the first method are described in claims 16-17.

The present invention discloses an electrical machine provided with means for carrying one or more cooling mediums for cooling of the electrical machine where the electrical machine includes having one or more composite material cooling layers for carrying a cooling medium, and which cooling layers are arranged for evenly distributing the cooling medium in the layer(s) and arranged for moving the cooling medium in a certain prescribed flowing direction. The means of carrying the cooling mediums can according to the present invention be done through multiple passages or channels. A further part of the present invention is a method for producing such cooling layers. More specifically, the invention relates to electrical machines having cooling layers comprising a double pile cloth having a face cloth attached to a back cloth by pile threads; the double pile cloth preferably being a 3D stitched composite fiber. These composite fibers can be glass, carbon or aramid fibers, depending on the desired properties of the cloth. The pile threads can be closer to each other in a first direction and spaced farther apart in a second direction of the cloth to achieve distinct channels or passages.

A method of producing cooling layers according to the invention is by using vacuum infusion process (VIP) of the cloth and waiting a specific time before releasing the vacuum and letting air inside the vacuum bag. A resin may then create walls between the pile threads that are closer to each other and channels or passages where the pile threads are farther from each other. The specific time to wait before letting air inside the vacuum bag depends on temperature, properties of the resin, desired viscosity of the resin, size of the cloth, and amount of the resin used. It's important that the resin has sufficient viscosity when the air is let inside the vacuum bag so that it doesn't drain of the pile threads. At the same time, the viscosity of the resin should not be too high as it would not let the face cloth and back cloth separate enough to create effective cooling channels or passages. The time to wait according to the invention could be from less than 10 minutes to 6 hours, depending on the chosen resin system.

An alternative method of producing a cooling layer according to the invention is by applying a resin to the cloth by using a roller, a brush or by spraying, known as the hand lay-up production method.

The cooling layer according to the invention is used for containing a cooling fluid for cooling the electrical machine. The cooling layer, preferably a double pile cloth impregnated in polyester, vinylester or epoxy, has a structural strength that enables for pressurized fluids flowing inside the cooling layer.

The double pile cloth according to the invention is flexible before it is impregnated and can therefore be shaped to fit surfaces. After impregnation the double pile cloth becomes a solid structure that can withstand both internal pressure and externally applied forces. Because of the strength of the cooling layer, it can be a part of the machine adding to the machine structural strength. Additional means to prevent the channels from collapsing because of external forces or pressures can also be superfluous because of the cooling layers' strength.

The cooling fluids are enclosed inside the cooling layer and does therefore not lead to frictional losses like a machine filled with oil as described by Johann Neiszer in EP 2,020,735 (A2). The cooling layer according to the present invention is also water tight and has a structural strength that can endure having cooling fluids flowing through it. The cooling layer further comprises only non-corrosive materials and is therefore better suited for containing cooling fluids than channels made of corrosive materials. The cooling layers can be used in axial flux (AF) rotating machines, radial flux (RF) rotating machines and linear machines, in machine containing iron laminations or machine having a non-iron stator and/or rotor. The cooling layers can further be used in stators and/or rotors and may be located next to the windings, around windings, between windings, around laminations, outside machine housing or anywhere else on or in an electrical machine where cooling is needed.

Further features will become apparent upon consideration of the claims and the following example description.

Examples

The invention will below be described in detail with reference to the attached drawings, where: Figure 1 shows an example of a cooling layer on a warm body,

Figure 2 shows an example with two cooling layers on a warm body,

Figure 3 shows a double pile cloth according to prior art that can be used in the present invention,

Figure 4 shows another view of a double pile cloth that can be used in the present invention,

Figure 5 shows an impregnated double pile cloth to be used as a cooling layer according to the present invention,

Figure 6 shows another impregnated double cloth to be used as a cooling layer,

Figure 7 shows a first example of windings having cooling layers,

Figure 8 shows a second example of windings having cooling layers,

Figure 9 shows a winding having cooling layers,

Figure 10 shows an electrical machine having a cooling layer,

Figure 11 shows another electrical machine having a cooling layer,

Figure 12 shows a part of an electrical machine with cooling layers around the windings, and Figure 13 shows a cooling layer and manifold at the end of the cooling layer.

Reference is now made to Figure 1 which shows a cross-section of a cooling layer 20 together with a warm object 21 according to the present invention. The cooling layer 20 is covering one side of the warm object 21 in an electrical machine 60 that needs cooling. The warm object 21 of the electrical machine 60 can be a coil or winding 50, laminations, housing or any other surface that needs cooling. The invention enables efficient cooling of an electrical machine 60 by having a cooling layer 20 comprising a cooling fluid that flows through the cooling layer 20 in a certain prescribed direction 23. According to the invention, the cooling layer 20 can be located close to the heat source and cover a large surface area. The cooling layer 20 may also follow the structure of the surface of the object 21 that needs cooling (not shown) and can also cover more than one side of the object 21 that needs cooling (not shown). The cooling layer 20 shown in Figure 1 includes channels 22 that lead the cooling fluid in a desired direction 23 to ensure even flow of cooling fluid over the whole cooling surface. An alternative cooling layer according to the present invention is a cooling layer 20 which is not divided into channels 22, but where the cooling fluid can flow more freely inside the cooling layer 20.

The cooling layer 20 may, according to the present invention, be located between objects 21 that need cooling. The cooling layer 20 may be located between laminations and windings 50, between laminations and machine housing, between two windings 50 of the machine 60 or between two other objects 21 in an electrical machine 60 that needs cooling.

The cooling layer 20 according to the invention can cover a large surface area in contrast to cooling solutions where single channels go through the machine (as e.g. in EP 2,020,735 (A2)). The present invention therefore provides better and more even cooling than prior art solutions. The cooling layer 20 according to the present invention also has the advantage that it is water tight and has a structural strength large enough to withstand pressurized cooling fluids flowing through it without any extra support means. The cooling layer confines the cooling fluid to a certain space and enables the use of cooling fluids circulating in a closed circuit using a heat exchange device to extract the heat from the cooling fluid before it is lead into the cooling layer 20 of the machine 60 again.

Reference is now made to Figure 2 which shows a schematic cross-sectional view of cooling layers 20 for cooling an object 21 of an electrical machine 60. The cooling layers 20 are located on top of each other and contain cooling fluids. The cooling fluids in Figure 2 have crosswise flow directions 23.

According to the present invention alternative embodiments may have cooling layers 20 where the flow 23 of cooling fluid is in the same direction or in opposite direction to each other. The number of cooling layers 20 shown in the figure is two, but the number of cooling layers 20 according to the invention may be different from two.

Reference is now made to Figure 3 which shows a double pile cloth 30 that is prior art and is described in patent US 5,175,034 (A) by Gilles Andre De La Porte et al. The double pile cloth 30 consists of a face cloth 31 and a back cloth 32 that both comprise warp threads 33 which are crossed with weft threads 34. The face cloth 31 and back cloth 32 are held together by pile threads 35 which, tied-in in the warp direction, are looped alternatively around a weft thread 34. The double pile cloth 30 described by Gilles Andre De La Porte et al. or similar cloths can be used in the present invention to produce a cooling layer 20 for electrical machines 60 with a large cooling surface and efficient cooling.

Reference is now made to Figure 4 which shows a cross-sectional view of a double pile cloth 30 that can be used to create a cooling layer 20 according to the present invention. The cross-sectional view is made at line A-A in Figure 3, between the face cloth 31 and back cloth 32 and shows the pile threads 35 going between the face cloth 31 and back cloth 32. The double pile cloth 30 according to the present invention comprises threads made of fiberglass, preferably creating a 3D stitched composite fiber. When having multiple cooling layers 20, as shown in Figure 2, the cloth may consist of separate layers of double pile cloths 30 put together or single pieces of face cloths 31 and back cloths 32 that are connected by pile threads 35. According to the present invention, the cloth is impregnated with a resin to create a cooling layer 20. The resin used is preferably a kind of polyester, vinylester or epoxy. The manufacturing process of an impregnated cloth to be used as a cooling layer 20 will be described in more detail below.

A cooling layer 20 according to the present invention provides an effective cooling solution that has structural strength, is water tight, non-corrosive and is easy to produce. Due to the strength of the cooling layer 20, it can be used as a part of the machine structure. Forces generated in the windings 50 of the machine 60 can be transmitted through the cooling layer 20 to a carrying structure without any other force transmitting means between the windings 50 and the carrying structure. The cooling layers 20 can be used for both electrical machines 60 having iron laminations or having ironless stators and/or rotors.

A preferred embodiment of the cloth according to the present invention includes arrangement of pile threads 35 closer to each other in one direction (Y) and farther apart from each other in a second direction (X). An alternative embodiment according to the present invention includes pile threads 35 being randomly located between the face cloth 31 and back cloth 32, or located in a pattern where the pile threads 35 do not create distinct channels 22. Reference is now made to Figure 5 shows a cross-sectional view of a cooling layer 20 comprising an impregnated double pile cloth 30 according to the present invention. By impregnating the cloth 30 using methods that will be described below, a cooling layer 20 may be achieved that includes distinct channels 22 to guide the flow 23 of cooling fluid. The channels 22 are achieved by resin creating walls 24 between the pile threads 35 that are closer to each other. The channels 22 ensure effective circulation of cooling fluid through the entire cooling layer 20 and can in addition contribute to the structural strength of the electrical machine 60.

Reference is now made to Figure 6 which shows another cross-sectional view of a cooling layer 20 according to the present invention using a double pile cloth 30. The pile threads 35 are located more or less randomly between the face cloth 31 and back cloth 32, not creating any distinct channels 22. The production of a cooling layer 20 like the one shown in the figure may be cheaper or easier to manufacture than a cooling layer 20 with distinct channels 22. A disadvantage with a cooling layer 20 without channels 22 is that the flow 23 of cooling fluid may start circulating 23a within the cooling layer 20. This may result in an uneven cooling of the electrical machine 60. The structural advantage like the example shown in Figure 5 is still maintained by the resin and the pile threads 35 between the face cloth 31 and back cloth 32.

A method for create a cooling layer 20 comprising a double pile cloth 30 according to the invention uses a vacuum infusion process (VIP) method which includes the following steps:

forming or arranging the cloth 30 to fit with a cooling surface or on a mold that represents the cooling surface - this will be referred to as a tooling surface for the cooling layer 20, a polymer vacuum bag is placed over the cloth 30 and sealed against the tooling surface, a vacuum is created inside the vacuum bag, compressing the cloth 30 so that the face cloth 31 and back cloth 32 are pressed together,

ensuring proper temperature control of the tooling surface and cloth 30,

- through an inlet in the vacuum bag, a predetermined amount of resin is allowed into the vacuum bag and the resin properly impregnates the cloth 30,

waiting a specific time, letting the resin cure until polymerization has increased the resin viscosity to a desired level,

releasing the vacuum and letting air inside the vacuum bag so the face cloth 31 and back cloth 32 are again separated from each other by fiber spring-back with only the pile threads 35 and resin holding them together,

letting the resin cure so it becomes solid. Before impregnation, the cloth 30 is flexible and can be made to fit the object 21 the cooling layer 20 is meant to cool. The cloth 30 in normal condition is bendable and the face cloth 31 and back cloth 32 are held separate by that they are stitched together with the pile threads 35. This gives the cloth 30 a spring effect where one can push the face cloth 31 and back cloth 32 together and they will separate again when the pressure is released. This is why, when the cloth 30 is put in a vacuum bag, the face cloth 31 and back cloth 32 are compressed together. When the resin is let into the vacuum bag, it will soak the cloth and impregnate the composite fibers. The resin needs a sufficiently low viscosity when let into the vacuum bag such that it is able to impregnate the composite fibers. By letting the resin cure for a specific time and at a specific temperature, the resin becomes thicker, i.e. viscosity increases. Air is let into the vacuum bag after a specific time, when the resin has the desired viscosity. Due to the spring-back effect of the pile threads 35 the face cloth 31 will rise up from the back cloth 32, separating them by a distance determined by the length of the pile threads 35. The resin must have a sufficiently high viscosity so that it creates walls 24 between the pile threads 35 in the cloth 30 that are closer to each other and that it doesn't drain of the cloth 30 or the pile threads 35. The time needed before the air is let into the vacuum bag depends on the temperature, curing properties of the resin, desired viscosity of the resin, size of the cloth 30, and the amount of the resin used. The viscosity needed depends on the properties of the cloth 30, material the cloth 30 is made of, distance between the pile threads 35, distance between the face cloth 31 and the back cloth 32, and the force the pile threads 35 have to separate the face cloth 31 and the back cloth 32. The time to wait according to the present invention could be from 10 minutes up to 6 hours, depending on curing temperature and chosen resin system. After the air has been let into the vacuum bag, the impregnated cloth 30 must further cure in order to become a solid and achieve its desired mechanical, electrical and chemical properties.

An alternative method for creating a cooling layer 20 according to the invention is known as the hand lay-up production method. This method is low-tech and well known from the composite boating industry and manufacturing of early wind turbine blades. A resin is applied on the cloth 30 by means of a brush, roller, spraying or some other means. The resin will, according to the invention, penetrate into the cloth 30 and soak the whole cloth 30. It will also create walls 24 between the pile threads 35 that are closer to each other between the face cloth 31 and the back cloth 32. The resin needs to have a sufficiently high viscosity when applied such that it does not drain of the pile threads 35. This method of applying the resin is easier and cheaper than the previous method using VIP, but can more easily result in air bubbles inside the molded cooling layer 20, imperfect channels 22, and inadequate impregnation of the composite fiber cloth 30. After application of the resin, the impregnated cloth 30 needs to be cured accordingly to the requirements of the chosen resin.

An alternative method for creating a cooling layer 20 according to the invention is vacuum infusion process of a double pile cloth where the channels are filled with a semi-rigid foam. After cure of the composite the foam is removed by a heating process, thereby leaving hollow channels for the cooling fluid to flow through.

Reference is now made to Figure 7 which shows a cross-sectional view of windings 50 consisting of shaped coils of an electrical machine 60 according to the present invention, having cooling layers 20 located on either side of the windings 50. A cooling fluid is flowing 23 inside each cooling layer 20 and the cooling layers 20 have cooling fluids flowing 23 in opposite directions along the windings 50. An alternative embodiment to this one includes arranging the cooling fluids so that they are flowing 23 in the same directions on either side of the windings 50.

Reference is now made to Figure 8 which shows another cross section of windings 50 consisting of shaped coils with cooling layers 20 according to the present invention. The cooling layers 20 in the figure contain cooling fluids flowing 23 generally orthogonal to the coil lengths and are flowing 23 in opposite direction to each other. In an alternative embodiment according to the invention the two layers 20 have cooling fluids flowing 23 in the same direction. The windings 50 in Figure 8 consist of an active length 51 that is generally straight and end windings 52 that are bent. The cooling layers 20 shown in the figure only covers the active parts 51 of the windings 50, but can alternatively also cover the end windings 52 to achieve improved cooling.

Reference is now made to Figure 9 which shows a cross-sectional view of a winding 50 in an electrical machine 60 consisting of shaped coils 55 having cooling layers 20 in between the coils 55. The cooling layers 20 have cooling fluids flowing 23 in opposite directions, generally orthogonal to the winding lengths. Alternatively the cooling fluids can flow 23 in the same directions and/or along the winding lengths. The winding 50 in Figure 9 has shaped coils 55, but according to the present invention the coils can be generally straight or alternatively bent in another way or direction.

It should be noted that the machine structures in Figure 7, 8 and 9 are not shown and the windings 50 can be located in the stator or in the rotor. The electrical machines 60 can have an ironless stator and/or rotor, or have iron laminations. The electrical machines 60 can further be axial flux machines, radial flux machines or linear machines. Since the cooling layers 20 can be made of non-magnetic materials, they do not disturb the magnetic fields and can therefore be located in an air gap of the electrical machine 60. Furthermore, Figures 7, 8 and 9 show windings 50 having two cooling layers 20, while an electrical machine 60 according to the present invention can alternatively have only one cooling layer 20 or more than two cooling layers 20. Alternatives for cooling the windings 50 of electrical machines 60 where combinations of Figure 7, 8 or 9 are used are also embodiments which are according to the present invention. For instance, windings 50 can have cooling layers 20 both in between the coils 55 and on the outside of the windings 50.

Reference is now made to Figure 10 which shows a cross-sectional view of a radial flux (RF) electrical machine 60 according to the present invention. The cooling layer 20 is located around a stator armature 61 to provide a flow 23 of cooling fluid going around the electrical machine 60. A machine housing (not shown) may be located outside the cooling layer 20 of the electrical machine 60 in Figure 10.

Alternatively the cooling layer 20 may be located outside the machine housing.

Reference is now made to Figure 11 which also shows a cross-sectional view of a radial flux (RF) electrical machine 60 according to the present invention. The cooling layer 20 of the electrical machine 60 is also here located outside the electrical machine 60, but the flow direction 23 of the cooling fluid is generally along the axial length of the electrical machine 60. Also here the machine housing (not shown) may be located either inside or outside the cooling layer 20. Figure 11 shows an electrical machine 60 having a cooling layer 20 that comprises channels 22. Alternatively the cooling layer 20 may not have the channels 22.

Reference is now made to Figure 12 which shows a cross-sectional view of a part of an electrical machine 60 with iron cores 66. Cooling layers 20 are located around the winding 50 inside a slot. The cooling layers 20 in the electrical machine 60 in Figure 12 do not only provide an efficient cooling method of the machine windings 50, but also an insulation layer between the windings 50 and iron cores 66/stator armature. Spacers 65 are preferably also arranged to ensure that the cooling layer 20 won't be damaged by the forces acting on the winding 50 when the electrical machine 60 is in use. The spacers 65 may not always be needed, as this will depend on the cooling layer 20 and the forces acting on the windings 50. The cooling layer 20 in Figure 12 is surrounding three of the four sides of the winding 50. According to the invention, the cooling layer 20 may surround any number of sides of the winding 50.

Reference is now made to Figure 13 shows a schematic view of an example of a cooling layer 20 according to the inventions with a warm object 21 and manifold 70 collecting a cooling fluid flowing 23 through the cooling layer 20. The cooling fluid flows in a prescribed direction along the warm body 21. The manifold 70 is located at the end of the cooling layer 20 collecting the cooling fluid. A pipe or hose 71 is mounted on the manifold 70 to guide the cooling fluid to a heat exchanger (not shown) to cool the cooling fluid before leading it back into the cooling layer 20. Although the cooling layer 20 may comprise many cooling channels 22, only one manifold 70 is needed on each end of the cooling layer 20. This means that the number of connections for a cooling system according to the invention is held to a minimum, thus having a simpler and more reliable cooling method than for instance presented in WO 2007128275 (Al).

A cooling layer according to the present invention may also be used for cooling linear machines, where the cooling layer may be located on the outside of the machine, inside machine structure or inside the air gap of the machine.

A cooling layer according to the present invention may also be molded to the warm object 21 after it is become solid or it can be molded to the warm object 21 as a part of the vacuum infusion process.

Claims

1. An electrical machine (60) provided with means for carrying one or more cooling mediums for cooling of the electrical machine (60), wherein the means include one or more composite material cooling layers (20) for carrying a cooling medium, and which cooling layers (20) are arranged for evenly distributing the cooling medium and arranged for moving the cooling medium in a certain prescribed flowing direction (23), characterized in that each cooling layer (20) includes multiple passages or channels (22) and each cooling layer (20) includes a double pile cloth (30) having a face cloth (31) bonded together with a back cloth (32) by pile threads (35).

2. An electrical machine according to claim 1, characterized in that the pile threads (35) are made of 3D stitched composite fiber.

3. An electrical machine (60) according to claim 1, characterized in that the cooling layer (20) is produced by using vacuum infusion process of the double pile cloth (30) and waiting a specific time so that the resin has a desired viscosity, before letting air inside a vacuum bag.

4. An electrical machine (60) according to claim 1, characterized in that the cooling layer (20) is produced by impregnating the double pile cloth (30) by applying a resin by using a roller, a brush or by spraying.

5. An electrical machine (60) according to claim 1, characterized in that the cooling layer (20) is produced by vacuum infusion process of the double pile cloth (30) where the channels (22) are filled with a semi-rigid foam during the vacuum infusion process.

6. An electrical machine (60) according to claim 5, characterized in that the foam is removed after cure of the composite by a heating process, thereby leaving hollow channels (22) for the cooling medium to flow through.

7. An electrical machine (60) according to any one of the claims 1-6, characterized in that the pile threads (35) are arranged closer to each other in a first direction of the double pile cloth (30) and spaced farther from each other in a second direction of the cloth (30), and that the introduction of the resin provides walls (24) between the pile threads (35) that are closer to each other and passages or channels (22) where the pile threads (35) are farther from each other.

8. An electrical machine (60) according to any one of the claims 1-7, characterized in that the pile threads (35) are distributed between the face cloth (31) and back cloth (32) so that no distinct channels (22) are created.

9. An electrical machine (60) according to any one of the claim 1-8, characterized in that the resin is polyester, vinylester, epoxy or polyurethane.

10. An electrical machine (60) according to claim 1, characterized in that the cooling layer (20) consists of two or more layers of face cloths (31) and back cloths (32) and that the cloths (31, 32) are connected by pile threads (35).

11. An electrical machine (60) according to any of the claims 1-10, characterized in that the electrical machine (60) is either an ironless machine or a machine containing iron cores.

12. An electrical machine (60) according to any of the claims 1-11, characterized in that the flowing direction (23) of the cooling medium is arranged for flowing (23) generally in axial, tangential or radial direction in each cooling layer (20).

13. An electrical machine (60) according to any of the claims 1-12, characterized in that the cooling layer (20) is arranged on the side of windings (50), in between neighboring windings (50), in between windings (50) in same slot or outside cores in the electrical machine (60).

14. An electrical machine (60) according to any of the claims 1-13, characterized in that it includes spacers (65) arranged to avoid that the cooling layer (20) will be damaged by pressure force.

15. Method for producing composite material cooling layers in the electrical machine (60) according to claim 1, characterized by

-using a double pile cloth (30) having a face cloth (31) bonded together with a back cloth (32) by pile threads (35), -arranging the pile threads (35) close to each other in a first direction of the cloth (30) and spacing them fa rther from each other in a second direction of the cloth (30),

-performing a vacuum infusion process of the cloth (30) by means of using a vacuum bag, and - waiting a specific time before letting air inside the vacuum bag, a llowing the fiber spring-back effect to take place so that the resin creates a wall (24) between the pile threads (35) that are close to each other and creates passages or channels (22) where the pile threads (35) a re farther from each other.

16. Method according to claim 15, characterized by using a resin wh ich is polyester, vinylester, epoxy or a polyurethane.

17. Method according to claim 16, characterized by using pile threads (35) of 3D stitched composite fiber.

18. Method for producing composite material cooling layers in the electrical machine (60) according to cla im 1, characterized by

-using a double pile cloth (30) having a face cloth (31) bonded together with a back cloth (32) by pile th reads (35),

-filling the channels with a semi-rigid foam

- applying heating to remove the foam after cure of the composite, thereby leaving hollow channels for the cooling fluid to flow through.