Winding assembly and related method

Abstract

To provide a winding assembly that reduces overheating and mechanical stress that accelerates insulation degradation.SOLUTION: A winding assembly 100 for an electric machine includes a plurality of windings having insulation strands. The plurality of windings includes a first winding 120 configured to be mounted around a base 210 of a stator tooth 200 and a second winding 130 configured to be mounted proximate a tip of the stator tooth. The first winding and the second winding are electrically connected. A stator segment and a pole piece comprising the winding assembly are also provided. A method of attaching the winding assembly to the stator tooth is also provided.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a winding assembly as well as a pole piece including such a winding assembly. The present disclosure further relates to an electric machine, for example a generator, including such a winding assembly or pole piece. The present disclosure further relates to a wind turbine including such a generator. The present disclosure also relates to a method of attaching a winding assembly to a stator tooth of an electric machine. [Background technology]

[0002] Advanced wind turbines are commonly used to provide electricity to the power grid. This type of wind turbine generally comprises a tower and a rotor disposed on the tower. The rotor, which typically comprises a hub and a number of blades, rotates under the influence of the wind on the blades. This rotation typically generates a torque that is transferred by the rotor shaft to a generator either directly ("direct drive" or "gearless") or by means of a gearbox. The generator thus generates electrical power that can be provided to the power grid.

[0003] Wind turbine generators, as well as other electric machines such as motors, typically comprise a rotor and a stator. The rotor and stator may be concentrically mounted with a radial gap between them. The rotor rotates relative to the stator. The rotor may form the inner structure and the stator may form the outer structure. Thus, the stator may radially surround the rotor. Or, in another configuration, the arrangement may be reversed, with the rotor radially surrounding the stator.

[0004] Large generators such as advanced wind turbines can be permanent magnet generators (PMG) or electrically excited generators. In a permanent magnet generator, the permanent magnets (PM) are typically located on the rotor, and the winding elements (i.e. coils) are usually contained in the stator. Permanent magnet generators are often considered suitable for offshore wind turbines because they are generally reliable and require less maintenance than other types of generators.

[0005] The permanent magnet generator may include a stator yoke having a plurality of radially projecting teeth. In generators where the stator surrounds the generator rotor, the teeth may project toward the center of the stator yoke. Alternatively, in generators where the generator rotor surrounds the stator, the teeth may project toward the radially outward side of the stator yoke. Additionally, a plurality of slots may be defined between adjacent teeth, and each slot may accommodate portions of a respective winding or different windings.

[0006] Electrically excited generators, on the other hand, typically include a rotor having a number of pole pieces and excitation windings (i.e., coils). In use, a current is applied to the excitation coils. The applied current creates a polarity of magnetic poles, with adjacent poles having different magnetic polarities. As the rotor rotates, the magnetic field from the pole pieces reaches the windings of the stator, creating a variable magnetic flux in the stator windings, which creates a voltage in the stator windings.

[0007] The windings are typically made of insulated copper wire, which is wound around the teeth to generate the required electromagnetic field. One of the major problems associated with windings in large electrical machines is overheating. When current flows through the copper wire in the windings, heat is generated and builds up, which can lead to degradation of the insulation and / or a reduction in the overall performance of the electrical machine. Overheating can result from a variety of factors, including high current densities, inadequate cooling or poor quality insulation. Moreover, overheating can lead to insulation breakdown, which can result in a short circuit and serious damage to the machine.

[0008] Another problem associated with windings is insulation failure. Insulating the copper wire is essential to prevent short circuits and other electrical problems. However, effectively insulating the windings means that the insulating material must be tightly secured around the winding surface. This means that the insulating material (e.g. insulating tape) is subjected to high loads, for example at the corners of the winding. This excessive mechanical stress can accelerate insulation degradation over time. Insulation failure can cause serious damage to the machine.

[0009] Such potential problems may be exacerbated as the size of the electric machine increases. As the size of the electric machine increases, the size of the stator teeth and corresponding windings may also increase. For example, large electric machines, particularly generators, are known in direct drive wind turbines, particularly direct drive wind turbines having a nominal power output of 10 MW or more. Such direct drive generators may have, for example, a diameter of 6-8 m or more and a length of 1-2 m or more. Large electric machines are also known in other technical fields, such as hydroelectric installations.

[0010] The present disclosure aims to provide a winding assembly and associated method that is suitable for large or even very large electric machines and that at least partially overcomes some of the above-mentioned disadvantages. Summary of the Invention

[0011] In one aspect of the disclosure, a winding assembly for a stator tooth of an electric machine is provided, the stator tooth extending radially from a base to a distal end. The winding assembly includes a first winding body configured to be mounted around a section of the stator tooth near a base of the stator tooth, the first winding body including a plurality of first insulating strands wound around the stator tooth. The winding assembly includes a second winding body configured to be mounted closer to the distal end of the stator tooth than the first winding body, the second winding body including a plurality of second insulating strands wound around the stator tooth. The second winding body is spaced apart from the first winding body.

[0012] Providing multiple windings simplifies insulation of the assembly, for example, each winding can have independent insulation, and the insulation material experiences less tensile load due to the reduced height of the windings. Also, in some examples, the first and second windings can be optimized for different purposes, as described below. Furthermore, the temperature of the disclosed winding assemblies can be more effectively controlled due to the increased external surface area to volume ratio compared to a single winding. Physical separation of the windings allows for additional cooling, as described below.

[0013] Another aspect of the present disclosure provides a stator segment including one or more stator teeth extending radially from a base to a distal end, the stator segment further comprising a winding assembly according to the previous aspect.

[0014] In yet another aspect, there is provided an electric machine comprising a rotor rotatable about a machine axis and a stator concentric with the rotor, the stator comprising a plurality of pole pieces according to the previous aspect.

[0015] In yet another aspect, there is also provided a wind turbine comprising such an electric machine.

[0016] In yet another aspect, a method of attaching a winding assembly to a stator tooth, the stator tooth extending radially from a base to a distal end, includes providing a first winding body by winding a plurality of first insulating strands on a section of the stator tooth near a base of the stator tooth and providing a second winding body by winding a plurality of second insulating strands on a section of the stator tooth near a distal end of the stator tooth, the method further includes electrically connecting the first winding body to the second winding body.

[0017] In yet another aspect, a pole piece for a stator of an electric machine is provided. The pole piece includes a stator tooth extending radially from a base to a distal end, the base of the pole piece being shaped to fit into a mating structure on the stator. The pole piece further includes a first winding body including a plurality of first insulating strands wound around a section of the stator tooth near the base of the stator tooth, and a second winding body including a plurality of second insulating strands wound around the stator tooth closer to a tip of the stator tooth than the first winding body. The second winding body is separate from the first winding body, and the first winding body is electrically connected to the second winding body.

[0018] Throughout this disclosure, the term "strand" refers to wires or cables having a circular or rounded cross section, as well as plate-like material, e.g., rectangular, square, or other cross-sectional shape. As used herein, plate-like material may have a certain thickness and may be considered, for example, as a strip or bar.

[0019] Additional objects, advantages and features of embodiments of the disclosed technology will become apparent to those skilled in the art from the following detailed description, or may be learned by practice of the technology. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic perspective view of an example wind turbine; [Diagram 2] 1 illustrates an example of a hub and nacelle of a wind turbine. [Diagram 3] FIG. 2 is a schematic perspective view of an example winding assembly according to the present disclosure attached to a stator tooth; [Figure 4] FIG. 4 is a schematic cross-sectional view taken along the line A-A' in FIG. [Diagram 5] 4 is a schematic cross-sectional view of another example of a winding assembly. [Figure 6] 4 is a flow chart of an example of a method for attaching a wind assembly to a stator tooth according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Various embodiments of the disclosed technology are described in detail below, one or more examples of which are illustrated in the drawings. Each example is for illustrative purposes only and is not intended to limit the present technology. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the present technology without departing from the scope and spirit of the claims. For example, features illustrated or described as part of one embodiment can be used with another embodiment to form yet another embodiment. Thus, the present disclosure encompasses modifications and variations that come within the scope of the appended claims and their equivalents.

[0022] FIG. 1 is a perspective view of an example of a wind turbine 10. In this example, the wind turbine 10 is a horizontal axis wind turbine. Alternatively, the wind turbine 10 may be a vertical axis wind turbine. In this example, the wind turbine 10 includes a tower 15 extending from a support system 14 on a ground surface 12, a nacelle 16 attached to the tower 15, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and one or more rotor blades 22 coupled to and extending outwardly from the hub 20. In this example, the rotor 18 has three rotor blades 22. In other embodiments, the rotor 18 includes less than three or more than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in FIG. 1) between the support system 14 and the nacelle 16. In other embodiments, the tower 15 may be any suitable type of tower having any suitable height. In other embodiments, the tower may be a hybrid tower including a concrete section and a tubular steel section. The tower may also be a partial or full lattice tower.

[0023] The rotor blades 22 are spaced about the hub 20 to rotate the rotor 18 and transfer kinetic energy from the wind into usable mechanical energy, and ultimately electrical energy. The rotor blades 22 are coupled to the hub 20 by joining blade base portions 24 to the hub 20 at a number of load transfer regions 26. The load transfer regions 26 may include hub load transfer regions and blade load transfer regions (neither of which are shown in FIG. 1 ). Loads generated by the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0024] In some examples, the rotor blades 22 may have a length ranging from about 15 m to about 90 m or more. The rotor blades 22 may have any suitable length that enables the wind turbine 10 to perform the functions described herein. For example, non-limiting examples of blade lengths include lengths of 20 m or less, 37 m, 48.7 m, 50.2 m, 52.2 m, or more than 91 m. When wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 rotates about a rotor axis 30. As the rotor blades 22 rotate and experience centrifugal forces, the rotor blades 22 are also subjected to various forces and moments. Thus, the rotor blades 22 may deflect and / or rotate from a neutral or undeflected position to a deflected position.

[0025] Additionally, the pitch angle of the rotor blades 22 (i.e., the angle at which the rotor blades 22 are oriented relative to the wind direction) may be varied by a pitch system 32 for controlling the load and power generated by the wind turbine 10 by adjusting the angular position of one or more rotor blades 22 relative to the wind vector. A pitch axis 34 of the rotor blades 22 is shown. During operation of the wind turbine 10, the pitch system 32 may vary the pitch angle of the rotor blades 22, particularly to reduce the angle of attack of (portions of) the rotor blades, to facilitate reducing the rotational speed and / or facilitate stalling of the rotor 18.

[0026] In this example, the blade pitch of each rotor blade 22 is individually controlled by the wind turbine controller 36 or pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0027] Also in this example, as wind direction 28 changes, the yaw direction of nacelle 16 may be rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0028] In this example, the wind turbine controller 36 is shown as centralized in the nacelle 16, however, the wind turbine controller 36 may be a distributed system throughout the wind turbine 10, on the support system 14, in the wind farm, and / or at a remote control center. The wind turbine controller 36 includes a processor 40 configured to perform the methods and / or steps described herein. Additionally, many of the other components described herein include a processor.

[0029] As used herein, the term "processor" is not limited to integrated circuits referred to in the art as computers, but broadly refers to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits and other programmable circuitry, and these terms are used interchangeably herein. The processor and / or control system may also include memory, input channels and / or output channels.

[0030] 2 is an enlarged cross-sectional view of a portion of the wind turbine 10. In this example, the wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to the nacelle 16. More specifically, a hub 20 of the rotor 18 is rotatably coupled to a motor-generator 42 located within the nacelle 16 by a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In this example, the main shaft 44 is disposed at least partially coaxially with respect to a longitudinal axis (not shown) of the nacelle 16. Rotation of the main shaft 44 drives the gearbox 46, which in turn drives the high-speed shaft 48 by converting the relatively slow rotational motion of the rotor 18 and main shaft 44 into a relatively fast rotational motion of the high-speed shaft 48. The latter is connected by the coupling 50 to a generator 42 for producing electrical energy. Additionally, a transformer 90 and / or appropriate electronics, switches, and / or inverters may be disposed within the nacelle 16 to convert the electrical energy produced by the generator 42 having a voltage between 400V-1000V into medium voltage (10-35KV) electrical energy. The electrical energy is conducted from the nacelle 16 to the tower 15 via a power cable.

[0031] The gearbox 46, generator 42 and transformer 90 may be supported by a main support structural frame of the nacelle 16, conveniently embodied as a main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 by one or more torque arms 103. In this example, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Additionally, the generator 42 may be mounted to the main frame 52 by a decoupling support means 54, particularly to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thereby becoming a source of noise generation.

[0032] Optionally, the main frame 52 is configured to carry the weight of the rotor 18 and nacelle 16 components as well as all loads resulting from wind and rotational loads, and further introduces these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and associated fastening, supporting, and / or fastening devices, including, but not limited to, supports 52, forward support bearing 60, and aft support bearing 62, may be referred to as a drive train 64.

[0033] In some examples, the wind turbine may be a direct drive wind turbine without a gearbox 46. The generators 42 operate at the same rotational speed as the rotor 18 in a direct drive wind turbine. Therefore, they generally have a much larger diameter than the generators used in wind turbines with gearboxes 46 to provide the same amount of power.

[0034] The nacelle 16 may include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 , and thus the rotor 18 , about the yaw axis 38 to control the overall position of the rotor blades 22 relative to the wind direction 28 .

[0035] To properly position the nacelle 16 with respect to the wind direction 28, the nacelle 16 may include one or more meteorological measurement systems 58, including a wind vane and anemometer. The meteorological measurement systems 58 may provide information, including the wind direction 28 and / or wind speed, to the wind turbine controller 36. In this example, the pitch system 32 is at least partially disposed within the hub 20 as a pitch assembly 66. The pitch assembly 66 includes one or more pitch drive systems 68 and one or more sensors 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in FIG. 1 ) for modulating the pitch angle of the rotor blade 22 along the pitch axis 34. Only one of the three pitch drive systems 68 is shown in FIG. 2 .

[0036] In this example, pitch assembly 66 includes one or more pitch bearings 72 coupled to hub 20 and coupled to each rotor blade 22 (shown in FIG. 1 ) for rotating each rotor blade 22 about pitch axis 34. Pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. Pitch drive motor 74 is coupled to pitch drive gearbox 76 to provide a mechanical force to pitch drive gearbox 76. Pitch drive gearbox 76 is coupled to pitch drive pinion 78, which in turn rotates pitch drive pinion 78. Pitch bearings 72 are coupled to pitch drive pinion 78, such that rotation of pitch drive pinion 78 causes rotation of pitch bearings 72.

[0037] The pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of the rotor blades 22 upon receiving one or more signals from the wind turbine controller 36. In this example, the pitch drive motor 74 is any suitable motor driven by an electrical power and / or hydraulic system that enables the pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components, such as, but not limited to, hydraulic cylinders, springs, and / or servo mechanisms. In one embodiment, the pitch drive motor 74 is driven by the rotational inertia of the hub 20 and / or energy extracted from a stored energy source (not shown) that provides energy to components of the wind turbine 10.

[0038] The pitch assembly 66 may include one or more pitch control systems 80 for controlling the pitch drive systems 68 according to control signals from the wind turbine controller 36 in the event of certain priority conditions and / or overspeed of the rotor 18. In this example, the pitch assembly 66 includes one or more pitch control systems 80 communicatively coupled to each pitch drive system 68 for controlling the pitch drive systems 68 independently of the wind turbine controller 36. In this example, the pitch control systems 80 are coupled to the pitch drive systems 68 and to sensors 70. During normal operation of the wind turbine 10, the wind turbine controller 36 controls the pitch drive systems 68 to adjust the pitch angle of the rotor blades 22.

[0039] In one embodiment, a power generator 84, including, for example, a battery and an electrical capacitor, is disposed at or within the hub 20 and coupled to the sensors 70, the pitch control system 80, and the pitch drive system 68 to provide a source of power to these components. In this example, the power generator 84 provides a continuous source of power to the pitch assembly 66 during operation of the wind turbine 10. In another embodiment, the power generator 84 provides power to the pitch assembly 66 only upon a loss of power to the wind turbine 10. A loss of power event may include a loss or dip in the power grid, a malfunction of the electrical system of the wind turbine 10, and / or a failure of the wind turbine controller 36. Upon loss of power, the power generator 84 operates to provide power to the pitch assembly 66 such that the pitch assembly 66 can operate during the loss of power event.

[0040] In this example, pitch drive system 68, sensor 70, pitch control system 80, cables, and power generator 84 are each disposed within a cavity 86 defined by an inner surface 88 of hub 20. In another embodiment, these components may be disposed relative to and directly or indirectly coupled to an outer roof surface of hub 20.

[0041] Figure 3 shows a schematic of a winding assembly 100 according to one example of the present disclosure. More precisely, the winding assembly 100 in Figure 3 is illustrated in an attached configuration, where the winding assembly 100 is attached to a stator tooth 200 of an electric machine.

[0042] 3, the stator teeth 200 extend in a radial direction RD from a base 210 to a distal end 220. The stator teeth 200 also extend along a longitudinal direction LD that is substantially perpendicular to the radial direction RD. The longitudinal direction LD may extend axially or parallel to the axis of rotation of the electric machine.

[0043] The stator teeth 200 may be attached to the remainder of the stator structure, such as the stator yoke, through the base 210 of each corresponding tooth. The distal ends 220 of the teeth are disposed on the sides of the air gap between the stator and rotor.

[0044] The winding assembly 100 includes a plurality of winding bodies 120, 130 including insulating strands 121, 131. The plurality of winding bodies 120, 130 includes a first winding body 120 configured to be attached around a section near a base 210 of a stator tooth 200, and a second winding body 130 configured to be attached closer to a tip 220 of the stator tooth 200 than the first winding body 120. The first and second winding bodies 120, 130 are electrically connected. In the example of FIG. 3, the first and second winding bodies 120, 130 are electrically connected via a connector 160.

[0045] The winding assembly 100 provided herein allows for the use of windings with lower height-to-width ratios than would be possible using a single winding. For example, the height-to-width ratio may be less than 5, and more specifically less than 3, for one or more windings, resulting in reduced insulation failure. Thus, the winding assembly allows for reduced tension on the insulating material 122, 132 to be secured around the insulators 120, 130. This simultaneously increases the resin content of the insulation near the corners of the windings 120, 130.

[0046] 3, the winding assembly 100 may further include a cooling channel 140 between the first and second windings 120, 130. The cooling channel 140 may carry a liquid or gas coolant.

[0047] In some examples, such as the example of FIG. 4, the first winding body 120 may have a greater height than the second winding body 130. Thus, most of the side surface of the stator tooth may be surrounded by the first winding body 120, with the second winding body 130 occupying only a relatively small portion of the side surface. In some examples, the first winding body 120 may have a height that is 150% or more of the height of the second winding body, and more specifically, the height of the first winding body may be 150-200% of the height of the second winding body.

[0048] Although not shown in FIG. 3, the winding assembly 100 may include a third winding body electrically connected to the first and second winding bodies 120, 130. The third winding body may be configured to be mounted closer to the tip 220 of the stator tooth 200 than the second winding body 130. In examples with more than one winding body, additional cooling channels or circuits may be provided between each additional winding body. In embodiments, the cooling channels between the winding bodies may have different cooling characteristics depending on the winding body in which they are provided. For example, the cooling passage 140 between the first and second winding bodies 120, 130 may be configured to carry a liquid coolant, and the cooling circuit between the second and third winding bodies may be configured to carry a cooling gas (e.g., air). In another example, the cooling channels may be configured to carry the same fluid and may have the same or different cooling flow rates.

[0049] Fig. 4 shows a schematic cross-sectional view taken along line AA' in Fig. 3. Note that cross sections of strands 121 and 131 are not shown in cross section for the sake of simplicity.

[0050] As is evident from Figure 4, the pole pieces may be provided as separate units that can be attached to a stator structure. A pole piece for a stator of an electric machine may comprise a stator tooth and a winding assembly including a plurality of windings according to any of the examples disclosed herein.

[0051] In a particular aspect, the present disclosure provides a pole piece comprising stator teeth 200 extending radially from a base 210 to a distal end 220. The base 210 of the pole piece is shaped to fit into a mating structure of a stator.

[0052] The pole piece further comprises a first winding body 120 including a plurality of first insulating strands 121 wound around a section of the stator tooth 200 closer to the base 210 of the stator tooth 200 and a second winding body 130 including a plurality of second insulating strands 131 wound around the stator tooth closer to the tip of the stator tooth than the first winding body. The second winding body 130 is separate from the first winding body 120, and the first winding body 120 is electrically connected to the second winding body 130.

[0053] As shown in Figure 4, each winding 120, 130 may have multiple insulating strands 121, 131. Also, each winding 120, 130 may have insulating elements 122, 132 that are independent of each other. The load acting on the insulating elements 122, 132 (e.g., insulating tape) may increase with the height of the winding. Thus, having a winding assembly 100 that includes multiple windings 120, 130 that are configured to be individually insulated reduces the possibility of insulation degradation and related problems.

[0054] FIG. 4 also shows that the first and second windings 120, 130 may be separated by a cooling channel 140. In this example, a cooling fluid may flow through the cooling channel 140. The coolant may be a liquid or a gas, such as cooling air provided to the air gap, or may branch off from cooling air provided to the air gap. The cooling channel may include baffles or structures that promote turbulence and have a serpentine configuration, etc. Details of the cooling system 140 are not shown in FIG. 4 for simplicity.

[0055] 4 shows an example of a winding assembly 100 with two electrically connected winding bodies 120, 130, the winding assembly 100 may include more than two winding bodies. For example, the winding assembly 100 may include three or four electrically connected winding bodies. Furthermore, some (or all) pairs of adjacent winding bodies may be separated by additional cooling circuits or by additional independent cooling systems.

[0056] 4, the pole piece or winding assembly 100 may further include one or more winding stops 150 (or other winding retaining elements) coupled to the sidewalls of the stator teeth 200 to hold the winding assembly 100 in place. The winding stops 150 may be located at or near the distal end 220 of the stator teeth 200, or at an intermediate location, i.e., between the first and second winding bodies 120, 130. The winding stops 150 may also include several components, such as retaining elements, elastic members, wedge-shaped elements, etc. Thus, in some examples, the winding stops 150 may have some components at (or near) the distal end 220 of the stator teeth 200 and other components between the winding bodies 120, 130. For example, a winding stopper 150 retention element may be located at (or near) the distal end 220 of the stator tooth 200, or a resilient element such as a ripple spring or wedge may be located between the first and second winding bodies 120, 130, or between the first and second winding bodies 120, 130 and the cooling system 140. Other configurations of winding retention elements may be included in the winding assembly 100.

[0057] The base 210 of the pole piece in this example is shaped to fit onto a stator, specifically a stator rim or stator yoke. More specifically, the base 210 in this example includes recesses 282, 284 in a sidewall 280 on each side of the base. Corresponding male structures may be provided on the mating structure of the stator, for example the stator yoke. Male structures on the stator yoke may reach into the recesses 282, 284 to hold the base 210. In this example, the pole piece may be slid axially onto the stator yoke in this manner.

[0058] In some other examples, the recesses 282, 284 may be used as cooling channels, ie, air may be flowed through these channels to control or reduce the temperature of the stator teeth.

[0059] The pole piece base 210 may further include a recess 296 in a bottom surface 290 of the base. The base may include a central hole in the bottom surface 290, which divides the base 210 into two portions, 292 and 294, and which may receive a nut 299. A bolt or similar fastener may be used to engage the nut 299 to securely attach the base 210 to the stator yoke.

[0060] Rather than a pole piece having a single stator tooth that can be attached as a unit to a stator structure, in yet another example, a stator segment including multiple stator teeth may be used. A stator segment may be considered herein as an assembly including one or more stator teeth (a stator segment also encompasses a pole piece). Multiple teeth of a stator segment, or each tooth of a stator segment, may include a winding assembly according to examples disclosed herein.

[0061] The stator segments may be attached to the rest of the stator structure as a unit. The base of the stator structure may be shaped (as illustrated for the pole pieces) to fit into the mating structure of the stator. Features (projections or recesses) may be incorporated into the base of the stator segments suitable for mating with corresponding features of the rest of the stator structure, particularly the stator rim or stator yoke.

[0062] In another example, the first and second winding assemblies (disposed around a stator tooth and possibly belonging to a stator shoe or belonging to a stator segment) need not be electrically connected to each other. In some examples, a first winding assembly disposed around a first tooth may connect to a second winding assembly on a second tooth. The first and second winding assemblies disposed on individual teeth may be connected in parallel rather than in series in these examples. In the case of a stator segment, the first and second teeth may form part of the same stator segment.

[0063] Figure 5 shows a schematic cross-section of another example of a winding assembly and pole piece for a stator of an electric machine. In the example of Figure 5, the winding assembly 100 includes a plurality of winding bodies 120, 130 made of insulated strands 121, 131. The plurality of winding bodies 120, 130 also includes a first winding body 120 configured to be mounted around a base 210 of a stator tooth 200 and a second winding body configured to be mounted closer to a tip 220 of the stator tooth 200 than the first winding body 120. Furthermore, the strands 121, 131 of the first and second winding bodies are different.

[0064] In the example of Figure 5, the first winding body 120 comprises strands 121 having a cross-sectional area larger than the cross-sectional area of ​​strands 131 of the second winding body 130. More precisely, the cross-sectional area of ​​strands 121 of the first winding body 120 is more than 50% larger than the cross-sectional area of ​​the second strands. The cross-sectional area ratio between the strands from the first and second winding bodies shown in Figure 5 is chosen for illustrative purposes only. Also, although strands 121 are shown as wires having a circular cross-sectional area, as noted elsewhere, the strands may have a substantially rectangular or other cross-section.

[0065] A winding assembly 100 including multiple windings 120, 130 may be configured such that eddy current losses and / or other losses are at least partially reduced.

[0066] Eddy currents are understood to be loops of electric current induced in a conductor by a changing magnetic field or by the relative motion of the conductor in a magnetic field. Eddy currents flow in closed loops in the conductor in a plane perpendicular to the magnetic field. The magnitude of the current in a particular loop is proportional to the strength of the magnetic field, the area of ​​the loop and the rate of change of the magnetic flux, and inversely proportional to the resistivity of the material. The rate of change of the magnetic flux is not constant along the height of the tooth, but is higher near the distal end of the tooth. To reduce eddy currents near the distal end of the tooth, the second winding assembly (or the third or fourth winding assembly, if present) may have strands of reduced cross section.

[0067] Electric current flowing through a conductor also dissipates energy as heat within the material. As the cross-sectional area decreases, the current density increases, resulting in more heat generation. However, near the distal end of the tooth, it has now been found that the main contributor to losses is the generation of eddy currents. Conversely, near the base of the tooth, the main contributor to losses is current density, so by increasing the cross-sectional area there, the overall losses can be controlled. Compared to prior art systems, the overall losses are reduced and the overall heat distribution is more uniform.

[0068] In some instances, strands from different winding assemblies may be made from different materials and have different resistivities.

[0069] FIG. 6 is a flow chart of an exemplary method 600 for attaching a winding assembly to a stator tooth 200 of an electric machine.

[0070] 6, the method 600 includes providing a first winding body 120 around a section of the tooth closer to a base 210 of the stator tooth 200 (block 602). The method 600 further includes providing a second winding body 130 around a section of the tooth closer to a distal end 220 of the stator tooth 200 than the first winding body 120 (block 604). The first and second winding bodies 120, 130 may include insulating strands 121, 131. The method 600 further includes electrically connecting the first winding body 120 to the second winding body 130 at block 606.

[0071] In some instances, the individual windings may be wrapped with an insulating material, such as insulating tape.

[0072] The method 600 may include additional embodiments, such as any combination of one or more of the embodiments described below and / or in connection with the winding assembly 100 described elsewhere herein. In a first embodiment, the cross-sectional area of ​​the strands of the first winding body 121 may be greater than the cross-sectional area of ​​the strands of the second winding body 131.

[0073] In some examples of the method 600, electrically connecting the windings 120, 130 may include welding or brazing the connector 160 to the first and second windings 120, 130.

[0074] In another embodiment, alone or in combination with one or more of the above-mentioned embodiments, the method 600 may further include providing a cooling system 140 between the first and second windings 120, 130.

[0075] In another embodiment, alone or in combination with one or more of the above-mentioned embodiments, the stator teeth 200 may be provided with the first winding body 120, the second winding body 130 and the cooling system 140 in one step.

[0076] Although Figure 6 illustrates example blocks of method 600, in some implementations, method 600 may include additional, fewer, different, or differently arranged blocks than those illustrated in Figure 6. Additionally, or alternatively, two or more of the blocks of method 600 may be performed in parallel.

[0077] All the features of the winding assembly can be included in the method for attaching the winding assembly to the stator teeth and vice versa.

[0078] The present specification discloses the present invention including preferred embodiments, and has been described by way of examples to enable those skilled in the art to practice the invention, including making and using the device or system and practicing the method. The patentable scope of the present invention is defined by the claims, and includes other examples that are obvious to those skilled in the art. Such other examples fall within the scope of the claims if they have elements that are not literally different from the claims, or have equivalent elements that are only insubstantial different from the claims. Those skilled in the art can appropriately combine various aspects of the various embodiments described in this application and other known equivalents of each aspect to construct additional embodiments and techniques in accordance with the principles of the present application. When reference numerals relating to the drawings are included in parentheses in the claims, such reference numerals are merely intended to facilitate understanding of the claims, and should not be construed as limiting the scope of the claims. [Explanation of symbols]

[0079] 10. Wind Turbines 15. Tower 16 Nacelle 18 Rotor 20 Rotor hub 22 rotor blades 100 Winding Assembly 120 Winding body 121 Insulating Strand 122 Insulating materials 130 Winding body 131 Insulating Strand 132 Insulating Materials 140 Cooling Channel 200 stator teeth 210 Base of stator tooth 220 Distal end of stator tooth

Claims

1. A winding assembly (100) for a stator tooth (200) of an electric machine, the stator tooth (200) extending radially from a base (210) to a distal end (220), the winding assembly (100) comprising: a first winding body (120) configured to be mounted around a section of the stator tooth (200) near a base of the stator tooth (200), the first winding body (120) comprising a plurality of first insulating strands (121) wound around the stator tooth (200); a second winding body (130) configured to be attached closer to a distal end of the stator tooth (200) than the first winding body (120), the second winding body (130) comprising a plurality of second insulating strands (131) wound around the stator tooth (200); wherein the second winding body (130) is spaced apart from the first winding body (120).

2. The winding assembly of claim 1 , wherein the first winding body (120) is electrically connected to the second winding body (130).

3. 3. A winding assembly according to claim 1 or claim 2, wherein the cross-sectional area of ​​the first strand (121) is greater than the cross-sectional area of ​​the second strand (131).

4. The winding assembly of claim 3 , wherein the cross-sectional area of ​​the first strands (121) is at least 50% greater than the cross-sectional area of ​​the second strands (131).

5. The winding assembly of claim 1 , further comprising a cooling channel (140) between the first winding body and the second winding body.

6. The winding assembly of claim 5 , wherein the cooling channel (140) is configured to carry a liquid coolant.

7. The winding assembly of any one of claims 1 to 6, wherein the first winding body (120) has a height equal to or greater than the second winding body (130).

8. 8. The winding assembly according to claim 7, wherein the first winding body (120) has a height that is 150% or more of the height of the second winding body (130), in particular the height of the first winding body (120) is 150% to 200% of the height of the second winding body (130).

9. 9. The winding assembly of claim 1, further comprising a third winding body electrically connected to the second winding body, the third winding body comprising a plurality of third insulated strands wound around the teeth, the third winding body configured to be mounted closer to a distal end of the stator tooth than the second winding body, optionally with a cross-sectional area of ​​the strands of the third winding body smaller than a cross-sectional area of ​​the strands of the second winding body, and further comprising an additional cooling circuit between the second winding body and the third winding body.

10. A stator segment comprising one or more stator teeth extending radially from a base to a distal end, and further comprising a winding assembly according to any one of claims 1 to 9 around each stator tooth.

11. The stator segment of claim 10 , wherein a base of the stator segment is shaped to mate with a mating structure of a stator.

12. 12. A stator segment according to claim 10 or claim 11, wherein the stator segment is a pole piece including a single stator tooth.

13. a rotor rotatable about a mechanical axis; A stator concentric with the rotor, the stator comprising one or more stator segments according to any one of claims 10 to 12. An electric machine comprising:

14. A wind turbine comprising an electric machine according to claim 13.

15. 10. A method of attaching a winding assembly as claimed in any one of claims 1 to 9 to a stator tooth, the stator tooth extending radially from a base to a distal end, the method comprising: providing a first winding by winding a plurality of first insulating strands around a section of a stator tooth near a base of the stator tooth; providing a second winding by winding a plurality of second insulating strands around a section of the stator tooth proximate a distal end of the stator tooth; electrically connecting the first winding body to the second winding body; A method comprising:

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