Field of the disclosure

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.

Background

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. For example, in a radial flux 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 exceeded. 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 other electrical machines, too.

An effective method for cooling a winding of an electrical machine is liquid cooling where cooling liquid, e.g. water, 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.

Liquid-cooled windings of the kind mentioned above are however not free from challenges. One of the challenges is related to cooling fluid connections which transfer cooling liquid between a winding conductor and an external cooling liquid circulation system. Especially, a part of a winding conductor that is between a cooling fluid connection and an end of the winding conductor connected to an external electrical system is prone to overheating because this part of the winding conductor conducts electric current but is not cooled by the cooling liquid.

Summary

The following presents a simplified summary in order 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.

In accordance with the invention, there is provided a new winding system for an electrical machine. The 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.

A winding system according to the invention comprises:

- at least one coil made of a winding conductor comprising electrically conductive material and a tubular cooling channel configured to conduct cooling fluid in the longitudinal direction of the winding conductor, and - at each end of the winding conductor, a coupling element made of electrically conductive material.

A first end of the coupling element is hollow and attached to an end of the winding conductor so that the first end of the coupling element surrounds the end of the winding conductor, and a second end of the coupling element comprises an interface to form a galvanic contact with an electrical conductor external to the winding conductor. The coupling element comprises a middle portion that is between the first and second ends of the coupling element on a flow path of electric current conducted by the coupling element. The middle portion comprises a channel being in a fluid conductive relation with the tubular cooling channel of the winding conductor.

The above-mentioned coupling element accomplishes both an electrical connection and a cooling fluid connection. The whole winding conductor can be cooled by the cooling fluid because the cooling fluid is conducted to the tubular cooling channel of the winding conductor via the middle portion of the coupling element which is between the electrical contacts accomplished at the first and second ends of the coupling element.

In accordance with the invention, there is also provided a new electrical machine that 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. An electrical machine according to the invention comprises a winding system according to the invention.

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

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.

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

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.

Brief description of the figures

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: figures 1 a, 1 b, 1 c, and 1d illustrate a winding system according to an exemplifying and non-limiting embodiment, figure 2 illustrates a part of a winding system according to an exemplifying and nonlimiting embodiment, figure 3 illustrates an electrical machine according to an exemplifying and nonlimiting embodiment, and figure 4 illustrates an electrical machine according to an exemplifying and nonlimiting embodiment.

Description of the exemplifying embodiments

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.

Figures 1 a, 1 b, 1 c, and 1d illustrate a winding system according to an exemplifying and non-limiting embodiment. The winding system comprises coils 101 , 102, and 103. Each of the coils 101-103 is made of a winding conductor that comprises electrically conductive material and a tubular cooling channel configured to conduct cooling fluid, for example water, in the longitudinal direction of the winding conductor. Furthermore, the winding conductor may comprise a layer of electrical insulator on the outer surface of the winding conductor. It is however also possible that a winding system according to an exemplifying and non-limiting embodiment comprises a coil-frame such that a winding conductor can be non-insulated. The electrically conductive material of the winding conductor can be for example copper. In figures 1 a-1 d, the winding conductor of the coil 101 is denoted with a reference 104.

The winding system comprises coupling elements at the ends of the winding conductors of the coils 101 -103. In figures 1 a and 1 b, the coupling elements at first ends of the winding conductors are denoted with references 105, 106, and 107. The coupling elements are made of electrically conductive material such as for example copper. In the exemplifying case illustrated in figures 1 a-1 c, the coupling elements 105-107 are configured to galvanically connect the coils 101-103 to electrical conductors of cables 130, 131 , and 132 that are external to the winding system. In figures 1 a-1 c, the second ends of the winding conductors of the coils 101 -103 are not shown. The coupling arrangement at the second ends of the winding conductors can be for example such as illustrated in figure 1d. The exemplifying coupling arrangement illustrated in figure 1d implements a star-point between the coils 101 - 103. It is however also possible that a different arrangement is used at the second ends of the winding conductors.

A more detailed description of the coupling element 105 is presented below. The coupling elements 106 and 107 can be like the coupling element 105. Figure 1 c shows a section view of the coupling element 105. The coupling element 105 comprises a first end 108 that is hollow and attached to the first end of the winding conductor 104 so that the hollow first end 108 of the coupling element 105 surrounds the end of the winding conductor 104. The attachment between the coupling element 105 and the winding conductor 104 may comprise for example a soldered joint. In this exemplifying case, the wall of the hollow first end 108 of the coupling element 105 comprises apertures 128 to allow molten soldering material to enter between the coupling element 105 and the winding conductor 104. It is however also possible that there is a compression joint or some other suitable joint between the hollow first end 108 of the coupling element 105 and the winding conductor 104. A second end 109 of the coupling element 105 comprises an interface 110 to form a galvanic contact with the electrical conductor 133 of the cable 130. In this exemplifying case, the second end 109 of the coupling element 105 is hollow to receive an end of an electrical conductor 133 of the cable 130. The attachment between the coupling element 105 and the electrical conductor 133 of the cable 130 may comprise for example a soldered joint. In this exemplifying case, the wall of the hollow second end 109 comprises apertures 129 to allow molten soldering material to enter between the coupling element 105 and the electrical conductor 133. It is however also possible that there is a compression joint or some other suitable joint between the second end 109 of the coupling element 105 and the electrical conductor 133.

Figure 1d shows a section view of a coupling element 114. In the exemplifying case shown in figure 1d, the coupling element 114 is at the second end of the winding conductor 104. The coupling element 114 comprises a first end 115 that is hollow and attached to the second end of the winding conductor 104 so that the hollow first end 115 of the coupling element 114 surrounds the second end of the winding conductor 104. The attachment between the coupling element 114 and the winding conductor 104 may comprise for example a soldered joint. A second end 116 of the coupling element 114 comprises an interface to 117 to form a galvanic contact with an electrically conductive element 134. In this exemplifying case, the interface 117 of the coupling element 114 comprises a threaded hole. Thus, as shown in figure 1d, the electrically conductive element 134 can be attached to the corresponding coupling elements with bolts.

As shown in figure 1 c, the coupling element 105 comprises a middle portion 111 that is between the first and second ends 108 and 109 of the coupling element 105 on a flow path of electric current conducted by the coupling element 105. The middle portion 111 comprises a channel 112 that is in a fluid conductive relation with the tubular cooling channel 113 of the winding conductor 104. The coupling element 105 implements both an electrical connection and a cooling fluid connection. As shown in figure 1 d, the coupling element 114 comprises a middle portion 123 that is between the first and second ends 115 and 116 of the coupling element 114 on a flow path of electric current conducted by the coupling element 114. The middle portion 123 comprises a channel that is in a fluid conductive relation with the tubular cooling channel 113 of the winding conductor 104. As can be understood based on figures 1 c and 1 d, the whole winding conductor 104 can be cooled by the cooling fluid.

The exemplifying winding system illustrated in figures 1 a-1d comprises a flow-guide element 118 that surrounds the middle portions of the coupling elements 105-107. The flow-guide element 118 comprises a connection section 120 for connecting to a cooling fluid circulation system external to the winding system. The cooling fluid circulation system is not shown in figures 1a-1d. The flow-guide element 118 is configured to guide the cooling fluid to flow via the channels of the middle portions of the coupling elements 105-107. In this exemplifying case, the flow-guide element 118 is a manifold that is made of electrically non-conductive material such as for example plastic. It is however also possible that the coupling elements 105-107 are provided with separate flow-guide elements each comprising a connection section for connecting to a cooling fluid circulation system. In this exemplifying case, the flow-guide elements which are separate from each other do not necessarily need to be made of electrically non-conductive material.

The exemplifying winding system illustrated in figures 1 a-1d comprises a flow-guide element 119 that is shown in figure 1d. The flow-guide element 119 is arranged to surround the middle portions of the coupling elements one of which is the abovedescribed coupling element 114. The flow-guide element 119 comprises a connection section 121 for connecting to an external cooling fluid circulation system. The cooling fluid circulation system can be for example such that the cooling fluid enters the winding system via the connection section 120 shown in figures 1a and 1 b and exits the winding system via the connection section 121 shown in figure 1 d, or vice versa. The flow-guide element 119 does not necessarily need to be made of electrically non-conductive material because the respective coupling elements are connected to a same electrical potential with the electrically conductive element 134.

Figure 1 b shows a section view of the flow-guide element 118 so that a geometric section plane is parallel with the xy-plane of a coordinate system 199. The flowguide element 118 comprises a first flow channel 126 that is between the connection section 120 and the middle-portion 111 of the coupling element 105 and a second flow channel 127 that is between the connection section 120 and the middle-portion of the coupling element 107. As shown in figure 1 b, the flow channels 126 and 127 are shaped to meander to increase the lengths of these flow channels. The increased lengths of the flow channels are advantageous because the coupling elements 105-107 have different electrical potentials, and electric field strengths in the flow channels can be reduced by increasing the lengths of the flow channels.

In the exemplifying winding system illustrated in figures 1 a-1d, a first end of the middle portion of each coupling element comprises a flange, a second end of the middle portion comprises a threaded outer surface, and the coupling element comprises a nut configured to attach the coupling element to the flow-guide element so that the flow-guide element is being pressed between the flange and the nut. In figure 1 c, the flange and the nut of the coupling element 105 are denoted with references 122 and 124. In the exemplifying winding system illustrated in figures l aid, the flow-guide elements 118 and 119 comprise annular seals, for example O- rings, between body parts of the flow-guide elements and outer surfaces of the middle portions of the coupling elements. In figure 1 c, two of the annular seals are denoted with a reference 125.

In the exemplifying winding system illustrated in figures 1 a-1d, the winding conductor of each coil comprises a cooling tube that can be made of material different from the electrical conductor of the winding conductor. The cooling tube can be made of for example stainless steel that is chemically stable against cooling fluid. In figure 1 c, the cooling tube is denoted with a reference 130. The electrical conductor of each winding conductor can be for example a single bar of electrically conductive material so that the bar is hollow and surrounds the cooling tube. It is however also possible that the winding conductor does not have a separate cooling tube, but the hollow electrical conductor constitutes the cooling channel. It also possible that an electrical conductor of each winding conductor comprises two or more electrically parallel connected bars of electrically conductive material and a cooling tube is placed between these bars. Furthermore, it is also possible that an electrical conductor of each winding conductor comprises a bundle of electrically parallel connected filaments of electrically conductive material and the bundle is arranged to surround a cooling tube. It is to be noted that embodiments of the invention are not limited to any specific constructions of winding conductors.

Figure 2 illustrates a part of a winding system according to an exemplifying and nonlimiting embodiment. The winding system comprises a coil 201 that is made of a winding conductor 204. The winding conductor 204 comprises electrically conductive material and a tubular cooling channel 213 configured to conduct cooling fluid in the longitudinal direction of the winding conductor 204. The winding system comprises coupling elements at the ends of the winding conductor 204. In figure 2, the coupling element at a first end of the winding conductor 204 is shown as a section view and denoted with a reference 205. The coupling element at the second end of the winding conductor 204 is not shown. A first end 208 of the coupling element 205 is hollow, and it is attached to the first end of the winding conductor 204 so that the hollow first end 208 of the coupling element 205 surrounds the first end of the winding conductor 204. A second end 209 of the coupling element comprises an interface 210 to form a galvanic contact with an electrical conductor 233 of a cable 230. The coupling element 205 comprises a middle portion 211 that is between the first and second ends 208 and 209 of the coupling element 205 on a flow path of electric current conducted by the coupling element 205. The middle portion 211 comprises a channel 212 that is in a fluid conductive relation with the tubular cooling channel 213 of the winding conductor 204. In the exemplifying winding system illustrated in figure 2, the coupling element 205 comprises a connection section 220 for connecting to an external cooling fluid circulation system. The cooling fluid circulation system is not shown in figure 2.

Figure 3 illustrates an electrical machine 340 according to an exemplifying and nonlimiting embodiment. In this exemplifying case, the electrical machine is a rotating electrical machine that comprises a stator 341 and a rotor. An end of a shaft 342 of the rotor is shown in figure 3. The electrical machine 340 can be for example an induction machine, a permanent magnet synchronous machine, an electrically excited synchronous machine, a synchronous reluctance machine, a switched reluctance machine, a flux-switched permanent magnet machine, a permanent magnet brushless direct current machine, or some other rotating electrical machine. The stator 341 of the electrical machine 340 comprises a three-phase winding system according to an embodiment of the invention. Coils of the three-phase winding system are galvanically connected to cables 330, 331 , and 332 with the aid of coupling elements of the three-phase winding system. The coupling elements can be for example such as the coupling elements 105-107 shown in figures 1 a and 1 b. The three-phase winding system comprises connection sections 320 and 321 for connecting to an external cooling fluid circulation system that may comprise for example a circulation pump, a cooling fluid tank, a heat exchanger, and a filter for purifying the cooling fluid. The cooling fluid circulation system is not shown in figure 3. In this exemplifying case, the three-phase winding system comprises a manifold 318 that can be for example such as the flow-guide element 118 shown in figures 1 a-1 c. The three-phase winding system comprises a manifold 319 that can be for example such as the flow-guide element 119 shown in figure 1d. In this exemplifying case, the three-phase winding system is a star-connected winding system whose star-point is implemented with an electrically conductive element 334 and with coupling elements configured to galvanically connect the coils of the three-phase winding system to the electrically conductive element 334. These coupling elements can be for example such as the coupling element 114 illustrated in figure 1d.

Figure 4 illustrates an electrical machine 440 according to an exemplifying and nonlimiting embodiment. In this exemplifying case, the electrical machine 440 is a single-phase choke that can be for example a direct current “DC” choke or an alternating current “AC” reactor. The electrical machine 440 comprises a ferromagnetic core 443 and a winding system according to an embodiment of the invention. The winding system comprises a coil 401 made of a winding conductor 404. The winding conductor 404 comprises electrically conductive material and a tubular cooling channel configured to conduct cooling fluid in the longitudinal direction of the winding conductor 404. The winding system comprises coupling elements 405 and 406 at the ends of the winding conductor 404. Each of the coupling elements 405 and 406 can be for example such as the coupling element 205 illustrated in figure 2. The coupling elements 405 and 406 are configured to implement a galvanic connection between an electrical conductor of a cable 430 and electrically conductive material of the winding conductor 404 and a galvanic connection between an electrical conductor of a cable 431 and the electrically conductive material of the winding conductor 404. The coupling elements 405 and 406 comprise connection sections 420 and 421 for connecting to an external cooling fluid circulation system that is not shown in figure 4.

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.