winding for an electric machine

Abstract

The present invention relates to a method (10) for manufacturing a winding (30) for an electric machine. The method comprises providing (11) an electrically conductive wire (21), extruding (12) a thermoplastic insulating layer (23) sheathing the wire (21), and extruding (13) a thermoplastic layer (24) sheathing the thermoplastic insulating layer (23), the thermoplastic layer comprising an electrically conductive additive.

Description

[0001] The present invention relates to a concept for insulating a winding for an electrical machine, in which conductor insulation is applied to the conductor by extrusion of a thermoplastic. Furthermore, a weakly conductive sheath is additionally applied to the insulation by extrusion of another thermoplastic with an electrically conductive additive. Furthermore, the invention relates to a stator, a rotor, and an electrical machine, for example, an electric motor, a transformer, or an electromagnet, which have such insulated and sheathed conductors.

[0002] Dynamoelectric machines, such as electric motors or generators, as well as transformers or electromagnets, typically have current-carrying windings. In addition to concentrated windings, electrical machines with distributed windings are also known in the state of the art. Distributed windings are typically manufactured using so-called hairpin technology, in which several conductor elements (hairpins) are inserted into the slots of a coil former and connected to form corresponding winding strands.

[0003] In concentrated or distributed windings, the individual conductors must be electrically insulated from their surroundings. The conductors are separated from each other by an insulating layer. This typically consists of the conductor insulation itself, with an additional filler material (impregnating resin) in the groove. For electrical insulation, the conductors can be insulated by wrapping them with mica tape or—if the potential difference to the surroundings is only slight—by impregnation. It is also known to coat impregnated winding wires using an extrusion process. Thermoplastics or high-temperature thermoplastics, which exhibit good bonding properties with impregnating agents, are used for the insulation.

[0004] Ideally, this insulation is completely homogeneous, so that the same electric field strength is present everywhere. However, defects, such as air bubbles or delaminated impregnating resin, cause the field strength to vary significantly locally. Ionization can occur at these locations, resulting in partial breakdown. This happens repeatedly, gradually destroying the insulation until failure occurs. These local discharges can also occur in the winding head, where conductors cross and there is usually no impregnating resin between the conductors.

[0005] Nominal voltages above 400 V can exacerbate this problem enormously; for example, 800 V systems are subject to significantly greater stress on the insulation system due to partial discharges, resulting in a correspondingly shorter service life. Alternatively, the insulation layer must be made excessively thick, which in turn impairs heat dissipation and reduces the available conductor cross-section.

[0006] Against this background, it is an object of the present invention to avoid or at least reduce such discharges and thus destruction of the conductor insulation.

[0007] This object is achieved by devices and / or methods according to the independent patent claims. Advantageous further developments arise from the dependent claims.

[0008] According to a first aspect, the present invention provides a conductor structure for a winding of an electrical machine. The conductor structure comprises an electrically conductive wire, a thermoplastic insulating layer surrounding the wire, and a thermoplastic layer surrounding the insulating layer, which layer comprises an electrically conductive additive.

[0009] According to a further aspect, the present invention provides a winding for an electrical machine. The winding comprises a coil former with a plurality of slots distributed over a circumference of the coil former. The winding further comprises at least one winding phase arranged in the slots and in a plurality of winding layers. The winding phase has an electrical conductor, a thermoplastic insulating layer encasing the conductor, and at least one thermoplastic layer encasing the insulating layer, which layer comprises an electrically conductive additive.

[0010] According to yet another aspect, the present invention provides an electric machine with the winding according to the invention. The electric machine can have a rated voltage greater than 600 volts, such as 800 volts.

[0011] The thermoplastic layer with an electrically conductive additive surrounding the insulation layer creates a weakly conductive, so-called corona layer. This allows an electrical potential to be controlled. A voltage can be specifically reduced to the surface of the conductor insulation, or it can be ensured that a potential gradient within the conductor insulation remains constant. This ensures that the potential on the surface of the conductors is identical, and no discharge can occur outside the insulation.

[0012] According to some embodiments, both the thermoplastic insulating layer and the thermoplastic layer encasing the insulating layer (corona layer) each comprise polyetheretherketone (PEEK). PEEK is a high-performance polymer with outstanding mechanical, thermal, and chemical properties. In electrical applications, such as windings of electric motors, generators, or transformer coils, PEEK can be used as an insulating material to protect the electrically conductive wires while ensuring good insulation between the turns. PEEK offers advantages such as thermal stability, chemical resistance, mechanical strength, electrical insulation, and low moisture absorption. In addition to PEEK, other thermoplastics, such as polyester or polyamide, could in principle also be used.

[0013] According to some embodiments, the electrically conductive additive comprises at least one of a carbon-based additive, metal particles, or an electrically conductive polymer. PEEK can be made weakly electrically conductive by adding conductive fillers. This process is also referred to as "compounding," in which electrically conductive particles are mixed into the PEEK material to achieve electrical conductivity while largely retaining the basic properties of PEEK. Conductive fillers that can be used in PEEK composites include, among others, carbon fibers or carbon nanotubes, metal particles (e.g., copper, aluminum, or silver), or graphene.The conductive PEEK composites can be used as corona layers where a certain electrical conductivity is required without compromising the excellent mechanical, thermal and chemical properties of PEEK.

[0014] The electrical conductivity of PEEK composites is generally weaker than that of pure metals or specially developed conductive polymers. The exact conductivity depends on the type and amount of conductive fillers used. According to some embodiments, the electrical conductivity of the thermoplastic layer (with conductive additive) surrounding the insulating layer is greater than that of the insulating layer and lower than that of the electrical conductor (electrically conductive wire).

[0015] According to some embodiments, the thermoplastic insulating layer and the thermoplastic layer (with conductive additive) encasing the insulating layer are each formed as extruded layers. Extrusion is a process in plastics processing in which thermoplastic polymers (plastics that melt when heated and harden again upon cooling) can be formed into a continuous shape by heating and melting. The extrusion process offers the possibility of producing a wide variety of shapes from plastics. Extrusion can be used to apply insulating and corona layers to conductors. This process is referred to as "extrusion coating" or "extrusion insulation."

[0016] According to some embodiments, the coil former is formed as a stator lamination stack. The stator lamination stack may comprise laminated laminations, which may be made of electrical silicon steel. These laminations may be stacked in a specific geometric arrangement to reduce eddy current losses and increase the efficiency of the motor or generator. The windings may be wound around teeth of the stator lamination stack. The windings consist of insulated copper or aluminum wires coated with a corona layer and serve to conduct current through the stator, thereby generating a changing electromagnetic field. According to other embodiments, the coil former may also be formed as a rotor lamination stack.

[0017] According to some embodiments, the winding strand is formed using a plurality of hairpins. Hairpins are special wire shapes that are becoming increasingly popular in the electromobility industry and other high-performance applications. This shape enables a compact and efficient arrangement of the windings in the stator slots. Hairpin technology refers to the use of specially shaped copper or aluminum wires that are bent into a U- or W-shape, similar to the appearance of hairpins. These bent pieces of wire are placed in the stator slots and thus form the windings. The use of hairpins offers several advantages, such as a more compact arrangement of the windings in the stator lamination stack, which leads to a higher power density. The special shape of the hairpins allows the winding wire to be packed more closely to the stator lamination, which reduces resistance and improves electrical efficiency.The orderly structure of the hairpins facilitates cooling of the windings, as air or coolant can flow more easily through the windings. Hairpins allow the use of winding wires with a relatively large cross-section, which can carry higher currents without excessive heat generation. The hairpins can be shaped to require minimal or no additional connections, reducing electrical resistance and potential sources of failure.

[0018] According to some embodiments, the winding includes a connection to a battery with a nominal voltage greater than 600 volts, such as 800 volts. Compared to conventional 400-volt systems, 800-volt systems can offer various advantages that are particularly important in electric vehicles. For example, batteries can be charged faster with 800-volt systems. For the same power, 800-volt systems can use thinner cables and smaller components because the current is lower at higher voltages. This leads to higher power density in the vehicle, which in turn can lead to more compact designs. Higher voltages for the same power mean lower currents. Since losses in cables and components are proportional to the square of the current (according to Joule's law), 800-volt systems can be more efficient due to the lower currents.By reducing the currents in the wiring and components, 800-volt systems can help minimize heat buildup. This can improve cooling and increase the lifespan of electrical components. The lower currents allow for the use of thinner and lighter cables, which in turn can reduce vehicle weight.

[0019] According to yet another aspect, the present invention provides a method for producing a winding for an electrical machine. The method comprises providing a conductor, extruding a thermoplastic insulating layer surrounding the conductor, and extruding a thermoplastic layer (corona layer) surrounding the thermoplastic insulating layer, which layer comprises an electrically conductive additive.

[0020] The resulting winding strand coated with the corona layer can then be arranged in a plurality of winding layers in slots distributed over the circumference of a coil body.

[0021] In the following, individual embodiments of the present invention are described by way of example with reference to the figures.

[0022] They show: Fig. 1 is a flowchart of a method according to the invention for producing a winding for an electrical machine; Fig. 2 shows an illustration of the manufacture of a winding according to an embodiment; Fig. 3 a representation of the conductor insulation and the corona layer around the conductor; Fig. 4 a winding head of a distributed winding for an electrical machine; and Fig. 5 an essentially U-shaped hairpin.

[0023] The Fig. 1 shows a flowchart of a method 10 according to the invention for producing a winding for an electrical machine.

[0024] The method 10 comprises a step 11 of providing an electrical conductor. The electrical conductor can, for example, comprise a wire made of copper (Cu) or aluminum (Al) and can be wound as a strip onto a spool or drum. The electrical conductor can, for example, be a wire with a rectangular or round cross-section.

[0025] The method 10 further comprises a step 12 of extruding a thermoplastic insulating layer enclosing the electrical conductor. The thermoplastic insulating layer can comprise PEEK, for example, as the insulating material. The insulating material can initially comprise thermoplastic granules or pellets. These pellets can be mixed with optional additives such as dyes, flame retardants, or other additives, depending on requirements. The thermoplastic insulating material can then be loaded into an extruder hopper. In the extruder, the pellets can be conveyed by a screw, for example, and simultaneously heated by heating elements in the extruder. This melts the pellets and turns them into a molten plastic mass. At the end of the extruder there can be an extrusion die, which enables the insulating layer to be shaped onto the electrical conductor. The electrical conductor orWire is fed through the nozzle while the molten plastic mass is simultaneously extruded around the electrical conductor. The extruded insulation layer can then be cooled by refrigeration to allow the plastic to harden again. This allows the desired shape and strength of the insulation layer to be achieved.

[0026] The method 100 further comprises a step 13 of extruding a further thermoplastic layer (corona layer) which comprises an electrically conductive additive and which encloses the thermoplastic insulating layer (and the wire). The further weakly electrically conductive corona layer is extruded around the thermoplastic insulating layer from step 12. For this purpose, a thermoplastic material, such as PEEK, with an electrically conductive additive is prepared. The thermoplastic material for the corona layer can in turn consist of thermoplastic granules or pellets. These pellets can be mixed with the electrically conductive additive. The electrically conductive additive can be at least one of a carbon-based additive, metal particles, or an electrically conductive polymer. Thermoplastics (e.g.PEEK) can be made weakly electrically conductive by the addition of electrically conductive fillers. Conductive fillers that can be used in PEEK composites can include, among others, carbon fibers or carbon nanotubes, metal particles (e.g., copper, aluminum, or silver), or graphene. The electrically conductive PEEK composites can be used here as an additional corona layer, where a certain degree of electrical conductivity is required without compromising the excellent mechanical, thermal, and chemical properties of PEEK. The electrically weakly conductive thermoplastic composite material can then be loaded into an extruder hopper. In the extruder, the pellets of the weakly conductive thermoplastic composite material can be fed through a screw and simultaneously heated by heating elements in the extruder.This melts the pellets of the low-conductivity thermoplastic composite material and transforms into a molten composite plastic mass. The extrusion die allows the corona layer to be formed on the previously extruded insulating layer. The electrical conductor with the previously extruded insulating layer is fed through the extrusion die, while simultaneously the molten low-conductivity composite plastic mass is extruded around the insulating layer. The extruded corona layer can then be cooled again to allow the composite plastic to harden again. This allows the desired shape and strength of the corona layer to be achieved.

[0027] The Fig. The method 10 described in Figure 1 for producing a winding is carried out by Fig. 2 is shown again somewhat differently.

[0028] The Fig. 2 shows an electrical conductor 21 made of rectangular or round wire wound onto a spool or drum. In a first optional step, the electrical conductor 21 can be unwound from the drum and provided with an optional polyamideimide (PAI) sheath 22 to obtain a PAI-sheathed conductor. PAI can be used to sheathe electronic components, cables, and connections to protect them from high heat, chemicals, and electric fields. In a second step (extrusion step 12), the PAI-sheathed conductor can be sheathed with the thermoplastic insulating layer (e.g., PEEK) 23 to obtain an electrically insulated conductor. In a further step (extrusion step 13), the electrically insulated conductor can be sheathed with the electrically weakly conductive thermoplastic layer (corona layer) 24 to obtain a conductor structure for the winding.A value of a surface resistance of the electrically weakly conductive thermoplastic layer (corona layer) 24 can, for example, be in the range 100 - 500 Ohm / m. 2 , depending on the application also up to about 10,000 Ohm / m 2 , move. Thus, the electrical conductivity of the corona layer 24 is greater than that of the insulating layer 23 and lower than that of the electrical conductor 21. Instead of just one corona layer 24, some embodiments also provide several corona layers, each with different conductivities.

[0029] Instead of coating the wire 21 only once with PEEK 23, according to the invention, an additional PEEK layer 24 is subsequently applied. However, the PEEK layer 24 is made electrically (weakly) conductive using additives. This does not extend the tolerance chain, and the use of the same base material (PEEK) ensures that the insulation 23 and the corona layer 24 are firmly bonded to each other, and the thermal, mechanical, and chemical resistance is also maintained.

[0030] As in Fig. As indicated in Figure 3, the potential can be controlled or monitored using the corona layer 24. The voltage is specifically reduced to the surface of the conductor insulation 23, or it is ensured that the potential gradient within the conductor insulation 23 is constant. The potential on the surface of the conductors 21 is thus identical, and no discharges can occur outside the insulation 23.

[0031] A winding for an electrical machine (e.g., an 800-volt system) can now be formed from the conductor structure coated with the additional corona layer 24. This can be a concentrated or a distributed winding. For this purpose, the winding phase coated with the corona layer 24 resulting from method 10 can be arranged in slots distributed over the circumference of a coil former in a plurality of winding layers. In the case of a distributed winding with a plurality of hairpins, hairpins can be formed from the conductor coated with the insulating layer 23 and corona layer 24 resulting from method 10. These hairpins can then, in turn, be inserted into the slots, and the winding phase can be formed by connecting the hairpins.

[0032] The Fig. 4 shows, by way of example, a winding head of a distributed winding 30 for an electrical machine. An electrical machine is a device that converts electrical energy into mechanical energy (e.g., movement) or, conversely, mechanical energy into electrical energy. Electrical machines include, for example, electric motors or generators. In the illustrated embodiment, a distributed winding 30 is used for a stator. A distributed winding for a rotor is also possible.

[0033] The distributed winding 30 comprises a substantially hollow-cylindrical coil former (e.g., stator or rotor laminated core) 31, which may be formed, for example, from layered sheets or laminations. The coil former 31 has a plurality of slots 32 distributed over a circumference of the coil former 31. The slots 32 are located here on an inner circumference of the coil former 31 and run in the axial direction (in the direction of the rotational axis of the coil former 31). Insulating paper (winding paper) 34 is inserted into each of the slots 32 and protrudes axially from the respective slot 32 by an axial projection. The insulating paper 34 serves to separate the winding system and the ground potential of the coil former 31. For this purpose, the insulating paper 34 may be formed from electrically insulating paper or plastic.

[0034] The distributed winding 30 further comprises a plurality of winding strands (coils). For example, there may be three winding strands for three different phases (current-carrying lines). A winding strand may be formed from a plurality of interconnected hairpins 33. A hairpin 33 refers to a special shape of winding strand in electrical machines. Hairpins may consist of a flat, U-shaped wire, which may be made of copper or aluminum, bent into an arc at both ends. This shape resembles a hairpin, which gives rise to the name "hairpin." Hairpin windings are often used in electrical machines such as motors and generators because they can provide higher current density and better cooling properties than conventional round wire windings.Furthermore, hairpin windings can be used in machines with limited space and complex shapes because they are flexible and easily adaptable. According to the present invention, the individual hairpins comprise a thermoplastic insulating layer 206 encasing the U-shaped wire and a thermoplastic layer (corona layer) 208 encasing the insulating layer 206, which contains an electrically conductive additive (e.g., graphene).

[0035] As in Fig. 5, individual hairpins 33 are generally bent into a substantially U-shape and can have a rectangular conductor cross-section. Due to their U-shape, individual hairpins 33 have two substantially parallel legs 33-N, which are also referred to below as slot sections because they are arranged in the slots 32 of the coil former 31 provided with insulating paper 34. In addition to hairpins in U-geometry, the so-called I-pin technology and the wave winding concept (continuous hairpin) are also among the methods of plug-in coil technologies and can be used in embodiments of the present invention. I-pins consist of straight flat copper wire elements that are inserted into the stator slots 32. In contrast to the U-topology, no forming processes are carried out here. Contact is made on both sides of the stator.With the wave winding concept, so-called winding mats are manufactured and then inserted into the core from the inside. Compared to U- and I-pin technology, the contacting effort can be reduced.

[0036] The hairpins 33 arranged in or on the coil former 31 each have axially extending groove sections 33-N, which are arranged in the radial direction in different winding layers in the grooves 32 of the coil former 31 provided with insulating paper 34. In other words, a plurality of axially extending grooves 32 are provided on the inner circumference of the coil former 31, in which groove sections 33-N of the hairpins 33 are arranged in several radially layered winding layers. For example, M winding layers can be arranged in each groove 32, i.e., M radially adjacent groove sections 33-N. For example, M can be 6, i.e., six winding layers. These M radially adjacent groove sections 33-N are then surrounded by the insulating paper 34 and thus insulated from the coil former 31.

[0037] After all hairpins 33 have been installed, the conductor ends projecting from the lower end of the coil former 31 (not shown) are bent in different directions and angles in the circumferential direction of the coil former 31, cut to length, and welded together. The winding strands or hairpins 33 overlap at the axially upper and lower ends of the coil former 31. This overlapping area is also called the winding head. Each of the winding strands has a connection area (not shown) at both of its ends, which can be formed by one end of a respective connection hairpin. Fig. 4 shows an upper winding head of the distributed winding 30. The upper winding head forms the side from which the hairpins 33 are inserted into the grooves 32, so that the bent sections 33-V of the hairpins 33 form the winding head.

[0038] In summary, the present invention proposes applying a weakly conductive or semiconductive material, the so-called corona layer 24, in a second process step (extrusion step 13) to reduce partial discharges on the surface of the conductor by applying a fixed potential to the conductor surface. The result is a conductor that already has a corona layer 24 integrated, which is also firmly bonded (virtually fused) to the insulation layer 23 and cannot detach again.

[0039] The exemplary embodiments described and shown in the figures are selected only as examples. Different exemplary embodiments can be combined with each other in their entirety or with regard to individual features. Furthermore, one exemplary embodiment can be supplemented by features of another exemplary embodiment.

[0040] Furthermore, the following claims are hereby incorporated into the Detailed Description, each claim may stand on its own as a separate example. While each claim may stand on its own as a separate example, it should be noted that although a dependent claim may refer to a particular combination with one or more other claims in the claims, other examples may include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are explicitly suggested herein unless it is stated that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be included, even if that claim is not made directly dependent on the independent claim. Reference symbol 10 Method for producing a winding for an electrical machine 11 Providing an electrically conductive wire 12 Extrusion of a thermoplastic insulating layer covering the wire 13 Extruding a thermoplastic layer encasing the thermoplastic insulating layer, which layer comprises an electrically conductive additive 21 electrically conductive wire, conductor 22 PAI sheath 23 thermoplastic insulation layer 24 thermoplastic layer with electrically conductive additive 30 windings 31 coil bodies 32 grooves 33 hairpins 34 insulation paper

Claims

[1] A winding (30) for an electrical machine, comprising a coil body (31) having a plurality of grooves (32) distributed over a circumference of the coil body; at least one winding strand arranged in the slots (32) and in a plurality of winding layers, the winding strand comprising: an electrically conductive wire (21); a thermoplastic insulating layer (23) surrounding the wire (21); and a thermoplastic layer (24) encasing the insulating layer (23) which comprises an electrically conductive additive. [2] The winding (30) according to claim 1, wherein the thermoplastic insulating layer (23) and the thermoplastic layer (24) encasing the insulating layer each comprise polyetheretherketone, PEEK. [3] The winding (30) according to any one of the preceding claims, wherein the electrically conductive additive comprises at least one of a carbon-based additive, metal particles, or an electrically conductive polymer. [4] The winding (30) according to any one of the preceding claims, wherein an electrical conductivity of the thermoplastic layer surrounding the insulating layer is greater than that of the insulating layer and less than that of the electrically conductive wire. [5] The winding (30) according to any one of the preceding claims, wherein the thermoplastic insulating layer (23) and the thermoplastic layer (24) encasing the insulating layer are each formed as extruded layers. [6] The winding (30) according to one of the preceding claims, wherein the coil body (31) is designed as a stator laminated core. [7] The winding (30) according to one of the preceding claims, wherein the winding strand is formed by means of a plurality of hairpins (33). [8] The winding (30) according to any one of the preceding claims, further comprising a connection of the winding to a battery having a nominal voltage greater than 600 V. [9] A conductor structure for a winding (30) of an electrical machine, comprising an electrically conductive wire (21); a thermoplastic insulating layer (23) surrounding the wire; and a thermoplastic layer (24) encasing the insulating layer (23) which comprises an electrically conductive additive. [10] A method (10) for producing a winding (30) for an electrical machine, comprising Providing (11) an electrically conductive wire (21); Extruding (12) a thermoplastic insulating layer (23) covering the wire (21); and Extruding (13) a thermoplastic layer (24) encasing the thermoplastic insulating layer (23) and comprising an electrically conductive additive.

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