Insulation material for the electrical insulation of winding conductors

Abstract

Insulating material (12) for electrical insulation of winding conductors (10) in electrical machines, consisting of an electrically insulating material, in particular PI, PAI, PEEK, which has a defined thickness and permittivity depending on a dielectric strength specified for the winding conductor (10), characterized in that highly porous microparticles (14) with microcavities to reduce the permittivity are introduced into the electrically insulating material (12).

Description

[0001] The invention relates to an insulating material for the electrical insulation of winding conductors in electrical machines with the features of the preamble according to claim 1, and to a winding conductor for an electrical machine with the features of the preamble according to claim 5 or according to claim 7.

[0002] Electrical machines are used to convert electrical energy into mechanical energy or vice versa. An electric machine designed as a drive machine for a motor vehicle is particularly suitable for use within the powertrain of a hybrid or fully electric vehicle. However, in modern applications, especially in the automotive sector, the electrical and thermal demands on insulation systems are constantly increasing. Higher voltage classes, steeper voltage edges due to fast switching inverters, larger voltage swings, increased switching frequencies, and higher operating temperatures cause conventional electrical insulation systems to age more rapidly and their service life to decrease drastically.

[0003] To meet these increased demands, the insulating layers must be very thick when using conventional insulating materials. Many of the plastics used in winding insulation have relatively high permittivity values, for example, approximately 3.2 for polyetheretherketone (PEEK) and about 4.2 for polyamide-imide (PAI). A high permittivity of the insulating material results in a low electric field strength within the insulating material, but a high electric field strength outside the insulation, for example, in the air. This promotes partial discharges, or rather, the partial discharge onset voltage of the system is lower. Conversely, the lower the permittivity of an insulating material, the higher its partial discharge onset voltage, or the thinner the insulating layer can be to meet given requirements.With currently available organic insulation materials, the increasing demands placed on electrical machines can only be met by drastically increasing layer thicknesses. Such large insulation thicknesses conflict with the limited installation space within electrical machines and can also reduce the possible copper fill factor.

[0004] Several prior art approaches attempt to improve the electrical load limits of winding insulation. One proposal is to reduce the permittivity of the insulating material by introducing gas bubbles. For example, US 2020 / 0033286 A1 describes the introduction of an insulating gas during the coating process to lower the relative permittivity of the wire insulation. A similar concept is proposed in Chinese patent application CN 115472332 A. While such air inclusions can influence the field distribution in the insulating material and reduce the effective permittivity, controlling the gas bubbles within the insulating layer is problematic. In particular, there is a risk of excessively large gas bubbles forming, which reduce the dielectric strength of the insulation and promote partial discharges.Air inclusions in a critical size range of approximately 10-20 µm exhibit minimal penetration (Paschen minimum curve), meaning that excessively large trapped air bubbles drastically impair the insulating properties. Conversely, very small gas bubbles have little effect on permittivity, making it difficult to achieve an effective compromise using conventional methods.

[0005] Furthermore, it is known to introduce inorganic fillers into wire insulation to increase partial discharge resistance, for example, mica particles in an insulating varnish. Since inorganic materials, unlike organic plastics, are generally insensitive to partial discharges, i.e., they do not exhibit aging under partial discharge stress, such an addition improves the partial discharge resistance of the insulating layer compared to purely organic insulation. However, partial discharges can still occur and then continue to damage the organic components of the insulation. While the service life is extended by the addition of inorganic particles, the organic content of the insulating material remains a limiting factor.

[0006] Currently, no insulation material is known that exhibits both significantly reduced permittivity and exceptional resistance to partial discharges. Known solutions either require unsatisfactorily large insulation layer thicknesses or, despite material combinations, still result in a limited service life of the insulation systems under high electrical loads.

[0007] The object of the invention is to provide an insulating material for winding conductors that exhibits reduced permittivity and increased partial discharge resistance even under high electrical and thermal stresses, without requiring excessive layer thicknesses; furthermore, to create a winding conductor provided with such an insulating material and correspondingly improved insulating properties.

[0008] The problem is solved with an insulating material for the electrical insulation of winding conductors in electrical machines, consisting of an electrically insulating material, in particular PI, PAI, PEEK, which has a defined thickness and permittivity depending on a dielectric strength specified for the winding conductor, wherein highly porous microparticles with microcavities are introduced into the electrically insulating material to reduce the permittivity.

[0009] By incorporating highly porous microparticles into the insulating material, the effective permittivity of the insulating layer is significantly reduced, as the microcavities within the particles are filled with gas—preferably air—which has a very low permittivity. At the same time, the fine branching (dendritic structure) of the microparticles ensures that the resulting air inclusions are extremely small and homogeneously distributed throughout the material. This prevents the formation of a continuous cavity that could lead to local field concentrations and premature partial discharges. In other words, while the numerous tiny air inclusions slightly reduce the dielectric strength of the insulating material, this remains tolerable because the base materials used (e.g., PEEK or PAI) possess a dielectric strength far exceeding the application-specific requirements.Overall, this method allows the permittivity of the insulation system to be reduced to such an extent that a significantly higher partial discharge inception voltage is achieved for a given electrical stress. Alternatively, for the same partial discharge inception voltage or partial discharge requirement, the insulating layer can be made thinner, which saves valuable installation space or allows the use of a conductor with a larger cross-section. Thus, the insulation material according to the invention contributes to an extended service life of the electrical machine without exceeding the available installation space.

[0010] It is particularly preferred that the microparticles have a size of less than 10 µm and that air is trapped within their dendritic structure. Limiting the particle size to below 10 µm ensures that the incorporated microparticles are very small relative to the thickness of the insulating layer. This allows for a uniform distribution of the particles throughout the entire insulating material without compromising the homogeneity or mechanical integrity of the layer. In particular, local weak points are avoided, as no particle is significantly larger than the layer thickness itself. Furthermore, air is trapped as an insulating gas within the fine-pored structures of the microparticles. Of all common insulating materials, air has the lowest relative permittivity and therefore results in a maximum reduction of the effective permittivity of the composite material.In principle, other gases with low permittivity can also be included in the microparticles instead of air (for example, noble gases or nitrogen) if this appears advantageous for certain applications.

[0011] It is also preferred that the microparticles are silicate-based aerogels. Additional advantages arise when the microparticles are silicate-based aerogel particles (e.g., silica aerogel). Aerogels made of inorganic materials are particularly resistant to partial discharges because they do not exhibit any signs of aging under partial discharge stress. The addition of such an inorganic filler thus significantly increases the partial discharge resistance of the insulating layer. Furthermore, silica aerogels exhibit extremely high thermal stability (especially a very high melting and decomposition temperature). This makes them ideally suited as a filler for winding conductor insulation, as they easily withstand the temperatures occurring during the manufacturing process—for example, during the curing of an insulating varnish or during an extrusion process.Even elevated temperatures occurring during the operation of an electric machine can be withstood without damage by silicate-based aerogel particles. Naturally, the invention is not limited to aerogel microparticles made of silicon dioxide; in principle, the highly porous microparticles can be produced from a wide variety of suitable materials, provided they exhibit the required fine pore structure. Depending on the specific requirements of the final product, a different aerogel material can therefore be selected to achieve optimal properties.

[0012] Furthermore, it is particularly advantageous that the insulating material is designed as a sheet insulating material, especially for wrapping the winding conductors or parts of the winding conductors and / or for lining stator slots, in sheet or strip form.

[0013] In this embodiment, the insulating material is a flexible film or strip material, which significantly expands its range of applications. The insulating material according to the invention can thus not only be applied directly to the conductor as a coating, but also be used in the form of a film-shaped insulating material. In particular, it can be wound as a strip or film around a winding conductor or around sections of a winding conductor. In this way, conductors that have already been formed or installed can be subsequently provided with the inventive insulation, or sections subject to particularly high stress can be additionally insulated. Furthermore, it is possible to line the stator slots of an electric motor with the surface insulating material before the winding conductors are inserted. This allows the invention to be used in areas where direct coating of the conductors would be technically difficult or uneconomical.Overall, providing the insulation material in sheet or strip form significantly increases the flexibility in insulating windings.

[0014] The problem is further solved by a winding conductor for an electric machine coated with the previously described insulating material according to the invention. Coating the conductor with the insulating material according to the invention makes the improved insulation properties directly usable. A winding conductor coated in this way can withstand significantly higher electric field strengths and faster voltage rises without partial discharges occurring. This means that even at high operating voltages and steep switching edges, the insulation remains intact and exhibits a delayed onset of partial discharges compared to conventional systems. Furthermore, the reduced permittivity of the insulating layer allows it to be designed thinner without compromising the required dielectric strength. Thinner insulation means that, for a given overall size of the electric machine, a conductor with a larger cross-section can be used.This increases the copper fill factor of the winding and reduces its electrical resistance, which in turn reduces losses and increases the power density of the machine. Overall, the winding conductor insulated according to the invention contributes to higher reliability and service life of the electric machine, since the insulation is subjected to less stress from partial discharges and thermal loads.

[0015] It may also be preferred that the winding conductor is designed as a flat wire winding conductor. If the winding conductor is designed as a flat wire with a rectangular cross-section, this is a particularly advantageous embodiment in the context of the invention. Flat wire windings enable a high copper fill factor and thus an increased power density of the electric motor. However, increased local field strengths occur, especially at the right-angled edges of a flat wire, which place high demands on the insulation. With the insulation material according to the invention, even such flat wire conductors can be reliably insulated against high voltages without having to excessively increase the layer thickness. In this way, the advantages of flat wire technology – more compact windings with a higher copper content – ​​can be fully exploited without having to compromise on insulation resistance.It should be noted that the invention is not limited to flat wire conductors; round wire winding conductors can also be coated with the described insulating material in the same way and benefit from its advantageous properties.

[0016] The problem is further solved by a winding conductor wrapped with the insulating material according to the invention. The possibility of wrapping the conductor with an insulating tape instead of a coating offers additional advantages in manufacturing and application. Particularly with large-dimensioned conductors or complex component geometries, it can be difficult to apply a homogeneous coating. In such cases, the insulating material according to the invention can be wrapped around the conductor in the form of a flexible tape. A winding conductor wrapped in this way gains the same advantages as a coated conductor: the insulation permittivity is reduced and the partial discharge resistance is increased. The key advantage of the wrapping is that a first-class insulating layer can still be applied subsequently – for example, after bending or mounting a conductor.This is useful, for example, in the manufacture of stators with pre-formed plug-in windings (hairpin technology), since the main insulation is only fully applied after the conductors have been inserted into the stator. With the present invention, this can be achieved by wrapping the stator bars with the insulating tape. Thus, the described advantages (low permittivity, high partial discharge resistance, and good thermal stability) can also be realized in cases where conventional wire coating is not practical.

[0017] In addition to the features defined in the claims, further advantageous embodiments of the invention can be provided. For example, the insulating material according to the invention can be used in various insulating systems. It is possible, for instance, to integrate the described microparticle filler into one or more layers of a multilayer insulating system. In a preferred embodiment, only one of several insulating layers—such as an adhesion promoter layer or an outer cover layer—contains the highly porous aerogel particles, while the remaining layers consist of conventional insulating material. In this way, the mechanical and adhesive properties of the insulation can be maintained while simultaneously reducing the permittivity and increasing the partial discharge resistance.Furthermore, the material is equally suitable for enamelled wires (wire enamel) and for extruded insulating tubing or tapes. Regardless of whether the insulation is applied by an enamelling process or by extrusion, the aerogel microparticles can be embedded in the insulating matrix. The invention can therefore be seamlessly integrated into existing manufacturing processes for electric motor windings and is applicable to both rectangular conductor cross-sections and round wires.

[0018] The invention is explained in more detail using the figures as examples. They are shown schematically and not to scale: Fig. 1: Rectangular winding conductor with insulating material Fig. 2: Partial section of a foil-shaped insulating material

[0019] In Fig. Figure 1 shows a section through an electrical winding conductor 10 with an insulating material 12. The winding conductor 10 has a largely rectangular cross-section and is thus designed as a flat wire winding conductor. The insulating material 12 is applied as a coating to all sides of the conductor and completely encases it. Several microparticles 14 are distributed within the insulating layer, which are schematically indicated here as small dots. These microparticles 14 correspond to the highly porous filler particles described above, which are incorporated into the insulating material to reduce its permittivity. The size of each microparticle 14 is actually very small compared to the thickness of the insulating layer; in the schematic representation of Fig. Figure 1 illustrates this in a simplified way.

[0020] Fig. Figure 2 shows a section of a film-shaped insulating material 12 with embedded microparticles 14. In this section, the microparticles 14 appear as small, irregular particles within the insulating layer. The numerous spaces within the particles 14 represent the microcavities, which are filled with air. It can be seen that the microparticle 14 consists predominantly of cavities (typically about 99.9% of its volume). This fine pore structure is on the nanometer to micrometer scale and ensures that the individual air inclusions do not exceed a diameter of only a few micrometers. This prevents—as explained above—the formation of air spaces in the insulating layer that would be large enough to cause partial discharges. Overall, this illustrates Fig.2 the special microstructure of the aerogel filler used, which reduces the permittivity while simultaneously increasing the partial discharge resistance. REFERENCE MARK LIST: 10 winding conductors 12 Insulation material 14 highly porous microparticles with microcavities QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2020 / 0033286 A1

[0004] CN 115472332 A

[0004]

Claims

[1] Insulation material (12) for electrical insulation of winding conductors (10) in electrical machines, consisting of an electrically insulating material, in particular PI, PAI, PEEK, which has a defined thickness and permittivity depending on a dielectric strength specified for the winding conductor (10), characterized by , that highly porous microparticles (14) with microcavities are incorporated into the electrically insulating material (12) to reduce the permittivity. [2] Insulation material according to claim 1, characterized by , that the microparticles (14) have a size of less than 10 µm and that air is trapped in their dendritic structure. [3] Insulation material according to claim 1 or 2, characterized by , that the microparticles (14) are silicate-based aerogels. [4] Insulation material according to any one of the preceding claims 1 to 3, characterized by, that the insulating material (12) is designed as a sheet insulating material, in particular for wrapping the winding conductors (10) or parts of the winding conductors and / or for lining stator slots, in sheet or strip form. [5] Winding conductor (10) for an electric machine, characterized by , that the winding conductor is coated with an insulating material (12) according to one of claims 1 to 3. [6] Winding conductor (10) for an electric machine according to claim 5, characterized by that the winding conductor is designed as a flat wire winding conductor. [7] Winding conductor (10) for an electric machine, characterized by , that the winding conductor is wrapped with an insulating material (12) according to one of claims 1 to 4.

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