High-voltage high-frequency stranded litz wire and method for manufacturing the same

Abstract

The application discloses a high-voltage high-frequency stranded Litz wire and a preparation method thereof, and belongs to the technical field of insulation of high-voltage high-frequency power equipment. The application solves the problem of electric field concentration caused by uneven electric field distribution of the existing stranded Litz wire. The application introduces a semi-conductive elastomer polymer outside the Litz wire, improves the uneven electric field distribution outside the stranded conductor, realizes the electric field homogenization effect, thereby inhibits the occurrence of partial discharge, avoids the increase of the electric field of the main insulation caused by the external shielding of the main insulation, and prolongs the service life of the insulation. By setting the equal-potential bare conductor with the Litz wire in the shielding layer, the potential difference between the Litz wire and the shielding layer is eliminated, the electric field distribution of the internal conductor of the main insulation is more uniform, and the reliability of the insulation system is improved. In addition, the stranded Litz wire provided by the application can flexibly set the shielding layer with different threshold electric field strengths according to the voltage grade to optimize the potential distribution, and has excellent scalability and process friendliness.

Description

Technical Field

[0001] This invention relates to a stranded Litz wire for high voltage and high frequency applications and its preparation method, belonging to the field of insulation technology for high voltage and high frequency power equipment. Background Technology

[0002] Stranded Litz wire, utilizing its high skin effect, is a key material for high-frequency, high-voltage, and high-current power equipment such as high-voltage wind turbines, solid-state power electronic transformers, wireless charging devices, and high-power charging piles. Its insulation structure and performance are a reliable guarantee for the safe operation of these equipment. Because the non-smooth edges of the stranded Litz wire bars can lead to electric field concentration, its traditional structure is prone to partial discharge as voltage levels and frequencies increase, resulting in a reduced lifespan of power equipment. Therefore, higher requirements are placed on the design of the insulation structure and key materials of stranded Litz wire.

[0003] Conventional stranded Litz wire is made by stranding or braiding multiple independently insulated Litz wires into a near-cylindrical shape, with polyimide self-adhesive tape wrapped around the surface. Some stranded wires are further pressed to become flat wires depending on the application requirements. Because the outer contour of the stranded wire cannot achieve a smooth and flat structure without special modification, local electric field concentration occurs after energization, which easily induces partial discharge and degrades the insulation performance and service life of the main insulation. Summary of the Invention

[0004] To address the problem of electric field concentration caused by the uneven electric field distribution in existing stranded Litz wires, this invention provides a stranded Litz wire for high voltage and high frequency applications and its preparation method.

[0005] The technical solution of this invention: One of the objectives of this invention is to provide a stranded Litz wire for high voltage and high frequency applications. The stranded Litz wire includes a core, a shielding layer wrapped around the core, a bare conductor located within the shielding layer, and an insulation layer covering the shielding layer. One end of the core is fused together and connected to one end of the bare conductor.

[0006] Furthermore, the core is made of multiple self-insulated wires twisted or braided together.

[0007] Furthermore, the self-insulated wire is enameled wire.

[0008] Further specifying, the shielding layer is made of a semi-conductive shielding elastomer coaxially extruded and wrapped around the core.

[0009] Furthermore, the semiconductive polymer elastomer has a tensile strength greater than 30 MPa, an elongation at break greater than 150%, and a volume resistivity of 10 Ω·cm. 2 -10 3 Ω·m, temperature rating greater than 120°C.

[0010] To be further specified, the semiconductive polymer elastomer includes a resin matrix and modified fillers.

[0011] Furthermore, the resin matrix is ​​specified as TPEE, PPSU, or TPU.

[0012] Furthermore, the modified filler is specified as carbon fiber or carbon black.

[0013] Further specifying, the insulating layer is a polyimide self-adhesive tape, an epoxy resin surface-modified self-adhesive polyimide film, or a thermoplastic polyimide surface-modified polyimide film.

[0014] The second objective of this invention is to provide a method for preparing the above-mentioned high-voltage, high-frequency stranded Litz wire, the method comprising the following steps: (1) A core is obtained by twisting or braiding multiple self-insulated wires; (2) The wire core and the bare conductor are coaxially arranged, and the semi-conductive shielding elastomer is wrapped around the wire core by coaxial extrusion to form a shielding layer, and the bare conductor is located inside the shielding layer; (3) Wrap an insulating layer around the shielding layer to complete the preparation of stranded Litz wire.

[0015] Beneficial effects: This invention provides an insulation structure for stranded Litz wire based on a coaxial extruded shielding layer of a semiconductive shielding elastomer, with a potential-limiting conductor added within the shielding layer. Utilizing a semiconductive polymer elastomer with adaptive electric field characteristics, the stranded wire is extruded in situ during the stranding process, forming a shielding layer with a homogenizing electric field on the outside of the stranded wire. During the extrusion process, a bare conductor is pre-embedded in the shielding layer, and this bare conductor is at the same potential as the stranded Litz wire. Compared with existing technologies, this invention offers at least the following advantages: (1) The present invention improves the uneven distribution of the electric field outside the stranded conductor by introducing a semiconducting elastomer polymer outside the Litz wire, thereby achieving the effect of electric field homogenization, suppressing the occurrence of partial discharge, avoiding the increase of the electric field of the main insulation caused by the external shielding of the main insulation, and improving the service life of the insulation.

[0016] (2) The shielding layer of the present invention is prepared by in-situ extrusion, which can ensure that the shielding layer has a large deformation capacity and maintain a smooth and flat contour during the deformation of the conductor, preventing the shielding layer from being damaged during the deformation of the conductor. At the same time, it avoids the risk of insufficient penetration and bubble formation in the coating process, reduces the risk of weak insulation caused by process defects, and avoids the problem that the coated shielding layer cannot fully penetrate into the winding. In addition, the selection of epoxy resin or thermoplastic polyimide surface-modified polyimide film as the resin matrix of the shielding layer can also provide stronger resistance to interface discharge in high-voltage applications.

[0017] (3) The present invention sets a bare conductor with the same potential as the Litz wire in the shielding layer, which eliminates the potential difference between the Litz wire and the shielding layer, making the electric field distribution of the conductor inside the main insulation more uniform and improving the reliability of the insulation system.

[0018] (4) The stranded Litz wire provided by the present invention can be flexibly set with shielding layers of different threshold electric field strengths according to the voltage level to optimize the potential distribution, and has excellent scalability and process friendliness. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of stranded Litz wire provided by the present invention; Figure 2 The electric field distribution of the stranded Litz wires provided in Example 1 and Comparative Examples 1-2 was analyzed using finite element simulation. Figure 1 1-Self-insulated wire, 2-Wire insulation varnish, 3-Shielding layer, 4-Insulation layer, 5-Bare wire. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0024] Example 1: like Figure 1 As shown, the high-voltage high-frequency stranded Litz wire provided in this embodiment includes a core formed by stranding multiple self-insulated conductors 1, a shielding layer 3 wrapped around the core, bare conductors 5 located inside the shielding layer 3, and an insulation layer 4 covering the shielding layer.

[0025] The core consists of 40 self-insulated copper wires twisted together and shaped into a square shape using a shaping tool.

[0026] The shielding layer 3 is made of a semi-conductive shielding elastomer coaxially extruded and wrapped around the core. The conductivity of the semi-conductive shielding elastomer is 100 Ω·cm. The insulating layer 4 is polyimide self-adhesive tape.

[0027] Using finite element simulation analysis, the electric field distribution of the stranded Litz wire provided in this embodiment was analyzed under the same electric field strength and grounding conditions. The results are as follows: Figure 2 In the middle (c), the voltage unit in the figure is kV.

[0028] Comparative Example 1: The difference between this comparative example and Example 1 is that it does not include the shielding layer 3, and the insulating layer 4 is directly wrapped around the outside of the core.

[0029] Using finite element simulation analysis, the electric field distribution of the stranded Litz wire provided in this embodiment was analyzed under the same electric field strength and grounding conditions. The results are as follows: Figure 2 (a)

[0030] Comparative Example 2: The difference between this comparative example and Example 1 is that it does not include the bare wire 5, but the rest of the structure is the same as that of Example 1.

[0031] Using finite element simulation analysis, the electric field distribution of the stranded Litz wire provided in this embodiment was analyzed under the same electric field strength and grounding conditions. The results are as follows: Figure 2 (b)

[0032] Depend on Figure 2 It is known that for the widely used stranded Litz wire insulation structure (Comparative Example 1), the electric field strength between the outer contour of the stranded conductor and the main insulation layer is significantly increased, and there is obvious electric field concentration at this point, which is the main reason why stranded Litz wire is prone to partial discharge. When a semi-conductive shielding elastomer layer is set in situ outside the stranded Litz wire (Comparative Example 2), there are a few local locations where the electric field increases between the outer contour of the stranded conductor and the semi-conductive shielding elastomer layer. The electric field distribution between the semi-conductive shielding elastomer layer and the main insulation layer is relatively uniform, but the electric field strength is high, which is detrimental to the insulation performance and service life of the main insulation. When the insulation structure provided by this invention is used (Example 1), that is, a semi-conductive shielding elastomer layer is set outside the stranded Litz wire, and a potential limiting conductor is added inside the shielding layer, the electric field distribution within this stranded Litz wire insulation structure is uniform, there is no significant electric field concentration, and the electric field strength of the shielding layer and the main insulation layer is low.

[0033] In summary, the insulation structure provided in Example 1 not only improves the electric field distribution within the stranded Litz wire, but also does not cause an increase in the electric field on the main insulation, thus significantly improving the overall reliability of the insulation system.

[0034] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A stranded Litz wire for high voltage and high frequency applications, characterized in that, It includes the conductor, the shielding layer surrounding the conductor, the bare conductor inside the shielding layer, and the insulation layer covering the shielding layer.

2. The stranded Litz wire according to claim 1, characterized in that, The conductor is made of multiple self-insulated wires twisted or braided together.

3. The stranded Litz wire according to claim 1, characterized in that, The insulated wire is enameled wire.

4. The stranded Litz wire according to claim 1, characterized in that, The shielding layer is made of a semi-conductive shielding elastomer that is coaxially extruded and wrapped around the core.

5. The stranded Litz wire according to claim 4, characterized in that, The semiconductive polymer elastomer has a tensile strength greater than 30 MPa, an elongation at break greater than 150%, and a volume resistivity of 10 Ω·cm. 2 -10 3 Ω·m, temperature rating greater than 120°C.

6. The stranded Litz wire according to claim 4, characterized in that, Semiconducting polymer elastomers consist of a resin matrix and modified fillers.

7. The stranded Litz wire according to claim 5, characterized in that, The resin matrix is ​​TPEE, PPSU or TPU.

8. The stranded Litz wire according to claim 5, characterized in that, The modified filler is carbon fiber or carbon black.

9. The stranded Litz wire according to claim 1, characterized in that, The insulation layer is a polyimide self-adhesive tape, an epoxy resin-modified self-adhesive polyimide film, or a thermoplastic polyimide-modified polyimide film.

10. A method for preparing high-voltage high-frequency stranded Litz wire according to any one of claims 1 to 9, characterized in that, include: (1) A core is obtained by twisting or braiding multiple self-insulated wires; (2) The semiconductive shielding elastomer is wrapped around the wire core by coaxial extrusion to form a shielding layer, and a bare wire is placed inside the shielding layer; (3) Wrap an insulating layer around the shielding layer to complete the preparation of stranded Litz wire.

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