Composite film wrapped high voltage pulse coaxial cable and method of manufacture

Abstract

The present application relates to a kind of high-voltage cable, to solve the problem that the insulating layer material used in prior art is damaged in the process of wrapping under high-voltage pulse condition, which causes local temperature rise and damages the film medium, reduces the cable energy density and pulse life.A kind of composite film wrapped high-voltage pulse coaxial cable and its manufacturing method are proposed, which includes an inner conductor and an insulating layer, an outer conductor and a protective layer wrapped on the inner conductor from inside to outside.The insulating layer includes an inner insulating layer, an intermediate insulating layer and an outer insulating layer wrapped from inside to outside.The inner insulating layer and the outer insulating layer are both wrapped by polyimide tape, and the intermediate insulating layer is wrapped by several layers of polypropylene film.The outer conductor is wrapped by aluminum foil, and the protective layer is wrapped by an inner protective layer of polyimide film and an outer protective layer of several layers of polypropylene film.A manufacturing method of composite film wrapped high-voltage pulse coaxial cable is also proposed.

Description

Technical Field

[0001] This invention relates to the field of cables, and particularly to a high-voltage cable, specifically a composite film-wrapped high-voltage pulse coaxial cable and its manufacturing method. Background Technology

[0002] High-voltage pulse cables are connecting cables used to transmit high-voltage pulses generated by pulse generators to various equipment loads. They were initially mainly used in radar equipment. With the development of pulse power technology, high-voltage pulse cables for pulse power drive sources have emerged. Pulse power devices are developing towards higher voltage, higher power, lighter weight, smaller size, and longer lifespan. This also places requirements on high-voltage pulse cables in terms of high voltage resistance, low attenuation, high energy density, and high reliability.

[0003] In existing high-voltage pulse cables, the insulation layer is made of cross-linked polyethylene, which can withstand high instantaneous pulse voltages. However, its insulation capacity is limited by micropores and impurities in the insulation material, resulting in a relatively small electric field strength that it can withstand. This leads to a larger insulation layer thickness, which restricts the reduction of cable size and the increase of energy storage density. The paper "Optimization Design of Insulation Thickness of High-Voltage XLPE Cables, Ouyang Benhong, Liu Songhua et al., High Voltage Engineering, 2016" conducted high-voltage withstand tests on various types of cross-linked polyethylene high-voltage cables, and the average breakdown field strength was only about 47kV / mm.

[0004] With the continuous improvement of polypropylene film technology, the breakdown field strength of the film can reach more than 500kV / mm, and the working field strength can reach more than 200kV / mm. Its energy storage density far exceeds that of cross-linked polyethylene high-voltage cables. Moreover, polypropylene film has good frequency response capability and has shown good application prospects in the field of pulse power technology. It is used as an energy storage medium for high-voltage capacitors, film-wound strip wires, etc. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that the insulating material used in the prior art generates corona under high voltage pulse conditions during the spiral winding process, which causes local temperature rise and damages the thin film dielectric, reducing the energy storage density and pulse life of the cable. The invention proposes a composite thin film-wound high voltage pulse coaxial cable and its manufacturing method.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A composite film-wound high-voltage pulse coaxial cable includes an inner conductor and an insulation layer, an outer conductor, and a protective layer wound sequentially from the inside to the outside of the inner conductor. Its unique feature is that:

[0008] The inner conductor is a cylindrical metal rod; the insulating layer includes an inner insulating layer, a middle insulating layer and an outer insulating layer wound from the inside to the outside. The inner insulating layer and the outer insulating layer are both formed by wrapping polyimide tape, and the middle insulating layer is formed by wrapping several layers of polypropylene film.

[0009] The number of wrapping layers of both the inner and outer insulating layers is not less than one layer.

[0010] The outer conductor is formed by wrapping aluminum foil;

[0011] The protective layer consists of an inner protective layer and an outer protective layer wound sequentially from the inside out. The inner protective layer is formed by wrapping several layers of polyimide film, and the outer protective layer is formed by wrapping several layers of polypropylene film.

[0012] The inner conductor, a cylindrical metal rod, has a smooth surface, ensuring good contact between the inner conductor and the inner insulation layer and reducing air gaps and impurities. Simultaneously, the diameter error of the inner conductor's cross-section at different positions is controlled within a certain range to ensure the uniformity of the cable impedance. Both the inner and outer insulation layers are wrapped with polyimide tape, which consists of a polyimide film and silicone. On one hand, the fluidity of silicone at high temperatures fills the spiral air gaps formed by the film wrapping, reducing the probability of corona discharge on the inner conductor surface. On the other hand, the high-temperature resistance and corona resistance of the polyimide film inhibit the corona discharge that may occur on the conductor surface from propagating into the middle insulation layer.

[0013] Furthermore, the inner and outer insulating layers have 2 to 4 layers, and the polyimide tape used for the inner and outer insulating layers has a thickness of 0.03 mm to 0.06 mm.

[0014] Furthermore, the thickness of the polypropylene film used in the intermediate insulating layer and the outer protective layer is 0.005 mm to 0.02 mm.

[0015] The intermediate insulation layer, formed by wrapping polypropylene film, is the main part of the cable insulation layer. Generally, there are no fewer than one hundred layers, so it has good insulation strength.

[0016] Furthermore, the thickness of the aluminum foil used in the outer conductor is 0.01 mm to 0.02 mm.

[0017] Furthermore, the inner conductor is made of pure aluminum.

[0018] Furthermore, the thickness of the polyimide film used in the inner protective layer is 0.02 mm to 0.05 mm.

[0019] Furthermore, the number of wrapping layers of the intermediate insulation layer is determined based on the actual current carrying capacity and cable impedance requirements. The specific dimensions and number of layers of the inner conductor, insulation layer, outer conductor, and protective layer should be determined based on factors such as the actual required current carrying capacity and cable impedance.

[0020] Meanwhile, this invention also proposes a method for manufacturing a composite film-wrapped high-voltage pulse coaxial cable, which is characterized by including the following steps:

[0021] Step 1: Determine the number of wrapping layers for the insulation layer, outer conductor, and protective layer based on actual needs;

[0022] Step 2: Wrap the imide tape evenly around the inner conductor according to the number of layers required by the design to form an inner insulating layer;

[0023] Step 3: Wrap the polypropylene film evenly around the inner insulating layer according to the number of layers required by the design to form the intermediate insulating layer;

[0024] Step 4: Evenly wrap the imide tape around the middle insulation layer according to the number of layers required by the design to form the outer insulation layer;

[0025] Step 5: Wrap the aluminum foil evenly around the outer insulating layer according to the number of layers required by the design to form the outer conductor;

[0026] Step 6: Wrap the polyimide film evenly around the outer conductor according to the number of layers required by the design to form an inner protective layer;

[0027] Step 7: Wrap the polypropylene film evenly around the inner protective layer according to the number of layers required by the design to form the outer protective layer, thus obtaining the wrapped high-voltage cable.

[0028] Step 8: Heat the high-voltage cable from Step 7 to allow the polyimide tape to flow within the formed inner and outer insulation layers. Simultaneously, the intermediate insulation layer and outer protective layer formed by the polypropylene film are heat-shrinked and cured, thus completing the manufacturing of the composite film-wrapped high-voltage pulse coaxial cable.

[0029] When the polyimide tape of the inner insulation layer is wrapped around the inner conductor, an air gap is formed on the surface of the inner conductor during the wrapping process. When the wrapped high-voltage cable is baked and heated, the silicone in the polyimide tape in the inner and outer insulation layers begins to flow and fill the air gap on the surface of the inner conductor under high temperature conditions. At the same time, the polypropylene film of the middle insulation layer and the outer protective layer heat shrinks and cures, which on the one hand removes the residual gas between the layers of film during the wrapping process, and on the other hand, plasticizes the insulation layer and the protective layer in the high-voltage cable into a whole, which improves the breakdown voltage and insulation capacity of the high-voltage cable, and makes it less susceptible to moisture and contamination, thus improving its stability and practicality.

[0030] Furthermore, the baking temperature in step eight is 120℃~130℃, and the preferred baking temperature is 125℃.

[0031] The beneficial effects of this invention are:

[0032] [1] The composite film-wrapped high-voltage pulse coaxial cable of the present invention uses polyimide tape and polypropylene film to form an insulation layer. First, the high breakdown field strength of polypropylene film is used to improve the overall insulation strength. Second, the corona resistance of polyimide film is used to compensate for the defect of polypropylene film being easily ablated at high corona temperature, which plays a role in blocking the corona on the electrode surface from developing into the cable. This further improves the overall insulation strength, energy storage density and pulse life of the high-voltage cable.

[0033] [2] The inner and outer insulation layers in this invention are formed by wrapping with polyimide tape. The polyimide tape is fluid at high temperature to fill the air gap left by the wrapping film on the inner conductor surface. This effectively reduces the probability and intensity of corona on the electrode surface under high voltage, thereby reducing the damage to the inner protective layer formed by repeated corona and high temperature under pulse conditions, extending its service life, and enabling the cable to have the ability to operate stably for a long time under high voltage pulse conditions.

[0034] [3] The intermediate insulation layer and the outer protective layer in this invention are formed by wrapping with polypropylene film. By heating the high-voltage cable, the intermediate insulation layer and the outer protective layer are heat-shrinked and cured, which can effectively remove the residual gas between the layers of film during the wrapping process; at the same time, the intermediate insulation layer and the outer protective layer can be plasticized into a whole, which improves the breakdown voltage and insulation capacity of the high-voltage cable, and makes it less susceptible to moisture and contamination, thus improving its stability and practicality. Attached image description:

[0035] Figure 1 This is a schematic cross-sectional view of the composite film-wrapped high-voltage pulse coaxial cable of the present invention.

[0036] Figure 2 This is a schematic diagram of the air gap generated between the inner insulating layer and the inner conductor during the wrapping process in an embodiment of the present invention;

[0037] Reference numerals: 1-Inner conductor, 2-Inner insulating layer, 3-Intermediate insulating layer, 4-Outer insulating layer, 5-Outer conductor, 6-Inner protective layer, 7-Outer protective layer, 8-Air gap surrounding the surface of the inner conductor. Detailed implementation method:

[0038] Example 1

[0039] Depend on Figure 1As can be seen, the composite film-wrapped high-voltage pulse coaxial cable proposed in this invention includes an inner conductor 1 and an insulation layer, an outer conductor, and a protective layer wound sequentially on the inner conductor 1 from the inside out. The inner conductor 1 is a cylindrical metal rod with a smooth and clean surface, which ensures good contact between the inner conductor 1 and the inner insulation layer 2 and reduces air gaps and impurities. At the same time, the cross-sectional diameter error of the inner conductor 1 at different positions is controlled within a certain range to ensure the uniformity of the cable impedance.

[0040] The insulating layer comprises an inner insulating layer 2, a middle insulating layer 3, and an outer insulating layer 4 wound sequentially from the inside out. Both the inner insulating layer 2 and the outer insulating layer 4 are formed by wrapping with polyimide tape, and the middle insulating layer 4 is formed by wrapping with several layers of polypropylene film. The inner insulating layer 2 and the outer insulating layer 4 are both wrapped with polyimide tape material, which is composed of polyimide film and silicone. On the one hand, the fluidity of silicone at high temperatures is used to fill the spiral air gap formed by wrapping the film, reducing the probability of corona discharge on the surface of the inner conductor. On the other hand, the high temperature resistance and corona resistance of the polyimide film are used to suppress the corona discharge that may be generated on the surface of the inner conductor 1 from developing into the middle insulating layer 3.

[0041] The inner insulation layer 2 and the outer insulation layer 4 each have at least one wrapping layer; generally, there are 2 to 4 wrapping layers. The thickness of the polyimide tape used for the inner insulation layer 2 and the outer insulation layer 4 is 0.03 mm to 0.06 mm. The intermediate insulation layer 3, formed by wrapping with polypropylene film, is the main part of the cable insulation layer. The thickness of the polypropylene film used for the intermediate insulation layer 3 is 0.005 mm to 0.02 mm, and generally, there are at least one hundred wrapping layers, thus it has good insulation strength.

[0042] The outer conductor 5 is formed by wrapping aluminum foil, and the thickness of the aluminum foil used in the outer conductor 5 is 0.01mm to 0.02mm;

[0043] The protective layers consist of an inner protective layer 6 and an outer protective layer 7, wound sequentially from the inside out. The inner protective layer 6 is formed by wrapping several layers of polyimide film, and the outer protective layer 7 is formed by wrapping several layers of polypropylene film. The thickness of the polyimide film used in the inner protective layer 6 is 0.02 mm to 0.05 mm, and the thickness of the polypropylene film used in the outer protective layer is 0.005 mm to 0.02 mm.

[0044] The specific dimensions and number of layers of the inner conductor 1, insulation layer, outer conductor and protective layer should be determined based on factors such as the actual required current carrying capacity and cable impedance.

[0045] Meanwhile, this invention also proposes a method for manufacturing a composite film-wrapped high-voltage pulse coaxial cable, comprising the following steps:

[0046] Step 1: Determine the number of wrapping layers for the insulation layer, outer conductor, and protective layer based on actual needs;

[0047] Step 2: Wrap the imide tape evenly around the inner conductor 1 according to the number of layers required by the design to form the inner insulation layer 2;

[0048] First, fix both ends of the smooth and clean inner conductor 1 to the wrapping device and straighten it. Install the polyimide tape reel on the eccentric wrapping device, aligning the inner conductor 1 with the rotation axis of the wrapping device. Then, start the wrapping device. As the inner conductor 1 moves along the rotation axis of the wrapping device, the polyimide tape is evenly wrapped around the inner conductor 1. By adjusting the rotation speed of the wrapping device, the wrapping pitch can be accurately controlled. However, during the wrapping process, air gaps 8 will form on the surface of the inner conductor. Continue wrapping until the polyimide tape reaches the end of the inner conductor 1. Cut the polyimide tape at the end position, reverse the traction mechanism, and pull the inner conductor 1 with partially wrapped polyimide tape back to the starting position. Repeat the aforementioned wrapping action until the required number of wrapping layers is reached. After the inner polyimide tape insulation layer 2 is wrapped, the corresponding number of polypropylene film, polyimide tape, aluminum foil, polyimide film, and polypropylene film are wrapped around the inner conductor 1 in the same way, specifically in the following steps:

[0049] Step 3: Wrap the polypropylene film evenly around the inner insulating layer 2 according to the number of layers required by the design to form the intermediate insulating layer 3;

[0050] Step 4: Wrap the imide tape evenly around the middle insulating layer 3 according to the number of layers required by the design to form the outer insulating layer 4;

[0051] Step 5: Wrap the aluminum foil evenly around the outer insulating layer 4 according to the number of layers required by the design to form the outer conductor 5;

[0052] Step 6: Wrap the polyimide film evenly around the outer conductor 5 according to the number of layers required by the design to form the inner protective layer 6;

[0053] Step 7: Wrap the polypropylene film evenly around the inner protective layer 6 according to the number of layers required by the design to form the outer protective layer 7, thus obtaining the wrapped high-voltage cable.

[0054] Step 8: The high-voltage cable from Step 7 is baked and heated, causing the polyimide tape to flow within the inner insulation layer 2 and the outer insulation layer 4, while the intermediate insulation layer 3 and the outer protective layer 7 formed by the polypropylene film are heat-shrinked and cured, thereby completing the manufacturing of the composite film-wrapped high-voltage pulse coaxial cable.

[0055] After the wrapping is completed, the entire high-voltage cable is heated in a baking device. Under high temperature conditions, the silicone in the inner insulation layer 2 begins to flow and fill the wrapping air gaps on the surface of the inner conductor 1. At the same time, the polypropylene film of the middle insulation layer 3 and the outer protective layer 7 is heat-shrinked and cured. On the one hand, this removes the residual gas between the layers of film during the wrapping process; on the other hand, it plasticizes the insulation layer and the protective layer in the high-voltage cable into a whole, which improves the breakdown voltage and insulation capacity of the high-voltage cable, and makes it less susceptible to moisture and contamination, thus improving its stability and practicality.

[0056] Example 2

[0057] Based on actual operating conditions, a film-wound high-voltage pulse coaxial cable with an operating condition of 75kV / 30μs pulse voltage and a pulse life exceeding 1 million cycles is required. Its specific design is as follows:

[0058] The inner conductor 1 is made of pure aluminum and has a diameter of 4.4 mm. The insulation layer and the protective layer are formed by wrapping a 0.055 mm thick polyimide tape to form the inner insulation layer 2, a 0.01 mm thick polypropylene film to form the middle insulation layer 3, and a 0.025 mm thick polyimide film to form the outer insulation layer 4. The inner protective layer 6 is formed by wrapping a 0.025 mm thick polyimide film, and the outer protective layer 7 is formed by wrapping a 0.01 mm thick polypropylene film.

[0059] The inner insulation layer 2, middle insulation layer 3, outer insulation layer 4, inner protective layer 6, and outer protective layer 7 use 2, 110, 2, 2, and 20 layers of wrapping film, respectively, with thicknesses of 0.11 mm, 1.05 mm, 0.11 mm, 0.05 mm, and 0.2 mm. The total insulation layer thickness is 1.27 mm, so the outer radius of the insulation layer is approximately 6.94 mm. The outer conductor 5 is wrapped with 4 layers of 0.015 mm thick aluminum foil, with a total thickness of 0.06 mm. Therefore, the diameter of the entire high-voltage pulse cable is 7.56 mm. After determining the dimensions, the polyimide film, polypropylene film, and aluminum foil are sequentially wrapped onto the inner conductor 1 according to the manufacturing method of the composite film-wrapped high-voltage pulse coaxial cable in Example 1, as per the design requirements. Then, the completed high-voltage cable is placed in a baking device and heated to 125°C in stages over approximately 16 hours, and then cooled to room temperature, so that the intermediate insulation layer and outer protective layer formed by the polypropylene film are plasticized into a whole, thereby completing the manufacturing of the composite film-wrapped high-voltage pulse coaxial cable.

[0060] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A composite film-wound high-voltage pulse coaxial cable, comprising an inner conductor (1) and an insulating layer, an outer conductor, and a protective layer wound sequentially from the inside to the outside on the inner conductor (1), characterized in that: The inner conductor (1) is a cylindrical metal rod; the insulation layer includes an inner insulation layer (2), a middle insulation layer (3) and an outer insulation layer (4) wound from the inside to the outside. The inner insulation layer (2) and the outer insulation layer (4) are both formed by wrapping polyimide tape, and the middle insulation layer (3) is formed by wrapping several layers of polypropylene film. The inner insulating layer (2) and the outer insulating layer (4) each have a wrapping layer of not less than 1 layer; the outer conductor (5) is formed by wrapping with aluminum foil; The protective layer consists of an inner protective layer (6) and an outer protective layer (7) wound sequentially from the inside to the outside. The inner protective layer (6) is formed by wrapping several layers of polyimide film, and the outer protective layer (7) is formed by wrapping several layers of polypropylene film. The polyimide tape is composed of a polyimide film and silicone. The fluidity of the silicone at high temperature is used to fill the spiral air gap formed by the film wrapping, thereby reducing the probability of corona discharge on the surface of the inner conductor (1).

2. The composite film-wrapped high-voltage pulse coaxial cable according to claim 1, characterized in that: The inner insulating layer (2) and the outer insulating layer (4) have 2 to 4 layers, and the polyimide tape used in the inner insulating layer (2) and the outer insulating layer (4) has a thickness of 0.03 mm to 0.06 mm.

3. The composite film-wrapped high-voltage pulse coaxial cable according to claim 2, characterized in that: The thickness of the polypropylene film used in the intermediate insulating layer (3) and the outer protective layer (7) is 0.005 mm to 0.02 mm.

4. The composite film-wrapped high-voltage pulse coaxial cable according to claim 3, characterized in that: The thickness of the aluminum foil used in the outer conductor (5) is 0.01 mm to 0.02 mm.

5. The composite film-wrapped high-voltage pulse coaxial cable according to claim 4, characterized in that: The inner conductor (1) is made of pure aluminum.

6. The composite film-wrapped high-voltage pulse coaxial cable according to claim 5, characterized in that: The thickness of the polyimide film used in the inner protective layer (6) is 0.02 mm to 0.05 mm.

7. The composite film-wrapped high-voltage pulse coaxial cable according to claim 6, characterized in that: The number of wrapping layers of the intermediate insulation layer (3) is determined according to the actual current carrying capacity and cable impedance requirements.

8. A method for manufacturing a composite film-wrapped high-voltage pulse coaxial cable according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Determine the number of wrapping layers for the insulation layer, outer conductor, and protective layer based on actual needs; Step 2: Wrap the polyimide tape evenly around the inner conductor (1) according to the number of layers required by the design to form the inner insulation layer (2). Step 3: Wrap the polypropylene film evenly around the inner insulating layer (2) according to the number of layers required by the design to form the intermediate insulating layer (3). Step 4: Wrap the polyimide tape evenly around the middle insulating layer (3) according to the number of layers required by the design to form the outer insulating layer (4); Step 5: Wrap the aluminum foil evenly around the outer insulating layer (4) according to the number of layers required by the design to form the outer conductor (5); Step 6: Wrap the polyimide film evenly around the outer conductor (5) according to the number of layers required by the design to form an inner protective layer (6). Step 7: Wrap the polypropylene film evenly around the inner protective layer (6) according to the number of layers required by the design to form the outer protective layer (7), and obtain the high-voltage cable after wrapping. Step 8: The high-voltage cable from Step 7 is baked and heated, causing the polyimide tape to flow within the inner insulation layer (2) and outer insulation layer (4) formed, while the intermediate insulation layer (3) and outer protective layer (7) formed by the polypropylene film are heat-shrinked and cured, thereby completing the manufacturing of the composite film-wrapped high-voltage pulse coaxial cable.

9. The method for manufacturing a composite film-wrapped high-voltage pulse coaxial cable according to claim 8, characterized in that: The baking temperature in step eight is 120℃~130℃.

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