A compression molding method for preparing a nonlinear conductive coating of a DC GIL insulator

Abstract

The present application relates to a kind of direct current GIL insulator nonlinear conductance coating compression moulding preparation method, by pressing insulator model in insulator mould to form certain thickness of conductance coating in insulator mould, then pouring insulator, so that nonlinear conductance coating is attached on the surface of insulator.Nonlinear conductance coating can self-adaptively homogenize electric field intensity of insulator surface, reduce insulator surface electric field distortion, reduce the probability of surface flashover occurrence.The method improves the surface smoothness and uniformity of nonlinear conductance coating by controlling the smoothness of insulator model surface, improving the vacuum degree of nonlinear conductance material, controlling the uniform stress of model, and further pouring insulator to make the coating completely combined on the surface of epoxy resin insulator, regulates the electric field intensity of insulator surface during the operation of coating insulator, suppresses electric field distortion, and improves the electrical endurance of insulator.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage equipment insulation technology, specifically relating to a molding method for preparing a nonlinear conductive coating on a DC GIL insulator. This method is used to prepare a uniform and smooth nonlinear conductive coating on the surface of the insulator to regulate the electric field distribution on the surface of the insulator and suppress electric field distortion. Background Technology

[0002] High-voltage direct current gas-insulated transmission lines (HVDC GILs) have promising applications in long-distance, high-capacity power transmission due to their advantages such as high transmission capacity, low transmission loss, high safety performance, and environmental friendliness. Insulators are crucial insulating components in HVDC GILs, playing key roles in mechanical support and electrical insulation; their insulation performance is closely related to the safe operation of the HVDC GIL.

[0003] In DC GILs, surface electric field distortion of the insulator is one of the main causes of insulation failure. The DC GIL contains a three-way interface between the insulator, the metallic conductor, and the insulating gas. Significant electric field distortion occurs at this location due to abrupt changes in dielectric parameters, leading to partial discharge and surface flashover. To suppress local electric field distortion in the insulator, various electric field control techniques have been proposed in the prior art, including optimizing the shielding electrode structure and adding shielding rings. However, these methods make the DC GIL structure more complex or may introduce new electric field distortions at other locations.

[0004] Nonlinear conductive composite materials are intelligent electric field-controlled materials whose conductivity exhibits nonlinear characteristics with respect to electric field strength. When the electric field strength is within the nonlinear region of the material, the conductivity increases sharply with increasing electric field strength, thereby reducing the resistive electric field strength in that area and achieving adaptive adjustment of the field strength. Applying a nonlinear conductive material coating to the surface of an insulator can alter its surface electrical properties, significantly suppressing surface electric field distortion and effectively reducing surface flashover.

[0005] Existing methods for preparing nonlinear conductive coatings for insulators mainly include brush coating, air spraying, electrostatic spraying, impregnation, and centrifugation. Brush coating is simple to operate but the coating thickness is difficult to control, resulting in poor surface uniformity. Air spraying suffers from problems such as paint splashing, easy formation of bubbles within the coating, and low surface smoothness. Electrostatic spraying requires specialized equipment, has complex process parameters, and for high-filler systems in nonlinear conductive coatings, uniformity is difficult to guarantee. Impregnation involves immersing the insulator in the coating; the coating thickness is controlled by the coating viscosity and dripping time, making precise control impossible, and the coating surface is prone to sagging defects. Centrifugation is suitable for rotating insulators, but its applicability is limited for insulators with complex shapes.

[0006] In addition, most existing coating preparation methods involve coating the surface of an already formed insulator. The interfacial bonding strength between the coating and the insulator body is limited, and problems such as coating peeling and cracking may occur during long-term operation, affecting the long-term reliability of the insulator.

[0007] Therefore, there is an urgent need to develop a method for preparing a nonlinear conductive coating that is simple to operate, has good coating uniformity, a smooth surface, controllable thickness, and high bonding strength with the insulator body. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a molding method for preparing a nonlinear conductive coating for DC GIL insulators. This invention utilizes a polytetrafluoroethylene (PTFE) insulator model of the same size as the insulator to be manufactured. The nonlinear conductive coating material is pressed into the insulator mold to form a nonlinear conductive coating with uniform thickness and a smooth surface. Then, the insulator body material is directly poured in, achieving integral curing and molding of the coating and the insulator body.

[0009] The technical solution adopted in this invention is as follows: A method for preparing a nonlinear conductivity coating for a DC GIL insulator by compression molding, comprising the following steps: 1) Preparation of nonlinear conductive coating materials: (1) Mix the epoxy resin matrix, silicon carbide filler, curing agent and diluent thoroughly in a mass ratio of 10:6:4:5; (2) The mixture was stirred by motor for 5 min, and then degassed under vacuum at -0.1 MPa for 10 min to obtain a nonlinear conductive coating material; 2) Preparation of nonlinear conductive coating: (1) Process a polytetrafluoroethylene insulator model with the same dimensions as the insulator to be manufactured, wherein the outer contour of the model is consistent with the inner contour of the insulator mold; (2) Coat the surface of the insulator mold with a release agent, and put the insulator mold and the polytetrafluoroethylene insulator model into the oven at the same time, preheat at 140°C for 1 h and then take them out. (3) Fix the preheated polytetrafluoroethylene insulator model on a sliding table that can move up and down and left and right in space, and place the preheated insulator mold below the insulator model; use the controller to adjust the position of the insulator model left and right so that the line connecting the center of the insulator model and the insulator mold is 90° with the horizontal plane. (4) The nonlinear conductivity coating material obtained in step 1) is evenly spread on the surface of the preheated insulator mold; (5) Use the controller to operate the slide table to move the insulator model down until the insulator model is embedded in the mold groove. Control the distance between the lower surface of the model and the upper surface of the insulator mold to the target coating thickness, and hold for 30 seconds to make the coating material evenly distributed on the mold surface and form a smooth surface. (6) Use the controller to move the insulator model upward until the model is completely removed from the mold, and let the mold stand until the coating is cured; 3) Fabrication of nonlinear conductive coated insulators: (1) Preheat epoxy resin, alumina filler and curing agent at 140°C for 1 h, and then mix them thoroughly at a mass ratio of 10:25:4; (2) Stirring with a motor for 0.5 h, and then degassing under vacuum at -0.1 MPa for 1 h; (3) The epoxy resin / alumina composite material obtained in step (2) is subjected to heat treatment by heating at 140°C for 0.5 h; (4) The heat-treated composite material is slowly injected into the insulator mold with the solidified nonlinear conductive coating, and heated at 140°C for 12 h to solidify, so that the nonlinear conductive coating and the insulator body are integrally formed.

[0010] Preferably, the epoxy resin in steps 1) and 3) is a bisphenol A type epoxy resin.

[0011] Preferably, the silicon carbide filler in step 1) is rod-shaped silicon carbide particles with an average length of 12 μm. The blocky silicon carbide particles readily form a conductive network within the epoxy resin matrix, causing the coating conductivity to exhibit a significant nonlinear change with the electric field strength.

[0012] Preferably, the curing agent in steps 1) and 3) is polyamide resin.

[0013] Preferably, the diluent in step 1) is ethyl acetate.

[0014] Preferably, the target coating thickness in step (5) of step 2) is 0.1 mm.

[0015] Preferably, the release agent in step (2) of step 2) is a silicone oil-based release agent.

[0016] Preferably, the coating curing conditions in step (6) of step 2) are: static curing at room temperature for 0.5 h.

[0017] Preferably, the slide in step (3) of step 2) is an electric servo slide with a positioning accuracy of no more than 0.01mm.

[0018] The present invention also provides a nonlinear conductivity coating for DC GIL insulators prepared by the above method, wherein the coating has a uniform thickness, a thickness deviation of no more than ±5%, and a surface roughness Ra of no more than 0.5 μm.

[0019] The present invention also provides a DC GIL insulator, comprising an insulator body and a nonlinear conductive coating integrally formed by the above method, wherein the nonlinear conductive coating is located on the surface of the insulator body, and the conductivity of the nonlinear conductive coating changes nonlinearly with the increase of electric field strength.

[0020] The beneficial effects of this invention are as follows: 1. Compression molding method ensures coating surface smoothness: This invention uses a smooth PTFE insulator model as the compression molding tool. The model has a high surface finish, and PTFE has excellent demolding properties. During the compression molding process, the lower surface of the model is in full contact with and pressed against the coating material, allowing the upper surface of the coating to replicate the smooth morphology of the model surface. This significantly improves the surface finish of the coating and avoids the surface roughness problems caused by spraying and brushing methods.

[0021] 2. Precise control of coating thickness: This invention uses a controller to precisely manipulate the slide table, controlling the distance between the lower surface of the insulator model and the upper surface of the insulator mold to achieve the target coating thickness. Due to the high positioning accuracy of the slide table (no more than 0.01 mm), precise control of the coating thickness can be achieved, resulting in good coating thickness uniformity with a thickness deviation of no more than ±5%. Compared with spraying and dipping methods, the thickness control accuracy of this invention is significantly improved.

[0022] 3. Reduced internal air bubbles in the coating: During the coating material preparation process, the present invention performs vacuum degassing (-0.1 MPa, 10 min) to remove most air bubbles. During the molding process, the insulator mold applies uniform pressure to the coating material, further expelling residual air bubbles and improving the coating's density. Compared to the problem of air entrapment during the coating formation process in spraying methods, the present invention significantly reduces the internal air bubble content of the coating.

[0023] 4. High bonding strength between the coating and the insulator body: This invention pre-fabricates a nonlinear conductive coating within a mold. After the coating cures, the insulator body material (epoxy resin / alumina composite material) is directly poured into the same mold. This allows the coating and the insulator body to form a chemical bond during the same curing process, achieving integral molding. Compared to methods that apply a coating to the surface of a pre-formed insulator, this invention provides a higher bonding strength between the coating and the body interface, resulting in better long-term operational reliability.

[0024] 5. Simple and convenient operation: The molding method of the present invention has a simple preparation process. It only requires controlling the model position, downward movement distance and holding time to complete the coating preparation. It does not require complicated spraying equipment or precise spraying process parameter control, which is convenient for industrial production.

[0025] 6. Adaptive Electric Field Control: The nonlinear conductive coating prepared in this invention uses epoxy resin as the matrix and silicon carbide as the filler. The conductivity of the coating exhibits a nonlinear change with increasing electric field strength. During DC GIL operation, when the local electric field strength on the insulator surface is high, the conductivity of the coating in that region increases sharply, automatically homogenizing the surface electric field distribution, suppressing electric field distortion caused by structures or foreign metal particles in the DC GIL, and improving the insulator's dielectric strength and surface flashover voltage. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process for preparing nonlinear coated insulators using the compression molding method of the present invention; Figure 2 This is a physical image of a nonlinear coated insulator manufactured using the molding method of this invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are provided to enable those skilled in the art to better understand the invention and do not constitute any limitation on the invention.

[0028] Example 1 This embodiment provides a molding method for preparing a nonlinear conductivity coating on a DC GIL basin insulator. The specific steps are as follows: 1) Preparation of nonlinear conductive coating materials: (1) Weigh 100 g of bisphenol A type epoxy resin, 60 g of blocky silicon carbide filler with an average length of 12 μm, 40 g of polyamide resin curing agent and 50 g of ethyl acetate diluent, and put them into a stirring container and mix them thoroughly. (2) Turn on the motor and stir for 5 min to disperse the components evenly; then put the stirring container into a vacuum chamber and degas it for 10 min at a vacuum degree of -0.1 MPa to obtain the nonlinear conductive coating material.

[0029] 2) Preparation of nonlinear conductive coating: (1) A model of an insulator of the same size as the pot-shaped insulator to be made is made using polytetrafluoroethylene material. The outer contour of the model is consistent with the inner contour of the insulator mold, and the surface roughness Ra of the model is 0.2 μm. (2) Coat the inner surface of the insulator mold with a silicone oil-based release agent. Place the insulator mold and the polytetrafluoroethylene insulator model into the oven at the same time and preheat at 140°C for 1 hour before taking them out. (3) Fix the preheated polytetrafluoroethylene insulator model on the electric servo slide, which can move up and down and left and right in space with a positioning accuracy of 0.01 mm; place the preheated insulator mold directly below the insulator model; use the controller to adjust the position of the insulator model left and right so that the line connecting the center of the insulator model and the insulator mold is 90° with the horizontal plane. (4) The nonlinear conductivity coating material obtained in step 1) is evenly spread on the inner surface of the preheated insulator mold; (5) Use the controller to operate the slide table to slowly move the insulator model down at a speed of 5 mm / min until the insulator model is embedded in the mold groove. Control the distance between the lower surface of the model and the upper surface of the insulator mold to be 0.1 mm (i.e. the target coating thickness), and hold for 30 s to make the coating material evenly distributed on the inner surface of the mold and form a smooth surface. (6) Use the controller to operate the slide to move the insulator model upward until the model is completely removed from the mold; let the mold stand at room temperature for 0.5 h to allow the coating to fully cure.

[0030] 3) Fabrication of nonlinear conductive coated insulators: (1) Weigh 100 g of bisphenol A type epoxy resin, 250 g of alumina filler and 40 g of polyamide resin curing agent, put them in an oven and preheat them at 140°C for 1 h, then take them out and mix them thoroughly. (2) Stir evenly with a motor for 0.5 h, and then degas under vacuum at -0.1 MPa for 1 h; (3) Heat treatment was performed by heating the vacuum degassed epoxy resin / alumina composite material at 140℃ for 0.5 h; (4) The heat-treated composite material is slowly injected into the insulator mold with the solidified nonlinear conductive coating, and then heated at 140°C for 12 h to solidify, so as to obtain a DC GIL basin insulator with the nonlinear conductive coating and the insulator body integrally formed.

[0031] Comparative Example 1 (Air Spraying Method) As a comparative example, a nonlinear conductive coating insulator was prepared using the existing air spraying method: (1) Bisphenol A type epoxy resin, polyamide resin curing agent and blocky silicon carbide particles with an average length of 12 μm are mixed in a mass ratio of 100:60:60 and stirred thoroughly to obtain EP / SiC solution; (2) Use an air spray gun to evenly spray the coating solution onto the surface of the mold, and control the spraying time to make the coating thickness about 500 μm; (3) Heat the mold at 120°C to accelerate the gelation of the coating; (4) Pour the EP / Al2O3 solution into the mold and cure it at 120°C for 10 h.

[0032] Performance Testing and Comparison Performance tests were conducted on the nonlinear conductive coating insulators prepared in Example 1 (molding method) and Comparative Example 1 (air spraying method): 1. Coating thickness uniformity test: Select 10 measurement points on the surface of the insulator and use a coating thickness gauge to measure the coating thickness.

[0033] Example 1: The coating thickness is 0.10 mm, and the thickness deviation at each measurement point is ±3%; Comparative Example 1: The coating thickness is 0.48~0.52 mm, and the thickness deviation at each measurement point is ±8%.

[0034] 2. Surface roughness test: The surface roughness Ra of the coating is measured using a surface roughness meter.

[0035] Example 1: Ra = 0.35 μm; Comparative Example 1: Ra = 1.8 μm.

[0036] 3. Detection of air bubbles inside the coating: After cutting the coating sample, observe the cross-section using a scanning electron microscope (SEM).

[0037] Example 1: The coating cross-section is dense, with almost no visible bubbles; Comparative Example 1: Bubbles with diameters of 10~50 μm are visible in the cross-section of the coating, with a bubble density of approximately 5 bubbles / mm².

[0038] 4. Coating-to-substrate adhesion strength test: The coating adhesion is tested using the cross-cut test.

[0039] Example 1: Cross-cut test grade 0 (coating cut edges are completely smooth, with no cells peeling off). Comparative Example 1: The cross-cut test grade is 1 (the coating has slight peeling at the cut edge, and the peeling area is less than 5%).

[0040] 5. Surface flashover voltage test: Apply a DC voltage to the insulator in dry air at 0.1 MPa, and increase the voltage at a rate of 1 kV / min until flashover occurs.

[0041] Example 1: The average surface flashover voltage is +28.5 kV; Comparative Example 1: The average surface flashover voltage is +24.2 kV; Uncoated conventional insulators: average surface flashover voltage is +18.6 kV.

[0042] Test results show that, compared with the air spraying method, the nonlinear conductive coating prepared by the molding method of the present invention has significant advantages such as good thickness uniformity, smooth surface, fewer internal bubbles, high bonding strength with the insulator body, and high surface flashover voltage.

[0043] Example 2 The difference between this embodiment and Embodiment 1 is that the target coating thickness in sub-step (5) of step 2) is 0.15 mm and the holding time is 45 s. The remaining steps are the same as in Embodiment 1.

[0044] Example 3 The difference between this embodiment and Embodiment 1 is that the mass ratio of epoxy resin matrix, silicon carbide filler, curing agent, and diluent in step 1) is 10:8:4:5. The remaining steps are the same as in Embodiment 1.

[0045] Example 4 The difference between this embodiment and Embodiment 1 is that the mass ratio of epoxy resin matrix, silicon carbide filler, curing agent, and diluent in step 1) is 10:7:4:5. The remaining steps are the same as in Embodiment 1.

[0046] Example 5 The difference between this embodiment and Embodiment 1 is that the mass ratio of epoxy resin matrix, silicon carbide filler, curing agent, and diluent in step 1) is 10:9:4:5. The remaining steps are the same as in Embodiment 1.

[0047] Example 6 The difference between this embodiment and Embodiment 1 is that the mass ratio of epoxy resin matrix, silicon carbide filler, curing agent, and diluent in step 1) is 10:10:4:5. The remaining steps are the same as in Embodiment 1.

[0048] Example 7 The difference between this embodiment and Embodiment 1 is that the mass ratio of epoxy resin matrix, silicon carbide filler, curing agent, and diluent in step 1) is 10:5:4:5. The remaining steps are the same as in Embodiment 1.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nonlinear conductivity coating for a DC GIL insulator using a die, characterized in that, Includes the following steps: 1) Preparation of nonlinear conductive coating materials: (1) Thoroughly mix the epoxy resin matrix, silicon carbide filler, curing agent and diluent; (2) The mixture is stirred by an electric motor and then degassed under vacuum to obtain a nonlinear conductive coating material; 2) Preparation of nonlinear conductive coating: (1) Process a polytetrafluoroethylene insulator model with the same dimensions as the insulator to be manufactured, wherein the outer contour of the model is consistent with the inner contour of the insulator mold; (2) Coat the surface of the insulator mold with a release agent, and place the insulator mold and the polytetrafluoroethylene insulator model into an oven at the same time, and take them out after preheating; (3) Fix the preheated polytetrafluoroethylene insulator model on a sliding table that can move up and down and left and right in a space, and place the preheated insulator mold below the insulator model; use the controller to adjust the position of the insulator model left and right so that the line connecting the center of the insulator model and the insulator mold is 90° with the horizontal plane. (4) The nonlinear conductivity coating material obtained in step 1) is evenly spread on the surface of the preheated insulator mold; (5) Use the controller to operate the slide table to move the insulator model down until the insulator model is embedded in the mold groove. Control the distance between the lower surface of the model and the upper surface of the insulator mold to the target coating thickness. Maintain this distance for a period of time to make the coating material evenly distributed on the mold surface and form a smooth surface. (6) Use the controller to move the insulator model upward until the model is completely removed from the mold, and let the mold stand until the coating is cured; 3) Fabrication of nonlinear conductive coated insulators: (1) Preheat the epoxy resin, alumina filler and curing agent and mix them thoroughly; (2) Motor stirring, vacuum degassing; (3) Heat-treat the epoxy resin / alumina composite material obtained in step (2); (4) The heat-treated composite material is slowly injected into the insulator mold with the solidified nonlinear conductive coating, and then heated and solidified so that the nonlinear conductive coating and the insulator body are integrally formed.

2. The method for preparing a compression mold according to claim 1, characterized in that, In step 1), the epoxy resin matrix, silicon carbide filler, curing agent and diluent are mixed in a mass ratio of 10:5-10:4:

5.

3. The method for preparing a compression mold according to claim 1, characterized in that, The silicon carbide filler in step 1) is blocky silicon carbide particles with an average length of 12 μm; the epoxy resin in steps 1) and 3) is bisphenol A type epoxy resin.

4. The method for preparing a compression mold according to claim 1, characterized in that, The curing agent in steps 1) and 3) is polyamide resin; the diluent in step 1) is ethyl acetate.

5. The method for preparing a compression mold according to claim 1, characterized in that, In step 3), epoxy resin, alumina filler and curing agent are mixed in a mass ratio of 10:25:

4.

6. The method for preparing a compression mold according to claim 1, characterized in that, The target coating thickness in step (5) of step 2) is 0.1 mm.

7. The method for preparing a compression mold according to claim 1, characterized in that, The release agent in step (2) of step 2) is a silicone oil-based release agent.

8. The method for preparing a compression mold according to claim 1, characterized in that, The coating curing conditions for sub-step (6) in step 2) are: static curing at room temperature for 0.5 h; The slide in step (3) of step 2) is an electric servo slide with a positioning accuracy of no more than 0.01 mm.

9. The nonlinear conductivity coating for a DC GIL insulator prepared by the molding method according to any one of claims 1 to 8, characterized in that, The coating has a uniform thickness with a thickness deviation of no more than ±5% and a surface roughness Ra of no more than 0.5 μm.

10. A DC GIL insulator, characterized in that, The invention includes an insulator body and a nonlinear conductive coating integrally formed by the method described in any one of claims 1 to 8, wherein the nonlinear conductive coating is located on the surface of the insulator body, and the conductivity of the nonlinear conductive coating changes nonlinearly with the increase of electric field strength.

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