High dielectric coating, insulator and preparation method for improving flashover strength

Abstract

The present invention relates to the technical field of improving the surface flashover strength of insulators, and in particular to a high-dielectric coating, an insulator, and a preparation method for improving the flashover strength. The high-dielectric coating includes a bottom layer and a top layer located outside the bottom layer; the bottom layer is an epoxy resin layer, and the raw materials for preparing the epoxy resin layer include epoxy resin; the top layer is a cyanoethyl cellulose layer, and the raw materials for preparing the cyanoethyl cellulose layer include cyanoethyl cellulose with different degrees of substitution; wherein the degree of substitution of the cyanoethyl group in the cyanoethyl cellulose is 1-2.8, and the relative dielectric constant of the cyanoethyl cellulose layer is 4-20. The high-dielectric coating uses cyanoethyl cellulose with a gradually decreasing degree of substitution of cyanoethyl groups from a high electric field region to a low electric field region, so that the corresponding relative dielectric constant decreases in a gradient, which plays a role in uniformizing the electric field on the surface of the insulator, thereby effectively improving the surface flashover strength.

Description

Technical Field

[0001] The present invention relates to the technical field of improving the surface flashover strength of insulators, and in particular to a high-dielectric coating for improving the flashover strength, an insulator and a preparation method thereof. Background Art

[0002] In many power equipment, the insulation structure serves both electrical insulation and mechanical support, necessitating the use of solid insulating media, leading to the widespread application of gas-solid composite insulation structures. For example, overhead transmission lines, metal-enclosed switchgear (GIS), and gas-insulated transmission lines (GIL) all employ gas-solid composite insulation structures. However, due to the significant differences in the dielectric properties of gases and solids, the electric field at the gas-solid interface is distorted, resulting in surface flashover strength far below the breakdown strength of the gas and solid, making it highly susceptible to surface flashover accidents in composite insulation. Therefore, improving surface flashover strength is crucial for ensuring the safe operation of power equipment.

[0003] Electric field distortion at the gas-solid interface is a major factor in reducing surface flashover strength. Researchers have proposed various methods to uniformly distribute the electric field. Among these methods, constructing functionally graded materials (FGMs)—materials whose dielectric constant varies with spatial position—holds great promise. Existing methods manipulate the effective dielectric constant of composite materials by doping insulating materials with high-dielectric-constant fillers such as BaTiO₃ and TiO₂. Changing the filler content effectively modulates the effective dielectric constant.

[0004] CN114502619B discloses a method for preparing a resin and a method for preparing an insulating structure, comprising: a filler mixing step of mixing a nanofiller with an epoxy resin at a ratio of 15 wt% or more to form a mixture; a shear mixing step of shear-mixing the mixture; a diluent mixing step of mixing a reactive diluent to reduce the viscosity of the epoxy resin with the mixture after the shear mixing step; and a curing agent mixing step of mixing an acid anhydride curing agent with the mixture after the diluent mixing step. The nanofiller comprises a non-conductive metal oxide.

[0005] However, the filler doping method has the following problems: ① The dielectric constant of the doped filler is different from that of the insulating material itself. Although it can improve the equivalent dielectric constant of the composite material, it distorts the electric field strength at the filler-insulating material interface and easily reduces the breakdown strength of the composite insulating material; ② In order to obtain a high equivalent dielectric constant, the filler doping content is usually very high, which can easily affect the mechanical properties of the composite material.

[0006] Based on the above situation, the insulation structure of the existing power equipment cannot simultaneously achieve uniform electric field distribution and prevent local electric field distortion and mechanical strength reduction, which are technical problems that need to be solved urgently. Summary of the Invention

[0007] In order to solve the above-mentioned technical problems, the present invention provides a high dielectric coating for improving flashover strength, wherein the high dielectric coating comprises a bottom layer and a top layer located outside the bottom layer;

[0008] The bottom layer is an epoxy resin layer, and the raw materials for preparing the epoxy resin layer include epoxy resin;

[0009] The top layer is a cyanoethyl cellulose layer, and the raw materials for preparing the cyanoethyl cellulose layer include cyanoethyl cellulose with different degrees of substitution;

[0010] The substitution degree of cyanoethyl groups in cyanoethyl cellulose is 1-2.8, and the relative dielectric constant of the cyanoethyl cellulose layer is 4-20.

[0011] Furthermore, the cyanoethyl cellulose layer is divided into three overlapping sections: a first section of a high-substitution cyanoethyl cellulose layer, a second section of a medium-substitution cyanoethyl cellulose layer, and a third section of a low-substitution cyanoethyl cellulose layer.

[0012] The thickness of the first high-substituted cyanoethyl cellulose layer is greater than that of the second medium-substituted cyanoethyl cellulose layer, and the thickness of the second medium-substituted cyanoethyl cellulose layer is greater than that of the third low-substituted cyanoethyl cellulose layer.

[0013] Furthermore, the thickness of the high dielectric coating gradually decreases from the high electric field region to the low electric field region, that is, the thickness of the high dielectric coating gradually decreases from the first section of the high-substitution cyanoethyl cellulose layer to the second section of the medium-substitution cyanoethyl cellulose layer, and then decreases from the second section of the medium-substitution cyanoethyl cellulose layer to the third section of the low-substitution cyanoethyl cellulose layer.

[0014] Furthermore, the maximum thickness of the top layer does not exceed 1 mm.

[0015] Furthermore, the thickness of the bottom layer is 50-200 μm.

[0016] Furthermore, the degree of substitution of cyanoethyl groups in the first section of high-substitution cyanoethyl cellulose layer is greater than 2.4 and less than or equal to 2.8, and the relative dielectric constant is greater than 13 and less than or equal to 20;

[0017] In the second section, the degree of substitution of cyanoethyl groups in the cyanoethyl cellulose layer is greater than 1.6 and less than or equal to 2.4, and the relative dielectric constant is greater than 7 and less than or equal to 13;

[0018] The degree of substitution of cyanoethyl groups in the third low-substitution cyanoethyl cellulose layer is greater than or equal to 1 and less than or equal to 1.6, and the relative dielectric constant is greater than or equal to 4 and less than or equal to 7.

[0019] Furthermore, the coating lengths of the first section of high-substitution cyanoethyl cellulose layer, the second section of medium-substitution cyanoethyl cellulose layer and the third section of low-substitution cyanoethyl cellulose layer are equal.

[0020] Furthermore, the first section of the high-substituted cyanoethyl cellulose layer is located at the triple junction formed by the electrode, solid and gas.

[0021] Furthermore, the epoxy resin is bisphenol A glycidyl ether.

[0022] Furthermore, the raw materials for preparing the epoxy resin layer also include a curing agent.

[0023] Furthermore, the curing agent is one of methyl tetrahydrophthalic anhydride, phthalic anhydride, methyl hexahydrophthalic anhydride, and phthalic anhydride.

[0024] Furthermore, the raw materials for preparing the epoxy resin layer also include an accelerator.

[0025] Furthermore, the accelerator is 2,4,6-triphenol.

[0026] Furthermore, when the raw materials for preparing the bottom layer include epoxy resin, curing agent, and accelerator, the mass ratio of epoxy resin, curing agent, and accelerator is (100-110): (70-90): (1-20).

[0027] The present invention further provides an insulator, comprising an insulator body and the high dielectric coating for improving flashover strength located on the surface of the insulator body.

[0028] Furthermore, the insulator body is one of a pot insulator, a post insulator or an insulator string.

[0029] Furthermore, the relative dielectric constant of the insulator body is 4, and the relative dielectric constant of the high dielectric coating for improving the flashover strength is 4-20.

[0030] Furthermore, when the insulator body is a pot-type insulator and a post insulator, it is used for metal-enclosed switchgear (GIS) and gas-insulated transmission lines (GIL) with rated voltages of 126kV, 252kV, 550kV and 1100kV;

[0031] Furthermore, when the insulator body is an insulator string, it is used for overhead transmission lines with rated voltages of 110kV, 220kV, 500kV, 750kV and 1000kV.

[0032] In air at one atmospheric pressure, the Weibull scale parameter of the surface flashover voltage of the insulator including the high dielectric coating for improving the flashover strength is increased by at least 5.2% compared to the surface flashover voltage of the insulator not including the high dielectric coating for improving the flashover strength;

[0033] In air at three atmospheres, the Weibull scale parameter of the surface flashover voltage of the insulator including the high dielectric coating for improving flashover strength increases by at least 13.8% compared with the insulator not including the high dielectric coating for improving flashover strength.

[0034] Furthermore, in air at one atmospheric pressure, the surface flashover voltage of the insulator including the high dielectric coating for improving the flashover strength is 24.89-27.82 kV;

[0035] In air at three atmospheres, the surface flashover voltage of the insulator including the high dielectric coating for improving the flashover strength is 44.61-48.83 kV.

[0036] Furthermore, the raw material for preparing the bottom layer is the same as the raw material for preparing the insulator.

[0037] The present invention also provides a method for preparing the above-mentioned insulator, comprising the following steps:

[0038] Step 1: Stir epoxy resin to obtain a base layer solution, and evenly apply the base layer solution on the surface of the insulator body to obtain an insulator containing the base layer;

[0039] Step 2: preparing cyanoethyl cellulose with different degrees of substitution by a homogeneous method and / or a heterogeneous method, respectively obtaining a first section of high-degree-of-substitution cyanoethyl cellulose, a second section of medium-degree-of-substitution cyanoethyl cellulose, and a third section of low-degree-of-substitution cyanoethyl cellulose;

[0040] Step 3, dissolving the cyanoethyl cellulose with different degrees of substitution prepared in Step 2 in an organic solvent respectively to obtain a first top layer solution, a second top layer solution, and a third top layer solution;

[0041] Step 4: coating the first top layer solution on the bottom layer near the triple junction formed by the electrode, solid and gas, and then coating the second top layer solution and the third top layer solution in sequence to obtain an insulator with the top layer coated on the bottom layer;

[0042] Step 5: Dry the insulator obtained in step 4.

[0043] Furthermore, the homogeneous method in step 2 is to prepare cyanoethyl cellulose with different degrees of substitution by Michael addition reaction of cellulose solution and acrylonitrile, and the specific steps are as follows:

[0044] Cellulose is dissolved in a 1M sodium hydroxide / 6M urea solution to prepare a cellulose solution with a cellulose concentration of 5 wt%; the cellulose solution is placed in an ice-water bath, acrylonitrile is slowly added dropwise during stirring, and the reaction is continued for 10 hours; after the reaction, the mixture is neutralized with acetic acid, centrifuged, and washed to obtain cyanoethyl cellulose; wherein the cellulose is microcrystalline cellulose.

[0045] The degree of substitution is controlled by changing the molar ratio of glucose units to acrylonitrile in cellulose. For example, when the molar ratio is 1:4, 1:6, 1:7 and 1:11, the degree of substitution is 1.5, 1.8, 1.9 and 2.0.

[0046] Furthermore, in step 2, the heterogeneous method is to activate cellulose to obtain alkali cellulose, and the alkali cellulose undergoes a Michael addition reaction with acrylonitrile to obtain cyanoethyl cellulose, and the specific steps are:

[0047] The cellulose was dissolved in a 1M sodium hydroxide / 6M potassium thiocyanate solution to prepare a cellulose solution with a cellulose concentration of 5 wt%, which was then filtered and pressed dry. The resulting raw material was reacted with excess acrylonitrile for a certain period of time, and then centrifuged and washed to obtain cyanoethyl cellulose.

[0048] The degree of substitution is controlled by changing the reaction time of cellulose and acrylonitrile, for example, the degrees of substitution when the reaction time is 70, 80, 90, 120, and 200 min are 1.7, 2.0, 2.2, 2.4, and 2.7.

[0049] Furthermore, in step 3, the organic solvent is one of N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0050] Furthermore, the concentration of the first section of highly substituted cyanoethyl cellulose in the first top layer solution is 0.05-0.2 g / mL;

[0051] The concentration of the substituted cyanoethyl cellulose in the second section of the second top layer solution is 0.05-0.2 g / mL;

[0052] The concentration of the third section low-substituted cyanoethyl cellulose in the third top layer solution is 0.05-0.2 g / mL.

[0053] Furthermore, the concentrations of cyanoethyl cellulose in the first top layer solution, the second top layer solution, and the third top layer solution are the same or different.

[0054] Furthermore, the drying temperature in step 5 is 80-100° C., and the drying time is 2-4 hours.

[0055] Furthermore, during the drying process in step 5, the high voltage electrode side of the insulator is placed downward, and under the action of gravity, a top layer structure is formed whose thickness gradually decreases from the high electric field area to the low electric field area.

[0056] Furthermore, continue coating on top of the top layer dried in step 5 to meet the thickness requirement during use. After each coating is completed, drying is required before the next coating can be performed.

[0057] The present invention also provides an assembly structure, which includes the above-mentioned insulator, a central high-voltage electrode and a grounding shell electrode.

[0058] The beneficial effects of the present invention are:

[0059] 1. A high-dielectric coating for improving flashover strength according to the present invention comprises a bottom layer and a top layer located outside the bottom layer, wherein the top layer is a cyanoethyl cellulose layer, and the raw materials for preparing the cyanoethyl cellulose layer include cyanoethyl cellulose with different degrees of substitution; wherein the degree of substitution of cyanoethyl groups in the cyanoethyl cellulose is 1-2.8, and the relative dielectric constant of the cyanoethyl cellulose layer is 4-20; the high-dielectric coating prepared by the present invention uses cyanoethyl cellulose with a gradually decreasing degree of substitution of cyanoethyl groups from a high electric field region to a low electric field region, so that the corresponding relative dielectric constant decreases in a gradient, thereby achieving a uniform electric field on the surface of the insulator, thereby effectively improving the surface flashover strength;

[0060] That is, a pure polymer material with a flexibly adjustable dielectric constant is used. By coating high, medium, and low electric field regions with polymer materials with successively decreasing relative dielectric constants, the electric field distribution can be uniformed, effectively solving problems such as local electric field distortion and reduced mechanical strength caused by filler doping.

[0061] 2. The present invention uses cyanoethyl cellulose with different degrees of substitution to control the relative dielectric constant. Cyanoethyl cellulose is a pure polymer material. Compared with the currently widely used method of increasing the dielectric constant by doping fillers, the present invention method does not have the problems of local electric field distortion and reduced mechanical strength caused by filler doping;

[0062] 3. By coating the first section of high-substituted cyanoethyl cellulose with a high relative dielectric constant at the triple junction formed by the electrode, solid and gas, the electric field intensity at the triple junction can be effectively reduced, thereby suppressing the generation of gas discharge;

[0063] 4. The high dielectric coating prepared by the present invention comprises a double-layer structure of a bottom layer and a top layer. The bottom layer is made of the same epoxy resin as the insulator body to ensure that the coating can adhere well to the insulator body.

[0064] 5. The coating preparation process of the present invention is simple, and the coating method is applicable to insulator bodies with complex structures and suitable for large-scale production applications; it can effectively improve the surface flashover strength and guide the design and development of new functional gradient materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 is a structural schematic diagram of an assembly structure including an insulator and an electrode;

[0066] Figure 2 This is the electric field distribution diagram obtained by finite element simulation;

[0067] Figure 3 Taking the high dielectric coating prepared in Example 1 as an example, a graph of surface flashover voltage results in air at a certain pressure is shown;

[0068] Figure 4 Taking the high dielectric coating prepared in Example 1 as an example, the surface flashover voltage results in air at three pressures are shown;

[0069] Figure 5 This is the simulation result of the electric field distribution of the doped BaTiO3 high dielectric constant filler material;

[0070] The labels in the figure are:

[0071] 1. Bottom layer; 2. First section of high-substitution cyanoethyl cellulose layer; 3. Second section of medium-substitution cyanoethyl cellulose layer; 4. Third section of low-substitution cyanoethyl cellulose layer; 5. Center high-voltage electrode; 6. Grounding shell electrode; 7. Basin insulator. DETAILED DESCRIPTION

[0072] Example 1

[0073] like Figure 1 FIG. 1 is a schematic diagram of an assembly structure including an insulator and an electrode. The insulator includes an insulator body and a high-dielectric coating located on the surface of the insulator body to improve flashover strength. The insulator body is a pot-type insulator 7. The high-dielectric coating includes a bottom layer 1 and a top layer located outside the bottom layer 1. The relative dielectric constant of the pot-type insulator 7 is 4.

[0074] The bottom layer 1 is an epoxy resin layer. The raw material for preparing the epoxy resin layer includes epoxy resin. In this embodiment, it is bisphenol A glycidyl ether, which is the same material as the pot-type insulator 7. It is used to ensure that the bottom layer 1 can be well adhered to the pot-type insulator 7 body.

[0075] The electrode assembly structure includes a central high-voltage electrode 5 and a grounded shell electrode 6.

[0076] The raw materials for preparing the epoxy resin layer also include a curing agent, methyl tetrahydroanhydride, and an accelerator, 2,4,6-triphenol. The curing temperature and speed of the epoxy resin can be controlled by changing the content of the accelerator. In this embodiment, the mass ratio of the epoxy resin, the curing agent, and the accelerator is 10:8:1.

[0077] The top layer is a cyanoethyl cellulose layer, and the raw materials for preparing the cyanoethyl cellulose layer include cyanoethyl cellulose with different degrees of substitution;

[0078] The substitution degree of cyanoethyl groups in cyanoethyl cellulose is 1.5-2.7, and the relative dielectric constant of the cyanoethyl cellulose layer is 6-18.

[0079] In this embodiment, the cyanoethyl cellulose layer is divided into three overlapping sections: a first section of high-substitution cyanoethyl cellulose layer 2, a second section of medium-substitution cyanoethyl cellulose layer 3, and a third section of low-substitution cyanoethyl cellulose layer 4.

[0080] The thickness of the first high-substituted cyanoethyl cellulose layer 2 is greater than the thickness of the second high-substituted cyanoethyl cellulose layer 3, and the thickness of the second high-substituted cyanoethyl cellulose layer 3 is greater than the thickness of the third low-substituted cyanoethyl cellulose layer 4.

[0081] The thickness of the high dielectric coating gradually decreases from the high electric field region to the low electric field region, that is, the thickness of the high dielectric coating gradually decreases from the first section of the high-substitution cyanoethyl cellulose layer 2 to the second section of the medium-substitution cyanoethyl cellulose layer 3, and then decreases from the second section of the medium-substitution cyanoethyl cellulose layer 3 to the third section of the low-substitution cyanoethyl cellulose layer 4.

[0082] In this embodiment, the maximum thickness of the top layer is 1 mm, and the thickness of the bottom layer 1 is 100 μm.

[0083] Specifically, the degree of substitution of cyanoethyl groups in the first section of high-substitution cyanoethyl cellulose layer 2 is 2.7, and the relative dielectric constant is 18;

[0084] In the second section, the degree of substitution of cyanoethyl groups in the cyanoethyl cellulose layer 3 is 2.2, and the relative dielectric constant is 12;

[0085] The degree of substitution of cyanoethyl groups in the third low-substitution cyanoethyl cellulose layer 4 is 1.5, and the relative dielectric constant is 6.

[0086] In this embodiment, the coating lengths of the first section high-substituted cyanoethyl cellulose layer 2, the second section medium-substituted cyanoethyl cellulose layer 3 and the third section low-substituted cyanoethyl cellulose layer 4 are equal.

[0087] The first section of the high-substituted cyanoethyl cellulose layer 2 is located at the triple junction formed by the electrode, solid and gas.

[0088] This embodiment also provides a method for preparing the above-mentioned insulator, comprising the following steps:

[0089] Step 1: Evenly stir epoxy resin, curing agent, and accelerator to obtain a base solution, and evenly apply the base solution to the surface of the pot-type insulator 7 to obtain the pot-type insulator 7 containing the base layer 1. By increasing the accelerator content, the epoxy resin is given a certain room temperature curing ability to avoid the problem of easy flow of the epoxy resin after coating;

[0090] Step 2: preparing cyanoethyl cellulose with different degrees of substitution by a homogeneous method and a heterogeneous method, respectively obtaining a first section of high-degree-of-substitution cyanoethyl cellulose, a second section of medium-degree-of-substitution cyanoethyl cellulose, and a third section of low-degree-of-substitution cyanoethyl cellulose;

[0091] In this embodiment, the first section of high-substituted cyanoethyl cellulose and the second section of medium-substituted cyanoethyl cellulose are activated by a heterogeneous method in the prior art to obtain alkali cellulose, and the alkali cellulose undergoes a Michael addition reaction with acrylonitrile to obtain cyanoethyl cellulose. The specific steps are as follows:

[0092] The cellulose solution is dissolved in a 1M sodium hydroxide / 6M potassium thiocyanate solution to prepare a cellulose solution with a cellulose concentration of 5 wt%, which is then filtered and squeezed dry. The resulting raw material is reacted with excess acrylonitrile for a certain period of time, and then centrifuged and washed to obtain cyanoethyl cellulose.

[0093] The degree of substitution is controlled by changing the reaction time of cellulose and acrylonitrile, and the degrees of substitution are 2.2 and 2.7 when the reaction time is 90 and 200 min respectively;

[0094] The third stage of low-degree-of-substitution cyanoethyl cellulose is prepared by a homogeneous method in the prior art. The homogeneous method is to use a Michael addition reaction of a cellulose solution with acrylonitrile to prepare cyanoethyl cellulose with different degrees of substitution. The specific steps are as follows:

[0095] Dissolving cellulose in a 1M sodium hydroxide / 6M urea solution to prepare a cellulose solution with a cellulose concentration of 5 wt%; placing the cellulose solution in an ice-water bath, slowly adding acrylonitrile dropwise during stirring, and continuing the reaction for 10 hours; neutralizing the reaction mixture with acetic acid, centrifuging, and washing to obtain cyanoethyl cellulose; wherein the cellulose is microcrystalline cellulose;

[0096] The degree of substitution is controlled by changing the molar ratio of glucose units to acrylonitrile in cellulose. When the molar ratio of the glucose units to acrylonitrile is 1:4, the degree of substitution is 1.5.

[0097] The degree of substitution of cyanoethyl cellulose prepared using homogeneous and heterogeneous methods ranges from 1.5 to 2.7. Since cyanoethyl groups are strongly polar groups that enhance the material's dipole polarization strength, increasing the degree of substitution effectively increases the relative dielectric constant of cyanoethyl cellulose, allowing the relative dielectric constant to be flexibly controlled between 6 and 18. By increasing the degree of substitution of cyanoethyl groups, the relative dielectric constant of cyanoethyl cellulose is higher than that of common polymer materials such as epoxy resin and polyvinylidene fluoride, and its relative dielectric constant is close to that of BaTiO3 composite materials. Therefore, using cyanoethyl cellulose as a coating material can effectively reduce the surface electric field strength.

[0098] Step 3, dissolving the cyanoethyl cellulose with different degrees of substitution prepared in Step 2 in an organic solvent N,N-dimethylformamide respectively to obtain a first top layer solution, a second top layer solution, and a third top layer solution;

[0099] The concentration of the first section of highly substituted cyanoethyl cellulose in the first top layer solution was 0.1 g / mL;

[0100] The concentration of the substituted cyanoethyl cellulose in the second section of the second top layer solution was 0.1 g / mL;

[0101] The concentration of the third section of low-substituted cyanoethyl cellulose in the third top layer solution was 0.1 g / mL;

[0102] The concentration of cyanoethyl cellulose should not be too low. If it is too low, the viscosity of the mixed solution will be insufficient, and the solution will flow easily after being applied to the bottom layer 1. In addition, the concentration of cyanoethyl cellulose should not be too high. If it is too high, the viscosity will be too high, making it difficult to apply a uniform coating. After multiple experimental comparisons, the most suitable concentration of cyanoethyl cellulose is 0.1g / mL.

[0103] Step 4: coating the first top layer solution on the bottom layer 1 including the triple junction point formed by the electrode, solid and gas, and then coating the second top layer solution and the third top layer solution in sequence to obtain a pot-type insulator 7 with the top layer coated on the bottom layer 1;

[0104] Step 5: Dry the insulator obtained in step 4 at a temperature of 90° C. for 3 hours. During the drying process, the high-voltage electrode side of the basin-type insulator 7 is placed downward, and under the action of gravity, a top layer structure is formed in which the thickness gradually decreases from the high electric field region to the low electric field region. From the perspective of a uniform electric field, the use of a dielectric constant functional gradient material can achieve a uniform electric field effect, and the gradient change structure of the top layer thickness also has a uniform electric field effect. Therefore, the top layer in the present invention is actually a dual-gradient structure in which the relative dielectric constant and the coating thickness complement each other.

[0105] In some embodiments, coating is continued on top of the top layer dried in step 5 to meet the thickness requirement during use. Each coating needs to be dried before the next coating can be performed.

[0106] Through the above preparation and arrangement of the cyanoethyl cellulose coating, the relative dielectric constant of the top layer material gradually decreases from the high electric field region to the low electric field region, which plays the role of uniforming the electric field on the surface of the insulator.

[0107] Comparative Example 1

[0108] This comparative example is the pot-type insulator 7 in Example 1 without the high dielectric coating.

[0109] Test Example 1

[0110] An insulator electric field distribution simulation model was established for the insulators in Example 1 and Comparative Example 1, including steps such as establishing an insulator geometric model, setting the material dielectric constant, setting boundary conditions, meshing, and performing finite element calculations. The insulator geometric model was established based on the actual insulator and electrode dimensions, and the electric field strength was calculated using the following equation:

[0111]

[0112] Where, is the dielectric constant, E is the electric field strength, is the electric potential.

[0113] The high-voltage electrode potential is set to 10 kV, the ground electrode potential is 0, the relative dielectric constant of the pot insulator 7 is 4, and the relative dielectric constants of the first high-substitution cyanoethyl cellulose layer, the second medium-substitution cyanoethyl cellulose layer, and the third low-substitution cyanoethyl cellulose layer in Example 1 are set to 18, 12, and 6, respectively. The simulation area is divided into quadrilateral grids, and then the electric field distribution is calculated using the finite element method. Figure 2 This is the electric field distribution diagram obtained by finite element simulation. A scaled-down basin-type insulator structure is used in the simulation. The figure compares the electric field distribution results of Comparative Example 1, which only contains an insulator body, and Example 1, in which a high dielectric coating is coated on the surface of the insulator body. It can be seen that when Comparative Example 1 does not have a high dielectric coating, the maximum electric field intensity is as high as 17.5 kV / cm, located near the central high-voltage electrode; when a high dielectric coating is added to Example 1, the peak electric field is reduced to 15.6 kV / cm. In addition, in Example 1, the high dielectric coating reduces the electric field intensity throughout the entire surface area of ​​the insulator. The above results show that coating the surface of the insulator body with a high dielectric coating can even out the electric field distribution on the surface of the insulator, thereby improving the surface flashover strength.

[0114] Test Example 2

[0115] The flashover voltage of the insulators in Example 1 and Comparative Example 1 was tested at 0.5 kVs -1 The AC voltage is applied at a rising rate until flashover occurs, and the flashover voltage is analyzed using a two-parameter Weibull distribution. Figure 3 、 Figure 4 , as shown in Table 1 and Table 2. Figure 4 Table 1 and Table 2 are the measurement results in air at one atmospheric pressure. It can be seen that the Weibull scale parameter of the surface flashover voltage of the insulator in Comparative Example 1 is 25.2 kV, and the Weibull scale parameter of the flashover voltage of Example 1 increases to 26.5 kV after the high dielectric coating is applied, with an increase of 5.2%. In addition, the flashover voltages of the nine experiments in Example 1 are generally higher than the flashover voltages of Comparative Example 1. Figure 5 Table 2 shows the measurement results in air at three atmospheric pressures. The Weibull scale parameter for the surface flashover voltage of the insulator in Comparative Example 1 is 38.4 kV. After the high-dielectric coating is applied to Example 1, the Weibull scale parameter for the flashover voltage increases to 43.7 kV, an increase of 13.8%. Furthermore, the flashover voltages of all nine experiments in Example 1 are higher than those in Comparative Example 1. These results demonstrate that the introduction of a high-dielectric coating effectively enhances the surface flashover strength of the gas-solid composite insulation system, primarily due to the uniform electric field distribution achieved by the high-dielectric coating.

[0116] Table 1 Flashover voltage of insulators with and without coating at one atmosphere (kV)

[0117]

[0118] Table 2 Flashover voltage of insulators with and without coating at three atmospheres (kV)

[0119]

[0120] Comparative Example 2

[0121] In order to illustrate the electric field distortion inside the material after doping with high dielectric constant fillers, an electric field distribution simulation model is established, including the steps of establishing a geometric model, setting the material dielectric constant, setting boundary conditions, meshing, and finite element calculation. The size of the simulation area is set to , 9 BaTiO3 fillers are set in this area, and the electric field strength is calculated according to the following equation:

[0122]

[0123] Where, is the dielectric constant, E is the electric field strength, is the electric potential.

[0124] The high voltage electrode potential is set to 0.45V, the ground electrode potential is 0, the relative dielectric constant of the coating substrate area is 4, and the relative dielectric constant of the BaTiO3 filler is 975. The simulation results are as follows Figure 5 As shown, it can be seen that the electric field intensity on the upper and lower sides of the BaTiO3 filler increases significantly, indicating that the BaTiO3 filler will distort the electric field distribution in the coating matrix. This electric field enhancement effect will reduce the surface flashover strength and breakdown strength.

[0125] In summary, the high dielectric constant coating prepared by the present invention uses cyanoethyl cellulose with a gradually decreasing degree of substitution of cyanoethyl groups from the high electric field region to the low electric field region, so that the corresponding relative dielectric constant decreases in a gradient, which plays a role in uniformizing the electric field on the surface of the insulator, thereby effectively improving the surface flashover strength.

[0126] That is, by using a pure polymer material with a flexibly adjustable dielectric constant, and by coating polymer materials with successively decreasing relative dielectric constants in high, medium, and low electric field regions, the electric field distribution can be uniformed, and the problems of local electric field distortion and reduced mechanical strength caused by filler doping can be effectively solved.

[0127] In addition, the coating preparation process is simple, and the coating method is suitable for insulator bodies with complex structures and suitable for large-scale production applications; it can effectively improve the surface flashover strength and guide the design and development of new functional gradient materials.

[0128] It should be understood that the present invention is not limited to what has been described above and shown in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A high dielectric coating for improving flashover strength, characterized in that: The high dielectric coating comprises a bottom layer and a top layer located outside the bottom layer; The bottom layer is an epoxy resin layer, and the raw materials for preparing the epoxy resin layer include epoxy resin; The top layer is a cyanoethyl cellulose layer, and the raw materials for preparing the cyanoethyl cellulose layer include cyanoethyl cellulose with different degrees of substitution; The cyanoethyl cellulose layer is divided into three overlapping sections: a first section of a high-substitution cyanoethyl cellulose layer, a second section of a medium-substitution cyanoethyl cellulose layer, and a third section of a low-substitution cyanoethyl cellulose layer. The thickness of the first section high-substituted cyanoethyl cellulose layer is greater than the thickness of the second section medium-substituted cyanoethyl cellulose layer, and the thickness of the second section medium-substituted cyanoethyl cellulose layer is greater than the thickness of the third section low-substituted cyanoethyl cellulose layer. The degree of substitution of cyanoethyl groups in the first high-substitution cyanoethyl cellulose layer is greater than 2.4 and less than or equal to 2.8, and the relative dielectric constant is greater than 13 and less than or equal to 20; In the second section, the degree of substitution of cyanoethyl groups in the cyanoethyl cellulose layer is greater than 1.6 and less than or equal to 2.4, and the relative dielectric constant is greater than 7 and less than or equal to 13; The degree of substitution of cyanoethyl groups in the third low-substitution cyanoethyl cellulose layer is greater than or equal to 1 and less than or equal to 1.6, and the relative dielectric constant is greater than or equal to 4 and less than or equal to 7.

2. The high dielectric coating for improving flashover strength according to claim 1, characterized in that: The raw materials for preparing the epoxy resin layer also include a curing agent.

3. An insulator, characterized in that: The insulator comprises an insulator body and a high dielectric coating for improving flashover strength according to any one of claims 1 to 2 located on the surface of the insulator body.

4. A method for preparing the insulator according to claim 3, characterized in that: The steps include: Step 1: Stir epoxy resin to obtain a base layer solution, and evenly apply the base layer solution on the surface of the insulator to obtain an insulator containing the base layer; Step 2: preparing cyanoethyl cellulose with different degrees of substitution by a homogeneous method and / or a heterogeneous method, respectively obtaining a first section of high-degree-of-substitution cyanoethyl cellulose, a second section of medium-degree-of-substitution cyanoethyl cellulose, and a third section of low-degree-of-substitution cyanoethyl cellulose; Step 3, dissolving the cyanoethyl cellulose with different degrees of substitution prepared in Step 2 in an organic solvent respectively to obtain a first top layer solution, a second top layer solution, and a third top layer solution; Step 4: coating the first top layer solution on the bottom layer near the triple junction formed by the electrode, solid and gas, and then coating the second top layer solution and the third top layer solution in sequence to obtain an insulator with the top layer coated on the bottom layer; Step 5: Dry the insulator obtained in step 4.

5. The method for preparing an insulator according to claim 4, characterized in that: The organic solvent in step 3 is one of N,N-dimethylformamide, dimethylacetamide and dimethyl sulfoxide.

6. The method for preparing an insulator according to claim 4, characterized in that: The concentration of the first section of highly substituted cyanoethyl cellulose in the first top layer solution is 0.05-0.2 g / mL; The concentration of the substituted cyanoethyl cellulose in the second section of the second top layer solution is 0.05-0.2 g / mL; The concentration of the third section low-substituted cyanoethyl cellulose in the third top layer solution is 0.05-0.2 g / mL.

7. The method for preparing an insulator according to claim 4, characterized in that: The drying temperature in step 5 is 80-100° C. and the drying time is 2-4 hours.

8. An assembly structure, characterized in that: The assembly structure includes the insulator according to claim 3, a central high-voltage electrode and a grounded shell electrode.

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