Epoxy insulator and preparation method thereof

Abstract

The present invention relates to an epoxy insulator and a preparation method thereof, comprising an epoxy insulator body, wherein the surface of the epoxy insulator body is provided with a bottom layer, an intermediate layer and a surface layer stacked sequentially from the inside to the outside, wherein, by mass, the raw material composition of the bottom layer comprises 2-4 parts of nano-scale Al2O3 particles, 8-12 parts of epoxy resin, 6-7 parts of a first thermal curing agent, and 0.2-0.4 parts of a first silane coupling agent, the raw material composition of the intermediate layer comprises 1-2 parts of nano-scale Al2O3 particles, 0.5-0.7 parts of nano-scale SiO2 particles, 8-12 parts of epoxy resin, 6-7 parts of a second thermal curing agent, and 0.1-0.3 parts of a second silane coupling agent, and the raw material composition of the surface layer comprises 1-3 parts of nano-scale SiO2 particles, 8-12 parts of epoxy resin, and 6-7 parts of a third thermal curing agent. The epoxy insulator of the present invention has good surface electric field uniformity, high flashover voltage and excellent insulation performance.

Description

Technical Field

[0001] The invention relates to an epoxy insulator and a preparation method thereof, and belongs to the field of insulators. Background Art

[0002] As a core component of gas-insulated transmission lines (GILs), epoxy insulators (also known as epoxy resin insulators) perform the dual functions of electrical insulation and mechanical support. Under the continuous action of a DC electric field, charge accumulation easily occurs on the epoxy insulator surface, leading to distortion of the electric field distribution. Furthermore, due to long-term exposure to complex operating conditions, epoxy insulators also face a series of problems, such as surface contamination deposition and degradation of hydrophobicity. These factors pose a serious threat to the insulation reliability of electrical equipment. Therefore, in-depth research on effective methods to inhibit charge accumulation on the epoxy insulator surface is of great research value.

[0003] Ni Xiaoru (Ni Xiaoru. Research on the charge dissipation process and surface flashover characteristics of the gas-solid interface of DC GIL insulator nanocoating [D]. North China Electric Power University (Beijing), 2020. DOI: 10.27140 / d.cnki.ghbbu.2020.000890.) used nano-SiC, montmorillonite, nano-TiO2 and other materials to prepare composite single-layer coatings with different nano-doping contents and applied them to the surface of the insulator. The results showed that the thermal stability of the insulator was greatly improved. At the same time, the introduction of nanoparticles would affect the surface charge dissipation rate.

[0004] Gao Xiang et al. (Gao Xiang, et al. Influence of surface coating on the charge characteristics of pot-type insulators under DC conditions [J]. Henan Science and Technology, 2022, 41(14): 32-37. DOI: 10.19968 / j.cnki.hnkj.1003-5168.2022.14.006.) conducted a study on coating a single layer of TiO2-doped epoxy resin on the surface of the insulating part to reduce the surface resistivity and accelerate the charge dissipation rate. The results showed that the average charge density of the insulating part coated with a single layer of TiO2-doped epoxy resin was reduced by 30.6% compared with the uncoated insulating part, and the maximum charge density was reduced by 35%. However, the influence of the coating layer on the DC flashover situation was not considered.

[0005] Chinese invention patent application CN111599551A uses an electrostatic spraying method to spray epoxy resin / silicon carbide coating on the surface of epoxy resin pot insulators. By controlling the electrostatic spraying position and the concentration of silicon carbide in the coating, controlling the position of the spray gun nozzle and the spraying time, electrostatic spraying is performed at different positions on the insulator surface for different times to form a conductivity gradient layer, thereby constructing a surface dielectric functional gradient material, optimizing the surface electric field distribution under DC voltage, and improving the insulator's electrical resistance. However, this invention does not address key issues such as charge injection suppression and trap characteristic regulation. In addition, this technology optimizes the electric field distribution by constructing an epoxy resin / silicon carbide coating with a conductivity gradient along the transverse gradient on the surface of the epoxy resin pot insulator. The control strategy is a single-dimensional surface charge transverse migration control, which may have the following problems: (1) A single transverse gradient change may lead to uncontrolled longitudinal charge injection; (2) Silicon carbide doping may introduce deep traps, resulting in the risk of charge retention; (3) The epoxy resin pot insulator of this patent lacks environmental protection design and is prone to secondary charge accumulation due to contamination deposition during service. Moreover, the coating thickness at different positions on the surface of the epoxy resin pot insulator of this patent is different, which may form a stepped surface structure, making it easy for dirt to deposit at the junction of positions with different thicknesses, easily leading to unexpected changes in the original conductivity gradient distribution, and also increasing the complexity of the preparation process. Summary of the Invention

[0006] In view of the shortcomings of the prior art, one of the objects of the present invention is to provide an epoxy insulator with high surface electric field uniformity, high flashover voltage and excellent insulation performance; the second object of the present invention is to provide a method for preparing a reduction insulator.

[0007] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0008] An epoxy insulator comprises an epoxy insulator body, wherein a bottom layer, an intermediate layer, and a surface layer are stacked in sequence from the inside out on the surface of the epoxy insulator body, and the thickness ratio of the bottom layer, the intermediate layer, and the surface layer is 1-3:1-3:1-3; in parts by mass, the raw material composition of the bottom layer comprises 2-4 parts of nano-sized Al2O3 particles, 8-12 parts of epoxy resin, 6-7 parts of a first thermal curing agent, 0.2-0.4 parts of a first silane coupling agent, and 11-15 parts of a first solvent; the raw material composition of the intermediate layer comprises 1-2 parts of nano-sized Al2O3 particles, 0.5-0.7 parts of nano-sized SiO2 particles, 8-12 parts of epoxy resin, 6-7 parts of a second thermal curing agent, 0.1-0.3 parts of a second silane coupling agent, and 10-14 parts of a second solvent; and the raw material composition of the surface layer comprises 1-3 parts of nano-sized SiO2 particles, 8-12 parts of epoxy resin, 6-7 parts of a third thermal curing agent, and 13-17 parts of a third solvent.

[0009] Furthermore, the raw material composition of the bottom layer includes 2.5-3.5 parts of nano-scale Al2O3 particles, 9-11 parts of epoxy resin, 6.2-6.8 parts of a first thermal curing agent, 0.25-0.35 parts of a first silane coupling agent, and 12-14 parts of a first solvent, the raw material composition of the middle layer includes 1.2-1.8 parts of nano-scale Al2O3 particles, 0.55-0.65 parts of nano-scale SiO2 particles, 9-11 parts of epoxy resin, 6.2-6.8 parts of a second thermal curing agent, 0.15-0.25 parts of a second silane coupling agent, and 11-13 parts of a second solvent, and the raw material composition of the surface layer includes 1.5-2.5 parts of nano-scale SiO2 particles, 9-11 parts of epoxy resin, 6.2-6.8 parts of a third thermal curing agent, and 14-16 parts of a third solvent.

[0010] Optionally, in the bottom layer, the mass of the nano-Al2O3 particles is 20-30% of the mass of the epoxy resin in the layer; and in the surface layer, the mass of the nano-SiO2 particles is 10-20% of the mass of the epoxy resin in the layer.

[0011] Optionally, the thickness ratio of the bottom layer, the middle layer and the surface layer is 1.5-2.5:1.5-2.5:1.5-2.5.

[0012] Optionally, the average particle size of the nano-sized Al2O3 particles is 50-70 nm, preferably 55-65 nm.

[0013] Optionally, the average particle size of the nano-sized SiO2 particles is 40-60 nm, preferably 45-55 nm.

[0014] Optionally, the number average molecular weight of the epoxy resin is 300-450, preferably 350-400.

[0015] Furthermore, the first thermal curing agent is one or more of methyltetrahydrophthalic anhydride (MTHPA), polyetheramine D230, and phenol formaldehyde amine (PFA); the first silane coupling agent is 3-aminopropyltrimethoxysilane (APTMS), epoxycyclohexylsilane (SILQUEST A-186), silane coupling agent KH-550 (γ-aminopropyltriethoxysilane); the first solvent is anhydrous ethanol; the second thermal curing agent is one or more of methyltetrahydrophthalic anhydride (MTHPA), polyetheramine D230, and phenol formaldehyde amine (PFA); the second silane coupling agent is one or more of silane coupling agent KH-560, silane coupling agent KH-570 (methacryloyloxysilane), and long-chain alkyl silane (heptadecafluorodecyltrimethoxysilane); the second solvent is anhydrous ethanol; the third thermal curing agent is one or more of methyltetrahydrophthalic anhydride (MTHPA), polyetheramine D230, and phenol formaldehyde amine (PFA); the third solvent is anhydrous ethanol.

[0016] Furthermore, the raw material composition of the surface layer also includes 0.2-0.4 parts of fluorosilane.

[0017] Furthermore, the fluorosilane is heptadecafluorodecyltrimethoxysilane (FAS-17).

[0018] Nano-SiO2 particles and FAS-17 can react as follows: SiO2OH+C8F 17 (CH2)2Si(OCH3)3→SiO2-O-Si-(CH2)2C8F 17 By modifying nano-SiO2 particles with fluorosilane to create a low-surface-energy surface, the adsorption of moisture, salt spray, and dust is suppressed, further reducing the impact of environmental factors on the performance of the three-layer composite layer, allowing the three-layer composite layer to function normally. Furthermore, the hydrophobic surface reduces the adhesion of external charged particles, further blocking the secondary accumulation of surface charge. At the same time, it strengthens the surface insulation performance and further increases the surface flashover voltage.

[0019] Furthermore, the sum of the thicknesses of the bottom layer, the middle layer and the surface layer is 50-100 μm, further 60-95 μm, and further 70-90 μm.

[0020] The method for preparing the epoxy insulator as described above comprises the following steps:

[0021] S1. Prepare the base coating, middle coating and top coating according to the formula;

[0022] S2, coating the surface of the epoxy insulator body with a primer and curing the coating to obtain a first blank;

[0023] S3, coating an intermediate layer of coating on the surface of the first body and curing the coating to obtain a second body;

[0024] S4. Apply a surface coating on the surface of the second blank and then cure the coating to obtain an epoxy insulator.

[0025] Furthermore, in S1, the preparation method of the primer is as follows: first, nano-Al2O3 particles, a first silane coupling agent, and a portion of the first solvent are mixed, stirred at 55-65°C at a rate of 900-1100 rpm for 2-4 hours, and then dried at 55-65°C for 1.5-2.5 hours to obtain a modified Al2O3 solution; then, the modified Al2O3 solution is mixed with an epoxy resin and the remaining first solvent, ultrasonically dispersed, and then a first thermal curing agent is added and mixed uniformly to obtain the primer;

[0026] The preparation method of the intermediate layer coating is as follows: first, nano-Al2O3 particles, nano-SiO2 particles, a second silane coupling agent and part of the second solvent are mixed, stirred at 900-1100 rpm for 2-4 hours, ultrasonically dispersed for 20-40 minutes, and dried at 55-65°C for 1.5-2.5 hours to obtain a modified mixed solution; then, the modified mixed solution is mixed with epoxy resin and the remaining second solvent, ultrasonically dispersed, and then a second thermal curing agent is added and mixed uniformly to obtain the intermediate layer coating;

[0027] The preparation method of the surface coating is as follows: first, nano-SiO2 particles are mixed with part of the third solvent, stirred at 35-45°C at a rate of 900-1100 rpm for 22-26 hours, and then dried at 35-45°C for 3-5 hours to obtain a SiO2 solution; the SiO2 solution is mixed with the epoxy resin and the remaining third solvent, ultrasonically dispersed, and then the third thermal curing agent is added and mixed evenly to obtain the product.

[0028] Furthermore, in S2, the first green body is obtained by first curing at 75-85°C for 50-70 minutes, then curing at 90-110°C for 110-130 minutes, and finally curing at 110-130°C for 160-200 minutes, to obtain a second green body. In S4, the first green body is obtained by curing at 55-65°C for 100-140 minutes, then curing at 70-90°C for 100-140 minutes, and finally curing at 95-105°C for 3.5-4.5 hours, to obtain an epoxy insulator. This helps to strengthen the interlayer bonding and make the bottom and middle layers more tightly bonded. At the same time, the bottom and middle layers can shrink in a coordinated manner during synchronous curing, reducing thermal stress concentration. In addition, it can improve efficiency and shorten the overall preparation time.

[0029] The present invention provides a three-layer composite coating, namely a bottom layer, an intermediate layer, and a surface layer, on the surface of the epoxy insulator body. The bottom layer uses nano-Al2O3 particles and a first silane coupling agent to construct a low-resistance path, inhibiting charge injection and accelerating the longitudinal migration of charges. The intermediate layer contains both nano-Al2O3 particles and nano-SiO2 particles, and the dielectric constant of this layer is adjusted. The dielectric constant gradient design alleviates the distortion of the interlayer electric field, avoids the accumulation of charges at the interface, and reduces the thermal stress caused by material mutation, preventing the layer structure on the surface of the epoxy insulator body from cracking. The surface layer can form a super-hydrophobic surface through the action of fluorosilane and nano-SiO2 particles, improving the insulation performance and blocking the adsorption of moisture and dust, so that the three-layer composite coating can achieve its target effect for a longer period of time. The present invention provides a multi-dimensional solution to the problems of surface charge and environmental protection of epoxy insulators and has good prospects for industrial application.

[0030] The epoxy insulator of the present invention can solve the functional limitation problem faced by traditional epoxy insulators with only a single layer of coating, and can simultaneously achieve multiple functions such as suppressing charge accumulation, promoting charge dissipation, and increasing surface flashover voltage.

[0031] In the present invention, the first silane coupling agent is used to react with the hydroxyl groups on the surface of the nano-Al2O3 particles to reduce the agglomeration between the particles. For example, when the first silane coupling agent is APTMS, the reaction mechanism is as follows:

[0032] (1) Hydrolysis reaction: The methoxy group (-OCH3) of APTMS is hydrolyzed in the first solvent to generate active silanol group (Si-OH). The reaction formula is as follows: NH2(CH2)3Si(OCH3)3+3H2O→NH2(CH2)3Si(OH)3+3CH3OH.

[0033] (2) Al2O3 surface condensation reaction: The silanol formed by hydrolysis condenses with the hydroxyl group (Al-OH) on the Al2O3 surface to form a stable Al-O-Si covalent bond. The reaction formula is as follows: Al2O3-OH+NH2(CH2)3Si(OH)3→Al2O3-O-Si(OH)2(CH2)3NH2+H2O.

[0034] (3) Cross-linking reaction between amino group and epoxy resin. The amino group (-NH2) of APTMS undergoes a ring-opening reaction with the epoxy group (-O-CH2-CH-O-) in the epoxy resin to form a β-hydroxyamine structure. The reaction formula is as follows: NH2(CH2)3Si-O-Al2O3+O-CH2-CH2-O→NH-CH2-CH(OH)-O-(CH2)3Si-O-Al2O3.

[0035] The composite of nano-Al2O3 particles and epoxy resin forms a foundational continuous conductive network (i.e., a conductive pathway), reducing surface resistivity and inhibiting charge injection into the epoxy insulator surface. Simultaneously, the conductive network provides a low-resistance path for surface charges, promoting directional charge migration toward the ground terminal and reducing electric field distortion caused by localized charge accumulation. Furthermore, the base layer, serving as the underlying structure of the three-layer composite coating, provides mechanical support for the intermediate and surface layers while ensuring chemical bonding strength with the epoxy insulator itself.

[0036] In the intermediate layer of the present invention, the second silane coupling agent reacts with the hydroxyl groups on the surface of the nano-SiO2 particles, so that the nano-SiO2 particles are better dispersed and agglomeration is reduced. For example, when the second silane coupling agent is silane coupling agent KH-560 (CH2-CH(O)-CH2-O-(CH2)3-Si(OCH3)3), the reaction mechanism is as follows:

[0037] (1) Hydrolysis reaction: The methoxy group of KH-560 is hydrolyzed to form silanol group.

[0038] (2) Some silanol groups react with the hydroxyl groups (Al-OH) on the Al2O3 surface to form stable Al-O-Si covalent bonds.

[0039] (3) Some silanol groups react with the hydroxyl groups on the SiO2 surface to form a Si-O-Si network structure.

[0040] Thus, by doping with Al2O3 and SiO2, the dielectric constant of the material is adjusted, suppressing charge injection while mitigating electric field distortion caused by material mutations, thereby improving electric field uniformity. Simultaneously, the difference in thermal expansion coefficients between different layers is reduced, lowering interfacial stress and preventing cracking or delamination of the layer structure. This creates a dielectric gradient from the bottom layer to the surface, guiding surface charge migration along the gradient and preventing charge accumulation at the interface.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention provides a bottom layer, an intermediate layer and a surface layer on the surface of the epoxy insulator body, and differentially controls the material composition and proportion of each layer, so that the dielectric constant has a gradient transition, alleviates the electric field distortion caused by material mutation, and improves the electric field uniformity, flashover voltage and insulation performance of the epoxy insulator surface.

[0043] (2) The epoxy insulator surface coating of the present invention constructs a three-dimensional charge control system with integrated gradient functions on the surface of the epoxy insulator through a three-layer composite structure design in the vertical direction. Different from the local optimization of traditional single-layer gradient coatings, the present invention innovatively combines the conductive layer (bottom layer), the dielectric gradient layer (middle layer) and the environmental protection layer (surface layer) in a continuous and gradual manner to form a smooth coating structure, eliminating the microstructural mutation caused by traditional single-layer coating from the root and effectively suppressing the accumulation of dust. The structure of the present invention realizes the deep integration of charge transport path optimization and external environmental erosion protection through the multi-dimensional synergistic mechanism of longitudinal charge transport-transverse electric field homogenization-surface environment blocking. The bottom layer directional guides the rapid dissipation of body charge, the middle layer actively regulates the uniformity of surface electric field distribution, and the surface layer blocks the external charge adsorption path through a chemical low surface energy interface. The three form a unified whole with spatial decoupling but functional coupling.

[0044] (3) Compared with traditional technologies, the present invention solves technical bottlenecks such as dynamic charge imbalance and environmental protection failure caused by the single functional dimension and sudden change of interface performance of traditional coatings, and provides an innovative solution for the reliable operation of UHVDC insulation components. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Graph showing the flashover voltage measurement results of the epoxy insulators of Comparative Examples 1-7.

[0046] Figure 2 Graph showing the flashover voltage measurement results of the epoxy insulators of Examples 1-4.

[0047] Figure 3 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 1.

[0048] Figure 4 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 2.

[0049] Figure 5 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 3.

[0050] Figure 6 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 4.

[0051] Figure 7 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 5.

[0052] Figure 8 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 6.

[0053] Figure 9 This is a diagram showing the surface potential distribution of the epoxy insulator of Comparative Example 7.

[0054] Figure 10 This is a diagram showing the surface potential distribution of the epoxy insulator of Example 1.

[0055] Figure 11 This is a diagram showing the surface potential distribution of the epoxy insulator of Example 2.

[0056] Figure 12 This is a diagram of the surface potential distribution of the epoxy insulator of Example 3.

[0057] Figure 13 This is a diagram of the surface potential distribution of the epoxy insulator of Example 4.

[0058] Figure 14 This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 1.

[0059] Figure 15 This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 2.

[0060] Figure 16 This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 3.

[0061] Figure 17 This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 4.

[0062] Figure 18This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 5.

[0063] Figure 19 This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 6.

[0064] Figure 20 This is a diagram showing the surface charge distribution of the epoxy insulator of Comparative Example 7.

[0065] Figure 21 This is a diagram of the surface charge distribution of the epoxy insulator of Example 1.

[0066] Figure 22 This is a diagram of the surface charge distribution of the epoxy insulator of Example 2.

[0067] Figure 23 This is a diagram of the surface charge distribution of the epoxy insulator of Example 3.

[0068] Figure 24 This is a diagram of the surface charge distribution of the epoxy insulator of Example 4.

[0069] Figure 25 Surface potential attenuation curves of the epoxy insulators of Comparative Examples 1-7 are shown.

[0070] Figure 26 Surface potential attenuation curves of the epoxy insulators of Examples 1-4 are shown.

[0071] Figure 27 This is a trap characteristic curve of the epoxy insulator of Comparative Example 1.

[0072] Figure 28 This is a trap characteristic curve of the epoxy insulator of Comparative Example 2.

[0073] Figure 29 This is a trap characteristic curve of the epoxy insulator of Comparative Example 3.

[0074] Figure 30 This is a trap characteristic curve of the epoxy insulator of Comparative Example 4.

[0075] Figure 31 This is a trap characteristic curve of the epoxy insulator of Comparative Example 5.

[0076] Figure 32 This is a trap characteristic curve of the epoxy insulator of Comparative Example 6.

[0077] Figure 33 This is a trap characteristic curve of the epoxy insulator of Comparative Example 7.

[0078] Figure 34 1 is a graph showing the trap characteristics of the epoxy insulator of Example 1.

[0079] Figure 35 Graph showing the trap characteristics of the epoxy insulator of Example 2.

[0080] Figure 36 Graph showing the trap characteristics of the epoxy insulator of Example 3.

[0081] Figure 37 Graph showing the trap characteristics of the epoxy insulator of Example 4. DETAILED DESCRIPTION

[0082] The present invention will be described in detail below with reference to the embodiments. It should be noted that, unless otherwise specified, the embodiments and features of the embodiments of the present invention may be combined with each other. Unless otherwise specified, the relevant percentages are percentages by mass. Example

[0083] The epoxy insulator of this embodiment includes an epoxy insulator body, the surface of which is provided with a bottom layer, an intermediate layer, and a surface layer stacked in sequence from the inside out. The epoxy insulator body is an epoxy insulator sheet with a radius of 20 mm and a thickness of 1 mm. The material composition of the epoxy insulator sheet is: bisphenol A epoxy resin (E-51, number average molecular weight of approximately 350-400), a curing agent (methylcyclohexene-1,2-dicarboxylic anhydride), and an accelerator [2,4,6-(dimethylaminomethyl)phenol], with the mass ratio of the three being 50:19:1.

[0084] The raw materials of the bottom layer are as follows: 10 g of epoxy resin [bisphenol A epoxy resin (E-51), number average molecular weight of about 350-400], 6.5 g of the first thermal curing agent (methyltetrahydrophthalic anhydride (MTHPA)) (65% of the mass of the epoxy resin), 3 g of nano-Al2O3 particles (purity 99.99%, average particle size 60 nm) (30% of the mass of the epoxy resin), 13 g of anhydrous ethanol, and 0.3 g of a silane coupling agent (APTMS, 10% of the mass of the nano-Al2O3 particles).

[0085] The raw materials of the middle layer are as follows: 10g of epoxy resin (bisphenol A type epoxy resin E-51, number average molecular weight of about 350-400), 6.5g of the second thermal curing agent [methyltetrahydrophthalic anhydride (MTHPA)] (65% of the mass of the epoxy resin), 1.5g of nano-Al2O3 particles (purity 99.99%, average particle size 60nm) (15% of the mass of the epoxy resin), 0.5g of nano-SiO2 particles (purity 99.5%, average particle size 50nm) (5% of the mass of the epoxy resin), 12g of anhydrous ethanol, and 0.2g of silane coupling agent (KH-560, 10% of the total mass of nano-Al2O3 particles and nano-SiO2 particles).

[0086] The raw materials of the surface layer are as follows: 10g epoxy resin (bisphenol A type epoxy resin E-51, number average molecular weight of about 350-400), 6.5g third thermal curing agent (methyltetrahydrophthalic anhydride (MTHPA)), 1.5g nano-SiO2 particles (purity 99.5%, average particle size 50) (15% of the mass of epoxy resin), 0.3g fluorosilane (FAS-17, 20% of the mass of nano-SiO2 particles), and 15g anhydrous ethanol.

[0087] The method for preparing the epoxy insulator as described above comprises the following steps:

[0088] S1. Prepare the base coating, middle coating and top coating according to the formula, specifically:

[0089] The preparation process for the primer used to construct the bottom layer is as follows: 3g of nano-Al2O3 particles and 0.3g of a silane coupling agent are dissolved in 5g of anhydrous ethanol. The mixture is magnetically stirred at 1000 rpm at 60°C for 3 hours to achieve chemical bonding. After stirring, the mixture is oven-dried at 60°C for 2 hours to obtain a modified Al2O3 solution. After drying, the modified Al2O3 solution is mixed with 10g of epoxy resin and the remaining 8g of anhydrous ethanol. The mixture is ultrasonically dispersed at 40kHz for 40 minutes. Finally, 6.5g of a first thermal curing agent is added, and the mixture is magnetically stirred at 2000 rpm for 30 minutes.

[0090] The preparation process for the intermediate layer coating is as follows: First, 1.5g of nano-Al2O3 particles, 0.5g of nano-SiO2 particles, and 0.5g of KH-560 are dissolved in 5g of anhydrous ethanol. After magnetic stirring at 1000rpm for 3h, due to the slow reaction between KH-560 and SiO2, ultrasonic dispersion is required at 40kHz for 30min to break up SiO2 agglomerates and ensure uniform dispersion of the nanoparticles. After ultrasonication, the modified mixed solution is oven-dried at 60°C for 2h to obtain a modified mixed solution. After drying, the modified mixed solution is mixed with 10g of epoxy resin and the remaining 7g of anhydrous ethanol and ultrasonically dispersed at 40kHz for 40min. Finally, 6.5g of a second thermal curing agent is added, and magnetic stirring is carried out at 2000rpm for 30min.

[0091] The surface coating used to construct the surface layer was prepared as follows: 1.5 g of nano-SiO2 particles and 0.3 g of FAS-17 were dissolved in 5 g of anhydrous ethanol. The mixture was magnetically stirred at 1000 rpm at 40°C for 24 hours, followed by drying at 40°C for 4 hours to prevent decomposition of the fluorosilane. This yielded a modified SiO2 solution. After drying, the modified SiO2 solution and 10 g of epoxy resin were dissolved in the remaining 10 g of anhydrous ethanol. Ultrasonic dispersion was performed at 40 kHz for 60 minutes, followed by the addition of 6.5 g of a third thermal curing agent and magnetic stirring at 1500 rpm for 20 minutes.

[0092] S2, coating a primer on the surface of the epoxy insulator body so that the epoxy insulator body is wrapped by the primer, and then curing the epoxy insulator body to obtain a first body having a primer layer;

[0093] S3, coating the surface of the first body with an intermediate coating so that the bottom coating layer of the first body is covered by the coated intermediate coating, and then curing the first body to obtain a second body having an intermediate coating layer;

[0094] S4. Apply a surface coating on the surface of the second blank so that the intermediate coating layer on the second blank is wrapped by the applied surface coating, and then cure to obtain an epoxy insulator.

[0095] In S2-S4, the same spraying parameters were used. Specifically, a Usuda S150 spray gun was used, with a pressure of 0.25 MPa. Three thin sprays were applied vertically, 20 cm from the surface of the epoxy insulator. Each coating layer was approximately 30 μm thick. Ultimately, the combined thickness of the base, middle, and surface layers was approximately 90 μm.

[0096] In S2, the first blank is obtained by curing at 80°C for 60 minutes and then at 100°C for 120 minutes. In S3, the second blank is obtained by curing at 80°C for 60 minutes, then at 100°C for 120 minutes, and then at 120°C for 180 minutes. In S4, the first blank is obtained by curing at 60°C for 120 minutes, then at 80°C for 120 minutes, and then at 100°C for 4 hours (to avoid high temperature damage to the CF bond) to obtain the epoxy insulator.

[0097] Comparative Example 1

[0098] Example 1 was repeated, with the only difference being that the coating was not formed on the epoxy insulator body, and the epoxy insulator body was directly used as a reduction insulator.

[0099] Comparative Example 2

[0100] Example 1 was repeated, with the following differences: only a bottom layer was constructed on the surface of the epoxy insulator body (i.e., the middle layer and the surface layer were discarded); and 9 thin sprayings were performed to ensure that the thickness of the constructed bottom layer was consistent with the total thickness of the three layers in Example 1.

[0101] Comparative Example 3

[0102] Example 1 was repeated, with the following differences: only the bottom layer and the middle layer were constructed on the surface of the epoxy insulator body (i.e., the surface layer was discarded); when constructing the bottom layer and the middle layer, 4 and 5 thin sprayings were performed, respectively, to ensure that the total thickness of the constructed bottom layer was consistent with that of the three layers in Example 1. Example

[0103] Example 1 was repeated, with the only difference being that in the bottom layer, the mass of the nano-Al2O3 particles was 20% of the mass of the epoxy resin in the layer.

[0104] Comparative Example 4

[0105] Example 1 was repeated, with the only difference being that in the bottom layer, the mass of the nano-Al2O3 particles was 15% of the mass of the epoxy resin in the layer. Example

[0106] Example 1 was repeated, with the following differences: in the bottom layer, the mass of the nano-Al2O3 particles was 30% of the mass of the epoxy resin in the layer; and in the surface layer, the mass of the nano-SiO2 particles was 10% of the mass of the epoxy resin in the layer. Example

[0107] Example 1 was repeated, with the following differences: in the bottom layer, the mass of the nano-Al2O3 particles was 30% of the mass of the epoxy resin in the layer; and in the surface layer, the mass of the nano-SiO2 particles was 20% of the mass of the epoxy resin in the layer.

[0108] Comparative Example 5

[0109] Example 1 was repeated, with the only difference being that in the bottom layer, the mass of the nano-Al2O3 particles was 35% of the mass of the epoxy resin in the layer.

[0110] The flashover voltage dropped to approximately 8.6 kV. This is likely due to the excessive alumina content in the base layer, which causes the nano-Al2O3 particles to agglomerate, disrupting the continuous conductive network and increasing the surface resistivity. This, in turn, inhibits charge dissipation and degrades the conductive properties. Furthermore, excessive nano-Al2O3 content can exacerbate the mismatch in thermal expansion coefficients, pushing interfacial thermal stresses close to the material limit and suscepting the coating to cracking. Furthermore, the increased density of deep traps makes it difficult for surface charge to dissipate, leading to an increase in surface charge density and intensified charge injection.

[0111] Comparative Example 6

[0112] Example 1 was repeated, with the only difference being that in the surface layer, the mass of the nano-SiO2 particles was 25% of the mass of the epoxy resin in the layer.

[0113] As a result, the flashover voltage dropped to approximately 8.76 kV. Furthermore, excessive silicon oxide content in the surface layer can easily lead to a loss of hydrophobicity, resulting in uncontrolled roughness, insufficient fluorosilane coverage, a reduced contact angle, and increased surface energy, which can easily lead to increased dust adsorption during service. The water film formed on the epoxy insulator surface during service can also trigger a field enhancement effect, reducing the flashover voltage and degrading insulation performance.

[0114] Comparative Example 7

[0115] Repeat Example 1, except that only the bottom layer and the surface layer are constructed on the surface of the epoxy insulator body (i.e., the middle layer is discarded);

[0116] When constructing the bottom layer and the surface layer, 4 and 5 thin sprayings were performed respectively to ensure that the total thickness of the constructed bottom layer was consistent with the total thickness of the three layers in Example 1.

[0117] As a result, the flashover voltage dropped to approximately 7.32 kV. Abandoning the intermediate transition layer leads to uncontrolled electric field distortion. The sudden change in dielectric constant significantly increases the interface electric field distortion rate, bringing the local field strength close to the breakdown threshold. This also hinders charge transport and significantly prolongs the charge decay time.

[0118] The DC flashover voltage test, surface charge accumulation characteristics, and trap energy level distribution are used to jointly characterize the relevant performance of the obtained epoxy insulator.

[0119] Under constant temperature and humidity conditions, the surface properties of the epoxy insulators obtained in each example and comparative example were compared and analyzed. Specifically, a positive-polarity DC power supply was used to test the DC flashover voltage in each case (the electrode gap was set to 5 mm, the test was repeated three times, and the average value was taken). Then, using a needle electrode to apply pressure, with the same pressure amplitude and time, the surface potential distribution of the epoxy insulator was measured using an electrostatic probe. The surface charge distribution was then derived using an inversion algorithm, thereby determining the surface charge accumulation characteristics under different conditions. Finally, pressure tests were performed using a needle electrode and a metal mesh to obtain the surface potential decay curve and trap energy level distribution.

[0120] See also Figure 1 and Figure 2When uncoated, the average flashover voltage of the epoxy insulator was 7.13 kV, the average flashover voltage of the epoxy insulator coated with only the bottom layer was 6.97 kV, the average flashover voltage of the epoxy insulator coated with both the bottom layer and the middle layer was 8.25 kV, and the average flashover voltage of the epoxy insulator of Example 1 was 10.13 kV. Compared with the uncoated case, the average flashover voltage of Example 1 increased by 42.1%; compared with the case with only the bottom layer, the average flashover voltage of Example 1 increased by 45.3%; and compared with the case with only the bottom layer and the middle layer, the average flashover voltage of Example 1 increased by 22.8%. It can be seen that the flashover voltage of the epoxy insulator of the present invention can be effectively improved, which can greatly improve the stability of the epoxy insulator during actual operation. It can also be seen that the amount of nano-Al2O3 particles in the bottom layer should not be too low or too high. If the amount of nano-Al2O3 particles is too low, the performance of the conductive network will be reduced, while if the amount of nano-Al2O3 particles is too high, it may cause the Al2O3 nanoparticles to agglomerate, destroying the continuous conductive network. When the mass of nano-Al2O3 particles is 20% of the epoxy resin in this layer, the flashover voltage can reach about 8.7kV; when the mass of nano-Al2O3 particles is 15% of the epoxy resin in this layer, the flashover voltage drops to about 8.1kV; and when the mass of nano-Al2O3 particles is 35% of the epoxy resin in this layer, the flashover voltage does not increase significantly, but instead drops to about 8.6kV. Similarly, in the surface layer, changes in the content of nano-SiO2 particles will affect the surface energy change. Too high a content will lead to an increase in surface energy. When the mass of nano-SiO2 particles is 25% of the epoxy resin in this layer, the flashover voltage drops to about 8.76kV. In addition, if the middle layer is discarded, that is, only the bottom layer and the surface layer are constructed on the surface of the epoxy insulator body, the electric field distortion will be out of control and the flashover voltage will drop to about 7.32kV.

[0121] The surface potential distribution of different epoxy insulators was measured by needle electrode charge injection experiment. Specifically, when the needle electrode was pressurized at 7kV for 5 minutes and the tip of the needle electrode was 15mm away from the insulator surface, the surface potential distribution of the epoxy insulators of the relevant embodiments and comparative examples was obtained. Figure 3-Figure 13 The uncoated epoxy insulator exhibits the highest peak potential and a wider accumulation range, while the three-layer composite coating (Example 1) exhibits the lowest peak potential and the smallest accumulation range. This demonstrates that the epoxy insulators of the present invention exhibit a more uniform surface potential distribution. Furthermore, controlling the content of nano-Al₂O₃ particles in the base layer and nano-SiO₂ particles in the surface layer contributes to improved surface potential uniformity.

[0122] Figure 14-Figure 24 The surface charge distribution diagram of the corresponding case is obtained by the inversion algorithm, which has a similar pattern to the potential distribution.

[0123] The surface potential decay curves and trap characteristic curves of epoxy insulators under different conditions were measured by isothermal surface potential decay (ISPD) experiments. Specifically, when the needle electrode was pressurized at 10 kV for 5 minutes, the metal mesh was pressurized at 2 kV for 5 minutes, the needle electrode tip was 15 mm away from the epoxy insulator surface, and the metal mesh was 5 mm away from the epoxy insulator surface (the metal mesh was located between the needle electrode tip and the epoxy insulator), the surface potential decay curves under different conditions were obtained (see Figure 25 and Figure 26 ) and the trap characteristic curve (see Figures 27-37 ). It can be seen that the surface potential of the epoxy insulator of the present invention decays faster. The addition of nano-Al2O3 particles in the bottom layer helps to accelerate the decay of the surface potential, and the addition of nano-SiO2 particles in the surface layer helps to accelerate the decay of the surface potential.

[0124] In the absence of coating, the number of deep and shallow traps is basically the same, the overall trap density is the highest, the energy levels of deep and shallow traps are both around 1.08 ev, and the charge dissipates slowly; in the case of only the bottom layer, deep traps dominate, the overall trap density decreases, the shallow trap energy level is around 1.01 ev, and the deep trap energy level is around 1.08 ev; in the case of only the bottom layer and the middle layer, shallow traps begin to dominate, the shallow trap energy level is around 0.98 ev, the deep trap energy level is around 1.06 ev, and the charge decay rate is greatly accelerated; in the case of setting the bottom layer, the middle layer and the surface layer at the same time, the overall trap density is the lowest, and the shallow trap density is slightly larger than the deep trap, which can avoid the charge retention caused by excessive shallow traps. The shallow trap energy level is around 0.95 ev, and the deep trap energy level is around 1.03 ev, which accelerates the decay rate of the surface potential and helps to improve the insulation performance of the epoxy insulator.

[0125] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art shall fall within the scope defined by the claims attached to this application.

Claims

1. An epoxy insulator, comprising an epoxy insulator body, characterized in that: The surface of the epoxy insulator body is provided with a bottom layer, an intermediate layer and a surface layer stacked in sequence from the inside to the outside, and the thickness ratio of the bottom layer, the intermediate layer and the surface layer is 1-3:1-3:1-3; in parts by mass, the raw material composition of the bottom layer includes 2-4 parts of nano-scale Al2O3 particles, 8-12 parts of epoxy resin, 6-7 parts of a first thermal curing agent, 0.2-0.4 parts of a first silane coupling agent, and 11-15 parts of a first solvent; the raw material composition of the intermediate layer includes 1-2 parts of nano-scale Al2O3 particles, 0.5-0.7 parts of nano-scale SiO2 particles, 8-12 parts of epoxy resin, 6-7 parts of a second thermal curing agent, and 11-15 parts of a second solvent. The invention relates to a method for preparing a silane coupling agent comprising: 0.1-0.3 parts of a silane coupling agent; 10-14 parts of a second solvent; and the raw material composition of the surface layer comprises 1-3 parts of nano-sized SiO2 particles; 8-12 parts of an epoxy resin; 6-7 parts of a third thermal curing agent; 13-17 parts of a third solvent; and 0.2-0.4 parts of a fluorosilane. The method comprises: in the bottom layer, the mass of the nano-Al2O3 particles is 20-30% of the mass of the epoxy resin in the layer; in the surface layer, the mass of the nano-SiO2 particles is 10-20% of the mass of the epoxy resin in the layer; and the first silane coupling agent is one or more of 3-aminopropyltrimethoxysilane and silane coupling agent KH-550.

2. The epoxy insulator according to claim 1, characterized in that: In parts by mass, the raw material composition of the bottom layer includes 2.5-3.5 parts of nano-scale Al2O3 particles, 9-11 parts of epoxy resin, 6.2-6.8 parts of a first thermal curing agent, 0.25-0.35 parts of a first silane coupling agent, and 12-14 parts of a first solvent; the raw material composition of the middle layer includes 1.2-1.8 parts of nano-scale Al2O3 particles, 0.55-0.65 parts of nano-scale SiO2 particles, 9-11 parts of epoxy resin, 6.2-6.8 parts of a second thermal curing agent, 0.15-0.25 parts of a second silane coupling agent, and 11-13 parts of a second solvent; the raw material composition of the surface layer includes 1.5-2.5 parts of nano-scale SiO2 particles, 9-11 parts of epoxy resin, 6.2-6.8 parts of a third thermal curing agent, and 14-16 parts of a third solvent.

3. The epoxy insulator according to claim 1 or 2, characterized in that: The first thermal curing agent is one or more of methyltetrahydrophthalic anhydride, polyetheramine D230, and phenol formaldehyde amine; the first solvent is anhydrous ethanol; the second thermal curing agent is one or more of methyltetrahydrophthalic anhydride, polyetheramine D230, and phenol formaldehyde amine; the second silane coupling agent is one or more of silane coupling agent KH-560, silane coupling agent KH-570, and long-chain alkyl silane; and the second solvent is anhydrous ethanol; the third thermal curing agent is one or more of methyltetrahydrophthalic anhydride, polyetheramine D230, and phenol formaldehyde amine; and the third solvent is anhydrous ethanol.

4. The epoxy insulator according to claim 1, characterized in that: The fluorosilane is heptadecafluorodecyltrimethoxysilane.

5. The epoxy insulator according to claim 1 or 2, characterized in that: The sum of the thickness of the bottom layer, the middle layer and the surface layer is 50-100 μm.

6. The method for preparing an epoxy insulator according to any one of claims 1 to 5, characterized in that: The steps include: S1. Prepare the base coating, middle coating and top coating according to the formula; S2, coating the surface of the epoxy insulator body with a primer and curing the coating to obtain a first blank; S3, coating an intermediate layer of coating on the surface of the first body and curing the coating to obtain a second body; S4. Apply a surface coating on the surface of the second blank and then cure the coating to obtain an epoxy insulator.

7. The preparation method according to claim 6, characterized in that In S1, the primer coating is prepared as follows: first, nano-Al2O3 particles, a first silane coupling agent, and a portion of the first solvent are mixed, stirred at 55-65°C at a rate of 900-1100 rpm for 2-4 hours, and then dried at 55-65°C for 1.5-2.5 hours to obtain a modified Al2O3 solution; then, the modified Al2O3 solution is mixed with an epoxy resin and the remaining first solvent, ultrasonically dispersed, and then a first thermal curing agent is added and mixed uniformly to obtain the primer coating; The preparation method of the intermediate layer coating is as follows: first, nano-Al2O3 particles, nano-SiO2 particles, a second silane coupling agent and part of the second solvent are mixed, stirred at 900-1100 rpm for 2-4 hours, ultrasonically dispersed for 20-40 minutes, and dried at 55-65°C for 1.5-2.5 hours to obtain a modified mixed solution; then, the modified mixed solution is mixed with epoxy resin and the remaining second solvent, ultrasonically dispersed, and then a second thermal curing agent is added and mixed uniformly to obtain the intermediate layer coating; The preparation method of the surface coating is as follows: first, nano-SiO2 particles are mixed with part of the third solvent, stirred at 35-45°C at a rate of 900-1100 rpm for 22-26 hours, and then dried at 35-45°C for 3-5 hours to obtain a SiO2 solution; the SiO2 solution is mixed with the epoxy resin and the remaining third solvent, ultrasonically dispersed, and then the third thermal curing agent is added and mixed evenly to obtain the product.

8. The preparation method according to claim 6, characterized in that In S2, the first step is curing at 75-85°C for 50-70 minutes, and then curing at 90-110°C for 110-130 minutes to obtain a first green body; in S3, the first step is curing at 75-85°C for 50-70 minutes, and then curing at 90-110°C for 110-130 minutes, and then curing at 110-130°C for 160-200 minutes to obtain a second green body; In S4, the epoxy insulator is first cured at 55-65° C. for 100-140 minutes, then cured at 70-90° C. for 100-140 minutes, and then cured at 95-105° C. for 3.5-4.5 hours to obtain the epoxy insulator.

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