A pollution flashover prevention composite insulator and a preparation method thereof

Abstract

The present disclosure relates to the field of composite insulators, in particular to a pollution flashover prevention composite insulator and a preparation method thereof. The pollution flashover prevention composite insulator comprises the following structures: a core rod, a first silicone rubber protective sleeve layer wrapped on the outer surface of the core rod, a second silicone rubber protective sleeve layer wrapped on the outer surface of the first silicone rubber protective sleeve layer, and a surface coating layer coated on the outer surface of the second silicone rubber protective sleeve layer; wherein the material of the core rod is glass fiber reinforced epoxy resin.

Description

Technical Field

[0001] This disclosure relates to the field of composite insulators, specifically to an anti-pollution flashover composite insulator and its preparation method. Background Technology

[0002] Composite insulators, due to their advantages such as light weight, good resistance to flashover, and long maintenance-free period, have gradually replaced traditional porcelain and glass insulators, becoming the core component of external insulation for high-voltage transmission lines. A typical composite insulator consists of a glass fiber reinforced epoxy resin core rod, a silicone rubber shed sheath, and end fittings. The core rod bears the mechanical load, while the silicone rubber shed sheath provides electrical insulation and weather protection.

[0003] However, the failure mode of composite insulators during long-term operation is not simply surface flashover, but rather progressive interface failure between the core rod and the silicone rubber sheath. The coefficient of thermal expansion of glass fiber reinforced epoxy resin is approximately 25 × 10⁻⁶. -6 / K to 35×10 -6 / K, while the coefficient of thermal expansion of high-temperature vulcanized silicone rubber is as high as 180×10 -6 / K to 220×10 -6 Both components generate significant radial thermal mismatch stress under temperature cycling caused by diurnal temperature variations, seasonal changes, and the thermal effect of load current. This stress concentrates at the mandrel-sheath interface, inducing the initiation and propagation of microcracks. Once the microcracks penetrate, moisture, salt spray, and other pollutants in the atmosphere permeate along the interface, forming a conductive water film under the influence of the electric field, ultimately leading to interfacial flashover. This failure mode is characterized by its high degree of concealment, suddenness, and destructiveness, and cannot be detected in advance through surface inspection.

[0004] To address the aforementioned issues, existing technologies primarily focus on improvements in two directions: First, optimizing the structure and material formulation of the silicone rubber umbrella skirt sheath to enhance its resistance to electrolytic corrosion and aging. Second, applying an anti-flashover coating, such as room temperature vulcanizing silicone rubber coating or fluorosilicone coating, to suppress moisture wetting and contaminant adhesion by reducing surface energy and increasing the static contact angle.

[0005] Negative thermal expansion materials offer a new solution to the aforementioned dilemma. Zirconium tungstate (ZrW₂O₈) exhibits isotropic negative thermal expansion over a wide temperature range, with a coefficient of thermal expansion of approximately -8.7 × 10⁻⁶. -6 Introducing it into the polymer matrix allows for volume expansion to compensate for the matrix's thermal contraction as the temperature decreases, thereby converting interfacial thermal stress into compressive stress and inhibiting crack initiation.

[0006] However, ZrW2O8 is prone to hydrolysis in humid environments, resulting in the loss of its negative expansion properties. This defect also limits its direct application in outdoor power equipment. Summary of the Invention

[0007] The purpose of this disclosure is to provide a pollution flashover-proof composite insulator and its preparation method to address the shortcomings in related technologies.

[0008] According to a first aspect of the present disclosure, a pollution flashover-proof composite insulator is provided, the pollution flashover-proof composite insulator comprising the following structure: a core rod, a first silicone rubber protective sleeve covering the outer surface of the core rod, a second silicone rubber protective sleeve covering the outer surface of the first silicone rubber protective sleeve, and a surface coating applied to the outer surface of the second silicone rubber protective sleeve; wherein the material of the core rod is glass fiber reinforced epoxy resin.

[0009] In one aspect of the embodiments of this disclosure, both the first silicone rubber protective sleeve layer and the second silicone rubber protective sleeve layer are obtained by compression molding and vulcanization of a methyl vinyl silicone rubber matrix, a composite modified negative thermal expansion filler, a first inorganic filler and a silane coupling agent.

[0010] In one aspect of the embodiments of this disclosure, both the first silicone rubber protective sleeve layer and the second silicone rubber protective sleeve layer are obtained by compression molding and vulcanizing a methyl vinyl silicone rubber matrix, a composite modified negative thermal expansion filler, a first inorganic filler, a silane coupling agent, a dispersing agent, zinc oxide and a peroxide vulcanizing agent. Furthermore, based on the total mass of the first silicone rubber protective sleeve, the mass percentage of the composite modified negative thermal expansion filler contained in the first silicone rubber protective sleeve is selected from 15% to 25%; Based on the total mass of the second silicone rubber protective sleeve, the mass percentage of the composite modified negative thermal expansion filler contained in the second silicone rubber protective sleeve is selected from 3% to 8%.

[0011] In one aspect of the embodiments of this disclosure, the first inorganic filler is selected from at least one of zirconium oxide, silicon nitride, silicon carbide, mullite, aluminum titanate, and aluminum magnesium spinel.

[0012] In one aspect of the embodiments of this disclosure, preferably, the first inorganic filler is selected from zirconium oxide or mullite; more preferably, the first inorganic filler is selected from mullite.

[0013] In one aspect of the embodiments of this disclosure, the silane coupling agent is selected from at least two of γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloyloxypropyltrimethoxysilane.

[0014] In one aspect of the embodiments of this disclosure, preferably, the silane coupling agent is selected from a compound of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane, or a compound of γ-glycidoxypropyltrimethoxysilane and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, or a compound of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; more preferably, the silane coupling agent is selected from a compound of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane, and the mass ratio of γ-glycidoxypropyltrimethoxysilane to γ-aminopropyltriethoxysilane is (1.5-2):1.

[0015] In one aspect of the embodiments of this disclosure, the dispersing agent is selected from silicone oil-based dispersing agents and / or non-silicone oil-based dispersing agents; the silicone oil-based dispersing agent is selected from hydroxyl silicone oil, dimethyl silicone oil, methylphenyl silicone oil, vinyl silicone oil, or low-viscosity fluorosilicone oil; the non-silicone oil-based dispersing agent is selected from tributyl phosphate, triphenyl phosphate, butyl stearate, oleamide, or polyethylene glycol-polypropylene glycol block copolymer.

[0016] In one aspect of the embodiments of this disclosure, preferably, the dispersing agent is selected from hydroxyl silicone oil, dimethyl silicone oil, or polyethylene glycol-polypropylene glycol block copolymer; more preferably, the dispersing agent is selected from hydroxyl silicone oil.

[0017] In one aspect of this disclosure, the peroxide vulcanizing agent is selected from at least one of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,4-di-tert-butylperoxyisopropylbenzene, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, dicumyl peroxide, tert-butylperoxyisopropylbenzene, 2,4-dichlorobenzoyl peroxide, and benzoyl peroxide.

[0018] In one aspect of the embodiments of this disclosure, preferably, the peroxide sulfiding agent is selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane or 1,4-di-tert-butylperoxyisopropylbenzene.

[0019] In one aspect of this disclosure, the composite modified negative thermal expansion filler is a negative thermal expansion filler coated with a second inorganic filler; wherein the second inorganic filler is selected from silicon oxide, aluminum oxide, titanium oxide, hafnium oxide, or tin oxide; and the negative thermal expansion filler is selected from ZrW2O8, HfW2O8, ZrMo2O8, ZrV2O7, ZrP2O7, or Sc2W3O. 12 Y2W3O 12 At least one of LiAlSiO4 and Al2TiO5.

[0020] In one aspect of the embodiments of this disclosure, preferably, the composite modified negative thermal expansion filler is ZrW2O8 coated with silica.

[0021] In one aspect of this disclosure, the composite modified negative thermal expansion filler, which is silica-coated ZrW2O8, is prepared through the following steps: Step 1-a: Prepare ZrW2O8 powder by hydrothermal method; Step 2-a: The prepared ZrW2O8 powder and quartz powder are mixed at a mass ratio of 1:(0.5-1.5), deionized water is added as a dispersion medium, and the mixture is added to a planetary ball mill and ball-milled at 150rpm-250rpm for 5-6h. After ball milling, the resulting slurry is vacuum dried and then ground through a 150-250 mesh sieve to obtain the product of step 2-a. The D50 particle size of the quartz powder is 1-5μm. Step 3-a: Add the product of step 2-a to an aqueous ethanol solution, add KH-560, and stir at room temperature for 30-45 min; then heat to 75℃-85℃ and reflux for 3-5 h; after the reaction is complete, centrifuge, wash, and dry to obtain the product of step 3-a; Step 4-a: Add the product of step 3-a and hexamethyldisilazane-treated hydrophobic fumed silica to a mixer at a mass ratio of 1:(0.1-0.3) and mix for 10-15 min; after discharge, the silica-coated ZrW2O8 is obtained.

[0022] In one aspect of this disclosure, step 1-a includes: Step 1-b: Prepare a solution containing Zr element using ZrOCl2·8H2O as the raw material; prepare a solution containing W element using Na2WO4·2H2O as the raw material; simultaneously titrate and mix the Zr-containing solution and the W-containing solution to obtain a white suspension, and then keep it in a 60℃ water bath for 1-3 hours; then add concentrated hydrochloric acid while stirring, and continue stirring for 0.5-2 hours; Step 2-b: Add the solution obtained in Step 1-b to a hydrothermal reactor, place it in an oven, and react at 170℃-190℃ for 8-12 hours. After naturally cooling to room temperature, add the precipitated powder obtained from the reaction to an ethanol aqueous solution for aging for 12-36 hours. Then, filter, wash, and dry to obtain ZrW2O7(OH)2(H2O)2 powder. Step 3-b: After grinding the ZrW2O7(OH)2(H2O)2 powder, place it in a muffle furnace, heat it to 525℃-575℃, calcine it for 5-10 hours, and then cool it naturally to room temperature to obtain ZrW2O8 powder.

[0023] In one aspect of this disclosure, the surface coating comprises polytrifluoropropylmethylsiloxane and hydrophobically modified nano-silica; wherein the hydrophobically modified nano-silica is obtained by modifying nano-silica using a fluorinated silane; the fluorinated silane is selected from perfluorodecyltrimethoxysilane, perfluorooctyltriethoxysilane, or perfluorohexyltrimethoxysilane.

[0024] In one aspect of this disclosure, the hydrophobically modified nano-silica is prepared by the following steps: Step 1-c: Add nano-silica to an ethanol aqueous solution, add perfluorodecyltrimethoxysilane, ultrasonically disperse for 30-45 min, heat to 60°C and reflux for 3-5 h, centrifuge and wash three times, and dry to obtain the hydrophobic modified nano-silica; wherein, the mass ratio of perfluorodecyltrimethoxysilane to nano-silica is selected from (3-8):100.

[0025] According to a second aspect of the present disclosure, a method for preparing the aforementioned anti-flashover composite insulator is provided, the method comprising the following steps: Step 1: Provide a mandrel; and prepare silicon oxide-coated ZrW2O8; Step 2: The methyl vinyl silicone rubber matrix, the first inorganic filler, the silane coupling agent, the dispersant, the zinc oxide, and the silica-coated ZrW2O8 obtained in Step 1 are mixed to obtain the first silicone rubber compound; wherein, based on the total mass of the first silicone rubber compound, the mass percentage of the silica-coated ZrW2O8 is 15%-25%; the first silicone rubber compound is coated on the outer surface of the mandrel, and molded and vulcanized at 165℃-180℃ and 10MPa-15MPa for 15-25 minutes to form the first silicone rubber protective sheath layer; Step 3: Mix the methyl vinyl silicone rubber matrix, the first inorganic filler, the silane coupling agent, the dispersant, the zinc oxide, and the silica-coated ZrW2O8 obtained in Step 1 to obtain a second silicone rubber compound; wherein, based on the total mass of the second silicone rubber compound, the mass percentage of the silica-coated ZrW2O8 is 3%-8%; coat the second silicone rubber compound onto the outer surface of the first silicone rubber protective layer, and mold and vulcanize it at 165℃-180℃ and 10MPa-15MPa for 15-25 minutes to form the second silicone rubber protective layer; Step 4: Prepare hydrophobically modified nano-silica; Step 5: Mix polytrifluoropropylmethylsiloxane, hydrophobically modified nano-silica, tetraethyl orthosilicate, and dibutyltin dilaurate; then add butyl acetate for dilution; then coat the mixture onto the outer surface of the second silicone rubber protective sheath layer, and cure it at 80℃-120℃ for 1-3 hours to form the surface coating; thus obtaining the anti-pollution flashover composite insulator.

[0026] Compared with the prior art, the beneficial effects of this disclosure are: This disclosure provides a composite insulator and its preparation method that can maintain the integrity of the interface structure and the surface anti-pollution flashover performance for a long time in environments with large temperature differences. By introducing composite modified negative thermal expansion fillers that have undergone specific sequential modification treatment into the first and second silicone rubber protective sheath layers, the thermal expansion coefficient of the inner sheath is close to that of the glass fiber reinforced epoxy resin core rod, and the thermal expansion coefficient of the outer sheath is close to that of the silicone rubber body and the surface coating. This forms a continuous thermal expansion gradient between the core rod and the coating, converting the radial thermal mismatch stress generated by temperature cycling into compressive stress and absorbing it, thereby inhibiting the initiation and propagation of interfacial microcracks and maintaining the surface anti-pollution flashover performance of the composite insulator. Detailed Implementation

[0027] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0029] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0030] In this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0031] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0032] Unless otherwise stated, the terms used in this disclosure have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this disclosure can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this disclosure).

[0033] The term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0034] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0035] In this disclosure, the anti-flashover composite insulator may further include sheds disposed on the outer surface of the second silicone rubber protective sheath and / or the outer surface of the surface coating; the sheds may be integrally molded and vulcanized with the second silicone rubber protective sheath, or they may be independent shed components assembled subsequently. In other embodiments, the anti-flashover composite insulator may not have sheds, but may consist only of the core rod, the first silicone rubber protective sheath, the second silicone rubber protective sheath, and the surface coating to form a smooth columnar or cylindrical external insulation structure. It is understood that regardless of whether sheds are provided or not, and the specific shape, size, and arrangement of the sheds, it does not affect the thermal expansion gradient buffering function achieved by the first silicone rubber protective sheath and the second silicone rubber protective sheath through the composite modified negative thermal expansion filler, or the superhydrophobic anti-flashover effect provided by the surface coating; therefore, this disclosure does not specifically limit whether the composite insulator includes sheds or their specific structure.

[0036] The present disclosure will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of the present disclosure are obtained through conventional commercial means. Unless otherwise specified, all contents mentioned below are mass contents. Unless otherwise specified, it is understood that the process is carried out at room temperature.

[0037] Example 1: Example 1 includes the following steps: 1. Preparation of ZrW2O8 powder: Zirconium oxychloride octahydrate (ZrOCl2·8H2O) was dissolved in deionized water to prepare a 120 mL solution with a concentration of 0.30 mol / L; sodium tungstate dihydrate (Na2WO4·2H2O) was dissolved in deionized water to prepare a 120 mL solution with a concentration of 0.60 mol / L. The two solutions were simultaneously titrated together under continuous stirring to form a milky white suspension. The suspension was incubated in a 60°C water bath for 2 hours, and then 60 mL of 12 mol / L concentrated hydrochloric acid was added while stirring, and the mixture was stirred continuously for 1 hour to obtain the hydrothermal precursor fluid.

[0038] The hydrothermal precursor liquid was transferred to a 500 mL hydrothermal reactor with a stainless steel outer shell and a polytetrafluoroethylene inner liner. After sealing the reactor, it was placed in an oven and reacted at 180°C for 10 h. After naturally cooling to room temperature, the resulting precipitate powder was immersed in a mixture of 100 mL deionized water and 100 mL anhydrous ethanol and aged for 24 h. Subsequently, it was filtered, washed, and dried to obtain ZrW2O7(OH)2(H2O)2 powder.

[0039] After grinding the ZrW2O7(OH)2(H2O)2 powder, it was placed in a muffle furnace and gradually heated to 550°C at a rate of 5°C / min. The powder was then calcined at this temperature for 8 hours and then naturally cooled to room temperature to obtain ZrW2O8 powder.

[0040] 2. Preparation of silicon dioxide-coated ZrW2O8: The prepared ZrW2O8 powder was mixed with quartz powder (D50 particle size of 2μm) at a mass ratio of 1:1, and deionized water was added as a dispersion medium. The mixture was placed in a planetary ball mill and ball-milled at a rate of 200 rpm for 5 hours. The mass ratio of raw material:zirconia balls:deionized water was 1:5:10. After ball milling, the resulting slurry was vacuum dried at 80°C for 12 hours and then ground through a 200-mesh sieve to obtain the ball-milled mixed powder.

[0041] The ball-milled powder was added to an ethanol-water solution (the volume ratio of anhydrous ethanol to deionized water was 9:1), and γ-glycidoxypropyltrimethoxysilane was added. The mixture was stirred at room temperature for 30 min, and then heated to 80°C and refluxed for 4 h. After the reaction was completed, the powder was centrifuged, washed, and dried to obtain the modified powder.

[0042] The modified powder and hydrophobic fumed silica (Aerosil R812S, with a native particle size of 7 nm) treated with hexamethyldisilazane were added to a high-speed mixer at a mass ratio of 1:0.15 and mixed for 10 min. After discharge, silica-coated ZrW2O8 was obtained.

[0043] 3. Preparation of the first silicone rubber protective sleeve layer: 100 parts by weight of methyl vinyl silicone rubber (MVQ, vinyl content 0.15 mol%), 15 parts by weight of mullite, 2 parts by weight of γ-glycidyl etheroxypropyltrimethoxysilane, 1 part by weight of γ-aminopropyltriethoxysilane, 3 parts by weight of hydroxyl silicone oil (molecular weight 1000), and 4 parts by weight of zinc oxide were sequentially added to a mixer and mixed at 45°C for 15 min. Then, 20 parts by weight of the prepared silica-coated ZrW2O8 powder were added and mixed for another 10 min. Finally, 1.5 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPMH) were added and the mixture was passed through a thin tube 5 times to obtain the first silicone rubber compound.

[0044] The obtained first silicone rubber compound was coated on the outer surface of the glass fiber reinforced epoxy resin mandrel, and then molded and vulcanized at 170°C and 12MPa for 20 minutes to form a first silicone rubber protective layer with a thickness of 1.5mm.

[0045] 4. Preparation of the second silicone rubber protective layer: 100 parts by weight of methyl vinyl silicone rubber (MVQ, vinyl content 0.15 mol%), 15 parts by weight of mullite, 2 parts by weight of γ-glycidyl etheroxypropyltrimethoxysilane, 1 part by weight of γ-aminopropyltriethoxysilane, 3 parts by weight of hydroxyl silicone oil (molecular weight 1000), and 4 parts by weight of zinc oxide were added to a mixer and mixed at 45°C for 15 min. Then, 5 parts by weight of the prepared silica-coated ZrW2O8 powder were added and the mixture was mixed for another 10 min. Finally, 1.5 parts by weight of DBPMH were added and the mixture was passed through a thin tube 5 times to obtain the second silicone rubber compound.

[0046] The obtained second silicone rubber compound was coated on the outer surface of the first silicone rubber protective layer, and then molded and vulcanized at 170°C and 12MPa for 20 minutes to form a second silicone rubber protective layer with a thickness of 2.5mm.

[0047] 5. Preparation of surface coating: Vapor-phase nano-silica (D50 particle size 30nm) was added to an ethanol aqueous solution (volume ratio of anhydrous ethanol to deionized water 9:1), and perfluorodecyltrimethoxysilane (5% of the mass of nano-silica) was added. The mixture was ultrasonically dispersed for 30 min, heated to 60°C and stirred under reflux for 4 h, centrifuged and washed three times, and then vacuum dried at 80°C for 12 h to obtain hydrophobically modified nano-silica.

[0048] 50 parts by weight of polytrifluoropropylmethylsiloxane oligomer, 12 parts by weight of hydrophobically modified nano-silica, 8 parts by weight of tetraethyl orthosilicate, and 0.2 parts by weight of dibutyltin dilaurate were mixed and diluted with 35 parts by weight of butyl acetate to obtain a surface coating. The above surface coating was sprayed onto the outer surface of the second silicone rubber protective layer, and the wet film thickness was controlled to be 100 μm. Then it was cured at 100°C for 2 hours to form a surface coating; thus, the anti-pollution flashover composite insulator of this embodiment was obtained.

[0049] Example 2: Example 2 includes the following steps: 1. Preparation of ZrW2O8 powder: The steps here are the same as in Example 1.

[0050] 2. Preparation of silicon dioxide-coated ZrW2O8: The prepared ZrW2O8 powder was mixed with quartz powder (D50 particle size of 2μm) at a mass ratio of 1:1, and deionized water was added as a dispersion medium. The mixture was placed in a planetary ball mill and ball-milled at a rate of 200 rpm for 5 hours. The mass ratio of raw material:zirconia balls:deionized water was 1:5:10. After ball milling, the resulting slurry was vacuum dried at 80°C for 12 hours and then ground through a 200-mesh sieve to obtain the ball-milled mixed powder.

[0051] The ball-milled powder was added to an ethanol-water solution (the volume ratio of anhydrous ethanol to deionized water was 9:1), and γ-glycidyl etheroxypropyltrimethoxysilane was added. The mixture was stirred at room temperature for 30 min, and then heated to 80°C and stirred under reflux for 4 h. After the reaction was completed, the powder was centrifuged, washed, and dried to obtain the silicon oxide-coated ZrW2O8 powder of this embodiment.

[0052] 3. Preparation of the first silicone rubber protective sleeve layer: The steps here are the same as in Example 1.

[0053] 4. Preparation of the second silicone rubber protective layer: The steps here are the same as in Example 1.

[0054] 5. Preparation of surface coating: The steps here are the same as in Example 1.

[0055] The main difference between Example 2 and Example 1 is that the silicon oxide-coated ZrW2O8 prepared in Example 2 was only mixed with quartz powder by ball milling, and was not mixed with hydrophobic fumed silica treated with hexamethyldisilazane.

[0056] Example 3: Example 3 includes the following steps: 1. Preparation of ZrW2O8 powder: The steps here are the same as in Example 1.

[0057] 2. Preparation of silicon dioxide-coated ZrW2O8: The prepared ZrW2O8 powder was added to an ethanol-water solution (the volume ratio of anhydrous ethanol to deionized water was 9:1), and γ-glycidyl etheroxypropyltrimethoxysilane was added. The mixture was stirred at room temperature for 30 min, and then heated to 80°C and stirred under reflux for 4 h. After the reaction was completed, the product was centrifuged, washed, and dried. Then, the product was added to a high-speed mixer at a mass ratio of 1:0.15 with hydrophobic fumed silica (Aerosil R812S, with a native particle size of 7 nm) treated with hexamethyldisilazane. The mixture was mixed for 10 min, and the product was discharged to obtain silica-coated ZrW2O8.

[0058] 3. Preparation of the first silicone rubber protective sleeve layer: The steps here are the same as in Example 1.

[0059] 4. Preparation of the second silicone rubber protective layer: The steps here are the same as in Example 1.

[0060] 5. Preparation of surface coating: The steps here are the same as in Example 1.

[0061] The main difference between Example 3 and Example 1 is that the silicon oxide-coated ZrW2O8 prepared in Example 3 was only mixed with hydrophobic fumed silica treated with hexamethyldisilazane, and was not mixed with quartz powder.

[0062] Example 4: Example 4 includes the following steps: 1. Preparation of ZrW2O8 powder: The steps here are the same as in Example 1.

[0063] 2. Preparation of silicon dioxide-coated ZrW2O8: The prepared ZrW2O8 powder was combined with hydrophobic fumed silica (Aerosil) treated with hexamethyldisilazane. R812S (with a native particle size of 7 nm) was added to a high-speed mixer at a mass ratio of 1:0.15 and mixed for 10 min. After discharge, the mixture was added to an ethanol-water solution (anhydrous ethanol to deionized water in a volume ratio of 9:1), and γ-glycidyl etheroxypropyltrimethoxysilane was added. The mixture was stirred at room temperature for 30 min, and then heated to 80°C and refluxed for 4 h. After the reaction was completed, the mixture was centrifuged, washed, and dried. The resulting powder was mixed with quartz powder (D50 particle size of 2 μm) at a mass ratio of 1:1, and deionized water was added as a dispersion medium. The mixture was then placed in a planetary ball mill and ball-milled at a rate of 200 rpm for 5 h. The mass ratio of raw material:zirconia balls:deionized water was 1:5:10. After ball milling, the resulting slurry was vacuum dried at 80°C for 12 h, and then ground through a 200-mesh sieve to obtain silica-coated ZrW2O8.

[0064] 3. Preparation of the first silicone rubber protective sleeve layer: The steps here are the same as in Example 1.

[0065] 4. Preparation of the second silicone rubber protective layer: The steps here are the same as in Example 1.

[0066] 5. Preparation of surface coating: The steps here are the same as in Example 1.

[0067] The main difference between Example 4 and Example 1 is that the silicon oxide-coated ZrW2O8 prepared in Example 3 was first mixed with hydrophobic fumed silica treated with hexamethyldisilazane, and then mixed with quartz powder.

[0068] Example 5: Example 5 includes the following steps: 1. Preparation of ZrW2O8 powder: The steps here are the same as in Example 1.

[0069] 2. Preparation of silicon dioxide-coated ZrW2O8: The steps here are the same as in Example 1.

[0070] 3. Preparation of the first silicone rubber protective sleeve layer: 100 parts by weight of methyl vinyl silicone rubber (MVQ, vinyl content 0.15 mol%), 15 parts by weight of mullite, 2 parts by weight of γ-glycidyl etheroxypropyltrimethoxysilane, 1 part by weight of γ-aminopropyltriethoxysilane, 3 parts by weight of hydroxyl silicone oil (molecular weight 1000), and 4 parts by weight of zinc oxide were sequentially added to a mixer and mixed at 45°C for 15 min. Then, 20 parts by weight of the prepared silica-coated ZrW2O8 powder were added and mixed for another 10 min. Finally, 1.5 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPMH) were added and the mixture was passed through a thin tube 5 times to obtain the first silicone rubber compound.

[0071] The obtained first silicone rubber compound was coated on the outer surface of the glass fiber reinforced epoxy resin mandrel, and then molded and vulcanized at 170°C and 12MPa for 20 minutes to form a first silicone rubber protective layer with a thickness of 4mm.

[0072] 4. Preparation of surface coating: Vapor-phase nano-silica (D50 particle size 30nm) was added to an ethanol aqueous solution (volume ratio of anhydrous ethanol to deionized water 9:1), and perfluorodecyltrimethoxysilane (5% of the mass of nano-silica) was added. The mixture was ultrasonically dispersed for 30 min, heated to 60°C and stirred under reflux for 4 h, centrifuged and washed three times, and then vacuum dried at 80°C for 12 h to obtain hydrophobically modified nano-silica.

[0073] 50 parts by weight of polytrifluoropropylmethylsiloxane oligomer, 12 parts by weight of hydrophobically modified nano-silica, 8 parts by weight of tetraethyl orthosilicate, and 0.2 parts by weight of dibutyltin dilaurate were mixed and diluted with 35 parts by weight of butyl acetate to obtain a surface coating. The above surface coating was sprayed onto the outer surface of the first silicone rubber protective sheath layer, and the wet film thickness was controlled to be 100 μm. Then it was cured at 100°C for 2 hours to form a surface coating; thus, the anti-pollution flashover composite insulator of this embodiment was obtained.

[0074] The main difference between Example 5 and Example 1 is that Example 5 does not include a second silicone rubber protective layer.

[0075] Comparative Example 1: Comparative Example 1 includes the following steps: 1. Preparation of the first silicone rubber protective sheath layer: 100 parts by weight of methyl vinyl silicone rubber (MVQ, vinyl content 0.15 mol%), 25 parts by weight of mullite, 2 parts by weight of γ-glycidoxypropyltrimethoxysilane, 1 part by weight of γ-aminopropyltriethoxysilane, 3 parts by weight of hydroxyl silicone oil (molecular weight 1000), and 4 parts by weight of zinc oxide were sequentially added to a mixer and mixed at 45°C for 15 min. Then, 10 parts by weight of titanium dioxide powder (D50 particle size 100 nm) were added and mixed for another 10 min. Finally, 1.5 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPMH) were added and the mixture was passed through a thin tube 5 times to obtain the first silicone rubber compound.

[0076] The obtained first silicone rubber compound was coated on the outer surface of the glass fiber reinforced epoxy resin mandrel, and then molded and vulcanized at 170°C and 12MPa for 20 minutes to form a first silicone rubber protective layer with a thickness of 1.5mm.

[0077] 4. Preparation of the second silicone rubber protective layer: 100 parts by weight of methyl vinyl silicone rubber (MVQ, vinyl content 0.15 mol%), 20 parts by weight of mullite, 2 parts by weight of γ-glycidyl etheroxypropyltrimethoxysilane, 1 part by weight of γ-aminopropyltriethoxysilane, 3 parts by weight of hydroxyl silicone oil (molecular weight 1000), and 4 parts by weight of zinc oxide were added to a mixer and mixed at 45°C for 15 min; then 1.5 parts by weight of DBPMH were added and the mixture was passed through a thin tube 5 times to obtain the second silicone rubber compound.

[0078] The obtained second silicone rubber compound was coated on the outer surface of the first silicone rubber protective layer, and then molded and vulcanized at 170°C and 12MPa for 20 minutes to form a second silicone rubber protective layer with a thickness of 2.5mm.

[0079] 5. Preparation of surface coating: Vapor-phase nano-silica (D50 particle size 30nm) was added to an ethanol aqueous solution (volume ratio of anhydrous ethanol to deionized water 9:1), and perfluorodecyltrimethoxysilane (5% of the mass of nano-silica) was added. The mixture was ultrasonically dispersed for 30 min, heated to 60°C and stirred under reflux for 4 h, centrifuged and washed three times, and then vacuum dried at 80°C for 12 h to obtain hydrophobically modified nano-silica.

[0080] 50 parts by weight of polytrifluoropropylmethylsiloxane oligomer, 12 parts by weight of hydrophobically modified nano-silica, 8 parts by weight of tetraethyl orthosilicate, and 0.2 parts by weight of dibutyltin dilaurate were mixed and diluted with 35 parts by weight of butyl acetate to obtain a surface coating. The above surface coating was sprayed onto the outer surface of the second silicone rubber protective layer, and the wet film thickness was controlled to be 100 μm. Then it was cured at 100°C for 2 hours to form a surface coating; thus, the anti-pollution flashover composite insulator of this comparative example was obtained.

[0081] Performance testing: The anti-flashover composite insulators prepared in Examples 1 to 5 and Comparative Example 1 were subjected to accelerated aging treatment, followed by cross-sectional microstructure observation and anti-flashover performance testing. All samples were left to stand in a standard environment (23°C, 50% RH) for 168 hours after preparation before testing.

[0082] The composite accelerated aging treatment includes: Each group of insulator samples was placed in a constant temperature and humidity chamber and continuously treated at 50°C and 95%RH for 168 hours. They were then immediately transferred to a temperature cycling chamber and subjected to a temperature cycle of -25°C for 2 hours followed by 45°C for 2 hours, repeated 50 times. This composite aging process was used to simulate the long-term operating conditions of composite insulators under humid and hot conditions with large diurnal temperature variations.

[0083] Cross-sectional microcrack observation: After composite aging treatment, each group of insulator samples was cut along the axial direction. The sample containing the first silicone rubber protective layer and the second silicone rubber protective layer was taken, subjected to liquid nitrogen embrittlement and then gold sputtering treatment. The cross-sectional morphology was observed using a scanning electron microscope (SEM) at magnifications of 500× and 2000×.

[0084] Anti-flashover performance test: Artificial contaminant layer preparation: Sodium chloride, diatomaceous earth with a particle size of 2000 mesh, and deionized water were mixed evenly at a mass ratio of 1:5:15 using a ball milling method to prepare a paste-like contaminant. The contaminant layer was then uniformly coated onto the outer surface (including the surface coating) of each group of insulator samples using a quantitative brushing method.

[0085] Wetting treatment: The coated sample was placed horizontally in an artificial ultrasonic fog test chamber, using deionized water as the fog source, and sprayed at 15.86 mL / (m 3 Atomization volume of ·min is continuously supplied for 30 minutes to wet the area.

[0086] Pressure flashover testing: A 600kV / 0.5A thyristor dual-feedback voltage doubler rectified DC test power supply was used. The dynamic voltage drop was less than 5% when the leakage current was 0.5A, and the voltage ripple coefficient during flashover was less than 3%. Cylindrical electrodes were used. A 200kV DC voltage was applied between the two cylindrical electrodes for 10 minutes; then the voltage was increased uniformly at a rate of 5kV / s until flashover occurred on the sample surface. The flashover voltage (the highest voltage value observed during the pressure application process) was recorded. Each sample was repeated three times, and the average value was taken.

[0087] The test results are shown in Table 1: Table 1 Example 1 No visible microcracks, dense cross-section The surface coating is intact and there is no peeling. 92 Example 2 Through-cracks appeared in the cross section Localized blistering and micro-cracks in the surface coating 60 Example 3 Discontinuous microcracks are visible in the cross-section. The surface coating is mostly intact, with localized micro-cracks. 69 Example 4 Network-like microcracks appeared in the cross section Localized blistering and micro-cracks in the surface coating 64 Example 5 Network-like microcracks appeared in the cross section Partial peeling of surface coating 60 Comparative Example 1 Severe through-cracks appeared in the cross section Large-area peeling of surface coating 53 As can be seen, after composite aging, no microcracks were observed in the cross-section of the protective sheath layer of Example 1 under SEM, and the surface coating remained intact without peeling. This is because the ZrW2O8 powder of Example 1 was sequentially subjected to quartz powder gradation, KH-560 primary modification, and HMDS hydrophobic fumed silica secondary coating. During the 168h high humidity heat treatment, the hydrolysis of ZrW2O8 was effectively suppressed, and its negative expansion characteristics were retained. In the subsequent 50 thermal cycles, a continuous thermal expansion gradient was formed between the first sheath layer and the core rod, and the second sheath layer. The thermal stress was absorbed by the gradient transition layer, and no microcracks were generated at the interface. Therefore, the anti-flashover performance was significantly better than that of Examples 2-4. Example 1 first mixed and coated ZrW2O8 powder with micron-sized quartz powder (D50 particle size of 2μm), and then filled the gaps with hydrophobic fumed silica treated with hexamethyldisilazane with a particle size of less than 20nm, achieving the best effect in suppressing ZrW2O8 hydrolysis, and therefore was superior to Examples 2-4. Example 5 omits the second silicone rubber protective sleeve layer and retains only the first protective sleeve layer with a thickness of 4mm. Although the thermal expansion coefficient of this sleeve layer is small compared with that of the mandrel, there is a significant thermal mismatch between it and the external environment and the surface coating. During 50 thermal cycles, the temperature stress is directly concentrated inside the first protective sleeve layer and at its interface with the mandrel, resulting in the appearance of network microcracks at the interface, peeling of the surface coating, and significantly inferior anti-flashover performance compared to Example 1.

[0088] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary; within the framework of this invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0089] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A composite insulator for preventing flashover, characterized in that, The anti-flashover composite insulator includes the following structure: a core rod, a first silicone rubber protective sleeve covering the outer surface of the core rod, a second silicone rubber protective sleeve covering the outer surface of the first silicone rubber protective sleeve, and a surface coating applied to the outer surface of the second silicone rubber protective sleeve; wherein, the material of the core rod is glass fiber reinforced epoxy resin.

2. The anti-flashover composite insulator according to claim 1, characterized in that, Both the first and second silicone rubber protective sleeves are obtained by compression molding and vulcanization of a methyl vinyl silicone rubber matrix, a composite modified negative thermal expansion filler, a first inorganic filler, and a silane coupling agent.

3. The anti-flashover composite insulator according to claim 2, characterized in that, Both the first and second silicone rubber protective sleeves are obtained by compression molding and vulcanizing a methyl vinyl silicone rubber matrix, a composite modified negative thermal expansion filler, a first inorganic filler, a silane coupling agent, a dispersing agent, zinc oxide, and a peroxide vulcanizing agent. Furthermore, based on the total mass of the first silicone rubber protective sleeve, the mass percentage of the composite modified negative thermal expansion filler contained in the first silicone rubber protective sleeve is selected from 15% to 25%; Based on the total mass of the second silicone rubber protective sleeve, the mass percentage of the composite modified negative thermal expansion filler contained in the second silicone rubber protective sleeve is selected from 3% to 8%.

4. The anti-flashover composite insulator according to claim 3, characterized in that, The first inorganic filler is selected from at least one of zirconium oxide, silicon nitride, silicon carbide, mullite, aluminum titanate, and aluminum magnesium spinel; The silane coupling agent is selected from at least two of the following: γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloyloxypropyltrimethoxysilane. The dispersing agent is selected from silicone oil-based dispersing agents and / or non-silicone oil-based dispersing agents; the silicone oil-based dispersing agent is selected from hydroxyl silicone oil, dimethyl silicone oil, methylphenyl silicone oil, vinyl silicone oil or low viscosity fluorosilicone oil; the non-silicone oil-based dispersing agent is selected from tributyl phosphate, triphenyl phosphate, butyl stearate, oleamide or polyethylene glycol-polypropylene glycol block copolymer; The peroxide vulcanizing agent is selected from at least one of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,4-di-tert-butylperoxyisopropylbenzene, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, dicumyl peroxide, tert-butylperoxyisopropylbenzene, 2,4-dichlorobenzoyl peroxide, and benzoyl peroxide.

5. The anti-flashover composite insulator according to claim 3, characterized in that, The composite modified negative thermal expansion filler is a negative thermal expansion filler coated with a second inorganic filler; The second inorganic filler is selected from silicon oxide, aluminum oxide, titanium oxide, hafnium oxide, or tin oxide; The negative thermal expansion filler is selected from ZrW2O8, HfW2O8, ZrMo2O8, ZrV2O7, ZrP2O7, and Sc2W3O. 12 Y2W3O 12 At least one of LiAlSiO4 and Al2TiO5.

6. The anti-flashover composite insulator according to claim 5, characterized in that, The composite modified negative thermal expansion filler is ZrW2O8 coated with silica.

7. The anti-flashover composite insulator according to claim 6, characterized in that, The composite modified negative thermal expansion filler, which is silica-coated ZrW2O8, is prepared through the following steps: Step 1-a: Prepare ZrW2O8 powder by hydrothermal method; Step 2-a: The prepared ZrW2O8 powder and quartz powder are mixed at a mass ratio of 1:(0.5-1.5), deionized water is added as a dispersion medium, and the mixture is added to a planetary ball mill and ball-milled at 150rpm-250rpm for 5-6h. After ball milling, the resulting slurry is vacuum dried and then ground through a 150-250 mesh sieve to obtain the product of step 2-a. The D50 particle size of the quartz powder is 1-5μm. Step 3-a: Add the product from step 2-a to an aqueous ethanol solution, add KH-560, and then stir at room temperature for 30-45 minutes; Then the temperature is raised to 75℃-85℃ and refluxed with stirring for 3-5 hours; after the reaction is completed, the product is centrifuged, washed and dried to obtain the product of step 3-a; Step 4-a: Add the product of step 3-a and hexamethyldisilazane-treated hydrophobic fumed silica to a mixer at a mass ratio of 1:(0.1-0.3) and mix for 10-15 min; after discharge, the silica-coated ZrW2O8 is obtained.

8. The anti-flashover composite insulator according to claim 7, characterized in that, Step 1-a includes: Step 1-b: Prepare a solution containing Zr element using ZrOCl2·8H2O as the raw material; prepare a solution containing W element using Na2WO4·2H2O as the raw material; simultaneously titrate and mix the Zr-containing solution and the W-containing solution to obtain a white suspension, and then keep it in a 60℃ water bath for 1-3 hours; then add concentrated hydrochloric acid while stirring, and continue stirring for 0.5-2 hours; Step 2-b: Add the solution obtained in Step 1-b to a hydrothermal reactor, place it in an oven, and react at 170℃-190℃ for 8-12 hours. After naturally cooling to room temperature, add the precipitated powder obtained from the reaction to an ethanol aqueous solution for aging for 12-36 hours. Then, filter, wash, and dry to obtain ZrW2O7(OH)2(H2O)2 powder. Step 3-b: After grinding the ZrW2O7(OH)2(H2O)2 powder, place it in a muffle furnace, heat it to 525℃-575℃, calcine it for 5-10 hours, and then cool it naturally to room temperature to obtain ZrW2O8 powder.

9. The anti-flashover composite insulator according to claim 1, characterized in that, The surface coating comprises polytrifluoropropylmethylsiloxane and hydrophobically modified nano-silica; wherein the hydrophobically modified nano-silica is obtained by modifying nano-silica with fluorinated silane; the fluorinated silane is selected from perfluorodecyltrimethoxysilane, perfluorooctyltriethoxysilane or perfluorohexyltrimethoxysilane.

10. A method for preparing the anti-pollution flashover composite insulator according to any one of claims 1-9, characterized in that, The method includes the following steps: Step 1: Provide a mandrel; and prepare silicon oxide-coated ZrW2O8; Step 2: The methyl vinyl silicone rubber matrix, the first inorganic filler, the silane coupling agent, the dispersant, the zinc oxide, and the silica-coated ZrW2O8 obtained in Step 1 are mixed to obtain the first silicone rubber compound; wherein, based on the total mass of the first silicone rubber compound, the mass percentage of the silica-coated ZrW2O8 is 15%-25%; the first silicone rubber compound is coated on the outer surface of the mandrel, and molded and vulcanized at 165℃-180℃ and 10MPa-15MPa for 15-25 minutes to form the first silicone rubber protective sheath layer; Step 3: Mix the methyl vinyl silicone rubber matrix, the first inorganic filler, the silane coupling agent, the dispersant, the zinc oxide, and the silica-coated ZrW2O8 obtained in Step 1 to obtain a second silicone rubber compound; wherein, based on the total mass of the second silicone rubber compound, the mass percentage of the silica-coated ZrW2O8 is 3%-8%; coat the second silicone rubber compound onto the outer surface of the first silicone rubber protective layer, and mold and vulcanize it at 165℃-180℃ and 10MPa-15MPa for 15-25 minutes to form the second silicone rubber protective layer; Step 4: Prepare hydrophobically modified nano-silica; Step 5: Mix polytrifluoropropylmethylsiloxane, hydrophobically modified nano-silica, tetraethyl orthosilicate, and dibutyltin dilaurate; then add butyl acetate for dilution; then coat the mixture onto the outer surface of the second silicone rubber protective sheath layer, and cure it at 80℃-120℃ for 1-3 hours to form the surface coating; thus obtaining the anti-pollution flashover composite insulator.