High-temperature resistant, high-current oil-immersed transformer body leads and their preparation method

Abstract

This invention discloses a high-temperature resistant, reinforced high-current oil-immersed transformer body lead wire and its preparation method, belonging to the field of insulated lead wire preparation. It addresses the technical problem that the insulation performance, oil resistance, and heat aging resistance of existing high-current oil-immersed transformer body leads need further improvement. Specifically, it includes a conductor and an insulating protective layer. The insulating protective layer comprises the following components by weight: 30-40 parts EVA, 10-16 parts POE-g-MAH, 60-70 parts composite silicone rubber, and 25-35 parts composite filler. This invention reinforces the transformer body leads with a composite silicone rubber (made from amino-terminated phosphorus-containing polysiloxane and methylphenyl silicone rubber), EVA, and POE-g-MAH using composite filler. This not only effectively improves the power frequency breakdown strength and oxygen index of the transformer body leads but also enhances the material's oil resistance and mechanical retention after heat aging.

Description

Technical Field

[0001] This invention relates to the field of insulating lead preparation, specifically to high-temperature resistant enhanced high-current oil-immersed transformer body leads and their preparation method. Background Technology

[0002] Oil-immersed transformers, as key equipment in power transmission and conversion systems, are widely used in power transmission and distribution, power equipment manufacturing, rail transportation, metallurgy, chemical industry, and new energy grid connection. The transformer body leads, as important conductive connection structures connecting windings, tap changers, and external conductive components, not only bear the function of large current transmission but also operate in a complex environment of high temperature rise, electric field effects, and immersion in insulating oil for extended periods. Therefore, the heat resistance, electrical insulation, oil resistance, and long-term operational stability of the insulation layer material directly affect the overall safety and reliability of the transformer.

[0003] Currently, the leads of high-current oil-immersed transformers are usually made by covering a polymer insulation layer with a metal conductor. The insulation materials used mainly include cross-linked polyethylene, ethylene-vinyl acetate copolymer, silicone rubber, and some modified polyolefin materials. Under the conditions of high current, long-term high-temperature operation and long-term immersion in transformer oil, there are still problems such as insufficient heat aging resistance, easy swelling or quality change under the action of oil medium, significant decay of mechanical properties, and local electric field concentration leading to a decrease in breakdown strength. Especially under high current operation, the heat generation of the transformer leads is more significant. The insulation layer is in a multi-factor coupled environment of heat, electricity and oil for a long time. Traditional matrix materials often cannot meet the multiple performance requirements of high temperature resistance, flame retardancy, electrical insulation and mechanical retention.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide high-temperature resistant, high-current oil-immersed transformer body leads and their preparation method, so as to solve the technical defects mentioned in the background art.

[0006] The objective of this invention can be achieved through the following technical solution: a high-temperature resistant, high-current oil-immersed transformer body lead wire, comprising a conductor and an insulating protective layer covering the outside of the conductor;

[0007] The insulating protective layer comprises the following components by weight: 30-40 parts EVA, 10-16 parts POE-g-MAH, 60-70 parts composite silicone rubber, 25-35 parts composite filler, and 3-4 parts additives.

[0008] The composite silicone rubber comprises the following components by weight: 30-40 parts of methylphenyl silicone rubber and 12-18 parts of amino-terminated phosphorus-containing polysiloxane.

[0009] The composite filler is obtained by modifying a mixture of BHT-modified filler and polyimide fiber with KH-560.

[0010] Furthermore, the preparation method of amino-terminated phosphorus-containing polysiloxane is as follows: octamethylcyclotetrasiloxane, trifluoropropylmethylcyclotrisiloxane, diethoxysilane-modified phosphate ester, and catalyst are mixed and stirred. The reaction system is heated to 85-95℃ and kept at this temperature for 4-5 hours. Then, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added to the reaction system, and the reaction is kept at this temperature for 60-80 minutes. After post-treatment, amino-terminated phosphorus-containing polysiloxane is obtained.

[0011] The synthesis reaction formula for amino-terminated phosphorus-containing polysiloxanes is as follows:

[0012]

[0013] In the formula:

[0014] Furthermore, the ratio of octamethylcyclotetrasiloxane, trifluoropropylmethylcyclotrisiloxane, diethoxysilane-modified phosphate, catalyst, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 10g:5-7g:3-5g:2-3mL:2.2-2.5g, the catalyst is 75-85wt% sulfuric acid, and the post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, toluene and deionized water are added to the reaction system, the mixture is stirred and dispersed for 20-30 minutes, the mixture is allowed to stand and separated, the organic phase is washed with purified water until neutral, the organic phase is transferred to a rotary evaporator with a water bath temperature of 80-90℃, and low-boiling substances are removed by vacuum evaporation to obtain amino-terminated phosphorus-containing polysiloxane.

[0015] Furthermore, the preparation method of diethoxysilane modified phosphate is as follows: under the protection of an inert gas atmosphere, diethyl (aminomethyl)phosphonate and tetrahydrofuran are mixed and stirred, the reaction system is heated to 50-60℃, isocyanate propylmethyldiethoxysilane is added to the reaction system, the reaction is kept at the temperature for 40-60 min, and after post-treatment, diethoxysilane modified phosphate is obtained.

[0016] The synthesis reaction formula for diethoxysilane-modified phosphate ester is as follows:

[0017]

[0018] Furthermore, the ratio of diethyl (aminomethyl)phosphonate to tetrahydrofuran is 1 g: 8 mL, the molar ratio of diethyl (aminomethyl)phosphonate to propylmethyldiethoxysilane isocyanate is 1 mol: 1 mol, and the post-treatment includes: after the reaction is completed, the reaction system is subjected to negative pressure, and low-boiling substances are removed by vacuum evaporation to obtain diethoxysilane-modified phosphate.

[0019] Furthermore, the BHT-modified filler is obtained through the following steps:

[0020] A1. Mix the mixed filler and buffer solution, sonicate for 30-50 min, add dopamine hydrochloride to the reaction system, keep the reaction at room temperature for 20-22 h, and then perform post-treatment to obtain dopamine modified filler.

[0021] A2. Under an inert gas atmosphere, dopamine-modified filler, 3,5-di-tert-butyl-4-hydroxybenzaldehyde and tetrahydrofuran were mixed and stirred. The reaction system was heated to 55-60℃ and kept at that temperature for 10-12 hours. After post-treatment, BHT-modified filler was obtained.

[0022] Further, in step A1, the ratio of the mixed packing material, buffer solution, and dopamine hydrochloride is 1g:50mL:0.2-0.3g. The buffer solution is a 0.1mol / L Tris buffer solution with pH=8.5. The mixed packing material is composed of boron nitride, nano-silica, and silicon carbide whiskers in a weight ratio of 10-14:6-8:4-6. The post-treatment includes: after the reaction is complete, filtration is performed, the filter cake is washed twice with purified water and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain dopamine-modified packing material.

[0023] Further, in step A2, the ratio of the dopamine-modified packing material, 3,5-di-tert-butyl-4-hydroxybenzaldehyde, and tetrahydrofuran is 6-7 g:1 g:50 mL. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed three times with purified water and then dried, the filter cake is transferred to a drying oven at 70-80°C and dried to constant weight to obtain the BHT-modified packing material.

[0024] Furthermore, the preparation method of the composite filler is as follows: BHT modified filler, polyimide fiber, anhydrous ethanol and KH-560 are mixed and ultrasonically dispersed for 30-50 min. The reaction system is heated to 50-60℃, an alkali solution is added to the reaction system, and the reaction is kept at the temperature for 40-50 min. After post-treatment, the composite filler is obtained.

[0025] Furthermore, the ratio of BHT modified filler, polyimide fiber, anhydrous ethanol, KH-560 and alkaline solution is 10g:2-3g:30mL:2.1-2.5g:5mL, and the alkaline solution is a 2-5mol / L sodium hydroxide aqueous solution. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at 70-80℃ and dried to constant weight to obtain the composite filler.

[0026] The preparation method of the high-temperature resistant and enhanced high-current oil-immersed transformer body lead includes the following steps: EVA, POE-g-MAH, composite silicone rubber, composite filler, and additives are melt-blended according to the formula for 5-7 minutes, then extruded and coated on the outside of the conductor. After cooling, an insulating protective layer is formed to obtain the transformer body lead.

[0027] The present invention has the following beneficial effects:

[0028] 1. The insulating protective layer of the present invention establishes an organosilicon functional phase with a heat-resistant skeleton, flame-retardant structure, and interfacial activity by constructing an amino-terminated phosphorus-containing polysiloxane and compositing it with methylphenyl silicone rubber. The phosphorus-containing structure, derived from diethyl (aminomethyl)phosphonate, is stably embedded in the polysiloxane system in a reactive manner, which can promote surface charring and inhibit thermo-oxidative chain degradation under high temperature or combustion conditions. At the same time, the Si-O-Si bonds in the polysiloxane backbone have high bond energy, which can improve the structural stability of the material under high temperature conditions, slow down the chain segment breakage and mechanical decay caused by aging, and the inhibitory effect of its trifluoropropyl side chain segments on medium intrusion and the promoting effect of amino-terminated structure on phase interface bonding enable the insulating protective layer to maintain high tensile strength after thermal aging, and exhibit a high oxygen index and low mass change rate, thereby significantly improving the material's heat aging resistance, flame retardancy and medium stability.

[0029] 2. This invention involves dopamine coating, BHT functionalization, and synergistic treatment of boron nitride, nano-silica, and silicon carbide whiskers with KH-560 and polyimide fibers. Boron nitride imparts excellent insulation properties to the filler system, nano-silica helps fill microscopic voids and improves system density, and silicon carbide whiskers and polyimide fibers together provide skeletal reinforcement. Dopamine modification forms a coating layer rich in active groups on the surface of the inorganic filler, improving filler dispersibility and providing reaction sites for subsequent grafting and coupling. BHT functionalization further... Improving the organic phase affinity and thermo-oxidative stability of the filler surface reduces the risk of interface degradation during thermal aging. KH-560 establishes a more stable interface connection between the inorganic and organic phases, reducing agglomeration, porosity, and debonding. Through a continuous technical path of "filler compounding - surface activation - organic functionalization - coupling enhancement", it reduces internal defects, homogenizes electric field distribution, and enhances stress transmission, thus constructing a composite filler system with multi-level interface control capabilities. This effectively improves the material's power frequency breakdown strength, tensile strength, and oil resistance.

[0030] 3. This invention also involves melt-blending and extruding composite silicone rubber, composite filler, EVA, and POE-g-MAH together. EVA provides basic processability and molding continuity, composite silicone rubber serves as both a heat-resistant insulating phase and a flame-retardant stabilizing phase, composite filler provides insulation reinforcement, dense filling, and mechanical reinforcement, while POE-g-MAH improves the compatibility between phases, reduces phase coarsening and interface defects, and constructs a multiphase component uniformly dispersed, tightly bonded, and macroscopically continuous and dense insulating protective layer. This allows the functions of phosphorus-containing polysiloxane and multi-level modified filler to be effectively transferred and stably reflected in the final product, achieving a balance between key indicators such as power frequency breakdown strength, oxygen index, mass change rate, and tensile strength before and after thermal aging. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] In this invention, the boron nitride has a particle size of 300-500 nm, an effective component content of 99.9%, and a microstructure of flakes.

[0033] In this invention, the nano-silica particles have a size of 325 mesh and an effective component content of 99.5%.

[0034] In this invention, the silicon carbide whiskers have a diameter of 0.1-1 μm, a length of 5-30 μm, and an effective component content of 99.9%.

[0035] In this invention, the polyimide fiber has a length of 1-3 mm and a density of 1.3-1.4 g / cm³. 3 ;

[0036] In this invention, the methyl phenyl silicone rubber is model KH-310, with an effective component content of 99% and a purity of ≥95.0%;

[0037] In this invention, EVA is an ethylene-vinyl acetate copolymer, grade V6110M, and the processing method is injection molding;

[0038] In this invention, the POE-g-MAH grade is N493, and the processing method is injection molding.

[0039] Example 1

[0040] This embodiment provides a method for preparing amino-terminated phosphorus-containing polysiloxanes, including the following steps:

[0041] Step 1: Preparation of diethoxysilane-modified phosphate ester

[0042] Weigh out 16.7 g of (aminomethyl)phosphonate diethyl ester and 133.6 mL of tetrahydrofuran and add them to a reaction flask under nitrogen protection. Stir the mixture and heat the reaction flask to 50 °C. Add 21.7 g of isocyanate propylmethyldiethoxysilane to the reaction flask and keep the mixture at this temperature for 40 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain diethoxysilane-modified phosphate ester.

[0043] In the reaction, the amino group in diethyl (aminomethyl)phosphonate undergoes a nucleophilic addition reaction with the isocyanate group in propylmethyldiethoxysilane, forming a urea-linked structure. This connects the phosphorus-containing structure to the organosilicon unit with the diethoxysilane end group within the same molecule. This transforms the phosphorus-containing component, which might otherwise exist in a small molecule form, into a reactive phosphorus-containing structure that can be further embedded in the siloxane system. Because this phosphorus-containing structure is not simply physically mixed but is stably introduced through chemical bonds, it is less prone to migration, precipitation, or volatilization during subsequent processing and use.

[0044] Phosphate ester / phosphonate derivative structures can promote dehydration and char formation and inhibit thermo-oxidative chain cracking under high temperature and combustion conditions, thereby improving the oxygen index of the material. Urea and diethoxysilane structures improve the binding ability of this intermediate with the subsequent siloxane system, reduce low molecular defect sources, and help maintain the uniformity of the internal microstructure of the material, thereby improving the power frequency breakdown strength and the retention rate of tensile strength after thermal aging.

[0045] Step 2: Preparation of amino-terminated phosphorus-containing polysiloxanes

[0046] Weigh out 100g of octamethylcyclotetrasiloxane, 50g of trifluoropropylmethylcyclotrisiloxane, 30g of diethoxysilane-modified phosphate ester, and 20mL of 75wt% sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 85℃. Keep the mixture at this temperature for 4h. Add 22g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction flask and keep the mixture at this temperature for 60min. Cool the reaction flask to room temperature and add 500mL of toluene and 300mL of deionized water. Stir and disperse the mixture for 20min. Let it stand and separate the liquids. Wash the organic phase with purified water until neutral. Transfer the organic phase to a rotary evaporator with a water bath temperature of 80℃ and remove low-boiling substances under reduced pressure to obtain amino-terminated phosphorus-containing polysiloxane.

[0047] In the reaction, octamethylcyclotetrasiloxane and trifluoropropylmethylcyclotrisiloxane undergo ring-opening of the Si-O-Si ring structure under sulfuric acid and high-temperature catalysis, forming growing linear polysiloxane segments; diethoxysilane-modified phosphate esters are embedded into the polysiloxane structure in the process in the form of copolymerization or grafting; 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane acts as a chain end capping agent, giving the resulting polysiloxane amino active end groups.

[0048] The Si-O bonds in the polysiloxane backbone have high bond energies and superior thermal stability compared to ordinary CC backbone polymers. Therefore, they can significantly improve the material's structural retention under thermal aging conditions, slow down chain segment breakage and embrittlement, and ensure that the material still has high tensile strength after thermal aging. The introduction of trifluoropropyl side chains reduces the surface energy of the molecular chain, enhances oleophobicity and media stability, thereby inhibiting penetration and swelling during mineral oil immersion. The amino-terminated structure makes this phosphorus-containing polysiloxane not only a heat-resistant and flame-retardant component, but also a compatibility bridge with interfacial activity. It can improve the interfacial bonding between the polysiloxane and methylphenyl silicone rubber, EVA, POE-g-MAH, and modified fillers through hydrogen bonding, polar interactions, and even synergy with coupling interfaces.

[0049] Example 2

[0050] This embodiment provides a method for preparing amino-terminated phosphorus-containing polysiloxanes, including the following steps:

[0051] Step 1: Preparation of diethoxysilane-modified phosphate ester

[0052] Weigh out 16.7 g of (aminomethyl)phosphonate diethyl ester and 133.6 mL of tetrahydrofuran and add them to a reaction flask under nitrogen protection. Stir the mixture and heat the reaction flask to 55 °C. Add 21.7 g of isocyanate propylmethyldiethoxysilane to the reaction flask and keep the mixture at this temperature for 50 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain diethoxysilane-modified phosphate ester.

[0053] Step 2: Preparation of amino-terminated phosphorus-containing polysiloxanes

[0054] Weigh out 100g of octamethylcyclotetrasiloxane, 60g of trifluoropropylmethylcyclotrisiloxane, 40g of diethoxysilane-modified phosphate ester, and 25mL of 80wt% sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 90℃. Keep the mixture at this temperature for 4.5h. Add 23.5g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction flask and keep the mixture at this temperature for 70min. Cool the reaction flask to room temperature and add 500mL of toluene and 300mL of deionized water. Stir and disperse the mixture for 25min. Allow the mixture to stand and separate the liquids. Wash the organic phase with purified water until neutral. Transfer the organic phase to a rotary evaporator with a water bath temperature of 85℃ and remove low-boiling substances under reduced pressure to obtain amino-terminated phosphorus-containing polysiloxane.

[0055] Example 3

[0056] This embodiment provides a method for preparing amino-terminated phosphorus-containing polysiloxanes, including the following steps:

[0057] Step 1: Preparation of diethoxysilane-modified phosphate ester

[0058] Weigh out 16.7 g of (aminomethyl)phosphonate diethyl ester and 133.6 mL of tetrahydrofuran and add them to a reaction flask under nitrogen protection. Stir the mixture and heat the reaction flask to 60 °C. Add 21.7 g of isocyanate propylmethyldiethoxysilane to the reaction flask and keep the mixture at this temperature for 60 min. Then, evacuate the reaction flask to -0.1 MPa and remove low-boiling substances by vacuum distillation to obtain diethoxysilane-modified phosphate ester.

[0059] Step 2: Preparation of amino-terminated phosphorus-containing polysiloxanes

[0060] Weigh out 100g of octamethylcyclotetrasiloxane, 70g of trifluoropropylmethylcyclotrisiloxane, 50g of diethoxysilane-modified phosphate ester, and 30mL of 85wt% sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 95℃. Keep the mixture at this temperature for 5h. Add 25g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction flask and keep the mixture at this temperature for 80min. Cool the reaction flask to room temperature and add 500mL of toluene and 300mL of deionized water. Stir and disperse the mixture for 30min. Let it stand and separate the liquids. Wash the organic phase with purified water until neutral. Transfer the organic phase to a rotary evaporator with a water bath temperature of 90℃ and remove low-boiling substances under reduced pressure to obtain amino-terminated phosphorus-containing polysiloxane.

[0061] Example 4

[0062] This embodiment provides a method for preparing a composite filler, including the following steps:

[0063] Step a: Preparation of dopamine-modified filler

[0064] Boron nitride, nano-silica, and silicon carbide whiskers were mixed evenly in a weight ratio of 10:6:4 to obtain a mixed filler.

[0065] Weigh out 100g of mixed packing material and 5000mL of 0.1mol / L Tris buffer solution (pH=8.5) and add them to the reaction flask. Disperse the mixture by sonication for 30min. Fix the reaction flask on an iron stand with mechanical stirring and stir. Add 20g of dopamine hydrochloride to the reaction flask. Incubate the reaction at room temperature for 20h. Filter the mixture. Wash the filter cake twice with purified water and dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain dopamine-modified packing material.

[0066] In the reaction, dopamine is oxidized in Tris buffer to form dopaquinone and its subsequent polymerization products, ultimately forming a polydopamine coating on the surfaces of boron nitride, nano-silica, and silicon carbide whiskers. This coating is rich in catechol hydroxyl and amino groups, exhibiting extremely strong surface adhesion and secondary reaction activity.

[0067] In the mixed filler, boron nitride itself has excellent insulation properties, nano-silica can fill micropores and improve density, and silicon carbide whiskers provide rigid reinforcement. However, if these three are directly added to the polymer matrix, interface defects are often formed due to differences in surface energy and agglomeration tendency, which will cause electric field concentration and stress concentration. The formation of the dopamine coating layer changes the surface of the inorganic filler from "inert and difficult to wet" to "wettable and reactive", which significantly improves its dispersion stability in the organic phase. After the dispersion is improved, the internal pores, agglomerates and local phase boundary defects of the material are reduced, and the electric field distribution is more uniform, thus improving the power frequency breakdown strength. At the same time, after the interface is more uniform, stress can be transmitted more effectively, and the tensile strength is also improved. When immersed in mineral oil, the interface is no longer easy to form penetration channels, improving the oil resistance of the material.

[0068] Step b: Preparation of BHT modified filler

[0069] Weigh out 60g of dopamine-modified filler, 10g of 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 5g of 4A molecular sieve, and 500mL of tetrahydrofuran and add them to a reaction flask under nitrogen protection. Stir the mixture and heat it to 55℃. Keep the mixture at this temperature for 10h. Cool the mixture to room temperature and filter it. Wash the filter cake three times with purified water and dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight. Sieve the mixture to remove the 4A molecular sieve and obtain the BHT-modified filler.

[0070] In the reaction, 3,5-di-tert-butyl-4-hydroxybenzaldehyde undergoes a Schiff base condensation reaction with the amino groups on the dopamine coating surface, i.e., the aldehyde group condenses with the primary amine to form a C=N bond, thereby grafting a hindered phenolic aromatic structure onto the filler surface. The 4A molecular sieve mainly plays a role in adsorbing and generating water, and driving the condensation equilibrium towards the product direction, forming an aromatic hindered phenolic structure with strong organic affinity on the filler surface. The hindered phenolic structure can improve the compatibility between the filler and the organic matrix, making the filler more stably embedded in the polymer network and reducing interfacial debinding and aggregation. Furthermore, the hindered phenol itself has a certain antioxidant and free radical scavenging tendency, which can slow down the oxidative degradation of polymer segments near the interface during thermal aging.

[0071] Step c: Preparation of composite filler

[0072] Weigh out 100g of BHT modified filler, 20g of polyimide fiber, 3000mL of anhydrous ethanol, and 21g of KH-560 and add them to a reaction flask. Disperse the mixture by sonication for 30min. Fix the reaction flask on an iron stand with a mechanical stirrer and stir. Heat the reaction flask to 50℃ and add 50mL of 2mol / L sodium hydroxide aqueous solution. Keep the reaction at this temperature for 40min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain the composite filler.

[0073] In the reaction, KH-560, or γ-glycidyl etheroxypropyltrimethoxysilane, undergoes alkoxy hydrolysis under ethanol / water and alkaline conditions to form silanol, which then condenses with the hydroxyl groups on the filler surface or the active sites in the polydopamine coating to form stable Si-O-Si or Si-OM interfacial bonds. The epoxy / organic segments at the other end can interact more strongly with the organic matrix, thus establishing a chemical or quasi-chemical bridge between the inorganic filler and the organic polymer. Polyimide nanofibers possess high heat resistance and high modulus, and can form a microfiber-reinforced network in the composite system. With the synergy of both, the filler becomes a composite reinforcing phase that is "surface-organized, interfacially coupled, and internally reinforced."

[0074] After interface coupling reinforcement, the voids around the filler and interface debonding are significantly reduced, the electrical trees and partial discharge initiation points are reduced, and the power frequency breakdown strength is improved; polyimide nanofibers and silicon carbide whiskers together form a three-dimensional reinforcing skeleton, which improves the material's load-bearing capacity; interface densification and network reinforcement reduce the channels for mineral oil to penetrate along the interface; the heat-resistant skeleton and stable interface further mitigate the structural degradation during thermal aging.

[0075] Example 5

[0076] This embodiment provides a method for preparing a composite filler, including the following steps:

[0077] Step a: Preparation of dopamine-modified filler

[0078] Boron nitride, nano-silica, and silicon carbide whiskers were mixed evenly in a weight ratio of 12:7:5 to obtain a mixed filler.

[0079] Weigh 100g of mixed packing material and 5000mL of 0.1mol / L Tris buffer solution (pH=8.5) and add them to the reaction flask. Disperse the mixture by sonication for 40min. Fix the reaction flask on an iron stand with mechanical stirring and stir. Add 25g of dopamine hydrochloride to the reaction flask. Incubate the reaction at room temperature for 21h. Filter the mixture. Wash the filter cake twice with purified water and dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain dopamine-modified packing material.

[0080] Step b: Preparation of BHT modified filler

[0081] Weigh out 65g of dopamine-modified filler, 10g of 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 5.5g of 4A molecular sieve, and 500mL of tetrahydrofuran and add them to a reaction flask under nitrogen protection. Stir the mixture and heat it to 57℃. Keep the mixture at this temperature for 11 hours. Cool the mixture to room temperature and filter it. Wash the filter cake three times with purified water and dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight. Sieve the mixture to remove the 4A molecular sieve and obtain the BHT-modified filler.

[0082] Step c: Preparation of composite filler

[0083] Weigh out 100g of BHT modified filler, 25g of polyimide fiber, 3000mL of anhydrous ethanol, and 23g of KH-560 and add them to a reaction flask. Disperse the mixture ultrasonically for 40min. Fix the reaction flask on an iron stand with a mechanical stirrer and stir. Heat the reaction flask to 55℃ and add 50mL of 3.5mol / L sodium hydroxide aqueous solution. Keep the reaction at this temperature for 45min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain the composite filler.

[0084] Example 6

[0085] This embodiment provides a method for preparing a composite filler, including the following steps:

[0086] Step a: Preparation of dopamine-modified filler

[0087] Boron nitride, nano-silica, and silicon carbide whiskers were mixed evenly in a weight ratio of 14:8:6 to obtain a mixed filler.

[0088] Weigh out 100g of mixed packing material and 5000mL of 0.1mol / L Tris buffer solution (pH=8.5) and add them to the reaction flask. Disperse the mixture by sonication for 50min. Fix the reaction flask on an iron stand with mechanical stirring and stir. Add 30g of dopamine hydrochloride to the reaction flask. Incubate the reaction at room temperature for 22h. Filter the mixture. Wash the filter cake twice with purified water and dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain dopamine-modified packing material.

[0089] Step b: Preparation of BHT modified filler

[0090] Weigh out 70g of dopamine-modified filler, 10g of 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 6g of 4A molecular sieve, and 500mL of tetrahydrofuran and add them to a reaction flask under nitrogen protection. Stir the mixture and heat it to 57℃. Keep the mixture at this temperature for 12h. Cool the mixture to room temperature and filter it. Wash the filter cake three times with purified water and dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight. Sieve the mixture to remove the 4A molecular sieve and obtain the BHT-modified filler.

[0091] Step c: Preparation of composite filler

[0092] Weigh out 100g of BHT modified filler, 30g of polyimide fiber, 3000mL of anhydrous ethanol, and 25g of KH-560 and add them to a reaction flask. Disperse the mixture ultrasonically for 50min. Fix the reaction flask on an iron stand with a mechanical stirrer and stir. Heat the reaction flask to 60℃ and add 50mL of 5mol / L sodium hydroxide aqueous solution. Keep the reaction at this temperature for 50min. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain the composite filler.

[0093] Example 7

[0094] This embodiment provides a method for preparing the high-temperature resistant, high-current oil-immersed transformer body leads, including the following steps:

[0095] Step S1: Preparation of composite silicone rubber

[0096] Weigh out 30 parts by weight of methylphenyl silicone rubber and 12 parts by weight of amino-terminated phosphorus-containing polysiloxane prepared in Example 1, add them to a mixer at 150°C, and mix for 20 minutes to obtain composite silicone rubber.

[0097] Step S2: Prepare transformer body leads

[0098] Carbon black, ethylene bis-stearamide, sodium stearate, butyl phthalate and antioxidant 405 are mixed evenly in a weight ratio of 10:3:5:6:3 to obtain the additive.

[0099] Weigh out the following components by weight: 30 parts EVA, 10 parts POE-g-MAH, 60 parts composite silicone rubber, 25 parts composite filler prepared in Example 4, and 3 parts additives. Add these components to a twin-screw extruder. Set the temperatures of the twin-screw extruder as follows: Zone I: 175°C, Zone II: 180°C, Zone III: 180°C, Zone IV: 180°C, Zone V: 180°C, Zone VI: 185°C, and Die Zone: 190°C. After melt blending for 5 minutes, extrude the mixture to coat the conductor. After cooling, an insulating protective layer with a thickness of 2 ± 0.1 mm is formed, resulting in the transformer body lead wire.

[0100] Example 8

[0101] This embodiment provides a method for preparing the high-temperature resistant, high-current oil-immersed transformer body leads, including the following steps:

[0102] Step S1: Preparation of composite silicone rubber

[0103] Weigh out 35 parts by weight of methylphenyl silicone rubber and 15 parts by weight of amino-terminated phosphorus-containing polysiloxane prepared in Example 2, add them to a mixer at a temperature of 155°C, and mix for 25 minutes to obtain composite silicone rubber.

[0104] Step S2: Prepare transformer body leads

[0105] Carbon black, ethylene bis-stearamide, calcium stearate, dioctyl phthalate and antioxidant 405 are mixed evenly in a weight ratio of 10:3:5:6:3 to obtain the additive.

[0106] Weigh out the following components by weight: 35 parts EVA, 13 parts POE-g-MAH, 65 parts composite silicone rubber, 30 parts composite filler prepared in Example 5, and 3.5 parts additives. Add these components to a twin-screw extruder. Set the temperatures of the twin-screw extruder as follows: Zone I: 175°C, Zone II: 180°C, Zone III: 180°C, Zone IV: 180°C, Zone V: 180°C, Zone VI: 185°C, and Die Zone: 190°C. After melt blending for 6 minutes, extrude the mixture to coat the conductor. After cooling, an insulating protective layer with a thickness of 2 ± 0.1 mm is formed, resulting in the transformer body lead wire.

[0107] Example 9

[0108] This embodiment provides a method for preparing the high-temperature resistant, high-current oil-immersed transformer body leads, including the following steps:

[0109] Step S1: Preparation of composite silicone rubber

[0110] Weigh out 40 parts by weight of methylphenyl silicone rubber and 18 parts by weight of amino-terminated phosphorus-containing polysiloxane prepared in Example 3, add them to a mixer at a temperature of 160°C, and mix for 30 minutes to obtain composite silicone rubber.

[0111] Step S2: Prepare transformer body leads

[0112] Carbon black, ethylene bis-stearamide, barium stearate, diisobutyl phthalate and antioxidant 405 are mixed evenly in a weight ratio of 10:3:5:6:3 to obtain the additive.

[0113] Weigh out the following components by weight: 40 parts EVA, 16 parts POE-g-MAH, 70 parts composite silicone rubber, 35 parts composite filler prepared in Example 6, and 4 parts additives. Add these components to a twin-screw extruder. Set the temperatures of the twin-screw extruder as follows: Zone I: 175°C, Zone II: 180°C, Zone III: 180°C, Zone IV: 180°C, Zone V: 180°C, Zone VI: 185°C, and Die Zone: 190°C. After melt blending for 7 minutes, extrude the mixture to coat the conductor. After cooling, an insulating protective layer with a thickness of 2 ± 0.1 mm is formed, resulting in the transformer body lead wire.

[0114] Comparative Example 1

[0115] The difference between this comparative example and Example 9 is that, in the preparation of the amino-terminated phosphorus-containing polysiloxane used, step 1 was omitted, and diethoxysilane-modified phosphate ester was not added in step 2.

[0116] Comparative Example 2

[0117] The difference between this comparative example and Example 9 is that KH-560 was not added in step c during the preparation of the composite filler.

[0118] Comparative Example 3

[0119] The difference between this comparative example and Example 9 is that, in the preparation of the composite filler, steps a and b are omitted, and the BHT modified filler in step c is replaced by the mixed filler in step a.

[0120] Comparative Example 4

[0121] The difference between this comparative example and Example 9 is that POE-g-MAH was not added in step S2.

[0122] Performance testing:

[0123] Referring to standard GB / T 1408.1-2016 "Electrical strength test method for insulating materials - Part 1: Power frequency test", the power frequency breakdown strength of the insulation protective layer of the transformer body leads prepared in Examples 7-9 and Comparative Examples 1-4 was determined at a voltage step-up rate of 2kV / s.

[0124] Referring to standard GB / T 2951.12-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 12: General Test Methods - Thermal Aging Test Method", the transformer body leads prepared in Examples 7-9 and Comparative Examples 1-4 were subjected to heat preservation aging treatment in an oven at 150°C for 160 hours. Referring to standard GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11: General Test Methods - Thickness and Dimensional Measurement - Mechanical Property Test", the tensile strength of the insulation protective layer of the transformer body leads before and after aging was determined.

[0125] The oxygen index of the insulating protective layer of the transformer body leads prepared in Examples 7-9 and Comparative Examples 1-4 was determined according to the standard GB / T 2406.2-2009 "Determination of flammability of plastics by oxygen index method - Part 2: Room temperature test".

[0126] Referring to the standard GB / T 1690-2010 "Test Method for Liquid Resistance of Vulcanized Rubber or Thermoplastic Rubber", the insulating protective layer of the transformer body leads prepared in Examples 7-9 and Comparative Examples 1-4 was immersed in mineral oil at 100℃ for 7 days, and the mass change rate of the samples was measured. The specific test data are shown in Table 1 below.

[0127] Table 1 - Performance Test Data of Samples

[0128]

[0129] Data Analysis:

[0130] Comparative analysis of the data in Table 1 shows that the power frequency breakdown strength of the insulation protective layer for transformer body leads prepared by this invention reaches 29.3-31.5 kV / mm, the oxygen index reaches 32.3-33.8%, the mass change rate after high-temperature oil immersion decreases to 1.47-1.61%, the tensile strength before aging reaches 15.3-16.5 MPa, and the tensile strength after aging reaches 14.6-15.6 MPa. All performance test data are superior to the comparative example, indicating that this invention prepares diethoxysilane-modified phosphate ester by reacting (aminomethyl)phosphonate diethyl ester with isocyanate propylmethyldiethoxysilane, and then reacts it with octamethylcyclotetrasiloxane and trifluoropropylmethylcyclotrisiloxane. Ring-opening polymerization of aminosiloxane yields a polysiloxane with both phosphorus-containing flame retardancy and amino active end groups. Simultaneously, using boron nitride, nano-silica, and silicon carbide whiskers as fillers, a composite filler with superior interfacial compatibility and heat resistance is prepared through dopamine coating, BHT grafting, and synergistic modification with KH-560 and polyimide fibers. Finally, methylphenyl silicone rubber is combined with the phosphorus-containing polysiloxane to form a composite silicone rubber, which is then melt-blended with EVA, POE-g-MAH, composite filler, and additives, and extruded onto the conductor surface to form an insulating protective layer. This results in a high-temperature reinforced transformer body lead wire with high power frequency breakdown strength, high oxygen index, good oil resistance, and good mechanical retention after thermal aging.

[0131] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. High-temperature resistant, high-current oil-immersed transformer body leads, characterized in that, Includes the conductor and the insulating protective layer covering the outside of the conductor; The insulating protective layer comprises the following components by weight: 30-40 parts EVA, 10-16 parts POE-g-MAH, 60-70 parts composite silicone rubber, 25-35 parts composite filler, and 3-4 parts additives. The composite silicone rubber comprises the following components by weight: 30-40 parts of methylphenyl silicone rubber and 12-18 parts of amino-terminated phosphorus-containing polysiloxane. The composite filler is obtained by modifying a mixture of BHT-modified filler and polyimide fiber with KH-560.

2. The high-temperature resistant, high-current oil-immersed transformer body leads according to claim 1, characterized in that, The preparation method of amino-terminated phosphorus-containing polysiloxane is as follows: octamethylcyclotetrasiloxane, trifluoropropylmethylcyclotrisiloxane, diethoxysilane-modified phosphate ester, and catalyst are mixed and stirred. The reaction system is heated to 85-95℃ and kept at this temperature for 4-5 hours. Then, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added to the reaction system, and the reaction is kept at this temperature for 60-80 minutes. After post-treatment, amino-terminated phosphorus-containing polysiloxane is obtained.

3. The high-temperature resistant, enhanced high-current oil-immersed transformer body leads according to claim 2, characterized in that, The ratio of octamethylcyclotetrasiloxane, trifluoropropylmethylcyclotrisiloxane, diethoxysilane-modified phosphate, catalyst, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 10g:5-7g:3-5g:2-3mL:2.2-2.5g, and the catalyst is 75-85wt% sulfuric acid.

4. The high-temperature resistant, high-current oil-immersed transformer body leads according to claim 2, characterized in that, The preparation method of diethoxysilane modified phosphate is as follows: under the protection of an inert gas atmosphere, diethyl (aminomethyl)phosphonate and tetrahydrofuran are mixed and stirred, the reaction system is heated to 50-60℃, isocyanate propylmethyldiethoxysilane is added to the reaction system, the reaction is kept at the temperature for 40-60 min, and after post-treatment, diethoxysilane modified phosphate is obtained.

5. The high-temperature resistant, high-current oil-immersed transformer body leads according to claim 4, characterized in that, The ratio of diethyl (aminomethyl)phosphonate to tetrahydrofuran is 1 g: 8 mL, and the molar ratio of diethyl (aminomethyl)phosphonate to isocyanate propylmethyldiethoxysilane is 1 mol: 1 mol.

6. The high-temperature resistant, high-current oil-immersed transformer body leads according to claim 1, characterized in that, BHT-modified filler is obtained through the following steps: A1. Mix the mixed filler and buffer solution, sonicate for 30-50 min, add dopamine hydrochloride to the reaction system, keep the reaction at room temperature for 20-22 h, and then perform post-treatment to obtain dopamine modified filler. A2. Under an inert gas atmosphere, dopamine-modified filler, 3,5-di-tert-butyl-4-hydroxybenzaldehyde and tetrahydrofuran were mixed and stirred. The reaction system was heated to 55-60℃ and kept at that temperature for 10-12 hours. After post-treatment, BHT-modified filler was obtained.

7. The high-temperature resistant, high-current oil-immersed transformer body leads according to claim 6, characterized in that, In step A1, the ratio of the mixed filler, buffer solution, and dopamine hydrochloride is 1g:50mL:0.2-0.3g. The buffer solution is a 0.1mol / L Tris buffer solution with pH=8.

5. The mixed filler is composed of boron nitride, nano-silica, and silicon carbide whiskers in a weight ratio of 10-14:6-8:4-6. In step A2, the ratio of the dopamine-modified filler, 3,5-di-tert-butyl-4-hydroxybenzaldehyde, and tetrahydrofuran is 6-7g:1g:50mL.

8. The high-temperature resistant, high-current oil-immersed transformer body leads according to claim 1, characterized in that, The preparation method of the composite filler is as follows: BHT modified filler, polyimide fiber, anhydrous ethanol and KH-560 are mixed and ultrasonically dispersed for 30-50 min. The reaction system is heated to 50-60℃, alkali solution is added to the reaction system, and the reaction is kept at the temperature for 40-50 min. After post-treatment, the composite filler is obtained.

9. The high-temperature resistant, enhanced high-current oil-immersed transformer body leads according to claim 8, characterized in that, The ratio of BHT modified filler, polyimide fiber, anhydrous ethanol, KH-560 and alkaline solution is 10g:2-3g:30mL:2.1-2.5g:5mL, and the alkaline solution is a 2-5mol / L sodium hydroxide aqueous solution.

10. The method for preparing the high-temperature resistant, high-current oil-immersed transformer body leads according to any one of claims 1-9, characterized in that, The process includes the following steps: EVA, POE-g-MAH, composite silicone rubber, composite filler, and additives are melt-blended according to the formula for 5-7 minutes, then extruded and coated onto the outside of the conductor. After cooling, an insulating protective layer is formed, resulting in the transformer body lead wire.

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