Preparation method of multifunctional microcapsule for targeted flame retardance and repair of insulating oil

Abstract

The invention relates to a preparation method of a multifunctional microcapsule for targeted flame retardance and repair of insulating oil, an insulating liquid is mixed oil of mineral oil and palm oil-based modified natural ester, and the inherent high flash point characteristic of the modified natural ester improves the fireproof safety of the insulating oil. A multifunctional microcapsule containing a repairing agent and a flame retardant is added into insulating oil, and a shell structure of the microcapsule contains TiO2, so that the microcapsule has the capability of targeted induction of an electric field. When the insulating oil has an arc fault, a high electric field can be generated at the fault position, under the action of the high electric field and the high temperature, the microcapsule directionally migrates to the fault position and cracks, the flame retardant and the repairing material are released, the flame retardant is heated to decompose and absorb heat, the fault temperature is reduced, and meanwhile the repairing agent can repair structural defects caused by arc discharge. The modified insulating oil prepared by the invention has high flame retardance and a targeted repair function, and the service life of the insulating oil is prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of insulating oil preparation, and more specifically, to a preparation method of a modified insulating oil with targeted flame retardancy and repair functions. Background Art

[0002] Mineral oil is widely used as an insulating medium in traditional transformers and power equipment, mainly playing the roles of insulation and cooling. However, with the increase in the operation time of power equipment and the influence of external factors, problems such as aging, breakdown, and arc discharge may occur in the insulating oil, resulting in a decline in its insulation performance and even causing power equipment failures. In addition, mineral oil itself is flammable and is prone to causing fires when electrical equipment fails, posing serious safety hazards. Therefore, developing a modified insulating oil with both flame retardancy and self-repair capabilities has important practical value.

[0003] Adding excessive modifiers to insulating oil not only wastes materials but also is bound to affect the intrinsic properties of the insulating oil, and a small amount of modifiers will not achieve a sufficient modification effect. Moreover, in the existing methods for improving the performance of insulating oil, the purpose of repairing the performance of insulating oil after a failure has not been achieved, and it cannot meet the requirements of all application scenarios. Based on the above requirements and considerations, the present invention proposes a preparation method of a modified insulating oil with targeted flame retardancy and repair functions, aiming to reduce the usage amount of modifiers, reduce the influence of excessive modifier usage on the performance of insulating oil, while improving the flame retardancy of insulating oil and endowing it with the function of targeted performance repair, and extending the service life of insulating oil. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a preparation method of a modified insulating oil with targeted flame retardancy and repair functions to solve the above technical problems.

[0005] To achieve the above purpose, the present application provides the following technical solutions:

[0006] The embodiments of the present application provide a preparation method of a modified insulating oil with targeted flame retardancy and repair functions, and the preparation method includes the following steps:

[0007] S1. Flame retardant modification: Grind magnesium hydroxide to obtain nanoscale magnesium hydroxide particles, and perform modification treatment with a silane coupling agent γ-aminopropyltriethoxysilane solution. After solid-liquid separation, washing, and drying treatments, obtain nanoscale modified magnesium hydroxide particles;

[0008] S2. Core material preparation: Use 1-ethyl-3-methylimidazolium acetate as the repair material and the modified magnesium hydroxide particles as the flame retardant, and mix the two to obtain a core material solution with flame retardancy and repair functions;

[0009] S3. Preparation of microcapsule shell material: Urea and formaldehyde are used to undergo a cross-linking reaction to generate urea-formaldehyde resin. Meanwhile, TiO₂ nanoparticles modified with silane coupling agent γ-aminopropyltriethoxysilane are added to obtain a urea-formaldehyde resin solution containing TiO₂ as the prepolymer of the microcapsule shell material;

[0010] S4. Preparation of microcapsules: The core material is emulsified to obtain a core material emulsion. The urea-formaldehyde resin solution containing TiO₂ is added dropwise to the emulsion. The urea-formaldehyde resin uniformly coats on the surface of the droplets to form a microcapsule solution. The microcapsules are subjected to a coating treatment, and after filtration and drying, microcapsule particles are obtained;

[0011] S5. The microcapsule particles are fully mixed with insulating oil, and then after drying and degassing treatments, a modified insulating oil with targeted flame retardancy and repair functions is obtained.

[0012] The treatment of magnesium hydroxide in step S1 includes the following steps:

[0013] S11. The magnesium hydroxide particles are placed in isopropyl alcohol for ultrasonic cleaning, dried at 60 - 80 °C for 24 hours, and the dried magnesium hydroxide particles are ground and milled for 1 - 2 h using a ball mill;

[0014] S12. γ-aminopropyltriethoxysilane (APTES) is added to the organic solvent isopropyl alcohol, and a small amount of deionized water is added dropwise to the silane solution. The solution is stirred for 30 minutes to obtain a silane coupling agent solution;

[0015] S13. The treated magnesium hydroxide particles are added to the silane coupling agent solution and stirred at 40 - 50 °C for 1 - 2 hours;

[0016] S14. A centrifugal device is used to separate the magnesium hydroxide from the solution, and it is washed 5 times with anhydrous ethanol, and then dried in an oven at 60 - 80 °C for more than 24 hours to obtain dry modified magnesium hydroxide nanoparticles.

[0017] In the preparation process of the core material in step S2, 1-ethyl-3-methylimidazolium acetate is selected as the ionic repair agent. 1-ethyl-3-methylimidazolium acetate is added to the n-hexane solvent and subjected to 1 hour of shaking dispersion to obtain a 1-ethyl-3-methylimidazolium acetate solution. In a 50 °C water bath, the 1-ethyl-3-methylimidazolium acetate solution and the modified magnesium hydroxide nanoparticles are mixed at a mass ratio of 6:4 and stirred for 1 hour to obtain a core material solution with flame retardancy and repair functions.

[0018] The preparation of the microcapsule shell material in step S3 includes the following steps:

[0019] S31. Modify TiO2: Add TiO2 nanoparticles into absolute ethanol, treat them with an ultrasonic disperser for 30 minutes, and add γ-aminopropyltriethoxysilane coupling agent to modify TiO2. Stir for 3 hours, separate the modified TiO2 particles by a centrifuge, and reserve them after drying treatment;

[0020] S32. Prepare the prepolymer of the shell material: Dissolve urea and formaldehyde with a molar ratio of 1:2 in deionized water, add ammonium chloride and stir. Conduct a cross-linking reaction at an ambient temperature of 80 °C for 3 h to obtain a urea-formaldehyde resin solution;

[0021] S33. Introduce TiO2 particles: Add TiO2 with electric field response characteristics into the urea-formaldehyde resin solution. In the present invention, the optimal incorporation amount of TiO2 is determined according to the relationship between the TiO2 incorporation amount and the microcapsule migration rate. The relationship is as follows:

[0022]

[0023] In the formula, v m represents the maximum migration speed of the microcapsule, with the unit of m / s; μ represents the migration rate of TiO2 in insulating oil. The magnitude of μ is related to the particle size of TiO2 and the viscosity of insulating oil; E m represents the maximum electric field strength in oil, with the unit of V / m; n c represents the mass percentage of TiO2 added in the urea-formaldehyde resin. The optimal incorporation amount of TiO2 obtained from the above formula is 12.5%. At this time, the microcapsules prepared have the maximum migration speed in insulating oil. After adding TiO2, continue to stir for 30 minutes.

[0024] In step S4, the preparation of microcapsules includes the following steps:

[0025] S41. Emulsification of the core material: Prepare a deionized water solution containing 1% polyvinyl alcohol, stir magnetically for 30 minutes until completely dissolved, and use it as the external phase solution for emulsifying the core material;

[0026] S42. Emulsify the core material: Take the core repair material as the internal phase, and gradually drop it into the external phase solution according to the ratio of internal phase:external phase = 1:5, and stir for 30 minutes to form a core material droplet emulsion;

[0027] S43. Coating process: Slowly add the urea-formaldehyde resin solution containing TiO2 into the core droplet emulsion, continuously stir and react at 85 °C for 3 hours, and the shell material is gradually deposited on the surface of the core droplets to form microcapsules;

[0028] S44: After the coating process is completed, cool to room temperature and let it stand still to fully harden the capsule wall. Add the microcapsules to an aqueous solution containing a small amount of polyvinyl alcohol (PVA), stir at 40 - 50 °C for 2 hours to form a hydrophobic coating on the outer surface of the microcapsule wall. Collect the microcapsules by centrifugal separation, wash them 5 times with deionized water, and dry them at 50 - 60 °C for 24 hours to obtain microcapsule particles capable of targeted flame retardancy and repair.

[0029] In step S5, the insulating oil is a mixture of mineral oil and palm oil-based modified natural ester. Add the microcapsules to the mixed insulating oil and perform mechanical stirring at a speed of 120 - 150 r / min for 2 h. Place the insulating oil in a vacuum drying oven for drying and degassing for 24 - 48 h, with a vacuum degree of -0.09 to -0.1 MPa and a temperature of 80 - 90 °C to obtain a modified insulating oil with targeted flame retardancy and repair functions.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, a flame retardant and a repair agent are blended to obtain a multifunctional modifier, which can not only improve the flame retardancy of the insulating oil but also enable the insulating oil to self-repair, restore its normal electrical performance, and extend its service life. The modifier is encapsulated in microcapsules and a material with electric field induction characteristics is added to the microcapsule shell layer, enabling the microcapsules to have the function of directional movement. When an arc fault occurs in the insulating oil, causing high temperature and high pressure, leading to a burning tendency and functional impairment of the insulating oil, the microcapsules can respond, migrate and aggregate to the fault area to release the modifier for targeted flame retardancy and repair. In addition, the microcapsules prepared by the present invention have the functions of targeted flame retardancy and repair, so there is no need to add too many microcapsules. When an arc fault occurs, the microcapsules can be directionally aggregated to the fault area to accurately release the modifier, ensuring the flame retardancy and repair effects while avoiding the influence of excessive addition of the modifier on the intrinsic properties of the insulating oil. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 is a process flow chart of the preparation of a modified insulating oil with targeted flame retardancy and repair functions. Detailed Embodiments

[0033] The following will describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings in the embodiments of the present application. It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0034] The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0035] The terms "first", "second", etc. are only used to distinguish one entity or operation from another entity or operation, and cannot be construed as indicating or implying relative importance, nor can it be construed as requiring or implying any actual relationship or order between these entities or operations. Coal-fired steam turbines generally use high-pressure cylinder start-up mode or medium-pressure cylinder start-up mode to control the speed. Different from coal-fired steam turbines, large-scale compressed air energy storage air turbines have problems such as over-large intake pipelines, large system capacity, and poor control accuracy of medium- and low-pressure intake regulating valves. If the speed control method of coal-fired steam turbines is directly adopted, due to the large system capacity and the reasons of residual pressure and poor control accuracy of medium- and low-pressure intake regulating valves, the air turbine will overspeed and the speed will oscillate repeatedly after the medium-pressure cylinder and low-pressure cylinder intake air.

[0036] As Figure 1 shown, this embodiment proposes a preparation method of a modified insulating oil with targeted flame retardancy and repair functions. The specific implementation steps are as follows:

[0037] A modified insulating oil with targeted flame retardancy and repair functions includes the following components: insulating oil with a mass fraction of 99%, microcapsule particles with a mass fraction of 1%. The insulating oil is a mixed oil composed of mineral oil and palm oil-based modified natural ester with mass fractions of 70% and 30% respectively. The core material of the microcapsule particles is a 1-ethyl-3-methylimidazolium acetate solution repair agent and a modified magnesium hydroxide flame retardant with a mass ratio of 6:4. The shell material of the microcapsule particles is urea-formaldehyde resin, and the urea-formaldehyde resin contains 12.5% by mass of TiO2.

[0038] The detailed preparation process of this modified insulating oil with targeted flame retardancy and repair functions is as follows:

[0039] S1. Flame retardant modification

[0040] S11. Place the magnesium hydroxide particles in isopropanol for ultrasonic cleaning, then dry them at 60 - 80 °C for 24 hours. Use a ball mill to crush and grind the dried magnesium hydroxide particles for 1 - 2 hours to obtain magnesium hydroxide with a nano-sized particle diameter.

[0041] S12. Add 5 g of γ-aminopropyltriethoxysilane (APTES) to 100 ml of isopropanol, and gradually add a small amount of deionized water dropwise to the silane solution. Stir the solution for 30 minutes to obtain a silane coupling agent solution.

[0042] S13. Add the treated magnesium hydroxide particles to the silane coupling agent solution and stir at 40 - 50 °C for 1 - 2 hours.

[0043] S14. Use a centrifuge to separate the magnesium hydroxide from the solution, wash it 5 times with absolute ethanol, and then dry it in an oven at 60 - 80 °C for more than 24 hours to obtain dry modified magnesium hydroxide nanoparticles.

[0044] S2. Preparation of the core material

[0045] Select 1-ethyl-3-methylimidazolium acetate as the ion repair agent. Add 1-ethyl-3-methylimidazolium acetate to the n-hexane solvent and perform shaking dispersion for 1 hour to obtain a 1-ethyl-3-methylimidazolium acetate solution. In a 50 °C water bath, mix the 1-ethyl-3-methylimidazolium acetate solution and the modified magnesium hydroxide nanoparticles at a mass ratio of 6:4, and stir for 1 hour to form a homogeneous mixed solution, thereby obtaining a core material solution with flame retardant and repair functions.

[0046] S3. Preparation of the microcapsule shell material

[0047] S31. Modify TiO₂: Add TiO₂ nanoparticles to absolute ethanol, treat them with an ultrasonic disperser for 30 minutes, and add γ-aminopropyltriethoxysilane coupling agent of model KH-550 to modify TiO₂. Stir for 3 hours, and use a centrifuge to separate the modified TiO₂ particles for drying and standby.

[0048] S32. Prepare the shell material prepolymer: Dissolve urea and formaldehyde with a molar ratio of 1:2 in deionized water, add ammonium chloride and stir. Perform a cross-linking reaction at an ambient temperature of 80 °C for 3 hours to obtain a urea-formaldehyde resin solution.

[0049] S33. Introduce TiO₂ particles: According to the relationship formula between the TiO₂ incorporation amount and the microcapsule migration rate in the present invention, the optimal TiO₂ incorporation amount is determined to be 12.5%. After adding TiO₂, continue to stir for 30 minutes to ensure the uniform distribution of the particles in the urea-formaldehyde resin. The relationship formula is as follows:

[0050]

[0051] In the formula, v m represents the maximum migration speed of the microcapsules, with the unit of m / s; μ represents the mobility of TiO2 in insulating oil, and the magnitude of μ is related to the particle size of TiO2 and the viscosity of the insulating oil, with the unit of m 2 / (V·s); E m represents the maximum electric field strength in the oil, with the unit of V / m; n c represents the mass percentage of TiO2 added in urea-formaldehyde resin.

[0052] S4. Preparation of microcapsules

[0053] S41. Emulsification of core materials: Prepare an aqueous deionized solution containing 1% polyvinyl alcohol, and magnetically stir for 30 minutes until completely dissolved, which is used as the external phase solution for emulsifying core materials;

[0054] S42. Emulsifying core materials: Take the core repair materials as the internal phase, and gradually add them dropwise into the external phase solution at a ratio of internal phase:external phase = 1:5, and stir in a homogenizer for 15 minutes to form a core material droplet emulsion.

[0055] S43. Coating process: Slowly add the urea-formaldehyde resin solution containing TiO2 into the core droplet emulsion, and continuously stir and react at 85 °C for 3 hours. The shell material is gradually deposited on the surface of the core droplets to form microcapsules.

[0056] S44: After the coating process is completed, cool to room temperature and let it stand still to fully harden the capsule wall. Add the microcapsules into an aqueous solution containing a small amount of polyvinyl alcohol (PVA), and stir at a temperature of 400 - 50 °C for 2 hours to form a hydrophobic coating on the outer surface of the microcapsule wall. Collect the microcapsules by centrifugal separation, wash them 5 times with deionized water, and dry them at 50 - 60 °C for 24 hours to obtain microcapsule particles with targeted flame retardancy and repair functions.

[0057] S5. Mixing microcapsule particles with insulating oil

[0058] Mix mineral oil and palm oil-based modified natural ester according to a mass ratio of 7:3 to obtain a mixed insulating oil. Add 1 g of microcapsules into 99 g of the mixed insulating oil, and perform mechanical stirring at a speed of 120 - 150 r / min for 2 h. Place the insulating oil containing microcapsules in a vacuum drying oven for 24 - 48 h of drying and degassing treatment, with a vacuum degree of -0.09 to -0.1 MPa and a temperature of 80 - 90 °C, to obtain a modified insulating oil with targeted flame retardancy and repair functions.

[0059] After testing, the power frequency breakdown voltage of the modified insulating oil prepared in the above embodiment is 73.6 kV. Compared with ordinary mineral oil (the power frequency basic voltage is 70 kV), the modified insulating oil in the embodiment still maintains excellent insulation performance; the flash point of the modified insulating oil is 324 °C, which is much higher than that of unmodified ordinary mineral oil; the dielectric loss factor (90 °C) of the modified insulating oil is 0.0053, the volume resistivity is 1.3×10¹² Ω·m, and the kinematic viscosity (25 °C) is 9 mm² / s. All the above performance indicators meet the usage requirements of insulating oil.

[0060] By using the method of arc discharge-induced damage, local damage is generated in the oil sample to observe the release of the microcapsule repair agent and its targeted repair effect. After repair, the breakdown voltage is measured again to evaluate the recovery of insulation performance. After applying arc discharge, the breakdown voltage of ordinary mineral oil drops to 45.4 kV, while the breakdown voltage of the oil sample in the embodiment is 66.2 kV after repair. The microcapsules in the oil sample in the embodiment aggregate and release the repair agent in the damaged area to repair the insulation performance of the insulating oil, proving that its targeted repair function is effective. Without affecting other intrinsic properties of the insulating oil, the present invention improves the flame retardant performance of the insulating oil, endows it with the function of performance repair, prolongs the service life of the insulating oil, and reduces the maintenance cost of the equipment.

[0061] The above are only the embodiments of the present application and are not intended to limit the protection scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of a modified insulating oil with targeted flame retardant and repair functions, characterized in that, The preparation method comprises the following steps: S1. Flame retardant modification: grinding magnesium hydroxide to obtain nano-scale magnesium hydroxide particles, and modifying the magnesium hydroxide particles using a silane coupling agent γ-aminopropyltriethoxysilane solution, and performing solid-liquid separation, washing and drying to obtain nano-scale modified magnesium hydroxide particles; S2. Preparation of core material: 1-ethyl-3-methylimidazolium acetate is used as a repair material, and modified magnesium hydroxide particles are used as a flame retardant, and the two are mixed to obtain a core material solution with flame retardant and repair functions; S3, preparation of microcapsule shell material: using urea and formaldehyde to generate urea-formaldehyde resin by cross-linking reaction, and adding TiO2 nanoparticles modified by silane coupling agent γ-aminopropyltriethoxysilane to obtain urea-formaldehyde resin solution containing TiO2 as a prepolymer of microcapsule shell material; S4, preparation of microcapsules: emulsifying the core material to obtain a core material emulsion, adding a urea-formaldehyde resin solution containing TiO2 dropwise into the emulsion, the urea-formaldehyde resin uniformly coats the surface of the droplets to form a microcapsule solution, coating the microcapsules, filtering and drying to obtain microcapsule particles; S5. The microcapsule particles are fully mixed with the insulating oil, and then dried and degassed to obtain a modified insulating oil with targeted flame retardant and repair functions.

2. The preparation method of a multifunctional microcapsule for targeted flame retardancy and repair of insulating oil according to claim 1, characterized in that, The treatment of magnesium hydroxide in step S1 comprises the following steps: S11. The magnesium hydroxide particles were ultrasonically cleaned in isopropanol, dried at 60-80 ° C for 24 hours, and the dried magnesium hydroxide particles were crushed and ground in a ball mill for 1-2h; S12. γ-aminopropyltriethoxysilane APTES was added to an organic solvent, isopropanol, and a small amount of deionized water was added dropwise to the silane solution, and the solution was stirred for 30 minutes to obtain a silane coupling agent solution; S13. The treated magnesium hydroxide particles are added to the silane coupling agent solution and stirred at 40-50 ° C for 1 to 2 hours; S14. Use a centrifugal device to separate the magnesium hydroxide from the solution, wash it with anhydrous ethanol for 5 times, and then dry it in an oven at 60-80° C. for more than 24 hours to obtain dried modified magnesium hydroxide nanoparticles.

3. A preparation method of a multifunctional microcapsule for targeted flame retardancy and repair of insulating oil according to claim 1, characterized in that, In the preparation process of the core material in step S2, 1-ethyl-3-methylimidazolium acetate is selected as the ion repair agent, 1-ethyl-3-methylimidazolium acetate is added to n-hexane solvent, and the 1-ethyl-3-methylimidazolium acetate solution is obtained by shaking and dispersing for 1 hour. In a 50°C water bath, the 1-ethyl-3-methylimidazolium acetate solution and modified magnesium hydroxide nanoparticles are mixed in a mass ratio of 6:4, and stirred for 1 hour to obtain a core material solution with flame retardant and repair functions.

4. A method for preparing a multifunctional microcapsule for targeted flame retardancy and repair of insulating oil according to claim 1, characterized in that, The preparation of the microcapsule shell material in step S3 includes the following steps: S31. Modification of TiO2: adding TiO2 nanoparticles to anhydrous ethanol, treating with an ultrasonic disperser for 30 minutes, adding γ-aminopropyl triethoxysilane coupling agent to modify TiO2, stirring for 3 hours, separating the modified TiO2 particles with a centrifuge, and drying for later use; S32. Preparation of the shell material prepolymer: Urea and formaldehyde with a molar ratio of 1:2 are dissolved in deionized water, and ammonium chloride is added and stirred. A cross-linking reaction is carried out at an ambient temperature of 80 °C for 3 h to obtain a urea-formaldehyde resin solution; S33. Introduction of TiO2 particles: TiO2 with electric field response characteristics is added to the urea-formaldehyde resin solution. In the present invention, the optimal incorporation amount of TiO2 is determined according to the relationship between the TiO2 incorporation amount and the microcapsule migration rate. The relationship is as follows: where v m represents the maximum migration speed of the microcapsules, with the unit of m / s; μ represents the mobility of TiO2 in the insulating oil, and the magnitude of μ is related to the particle size of TiO2 and the viscosity of the insulating oil; E m represents the maximum electric field strength in the oil, with the unit of V / m; n c represents the mass percentage of TiO2 added in the urea-formaldehyde resin. From the above formula, the optimal doping amount of TiO2 is 12.5%. At this time, the migration speed of the prepared microcapsules in the insulating oil is the largest. After adding TiO2, stir for another 30 minutes.

5. A preparation method of a multifunctional microcapsule for targeted flame retardancy and repair of insulating oil, characterized in that, In step S4, the preparation of the microcapsules includes the following steps: S41. Emulsification of the core material: Prepare an aqueous solution of deionized water containing 1% polyvinyl alcohol and stir magnetically for 30 minutes until completely dissolved as the outer phase solution for emulsifying the core material; S42. Emulsifying the core material: Take the core repair material as the inner phase and gradually add it dropwise to the outer phase solution at a ratio of inner phase:outer phase = 1:5, and stir for 30 minutes to form a core material droplet emulsion; S43. Coating process: Slowly add the urea-formaldehyde resin solution containing TiO2 to the core droplet emulsion, and continuously stir and react at 85 °C for 3 h. The shell material is gradually deposited on the surface of the core droplets to form microcapsules; S44: After the coating process is completed, cool to room temperature and let it stand to fully harden the capsule wall. Add the microcapsules to an aqueous solution containing a small amount of polyvinyl alcohol PVA and stir at a temperature of 40 - 50 °C for 2 h to form a hydrophobic coating on the outer surface of the microcapsule wall. Collect the microcapsules by centrifugal separation, wash them 5 times with deionized water, and dry them at 50 - 60 °C for 24 h to obtain microcapsule particles capable of targeted flame retardancy and repair.

6. A preparation method of a multifunctional microcapsule for targeted flame retardancy and repair of insulating oil according to claim 1, characterized in that, In step S5, the insulating oil is a mixture of mineral oil and palm oil-based modified natural ester. Add the microcapsules to the mixed insulating oil and carry out mechanical stirring at a speed of 120 - 150 r / min for 2 h. Place the insulating oil in a vacuum drying oven for 24 - 48 h of drying and degassing treatment. The vacuum degree is -0.09 to -0.1 MPa, and the temperature is 80 - 90 °C to obtain a modified insulating oil with targeted flame retardancy and repair functions.

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