Cellulose insulation paper damage repairing method based on mechanical enhanced microcapsule

Abstract

The invention discloses a cellulose insulation paper damage repairing method based on a mechanical enhanced microcapsule, and relates to the technical field of high voltage and insulation. According to the repairing method, damage repairing is conducted on cellulose insulation paper based on a mechanical enhanced microcapsule, the mechanical enhanced microcapsule is mainly prepared from a capsule wall and a core material, the capsule wall comprises polyurethane and nano-silica, and the core material comprises DCPD and a Hoveyda-Grubbs catalyst. The problems that a repairing agent leaks too early and the repairing efficiency is low due to the fact that microcapsules in traditional insulation paper are prone to being broken in advance under external stress are solved, damage repairing is conducted through the insulation paper containing the microcapsules, and the efficiency and accuracy in the repairing process can be improved.

Description

Technical Field

[0001] The invention relates to the field of high voltage and insulation technology, and in particular to a method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules. Background Art

[0002] In the field of high voltage and insulation technology, cellulose insulation paper is widely used in various electrical equipment as a key insulating material in transformers, power generation equipment and power transmission equipment. However, during long-term operation, the insulation paper is affected by various factors such as electric field, thermal stress and mechanical stress, and is prone to electrical damage such as electrical trees and cracks. These damages will weaken the mechanical strength of the insulation paper and reduce its dielectric properties, thereby causing partial discharge and even insulation breakdown, seriously affecting the safety and reliability of electrical equipment. Therefore, how to effectively repair the electrical damage of insulation paper, improve its electrical and mechanical properties, and extend its service life has become a major technical problem in the field of insulation technology.

[0003] In recent years, microcapsule technology has received widespread attention in the field of self-repair of materials. Microcapsules encapsulate the repair agent. When external factors cause the microcapsule to rupture, the repair agent can be released and chemically react with the damaged part, thereby realizing the self-repair function. However, traditional microcapsules have some limitations, especially they are prone to premature rupture under external stress, resulting in premature leakage of the repair agent and reduced repair efficiency. In addition, the mechanical properties of traditional capsule wall materials are poor and it is difficult to remain stable under high stress environments. Therefore, improving the mechanical strength of microcapsules, avoiding premature leakage of the repair agent, and ensuring that the repair agent is released accurately and efficiently when damage occurs are important directions for improving the repair effect of insulating paper. Patent document with publication number CN116574437A discloses a self-repairing insulating material for power equipment and a preparation method thereof. The insulating material is prepared by mixing self-repairing microcapsules with aqueous polyurethane-acrylate composite emulsion, surface modifier, and nanoparticles, stirring evenly, ultrasonically treating, and then mixing with a curing agent. The self-repairing microcapsules are made of a capsule wall and a core material. The capsule wall is a modified urea-formaldehyde resin, and the core material is hexamethylene diisocyanate or isophorone diisocyanate, which can repair cracks. However, the overall mechanical properties of the self-repairing microcapsules and the density of the capsule wall have not been confirmed, and it is not clear whether they can avoid premature leakage of the repair agent.

[0004] Based on the above problems, the purpose of this application is to provide a method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules. Summary of the invention

[0005] In view of the above shortcomings, the present invention provides a method for repairing cellulose insulation paper damage based on mechanically enhanced microcapsules, which solves the problem that the microcapsules in traditional insulation paper are prone to premature rupture under external stress, resulting in premature leakage of the repair agent and low repair efficiency. The microcapsules of the present invention can effectively enhance the mechanical and electrical properties of the insulation paper. The use of the cellulose insulation paper of the present invention for electrical damage repair can improve the efficiency and accuracy of the repair process. The specific technical solution is as follows:

[0006] A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules is used to repair damage to cellulose insulation paper based on mechanically enhanced microcapsules. The mechanically enhanced microcapsules are mainly made of capsule walls and core materials, the capsule walls include polyurethane and nano-silicon dioxide, and the core materials include DCPD (dicyclopentadiene) and a Hoveyda-Grubbs catalyst.

[0007] Preferably, the particle size of the mechanically enhanced microcapsules is 2 μm to 10 μm, and the capsule wall thickness is 200 nm to 1 μm.

[0008] Preferably, the particle size of the nano-silicon dioxide is 20 nm to 50 nm.

[0009] Preferably, it is characterized in that the method for preparing the mechanically enhanced microcapsules comprises the following steps:

[0010] (1) Nano-silicon dioxide dispersion treatment: Disperse nano-silicon dioxide in water or ethanol, and perform ultrasonic treatment or high-speed stirring to obtain a nano-silicon dioxide suspension;

[0011] (2) Preparation of core material solution: After dissolving DCPD in an organic solvent, slowly add 0.5 to 5 mol% of the total amount of DCPD into Hoveyda-Grubbs catalyst, and stir evenly to form a core material solution;

[0012] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-silicon dioxide suspension, and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-silicon dioxide suspension is 1:4-6;

[0013] (4) preparing an emulsion: adding the core material solution dropwise into the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 1000 to 3000 rpm to obtain an emulsion;

[0014] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 7-9, and the temperature is raised to 50-70° C. to generate a polyurethane capsule wall through an interfacial polymerization reaction, and nano-silicon dioxide is uniformly embedded in the capsule wall to form microcapsules;

[0015] (6) separation and washing of microcapsules: filtering or centrifuging the material after the reaction in step (5), and washing the separated microcapsules;

[0016] (7) Curing and drying treatment: The washed microcapsules are dried at 60-80° C. to obtain the enhanced microcapsules.

[0017] Preferably, in step (2), the organic solvent is toluene.

[0018] Preferably, in step (3), the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1 to 1.1.

[0019] Preferably, the cellulose insulating paper based on mechanically enhanced microcapsules comprises the following raw materials in weight percentage: 1-4% mechanically enhanced microcapsules, 80-90% coniferous wood pulp, 3-7% polyamide fibers, 1-5% nanofiller, 0.5-2.5% antioxidant and 0.5-2% lubricant.

[0020] Preferably, the nano filler is nano alumina, the antioxidant is tocopherol, and the lubricant is dimethyl silicone oil.

[0021] Preferably, the method for preparing the cellulose insulating paper based on mechanically enhanced microcapsules comprises the following steps:

[0022] (1) Weigh each raw material according to weight percentage;

[0023] (2) first soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water and mixing and stirring uniformly to prepare a slurry with a concentration of 5-10%, then adding the nanofiller, antioxidant and lubricant into the slurry and mixing and stirring uniformly, and finally adding the mechanically enhanced microcapsules and stirring at a low speed of 50-70 rpm for 5-10 minutes to obtain a mixed slurry;

[0024] (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank, and after vacuum water absorption and pressing, it is dried at 80 to 120° C. for 1 to 2 hours, and the dried paper is subjected to high temperature and high pressure treatment and calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules.

[0025] Preferably, the temperature of the high temperature and high pressure treatment is 150-200°C, and the pressure is 12-15 MPa; the temperature of the calendering treatment is controlled at 100-150°C, the pressure is 10-20 MPa, and the calendering speed is controlled at 1-2 m / min.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention improves the microcapsules in the cellulose insulating paper, thereby effectively reducing the premature leakage of the repair agent and ensuring that the repair agent can be accurately released when damage occurs; the microcapsules of the present invention can effectively enhance the mechanical and electrical properties of the insulating paper, and the cellulose insulating paper of the present invention is used for damage repair, which can improve the efficiency and accuracy of the repair process, and provides a new technical approach to solve the problem of electrical damage repair of cellulose insulating paper, and has broad application prospects.

[0028] 2. The improvement of the microcapsule of the present invention is specifically to use polyurethane as the capsule wall material, and dope silicon dioxide (SiO2) nanoparticles in the capsule wall. The polyurethane in the capsule wall has good elasticity and durability, and can effectively resist external stress, while the silicon dioxide nanoparticles as reinforcing materials have high hardness, excellent thermal stability and mechanical properties, and can further improve the tensile strength and fracture toughness of the microcapsule. The silicon dioxide particles are uniformly dispersed in the polyurethane matrix, and the formed nanocomposite material not only enhances the overall mechanical properties of the microcapsule, enhances the stability of the microcapsule under high stress conditions, but also improves the compactness of the capsule wall, reduces the risk of premature leakage of the repair agent, and ensures the efficient conduct of the repair process.

[0029] 3. When damage such as electrical tree branches and cracks occurs, the microcapsules of the present invention can release the repair agent in time to carry out effective self-repair, especially when using a two-component repair agent (DCPD and Hoveyda-Grubbs catalytic system), the repair reaction can be carried out quickly, further improving the repair efficiency. The use of the mechanically enhanced microcapsules to repair cellulose insulating paper can not only effectively delay the expansion of electrical tree branches and repair cracks, but also significantly improve the dielectric constant and breakdown strength of the insulating paper and other key performance indicators, thereby improving the overall performance and service life of the insulating paper.

[0030] 4. The present invention reduces material waste and the negative impact on substrate performance by optimizing the release mechanism of microcapsules, meets the requirements of green environmental protection and sustainable development, and reduces the cost of repair materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0032] Figure 1 : A flow chart of the method of the present invention, specifically including the steps of microcapsule and cellulose insulation paper modeling, molecular simulation to performance evaluation;

[0033] Figure 2 :Comparison of tensile strength properties of microcapsules doped with different nanomaterials:

[0034] Figure 3: Comparison of fracture toughness properties of microcapsules doped with different nanomaterials;

[0035] Figure 4 : Comparison of elastic modulus properties of microcapsules doped with different nanomaterials;

[0036] Figure 5 : Comparison of fracture toughness of insulating paper after repair with different microcapsules (non-doped microcapsules and mechanically enhanced microcapsules doped with nano-silica);

[0037] Figure 6 : Comparison of tensile strength of insulating paper after repair with different microcapsules (non-doped microcapsules and mechanically enhanced microcapsules doped with nano-silica);

[0038] Figure 7 : Comparison of dielectric constants of insulating paper after repair with different microcapsules (non-doped microcapsules and mechanically enhanced microcapsules doped with nano-silica);

[0039] Figure 8 : Comparison of the breakdown strength of insulating paper after repair with different microcapsules (undoped microcapsules and mechanically enhanced microcapsules doped with nano-silica). DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0041] Example 1

[0042] The capsule wall material of the mechanically enhanced microcapsules of this embodiment is polyurethane (PU) and nano-silicon dioxide (particle size is 20nm), and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. The particle size of the mechanically enhanced microcapsules of this embodiment is 2μm, the capsule wall thickness is 200nm, and the preparation method is as follows:

[0043] (1) Nano-silicon dioxide dispersion treatment: disperse nano-SiO2 in water and treat with ultrasonic waves to obtain nano-SiO2 suspension;

[0044] (2) Preparation of core material solution: After dissolving DCPD in toluene, slowly add 0.5 mol% of the total amount of DCPD into Hoveyda-Grubbs catalyst, and stir evenly to form a core material solution;

[0045] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-SiO2 suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-SiO2 suspension is 1:4; the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1;

[0046] (4) Preparation of emulsion: adding the core material solution dropwise into the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 1000 rpm to obtain an emulsion;

[0047] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 7, and the temperature is raised to 50° C., a polyurethane capsule wall is generated by interfacial polymerization, and nano-SiO2 is uniformly embedded in the capsule wall to form microcapsules;

[0048] (6) separation and washing of microcapsules: filtering the material after the reaction in step (5), and washing the separated microcapsules;

[0049] (7) Curing and drying treatment: The washed microcapsules are dried at 60° C. to obtain the enhanced microcapsules.

[0050] In this embodiment, a cellulose insulating paper based on mechanically enhanced microcapsules comprises the following raw materials in weight percentage: 1% mechanically enhanced microcapsules, 90% softwood pulp, 3% polyamide fiber, 1% nano-alumina, 2.5% tocopherol, and 2.5% dimethyl silicone oil. The preparation method is:

[0051] (1) Weigh each raw material according to weight percentage;

[0052] (2) first soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water and mixing and stirring uniformly to prepare a slurry with a concentration of 5%, then adding the nano-alumina, tocopherol and dimethyl silicone oil into the slurry and mixing and stirring uniformly, and finally adding the mechanically enhanced microcapsules and stirring at a low speed of 50 rpm for 10 minutes to obtain a mixed slurry;

[0053] (3) The mixed slurry is evenly spread on the filter screen to form a wet paper embryo, which is vacuum-absorbed and pressed, and then dried at 80°C for 1 hour. The dried paper is subjected to high temperature and high pressure treatment and calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules. The temperature of the high temperature and high pressure treatment is 150°C and the pressure is 12MPa; the temperature of the calendering treatment is controlled at 100°C and the pressure is 10MPa, and the calendering speed is controlled at 1m / min.

[0054] Example 2

[0055] The capsule wall material of the mechanically enhanced microcapsules of this embodiment is polyurethane (PU) and nano-silicon dioxide (particle size is 50nm), and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. The particle size of the mechanically enhanced microcapsules of this embodiment is 10μm, the capsule wall thickness is 1μm, and the preparation method is as follows:

[0056] (1) Nano-silicon dioxide dispersion treatment: disperse nano-SiO2 in water and treat with ultrasonic waves to obtain nano-SiO2 suspension;

[0057] (2) Preparation of core material solution: After dissolving DCPD in toluene, slowly add 5 mol% of the total amount of DCPD Hoveyda-Grubbs catalyst, and stir evenly to form a core material solution;

[0058] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-SiO2 suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-SiO2 suspension is 1:6; the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1.1;

[0059] (4) emulsion preparation: adding the core material solution dropwise into the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 3000 rpm to obtain an emulsion;

[0060] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 9, and the temperature is raised to 70° C., a polyurethane capsule wall is generated by interfacial polymerization, and nano-SiO2 is uniformly embedded in the capsule wall to form microcapsules;

[0061] (6) separation and washing of microcapsules: centrifuging the material after the reaction in step (5), and washing the separated microcapsules;

[0062] (7) Curing and drying treatment: The washed microcapsules are dried at 80° C. to obtain the enhanced microcapsules.

[0063] In this embodiment, a cellulose insulating paper based on mechanically enhanced microcapsules comprises the following raw materials in weight percentage: 4% mechanically enhanced microcapsules, 83% softwood pulp, 7% polyamide fiber, 5% nano-alumina, 0.5% tocopherol, and 0.5% dimethyl silicone oil. The preparation method is:

[0064] (1) Weigh each raw material according to weight percentage;

[0065] (2) first soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water and mixing and stirring uniformly to prepare a slurry with a concentration of 10%, then adding the nano-alumina, tocopherol and dimethyl silicone oil into the slurry and mixing and stirring uniformly, and finally adding the mechanically enhanced microcapsules and stirring at a low speed of 70 rpm for 5 minutes to obtain a mixed slurry;

[0066] (3) The mixed slurry is evenly spread on the filter screen to form a wet paper embryo, which is vacuum-absorbed and pressed, and then dried at 120° C. for 2 hours. The dried paper is subjected to high temperature and high pressure treatment and calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules. The temperature of the high temperature and high pressure treatment is 200° C. and the pressure is 15 MPa; the temperature of the calendering treatment is controlled at 150° C. and the pressure is 20 MPa, and the calendering speed is controlled at 2 m / min.

[0067] Example 3

[0068] The capsule wall material of the mechanically enhanced microcapsules of this embodiment is polyurethane (PU) and nano-silicon dioxide (particle size is 30nm), and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. The particle size of the mechanically enhanced microcapsules of this embodiment is 6μm, and the capsule wall thickness is 600nm. The preparation method is as follows:

[0069] (1) Nano-silicon dioxide dispersion treatment: Disperse nano-SiO2 in water or ethanol, and perform ultrasonic treatment or high-speed stirring to obtain a nano-SiO2 suspension;

[0070] (2) Preparation of core material solution: After dissolving DCPD in toluene, slowly add 3 mol% of the total amount of DCPD Hoveyda-Grubbs catalyst, and stir evenly to form a core material solution;

[0071] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-SiO2 suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-SiO2 suspension is 1:5; the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1.1;

[0072] (4) emulsion preparation: adding the core material solution dropwise into the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 2000 rpm to obtain an emulsion;

[0073] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 8, and the temperature is raised to 60° C., a polyurethane capsule wall is generated by interfacial polymerization, and nano-SiO2 is uniformly embedded in the capsule wall to form microcapsules;

[0074] (6) separation and washing of microcapsules: filtering the material after the reaction in step (5), and washing the separated microcapsules;

[0075] (7) Curing and drying treatment: The washed microcapsules are dried at 70° C. to obtain the enhanced microcapsules.

[0076] In this embodiment, a cellulose insulating paper based on mechanically enhanced microcapsules comprises the following raw materials in weight percentage: 2% mechanically enhanced microcapsules, 88% softwood pulp, 5% polyamide fiber, 3% nano-alumina, 1% tocopherol, and 1% dimethyl silicone oil. The preparation method is:

[0077] (1) Weigh each raw material according to weight percentage;

[0078] (2) soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments into deionized water, mixing and stirring, and preparing a slurry with a concentration of 7%, then adding the nanofiller, antioxidant and lubricant into the slurry, mixing and stirring, and finally adding the mechanically enhanced microcapsules, stirring at a low speed of 60 rpm for 8 minutes, to obtain a mixed slurry;

[0079] (3) The mixed slurry is evenly spread on the filter screen to form a wet paper blank, which is vacuum-absorbed and pressed, and then dried at 100°C for 1.5 hours. The dried paper is subjected to high temperature and high pressure treatment and calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules. The temperature of the high temperature and high pressure treatment is 180°C and the pressure is 14MPa; the temperature of the calendering treatment is controlled at 120°C and the pressure is 15MPa, and the calendering speed is controlled at 1.5m / min.

[0080] Comparative Example 1

[0081] The capsule wall material of the microcapsule of this comparative example is polyurethane (PU), and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. Other raw materials and preparation methods are the same as those in Example 1.

[0082] Comparative Example 2

[0083] The capsule wall material of the microcapsule of this comparative example is polyurethane (PU) and nano-aluminum oxide, and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. Other raw materials and preparation methods are the same as those in Example 1.

[0084] Comparative Example 3

[0085] The capsule wall material of the microcapsule of this comparative example is polyurethane (PU) and nano-magnesium oxide, and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. Other raw materials and preparation methods are the same as those in Example 1.

[0086] Performance Test:

[0087] 1. Performance testing of the microcapsules prepared in Example 1 and the comparative examples by constructing a model

[0088] (1) Establishing a microcapsule model of Comparative Example 1: Polyurethane (PU) was selected as the capsule wall material of the microcapsule, DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core material, and a microcapsule model was established.

[0089] (2) Establishing the mechanically enhanced microcapsule model of Example 1: Polyurethane (PU) and silica nanoparticles were selected as the capsule wall materials of the microcapsule, DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core materials, and a mechanically enhanced microcapsule model was established.

[0090] (3) Establishing the microcapsule model of Comparative Example 2: Polyurethane (PU) and nano-aluminum oxide were selected as the capsule wall materials of the microcapsule, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core materials to establish a mechanically enhanced microcapsule model.

[0091] (4) Establishing the microcapsule model of Comparative Example 3: Polyurethane (PU) and nano-magnesium oxide were selected as the capsule wall materials of the microcapsule, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core materials to establish a mechanically enhanced microcapsule model.

[0092] The tensile strength and fracture toughness of the above microcapsule models were analyzed by the Structural Mechanics Module in COMSOL software, and the differences in mechanical properties under different capsule wall structures were compared. The results are shown in Table 1.

[0093] Table 1 Improvement of mechanical properties of microcapsules doped with three nanomaterials

[0094]

[0095] The table above shows that: doping with nano-silicon dioxide can usually improve the compressive strength and flexural strength of the material because it has high hardness and good wear resistance. Doping with nano-aluminum oxide can significantly improve the strength and hardness of the material, especially in terms of wear resistance, and can increase a certain toughness while maintaining strength. Doping with nano-magnesium oxide can usually improve the tensile strength of the material, but the increase may not be as significant as that of nano-silicon dioxide and nano-aluminum oxide. Nano-magnesium oxide helps to improve the toughness of the material and reduce the risk of brittle fracture.

[0096] A comprehensive comparison of the improvement of the mechanical properties of microcapsules by adding the three materials shows that nano-silicon dioxide significantly improves the elastic modulus and tensile strength, while nano-aluminum oxide improves the fracture toughness index slightly more than nano-silicon dioxide, and the Poisson's ratio does not change much. The improvement of mechanical properties by adding nano-magnesium oxide is not as good as the first two, and nano-magnesium oxide will reduce the lateral deformation capacity of the material when subjected to stress, resulting in a slight decrease in the Poisson's ratio. Nano-silicon dioxide is low in cost, easy to obtain, and environmentally friendly. Nano-aluminum oxide is relatively expensive, so overall, using nano-silicon dioxide is the best choice.

[0097] 2. Explain the repair of insulation paper by microcapsules through model construction

[0098] (1) Establish a three-dimensional geometric model of cellulose insulation paper: Use the Structural Mechanics Module in the COMSOL software to establish a three-dimensional geometric model of cellulose insulation paper and simulate its mechanical properties. Set the material parameter range as follows: the elastic modulus of cellulose is 10 GPa, and the Poisson's ratio is 0.3; the elastic modulus of PU microcapsules is 1.8 GPa, and the Poisson's ratio is 0.35; the elastic modulus of DCPD / Hoveyad-Grubbs repair agent is 1.5 GPa, and the Poisson's ratio is 0.35. Set the lower boundary to be fixed, and apply a tensile load of 50 MPa to the top. Apply the same external force to the two microcapsule models of Example 1 and Comparative Example 1, observe their deformation and rupture behavior under stress, and record mechanical properties such as tensile strength, fracture toughness and elastic modulus.

[0099] (2) Establish crack model and electrical tree model of cellulose insulation paper: In COMSOL software, use AC / DCModule to establish crack model and electrical tree model of cellulose insulation paper, and simulate the generation and expansion process of electrical tree. Introduce the microcapsule model of Example 1 and Comparative Example 1, and use the Electrostatics interface of the module to simulate the release and diffusion process of the repair agent after the mechanically enhanced microcapsule breaks at the cracks and electrical tree. Observe the reaction effect of the core material at the damaged part and analyze the mechanism of the repair process. At the same time, use the Dielectric Breakdown function to analyze electrical properties such as dielectric constant and breakdown strength.

[0100] (3) Record the mechanical and electrical properties of cellulose insulation paper before and after repair. Use the Structural Mechanics Module to focus on testing its mechanical properties such as tensile strength, fracture toughness and modulus, and use the AC / DC Module to focus on testing its electrical properties such as dielectric constant and breakdown strength. Use the Multiphysics (multi-physics field coupling) function to combine the coupling analysis of mechanical and electrical properties to evaluate the effect of microcapsules on the performance of insulation paper. At the same time, use the Electric Field (electric field) interface to observe the changes in the electric field distribution after repair, and record the electrical breakdown behavior to complete the overall evaluation of the repair effect.

[0101] Create a three-dimensional geometric model of cellulose insulation paper in the geometry module of COMSOL, set the thickness to 0.2mm, the width to 600mm, and the length to 1500mm. Select cellulose material in the "Material" module. Set the elastic modulus to 8-12GPa and the Poisson's ratio to 0.25-0.35. In the "Physics Module", select "Solid Mechanics", set the boundary conditions, and set the bottom boundary to a fixed boundary condition without any displacement. Apply uniform tensile stress or displacement to the upper surface (z = 0.2mm), and the tensile stress in the vertical direction can be set to 40-60MPa. It is used to simulate the tensile load on the insulation paper under actual working conditions, so as to analyze its stress and deformation under the action of load. The measured boundary is set as a free boundary, and no constraints and loads are applied. Left side (x = 0), right side (x = 1500mm), front side (y = 0), back side (y = 600mm): free boundary.

[0102] Duplicate the first insulation paper model and name it "micro crack model". Add micro crack features to the geometry (use the "cut" function to create a crack in the insulation paper with a length of 0.5mm and a width of 0.1mm. Create a rectangle or line segment at the appropriate position of the insulation paper to represent the crack. Make sure it penetrates the thickness of the insulation paper by 0.2mm). Make sure the material properties are the same as the first model. In the boundary conditions, simulate electrical damage (you can set non-uniform loads or local stress concentrations). Run the simulation and record the stress concentration and deformation in the crack area.

[0103] Use the microcapsule model in Example 1 to repair the microcracks in the insulating paper. In the "Physics" module, select the contact type (such as "Adhesion" or "Contact") to simulate the interaction between the microcapsules and the cracks. Apply boundary conditions. Fix the boundary and keep the bottom of the insulating paper fixed (z = 0). Apply a tensile load: Apply a uniform tensile stress (for example, 40-60MPa) on the upper surface to simulate external conditions. Run the simulation and observe the stress distribution and performance recovery of the repaired model (see Tables 2 and 3 for details).

[0104] Table 2 Changes in mechanical properties of insulation paper

[0105] parameter Cellulose insulation paper (undamaged) Microcrack model Repaired insulation paper Tensile strength(MPa) 50 40 60 Fracture toughness (MPa·m^1 / 2) 1.6 1.2 1.84 Elastic modulus(GPa) 10 8 9

[0106] Table 3 Changes in electrical properties of insulating paper

[0107] parameter Cellulose insulation paper (undamaged) Microcrack model Repaired insulation paper Dielectric constant 3.5 2.5 3.2 Breakdown strength (kV / mm) 20 15 19

[0108] Microcapsules without nano-silica doping (Comparative Example 1) were used to repair micro-cracked insulating paper. The effects of microcapsules doped with nano-silica and microcapsules without nano-silica doping on repairing cracks in insulating paper were compared, including the expected data of mechanical and electrical properties. The results are shown in Tables 4 and 5.

[0109] Table 4 Comparison of mechanical properties of two microcapsule repaired insulation papers

[0110] parameter Microcapsule repair with nano-silica Microcapsule repair without nano-silica Tensile strength(MPa) 60 55 Fracture toughness (MPa·m^1 / 2) 1.84 1.76 Elastic modulus(GPa) 9 7

[0111] Table 5 Comparison of electrical properties of two microcapsule repaired insulating papers

[0112] parameter Microcapsule repair with nano-silica Microcapsule repair without nano-silica Dielectric constant 3.2 2.8 Breakdown strength (kV / mm) 19 16

[0113] In terms of tensile strength, the microcapsules doped with nano-silica provide better filling and adhesion, enhance the reinforcement of cracks, and prevent the brittle fracture of the material. In terms of fracture toughness, the introduction of nano-silica improves the toughness of the microcapsules, allowing the material to better disperse stress when subjected to force and enhance its resistance to impact. In terms of elastic modulus, the doped material improves the rigidity of the polyurethane. Although the elastic modulus of the undamaged material is higher, it still maintains a relatively high value after repair. From the analysis of the dielectric constant, the structural density of the repaired material is improved, and the addition of nano-silica may improve the electrical insulation performance. The high surface area and good dispersibility of nano-silica can fill the cracks and form a more uniform repair layer, thereby reducing the air gap in the cracks, reducing the local electric field concentration effect, and slightly increasing the dielectric constant. In terms of breakdown strength, nano-silica has a relatively high dielectric constant. The insulation performance of the microcapsules is improved after doping, and a more stable electric field distribution can be formed after filling the cracks, thereby improving the breakdown strength. At the same time, nano-silica particles have a tiny size and high surface area at the nanoscale, which makes it easier for them to be distributed in the microcracks when the microcapsule breaks, reducing the electric field concentration phenomenon, thereby improving the integrity and effectiveness of the repair layer. The internal structure of the repaired material is more uniform and the defects are reduced, so it can withstand higher electric field strengths and improve the breakdown strength.

[0114] Nano-silica-doped microcapsules offer significant advantages in repairing insulating paper, effectively improving tensile strength, fracture toughness and electrical properties. Compared with undoped microcapsules, doped microcapsules have significantly higher repair efficiency in various indicators, showing better repair effects.

[0115] In summary, the present invention improves the microcapsules in the cellulose insulating paper, thereby effectively reducing the premature leakage of the repair agent and ensuring that the repair agent can be accurately released when damage occurs; the microcapsules of the present invention can effectively enhance the mechanical and electrical properties of the insulating paper, and the cellulose insulating paper of the present invention is used to repair electrical damage, which can improve the efficiency and accuracy of the repair process, and provides a new technical approach to solve the problem of electrical damage repair of cellulose insulating paper, which has broad application prospects.

[0116] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules, characterized in that: Cellulose insulating paper based on mechanically enhanced microcapsules is used for damage repair. The mechanically enhanced microcapsules are mainly made of capsule walls and core materials. The capsule walls include polyurethane and nano-silicon dioxide, and the core materials include DCPD and Hoveyda-Grubbs catalyst.

2. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: The particle size of the mechanically enhanced microcapsule is 2 μm to 10 μm, and the capsule wall thickness is 200 nm to 1 μm.

3. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: The particle size of the nano silicon dioxide is 20nm to 50nm.

4. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to any one of claims 1 to 3, characterized in that: The method for preparing the mechanically enhanced microcapsules comprises the following steps: (1) Nano-silicon dioxide dispersion treatment: Nano-silicon dioxide is dispersed in ethanol and subjected to ultrasonic treatment to obtain a nano-silicon dioxide suspension; (2) Preparation of core material solution: After dissolving DCPD in an organic solvent, slowly add 0.5 to 5 mol% of the total amount of DCPD into the Hoveyda-Grubbs catalyst and stir evenly to form a core material solution; (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-silicon dioxide suspension, and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-silicon dioxide suspension is 1:4-6; (4) preparing an emulsion: adding the core material solution dropwise into the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant, and stirring at high speed to obtain an emulsion; (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 7-9, and the temperature is raised to 50-70° C. to generate a polyurethane capsule wall through an interfacial polymerization reaction, and nano-silicon dioxide is uniformly embedded in the capsule wall to form microcapsules; (6) separation and washing of microcapsules: filtering the material after the reaction in step (5), and washing the separated microcapsules; (7) Curing and drying treatment: The washed microcapsules are dried at 60-80° C. to obtain the enhanced microcapsules.

5. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 4, characterized in that: In step (2), the organic solvent is toluene.

6. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 4, characterized in that: In step (3), the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1 to 1.

1.

7. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: The cellulose insulating paper based on mechanically enhanced microcapsules comprises the following raw materials in weight percentage: 1-4% mechanically enhanced microcapsules, 80-90% conifer pulp, 3-7% polyamide fibers, 1-5% nano fillers, 0.5-2.5% antioxidants and 0.5-2% lubricants.

8. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 7, characterized in that: The nano filler is nano alumina, the antioxidant is tocopherol, and the lubricant is dimethyl silicone oil.

9. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 7, characterized in that: The method for preparing the cellulose insulating paper based on mechanically enhanced microcapsules comprises the following steps: (1) Weigh each raw material according to weight percentage; (2) first soaking and dispersing the softwood pulp, chopping the polyamide fibers, adding them together into deionized water, mixing and stirring them uniformly, to prepare a slurry with a concentration of 5 to 10%, then adding the nanofiller, antioxidant and lubricant into the slurry, mixing and stirring them uniformly, and finally adding the mechanically enhanced microcapsules, stirring at a low speed of 50 to 70 rpm for 5 to 10 minutes, to obtain a mixed slurry; (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank, and after vacuum water absorption and pressing, it is dried at 80 to 120° C. for 1 to 2 hours, and the dried paper is subjected to high temperature and high pressure treatment and calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules.

10. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 9, characterized in that: The temperature of the high temperature and high pressure treatment is 150-200° C., and the pressure is 12-15 MPa; the temperature of the calendering treatment is controlled at 100-150° C., the pressure is 10-20 MPa, and the calendering speed is controlled at 1-2 m / min.

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