A method for targeted repair of microcracks in insulating paper based on magnetically responsive microcapsules

Abstract

The present invention discloses a method for targeted repair of microcracks in insulating paper based on magnetic responsive microcapsules, which relates to the field of high voltage and insulation technology. The specific steps include: using ABAQUS software to establish a three-dimensional geometric model of cellulose insulating paper, and creating a model of uniformly distributed and surface-distributed magnetic responsive microcapsules; performing finite element simulation to analyze stress concentration under different distribution modes; establishing molecular models of PUF microcapsules, IPDI and water molecules, simulating the diffusion of IPDI and the reaction process with water molecules in a humid environment, and generating polyurea molecules; establishing a crack model of cellulose insulating paper, introducing the generated polyurea molecules, and simulating the filling process; performing comparative analysis before and after repair. The insulating paper repaired by the method of the present invention has significant improvements in tensile strength, fracture toughness, modulus, dielectric constant and breakdown strength. Through the targeted repair of magnetic responsive microcapsules, the overall performance and service life of the insulating paper can be effectively improved, which has important engineering application value.

Description

Technical Field

[0001] The present invention relates to the field of high voltage and insulation technology, and in particular to a method for targeted repairing microcracks in insulating paper based on magnetic responsive microcapsules. Background Art

[0002] In the power system, the oil-immersed transformer is one of the core equipment of the substation. Its operational safety and reliability are directly related to the stability of the entire power system. Insulation paper is an important insulating material in oil-immersed transformers, mainly used for insulation and fixation between windings. Insulation paper has excellent electrical insulation properties and mechanical strength. However, under the action of electric fields, thermal stress and mechanical stress for a long time, the insulation paper is prone to microcracks, which leads to a decrease in insulation performance and affects the normal operation of the transformer. Traditional insulation paper repair methods are usually difficult to perform without disassembling the equipment, and the repair effect is limited. Therefore, it is of great significance to develop a method that can effectively repair insulation paper during operation.

[0003] Finite element analysis (FEA) and molecular dynamics (MD) simulations provide powerful tools for studying microcapsule self-healing. These simulation techniques accurately simulate microstructure and mechanical behavior, helping researchers gain a deeper understanding of the distribution of microcapsules within a material and its impact on its properties. Simulations using ABAQUS and Materials Studio software allow detailed study of microcapsule behavior under varying conditions, thereby optimizing their application in insulating paper. These simulation techniques not only contribute to understanding the self-healing mechanisms of microcapsules but also provide theoretical support for the design and application of microcapsule materials.

[0004] It is of great necessity and significance to use microcapsules to repair cellulose insulating paper. Insulating paper plays a vital insulating role in transformers, but it is prone to microcracks during long-term use, which affects the insulation performance. By evenly distributing microcapsules in the insulating paper, the microcapsules will rupture and release repair agents when cracks appear, which can effectively repair the cracks and restore the performance of the insulating paper. However, if the microcapsules are too evenly distributed in the matrix material and the concentration is too high, it will have an adverse effect on the mechanical strength and electrical properties of the substrate. Therefore, studying magnetically responsive microcapsules and using a magnetic field to direct their adsorption to vulnerable areas can significantly improve the accuracy and efficiency of repair, while reducing the adverse effects on material properties, thereby improving the overall performance and service life of the insulating paper.

[0005] In summary, the development of an efficient, precise, economical and environmentally friendly method for repairing microcracks in insulating paper can not only effectively improve the performance of insulating paper, but also reduce the amount of repair materials used and improve the repair efficiency, providing new technical support for the safe operation and reliability improvement of power systems, and has important engineering application value and research significance. Summary of the Invention

[0006] To address these shortcomings, the present invention provides a method for targeted repair of microcracks in insulating paper based on magnetically responsive microcapsules. This method not only improves the efficiency and accuracy of repair but also reduces the negative impact of the microcapsules on substrate performance. By combining finite element analysis and molecular dynamics simulation, this method provides new insights and technical means for the optimized design and application of insulating materials, possessing significant application prospects and research value. The specific technical solution is as follows:

[0007] A method for targeted repair of microcracks in insulating paper based on magnetic responsive microcapsules, comprising the following steps:

[0008] (1) ABAQUS software was used to establish a three-dimensional geometric model of cellulose insulation paper. Microcapsules distributed only on the surface of the matrix material and microcapsules uniformly distributed in the matrix material were modeled. Through finite element simulation analysis, the stress concentration under the two distribution modes was compared, the crack generation and propagation in the stress concentration area were analyzed, and the advantages of surface distributed microcapsules in crack repair were analyzed.

[0009] (2) Establish the molecular model of PUF (polyurea-formaldehyde) microcapsules, repair agent and water molecules in Materials Studio software, select COMPASS force field, and define the interaction parameters between the repair agent and water (including van der Waals force and electrostatic force).

[0010] Simulate a humid environment and set the distribution and density of water molecules. Interaction parameters: van der Waals force constant between the repair agent and water: 0.005-0.02 kcal / mol, electrostatic force constant: 0.02-0.1 kcal / mol. Simulate a humid environment: set the water density to 50-150 molecules per cubic nanometer. Use molecular dynamics simulations to observe the diffusion of the repair agent and its reaction with water molecules after microcapsule rupture, and record the polyurea molecules generated by the reaction.

[0011] The chemical reaction formula of the repair agent IPDI reacting with water molecules is as follows:

[0012] R-NCO+H2O→R-NH2+CO2

[0013] R-NH2+R-NCO→R-NH-CO-NH-R

[0014] (3) Use the Molecular Builder tool in Materials Studio to create a crack model for cellulose insulation paper and a molecular model of the curing reaction polyurea. Introduce the polyurea molecules generated in step (2) and simulate the polyurea filling process at the crack. Observe the distribution and filling effect of the polyurea at the crack and record the molecular behavior during the repair process.

[0015] (4) Record the mechanical and electrical properties of the unrepaired crack model and the repaired crack model in step (3) respectively. Use the Analysis module of Materials Studio software to display and compare charts and analyze the differences and improvements in the electrical and mechanical properties of the unrepaired and repaired insulation paper. Use the electric field simulation module to observe the electric field distribution and electrical breakdown behavior after repair, and compare and analyze the changes in electrical properties before and after repair.

[0016] Preferably, the capsule wall of the microcapsule is PUF (polyurea-formaldehyde) doped Fe3O4@SiO2 (PUF-Fe3O4@SiO2).

[0017] More preferably, the capsule wall of the microcapsule is high molecular weight PUF-doped Fe3O4@SiO2 (PUF-Fe3O4@SiO2) with a molecular weight of 40,000 to 60,000 g / mol.

[0018] Preferably, the repair agent is IPDI (isophorone diisocyanate).

[0019] Preferably, in step (1), in order to simulate the stress distribution in the actual working environment, it is necessary to set material parameters and boundary conditions. Material parameters: cellulose elastic modulus 8-12GPa, Poisson's ratio 0.25-0.35; PUF elastic modulus 1.5-2.5GPa, Poisson's ratio 0.3-0.4; repair agent IPDI elastic modulus 1-2GPa, Poisson's ratio 0.35-0.45. Boundary conditions: The lower boundary of the model is fixed, and a uniform upward tensile stress of 40-60MP is applied to the upper surface. Run the simulation model and record the stress distribution and crack generation in the stress concentration area.

[0020] Preferably, the mechanical properties include tensile strength, fracture toughness and modulus; the electrical properties include stress-strain curve, dielectric constant and breakdown strength.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention provides an efficient, accurate, economical and environmentally friendly method for repairing microcracks in insulating paper, which provides new technical support for the safe operation and reliability improvement of power systems. Through the directional adsorption technology of magnetically responsive microcapsules made of PUF-doped Fe3O4@SiO2 materials, the repair agent can be accurately distributed to the vulnerable parts of the insulating paper, significantly improving the accuracy of the repair. Compared with the traditional uniform distribution method, the magnetically responsive microcapsules can form a high concentration of repair agent in the crack area, effectively filling the cracks and restoring the mechanical properties and electrical insulation properties of the material. The repaired insulating paper is significantly improved in terms of mechanical strength, fracture toughness, dielectric constant and breakdown strength, which extends the service life of the insulating paper and improves its reliability and stability in high voltage environments.

[0023] 2. Under the influence of an external magnetic field, magnetically responsive microcapsules can rapidly move and accumulate in cracked areas, enabling rapid response and repair. This approach not only shortens repair time and improves repair efficiency, but also reduces the risk of performance degradation and failure caused by microcracks. Because microcapsules can be targeted to the area requiring repair, the total amount of repair agent used can be reduced, lowering material costs and manufacturing complexity while minimizing negative impacts on the substrate and maintaining the overall performance of the material.

[0024] 3. The present invention adopts magnetic responsive microcapsule technology, which effectively reduces the waste of chemical repair agents and environmental pollution, and meets the requirements of green environmental protection and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0026] Figure 1 : Flowchart of the method of the present invention, specifically including the steps from microcapsule modeling, molecular simulation to performance evaluation;

[0027] Figure 2 : Comparison curve of stress concentration of uniformly distributed and surface distributed microcapsules simulated in ABAQUS;

[0028] Figure 3 : The process curve of IPDI diffusion and reaction with water molecules to form polyurea in a humid environment;

[0029] Figure 4 : Density change curve during the whole system repair process;

[0030] Figure 5: Comparison of shear modulus of insulation paper before and after repair;

[0031] Figure 6 : Comparison curve of electrical performance of insulation paper before and after repair;

[0032] Figure 7 : Graph of the number of polyurea molecules generated during the repair process with and without the participation of water molecules. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Unless otherwise defined, all technical terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0034] Example 1

[0035] Combine Figure 1 The repair method of this embodiment includes the following steps:

[0036] (1) A three-dimensional geometric model of cellulose insulation paper was established using ABAQUS software. Microcapsules distributed only on the surface of the matrix material and those uniformly distributed throughout the matrix were modeled. Material parameters were set as follows: cellulose elastic modulus of 10 GPa, Poisson's ratio of 0.3; PUF elastic modulus of 2 GPa, Poisson's ratio of 0.35; IPDI elastic modulus of 1.5 GPa, Poisson's ratio of 0.4. Boundary conditions were set: the lower boundary of the model was fixed, and a uniform upward tensile stress of 50 MP was applied to the upper surface. The simulation model was run, and finite element analysis was performed to compare the stress concentration under the two distribution methods. The crack generation and propagation in the stress concentration area were analyzed and recorded, and the advantages of surface-distributed microcapsules in crack repair were analyzed.

[0037] (2) A molecular model of the PUF microcapsules, the repair agent, and water molecules was created in Materials Studio software. The COMPASS force field was selected, and the van der Waals force constant between IPDI and water was defined as 0.01 kcal / mol, and the electrostatic force constant was defined as 0.05 kcal / mol. A humid environment was simulated, and the water molecule density was set to 100 water molecules per cubic nanometer. Molecular dynamics simulation was used to observe the diffusion of the repair agent and its reaction with water molecules after the microcapsules ruptured, and the polyurea molecules generated by the reaction were recorded.

[0038] (3) Use the Molecular Builder tool in Materials Studio to create a crack model for cellulose insulation paper and a molecular model of the curing reaction polyurea. Introduce the polyurea molecules generated in step (2) and simulate the polyurea filling process at the crack. Observe the distribution and filling effect of the polyurea at the crack and record the molecular behavior during the repair process.

[0039] (4) Record the mechanical and electrical properties of the unrepaired crack model and the repaired crack model in step (3) respectively. Use the Analysis module of Materials Studio software to display and compare charts and analyze the tensile strength, fracture toughness and modulus, stress-strain curve, dielectric constant, and breakdown strength of the unrepaired and repaired insulation paper. Use the electric field simulation module to observe the electric field distribution and electrical breakdown behavior after repair, and compare and analyze the changes in electrical properties before and after repair.

[0040] Example 2

[0041] This example differs from Example 1 in that a microcapsule material is used, using PUF-Fe3O4@SiO2 with a higher molecular weight of 50,000 g / mol. This increases the elastic modulus to 2.5 GPa, while maintaining the Poisson's ratio at 0.35. The same repair process and performance evaluation demonstrate that the improved microcapsule material is more effective in improving the performance of insulating paper, as shown in Table 1 below.

[0042] Table 1 Performance indexes of microcapsule materials of Example 1 and Example 2

[0043] Performance indicators Example 1 Example 2 Tensile strength (MPa) 120 140 Fracture toughness (MPa·m^1 / 2) 3 3.8 Modulus (GPa) 11 13 Dielectric constant 3 2.8 Breakdown strength (kV / mm) 35 45

[0044] As shown in Table 1 above, using PUF-doped Fe3O4@SiO2 (PUF-Fe3O4@SiO2) with a molecular weight of 50,000 g / mol as the microcapsule material increases the elastic modulus to 2.5 GPa, maintains the Poisson's ratio at 0.35, and exhibits better tensile strength, fracture toughness, modulus, dielectric constant, and breakdown strength.

[0045] Example 3

[0046] The difference between this embodiment and embodiment 1 is that the microcapsules are distributed in a different way. The microcapsules are evenly distributed in the entire volume of the insulating paper. Through the same repair process and performance evaluation, the results are as follows: Figure 2 As shown, the overall distribution of microcapsules is not as significant as the targeted distribution achieved by magnetically corresponding microcapsules in reducing stress concentration and improving material properties.

[0047] Example 4

[0048] This example differs from Example 1 in that magnetically responsive microcapsules are not used. Instead, ordinary PUF microcapsules are used, undoped with Fe₃O₄@SiO₂. The same repair process and performance evaluation results show that the tensile strength, fracture toughness, modulus, dielectric constant, and breakdown strength of the non-magnetically responsive microcapsules are not as significant as those of the magnetically responsive microcapsules, particularly in terms of precise repair and performance improvement. This is shown in Table 2 below.

[0049] Table 2 Performance indicators of the microcapsules of Example 4 and Example 1

[0050] Performance indicators Example 4 Example 1 Tensile strength (MPa) 100 120 Fracture toughness (MPa·m^1 / 2) 2.5 3 Modulus (GPa) 10 11 Dielectric constant 3.2 3 Breakdown strength (kV / mm) 30 35

[0051] Example 5

[0052] The difference between this embodiment and embodiment 1 is that no water molecules are added during the repair process. The reaction process of IPDI alone is observed in molecular dynamics simulation. Through the same repair process and performance evaluation, the results show that the repair process without the participation of water molecules generates fewer polyurea molecules, and the repair effect is not as significant as that with the participation of water molecules. Figure 7 shown.

[0053] Comparative Example 1

[0054] The difference between this comparative example 1 and example 1 is that the repair agent IPDI is not added during the repair process. Through the same repair process and performance evaluation, the results are as follows Figure 4 、 5 As shown in the figure, the repair effect of the repair agent IPDI is better than that of the repair agent without the repair agent, the repair process density and shear modulus are higher, and the breakdown probability is lower.

[0055] By comparing the above specific embodiments, it can be seen that the insulating paper targeted repaired by magnetically responsive microcapsules using PUF-doped Fe3O4@SiO2 as the microcapsule material has significantly improved mechanical and electrical properties. After the IPDI reaction in a humid environment generates polyurea to fill the cracks, the breakdown strength, shear modulus and dielectric constant of the insulating paper are significantly improved. The improvement in the surface distribution of the microcapsules improves stress concentration, thereby improving the tensile strength and fracture toughness of the insulating paper.

[0056] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for targeted repair of microcracks in insulating paper based on magnetic responsive microcapsules, characterized in that: The following steps are involved: (1) Use ABAQUS software to establish a three-dimensional geometric model of cellulose insulation paper, and model the microcapsules distributed only on the surface of the matrix material and the microcapsules uniformly distributed in the matrix material. Through finite element simulation analysis, compare the stress concentration under the two distribution modes, and analyze the crack generation and expansion in the stress concentration area. It is necessary to set the parameters of the elastic modulus and Poisson's ratio of cellulose, PUF, and repair agent; set the boundary conditions and loads of the model to simulate the stress distribution in the actual working environment; (2) Use the Molecular Builder tool in Materials Studio software to construct a molecular model of PUF microcapsules, repair agents, and water molecules. Select the COMPASS force field in the Forcefield module and set the interaction parameters between the repair agent and water molecules. The interaction parameters include van der Waals force and electrostatic force. Simulate the humid environment and set the distribution and density of water molecules. Use molecular dynamics simulation to observe the diffusion of the repair agent and the reaction process with water molecules after the microcapsule ruptures, and record the polyurea molecules generated by the reaction. The capsule wall material of the microcapsule is PUF-doped Fe3O4@SiO2; the repair agent is IPDI. (3) Use the Molecular Builder tool in Materials Studio software to establish a crack model of cellulose insulation paper and a curing reaction polyurea molecular model. Introduce the polyurea molecules generated in step (2), run a simulation of the polyurea filling process at the crack, observe the distribution and effect of the polyurea at the crack, and analyze the filling effect of the polyurea on the crack. (4) Record the mechanical properties and electrical properties of the unrepaired crack model and the repaired crack model in step (3) respectively; (5) Compare the mechanical and electrical properties of the unrepaired and repaired insulation paper, and evaluate the repair effects of the mechanical and electrical properties.

2. The method for targeted repair of microcracks in insulating paper based on magnetic responsive microcapsules according to claim 1, characterized in that: In step (4), the mechanical properties include tensile strength, fracture toughness and modulus, and the electrical properties include stress-strain curve, dielectric constant and breakdown strength.

3. The method for targeted repair of microcracks in insulating paper based on magnetic responsive microcapsules according to claim 1, characterized in that: In step (5), the improvement in the electrical and mechanical properties of the unrepaired and repaired insulation paper is analyzed by using the Analysis module of Materials Studio software to perform a graphical display comparison.

4. The method for targeted repair of microcracks in insulating paper based on magnetic responsive microcapsules according to claim 1, characterized in that: Step (5) also includes using electric field simulation to observe the electric field distribution and electrical breakdown behavior after repair.

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