Method for evaluating aging characteristics of oil impregnated paper based on microscopic parameters

Abstract

The invention provides a method for evaluating the aging characteristic of oil-impregnated paper based on microscopic parameters, which comprises the following steps of: constructing an oil-impregnated paper model of insulating paper and insulating oil, and performing molecular dynamics simulation on the oil-impregnated paper model to obtain physical parameters related to the aging life of the oil-impregnated paper, such as a self-diffusion coefficient, isobaric heat capacity, the number of hydrogen bonds, the service life of the hydrogen bonds and the like from the oil-impregnated paper model; the aging performance of the oil-impregnated paper is evaluated through physical parameters of the materials, the accuracy is high, manpower and time are saved, and theoretical guidance is provided for accurately, efficiently and conveniently evaluating the aging performance of the oil-impregnated paper delayed by different insulating oils.

Description

Technical Field

[0001] The present invention belongs to the technical field of transformer insulating materials, and particularly relates to an evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters. Background Art

[0002] To adapt to the development of power equipment towards green, environmental-friendly and sustainable directions, insulating materials are transforming from traditional non-renewable resources to renewable resources. Oil-immersed transformers are extremely important and crucial parts of the power grid. The insulating performance of oil-paper is the core of the transformer, and high requirements are imposed on its insulation and heat dissipation performances. In recent years, liquid dielectrics such as ester insulating oils with high flame retardancy, environmental friendliness, renewability and excellent performances have developed rapidly and are expected to become substitutes for traditional fossil insulating oils. In the development process of insulating oils, not only the excellent performances of the insulating oils themselves should be concerned, but also the matching characteristics of the insulating oils and insulating papers should be concerned.

[0003] During the actual operation process of transformers, the insulating paper is prone to aging and decomposition under the action of thermal stress, and the performance of the insulating paper will gradually be lost. During the research and development process of new insulating oils, the aging characteristics of new oil-impregnated papers are an important part of the life evaluation and prediction of new oil-insulating transformers. The traditional methods for studying the aging of oil-impregnated paper mainly adopt experimental methods, and accelerated thermal aging tests of oil-impregnated paper in insulating oil are carried out at 110 - 130 °C, and the test cycle reaches thousands of hours. The thermal aging characteristics of oil-impregnated paper are evaluated according to the changes of parameters such as the degree of polymerization of the insulating paper during the accelerated thermal aging test of the oil-impregnated paper. The traditional method for evaluating the aging characteristics of oil-impregnated paper is extremely time-consuming, the test method for the degree of polymerization of the insulating paper is complex, the overall process requires a large amount of manpower and material resources, and the cost is extremely high. The evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters has rarely been reported at present. Summary of the Invention

[0004] The purpose of the present invention is to provide an evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters, and the evaluation method in the present invention can provide theoretical guidance for accurately, efficiently and conveniently evaluating the aging performance of different insulating oils in delaying the aging of oil-impregnated paper.

[0005] The present invention provides an evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters, including the following steps:

[0006] A) Obtain the oil impregnation rate of the insulating paper;

[0007] B) Use Gaussian View software to draw the monomer molecular structure model of the main component cellulose of the oil-impregnated paper and the single molecule structure model of the insulating oil, use Packmol software to construct a periodic structure model of the oil-impregnated paper, and set the ratio of the monomer molecular structure model of cellulose and the single molecule structure model of the insulating oil in the oil-impregnated paper model according to the oil impregnation rate of the insulating paper;

[0008] C) The energy minimization of the oil-impregnated paper model was carried out using Gromacs software, and then molecular dynamics simulation was performed under the NPT ensemble to obtain the simulation trajectory of the molecular dynamics of the oil-impregnated paper model;

[0009] D) Based on the simulation trajectory of the molecular dynamics of the oil-impregnated paper model, the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime of the oil-impregnated paper model were calculated, and the aging characteristics of the oil-impregnated paper were evaluated according to the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime.

[0010] Preferably, the oil impregnation rate of the insulating paper is obtained according to the following steps:

[0011] The insulating paper was dried and weighed to obtain the mass of the insulating paper;

[0012] The insulating paper was immersed in insulating oil and impregnated under vacuum conditions. After the impregnation was completed, the oil-impregnated paper was removed, and after removing the surface oil stain, it was weighed to obtain the mass of the oil-impregnated paper;

[0013] The oil impregnation rate of the insulating paper was calculated based on the difference between the mass of the oil-impregnated paper and the mass of the insulating paper.

[0014] Preferably, the degree of polymerization n of the monomer molecular structure model of cellulose is ≥10, and -OH saturation treatment is added to the end of the monomer molecular structure model of cellulose.

[0015] Preferably, based on density functional theory, the B3LYP functional of Gaussian software and the 6-311G(d,p) basis set plus the D3 dispersion correction method were used to geometrically optimize the monomer molecular structure model of cellulose and the single-molecule structure model of insulating oil, and then the oil-impregnated paper model was constructed.

[0016] Preferably, in the oil-impregnated paper model, the number of monomer molecular structure models of cellulose is ≥30.

[0017] Preferably, after obtaining the oil-impregnated paper structure model, based on Gaussian geometric optimization, the wave function file of the simulation results of the monomer molecular structure model of cellulose and the molecular structure model of insulating oil was obtained. The Resp charge was calculated in the Multiwfn software. The top and itp files required for the simulation of the monomer molecular structure model of cellulose under the Glycam force field were generated using the Ambertools tool in cooperation with the Acpype script. The top and itp files required for the simulation of the single-molecule structure model of insulating oil under the GAFF force field were obtained using the Sobtop software. The top files of the monomer molecular structure model of cellulose and the single-molecule structure model of insulating oil were merged, and the calculated RESP charge was replaced into the corresponding itp file, and then the energy minimization of the oil-impregnated paper model was carried out.

[0018] Preferably, the steepest gradient method is used to minimize the energy of the oil-impregnated paper model.

[0019] Preferably, the self-diffusion coefficient of the oil-impregnated paper model is calculated according to formula (1):

[0020]

[0021] In formula (1), N is the number of total atoms, i is the atomic serial number, r i (t) and r i (0) respectively represent the position vectors of the i-th atom at time t and at time 0.

[0022] Preferably, the isobaric heat capacity of the oil-impregnated paper model is calculated according to formula (2):

[0023]

[0024] In formula (2), C P is the isobaric heat capacity, H is the enthalpy of the model, T is the model temperature, k B is the Boltzmann constant.

[0025] Preferably, the lifetime of the hydrogen bond is calculated according to formula (3):

[0026]

[0027] In formula (3), τ HB is the hydrogen bond lifetime, i is the hydrogen bond serial number, and t0 represents the initial time;

[0028] S i (t0) represents the existence of the i-th hydrogen bond at time t0. If the i-th hydrogen bond does not exist at time t0, then S i (t0) is 0. If the i-th hydrogen bond exists at time t0, then S i (t0) is 1;

[0029] S i (t0 + t) represents the existence of the i-th hydrogen bond at time t0 + t. If the i-th hydrogen bond does not exist at time t0 + t, then S i (t0 + t) is 0. If the i-th hydrogen bond exists at time t0 + t, then S i (t0 + t) is 1.

[0030] The present invention provides an evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters, comprising the following steps: A) obtaining the oil impregnation rate of the insulating paper; B) using Gaussian View software to draw the monomer molecular structure model of the main component cellulose of the oil-impregnated paper and the single-molecule structure model of the insulating oil, using Packmol software to construct a periodic structure oil-impregnated paper model, and setting the ratio of the cellulose monomer molecular structure model and the insulating oil single-molecule structure model in the oil-impregnated paper model according to the oil impregnation rate of the insulating paper; C) using Gromacs software to minimize the energy of the oil-impregnated paper model, and then performing molecular dynamics simulation under the NPT ensemble to obtain the simulation trajectory of the molecular dynamics of the oil-impregnated paper model; D) based on the simulation trajectory of the molecular dynamics of the oil-impregnated paper model, calculating the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds and hydrogen bond lifetime of the oil-impregnated paper model, and evaluating the aging characteristics of the oil-impregnated paper according to the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds and hydrogen bond lifetime. By constructing an oil-impregnated paper model of insulating paper and insulating oil, and performing molecular dynamics simulation on it, physical parameters related to the aging life of the oil-impregnated paper such as self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds and hydrogen bond lifetime are obtained from it, and the aging performance of the oil-impregnated paper is evaluated through these physical parameters of the materials, with high accuracy, and saving manpower and time, providing theoretical guidance for accurately, efficiently and conveniently evaluating the aging performance of different insulating oils in delaying oil-impregnated paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0032] Figure 1 Schematic diagram of the mineral oil-impregnated paper model in the embodiment of the present invention;

[0033] Figure 2 Schematic diagram of the soybean-based natural ester oil-impregnated paper model in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention provides an evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters, mainly comprising the following steps:

[0035] The first step: testing the oil impregnation rate of the insulating paper.

[0036] Prepare two or more pieces of untreated insulating paper with the same density and thickness. There are no specific requirements for the size and shape. Place them in a vacuum drying oven and dry at 80 - 100 °C for 24 - 36 h, more preferably dry at 90 °C for 24 hours. Test the moisture content of the oil-impregnated paper to ensure it is less than 0.5%.

[0037] Weigh the insulating paper separately on an electronic balance and record the mass. Immerse the insulating paper separately in insulating oil so that the insulating oil fully covers the insulating paper, and perform vacuum oil impregnation in a vacuum drying oven to obtain multiple different oil-impregnated papers.

[0038] In the present invention, the insulating oil used for the different insulating papers can be the same or different; the temperature of the vacuum oil impregnation is preferably 50 - 80 °C, more preferably 60 - 65 °C, and the time of the vacuum oil impregnation is preferably 48 - 72 hours.

[0039] Take out the oil-impregnated paper, wipe the oil stains on the surface, and weigh it on an electronic balance to obtain the mass of the oil-impregnated paper.

[0040] Based on the dried insulating paper, calculate the oil impregnation rate of the oil-impregnated paper by using the ratio of the mass difference between the insulating paper before and after oil impregnation to the mass of the insulating paper before oil impregnation.

[0041] Step 2: Molecular dynamics simulation of the oil-impregnated paper.

[0042] Use Gaussian View software to draw the monomer molecular structure model of cellulose, the main component of the oil-impregnated paper. To ensure the accuracy of the simulation results, the degree of polymerization of the monomer model of the polymer insulating material is not less than 10, and perform -OH saturation treatment on the end of cellulose; construct the single-molecule structure model of the insulating oil according to the composition of the insulating oil.

[0043] Based on the density functional theory, use the B3LYP functional of Gaussian software and the 6-311G(d,p) basis set plus the D3 dispersion correction method to perform geometric optimization on the constructed cellulose monomer model and the insulating oil single-molecule model to make the model closer to the real structure.

[0044] Based on the geometrically optimized model and the oil impregnation rate of the insulating paper obtained in the previous step, use Packmol software to construct two or more periodic structure models of the oil-impregnated paper, where the number of cellulose with a degree of polymerization not less than 10 is not less than 30, and the number of the insulating oil single-molecule structure models is calculated according to the oil impregnation rate.

[0045] Based on the wave function file of the simulation results of the cellulose and insulating oil molecular models obtained by Gaussian geometric optimization, the Resp charges are calculated in the Multiwfn software. The Ambertools tool is used in conjunction with the Acpype script to generate the top and itp files required for the simulation of cellulose monomers under the Glycam force field. The Sobtop software is used to obtain the top and itp files required for the simulation of insulating oil under the GAFF force field. The top files of cellulose and insulating oil are merged and the calculated RESP charges are replaced into the corresponding itp files. The Gromacs software is used to minimize the energy of the oil-impregnated paper model, using the steepest gradient method. Under the NPT ensemble, first perform equilibration for 20 - 25 ns, and then perform simulation for 10 - 15 ns. The obtained trajectory is used for the calculation of various properties. The simulation temperature is set to the temperature at which the aging characteristics of the oil-impregnated paper are actually desired to be obtained.

[0046] Step 3: Calculation of the microscopic parameters of the oil-impregnated paper.

[0047] Based on the 10-ns molecular dynamics simulation trajectory of the oil-impregnated paper model obtained in the second step, calculate the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime of different oil-impregnated paper models.

[0048] The self-diffusion coefficient of the oil-impregnated paper model is calculated according to formula (1):

[0049]

[0050] In formula (1), N is the total number of atoms, i is the atomic number, r i (t) and r i (0) represent the position vectors of the i-th atom at time t and time 0, respectively.

[0051] The isobaric heat capacity of the oil-impregnated paper model is calculated according to formula (2):

[0052]

[0053] In formula (2), C P is the isobaric heat capacity, H is the enthalpy of the model, T is the model temperature, k B is the Boltzmann constant.

[0054] The hydrogen bond lifetime is calculated according to formula (3):

[0055]

[0056] In formula (3), τ HB is the hydrogen bond lifetime, i is the hydrogen bond number, and t0 represents the initial time;

[0057] S i(t0) represents the existence of the i-th hydrogen bond at time t0. If the i-th hydrogen bond does not exist at time t0, then S i (t0) is 0. If the i-th hydrogen bond exists at time t0, then S i (t0) is 1;

[0058] S i (t0 + t) represents the existence of the i-th hydrogen bond at time t0 + t. If the i-th hydrogen bond does not exist at time t0 + t, then S i (t0 + t) is 0. If the i-th hydrogen bond exists at time t0 + t, then S i (t0 + t) is 1.

[0059] Step 4: Evaluate the aging characteristics of different oil-impregnated papers based on the differences in their microscopic parameters.

[0060] Based on the calculation results of the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime of different oil-impregnated paper models obtained in the third step, summarize the variation laws of the microscopic parameters of different aged oil-impregnated paper models. The self-diffusion coefficient of the oil-impregnated paper characterizes the strength of its thermal stability. The isobaric heat capacity of the oil-impregnated paper represents the amount of heat required to raise its temperature by 1 degree. The greater the number and lifetime of the hydrogen bonds in the oil-impregnated paper, the stronger the intermolecular force, and it is not easily decomposed during the thermal process. The smaller the self-diffusion coefficient of the oil-impregnated paper, and the greater the isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime, the more excellent its heat-resistant aging performance. Therefore, by comparing the magnitudes of the four parameters of the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime of different oil-impregnated paper models, it is possible to evaluate different oil-impregnated paper systems and obtain the required oil-impregnated paper system.

[0061] To further illustrate the present invention, the following describes in detail an evaluation method for the aging characteristics of oil-impregnated paper based on microscopic parameters provided by the present invention in combination with embodiments, but it should not be construed as a limitation on the protection scope of the present invention.

[0062] Embodiment

[0063] Take mineral oil-impregnated paper and soybean-based natural ester oil-impregnated paper as examples to verify the effect of this patent.

[0064] Take two insulating papers of the same size and density, dry them in a vacuum drying oven at 90°C for 24 h, inject the two insulating papers into two insulating oils respectively, make the insulating oil fully cover the insulating papers, and vacuum impregnate the oils in a vacuum drying oven at 60°C for 48 h to obtain 2 different oil-impregnated papers. Calculate the mass difference before and after oil impregnation, and calculate that the oil impregnation rates of the two oil-impregnated papers are both about 20%.

[0065] The cellulose model with a degree of polymerization of 10 was drawn using Gaussian View software, and a single-molecule model of insulating oil was constructed based on the components of mineral oil and soybean-based natural ester. The constructed cellulose monomer model and insulating oil single-molecule model were geometrically optimized using the B3LYP functional and 6-311G(d,p) basis set with D3 dispersion correction method in Gaussian software to make the models closer to the real structure.

[0066] Two oil-impregnated paper models were constructed using Packmol, where the number of cellulose was 30, and the mass ratios of mineral oil and soybean oil in the oil-impregnated paper models were both 20%. The two oil-impregnated paper models are as Figures 1-2 shown, where Figure 1 is the mineral oil-impregnated paper model, Figure 2 and is the soybean-based natural ester oil-impregnated paper model.

[0067] Based on the wave function files of the simulation results of the cellulose and insulating oil molecular models obtained by Gaussian geometric optimization, the Resp charges were calculated in Multiwfn software. The top and itp files required for the simulation of cellulose monomers under the Glycam force field were generated using Ambertools tools in conjunction with the Acpype script. The top and itp files required for the simulation of insulating oil under the GAFF force field were obtained using Sobtop software. The top files of cellulose and insulating oil were merged, and the calculated RESP charges were replaced into the corresponding itp files. The energy minimization of the oil-impregnated paper model was carried out using Gromacs software with the steepest gradient method. First, 20 ns of equilibration was carried out under the NPT ensemble, and then 10 ns of simulation was carried out. The obtained trajectory was used for the calculation of various properties. The simulation temperature was set to the temperature at which the aging characteristics of the oil-impregnated paper were actually desired. The temperature was set to 393 K, and the simulation step size was 1 fs.

[0068] Based on the obtained 10-ns molecular dynamics simulation trajectory of the oil-impregnated paper model, the differences in the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime of different oil-impregnated paper models were calculated. The results are shown in Table 1.

[0069] Table 1 Calculation results of the microscopic parameters of oil-impregnated paper

[0070]

[0071] As can be seen from Table 1, the self-diffusion coefficient of the soybean-based natural ester oil-impregnated paper is lower, and the isobaric heat capacity, number of hydrogen bonds, and hydrogen bond lifetime are higher. Therefore, the thermal aging performance of the soybean-based oil-impregnated paper is excellent. Verification example

[0072] Accelerated thermal aging tests of the two oil-impregnated papers were carried out to further verify the simulation results. The steps of the thermal aging test are as follows:

[0073] 1. Put mineral oil and soybean-based natural ester into a vacuum drying oven and dry them at 90 °C / 50 Pa for 48 h. After drying, control the moisture content of the insulating oil below 50 ppm.

[0074] 2. Cut the insulating cardboard with a thickness of 0.5 mm and a density of 1.5 g / cm 3 into pieces of 6 cm × 6 cm size and dry them at 90 °C / 50 Pa for 24 h. Test that the moisture content of the insulating paper is below 0.5%.

[0075] 3. Prepare multiple wide-mouth glass bottles, pour 1 L of dried insulating oil into each bottle, and soak the oil for 48 h at 60 °C / 50 Pa according to the ratio of insulating oil to insulating paper of 10:1.

[0076] 4. Conduct an accelerated thermal aging test at 120 °C, take samples at different time intervals, and test the degree of polymerization of the insulating paper according to IEC 60450.

[0077] The changes in the degree of polymerization of the two oil-impregnated papers at different aging days are shown in Table 2.

[0078] Table 2 Polymerization of the two oil-impregnated papers at different aging days

[0079] 0 days 12 days 85 days 166 days 221 days Mineral oil-impregnated paper 1041.1 793.38 433.5 360.94 306.22 Soybean-based natural ester oil-impregnated paper 1054.89 898.71 636.24 618.43 523.84

[0080] It can be seen from Table 2 that within 221 days of aging, the degree of polymerization of the soybean-based natural ester oil-impregnated paper is higher than that of the mineral oil-impregnated paper, which proves the effectiveness of the simulation results.

[0081] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters, comprising the following steps: A) Obtaining the oil impregnation rate of insulating paper; B) using Gaussian View software to draw the monomer molecular structure model of cellulose, the main component of oil-impregnated paper, and the single molecular structure model of insulating oil, using Packmol software to construct an oil-impregnated paper model with a periodic structure, and setting the ratio of the cellulose monomer molecular structure model and the insulating oil single molecular structure model in the oil-impregnated paper model according to the oil impregnation rate of the insulating paper; C) using Gromacs software to minimize the energy of the oil-immersed paper model, and then performing molecular dynamics simulation under the NPT ensemble to obtain the simulation trajectory of the molecular dynamics of the oil-immersed paper model; D) Based on the simulation trajectory of molecular dynamics of the oil-impregnated paper model, the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds and hydrogen bond lifetime of the oil-impregnated paper model are calculated, and the aging characteristics of the oil-impregnated paper are evaluated based on the self-diffusion coefficient, isobaric heat capacity, number of hydrogen bonds and hydrogen bond lifetime.

2. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: Follow the steps below to get the oil impregnation rate of the insulation paper: Weigh the insulating paper after drying to obtain the mass of the insulating paper; The insulating paper is immersed in insulating oil under vacuum conditions, and the oil-immersed paper is removed after the oil immersion is completed, and the surface oil stains are removed and weighed to obtain the mass of the oil-immersed paper; The oil impregnation rate of the insulating paper is calculated based on the difference between the mass of the oil-impregnated paper and the mass of the insulating paper.

3. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: The polymerization degree n of the monomer molecular structure model of cellulose is greater than or equal to 10, and -OH is added to the tail end of the monomer molecular structure model of cellulose for saturation treatment.

4. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: Based on density functional theory, the Gaussian software B3LYP functional and 6-311G(d,p) basis set plus D3 dispersion correction method were used to geometrically optimize the cellulose monomer molecular structure model and the insulating oil single molecule structure model, and then the oil-impregnated paper model was constructed.

5. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: In the oil-impregnated paper model, the number of cellulose monomer molecular structure models is ≥30.

6. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: After obtaining the oil-impregnated paper structure model, the wave function files of the simulation results of the cellulose monomer molecular structure model and the insulating oil molecular structure model are obtained based on Gaussian geometry optimization, the Resp charge is calculated in the Multiwfn software, and the Ambertools tool is used in conjunction with the Acpype script to generate the top and itp files required for the simulation of the cellulose monomer molecular structure model under the Glycam force field. The Sobtop software is used to obtain the top and itp files required for the simulation of the insulating oil single molecule structure model under the GAFF force field. The top files of the cellulose monomer molecular structure model and the insulating oil single molecule structure model are merged, and the calculated RESP charge is replaced into the corresponding itp file, and then the energy of the oil-impregnated paper model is minimized.

7. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: The energy minimization of the oil-immersed paper model was performed using the steepest gradient method.

8. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: The self-diffusion coefficient of the oil-immersed paper model is calculated according to formula (1): In formula (1), N is the total number of atoms, i is the atomic number, and r is i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0 respectively.

9. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: The isobaric heat capacity of the oil-immersed paper model is calculated according to formula (2): In formula (2), C P is the isobaric heat capacity, H is the enthalpy of the model, T is the model temperature, k B is the Boltzmann constant.

10. The method for evaluating the aging characteristics of oil-impregnated paper based on microscopic parameters according to claim 1, characterized in that: The lifetime of the hydrogen bond is calculated according to formula (3): In formula (3), τ HB is the hydrogen bond lifetime, i is the hydrogen bond number, and t0 represents the initial time; S i (t0) indicates the existence of the i-th hydrogen bond at time t0. If the i-th hydrogen bond does not exist at time t0, then S i (t0) is 0, and the i-th hydrogen bond exists at time t0, then S i (t0) is 1; S i (t0+t) indicates the existence of the i-th hydrogen bond at time t0+t. If the i-th hydrogen bond does not exist at time t0+t, then S i (t0+t) is 0, and the i-th hydrogen bond exists at time t0+t, then S i (t0+t) is 1.

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