Insulation paper aging degree evaluation method based on methanol between-oil-paper balance model

Abstract

The invention discloses an insulation paper aging degree evaluation method based on a methanol inter-oil-paper balance model, relates to the field of power equipment state monitoring, and aims to solve the problem of low aging evaluation accuracy of existing transformer oil paper insulation. And in combination with an existing evaluation model, obtaining a corrected evaluation model. According to the technical scheme, the transformer oil paper insulation aging diagnosis problem under different oil paper proportions and different water contents is considered, so that the aging evaluation accuracy of transformer oil paper insulation is greatly improved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of power equipment state monitoring, in particular to an insulation paper aging degree evaluation method based on a methanol inter-oil-paper balance model. BACKGROUND

[0002] A transformer is the "heart" of a power system, and an oil-paper insulation system (consisting of insulating oil and insulation paper / paperboard) is the "soul" of the transformer, and its state directly determines the service life and operation reliability of the transformer. The core role of the aging evaluation of the transformer oil-paper insulation is to scientifically diagnose the current health state of the insulation system, predict the remaining service life, and provide key basis for the maintenance, repair or replacement decision of the equipment, so as to ensure the safe, stable and economic operation of the power grid.

[0003] The power part and related power enterprises usually use a degree of polymerization (DP) value to represent the aging degree of the insulation paper, but it is found in actual operation that the degree of polymerization of the insulation paper is difficult to directly measure, and needs to be measured after the transformer is stopped and the core is lifted from the winding insulation layer. This not only is inconvenient for actual operation, but also damages the insulation structure, and the operation and maintenance cost is also high. Therefore, researchers propose to calculate the degree of polymerization value by using the content of the aging product in the oil to indirectly evaluate the aging degree of the insulation paper, and the actual application is the national standard in the power operation and maintenance engineering.

[0004] In recent years, it has been found that methanol in the oil (one of the aging products in the oil) can be used to evaluate the degree of polymerization of the insulation paper, and a large amount of research work has been carried out around the transformer oil-paper insulation aging evaluation technology based on the characteristic quantity of methanol in the oil, the mechanism of the methanol (total amount) produced by the cellulose cracking is explored, and the methanol (total amount)-degree of polymerization evaluation model is constructed. Methanol is produced and forms a dynamic balance between oil and paper, but it is found in actual application that the methanol detection in the paper is difficult to realize, and the degree of polymerization value is usually indirectly evaluated by detecting the methanol content in the oil, and the methanol (in the oil)-degree of polymerization evaluation model is constructed. The balance coefficient between the oil and the paper is regarded as a constant in the evaluation method, but it is found in actual experiments that the balance coefficient between the oil and the paper is not constant, but changes with the development of aging.

[0005] With the increase of the operation time, the aging degree of the transformer oil-paper insulation deepens, which affects the polar adsorption of the methanol by the insulation paper, affects the balance rule of the methanol between the oil and the paper, causes the concentration of the methanol in the transformer oil to change, and meanwhile, the water content ratio of the transformer insulation paper and the oil-paper ratio also affect the concentration of the methanol in the oil in the process of the transformer operation, and these factors jointly cause the problem of low accuracy of the existing aging evaluation of the transformer oil-paper insulation. SUMMARY

[0006] The purpose of this invention is to provide a method for assessing the aging degree of insulating paper based on a methanol equilibrium model between oil and paper, addressing the problem of low accuracy in existing transformer oil-paper insulation aging assessments.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] The method for assessing the aging degree of insulating paper based on the methanol equilibrium model between oil and paper includes the following steps:

[0009] Step 1: Construct an equilibrium model of methanol between oil and paper;

[0010] Step 2: Based on the equilibrium model of methanol between oil and paper, fit different oil-paper ratios and different moisture contents to obtain the oil-paper ratio correction coefficient and the moisture content correction coefficient.

[0011] Step 3: Introduce the oil-paper ratio correction factor and moisture content correction factor into the methanol-polymerization degree evaluation model to obtain the corrected evaluation model under different oil-paper ratios and different moisture contents;

[0012] Step 4: Obtain the methanol content in the transformer insulating oil and use the modified evaluation model to obtain the corresponding degree of polymerization value. Finally, obtain the aging evaluation result of the transformer oil-paper insulation based on the output degree of polymerization value.

[0013] Furthermore, the specific steps of step 1 are as follows:

[0014] Step 11: Use an oil filter to filter the insulating oil, and put the filtered insulating oil into a vacuum drying oven for 48 hours at 100°C.

[0015] Step 12: Cut the insulating paper into strips of 7cm × 1.8cm, and put the insulating paper strips into a vacuum drying oven for 48 hours at 100℃.

[0016] Step 13: Place the dried insulating paper tape into an aging chamber and set the temperature of the aging chamber to 130℃. The aging time is 49 days. Take out the insulating paper tape every 7 days to obtain insulating paper tapes with different aging degrees, and fix the insulating paper tapes with different aging degrees to 12g.

[0017] Step 14: Add dried insulating oil to insulating paper tapes with different aging levels to obtain insulating paper tapes with different oil-to-paper ratios;

[0018] Step 15: Evenly suspend the insulating paper tapes with different oil-paper ratios on the metal rack inside the humidification chamber. Set the relative humidity of the humidification chamber to 80% and the temperature to 35℃. Remove the insulating paper tapes from the humidification chamber at 0 min, 5 min, 10 min, 20 min, 30 min, 40 min, and 50 min respectively. Weigh the insulating paper tapes before and after moisture absorption using a high-precision electronic balance, and then calculate the moisture content. ;

[0019] Step 16: Select insulating paper tapes with different oil-paper ratios and different moisture contents for accelerated thermal aging experiments;

[0020] Step 17: After the accelerated thermal aging experiment, obtain the degree of polymerization of the insulating paper tape and the methanol content in the oil;

[0021] Step 18: Fit the different degrees of polymerization and their corresponding methanol concentrations in the oil to obtain the equilibrium model of methanol between the oil and paper.

[0022] Furthermore, the moisture content Represented as:

[0023] ,

[0024] in, For the quality of dry insulating paper tape, The quality of the insulating paper tape after it has absorbed moisture.

[0025] Furthermore, step 17 specifically includes:

[0026] Take out the insulating paper tape, soak the insulating paper tape in n-hexane for 24 hours. After soaking, let the insulating paper tape dry at room temperature, and measure the degree of polymerization of the insulating paper using the Ubbelohde viscometry method.

[0027] The insulating paper tape was placed in a temperature-controlled chamber at 40°C for 5 days to equilibrate, and then the methanol concentration in the oil was measured using GC-FID.

[0028] Furthermore, the equilibrium model of methanol between the oil and paper is expressed as follows:

[0029] ,

[0030] in, , For fitting parameters, This represents the degree of polymerization.

[0031] Furthermore, the insulating paper tapes with different oil-paper ratios and different moisture contents selected in step 16 are oil-paper insulation samples with oil-paper ratios of 14:1, 16:1, 18:1, and 20:1, and insulating paper with moisture contents of 2.5%, 3%, 3.5%, and 5%.

[0032] Furthermore, the oil-paper ratio correction factor is expressed as:

[0033] ,

[0034] in, and The parameters to be fitted are... This refers to the ratio of oil paper to paper.

[0035] Furthermore, the moisture content correction factor is expressed as:

[0036] ,

[0037] in, , The parameters to be fitted are... This represents the water content in the oil.

[0038] Furthermore, the methanol-polymerization degree evaluation model is expressed as follows:

[0039] ,

[0040] ,

[0041] in, The methanol content in the amorphous region of the insulating paper reaches saturation. This represents the number of times each cellulose molecular chain breaks due to aging. The linear contribution of various slow reactions to the degradation of amorphous regions. The conversion rate of cellulose degradation within the amorphous and crystalline regions. This represents the proportion of methanol in the oil to the total methanol content. This represents the proportion of methanol in the total methanol content of the standard group's oil.

[0042] Furthermore, the modified evaluation model is expressed as:

[0043] ,

[0044] in, The methanol content in the amorphous region of the insulating paper reaches saturation. This represents the number of times each cellulose molecular chain breaks due to aging. The linear contribution of various slow reactions to the degradation of amorphous regions. The conversion rate of cellulose degradation in the amorphous and crystalline regions.

[0045] The beneficial effects of this invention are:

[0046] This application first constructs a methanol equilibrium model between oil and paper, then introduces correction coefficients for the oil-paper ratio and moisture content, and combines them with existing evaluation models to obtain a corrected evaluation model. The technical solution of this application considers the aging diagnosis problem of transformer oil-paper insulation under different oil-paper ratios and moisture contents, thus significantly improving the accuracy of aging assessment of transformer oil-paper insulation. Attached Figure Description

[0047] Fig. 1 Build an overall flowchart for the model;

[0048] Fig. 2 A schematic diagram showing the correction factor for oil paper ratio under different oil paper ratios;

[0049] Fig. 3 This is a schematic diagram showing the moisture content correction coefficients for different moisture contents. Detailed Implementation

[0050] It should be noted that, where there is no conflict, the various embodiments disclosed in this application can be combined with each other.

[0051] Specific Implementation Method 1: The method for assessing the aging degree of insulating paper based on the methanol equilibrium model between oil and paper described in this implementation method includes:

[0052] Equilibrium models of methanol in oil and paper were constructed under different aging states of insulating paper. The methanol content in the oil was measured under different oil-paper ratios and different moisture contents. The correction parameters of the evaluation model under the current state were obtained by fitting the oil-paper ratio and moisture content under the current state. The correction parameters under the current state and the methanol content in the oil were substituted into the evaluation model to obtain the degree of polymerization of the tested insulating paper, thereby realizing the aging diagnosis of oil-paper insulation.

[0053] To investigate the equilibrium law of methanol between oil and paper and the influence of different oil-paper ratios and moisture contents on this equilibrium law, it is necessary to construct an equilibrium model for methanol between oil and paper. Then, by introducing correction coefficients for different oil-paper ratios and moisture contents, a corrected evaluation model can be constructed to accurately assess the degree of polymerization of insulating paper under different moisture contents and oil-paper ratios, thereby achieving reliable assessment of the insulation condition under different oil-paper ratios and moisture contents. (Reference) Figs. 1-3 This embodiment will be described in detail, including the calculation method and correction strategy for the methanol equilibrium law between oil and paper.

[0054] The equilibrium coefficient R of methanol between oil and paper and the proportion d of methanol in oil to total methanol were introduced to analyze the equilibrium law of methanol between oil and paper, and an equilibrium model of methanol between oil and paper was constructed. Correction factors for different oil-paper ratios and different moisture contents were introduced to correct the methanol concentration. The existing evaluation model was modified by incorporating different oil-paper ratios and different moisture contents correction factors. Details are as follows:

[0055] (1) Sample preparation: An accelerated thermal aging test was conducted on the water-free insulating paper samples for 49 days, and aging samples were taken every 7 days. Then, insulating paper samples with different moisture contents were obtained by the insulating paper moisture absorption test. By fixing the mass of the aged insulating paper to 12g and adjusting the mass of the insulating oil, oil-paper insulation test samples with different oil-paper ratios were obtained.

[0056] First, the insulating paper and insulating oil are pretreated. The insulating oil is filtered using an oil filter to initially remove impurities, moisture, and dissolved gases. The filtered insulating oil is then placed in a vacuum drying oven at 100°C for 48 hours to further degas and dehydrate. The insulating paper is then cut into 7 cm × 1.8 cm strips. These strips are then placed in a vacuum drying oven for 48 hours at 100°C for dehydration and drying.

[0057] Secondly, accelerated thermal aging experiments were conducted. The temperature of the aging chamber was set to 130℃, the aging time was 49 days, and samples were taken every 7 days to obtain insulating paper samples with different aging degrees.

[0058] Finally, a moisture absorption experiment was conducted on the insulating paper. The insulating paper strips were evenly suspended on a metal rack inside the humidification chamber to avoid contact with the chamber surface and causing localized humidity differences. The relative humidity of the humidification chamber was set to 80% and the temperature to 35℃. The constant humidity control system was activated to allow the insulating paper strips to fully absorb moisture in a sealed environment. The insulating paper strips were removed from the constant humidity and temperature chamber at 0 min, 5 min, 10 min, 20 min, 30 min, 40 min, and 50 min, respectively. The mass change of the insulating paper strips before and after moisture absorption was measured using a high-precision electronic balance, and the moisture content was calculated. The calculation is shown in the following formula:

[0059] ,

[0060] In the formula: The mass of the dried insulating paper tape is in grams (g). The mass of the insulating paper tape after moisture absorption is expressed in grams (g).

[0061] Meanwhile, by fixing the insulating paper in different aging states at 12g, experimental samples with different oil-paper ratios were obtained by changing the mass of insulating oil.

[0062] Correction factors for different oil paper ratios and different moisture contents are as follows: Fig. 2 , 3As shown, the oil-paper ratio and moisture content are basically linearly related to the correction coefficient under this scenario. Accelerated thermal aging tests were conducted on oil-paper insulation samples with oil-paper ratios of 14:1, 16:1, 18:1, and 20:1, and insulation paper with moisture contents of 2.5%, 3%, 3.5%, and 5%.

[0063] (2) Experimental data collection: The degree of polymerization of the insulating paper was tested after aging. After equilibrium was reached, the methanol content in the oil was tested. Details are as follows:

[0064] Degree of polymerization test: Remove the insulating paper and soak it in n-hexane for 24 hours (to further remove the insulating oil on the surface of the insulating paper). After soaking, let the insulating paper air dry at room temperature, and measure the degree of polymerization of the insulating paper using the Ubbelohde viscometry method.

[0065] Methanol concentration detection in oil: After equilibration, the methanol concentration in oil is measured using GC-FID.

[0066] (3) Equilibrium model construction: The methanol concentration and degree of polymerization in the oil at different degrees of polymerization were fitted to obtain the equilibrium model of methanol between the oil and paper at this aging degree, as follows:

[0067] The methanol equilibrium experiment between oil paper includes:

[0068] Prepare a methanol insulating oil standard solution with a methanol concentration of 20 ppm. Add anhydrous and aged insulating paper with different moisture contents to the standard solution. Place the samples in an oven and equilibrate at 40°C for 5 days. Measure the methanol concentration in the oil to obtain the methanol equilibrium between the oil and the paper.

[0069] For experimental samples with different oil-paper ratios, insulating papers with different aging degrees were placed in insulating oil according to a set oil-paper mass ratio. The samples were then placed in a 40℃ temperature-controlled chamber for 5 days to ensure that methanol reached equilibrium between the insulating paper and the insulating oil. After equilibrium, the methanol concentration in the oil was measured using GC-FID and compared with the concentration of a 20 ppm standard solution to obtain the influence of different aging degrees of insulating paper and the oil-paper ratio on the equilibrium of methanol between the oil and paper.

[0070] The tests performed on the GC-FID and aggregation degree of the samples include:

[0071] The degree of polymerization of the insulating paper was measured using the Ubbelohde viscosity method, and the methanol content in the oil of the oil-paper insulation sample after equilibrium was determined using GC-FID.

[0072] Prior to the accelerated thermal aging test, the following were also included:

[0073] The insulating oil is filtered using an oil filter machine. The filtered insulating oil is then placed in a vacuum drying oven and dried at 100°C for 48 hours. The insulating paper is then cut into strips and placed in the vacuum drying oven for another 48 hours of dehydration drying at 100°C.

[0074] The equilibrium coefficient of methanol between oil paper The calculation process includes:

[0075] Considering the equilibrium of methanol from oil to paper, since the methanol concentration in the methanol-insulating oil standard solution is known, the methanol concentration in the paper can be determined by measuring the residual methanol concentration in the oil after equilibrium is reached. Furthermore, the methanol equilibrium coefficient between the oil and paper can be obtained. The formula for calculation is:

[0076] ,

[0077] in The methanol content in the methanol-insulating oil standard solution is expressed in ppm. The residual methanol content in the insulating oil after methanol has reached equilibrium between the oil and paper is expressed in ppm. This is the equilibrium coefficient of methanol between oil and paper, which is the ratio of the methanol content in the paper to the methanol content in the oil. >0.

[0078] Considering the equilibrium of methanol from paper to oil, since the methanol content in the paper before diffusion is known, the residual methanol content in the paper can be obtained by measuring the methanol concentration in the oil after equilibrium. Furthermore, the formula for calculating the methanol equilibrium coefficient R between the paper and oil can be derived as follows:

[0079] ,

[0080] in The initial methanol content adsorbed by the insulating paper is expressed in mg. The methanol content in the insulating oil after methanol has reached equilibrium between the oil and paper is expressed in ppm; the weight of the insulating oil is expressed in g.

[0081] The calculation process for the proportion d of methanol in the oil to the total methanol includes:

[0082] ,

[0083] in This represents the proportion of methanol in the oil to the total methanol content. This is the equilibrium coefficient of methanol between the oil and paper.

[0084] The construction of an equilibrium model for methanol in insulating paper under different aging states includes:

[0085] Selecting insulating paper The value is the independent variable in the equilibrium coefficient model, and the methanol-oil-paper equilibrium coefficient is the dependent variable in the model. The equilibrium coefficient of methanol between oil and paper and the insulating paper are established. The fitting equation for the value is:

[0086] ,

[0087] , For fitting parameters, This represents the degree of polymerization.

[0088] Specific parameter values ​​are shown in Table 1; The equilibrium coefficient of methanol between oil and paper at an oil-to-paper ratio of 16:1 and an equilibrium temperature of 40℃, without water.

[0089] Table 1 and Parameter values

[0090]

[0091] The preparation process of the samples with different oil paper ratios includes:

[0092] Four experimental samples with different oil-to-paper ratios were prepared by mixing insulating oil and insulating paper of different aging stages at mass ratios of 14:1, 16:1, 18:1, and 20:1. The mass of the insulating paper was 12g. The mass of the insulating oil was adjusted according to the different oil-to-paper ratios to prepare experimental samples of oil-to-paper insulation with different oil-to-paper ratios.

[0093] The moisture absorption test of the insulating paper includes:

[0094] The insulating paper is evenly suspended in a humidification box with a relative humidity of 80% and a temperature of 35℃, so that the insulating paper can fully absorb moisture in a closed environment.

[0095] Calculate the moisture content of the insulating paper at 0 min, 5 min, 10 min, 20 min, 30 min, 40 min, and 50 min respectively.

[0096] (4) Correction coefficient fitting: The experimental data were fitted using the fitting equation of the equilibrium coefficient of methanol between the oil paper and the DP value of the insulating paper to obtain the correction coefficients for different oil paper ratios and moisture contents, as follows:

[0097] The formula for calculating the oil paper ratio correction factor is:

[0098] ,

[0099] in, This is the correction factor for the oil-paper ratio. and The parameters to be fitted are... This refers to the ratio of oil paper to paper.

[0100] The formula for calculating the moisture content correction factor is:

[0101] ,

[0102] The moisture correction factor is: , , These are the parameters to be fitted; This represents the water content in the oil, expressed in ppm.

[0103] Corrected proportion of methanol in oil to total methanol for:

[0104] ,

[0105] in This represents the proportion of methanol in the total methanol content of the standard group's oil.

[0106] (5) Establishment of a corrected evaluation model by introducing correction coefficients and equilibrium model: The above correction coefficients for oil-paper ratio and moisture content are introduced into the existing methanol-polymerization degree evaluation model (existing model, Study on Aging Assessment Model of Transformer Cellulose Insulation Paper Based on Methanol in Oil) to construct a corrected evaluation model for different oil-paper ratios and different moisture contents, as follows:

[0107] Based on the existing methanol (in oil) degree of polymerization assessment model, the following calculation formula is used:

[0108] ,

[0109] in This indicates the methanol content in the oil, expressed in ppm, at an operating temperature of T (°C). = , This indicates the saturation content of methanol in the amorphous region of the insulating paper. This refers to the number of breaks in each cellulose molecular chain due to aging, and the "conversion rate" between cellulose degradation and methanol formation in the amorphous and crystalline regions are respectively... and And for conduct Substitution, It is believed that various slow reactions contribute linearly to the degradation of amorphous regions.

[0110] The methanol (in oil) degree of polymerization assessment correction model after introducing the above correction coefficients is as follows:

[0111] ,

[0112] This application conducts an accelerated thermal aging experiment on anhydrous insulating paper at 130℃ for 49 days. The degree of polymerization of the insulating paper is measured using the Ubbelohde viscosity method. Insulating papers with different initial moisture contents are prepared through a moisture absorption experiment. The aged insulating paper is then mixed with insulating oil according to a predetermined oil-paper ratio to prepare experimental samples with different oil-paper ratios. After equilibrium, GC-FID testing is used to obtain data on the methanol content in the oil. An equilibrium model of methanol between oil and paper is constructed based on the aforementioned degree of polymerization and methanol content in the oil. Furthermore, correction coefficients for the oil-paper ratio and moisture content are proposed and introduced into existing methanol-degree of polymerization evaluation models, resulting in corrected evaluation models for different oil-paper ratios and moisture contents. This application solves the problems of the lack of quantitative calculation and analysis of mathematical models for the equilibrium law of methanol between oil and paper, and the poor evaluation accuracy of traditional evaluation models under different moisture contents and oil-paper ratios. It can achieve high-precision evaluation of the aging state of oil-paper insulation under different oil-paper ratios and moisture contents, providing a reliable solution for insulation state evaluation under complex working conditions and possessing high engineering application value.

[0113] This application designs an accelerated thermal aging experiment for anhydrous insulating paper to obtain insulating paper samples with different aging degrees. The Ubbelohde viscosity method is used to measure the degree of polymerization of the insulating paper. Aging insulating paper is mixed with insulating oil according to a set oil-to-paper ratio to prepare experimental samples with different oil-to-paper ratios. The aged insulating paper is then subjected to a moisture absorption experiment to obtain insulating paper samples with different moisture contents. GC-FID is used to test the samples after aging equilibrium to obtain the methanol content in the oil of the aged samples. An equilibrium model of methanol between oil and paper is constructed to quantitatively analyze the equilibrium law of methanol between oil and paper. A fitting formula for oil-to-paper ratio and moisture content is constructed, and a correction coefficient is obtained through experimental data. This correction coefficient is then integrated into an existing insulating paper polymerization degree evaluation model based on methanol characteristic values ​​to achieve the construction of a corrected model. This application solves the problems of the lack of a mathematical calculation model for the equilibrium law of methanol between oil and paper, and the failure of traditional evaluation models caused by changes in methanol concentration in oil under different oil-paper ratios and different moisture contents. It can achieve high-precision aging evaluation under different oil-paper ratios and different moisture contents, and provides a reliable solution for evaluating the insulation status of actual transformers operating in complex environments, which has high engineering application value.

[0114] It should be noted that the specific embodiments are merely explanations and illustrations of the technical solution of the present invention and should not be used to limit the scope of protection. Any modifications made in accordance with the claims and specification of the present invention that are only partial should still fall within the protection scope of the present invention.

Claims

1. A method for assessing the aging degree of insulating paper based on a methanol equilibrium model between oil and paper, characterized in that... Includes the following steps: Step 1: Construct an equilibrium model of methanol between oil and paper; Step 2: Based on the equilibrium model of methanol between oil and paper, fit different oil-paper ratios and different moisture contents to obtain the oil-paper ratio correction coefficient and the moisture content correction coefficient. Step 3: Introduce the oil-paper ratio correction factor and moisture content correction factor into the methanol-polymerization degree evaluation model to obtain the corrected evaluation model under different oil-paper ratios and different moisture contents; Step 4: Obtain the methanol content in the transformer insulating oil and use the modified evaluation model to obtain the corresponding degree of polymerization value. Finally, obtain the aging evaluation result of the transformer oil-paper insulation based on the output degree of polymerization value.

2. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper as described in claim 1, characterized in that... The specific steps of step 1 are as follows: Step 11: Use an oil filter to filter the insulating oil, and put the filtered insulating oil into a vacuum drying oven for 48 hours at 100°C. Step 12: Cut the insulating paper into strips of 7cm × 1.8cm, and put the insulating paper strips into a vacuum drying oven for 48 hours at 100℃. Step 13: Place the dried insulating paper tape into an aging chamber and set the temperature of the aging chamber to 130℃. The aging time is 49 days. Take out the insulating paper tape every 7 days to obtain insulating paper tapes with different aging degrees, and fix the insulating paper tapes with different aging degrees to 12g. Step 14: Add dried insulating oil to insulating paper tapes with different aging levels to obtain insulating paper tapes with different oil-to-paper ratios; Step 15: Evenly suspend the insulating paper tapes with different oil-paper ratios on the metal rack inside the humidification chamber. Set the relative humidity of the humidification chamber to 80% and the temperature to 35℃. Remove the insulating paper tapes from the humidification chamber at 0 min, 5 min, 10 min, 20 min, 30 min, 40 min, and 50 min respectively. Weigh the insulating paper tapes before and after moisture absorption using a high-precision electronic balance, and then calculate the moisture content. ; Step 16: Select insulating paper tapes with different oil-paper ratios and different moisture contents for accelerated thermal aging experiments; Step 17: After the accelerated thermal aging experiment, obtain the degree of polymerization of the insulating paper tape and the methanol content in the oil; Step 18: Fit the different degrees of polymerization and their corresponding methanol concentrations in the oil to obtain the equilibrium model of methanol between the oil and paper.

3. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 2, characterized in that... The moisture content Represented as: ， in, For the quality of dry insulating paper tape, The quality of the insulating paper tape after it has absorbed moisture.

4. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 3, characterized in that... Step 17 specifically involves: Take out the insulating paper tape, soak the insulating paper tape in n-hexane for 24 hours. After soaking, let the insulating paper tape dry at room temperature, and measure the degree of polymerization of the insulating paper using the Ubbelohde viscometry method. The insulating paper tape was placed in a temperature-controlled chamber at 40°C for 5 days to equilibrate, and then the methanol concentration in the oil was measured using GC-FID.

5. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 4, characterized in that... The equilibrium model of methanol between oil and paper is expressed as follows: ， in, , For the fitting parameters, This represents the degree of polymerization.

6. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 5, characterized in that... The insulating paper tapes with different oil-paper ratios and different moisture contents selected in step 16 are oil-paper insulation samples with oil-paper ratios of 14:1, 16:1, 18:1, and 20:1, and insulating paper with moisture contents of 2.5%, 3%, 3.5%, and 5%.

7. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 6, characterized in that... The oil paper ratio correction factor is expressed as follows: ， in, and The parameters to be fitted are... This refers to the ratio of oil paper to paper.

8. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 7, characterized in that... The moisture content correction factor is expressed as follows: ， in, , The parameters to be fitted are... This represents the water content in the oil.

9. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 8, characterized in that... The methanol-polymerization degree evaluation model is expressed as follows: ， ， in, The methanol content in the amorphous region of the insulating paper reaches saturation. This represents the number of times each cellulose molecular chain breaks due to aging. The linear contribution of various slow reactions to the degradation of amorphous regions. The conversion rate of cellulose degradation within the amorphous and crystalline regions. This represents the proportion of methanol in the oil to the total methanol content. This represents the proportion of methanol in the total methanol content of the standard group's oil.

10. The method for evaluating the aging degree of insulating paper based on the methanol equilibrium model between oil and paper according to claim 9, characterized in that... The modified evaluation model is expressed as follows: ， in, The methanol content in the amorphous region of the insulating paper reaches saturation. This represents the number of times each cellulose molecular chain breaks due to aging. The linear contribution of various slow reactions to the degradation of amorphous regions. The conversion rate of cellulose degradation in the amorphous and crystalline regions.

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