Method for predicting electrical strength of converter transformer oil under time and temperature changes

Abstract

The invention discloses a method for predicting the electrical strength of converter transformer oil under time and temperature changes, and particularly relates to the technical field of electrical strength analysis. Comprising the steps of S01, conversion of high-temperature aging time of converter transformer oil, S02, acquisition of breakdown field strength data of the converter transformer oil, S03, evaluation of an electric field distribution state, S04, establishment of a converter transformer oil breakdown field strength prediction model, S05, analysis of the fitting degree of the breakdown field strength of the converter transformer oil, and S06, evaluation of the fitting degree of the breakdown field strength of the converter transformer oil. According to the method, the aging acceleration factor is used for converting the high-temperature aging time of the converter transformer oil into the actual operation time, so that the aging rate and the service life under different temperature conditions can be evaluated, an electric field distribution state evaluation index and a breakdown field strength prediction index are calculated, and a breakdown field strength fitting degree coefficient is analyzed; therefore, the electrical strength change of the oil product in operation can be predicted, and potential electrical risks can be found.

Description

Technical Field

[0001] The present invention relates to the technical field, and more particularly to a method for predicting the electrical strength of converter transformer oil under time and temperature changes. Background Art

[0002] As a key equipment in modern power systems, converter transformers are widely used in high-voltage direct current transmission systems and undertake the core functions of power conversion and transmission. Since their working environment usually has extreme conditions such as high temperature and high electric field, transformer oil is the main insulating medium, and its electrical performance stability and reliability directly affect the safe operation and service life of the converter transformer.

[0003] Transformer oil not only has excellent insulation properties, but can also effectively cool the internal components of the transformer. However, as the operating time increases, the transformer oil will undergo thermal aging due to long-term exposure to high temperatures and high voltages, causing its electrical strength to gradually decrease. This in turn affects the insulation performance of the converter transformer and may even cause equipment failure, threatening the stable operation of the power system.

[0004] However, it still has some shortcomings in actual use. For example, the existing research on thermal aging of transformer oil lacks theoretical analysis on the changes in the electrical strength of converter transformer oil under different aging conditions, especially the changes in its breakdown field strength under different temperatures and voltages.

[0005] The existing transformer oil breakdown field strength variation law under different aging time and temperature conditions lacks an accurate prediction model, which cannot provide a scientific basis for transformer oil service life prediction and electrical performance evaluation. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a method for predicting the electrical strength of converter transformer oil under time and temperature changes, which is used to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for predicting the electrical strength of converter transformer oil under time and temperature changes, comprising the following steps:

[0008] Step S01: Converting the high-temperature aging time of converter transformer oil: converting the oil-paper insulation sample subjected to high-temperature aging of converter transformer oil into the actual operating time under actual lower temperature using an aging acceleration factor.

[0009] Step S02: Collecting the breakdown field strength data of the converter transformer oil: used to collect the breakdown field strength data of the insulating oil after the sample aging time is completed. The step S02: collecting the high-temperature aging data of the converter transformer oil includes the sub-steps of collecting the breakdown data of the non-aged transformer oil and the sub-steps of collecting the breakdown data of the aged transformer oil.

[0010] Step S03: Electric field distribution state evaluation: Based on the positive polarity DC breakdown voltage of the non-aged insulating oil sample at various temperatures, the electric field distribution state evaluation index of the non-aged insulating oil sample at various temperatures is calculated to evaluate whether the electric field distribution of the electric ball electrode is concentrated.

[0011] Step S04: Converter transformer oil breakdown field strength prediction model: Based on the aged transformer oil breakdown data collected in the aged transformer oil breakdown data collection sub-step, a breakdown field strength prediction index of the insulating oil after the sample aging time is completed is calculated.

[0012] Step S05: Analysis of the breakdown field strength fitting of converter transformer oil: obtaining the actual breakdown strength data of the insulating oil after the sample aging time is completed, and analyzing and obtaining the breakdown field strength fitting coefficient after the sample aging time is completed based on the breakdown field strength prediction index.

[0013] Step S06: Converter transformer oil breakdown field strength fitting evaluation: used to obtain the breakdown field strength fitting coefficient after the sample aging time is completed, compare it with the preset breakdown field strength fitting coefficient, and process it.

[0014] Preferably, the step S01: converting the high-temperature aging time of the converter transformer oil is specifically as follows:

[0015] S101: Take an oil-paper insulation sample and completely immerse it in a glass bottle filled with insulating oil. Cover the bottle with a cap. Based on the selected sample aging time, the oil-paper insulation samples aged at high temperature of the converter transformer oil are numbered 1, 2, ...i, ...n in sequence.

[0016] S102: Collect the aging temperature of the oil-paper insulation sample of the converter transformer oil at high temperature aging, marked as hl i , where i = 1, 2, ... n, i represents the number of the i-th specimen;

[0017] S103: The calculation formula of the aging acceleration factor is:

[0018]

[0019] Among them, AH i Expressed as the aging acceleration factor of the i-th sample, hl i Expressed as the aging temperature of the i-th sample, E a Expressed as chemical activation energy, ht iis the actual operating temperature of the i-th sample, k is the Boltzmann constant, and the reference value is 1.380649×10-23J / K;

[0020] Since the normal maximum insulation temperature of the current transformer is 80℃ and the maximum fault temperature does not exceed 110℃, the aging time multiplied by the accelerated aging factor is equal to the actual operating time of the current transformer oil-paper.

[0021] Preferably, the step S02: collecting converter transformer oil breakdown field strength data is specifically as follows:

[0022] Unaged transformer oil breakdown data collection sub-steps: Control the temperature of the unaged insulating oil sample through the thermostat, adjust the working state of the strip heater to reach the set temperature of the unaged insulating oil sample, collect the positive polarity DC breakdown voltage of the unaged insulating oil sample at various temperatures, and mark it as Where j = 1, 2, ... m, j represents the number of the j-th set temperature;

[0023] Aging transformer oil breakdown data collection sub-step: collect the sample aging days and sample aging temperature of the insulating oil after the sample aging time is completed, marked as xh respectively i 、xy i .

[0024] Preferably, the step S03: evaluating the electric field distribution state is specifically as follows:

[0025] S301: The calculation formula of the electric field distribution state evaluation index is:

[0026]

[0027] in, Expressed as the electric field distribution state evaluation index at the jth set temperature, Expressed as the positive polarity DC breakdown voltage at the jth set temperature, Expressed as the maximum value of the positive polarity DC breakdown voltage at the jth set temperature, It is expressed as the minimum value of the positive polarity DC breakdown voltage at the jth set temperature;

[0028] S302: Obtain the electric field distribution state evaluation index of the non-aged insulating oil sample, and calculate the voltage deviation with the positive polarity DC breakdown voltage data at each temperature. If If the voltage deviation is greater than the preset value, it indicates that the electric field distribution of the electric ball electrode at this temperature is uneven, and the management personnel should be notified to make adjustments. Otherwise, it indicates that the electric field distribution of the electric ball electrode at this temperature is uniform.

[0029] Preferably, the calculation formula of the breakdown field strength prediction index is:

[0030] α i =ε0+λ1×xh i +λ2×xy i +λ3×xh i 2 +λ4×xy i 2 +λ5×xh i ×xy i

[0031] Among them, α i It is expressed as the breakdown field strength prediction index of the i-th sample, ε0 is expressed as a constant, and xh i Expressed as the number of days of sample aging for the i-th sample, xy i is the sample aging temperature of the i-th sample, and λ1, λ2, λ3, λ4, and λ5 are the interaction coefficients of the breakdown field strength prediction index, respectively.

[0032] Preferably, the calculation formula of the breakdown field strength fitting coefficient is:

[0033]

[0034] Among them, R 2 Expressed as the breakdown field strength fitting coefficient, α i Expressed as the breakdown field strength prediction index of the i-th sample, α 实 It is expressed as the actual breakdown field strength prediction index, Δα is expressed as the mean of the actual breakdown field strength prediction index, and n is expressed as the number of samples.

[0035] Preferably, the step S06: evaluating the converter transformer oil breakdown field strength fitting degree is specifically as follows:

[0036] Obtain the breakdown field strength fitting coefficient after the sample aging time is completed, and compare it with the preset breakdown field strength fitting coefficient. If the breakdown field strength fitting coefficient after the sample aging time is completed is less than the preset breakdown field strength fitting coefficient, it indicates that there is a potential electrical fault risk in the operation of the converter transformer oil, and the management personnel should be notified to replace or handle the insulating oil in time. Otherwise, it indicates that there is no abnormality in the operating performance of the converter transformer oil.

[0037] Technical effects and advantages of the present invention:

[0038] 1. The present invention provides a method for predicting the electrical strength of converter transformer oil under time and temperature changes. By collecting the aging temperature of oil-paper insulation samples subjected to high-temperature aging of converter transformer oil, the oil-paper insulation samples subjected to high-temperature aging of converter transformer oil are converted into actual operating time at a lower temperature using an aging acceleration factor. This method is conducive to accurately evaluating the aging rate and service life of converter transformer oil under different temperature conditions.

[0039] 2. The present invention provides a method for predicting the electrical strength of converter transformer oil under time and temperature changes. The method collects the breakdown field strength data of the insulating oil after the sample aging time is completed, calculates the electric field distribution state evaluation index of the non-aged insulating oil sample at each temperature based on the positive polarity DC breakdown voltage of the non-aged insulating oil sample at each temperature, evaluates whether the electric field distribution of the electric ball electrode is concentrated, calculates the breakdown field strength prediction index of the insulating oil after the sample aging time is completed based on the breakdown data of the aged transformer oil collected in the aged transformer oil breakdown data collection sub-step, and then obtains the actual breakdown strength data of the insulating oil after the sample aging time is completed, and analyzes the sample aging time. The breakdown field strength fitting coefficient after the aging time is compared with the preset breakdown field strength fitting coefficient. If the breakdown field strength fitting coefficient after the aging time of the sample is less than the preset breakdown field strength fitting coefficient, it indicates that there is a potential electrical fault risk in the operation of the converter transformer oil, and the management personnel should be notified to replace or handle the insulating oil in time. Otherwise, it indicates that there is no abnormality in the operating performance of the converter transformer oil. By establishing a breakdown field strength prediction model based on aging time and temperature, the changes in the electrical strength of the oil during long-term operation are predicted, and potential electrical risks are discovered in advance to reduce the failure risk of the transformer due to oil aging and ensure the long-term stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a flow chart of the method for predicting the electrical strength of converter transformer oil under time and temperature changes according to the present invention. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] See also Figure 1 As shown, the present invention provides a method for predicting the electrical strength of converter transformer oil under time and temperature changes, including step S01: converting the high-temperature aging time of converter transformer oil, step S02: collecting breakdown field strength data of converter transformer oil, step S03: evaluating the electric field distribution state, step S04: developing a breakdown field strength prediction model for converter transformer oil, step S05: analyzing the breakdown field strength fitting of converter transformer oil, and step S06: evaluating the breakdown field strength fitting of converter transformer oil.

[0043] The step S01: conversion of the high-temperature aging time of the converter transformer oil is connected with the step S02: acquisition of the breakdown field strength data of the converter transformer oil, the step S02: acquisition of the breakdown field strength data of the converter transformer oil is connected with the step S03: evaluation of the electric field distribution state, the step S03: evaluation of the electric field distribution state is connected with the step S04: prediction model of the breakdown field strength of the converter transformer oil, the step S04: prediction model of the breakdown field strength of the converter transformer oil is connected with the step S05: analysis of the fitting degree of the breakdown field strength of the converter transformer oil, and the step S05: analysis of the fitting degree of the breakdown field strength of the converter transformer oil is connected with the step S06: evaluation of the fitting degree of the breakdown field strength of the converter transformer oil.

[0044] The step S01: converting the high-temperature aging time of the converter transformer oil: converting the oil-paper insulation sample subjected to high-temperature aging of the converter transformer oil into the actual operating time under actual lower temperature using an aging acceleration factor.

[0045] In a possible design, the step S01: converting the high-temperature aging time of the converter transformer oil is specifically as follows:

[0046] S101: Take an oil-paper insulation sample and completely immerse it in a glass bottle filled with insulating oil. Cover the bottle with a cap. Based on the selected sample aging time, the oil-paper insulation samples aged at high temperature of the converter transformer oil are numbered 1, 2, ...i, ...n in sequence.

[0047] S102: Collect the aging temperature of the oil-paper insulation sample of the converter transformer oil at high temperature aging, marked as hl i , where i = 1, 2, ... n, i represents the number of the i-th specimen;

[0048] S103: The calculation formula of the aging acceleration factor is:

[0049]

[0050] Among them, AH i Expressed as the aging acceleration factor of the i-th sample, hl i Expressed as the aging temperature of the i-th sample, E a Expressed as chemical activation energy, ht i is the actual operating temperature of the i-th sample, k is the Boltzmann constant, and the reference value is 1.380649×10-23J / K;

[0051] Since the normal maximum insulation temperature of the current transformer is 80℃ and the maximum fault temperature does not exceed 110℃, the aging time multiplied by the accelerated aging factor is equal to the actual operating time of the current transformer oil-paper.

[0052] In this embodiment, it should be specifically noted that the chemical activation energy of oil-paper insulation ranges from 80 to 100 kJ / mol, and in this embodiment, the value is 80 kJ / mol, and the value of k is 1.380649×10-23 J / K.

[0053] The step S02: collecting breakdown field strength data of the converter transformer oil is used to collect the breakdown field strength data of the insulating oil after the sample aging time is completed. The step S02: collecting high-temperature aging data of the converter transformer oil includes a sub-step of collecting breakdown data of the non-aged transformer oil and a sub-step of collecting breakdown data of the aged transformer oil. The breakdown field strength data includes the breakdown data of the non-aged transformer oil and the breakdown data of the aged transformer oil.

[0054] In one possible design, the step S02: collecting converter transformer oil breakdown field strength data is specifically as follows:

[0055] Unaged transformer oil breakdown data collection sub-steps: Control the temperature of the unaged insulating oil sample through the thermostat, adjust the working state of the strip heater to reach the set temperature of the unaged insulating oil sample, collect the positive polarity DC breakdown voltage of the unaged insulating oil sample at various temperatures, and mark it as Where j = 1, 2, ... m, j represents the number of the j-th set temperature;

[0056] Aging transformer oil breakdown data collection sub-step: collect the sample aging days and sample aging temperature of the insulating oil after the sample aging time is completed, marked as xh respectively i 、xy i .

[0057] The step S03: electric field distribution state evaluation: according to the positive polarity DC breakdown voltage of the non-aged insulating oil sample at each temperature, the electric field distribution state evaluation index of the non-aged insulating oil sample at each temperature is calculated to evaluate whether the electric field distribution of the electric ball electrode is concentrated.

[0058] In a possible design, the step S03: evaluating the electric field distribution state is specifically as follows:

[0059] S301: The calculation formula of the electric field distribution state evaluation index is:

[0060]

[0061] in, Expressed as the electric field distribution state evaluation index at the jth set temperature, Expressed as the positive polarity DC breakdown voltage at the jth set temperature, Expressed as the maximum value of the positive polarity DC breakdown voltage at the jth set temperature, It is expressed as the minimum value of the positive polarity DC breakdown voltage at the jth set temperature;

[0062] S302: Obtain the electric field distribution state evaluation index of the non-aged insulating oil sample, and calculate the voltage deviation with the positive polarity DC breakdown voltage data at each temperature. If If the voltage deviation is greater than the preset value, it indicates that the electric field distribution of the electric ball electrode at this temperature is uneven, and the management personnel should be notified to make adjustments. Otherwise, it indicates that the electric field distribution of the electric ball electrode at this temperature is uniform.

[0063] In this embodiment, it should be specifically explained that the power source used in the present invention is an AC or DC power source, and the shape of the electrodes used is hemispherical.

[0064] The step S04: a converter transformer oil breakdown field strength prediction model: based on the aging transformer oil breakdown data collected in the aging transformer oil breakdown data collection sub-step, a breakdown field strength prediction index of the insulating oil after the sample aging time is completed is calculated.

[0065] In one possible design, the calculation formula of the breakdown field strength prediction index is:

[0066] α i =ε0+λ1×xh i +λ2×xy i +λ3×xh i 2 +λ4×xy i 2 +λ5×xh i ×xy i

[0067] Among them, α i It is expressed as the breakdown field strength prediction index of the i-th sample, ε0 is expressed as a constant, and xh i Expressed as the number of days of sample aging for the i-th sample, xy i is the sample aging temperature of the i-th sample, and λ1, λ2, λ3, λ4, and λ5 are the interaction coefficients of the breakdown field strength prediction index, respectively.

[0068] Among them, by testing the breakdown field strength of the samples at different aging days and sample aging temperatures, a set of data points can be obtained, and these data are used for regression analysis to finally obtain the optimal value of each coefficient. In this embodiment, the reference value of λ1 is -0.47173, the reference value of λ2 is -0.27694, the reference value of λ3 is 0.00524, the reference value of λ4 is 5.04945E-4, the reference value of λ5 is 0.00275, and the reference value of ε0 is 29.71086.

[0069] The step S05: converter transformer oil breakdown field strength fitting analysis: obtaining actual breakdown strength data of the insulating oil after the sample aging time is completed, and analyzing the breakdown field strength fitting coefficient after the sample aging time is completed based on the breakdown field strength prediction index.

[0070] In a possible design, the calculation formula of the breakdown field strength fitting coefficient is:

[0071]

[0072] Among them, R 2 Expressed as the breakdown field strength fitting coefficient, α i Expressed as the breakdown field strength prediction index of the i-th sample, α 实 It is expressed as the actual breakdown field strength prediction index, Δα is expressed as the mean of the actual breakdown field strength prediction index, and n is expressed as the number of samples.

[0073] The step S06: converter transformer oil breakdown field strength fitting evaluation: is used to obtain the breakdown field strength fitting coefficient of the sample after the aging time is completed, compare it with the preset breakdown field strength fitting coefficient, and process it.

[0074] In a possible design, the step S06: evaluating the converter transformer oil breakdown field strength fitting degree is specifically as follows:

[0075] Obtain the breakdown field strength fitting coefficient after the sample aging time is completed, and compare it with the preset breakdown field strength fitting coefficient. If the breakdown field strength fitting coefficient after the sample aging time is completed is less than the preset breakdown field strength fitting coefficient, it indicates that there is a potential electrical fault risk in the operation of the converter transformer oil, and the management personnel should be notified to replace or handle the insulating oil in time. Otherwise, it indicates that there is no abnormality in the operating performance of the converter transformer oil.

[0076] In this embodiment, it should be specifically explained that the present invention collects the aging temperature of the oil-paper insulation sample subjected to high-temperature aging of the converter transformer oil, and converts the oil-paper insulation sample subjected to high-temperature aging of the converter transformer oil into the actual operating time of the actual lower temperature operation using the aging acceleration factor, which is conducive to accurately evaluating the aging rate and service life of the converter transformer oil under different temperature conditions;

[0077] The present invention collects breakdown field strength data of insulating oil after sample aging time is completed, calculates the electric field distribution state evaluation index of the non-aged insulating oil sample at various temperatures based on the positive polarity DC breakdown voltage of the non-aged insulating oil sample at various temperatures, evaluates whether the electric field distribution of the electric ball electrode is concentrated, calculates the breakdown field strength prediction index of the insulating oil after sample aging time is completed based on the aged transformer oil breakdown data collected in the aged transformer oil breakdown data collection sub-step, and then obtains the actual breakdown strength data of the insulating oil after sample aging time is completed, and analyzes to obtain the breakdown field strength fitting coefficient after sample aging time is completed. By comparing with the preset breakdown field strength fitting coefficient, if the breakdown field strength fitting coefficient of the sample after the aging time is less than the preset breakdown field strength fitting coefficient, it indicates that there is a potential electrical failure risk in the operation of the converter transformer oil, and the management personnel should be notified to replace or handle the insulating oil in time. Otherwise, it indicates that there is no abnormality in the operating performance of the converter transformer oil. By establishing a breakdown field strength prediction model based on aging time and temperature, the changes in the electrical strength of the oil during long-term operation are predicted, and potential electrical risks are discovered in advance to reduce the failure risk of the transformer due to oil aging and ensure the long-term stable operation of the power system.

[0078] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting the electrical strength of converter transformer oil under time and temperature changes, characterized in that: include: Step S01: Converting the high-temperature aging time of converter transformer oil: converting the oil-paper insulation sample subjected to high-temperature aging of converter transformer oil into the actual operating time under actual lower temperature using an aging acceleration factor; Step S02: Collecting the breakdown field strength data of the converter transformer oil: used to collect the breakdown field strength data of the insulating oil after the sample aging time is completed. The step S02: collecting the high-temperature aging data of the converter transformer oil includes a sub-step of collecting the breakdown data of the unaged transformer oil and a sub-step of collecting the breakdown data of the aged transformer oil. Step S03: Electric field distribution state evaluation: Based on the positive polarity DC breakdown voltage of the non-aged insulating oil sample at each temperature, the electric field distribution state evaluation index of the non-aged insulating oil sample at each temperature is calculated to evaluate whether the electric field distribution of the electric ball electrode is concentrated; Step S04: a converter transformer oil breakdown field strength prediction model: based on the aged transformer oil breakdown data collected in the aged transformer oil breakdown data collection sub-step, a breakdown field strength prediction index of the insulating oil after the sample aging time is completed is calculated; Step S05: Analysis of the breakdown field strength fitting degree of converter transformer oil: obtaining the actual breakdown strength data of the insulating oil after the sample aging time is completed, and analyzing and obtaining the breakdown field strength fitting degree coefficient after the sample aging time is completed based on the breakdown field strength prediction index; Step S06: Converter transformer oil breakdown field strength fitting evaluation: used to obtain the breakdown field strength fitting coefficient after the sample aging time is completed, compare it with the preset breakdown field strength fitting coefficient, and process it.

2. The method for predicting the electrical strength of converter transformer oil under time and temperature changes according to claim 1, characterized in that: The step S01: converting the high-temperature aging time of the converter transformer oil into: S101: Take an oil-paper insulation sample and completely immerse it in a glass bottle filled with insulating oil. Cover the bottle with a cap. Based on the selected sample aging time, the oil-paper insulation samples aged at high temperature of the converter transformer oil are numbered 1, 2, ...i, ...n in sequence. S102: Collect the aging temperature of the oil-paper insulation sample of the converter transformer oil at high temperature aging, marked as hl i , where i = 1, 2, ... n, i represents the number of the i-th specimen; S103: The calculation formula of the aging acceleration factor is: Among them, AH i Expressed as the aging acceleration factor of the i-th sample, hl i Expressed as the aging temperature of the i-th sample, E a Expressed as chemical activation energy, ht i is the actual operating temperature of the i-th sample, k is the Boltzmann constant, and the reference value is 1.380649×10-23J / K.

3. The method for predicting the electrical strength of converter transformer oil under time and temperature changes according to claim 1, characterized in that: The step S02: collecting converter transformer oil breakdown field strength data is specifically as follows: Unaged transformer oil breakdown data collection sub-steps: Control the temperature of the unaged insulating oil sample through the thermostat, adjust the working state of the strip heater to reach the set temperature of the unaged insulating oil sample, collect the positive polarity DC breakdown voltage of the unaged insulating oil sample at various temperatures, and mark it as Where j = 1, 2, ... m, j represents the number of the j-th set temperature; Aging transformer oil breakdown data collection sub-step: collect the sample aging days and sample aging temperature of the insulating oil after the sample aging time is completed, marked as xh respectively i 、xy i .

4. The method for predicting the electrical strength of converter transformer oil under time and temperature changes according to claim 1, characterized in that: The step S03: evaluating the electric field distribution state is specifically as follows: S301: The calculation formula of the electric field distribution state evaluation index is: in, Expressed as the electric field distribution state evaluation index at the jth set temperature, Expressed as the positive polarity DC breakdown voltage at the jth set temperature, Expressed as the maximum value of the positive polarity DC breakdown voltage at the jth set temperature, It is expressed as the minimum value of the positive polarity DC breakdown voltage at the jth set temperature; S302: Obtain the electric field distribution state evaluation index of the non-aged insulating oil sample, and calculate the voltage deviation with the positive polarity DC breakdown voltage data at each temperature. If If the voltage deviation is greater than the preset value, it indicates that the electric field distribution of the electric ball electrode at this temperature is uneven, and the management personnel should be notified to make adjustments. Otherwise, it indicates that the electric field distribution of the electric ball electrode at this temperature is uniform.

5. The method for predicting the electrical strength of converter transformer oil under time and temperature changes according to claim 1, characterized in that: The calculation formula of the breakdown field strength prediction index is: a i =ε0+λ1×xh i +λ2×xy i +λ3×xh i 2 +λ4×xy i 2 +λ5×xh i ×xy i Among them, α i It is expressed as the breakdown field strength prediction index of the i-th sample, ε0 is expressed as a constant, and xh i Expressed as the number of days of sample aging for the i-th sample, xy i is the sample aging temperature of the i-th sample, and λ1, λ2, λ3, λ4, and λ5 are the interaction coefficients of the breakdown field strength prediction index, respectively.

6. The method for predicting the electrical strength of converter transformer oil under time and temperature changes according to claim 1, characterized in that: The calculation formula of the breakdown field strength fitting coefficient is: Among them, R 2 Expressed as the breakdown field strength fitting coefficient, α i Expressed as the breakdown field strength prediction index of the i-th sample, α 实 It is expressed as the actual breakdown field strength prediction index, Δα is expressed as the mean of the actual breakdown field strength prediction index, and n is expressed as the number of samples.

7. The method for predicting the electrical strength of converter transformer oil under time and temperature changes according to claim 1, characterized in that: The step S06: evaluating the fitting degree of the converter transformer oil breakdown field strength is specifically as follows: Obtain the breakdown field strength fitting coefficient after the sample aging time is completed, and compare it with the preset breakdown field strength fitting coefficient. If the breakdown field strength fitting coefficient after the sample aging time is completed is less than the preset breakdown field strength fitting coefficient, it indicates that there is a potential electrical fault risk in the operation of the converter transformer oil, and the management personnel should be notified to replace or handle the insulating oil in time. Otherwise, it indicates that there is no abnormality in the operating performance of the converter transformer oil.

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