Method and system for evaluating insulation state of oil-immersed current transformer
By obtaining the initial parameters of new equipment of the same model, and combining depolarization current and RVM tests, a Debye equivalent circuit model was established. A temperature correction factor was introduced, which solved the problem of accuracy in assessing the insulation status of oil-immersed current transformers. This enabled a fast and non-destructive assessment method, improving the accuracy and economy of the assessment.
Patent Information
- Application Number
- CN202511238444.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-01
- Publication Date
- 2025-11-14
AI Technical Summary
In the existing technology, the insulation condition assessment method for oil-immersed current transformers is prone to misjudgment due to a single parameter and the temperature is not accurately corrected, resulting in inaccurate assessment and difficulty in quickly and non-destructively determining the aging condition of the equipment.
By obtaining the initial baseline parameters of the same model of new equipment, the initial methanol content, trace water content and degree of polymerization were measured using headspace sampling-gas chromatography-mass spectrometry, Karl Fischer titration and viscosity method. Combined with depolarization current test and RVM test, a Debye equivalent circuit model was established, a temperature correction factor was introduced, and the polarization branch resistance and capacitance were calculated to achieve accurate assessment of the insulation status.
It enables rapid, non-destructive, and accurate assessment of the insulation status of oil-immersed current transformers, simplifies the assessment process, saves labor costs, improves assessment accuracy, and ensures the safe and stable operation of the equipment.
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Figure CN120948980A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of insulation fault diagnosis of electrical equipment, and specifically to a method and system for assessing the insulation status of an oil-immersed current transformer. Background Technology
[0002] The rapid development of the social economy has driven a surge in electricity demand and a continuous expansion of the power grid, placing increasingly stringent demands on the safe and stable operation of the power system and the reliability of power supply. Current transformers, as core equipment in the power system that performs functions such as current measurement and relay protection, play a crucial role in power transmission and distribution. However, in actual operating scenarios, current transformers often lack targeted local or remote protection mechanisms and are subjected to a complex environment of electrical, thermal, mechanical, and chemical stresses over long periods. Their insulation performance gradually deteriorates with operating time, becoming a potential risk point for equipment failure. Extensive engineering practice shows that the vast majority of high-voltage equipment failures or damages are caused by insulation failure. Currently, numerous oil-immersed current transformers have been in operation for two to three decades both domestically and internationally. Determining the insulation condition of these devices, whether they can continue to serve safely, and whether their service life can be extended through scientific operation and maintenance methods have become critical issues that power sector managers urgently need to address. Therefore, conducting insulation diagnosis and aging condition assessment of current transformers is an urgent practical necessity.
[0003] The service life of power equipment largely depends on the aging degree of solid insulation materials such as insulating paper. Obtaining aging information of the internal insulating paper of current transformers is crucial for assessing the overall aging level of the equipment. However, in practical applications, traditional detection parameters such as insulation resistance, power frequency dielectric loss, and capacitance are limited by offline measurement methods and cannot accurately reflect the slow aging process or slight moisture absorption of the insulation. Fault gas analysis results are easily affected by factors such as equipment operating load and oil change / filtration operations. Partial discharge measurements are also often affected by external factors such as corona discharge and spatial electric fields, leading to reduced measurement accuracy. Therefore, there is an urgent need to develop an assessment method that can quickly and non-destructively determine the insulation status of oil-immersed current transformers to overcome the shortcomings of existing technologies and ensure the safe and stable operation of power grid equipment. Summary of the Invention
[0004] The technical problem to be solved by this invention is how to solve the problems of easy misjudgment of a single parameter and inaccurate temperature correction in existing methods.
[0005] This invention solves the above-mentioned technical problems through the following technical means: a method for evaluating the insulation status of an oil-immersed current transformer, comprising:
[0006] S1. Obtain an oil sample and an insulating paper sample from the manufacturer of the same model of oil-immersed current transformer as the device under test. Measure the initial methanol content M0 in the oil when the device leaves the factory using headspace sampling-gas chromatography-mass spectrometry, measure the initial trace water content W0 in the oil using Karl Fischer titration, and measure the initial degree of polymerization DP0 of the insulating paper using the viscosity method.
[0007] S2. Perform depolarization current test and RVM test on the oil-immersed current transformer to obtain the depolarization current i. dopl The curve and RVM characteristic parameters include polarization voltage U0 and charging time t. c Discharge time t d ;
[0008] S3. Based on the obtained depolarization current curve and RVM characteristic data, establish the Debye equivalent circuit model of the oil-immersed current transformer, including the polarization branch resistance R. i and capacitor C i Calculate the equation;
[0009] S4. Introduce a temperature correction factor β to correct the degree of polymerization, based on the corrected degree of polymerization DP of the internal insulating paper of the oil-immersed current transformer. t Combined with the polarization branch resistance R calculated in step S3 i Capacitor C i and initialization parameter R i0 C i0 Verify the aging status of the internal insulation of oil-immersed current transformers in service:
[0010] If DP t ≥250 and R i ≥0.7R i0 If the insulation is in a state of mild aging, the equipment can continue to be used.
[0011] If 150 < DP t <250 and C i ≤1.2C i0 If W ≤ 2.5%, the insulation is judged to be in a moderate aging state, where W is the trace water content in the oil at the time of testing;
[0012] If DP t ≤150, regardless of R i C i Regardless of the numerical value, the insulation is determined to be in a state of severe aging.
[0013] This invention obtains initial reference parameters from new equipment of the same model, acquires depolarization electrical curves and RVM characteristic parameters, constructs a Debye equivalent circuit model to calculate polarization branch resistance and capacitance parameters, introduces a temperature correction factor based on the thermal aging characteristics of insulating paper to correct the degree of polymerization, and then combines polarization parameters for consistency verification. This enables rapid, non-destructive, and accurate assessment of the insulation state of oil-immersed current transformers, providing a scientific basis for equipment operation and maintenance. Compared to traditional testing methods, this invention eliminates the need for complex offline operations, simplifies the assessment process, and saves labor costs. While meeting the aging detection requirements of current transformers, it achieves the goals of high efficiency and low cost, ensuring both the economic viability of the assessment and effectively improving its accuracy, thus maximizing economic benefits.
[0014] Furthermore, in step S3, the polarization branch parameter resistance R of the Debye equivalent circuit model... i and capacitor C i The calculation process includes:
[0015] The attenuation constant μ of the i-th branch is obtained by fitting the depolarization current curve. i and decay exponent R i C i
[0016]
[0017] The formulas for calculating the resistance and capacitance of each polarization branch are as follows:
[0018]
[0019] Among them, i dopl μ represents the depolarization current in amperes (A); t represents the independent variable time in seconds (s); i U represents the attenuation constant of the i-th branch; U0 represents the polarization high voltage applied across the dielectric, in volts (V); t d R represents the measured discharge time, in seconds (s); i C represents the resistance value of the i-th polarization branch, in ohms (Ω); i This represents the capacitance value of the i-th polarization branch, in picofarads (pF).
[0020] Furthermore, based on the method for solving the parameters of the Debye equivalent circuit model in step S3, a Debye model for a single-polarization branch is established and calculated using the following formula:
[0021]
[0022] Among them, U r1(t) represents the time-domain recovery voltage of the single-polarization branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); k1 represents the ratio coefficient of the recovery voltage to the bypass capacitor voltage in the frequency domain; p1 and p2 represent the poles in the operational circuit equations; t c α represents the charging time in seconds (s); α represents the relaxation polarization time constant.
[0023] Furthermore, based on the method for solving the parameters of the Debye equivalent circuit model in step S3, a formula for the polarization spectrum curve of the multi-polarization branch Debye model is established, and the calculation formula is as follows:
[0024]
[0025] Among them, U r (t) represents the time-domain recovery voltage of the multipolarized branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); n represents the total number of polarization branches; k i p represents the ratio coefficient of the recovery voltage to the capacitor voltage of the i-th polarization branch in the frequency domain; 2i-1 p 2i α represents the poles in the operational circuit equations; α represents the relaxation polarization time constant.
[0026] Furthermore, when the degree of polymerization of the paper sample in S4 is not less than 250, the relationship between the degree of polymerization and the methanol and trace water content in the oil is as follows:
[0027]
[0028] Where DP0 is the initial degree of polymerization of the oil-impregnated paper, DP t β is the degree of polymerization of the oil-impregnated paper at each stage of testing, dimensionless; β is the temperature correction factor; W0 is the initial trace water content in the oil; W is the trace water content in the oil at the time of testing, which should be less than 3%; M is the methanol content in the oil, in ppm, which is only used for numerical calculation in the formula. M0 = 0 at the time of leaving the factory, so it is not considered.
[0029] The present invention also provides an insulation condition assessment system for oil-immersed current transformers, comprising:
[0030] Sample acquisition and initialization parameter measurement module: used to obtain internal oil and insulating paper samples of the same model of oil-immersed current transformer as the device under test from the manufacturer, measure the initial methanol content M0 in the oil when the model leaves the factory using headspace sampling-gas chromatography-mass spectrometry, measure the initial trace water content W0 in the oil using Karl Fischer titration, and measure the initial degree of polymerization DP0 of the insulating paper using the viscosity method.
[0031] Depolarization Current and Recovery Voltage Test Module: Used to perform depolarization current and recovery voltage tests on oil-immersed current transformers, and obtain the depolarization current i. dopl The curve and RVM characteristic parameters include polarization voltage U0 and charging time t. c Discharge time t d ;
[0032] The Debye equivalent circuit model polarization branch parameter calculation module is used to establish the polarization branch parameter resistance R of the oil-immersed current transformer based on the acquired depolarization current curve and RVM characteristic data. i and capacitor C i Calculate the equation;
[0033] Correction and insulation aging condition determination module: used to introduce a temperature correction factor β to correct the degree of polymerization, based on the corrected degree of polymerization DP of the internal insulation paper of the oil-immersed current transformer. t The polarization branch resistance R is calculated by combining the polarization branch parameter calculation module of the Debye equivalent circuit model. i Capacitor C i and initialization parameter R i0 C i0 Verify the aging status of the internal insulation of oil-immersed current transformers in service:
[0034] If DP t ≥250 and R i ≥0.7R i0 If the insulation is in a state of mild aging, the equipment can continue to be used.
[0035] If 150 < DP t <250 and C i ≤1.2C i0 If W ≤ 2.5%, the insulation is judged to be in a moderate aging state, where W is the trace water content in the oil at the time of testing;
[0036] If DP t ≤150, regardless of R i C i Regardless of the numerical value, the insulation is determined to be in a state of severe aging.
[0037] Furthermore, the Debye equivalent circuit model polarization branch parameter calculation module includes the Debye equivalent circuit model polarization branch parameter resistance R. i and capacitor C i The calculation process includes:
[0038] The attenuation constant μ of the i-th branch is obtained by fitting the depolarization current curve. i and decay exponent R i C i
[0039]
[0040] The formulas for calculating the resistance and capacitance of each polarization branch are as follows:
[0041]
[0042] Among them, i dopl μ represents the depolarization current in amperes (A); t represents the independent variable time in seconds (s); i U represents the attenuation constant of the i-th branch; U0 represents the polarization high voltage applied across the dielectric, in volts (V); t d R represents the measured discharge time, in seconds (s); i C represents the resistance value of the i-th polarization branch, in ohms (Ω); i This represents the capacitance value of the i-th polarization branch, in picofarads (pF).
[0043] Furthermore, based on the Debye equivalent circuit model parameter solving method in the Debye equivalent circuit model polarization branch parameter calculation module, a single-polarization branch Debye model and calculation are established, and the calculation formula is as follows:
[0044]
[0045] Among them, U r1 (t) represents the time-domain recovery voltage of the single-polarization branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); k1 represents the ratio coefficient of the recovery voltage to the bypass capacitor voltage in the frequency domain; p1 and p2 represent the poles in the operational circuit equations; t c α represents the charging time in seconds (s); α represents the relaxation polarization time constant.
[0046] Furthermore, based on the Debye equivalent circuit model parameter solution method in the Debye equivalent circuit model polarization branch parameter calculation module, a formula for the polarization spectrum curve of the multi-polarization branch Debye model is established, and the calculation formula is as follows:
[0047]
[0048] Among them, U r (t) represents the time-domain recovery voltage of the multipolarized branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); n represents the total number of polarization branches; k i p represents the ratio coefficient of the recovery voltage to the capacitor voltage of the i-th polarization branch in the frequency domain; 2i-1 p 2i α represents the poles in the operational circuit equations; α represents the relaxation polarization time constant.
[0049] Furthermore, in the correction and insulation aging state determination module, when the degree of polymerization of the paper sample is not less than 250, the relationship between the degree of polymerization and the methanol and trace water content in the oil is as follows:
[0050]
[0051] Where DP0 is the initial degree of polymerization of the oil-impregnated paper, DP t β is the degree of polymerization of the oil-impregnated paper at each stage of testing, dimensionless; β is the temperature correction factor; W0 is the initial trace water content in the oil; W is the trace water content in the oil at the time of testing, which should be less than 3%; M is the methanol content in the oil, in ppm, which is only used for numerical calculation in the formula. M0 = 0 at the time of leaving the factory, so it is not considered.
[0052] The advantages of this invention are:
[0053] This invention obtains initial reference parameters from new equipment of the same model, acquires depolarization electrical curves and RVM characteristic parameters, constructs a Debye equivalent circuit model to calculate polarization branch resistance and capacitance parameters, introduces a temperature correction factor based on the thermal aging characteristics of insulating paper to correct the degree of polymerization, and then combines polarization parameters for consistency verification. This enables rapid, non-destructive, and accurate assessment of the insulation state of oil-immersed current transformers, providing a scientific basis for equipment operation and maintenance. Compared to traditional testing methods, this invention eliminates the need for complex offline operations, simplifies the assessment process, and saves labor costs. While meeting the aging detection requirements of current transformers, it achieves the goals of high efficiency and low cost, ensuring both the economic viability of the assessment and effectively improving its accuracy, thus maximizing economic benefits. Attached Figure Description
[0054] Figure 1 This is a flowchart of an insulation condition assessment method for an oil-immersed current transformer according to Embodiment 1 of the present invention. Detailed Implementation
[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0056] Example 1
[0057] like Figure 1 The diagram shows a flowchart of a method for assessing the insulation condition of an oil-immersed current transformer. The method includes:
[0058] S1. Obtain an oil sample and an insulating paper sample from the manufacturer of the same model of oil-immersed current transformer as the device under test. Measure the initial methanol content M0 in the oil when the device leaves the factory using headspace sampling-gas chromatography-mass spectrometry, measure the initial trace water content W0 in the oil using Karl Fischer titration, and measure the initial degree of polymerization DP0 of the insulating paper using the viscosity method.
[0059] S2. Perform depolarization current test and RVM test on the oil-immersed current transformer to obtain the depolarization current i. dopl The curve and RVM characteristic parameters include polarization voltage U0 and charging time t. c Discharge time t d ;
[0060] S3. Based on the obtained depolarization current curve and RVM characteristic data, establish the Debye equivalent circuit model of the oil-immersed current transformer, including the polarization branch resistance R. i and capacitor C i Calculate the equation;
[0061] Specifically, the calculation equations for polarization branch parameters of the Debye equivalent circuit model of the oil-immersed current transformer are established. According to the linear homogeneity theory, the relationship between the polarization process of the insulating medium and a time τ can be represented by the Debye equivalent circuit. The time constant τ and the RC parallel circuit are equivalent, characterizing the losses caused by leakage current during the polarization process of the insulating medium. The relaxed polarization in the dielectric polarization equivalent model can be equivalently replaced by the RC equivalent circuit. The geometric capacitance C0 of the main circuit in the Debye model is measured using a traditional power frequency capacitance meter. The insulation resistance R0 of the main circuit is the insulation resistance of the current transformer, which can be measured according to the national standards for current transformers of different voltage levels. For the parameters R of each polarization branch... i and C i The solution is obtained by fitting the depolarization current curve to obtain the attenuation constant μ of the i-th branch. i and decay exponent R i C i Next, solve for the resistance and capacitance of each polarization branch, and the attenuation index R. i C i The order of magnitude is 10 i-1 ;
[0062]
[0063] Among them, i dopl μ represents the depolarization current in amperes (A); t represents the independent variable time in seconds (s); i U represents the attenuation constant of the i-th branch; U0 represents the polarization high voltage applied across the dielectric, in volts (V); t d R represents the measured discharge time, in seconds (s);i C represents the resistance value of the i-th polarization branch, in ohms (Ω); i This represents the capacitance value of the i-th polarization branch, in picofarads (pF).
[0064] Based on the method for solving the parameters of the Debye equivalent circuit model in step S3, a Debye model for a single-polarization branch is established and calculated using the following formula:
[0065]
[0066] Among them, U r1 (t) represents the time-domain recovery voltage of the single-polarization branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); k1 represents the ratio coefficient of the recovery voltage to the bypass capacitor voltage in the frequency domain; p1 and p2 represent the poles in the operational circuit equations; t c α represents the charging time in seconds (s); α represents the relaxation polarization time constant.
[0067] Based on the method for solving the parameters of the Debye equivalent circuit model in step S3, the polarization spectrum curve formula for the multi-polarization branch Debye model is established, and the calculation formula is as follows:
[0068]
[0069] Among them, U r (t) represents the time-domain recovery voltage of the multipolarized branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); n represents the total number of polarization branches; k i p represents the ratio coefficient of the recovery voltage to the capacitor voltage of the i-th polarization branch in the frequency domain; 2i-1 p 2i α represents the poles in the operational circuit equations; α represents the relaxation polarization time constant.
[0070] S4. Introduce a temperature correction factor β to correct the degree of polymerization, based on the corrected degree of polymerization DP of the internal insulating paper of the oil-immersed current transformer. t Combined with the polarization branch resistance R calculated in step S3 i Capacitor C i and initialization parameter R i0 C i0 Verify the aging status of the internal insulation of oil-immersed current transformers in service:
[0071] If DP t ≥250 and R i ≥0.7R i0 If the insulation is in a state of mild aging, the equipment can continue to be used.
[0072] If 150 < DP t <250 and C i ≤1.2C i0 If W ≤ 2.5%, the insulation is judged to be in a moderate aging state, where W is the trace water content in the oil at the time of testing;
[0073] If DP t ≤150, regardless of R i C i Regardless of the numerical value, the insulation is determined to be in a state of severe aging.
[0074] Specifically, a temperature correction factor β is introduced to correct the degree of polymerization. Based on the corrected degree of polymerization of the internal insulating paper of the oil-immersed current transformer, combined with R... i C i The verification results assess the aging state of the internal insulation of the oil-immersed current transformer during service. The methanol content measurement device in the oil described in this invention uses an Agilent G1888 static headspace sampler, a 7890A gas chromatograph, and a 5975C mass spectrometer. The initial temperature of the gas chromatograph column oven is 30℃, the injection port temperature is 240℃, the carrier gas is high-purity helium, and the flow rate is 0.5 mL / min. When the degree of polymerization of the paper sample is not less than 250, the formulas for calculating the relationship between the degree of polymerization and the methanol and trace water content in the oil are as follows:
[0075]
[0076] Where DP0 is the initial degree of polymerization of the oil-impregnated paper, DP t β is the degree of polymerization of the oil-impregnated paper at each stage of testing, dimensionless; β is the temperature correction factor; W0 is the initial trace water content in the oil; W is the trace water content in the oil at the time of testing, which should be less than 3%; M is the methanol content in the oil, in ppm, which is only used for numerical calculation in the formula. M0 = 0 at the time of leaving the factory, so it is not considered.
[0077] Example 2
[0078] Based on Embodiment 1, the present invention also provides an insulation condition assessment system for an oil-immersed current transformer, comprising:
[0079] Sample acquisition and initialization parameter measurement module: used to obtain internal oil and insulating paper samples of the same model of oil-immersed current transformer as the device under test from the manufacturer, measure the initial methanol content M0 in the oil when the model leaves the factory using headspace sampling-gas chromatography-mass spectrometry, measure the initial trace water content W0 in the oil using Karl Fischer titration, and measure the initial degree of polymerization DP0 of the insulating paper using the viscosity method.
[0080] Depolarization Current and Recovery Voltage Test Module: Used to perform depolarization current and recovery voltage tests on oil-immersed current transformers, and obtain the depolarization current i. doplThe curve and RVM characteristic parameters include polarization voltage U0 and charging time t. c Discharge time t d ;
[0081] The Debye equivalent circuit model polarization branch parameter calculation module is used to establish the polarization branch parameter resistance R of the oil-immersed current transformer based on the acquired depolarization current curve and RVM characteristic data. i and capacitor C i Calculate the equation;
[0082] Specifically, in the Debye equivalent circuit model polarization branch parameter calculation module, the Debye equivalent circuit model polarization branch parameter resistance R... i and capacitor C i The calculation process includes:
[0083] The attenuation constant μ of the i-th branch is obtained by fitting the depolarization current curve. i and decay exponent R i C i
[0084]
[0085] The formulas for calculating the resistance and capacitance of each polarization branch are as follows:
[0086]
[0087] Among them, i dopl μ represents the depolarization current in amperes (A); t represents the independent variable time in seconds (s); i U represents the attenuation constant of the i-th branch; U0 represents the polarization high voltage applied across the dielectric, in volts (V); t d R represents the measured discharge time, in seconds (s); i C represents the resistance value of the i-th polarization branch, in ohms (Ω); i This represents the capacitance value of the i-th polarization branch, in picofarads (pF).
[0088] Based on the Debye equivalent circuit model parameter solution method in the polarization branch parameter calculation module, a single-polarization branch Debye model and calculation are established, and the calculation formula is as follows:
[0089]
[0090] Among them, U r1(t) represents the time-domain recovery voltage of the single-polarization branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); k1 represents the ratio coefficient of the recovery voltage to the bypass capacitor voltage in the frequency domain; p1 and p2 represent the poles in the operational circuit equations; t c α represents the charging time in seconds (s); α represents the relaxation polarization time constant.
[0091] Based on the Debye equivalent circuit model parameter solution method in the Debye equivalent circuit model polarization branch parameter calculation module, a formula for the polarization spectrum curve of the multi-polarization branch Debye model is established, and the calculation formula is as follows:
[0092]
[0093] Among them, U r (t) represents the time-domain recovery voltage of the multipolarized branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); n represents the total number of polarization branches; k i p represents the ratio coefficient of the recovery voltage to the capacitor voltage of the i-th polarization branch in the frequency domain; 2i-1 p 2i α represents the poles in the operational circuit equations; α represents the relaxation polarization time constant.
[0094] Correction and insulation aging condition determination module: used to introduce a temperature correction factor β to correct the degree of polymerization, based on the corrected degree of polymerization DP of the internal insulation paper of the oil-immersed current transformer. t The polarization branch resistance R is calculated by combining the polarization branch parameter calculation module of the Debye equivalent circuit model. i Capacitor C i and initialization parameter R i0 C i0 Verify the aging status of the internal insulation of oil-immersed current transformers in service:
[0095] If DP t ≥250 and R i ≥0.7R i0 If the insulation is in a state of mild aging, the equipment can continue to be used.
[0096] If 150 < DP t <250 and C i ≤1.2C i0 If W ≤ 2.5%, the insulation is judged to be in a moderate aging state, where W is the trace water content in the oil at the time of testing;
[0097] If DP t ≤150, regardless of R i C iRegardless of the numerical value, the insulation is determined to be in a state of severe aging.
[0098] Specifically, in the correction and insulation aging state determination module, when the degree of polymerization of the paper sample is not less than 250, the relationship between the degree of polymerization and the methanol and trace water content in the oil is as follows:
[0099]
[0100] Where DP0 is the initial degree of polymerization of the oil-impregnated paper, DP t β is the degree of polymerization of the oil-impregnated paper at each stage of testing, dimensionless; β is the temperature correction factor; W0 is the initial trace water content in the oil; W is the trace water content in the oil at the time of testing, which should be less than 3%; M is the methanol content in the oil, in ppm, which is only used for numerical calculation in the formula. M0 = 0 at the time of leaving the factory, so it is not considered.
[0101] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for assessing the insulation condition of an oil-immersed current transformer, characterized in that, include: S1. Obtain an oil sample and an insulating paper sample from the manufacturer of the same model of oil-immersed current transformer as the device under test. Measure the initial methanol content M0 in the oil when the device leaves the factory using headspace sampling-gas chromatography-mass spectrometry, measure the initial trace water content W0 in the oil using Karl Fischer titration, and measure the initial degree of polymerization DP0 of the insulating paper using the viscosity method. S2. Perform depolarization current test and RVM test on the oil-immersed current transformer to obtain the depolarization current i. dopl The curve and RVM characteristic parameters include polarization voltage U0 and charging time t. c Discharge time t d ; S3. Based on the obtained depolarization current curve and RVM characteristic data, establish the Debye equivalent circuit model of the oil-immersed current transformer, including the polarization branch resistance R. i and capacitor C i Calculate the equation; S4. Introduce a temperature correction factor β to correct the degree of polymerization, based on the corrected degree of polymerization DP of the internal insulating paper of the oil-immersed current transformer. t Combined with the polarization branch resistance R calculated in step S3 i Capacitor C i and initialization parameter R i0 C i0 Verify the aging status of the internal insulation of oil-immersed current transformers in service: If DP t ≥250 and R i ≥0.7R i0 If the insulation is in a state of mild aging, the equipment can continue to be used. If 150 < DP t <250 and C i ≤1.2C i0 If W ≤ 2.5%, the insulation is judged to be in a moderate aging state, where W is the trace water content in the oil at the time of testing; If DP t ≤150, regardless of R i C i Regardless of the numerical value, the insulation is determined to be in a state of severe aging.
2. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 1, characterized in that, In step S3, the polarization branch parameter resistance R of the Debye equivalent circuit model i and capacitor C i The calculation process includes: The attenuation constant μ of the i-th branch is obtained by fitting the depolarization current curve. i and decay exponent R i C i The formulas for calculating the resistance and capacitance of each polarization branch are as follows: Among them, i dopl μ represents the depolarization current in amperes (A); t represents the independent variable time in seconds (s); i U represents the attenuation constant of the i-th branch; U0 represents the polarization high voltage applied across the dielectric, in volts (V); t d R represents the measured discharge time, in seconds (s); i C represents the resistance value of the i-th polarization branch, in ohms (Ω); i This represents the capacitance value of the i-th polarization branch, in picofarads (pF).
3. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 1, characterized in that, Based on the method for solving the parameters of the Debye equivalent circuit model in step S3, a Debye model for a single-polarization branch is established and calculated using the following formula: Among them, U r1 (t) represents the time-domain recovery voltage of the single-polarization branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); k1 represents the ratio coefficient of the recovery voltage to the bypass capacitor voltage in the frequency domain; p1 and p2 represent the poles in the operational circuit equations; t c α represents the charging time in seconds (s); α represents the relaxation polarization time constant.
4. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 1, characterized in that, Based on the method for solving the parameters of the Debye equivalent circuit model in step S3, the polarization spectrum curve formula for the multi-polarization branch Debye model is established, and the calculation formula is as follows: Among them, U r (t) represents the time-domain recovery voltage of the multipolarized branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); n represents the total number of polarization branches; k i p represents the ratio coefficient of the recovery voltage to the capacitor voltage of the i-th polarization branch in the frequency domain; 2i-1 p 2i α represents the poles in the operational circuit equations; α represents the relaxation polarization time constant.
5. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 1, characterized in that, When the degree of polymerization of the paper sample in S4 is not less than 250, the relationship between the degree of polymerization and the methanol and trace water content in the oil is as follows: Where DP0 is the initial degree of polymerization of the oil-impregnated paper, DP t β is the degree of polymerization of the oil-impregnated paper at each stage of testing, dimensionless; β is the temperature correction factor; W0 is the initial trace water content in the oil; W is the trace water content in the oil at the time of testing, which should be less than 3%; M is the methanol content in the oil, in ppm, which is only used for numerical calculation in the formula. M0 = 0 at the time of leaving the factory, so it is not considered.
6. A system for assessing the insulation condition of an oil-immersed current transformer, characterized in that, include: Sample acquisition and initialization parameter measurement module: used to obtain internal oil and insulating paper samples of the same model of oil-immersed current transformer as the device under test from the manufacturer, measure the initial methanol content M0 in the oil when the model leaves the factory using headspace sampling-gas chromatography-mass spectrometry, measure the initial trace water content W0 in the oil using Karl Fischer titration, and measure the initial degree of polymerization DP0 of the insulating paper using the viscosity method. Depolarization Current and Recovery Voltage Test Module: Used to perform depolarization current and recovery voltage tests on oil-immersed current transformers, and obtain the depolarization current i. dopl The curve and RVM characteristic parameters include polarization voltage U0 and charging time t. c Discharge time t d ; The Debye equivalent circuit model polarization branch parameter calculation module is used to establish the polarization branch parameter resistance R of the oil-immersed current transformer based on the acquired depolarization current curve and RVM characteristic data. i and capacitor C i Calculate the equation; Correction and insulation aging condition determination module: used to introduce a temperature correction factor β to correct the degree of polymerization, based on the corrected degree of polymerization DP of the internal insulation paper of the oil-immersed current transformer. t The polarization branch resistance R is calculated by combining the polarization branch parameter calculation module of the Debye equivalent circuit model. i Capacitor C i and initialization parameter R i0 C i0 Verify and evaluate the aging condition of the internal insulation of oil-immersed current transformers in service: If DP t ≥250 and R i ≥0.7R i0 If the insulation is in a state of mild aging, the equipment can continue to be used. If 150 < DP t <250 and C i ≤1.2C i0 If W ≤ 2.5%, the insulation is judged to be in a moderate aging state, where W is the trace water content in the oil at the time of testing; If DP t ≤150, regardless of R i C i Regardless of the numerical value, the insulation is determined to be in a state of severe aging.
7. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 6, characterized in that, The Debye equivalent circuit model polarization branch parameter calculation module includes the Debye equivalent circuit model polarization branch parameter resistance R. i and capacitor C i The calculation process includes: The attenuation constant μ of the i-th branch is obtained by fitting the depolarization current curve. i and decay exponent R i C i The formulas for calculating the resistance and capacitance of each polarization branch are as follows: Among them, i dopl μ represents the depolarization current in amperes (A); t represents the independent variable time in seconds (s); i U represents the attenuation constant of the i-th branch; U0 represents the polarization high voltage applied across the dielectric, in volts (V); t d R represents the measured discharge time, in seconds (s); i C represents the resistance value of the i-th polarization branch, in ohms (Ω); i This represents the capacitance value of the i-th polarization branch, in picofarads (pF).
8. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 6, characterized in that, Based on the Debye equivalent circuit model parameter solution method in the polarization branch parameter calculation module, a single-polarization branch Debye model and calculation are established, and the calculation formula is as follows: Among them, U r1 (t) represents the time-domain recovery voltage of the single-polarization branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); k1 represents the ratio coefficient of the recovery voltage to the bypass capacitor voltage in the frequency domain; p1 and p2 represent the poles in the operational circuit equations; t c α represents the charging time in seconds (s); α represents the relaxation polarization time constant.
9. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 6, characterized in that, Based on the Debye equivalent circuit model parameter solution method in the Debye equivalent circuit model polarization branch parameter calculation module, a formula for the polarization spectrum curve of the multi-polarization branch Debye model is established, and the calculation formula is as follows: Among them, U r (t) represents the time-domain recovery voltage of the multipolarized branch, in volts (V); t represents the independent variable time, in seconds (s); U0 represents the polarization high voltage applied across the dielectric, in volts (V); n represents the total number of polarization branches; k i p represents the ratio coefficient of the recovery voltage to the capacitor voltage of the i-th polarization branch in the frequency domain; 2i-1 p 2i α represents the poles in the operational circuit equations; α represents the relaxation polarization time constant.
10. The method for evaluating the insulation condition of an oil-immersed current transformer according to claim 6, characterized in that, When the degree of polymerization of the paper sample in the correction and insulation aging state determination module is not less than 250, the relationship between the degree of polymerization and the methanol and trace water content in the oil is as follows: Where DP0 is the initial degree of polymerization of the oil-impregnated paper, DP t β is the degree of polymerization of the oil-impregnated paper at each stage of testing, dimensionless; β is the temperature correction factor; W0 is the initial trace water content in the oil; W is the trace water content in the oil at the time of testing, which should be less than 3%; M is the methanol content in the oil, in ppm, which is only used for numerical calculation in the formula. M0 = 0 at the time of leaving the factory, so it is not considered.