An insulation diagnosis method and system for an oil-immersed current transformer

Abstract

The application discloses an insulation diagnosis method and system of an oil-immersed current transformer, and comprises the following steps: accelerating aging test is carried out on the oil-immersed current transformer; the aggregation degree DP of oil-immersed paper is obtained, and meanwhile, frequency domain dielectric loss test is carried out on the oil-immersed current transformer at different aging stages to obtain the frequency domain dielectric spectrum curve and the curve slope k1 and k2 at the frequencies of 10 ‑2 Hz and 10 2 Hz respectively; the relaxation time constant tau and the time constant alpha of relaxation polarization at different aging stages are fitted; the relationship between the characteristic quantity and the aggregation degree of oil-immersed paper is established by using k1, k2, tau and alpha; the frequency domain dielectric loss test is carried out on the oil-immersed current transformer to be tested, and the frequency domain dielectric spectrum is reconstructed to obtain the aggregation degree of oil-immersed paper inside the equipment, and the aging degree of the internal main insulation of the oil-immersed current transformer to be tested is judged; the application has the advantages of strong anti-interference capability and suitability for on-site insulation diagnosis of the oil-immersed current transformer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of current transformer aging detection, and particularly relates to an insulation diagnosis method and system for an oil-immersed current transformer. BACKGROUND

[0002] The continuous growth of power demand and the continuous expansion of power grid capacity put forward more stringent requirements for the safe operation and power supply reliability of the power system. As an important component in the power infrastructure, although the current transformer plays an important role in measurement and protection, it is rarely protected locally or remotely in actual operation. In the long-term operation process, the insulation strength of the current transformer will continuously decrease due to the combined action of electric, thermal, mechanical, chemical and other stresses, thereby causing the occurrence of faults. It has been proved that most of the damage or failure of high-voltage equipment is caused by the damage of insulation. Most of the oil-immersed current transformers at home and abroad have been in service for 20-30 years. How is the insulation state of this type of equipment, whether it can continue to operate, and whether it can extend its service life through scientific maintenance technology? These are the problems that power managers urgently need to solve. Therefore, it is necessary to conduct insulation diagnosis and aging state detection on the current transformer.

[0003] The service life of power equipment mainly depends on the service life of solid insulation materials such as insulation paper, but for the site, insulation diagnosis of the current transformer is mainly performed through offline measurement of the insulation resistance, power frequency dielectric loss and capacitance of the winding and the end screen, through oil dissolved gas analysis (DGA) and partial discharge detection, etc. For example, the transformer insulation paperboard aging quantitative evaluation method based on dielectric response characteristics disclosed in Chinese Patent Publication No. CN108828413A mainly obtains the relationship between the transformer dielectric loss factor and the aging degree of the insulation paperboard, and obtains the corresponding aging degree of the insulation paperboard according to the dielectric loss factor, so that the evaluation process mainly depends on the power frequency dielectric loss. In actual application, the insulation resistance, power frequency dielectric loss and capacitance cannot well reflect the slow aging or slight damp of insulation due to the limitation of offline measurement. The analysis of fault gas is affected by factors such as equipment operating conditions, oil change and oil filtration. The partial discharge measurement is easily disturbed by corona discharge and space electric field. Therefore, it is necessary to introduce an insulation diagnosis method with strong anti-interference ability and suitable for the site to effectively supplement the traditional measurement method. SUMMARY

[0004] The technical problem to be solved by the present application is how to provide an insulation diagnosis method for an oil-immersed current transformer with strong anti-interference ability and suitable for the site.

[0005] The present application solves the above technical problems by the following technical means: an insulation diagnosis method for an oil-immersed current transformer, comprising the following steps:

[0006] Step one, carry out accelerated aging test on oil-immersed current transformer;

[0007] Step two, extract paper samples at different aging stages for physical and chemical tests to obtain the degree of polymerization DP of oil-immersed paper, and conduct frequency domain dielectric loss tests on oil-immersed current transformers at different aging stages to obtain frequency domain dielectric spectrum curves and curve slopes k1 and k2 at frequencies of 10 -2 Hz, 10 2 Hz, respectively;

[0008] Step three, reconstruct the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, and use the least squares method to fit the relaxation time constant τ and the time constant α of relaxation polarization in the relative dielectric constant formula at different aging stages;

[0009] Step four, take k1, k2, τ, and α as characteristic quantities representing the change of the degree of polymerization of oil-immersed paper, and establish the relationship between the characteristic quantities and the degree of polymerization of oil-immersed paper;

[0010] Step five, conduct frequency domain dielectric loss tests on the oil-immersed current transformer to be tested and reconstruct the frequency domain dielectric spectrum to obtain the degree of polymerization of the oil-immersed paper inside the device, and judge the aging degree of the internal main insulation of the oil-immersed current transformer to be tested.

[0011] Further, in step two, the IDAX-300 frequency spectrometer is used to obtain the frequency domain dielectric spectrum of the oil-immersed current transformer at different aging stages.

[0012] Further, in step three, the relative dielectric constant formula is obtained by reconstructing the frequency domain dielectric spectrum based on the dielectric response model, which includes:

[0013]

[0014] In the formula, ε(ω) is the relative dielectric constant at frequency ω, ε ∞ is the high-frequency relative dielectric constant, ε1 and ε2 are the dielectric constants at frequencies of 10 -2 Hz and 10 2 Hz at the initial aging stage, τ is the relaxation time constant, α is the time constant of relaxation polarization, j is the imaginary unit, and k1 and k2 satisfy

[0015] Further, step four includes:

[0016] Take k1, k2, τ, and α as characteristic quantities representing the change of the degree of polymerization of oil-immersed paper, and after n measurements, obtain a characteristic quantity database, and based on the characteristic quantity database, use the least squares method to fit to obtain the relationship between the characteristic quantities and the degree of polymerization of oil-immersed paper. The fitting formula is as follows:

[0017]

[0018] Where k0 is the coefficient to be fitted.

[0019] Furthermore, the step five includes:

[0020] After obtaining the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper, a frequency domain dielectric loss test is performed on the oil-immersed current transformer to be tested and the frequency domain dielectric spectrum is reconstructed to obtain the characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper. The characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper is substituted into the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper to obtain the polymerization degree of the oil-immersed paper inside the equipment. When the polymerization degree of the oil-immersed paper is between 1000 and 1200, the main insulation inside the oil-immersed current transformer to be tested is determined to be new insulation paper; when the polymerization degree of the oil-immersed paper is between 650 and 1000, the main insulation inside the oil-immersed current transformer to be tested is determined to have excellent insulation performance; when the polymerization degree of the oil-immersed paper is between 350 and 650, the main insulation inside the oil-immersed current transformer to be tested is determined to have medium insulation performance; and when the polymerization degree of the oil-immersed paper is less than 350, the main insulation inside the oil-immersed current transformer to be tested is determined to be in an aging state and needs to be retired.

[0021] The present invention also provides an insulation diagnosis system for an oil-immersed current transformer, comprising:

[0022] Aging test module, used to perform accelerated aging tests on oil-immersed current transformers;

[0023] The first parameter extraction module is used to extract paper samples at different aging stages for physical and chemical testing to obtain the degree of polymerization (DP) of oil-immersed paper. At the same time, frequency domain dielectric loss tests are performed on oil-immersed current transformers at different aging stages to obtain frequency domain dielectric spectrum curves and the frequency of 10 -2 Hz, 10 2 The slopes of the curves k1 and k2 at Hz;

[0024] The second parameter extraction module is used to reconstruct the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, and use the least squares method to fit the relaxation time constant τ and the relaxation polarization time constant α in the relative dielectric constant formula at different aging stages;

[0025] A relationship acquisition module is used to establish a relationship between the characteristic quantities and the polymerization degree of the oil-impregnated paper using k1, k2, τ, and α as characteristic quantities characterizing the change in the polymerization degree of the oil-impregnated paper;

[0026] The insulation diagnosis module is used to perform frequency domain dielectric loss testing on the oil-immersed current transformer to be tested and reconstruct the frequency domain dielectric spectrum to obtain the polymerization degree of the oil-immersed paper inside the equipment and determine the degree of aging of the main insulation inside the oil-immersed current transformer to be tested.

[0027] Furthermore, the first parameter extraction module uses an IDAX-300 spectrum analyzer to obtain frequency domain dielectric spectra of the oil-immersed current transformer at different aging stages.

[0028] Furthermore, the second parameter extraction module reconstructs the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, including:

[0029]

[0030] Where ε(ω) is the relative dielectric constant at frequency ω, ε ∞ is the high frequency relative dielectric constant, ε1 and ε2 are the initial aging frequency 10 -2 Hz, 10 2 The dielectric constant at Hz, τ is the relaxation time constant, α is the time constant of relaxation polarization, j is the imaginary unit, k1 and k2 satisfy

[0031] Furthermore, the relationship acquisition module is further configured to:

[0032] Taking k1, k2, τ, and α as characteristic quantities to characterize the change in the degree of polymerization of oil-impregnated paper, after n measurements, a characteristic quantity database is obtained. Based on the characteristic quantity database, the least squares method is used for fitting to obtain the relationship between the characteristic quantities and the degree of polymerization of oil-impregnated paper. The fitting formula is as follows:

[0033]

[0034] Where k0 is the coefficient to be fitted.

[0035] Furthermore, the insulation diagnosis module is also used for:

[0036] After obtaining the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper, a frequency domain dielectric loss test is performed on the oil-immersed current transformer to be tested and the frequency domain dielectric spectrum is reconstructed to obtain the characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper. The characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper is substituted into the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper to obtain the polymerization degree of the oil-immersed paper inside the equipment. When the polymerization degree of the oil-immersed paper is between 1000 and 1200, the main insulation inside the oil-immersed current transformer to be tested is determined to be new insulation paper; when the polymerization degree of the oil-immersed paper is between 650 and 1000, the main insulation inside the oil-immersed current transformer to be tested is determined to have excellent insulation performance; when the polymerization degree of the oil-immersed paper is between 350 and 650, the main insulation inside the oil-immersed current transformer to be tested is determined to have medium insulation performance; and when the polymerization degree of the oil-immersed paper is less than 350, the main insulation inside the oil-immersed current transformer to be tested is determined to be in an aging state and needs to be retired.

[0037] The advantages of the present invention are:

[0038] (1) The present invention is based on a thermal aging test platform for oil-immersed current transformers, performs frequency domain dielectric spectrum tests on oil-immersed current transformers at different aging stages, and obtains the polymerization degree of oil-immersed paper at the corresponding stage and characteristic quantities characterizing the changes in the polymerization degree of oil-immersed paper, thereby determining the correlation between the various characteristic quantities of the frequency domain dielectric spectrum and the degree of insulation aging. Based on the above-obtained correlation, in actual applications, by performing a frequency domain dielectric loss test on the oil-immersed current transformer to be tested and reconstructing the frequency domain dielectric spectrum, the polymerization degree of oil-immersed paper inside the equipment can be obtained, thereby evaluating the degree of main insulation aging inside the oil-immersed current transformer to be tested, thereby achieving on-site insulation aging evaluation of the oil-immersed current transformer, and the entire process does not require partial discharge measurement, is not interfered by corona discharge and spatial electric field, and has strong anti-interference ability.

[0039] (2) The present invention is a technical study based on the existing problems of long routine test time for oil-immersed current transformers and inability to accurately reflect the slow aging or slight moisture of the equipment insulation. By determining the correlation between the frequency domain dielectric spectrum of the oil-immersed current transformer and the degree of insulation aging, the aging of the equipment can be quickly reflected. Compared with the traditional method, the working status of the oil-immersed current transformer is more accurately analyzed, and the aging evaluation of the oil-immersed current transformer can be performed more conveniently. The traditional detection method is simplified, and manpower is saved. On the basis of meeting the aging detection of the oil-immersed current transformer, high efficiency and low cost are achieved. While ensuring economy, the evaluation accuracy can be improved to a certain extent, thereby maximizing economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of an insulation diagnosis method for an oil-immersed current transformer disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in 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 part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] Example 1

[0043] like Figure 1 As shown, embodiment 1 of the present invention provides an insulation diagnosis method for an oil-immersed current transformer, comprising the following steps:

[0044] S1. Carry out accelerated aging test on oil-immersed current transformer; the specific process is as follows:

[0045] The present invention first develops a true prototype of a 500kV oil-immersed inverted current transformer. The prototype contains 11 capacitor screens, an oil weight of 820kg, and a total weight of 3500kg. The insulation level of the prototype is equivalent to an insulating paper package placed in the upper oil storage cabinet, fixed by a copper wire, and the copper wire is extended to the top through an expander. The primary guide rod of the prototype is short-circuited, and the secondary side is pressurized and circulated to make the upper oil storage cabinet reach 130°C. The insulating ring part and the paper package in the prototype are accelerated aged at approximately the same temperature, and multiple thermocouples are set to record the temperature changes in the upper oil storage cabinet. The paper package is taken out at different aging stages to measure its polymerization degree. This process is mainly to perform an aging test on the oil-immersed current transformer, so as to obtain various data in the test stage, such as detecting the polymerization degree DP of the oil-immersed paper, in preparation for fitting the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper below.

[0046] S2. Extract paper samples at different aging stages for physical and chemical testing to obtain the degree of polymerization (DP) of oil-immersed paper. At the same time, perform frequency domain dielectric loss tests on oil-immersed current transformers at different aging stages to obtain frequency domain dielectric spectrum curves and the frequency of 10 - 2 Hz, 10 2 Hz. In this embodiment, the frequency domain dielectric spectrum of the oil-immersed current transformer at different aging stages is obtained by using an IDAX-300 spectrum analyzer to obtain a frequency domain dielectric spectrum curve. Then, the frequency domain dielectric spectrum curves are found on the curve at 10 -2 Hz, 10 2 The corresponding curve slopes k1 and k2 at Hz.

[0047] S3. Reconstruct the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula. Use the least squares method to fit the relaxation time constant τ and the relaxation polarization time constant α in the relative dielectric constant formula at different aging stages. The specific process is as follows:

[0048] Based on the Atachi configuration 500kV oil-immersed inverted current transformer, the secondary side is short-circuited and the current is passed to make the upper oil storage cabinet reach 130℃. After reconstructing the frequency domain dielectric spectrum of the equipment using the dielectric response model, the relative dielectric constant formula is:

[0049]

[0050] Where ε(ω) is the relative dielectric constant at frequency ω, ε ∞ is the high frequency relative dielectric constant, ε1 and ε2 are the initial aging frequency 10 -2 Hz, 10 2 The dielectric constant at Hz, τ is the relaxation time constant, α is the time constant of relaxation polarization, j is the imaginary unit, k1 and k2 satisfy In the above relative dielectric constant formula, k1, k2, and ε ∞, ε1, ε2, and ω are all known quantities obtained during the above-mentioned aging tests and physical and chemical tests. By fitting multiple sets of data obtained at different aging stages using the least squares method, we can obtain the relaxation time constant τ and the relaxation polarization time constant α.

[0051] S4. Using k1, k2, τ, and α as characteristic quantities to characterize the change in the degree of polymerization of the oil-impregnated paper, a relationship between the characteristic quantities and the degree of polymerization of the oil-impregnated paper is established. The specific process is as follows:

[0052] Take k1, k2, τ, α as the characteristic quantity to characterize the change of polymerization degree of oil-soaked paper, and after n times of measurement, obtain the characteristic quantity database k1(k 11 ,k 12 …k 1n ), k2(k 21 ,k 22 …k 2n ), τ(τ1,τ2,…τ n ), α(α1,α2…α n ), the least squares method was used to fit the characteristic quantity database to obtain the relationship between the characteristic quantity and the degree of polymerization of the oil-impregnated paper. The specific fitting formula is as follows:

[0053]

[0054] Wherein, k0 is the coefficient to be fitted. The above formula is obtained by fitting multiple sets of characteristic quantities using the least squares method to obtain the coefficient to be fitted k0. In practical applications, the coefficient to be fitted k0 is substituted into the above formula, with the coefficient to be fitted k0 as the known quantity, k1, k2, τ, and α as the unknown quantities, and the degree of polymerization of the oil-impregnated paper DP as the data to be solved. The relationship between the characteristic quantity and the degree of polymerization of the oil-impregnated paper is obtained. When performing insulation diagnosis on the oil-immersed current transformer to be tested, it is only necessary to obtain k1, k2, τ, and α through testing and substitute them into the relationship between the characteristic quantity and the degree of polymerization of the oil-impregnated paper to obtain the degree of polymerization of the oil-impregnated paper DP. Insulation diagnosis of the oil-immersed current transformer to be tested can be performed based on the numerical range of the degree of polymerization of the oil-impregnated paper DP. The specific process is shown in step S5.

[0055] S5. Perform a frequency domain dielectric loss test on the oil-immersed current transformer to be tested and reconstruct the frequency domain dielectric spectrum to obtain the degree of polymerization of the oil-immersed paper inside the equipment and determine the degree of aging of the main insulation inside the oil-immersed current transformer to be tested. The specific process is as follows:

[0056] After obtaining the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper, a frequency domain dielectric loss test is performed on the oil-immersed current transformer to be tested and the frequency domain dielectric spectrum is reconstructed to obtain the characteristic quantities k1, k2, τ, and α that characterize the change in the polymerization degree of the oil-immersed paper. The characteristic quantities k1, k2, τ, and α that characterize the change in the polymerization degree of the oil-immersed paper are substituted into the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper to obtain the polymerization degree of the oil-immersed paper inside the equipment. When the polymerization degree of the oil-immersed paper is between 1000 and 1200, the main insulation inside the oil-immersed current transformer to be tested is determined to be new insulation paper. When the polymerization degree of the oil-immersed paper is between 650 and 1000, the main insulation inside the oil-immersed current transformer to be tested is determined to have excellent insulation performance. When the polymerization degree of the oil-immersed paper is between 350 and 650, the main insulation inside the oil-immersed current transformer to be tested is determined to have medium insulation performance. When the polymerization degree of the oil-immersed paper is less than 350, the main insulation inside the oil-immersed current transformer to be tested is determined to be in an aging state and needs to be retired.

[0057] Through the above technical solution, the present invention obtains the polymerization degree of oil-immersed paper and the frequency-domain dielectric spectrum of the current transformer at different aging stages on the basis of a real prototype, reconstructs the dielectric spectrum through a dielectric response model, extracts characteristic quantities to establish a relationship with the polymerization degree, that is, determines the correlation between various characteristic quantities of the frequency-domain dielectric spectrum and the degree of insulation aging. Based on the above-obtained correlation, in actual applications, by performing a frequency-domain dielectric loss test on the oil-immersed current transformer to be tested and reconstructing the frequency-domain dielectric spectrum, the polymerization degree of the oil-immersed paper inside the equipment can be obtained, thereby evaluating the degree of main insulation aging inside the oil-immersed current transformer to be tested, thereby achieving on-site insulation aging evaluation of the oil-immersed current transformer, and the entire process does not require partial discharge measurement, is not affected by corona discharge and spatial electric field, and has strong anti-interference ability.

[0058] Example 2

[0059] Based on the first embodiment, the second embodiment of the present invention further provides an insulation diagnosis system for an oil-immersed current transformer, comprising:

[0060] Aging test module, used to perform accelerated aging tests on oil-immersed current transformers;

[0061] The first parameter extraction module is used to extract paper samples at different aging stages for physical and chemical testing to obtain the degree of polymerization (DP) of oil-immersed paper. At the same time, frequency domain dielectric loss tests are performed on oil-immersed current transformers at different aging stages to obtain frequency domain dielectric spectrum curves and the frequency of 10 -2 Hz, 10 2 The slopes of the curves k1 and k2 at Hz;

[0062] The second parameter extraction module is used to reconstruct the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, and use the least squares method to fit the relaxation time constant τ and the relaxation polarization time constant α in the relative dielectric constant formula at different aging stages;

[0063] A relationship acquisition module is used to establish a relationship between the characteristic quantities and the polymerization degree of the oil-impregnated paper using k1, k2, τ, and α as characteristic quantities characterizing the change in the polymerization degree of the oil-impregnated paper;

[0064] The insulation diagnosis module is used to perform frequency domain dielectric loss testing on the oil-immersed current transformer to be tested and reconstruct the frequency domain dielectric spectrum to obtain the polymerization degree of the oil-immersed paper inside the equipment and determine the degree of aging of the main insulation inside the oil-immersed current transformer to be tested.

[0065] Specifically, the first parameter extraction module uses an IDAX-300 spectrum analyzer to obtain frequency domain dielectric spectra of the oil-immersed current transformer at different aging stages.

[0066] Specifically, the second parameter extraction module reconstructs the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, including:

[0067]

[0068] Where ε(ω) is the relative dielectric constant at frequency ω, ε ∞ is the high frequency relative dielectric constant, ε1 and ε2 are the initial aging frequency 10 -2 Hz, 10 2 The dielectric constant at Hz, τ is the relaxation time constant, α is the time constant of relaxation polarization, j is the imaginary unit, k1 and k2 satisfy

[0069] Specifically, the relationship acquisition module is further used to:

[0070] Taking k1, k2, τ, and α as characteristic quantities to characterize the change in the degree of polymerization of oil-impregnated paper, after n measurements, a characteristic quantity database is obtained. Based on the characteristic quantity database, the least squares method is used for fitting to obtain the relationship between the characteristic quantities and the degree of polymerization of oil-impregnated paper. The fitting formula is as follows:

[0071]

[0072] Where k0 is the coefficient to be fitted.

[0073] Specifically, the insulation diagnosis module is further used for:

[0074] After obtaining the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper, a frequency domain dielectric loss test is performed on the oil-immersed current transformer to be tested and the frequency domain dielectric spectrum is reconstructed to obtain the characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper. The characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper is substituted into the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper to obtain the polymerization degree of the oil-immersed paper inside the equipment. When the polymerization degree of the oil-immersed paper is between 1000 and 1200, the main insulation inside the oil-immersed current transformer to be tested is determined to be new insulation paper; when the polymerization degree of the oil-immersed paper is between 650 and 1000, the main insulation inside the oil-immersed current transformer to be tested is determined to have excellent insulation performance; when the polymerization degree of the oil-immersed paper is between 350 and 650, the main insulation inside the oil-immersed current transformer to be tested is determined to have medium insulation performance; and when the polymerization degree of the oil-immersed paper is less than 350, the main insulation inside the oil-immersed current transformer to be tested is determined to be in an aging state and needs to be retired.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for diagnosing insulation of an oil-immersed current transformer, characterized in that: The following steps are involved: Step 1: Conduct accelerated aging test on oil-immersed current transformer; Step 2: Extract paper samples at different aging stages for physical and chemical testing to obtain the degree of polymerization (DP) of oil-immersed paper. At the same time, perform frequency domain dielectric loss tests on oil-immersed current transformers at different aging stages to obtain frequency domain dielectric spectrum curves and the frequency of 10 - 2 Hz, 10 2 The slopes of the curves k1 and k2 at Hz; Step 3: Reconstruct the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, and use the least squares method to fit the relaxation time constant τ and the relaxation polarization time constant α in the relative dielectric constant formula at different aging stages; Step 4: Using k1, k2, τ, and α as characteristic quantities to characterize the change in the degree of polymerization of the oil-impregnated paper, a relationship between the characteristic quantities and the degree of polymerization of the oil-impregnated paper is established; Step 5: Perform a frequency domain dielectric loss test on the oil-immersed current transformer to be tested and reconstruct the frequency domain dielectric spectrum to obtain the polymerization degree of the oil-immersed paper inside the device and determine the aging degree of the main insulation inside the oil-immersed current transformer to be tested.

2. The insulation diagnosis method for an oil-immersed current transformer according to claim 1, characterized in that: In the step 2, the frequency domain dielectric spectra of the oil-immersed current transformer at different aging stages are obtained using an IDAX-300 spectrum analyzer.

3. The insulation diagnosis method for an oil-immersed current transformer according to claim 1, characterized in that: In step 3, the frequency domain dielectric spectrum is reconstructed based on the dielectric response model to obtain the relative dielectric constant formula, including: Where ε(ω) is the relative dielectric constant at frequency ω, ε ∞ is the high frequency relative dielectric constant, ε1 and ε2 are the initial aging frequency 10 -2 Hz, 10 2 The dielectric constant at Hz, τ is the relaxation time constant, α is the time constant of relaxation polarization, j is the imaginary unit, k1 and k2 satisfy 4. The insulation diagnosis method for an oil-immersed current transformer according to claim 1, characterized in that: The fourth step includes: Taking k1, k2, τ, and α as characteristic quantities to characterize the change in the degree of polymerization of oil-impregnated paper, after n measurements, a characteristic quantity database is obtained. Based on the characteristic quantity database, the least squares method is used for fitting to obtain the relationship between the characteristic quantities and the degree of polymerization of oil-impregnated paper. The fitting formula is as follows: Where k0 is the coefficient to be fitted.

5. The insulation diagnosis method for an oil-immersed current transformer according to claim 1, characterized in that: The step five includes: After obtaining the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper, a frequency domain dielectric loss test is performed on the oil-immersed current transformer to be tested and the frequency domain dielectric spectrum is reconstructed to obtain the characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper. The characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper is substituted into the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper to obtain the polymerization degree of the oil-immersed paper inside the equipment. When the polymerization degree of the oil-immersed paper is between 1000 and 1200, the main insulation inside the oil-immersed current transformer to be tested is determined to be new insulation paper; when the polymerization degree of the oil-immersed paper is between 650 and 1000, the main insulation inside the oil-immersed current transformer to be tested is determined to have excellent insulation performance; when the polymerization degree of the oil-immersed paper is between 350 and 650, the main insulation inside the oil-immersed current transformer to be tested is determined to have medium insulation performance; and when the polymerization degree of the oil-immersed paper is less than 350, the main insulation inside the oil-immersed current transformer to be tested is determined to be in an aging state and needs to be retired.

6. An insulation diagnostic system for an oil-immersed current transformer, characterized in that: include: Aging test module, used to perform accelerated aging tests on oil-immersed current transformers; The first parameter extraction module is used to extract paper samples at different aging stages for physical and chemical testing to obtain the degree of polymerization (DP) of oil-immersed paper. At the same time, frequency domain dielectric loss tests are performed on oil-immersed current transformers at different aging stages to obtain frequency domain dielectric spectrum curves and the frequency of 10 -2 Hz, 10 2 The slopes of the curves k1 and k2 at Hz; The second parameter extraction module is used to reconstruct the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, and use the least squares method to fit the relaxation time constant τ and the relaxation polarization time constant α in the relative dielectric constant formula at different aging stages; A relationship acquisition module is used to establish a relationship between the characteristic quantities and the polymerization degree of the oil-impregnated paper using k1, k2, τ, and α as characteristic quantities characterizing the change in the polymerization degree of the oil-impregnated paper; The insulation diagnosis module is used to perform frequency domain dielectric loss testing on the oil-immersed current transformer to be tested and reconstruct the frequency domain dielectric spectrum to obtain the polymerization degree of the oil-immersed paper inside the equipment and determine the degree of aging of the main insulation inside the oil-immersed current transformer to be tested.

7. The insulation diagnosis system for an oil-immersed current transformer according to claim 6, characterized in that: In the first parameter extraction module, an IDAX-300 spectrum analyzer is used to obtain frequency domain dielectric spectra of the oil-immersed current transformer at different aging stages.

8. The insulation diagnosis system for an oil-immersed current transformer according to claim 6, characterized in that: The second parameter extraction module reconstructs the frequency domain dielectric spectrum based on the dielectric response model to obtain the relative dielectric constant formula, including: Where ε(ω) is the relative dielectric constant at frequency ω, ε ∞ is the high frequency relative dielectric constant, ε1 and ε2 are the initial aging frequency 10 -2 Hz, 10 2 The dielectric constant at Hz, τ is the relaxation time constant, α is the time constant of relaxation polarization, j is the imaginary unit, k1 and k2 satisfy 9. The insulation diagnosis system for an oil-immersed current transformer according to claim 6, characterized in that: The relationship acquisition module is further configured to: Taking k1, k2, τ, and α as characteristic quantities to characterize the change in the degree of polymerization of oil-impregnated paper, after n measurements, a characteristic quantity database is obtained. Based on the characteristic quantity database, the least squares method is used for fitting to obtain the relationship between the characteristic quantities and the degree of polymerization of oil-impregnated paper. The fitting formula is as follows: Where k0 is the coefficient to be fitted.

10. The insulation diagnosis system for oil-immersed current transformer according to claim 6, characterized in that: The insulation diagnostic module is also used to: After obtaining the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper, a frequency domain dielectric loss test is performed on the oil-immersed current transformer to be tested and the frequency domain dielectric spectrum is reconstructed to obtain the characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper. The characteristic quantity characterizing the change in the polymerization degree of the oil-immersed paper is substituted into the relationship between the characteristic quantity and the polymerization degree of the oil-immersed paper to obtain the polymerization degree of the oil-immersed paper inside the equipment. When the polymerization degree of the oil-immersed paper is between 1000 and 1200, the main insulation inside the oil-immersed current transformer to be tested is determined to be new insulation paper; when the polymerization degree of the oil-immersed paper is between 650 and 1000, the main insulation inside the oil-immersed current transformer to be tested is determined to have excellent insulation performance; when the polymerization degree of the oil-immersed paper is between 350 and 650, the main insulation inside the oil-immersed current transformer to be tested is determined to have medium insulation performance; and when the polymerization degree of the oil-immersed paper is less than 350, the main insulation inside the oil-immersed current transformer to be tested is determined to be in an aging state and needs to be retired.

Images