Oil paper insulation equipment series-parallel equivalent circuit parameter identification method based on spectrum unfolding method

Abstract

The invention provides an oil-paper insulation equipment series-parallel equivalent circuit parameter identification method based on a spectrum unfolding method, and the method comprises the steps: firstly, starting from the tail end of a depolarization current secondary differential time domain spectral line, solving series sub-spectral line parameters through a point taking method, and further identifying the polarization resistance and polarization capacitance of a corresponding large time constant branch. And then, the parallel-serial sub-spectral line parameters are solved through the same method, and then the polarization resistance and polarization capacitance of the medium-time constant branch are identified. And finally, solving the serial sub-spectral line parameters by using the point taking method again, and identifying the polarization resistance and polarization capacitance of the small time constant branch. The method is characterized in that a depolarization current quadratic differential time-domain function expression is utilized, equivalent circuit parameters are identified through a spectrum unfolding method, and the problems of complex iterative calculation and local optimal solution of a traditional intelligent optimization algorithm are avoided. In addition, each sub-spectral line parameter is fixed and unique, so that the oil paper insulation equipment series-parallel equivalent circuit parameter identified by the method has uniqueness and high accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of series - parallel equivalent circuits, and particularly to a method for identifying the parameters of a series - parallel equivalent circuit of an oil - paper insulation device based on a spectrum - decomposition method. Background Art

[0002] In the power system, oil - paper insulation devices such as transformers and cables play a crucial role in transmitting and distributing electrical energy. The insulating materials of these devices, usually composed of oil and paper materials, are the key to ensuring the normal operation of the devices. However, due to the influence of long - term operation and environmental factors, the insulating materials will gradually age, resulting in a decline in insulation performance and an increased risk of equipment failure.

[0003] To ensure the reliability and safety of the power system, it is particularly important to accurately evaluate the insulation state of oil - paper insulation devices. Currently on the market, the main method for the aging state of the internal insulating medium of oil - paper insulation devices is to use a series - parallel equivalent circuit model; the unique series - parallel branches of this model can effectively characterize the polarization relaxation characteristics of the oil - paper interface. This model predicts and evaluates the insulation state by simulating the polarization and depolarization processes of the internal insulating medium of the device; specifically, the parameters of the series - parallel equivalent circuit are mainly identified by using time - domain dielectric spectroscopy characteristic quantities combined with intelligent optimization algorithms such as particle swarm optimization. Here, the time - domain dielectric spectroscopy characteristic quantities refer to voltage characteristic quantities or polarization - depolarization current characteristic quantities.

[0004] Although intelligent optimization algorithms such as particle swarm optimization play a certain role in estimating the equivalent circuit parameters of the oil - paper insulation system, due to problems such as the complex iterative update calculation and the tendency to fall into local optimal solutions in the algorithm itself, it will lead to non - optimal solutions for the equivalent circuit parameters obtained. And because the relationship between the series - parallel equivalent circuit parameters and each time - domain dielectric spectroscopy characteristic quantity is a functional relationship of a complex non - linear polynomial, the parameter values of the series - parallel equivalent circuit obtained by identifying through intelligent optimization algorithms such as particle swarm optimization are not fixed and do not have uniqueness.

[0005] In view of this, the present application is proposed. Summary of the Invention

[0006] The present invention provides a method for identifying the parameters of a series - parallel equivalent circuit of an oil - paper insulation device based on a spectrum - decomposition method, which can at least partially improve the above problems.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for identifying the parameters of a series - parallel equivalent circuit of an oil - paper insulation device based on a spectrum - decomposition method, which includes:

[0009] Apply a DC voltage source across both ends of the oil-paper insulation equipment and charge for a preset duration. Measure the depolarization current in the parallel-series equivalent circuit of the oil-paper insulation equipment according to Kirchhoff's current law to obtain a depolarization current curve. Here, the depolarization current is the sum of the currents of each series polarization branch and parallel-series polarization branch;

[0010] Perform a second-order differential preprocessing on the depolarization current curve to obtain a second-order differential time-domain spectrum line of the depolarization current;

[0011] Starting from the end of the second-order differential time-domain spectrum line of the depolarization current, perform parameter de-spectrumming processing on all peak points within the first preset time range and the third preset time range by the point-taking method to obtain the parameters of all RC series polarization branches;

[0012] Perform parameter de-spectrumming processing on all peak points within the second preset time range by the point-taking method to obtain the parameters of all RC parallel-series polarization branches;

[0013] Based on the parameters of all RC series polarization branches and the parameters of all RC parallel-series polarization branches, obtain the parameter identification result in the parallel-series equivalent circuit of the oil-paper insulation equipment.

[0014] In summary, the method for identifying the parameters of the parallel-series equivalent circuit of oil-paper insulation equipment based on the de-spectrumming method aims to improve the accuracy and efficiency of aging diagnosis of oil-paper insulation equipment. This method simplifies the parameter identification process of the parallel-series equivalent circuit by analyzing the second-order differential time-domain spectrum line of the depolarization current and utilizing the mathematical relationship between the parameters of its internal sub-spectrum lines and the parameters of each polarization branch of the parallel-series equivalent circuit. Specifically, the method for identifying the parameters of the parallel-series equivalent circuit of oil-paper insulation equipment based on the de-spectrumming method first starts from the end of the second-order differential time-domain spectrum line of the depolarization current, solves the parameters of the series-type sub-spectrum line by the point-taking method, and then identifies the polarization resistance and polarization capacitance of the corresponding large time constant branch. Subsequently, solve the parameters of the parallel-series type sub-spectrum line by the same method, and then identify the polarization resistance and polarization capacitance of the medium time constant branch. Finally, use the point-taking method again to solve the parameters of the series-type sub-spectrum line and identify the polarization resistance and polarization capacitance of the small time constant branch.

[0015] The key lies in using the second-order differential time-domain function expression of the depolarization current and identifying the equivalent circuit parameters by the de-spectrumming method, avoiding the complex iterative calculation and local optimal solution problems of traditional intelligent optimization algorithms. In addition, the parameters of each sub-spectrum line are fixed and unique, making the parameters of the parallel-series equivalent circuit of the oil-paper insulation equipment identified by this method have uniqueness and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic flowchart of the method for identifying the parameters of the parallel-series equivalent circuit of oil-paper insulation equipment based on the de-spectrumming method provided by an embodiment of the present invention;

[0017] Figure 2 It is the topological structure diagram of the hybrid equivalent circuit of the oil-paper insulation equipment provided by the embodiment of the present invention;

[0018] Figure 3 It is the superimposed diagram of the secondary differential time-domain sub-spectrum lines of the depolarization current provided by the embodiment of the present invention;

[0019] Figure 4 It is the schematic diagram of the first spectral decomposition provided by the embodiment of the present invention;

[0020] Figure 5 It is the schematic diagram of the second spectral decomposition provided by the embodiment of the present invention;

[0021] Figure 6 It is the schematic diagram of the third spectral decomposition provided by the embodiment of the present invention;

[0022] Figure 7 It is the schematic diagram of the fourth spectral decomposition provided by the embodiment of the present invention;

[0023] Figure 8 It is the schematic diagram of the fifth spectral decomposition provided by the embodiment of the present invention;

[0024] Figure 9 It is the schematic diagram of the sixth spectral decomposition provided by the embodiment of the present invention;

[0025] Figure 10 It is the schematic diagram of the depolarization current secondary differential time-domain spectrum line and its sub-spectrum line provided by the embodiment of the present invention;

[0026] Figure 11 It is the schematic diagram of the comparison between the calculated value and the measured value of the depolarization current provided by the embodiment of the present invention. Specific Embodiment

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Reference Figure 1 As shown, the first embodiment of the present invention discloses a method for identifying the parameters of the hybrid equivalent circuit of oil-paper insulation equipment based on the spectral decomposition method, which can be executed by the equipment for identifying the parameters of the hybrid equivalent circuit of oil-paper insulation equipment based on the spectral decomposition method (hereinafter referred to as the parameter identification equipment), and particularly, executed by one or more processors in the parameter identification equipment to implement the following method:

[0029] S1. Apply a DC voltage source across both ends of the oil-paper insulation equipment and charge for a preset duration. Measure the depolarization current in the series-parallel equivalent circuit of the oil-paper insulation equipment according to Kirchhoff's current law to obtain the depolarization current curve. Here, the depolarization current is the sum of the currents of each series polarization branch and series-parallel polarization branch;

[0030] Please refer to Figure 2 , preferably, the series-parallel equivalent circuit of the oil-paper insulation equipment includes a geometric polarization equivalent circuit, a series polarization equivalent circuit, and a series-parallel polarization equivalent circuit. The geometric polarization equivalent circuit, the series polarization equivalent circuit, and the series-parallel polarization equivalent circuit are in parallel. Here, the geometric polarization equivalent circuit consists of an insulation resistance R g and a geometric capacitance C g in parallel. The series polarization equivalent circuit consists of K RC series polarization branches in parallel. The series-parallel polarization equivalent circuit consists of M RC series-parallel polarization branches in parallel. Both K and M are natural numbers;

[0031] Each of the RC series polarization branches includes a series polarization resistance and a series polarization capacitance, where the series polarization capacitance and the series polarization resistance are in series;

[0032] Each of the RC series-parallel polarization branches includes two series-parallel polarization resistances and a series-parallel polarization capacitance, where the second series-parallel polarization resistance is in parallel with the series-parallel polarization capacitance and then in series with the first series-parallel polarization resistance.

[0033] Specifically, step S1 includes: Apply a DC voltage source U 0 across both ends of the oil-paper insulation equipment and charge for a preset duration t c ;

[0034] Calculate the voltage of the series polarization capacitance on the i-th RC series polarization branch during the depolarization process. The calculation formula is: where i = 1, 2,..., K, t is time, is an exponent related to the t c , τ pi parameters, is an exponential function with t as the variable;

[0035] Calculate the time constant of the series polarization capacitance on the i-th RC series polarization branch during the depolarization process. The calculation formula is: τ pi = R pi C pi , where R pi is the value of the series polarization resistance on the i-th RC series polarization branch, and C pi is the value of the series polarization capacitance on the i-th RC series polarization branch;

[0036] During the depolarization process, calculate the voltage of the series-parallel polarization capacitor on the j-th RC series-parallel polarization branch. The calculation formula is as follows: where j = 1, 2,..., M, R h(2j) is the second series-parallel polarization resistor on the j-th RC series-parallel polarization branch, and R h(2j-1) is the first series-parallel polarization resistor on the j-th RC series-parallel polarization branch. is the exponent related to the t c , τ hj parameters, is an exponential function with t as the variable;

[0037] During the depolarization process, calculate the time constant of the series-parallel polarization capacitor on the j-th RC series-parallel polarization branch. The calculation formula is as follows: C hj is the series-parallel polarization capacitor on the j-th RC series-parallel polarization branch;

[0038] Based on Kirchhoff's current law, measure the depolarization current in the series-parallel equivalent circuit to obtain the depolarization current curve. The calculation formula is as follows: where B i is the relaxation contribution coefficient of the i-th series polarization branch to the depolarization current, and E j is the relaxation contribution coefficient of the j-th series-parallel polarization branch to the depolarization current.

[0039] In this embodiment, the topological structure of the series-parallel equivalent circuit of the oil-paper insulation equipment is as Figure 2 shown, including a geometric polarization equivalent circuit (including insulation resistance R g , geometric capacitance C g ), a series polarization equivalent circuit (including K RC series polarization branches), and a series-parallel polarization equivalent circuit (including M RC series-parallel polarization branches).

[0040] According to the time-domain dielectric spectroscopy test principle and basic circuit theory, when a DC voltage source U 0 is applied across the oil-paper insulation equipment and the charging time is t c , during the depolarization process, the voltage U Ci (t) and the time constant τ pi of the polarization capacitor on the i-th series polarization branch are expressed as: τ pi = R pi C pi .

[0041] Similarly, after the charging time t c , the voltage U Cj(t) and time constant τ hj The expression is: According to Kirchhoff's current law, the depolarization current in the series-parallel equivalent circuit is equal to the sum of the currents in each series polarization branch and series-parallel polarization branch, that is

[0042]

[0043] S2, perform second-order differential preprocessing on the depolarization current curve to obtain the second-order differential time-domain spectrum line of the depolarization current;

[0044] Specifically, step S2 includes: performing second-order differential on the depolarization current curve and then multiplying by a preset time t 2 , to obtain the second-order differential time-domain spectrum line of the depolarization current, and the mathematical expression is:

[0046] Among them, is the i-th second-order differential time-domain series-type sub-spectrum line of the depolarization current, is the j-th second-order differential time-domain series-parallel type sub-spectrum line of the depolarization current.

[0047] Preferably, both the horizontal and vertical coordinates are selected as logarithms to make the peak points of the second-order differential time-domain spectrum line of the depolarization current clear.

[0048] In this embodiment, perform second-order differential on the depolarization current curve and then multiply by the time t 2 , to obtain the second-order differential time-domain function expression of the depolarization current:

[0050] Among them, is the i-th second-order differential time-domain series-type sub-spectrum line of the depolarization current, hereinafter referred to as the series-type sub-spectrum line; is the j-th second-order differential time-domain series-parallel type sub-spectrum line of the depolarization current, hereinafter referred to as the series-parallel type sub-spectrum line.

[0051] Specifically, in this embodiment, in order to study the characteristics of the second-order differential time-domain spectrum line of the depolarization current superimposed by multiple sub-spectrum lines, three different time constants, τ 1 = 0.035, τ 2 = 0.11, τ 3 = 0.46 of the sub-spectrum lines are selected, and the second-order differential time-domain spectrum line formed by the superposition of sub-spectrum line 1, sub-spectrum line 2, and sub-spectrum line 3 is studied respectively. The superposition situation is as Figure 3 shown. From Figure 3It can be known that the second differential time-domain spectrum line of the depolarization current has the following characteristics: 1. The second differential time-domain spectrum line of the depolarization current has obvious peak points, and the number of peak points is equal to the number of sub-spectrum lines; 2. The internal sub-spectrum lines of the second differential time-domain spectrum line of the depolarization current have a unique peak point and rapidly decay to 0 on both sides; 3. The sub-spectrum lines with larger time constants inside the second differential time-domain spectrum line of the depolarization current affect the peak values of the adjacent sub-spectrum lines with smaller time constants on the left, but the sub-spectrum lines with smaller time constants have almost no influence on the peak values of the adjacent sub-spectrum lines with larger time constants on the right. Therefore, based on the above characteristics, each sub-spectrum line can be de-spectrally analyzed in sequence from the end of the second differential time-domain spectrum line of the depolarization current, and the equivalent circuit parameters can be identified according to the internal relationship between the sub-spectrum line parameters and the corresponding polarization branch parameters.

[0052] In this embodiment, the second differential time-domain spectrum line of the depolarization current is obtained , and both the horizontal and vertical coordinates are logarithmically taken to make the peak points of the spectrum line clearer.

[0053] S3. Starting from the end of the second differential time-domain spectrum line of the depolarization current, parameter de-spectral analysis is performed on all peak points within the first preset time range and the third preset time range through the point-taking method to obtain the parameters of all RC series polarization branches;

[0054] Specifically, step S3 includes: starting from the end of the second differential time-domain spectrum line of the depolarization current, reading the coordinates of the first peak point (t 1peak , φ 1peak );

[0055] According to the coordinates of the peak point (t 1peak , φ 1peak ), calculate the parameters B 1 and τ p1 of the series-type sub-spectrum line with the largest time constant, and obtain the first second differential time-domain series-type sub-spectrum line of the depolarization current. The calculation formula is:

[0056] Substitute the parameters B 1 and τ p1 into the identification formula to identify the parameters R p1 and C p1 of the first RC series polarization branch. The calculation formula is:

[0057] Repeat the above steps to calculate the parameters of the second differential time-domain series-type sub-spectrum lines corresponding to all peak points within the first preset time range and the third preset time range, and obtain the parameters of all RC series polarization branches.

[0058] Preferably, the first preset time range is t≥200s, and the third preset time range is t≤2s.

[0059] In this embodiment, the de-spectrumming and parameter solving of the series polarization equivalent circuit parameters are first explained. Starting from the end of the spectrum line, read the coordinates of the first peak point and substitute it into Equation to obtain the parameters B 1 and τ p1 of the series sub-spectrum line with the largest time constant, that is, the function of the first series sub-spectrum line is obtained. Substitute the known parameters B 1 and τ p1 into Equation to identify the parameters R p1 and C p1 of this series polarization branch.

[0060] Subtract the first sub-spectrum line from the current differential spectrum line to obtain the current remaining differential spectrum line; repeat the above steps for the current remaining differential spectrum line to solve the functions of the 2nd, 3rd, …, Kth sub-spectrum lines, and identify the parameters R p2 , C p2 , …, R pK and C pK of the corresponding series polarization branches. When the de-spectrumming of the series sub-spectrum line corresponding to the last peak point within the range of t≤2s is completed, the entire de-spectrumming process ends, and the parameters of all series polarization branches can be solved.

[0061] S4. Perform parameter de-spectrumming processing on all peak points within the second preset time range by the point-taking method to obtain the parameters of all RC parallel-series polarization branches;

[0062] Specifically, step S4 includes: when it is determined that the de-spectrumming of the parameters of the last series sub-spectrum line of the depolarization current second differential time domain within the first preset time range is completed, read the coordinates of the peak point at the end of the current remaining differential spectrum line

[0063] Substitute the coordinates of the peak point at the end of the current remaining differential spectrum line into the formula to identify the parameters E 1 and τ h1 of the first depolarization current second differential time domain parallel-series sub-spectrum line corresponding thereto;

[0064] Starting from the end of the current remaining depolarization current second differential time domain spectrum line, randomly select a point (t′ 1 , y′ 1 ) on the right side of its peak point;

[0065] Substitute the parameters E of the first depolarization current second differential time domain parallel-series sub-spectrum line1 and τ h1 Substitute into the formula to identify the parameters R h1 , R h2 and C h1 of the first RC series - parallel polarization branch;

[0066] Repeat the above steps to calculate the parameters of the depolarization current second - order differential time - domain series - parallel sub - spectral lines corresponding to all peak points within the second preset time range, and obtain the parameters of all RC series - parallel polarization branches.

[0067] Preferably, the second preset time range is 2s < t < 200s.

[0068] In this embodiment, first, the spectral decomposition and parameter solution of the series - parallel polarization equivalent circuit parameters are explained. When the spectral decomposition of the last series - type sub - spectral line within the range of t ≥ 200s is completed, read the coordinates of the peak point at the end of the current remaining differential spectral line and substitute them into Equation to identify the parameters E 1 and τ h1 of the corresponding series - parallel sub - spectral line, that is, obtain the function of the first series - parallel sub - spectral line. Arbitrarily take a point (t′ 1 , y′ 1 ) on the right side of the peak point at the end of the current remaining differential spectral line. At the same time, substitute the parameters E 1 and τ h1 of the first sub - spectral line obtained in step one into Equation to thereby identify the parameters R h1 , R h2 and C h1 of the first RC series - parallel polarization branch.

[0069] Subtract the first sub - spectral line from the current differential spectral line to obtain the current remaining differential spectral line; repeat steps one to three for the current remaining differential spectral line to solve the functions of the 2nd, 3rd, … Mth series - parallel sub - spectral lines, and identify the parameters R h3 , R h4 , C h2 , … R h(2M-1) , R h(2M) , C hM of the corresponding RC series - parallel polarization branches. When the spectral decomposition of the series - parallel sub - spectral line corresponding to the last peak point within the range of 2s < t < 200s is completed, the spectral decomposition of the series - parallel sub - spectral line ends, and then the parameters of all RC series - parallel polarization branches can be solved.

[0070] Briefly speaking, the overall idea of identifying the equivalent circuit parameters by the depolarization current second differential time-domain spectrum method in the method for identifying the parameters of the series-parallel equivalent circuit of oil-paper insulation equipment based on the spectrum decomposition method can be described as follows: First, starting from the end of the depolarization current second differential time-domain spectrum, the parameters of the series-type sub-spectrum line for t≥200s are solved by the point-taking method, and then the polarization resistance and polarization capacitance of the branch with the large time constant are solved; then, the parameters of the series-parallel type sub-spectrum line for 2s<t<200s are solved by the point-taking method, and then the polarization resistance and polarization capacitance of the branch with the medium time constant are solved; finally, the parameters of the series-type sub-spectrum line for t≤2s are solved by the point-taking method, and then the polarization resistance and polarization capacitance of the branch with the small time constant are solved.

[0071] S5. Obtain the parameter identification result in the series-parallel equivalent circuit of the oil-paper insulation equipment according to the parameters of all RC series polarization branches and the parameters of all RC series-parallel polarization branches.

[0072] Specifically, in this embodiment, the depolarization current curve of a transformer T1 with a voltage level of 220 kV and a capacity of 180 MVA (i.e., t c = 5000 s) is used to verify the discrimination accuracy of this method. According to the method for identifying the parameters of the series-parallel equivalent circuit of oil-paper insulation equipment based on the spectrum decomposition method, a study is carried out on the transformer T1, and its spectrum decomposition result is as Figures 4 to 10 shown, and the parameter identification results of each polarization branch are shown in Table 1.

[0073] Table 1 Parameters of the series-parallel equivalent circuit of the transformer

[0074]

[0075]

[0076] In this embodiment, to verify the accuracy and superiority of the parameter identification result, the depolarization current curves corresponding to the equivalent circuit parameters identified by the traditional intelligent optimization algorithm and the spectrum decomposition method proposed in this method are respectively calculated, and compared with the measured depolarization current curve, and the comparison result is as Figure 11 shown. It can be intuitively known from Figure 11 that the depolarization current curve calculated based on the spectrum decomposition method proposed in this method almost completely coincides with the measured depolarization current curve, while the coincidence of the depolarization current curve calculated based on the traditional intelligent optimization algorithm is relatively poor. To further quantitatively analyze the coincidence of the two, the coincidence degree shown in Equation is proposed for analysis, where i d is the on-site measured value, is the calculated value.

[0077] According to Figure 11 the data of the three curves in, combined with Equation Calculation shows that the coincidence degree between the depolarization current curve obtained by the spectral decomposition method and the measured value is 98.33%, and the coincidence degree between the depolarization current curve obtained by the traditional intelligent optimization algorithm and the measured value is 88.19%. This further verifies that the parameters of the parallel equivalent circuit of the oil-paper insulation equipment identified by the spectral decomposition method proposed in this method have high accuracy and reliability, and can reflect the aging information of the depolarization current curve more accurately than the equivalent circuit parameters identified by the traditional intelligent optimization algorithm, which is beneficial to the subsequent accurate assessment of the aging state of the oil-paper insulation equipment.

[0078] In summary, the method for identifying the parameters of the parallel equivalent circuit of the oil-paper insulation equipment based on the spectral decomposition method uses the spectral decomposition method of the second derivative time-domain spectrum line of the depolarization current to identify the parameters of the parallel equivalent circuit of the oil-paper insulation equipment. It utilizes the simple mathematical formula between the internal sub-spectrum line parameters and the parameters of each polarization branch of the parallel equivalent circuit, rather than complex algorithm iteration. The parameter identification result has the advantage of high accuracy. And each sub-spectrum line parameter is fixed and unique. Therefore, the parameters of the parallel equivalent circuit of the oil-paper insulation equipment identified by this method based on the sub-spectrum line parameters have the advantage of uniqueness, which is a feature not possessed by the traditional intelligent algorithms.

[0079] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A method for identifying parameters of a series-parallel equivalent circuit of oil-paper insulation equipment based on spectrum analysis, characterized in that: include: A DC voltage source is added to both ends of the oil-paper insulation device, and the device is charged for a preset time. The depolarization current in the parallel-parallel equivalent circuit of the oil-paper insulation device is obtained by testing according to Kirchhoff's current law, and a depolarization current curve is obtained, wherein the depolarization current is the sum of the currents of each series polarization branch and the parallel-parallel polarization branch; Performing secondary differential preprocessing on the depolarization current curve to obtain a secondary differential time-domain spectrum line of the depolarization current; Starting from the end of the second differential time domain spectrum of the depolarization current, all peak points within the first preset time range and the third preset time range are subjected to parameter spectrum decomposition processing by a point selection method to obtain parameters of all RC series polarization branches; Performing parameter spectrum analysis on all peak points within the second preset time range by using a point selection method to obtain parameters of all RC hybrid polarization branches; According to the parameters of all RC series polarization branches and the parameters of all RC hybrid polarization branches, the parameter identification results in the hybrid equivalent circuit of the oil-paper insulation equipment are obtained.

2. The method for identifying parameters of a parallel-parallel equivalent circuit of oil-paper insulated equipment based on spectrum analysis according to claim 1 is characterized in that: The parallel-parallel equivalent circuit of the oil-paper insulation equipment includes a geometric polarization equivalent circuit, a series polarization equivalent circuit and a parallel-parallel polarization equivalent circuit, wherein the geometric polarization equivalent circuit, the series polarization equivalent circuit and the parallel-parallel polarization equivalent circuit are connected in parallel, wherein the geometric polarization equivalent circuit is composed of an insulation resistance R g and geometric capacitance C g The series polarization equivalent circuit is composed of K RC series polarization branches connected in parallel, and the hybrid polarization equivalent circuit is composed of M RC hybrid polarization branches connected in parallel, where K and M are both natural numbers; Each of the RC series polarization branches includes a series polarization resistor and a series polarization capacitor, wherein the series polarization capacitor and the series polarization resistor are connected in series; Each of the RC hybrid polarization branches includes two hybrid polarization resistors and one hybrid polarization capacitor, wherein the second hybrid polarization resistor is connected in parallel with the hybrid polarization capacitor and then connected in series with the first hybrid polarization resistor.

3. The method for identifying parameters of a series-parallel equivalent circuit of oil-paper insulated equipment based on spectrum analysis according to claim 2 is characterized in that: A DC voltage source is added to both ends of the oil-paper insulation device and charged for a preset time. The depolarization current in the parallel-parallel equivalent circuit of the oil-paper insulation device is obtained according to Kirchhoff's current law, and the depolarization current curve is obtained, which is specifically: Add a DC voltage source U0 at both ends of the oil-paper insulation device and charge it for a preset time t c ; Calculate the voltage of the series polarized capacitor on the i-th RC series polarized branch during the depolarization process. The calculation formula is: Where i = 1, 2, ..., K, t is time, For c , τ pi Parameters related to the index, is an exponential function with t as the variable; Calculate the time constant of the series polarization capacitor on the i-th RC series polarization branch during the depolarization process. The calculation formula is: τ pi =R pi C pi , where R pi is the series polarization resistance value of the i-th RC series polarization branch, C pi is the series polarization capacitance value of the i-th RC series polarization branch; Calculate the voltage of the hybrid polarization capacitor on the jth RC hybrid polarization branch during the depolarization process. The calculation formula is: Where j = 1, 2, ..., M, R h(2j) is the second parallel-connection polarization resistor on the jth RC parallel-connection polarization branch, R h(2j-1) is the first hybrid polarization resistor on the jth RC hybrid polarization branch, For c , τ hj Parameters related to the index, is an exponential function with t as the variable; Calculate the time constant of the hybrid polarization capacitor on the jth RC hybrid polarization branch during the depolarization process. The calculation formula is: C hj is the hybrid polarization capacitor on the jth RC hybrid polarization branch; Based on Kirchhoff's current law, the depolarization current in the hybrid equivalent circuit is tested and the depolarization current curve is obtained. The calculation formula is: Among them, B i is the relaxation contribution coefficient of the ith series polarization branch to the depolarization current, E j is the relaxation contribution coefficient of the jth hybrid polarization branch to the depolarization current.

4. The method for identifying parameters of a series-parallel equivalent circuit of oil-paper insulation equipment based on spectrum analysis according to claim 3 is characterized in that: The depolarization current curve is subjected to secondary differential preprocessing to obtain the secondary differential time domain spectrum of the depolarization current, specifically: The depolarization current curve is differentiated twice and then multiplied by the preset time t 2 , the second differential time domain spectrum of the depolarization current is obtained, and the mathematical expression is: in, is the ith depolarization current second-order differential time-domain series sub-spectrum line, It is the jth depolarization current secondary differential time domain mixed sub-spectrum line.

5. The method for identifying parameters of a series-parallel equivalent circuit of oil-paper insulated equipment based on spectrum analysis according to claim 4 is characterized in that: After performing secondary differential preprocessing on the depolarization current curve, the method further includes: selecting the horizontal and vertical coordinates as logarithms at the same time, so as to make the peak point of the secondary differential time domain spectrum line of the depolarization current clear.

6. The method for identifying parameters of a parallel-parallel equivalent circuit of oil-paper insulated equipment based on spectrum analysis according to claim 4 or claim 5, characterized in that: Starting from the end of the second differential time domain spectrum of the depolarization current, all peak points within the first preset time range and the third preset time range are subjected to parameter spectrum analysis by using a point selection method, specifically: Starting from the end of the second differential time-domain spectrum of the depolarization current, read the coordinates of the first peak point According to the peak point coordinates Calculate the parameters B1 and τ of the tandem sub-spectral line with the largest time constant p1 , the first depolarization current second-order differential time domain series sub-spectrum line is obtained, and the calculation formula is: The parameters B1 and τ p1 Substituting into the identification formula, the parameter R of the first RC series polarization branch is obtained. p1 and C p1 , the calculation formula is: Repeat the above steps to calculate the parameters of the depolarization current second differential time domain series sub-spectrum corresponding to all peak points within the first preset time range and the third preset time range, and obtain the parameters of all RC series polarization branches.

7. The method for identifying parameters of a series-parallel equivalent circuit of oil-paper insulation equipment based on spectrum analysis according to claim 6 is characterized in that: The first preset time range is t≥200s, and the third preset time range is t≤2s.

8. The method for identifying parameters of a parallel-parallel equivalent circuit of oil-paper insulated equipment based on spectrum analysis according to claim 7 is characterized in that: The parameter spectrum is processed for all peak points within the second preset time range by the point selection method to obtain the parameters of all RC hybrid polarization branches, which are specifically: When the last depolarization current second-order differential time-domain series sub-spectral line parameter decomposition is completed within the first preset time range, the coordinates of the peak point at the end of the current remaining differential spectral line are read. Set the peak point coordinates of the current remaining differential spectrum line end Substitute into the formula In the above example, we identify the parameters E1 and τ of the first depolarization current secondary micro-division time domain hybrid sub-spectrum. h1 ; Starting from the end of the second differential time-domain spectrum of the residual depolarization current, take any point (t ′ 1,y ′ 1); The first depolarization current is divided into the parameters E1 and τ of the time-domain hybrid sub-spectral line h1 Substitute into the formula In the above example, the parameter R of the first RC hybrid polarization branch is identified. h1 , R h2 and C h1 ; Repeat the above steps to calculate the parameters of the depolarization current secondary micro-division time domain hybrid type sub-spectrum lines corresponding to all peak points within the second preset time range, and obtain the parameters of all RC hybrid polarization branches.

9. The method for identifying parameters of a series-parallel equivalent circuit of oil-paper insulated equipment based on spectrum analysis according to claim 8, characterized in that: The second preset time range is 2s <t<200s。

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