Oil paper insulation time-frequency domain response synchronous testing device and aging state evaluation method

Abstract

The invention discloses an oil paper insulation time-frequency domain response synchronous testing device and an aging state evaluation method, belongs to the technical field of insulation material aging detection, and aims to solve the problem that time / frequency domain dielectric response synchronous measurement cannot be realized in the prior art. According to the scheme, an upper computer outputs a frequency domain excitation instruction to a signal generator, a generated alternating-current voltage signal is amplified by a power amplifier and applied to a to-be-tested product through an alternating-current side protection resistor, and a responded alternating-current signal is collected after passing through a blocking capacitor; the upper computer outputs a time domain excitation instruction to the high-voltage direct-current power supply and synchronously applies a generated direct-current voltage signal to a to-be-tested product through the direct-current side protection resistor, and a responded direct-current signal is collected after passing through the high-voltage silicon stack; and the upper computer calculates a change curve of an alternating current side impedance module value and frequency and a change curve of a direct current side impedance module value and time according to the synchronously acquired alternating current signal and direct current signal so as to obtain a DP value of the to-be-tested product to realize quantitative evaluation of the aging degree of the transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating material aging detection, and in particular to a synchronous testing device for time-frequency domain response of oil-paper insulation and an aging state evaluation method. Background Art

[0002] As key equipment in the power system, oil-immersed power equipment and its components (transformers, mutual inductors, high-voltage bushings) are of vital importance for stable operation. Under long-term and complex operating conditions, the insulation of oil-immersed power equipment and its components will age. Therefore, it is important to accurately obtain the degree of insulation aging during regular inspections and formulate corresponding maintenance strategies.

[0003] my country's power operation and maintenance departments regularly carry out equipment maintenance plans in spring and autumn, and conduct offline inspections of equipment according to the DL / T596-2021 preventive test procedures for power equipment, such as partial discharge, power frequency withstand voltage, power frequency dielectric loss, insulation resistance, dissolved gas analysis in oil, infrared imaging temperature, winding DC resistance test, etc. The above test results reflect the operating status of the equipment. According to the feedback from a large number of on-site test evaluation results, the above method is more accurate for the evaluation results of problems such as concentrated insulation defects or developed latent faults in the equipment, but it is still impossible to quantify and analyze problems such as insulation aging, and can only be qualitatively compared based on the factory parameter values ​​or the test values ​​between the three phases of the current power equipment (power frequency dielectric loss, insulation resistance).

[0004] In order to further quantify the degree of insulation aging, time-frequency domain equipment / technology has been gradually used by the power industry and testing agencies from preliminary university scientific research. The existing time-frequency domain dielectric response test technology needs to be tested independently. The time-domain dielectric response test cycle is 40 minutes (polarization process only), and the frequency-domain dielectric response test (0.001 Hz to 1000 Hz) cycle is 35 minutes. For on-site testers, due to the limited equipment maintenance cycle, if the two test methods are carried out in sequence, the equipment detection cycle will be increased. At the same time, the detection parameters considered in the two traditional test methods are different. The time domain mainly analyzes polarization and depolarization currents (related to the insulation structure size of the test equipment), and the frequency domain mainly considers the dielectric loss factor under broadband excitation (irrelevant to the structural size of the insulation of the test equipment). The response parameters obtained under the two test methods are not directly comparable. The prior art has a solution of applying AC / DC superimposed electric fields to the product to be tested, but it is unable to achieve synchronous measurement of dielectric response in the time / frequency domain. At the same time, the consistency of the results obtained by the two test methods is also not considered, which makes the evaluation results of the aging state of oil-paper insulation too one-sided and incomparable. A new technical solution is urgently needed to solve the above problems. Summary of the invention

[0005] In view of the problem that the synchronous measurement of dielectric response in time / frequency domain cannot be achieved in the prior art, the present invention provides a synchronous testing device for time-frequency domain response of oil-paper insulation and an aging state evaluation method.

[0006] In one aspect of the present invention, a synchronous test device for time-frequency domain response of oil-paper insulation is provided, comprising a signal generator 1, a power amplifier 2, an AC side protection resistor 3, a DC side protection resistor 4, a high-voltage DC power supply 5, an AC micro-current acquisition module 6, a DC blocking capacitor 7, a high-voltage silicon stack 9, a DC micro-current acquisition module 10 and a host computer 11;

[0007] The host computer 11 outputs a frequency domain excitation instruction to the signal generator 1. The AC voltage signal generated by the signal generator 1 is amplified by the power amplifier 2. The amplified AC voltage signal is applied to the test product 8 via the AC side protection resistor 3. The AC signal responded by the test product 8 is collected by the AC micro-current acquisition module 6 after passing through the DC isolation capacitor 7 and fed back to the host computer 11.

[0008] The host computer 11 outputs a time domain excitation instruction to the high-voltage DC power supply 5. The DC voltage signal generated by the high-voltage DC power supply 5 is synchronously applied to the test product 8 via the DC side protection resistor 4. The DC signal responded by the test product 8 is collected by the DC micro-current acquisition module 10 after passing through the high-voltage silicon stack 9 and fed back to the host computer 11.

[0009] The host computer 11 calculates the change curve of the AC side impedance modulus and frequency and the change curve of the DC side impedance modulus and time based on the synchronously collected AC signal and DC signal, and obtains the DP value of the test product 8 based on the change curve of the AC side impedance modulus and frequency and the change curve of the DC side impedance modulus and time to achieve quantitative evaluation of the degree of transformer aging.

[0010] Preferably, the frequency domain excitation instruction is an excitation signal for setting a sweep frequency range and an AC voltage amplitude, the sweep frequency range is 0.001 to 1000 Hz, the AC voltage amplitude range is 0 to 5 volts, and the peak-to-peak value of the voltage output by the excitation signal after passing through the power amplifier (2) is 0 to 2000 volts; the time domain excitation instruction is for setting a DC voltage amplitude, and the DC voltage amplitude range is 0 to 2000 volts.

[0011] Preferably, the AC side protection resistor (3) and the DC side protection resistor (4) are used to prevent the AC voltage source and the DC voltage source from being damaged after the test object (8) breaks down, and the AC side protection resistor (3) and the DC side protection resistor (4) adopt a first set value.

[0012] Preferably, the DC blocking capacitor (7) is used to prevent the DC side voltage from being applied to the AC signal source; and the high-voltage silicon stack (9) adopts a product with a second set value withstand voltage grade to prevent the AC voltage from being applied to the DC high voltage side.

[0013] Another aspect of the present invention provides an aging state evaluation method for oil-paper insulation time-frequency domain response synchronization test, the method is implemented based on the oil-paper insulation time-frequency domain response synchronization test device, the method comprises the following steps:

[0014] Step 1, setting the frequency domain excitation instruction including the sweep frequency range and the AC voltage amplitude, the time domain excitation instruction including the DC voltage amplitude on the DC side, and the test temperature;

[0015] Step 2: Perform a time-frequency domain response synchronization test on the AC side at each frequency point within the frequency sweep range, and collect the AC signal of the test product on the AC side and the DC signal of the test product on the DC side during the test at each frequency point;

[0016] Step 3: The host computer obtains the AC impedance at the set test temperature according to the collected AC signal and the AC voltage amplitude applied to the product to be tested, and draws the AC impedance and frequency change curve; the host computer obtains the DC impedance at the set test temperature according to the collected DC signal and the DC voltage amplitude applied to the product to be tested, and draws the DC impedance and time change curve;

[0017] Step 4: Fourier transform the AC impedance and frequency change curve and the DC impedance and time change curve obtained by the test to generate two corresponding transformed impedance curves, calculate the mean of the transformed impedance modulus in the transformed impedance curve and the original impedance modulus in the test curve and normalize them to obtain the normalized impedance modulus and frequency change curve of the AC side and the normalized impedance modulus and time change curve of the DC side;

[0018] Step 5: Obtain the DP value based on the AC side normalized impedance module value and frequency change curve and the DC side normalized impedance module value and time change curve, and combine the following formula:

[0019]

[0020] Where DP is the degree of polymerization of the oil-impregnated paperboard; A(T) is the fitting parameter on the AC side, and B(T) is the fitting parameter on the DC side, which is related to the test temperature T; Z ac (f n ) is the nth test frequency point f n Normalized impedance modulus value of the AC side under, n = 1, 2,,,, N, N is the number of test frequency points, Z ac (f n ) is in ohms; Z dc (t m ) is the mth test time point t m Normalized impedance modulus value of the DC side at , m=1,2,…,M, M is the number of test time points, Z dc (t m) is measured in ohms.

[0021] Preferably, the AC side fitting parameter A(T) and the DC side fitting parameter B(T) are obtained through preliminary experiments, and the specific process includes the following steps:

[0022] Step 1, set the test temperature range and interval; prepare group P of test products 8 with known DP values;

[0023] Step 2: Within the set test temperature range, Q test temperatures are extracted according to the set intervals, and a time-frequency domain response synchronization test experiment is performed on the test product 8 of the P group DP value at each test temperature. The time-frequency domain response synchronization test experiment is implemented in steps 1 to 5; the overdetermined equation group is obtained by the experiment:

[0024]

[0025] In the overdetermined system, DP1, DP2, ... DP P is the DP value of the P group of test items 8, and the P DP values ​​are not equal;

[0026] A(T i ) and B(T i ) is the i-th test temperature T within the test range i AC and DC parameters, i = 1, 2, ..., Q; A (T i ) and B(T i ) is obtained by automatically optimizing the above-mentioned overdetermined equations;

[0027] Step 4: The AC parameter test data A(T1), A(T2), ..., A(T Q ) is fitted to the AC side fitting parameter A(T):

[0028] A(T)=3.45e 0.025T / 4.35+0.448

[0029] Step 5: The DC parameter test data B(T1), B(T2), ..., B(T Q ) is fitted to the DC side fitting parameter B(T):

[0030] B(T)=0.255e 0.01T+0.468 .

[0031] Preferably, the test temperature T ranges from 10 degrees Celsius to 90 degrees Celsius, and the test temperature T interval is a third set value.

[0032] Preferably, a DC impedance and time variation curve is drawn, including: dividing the time spent on testing the product to be tested into m test time periods, the equivalent impedance value of each test time period is the average value of the impedance of the head test point and the impedance of the end test point in the test time period, and drawing the DC impedance and time variation curve according to the impedance value of each test time period and the time spent on testing the product to be tested.

[0033] Beneficial effects of the present invention:

[0034] 1. A time / frequency domain synchronous detection device and an aging degree assessment method are provided for the aging state detection of oil-immersed power equipment. The present invention does not collect the results of applying AC / DC superimposed electric fields to the test product, but collects AC and DC data in real time, in order to perform synchronous measurement of dielectric response in the time / frequency domain.

[0035] 2. The time domain impedance characteristics and frequency domain impedance characteristics of oil-paper insulation can be obtained simultaneously through one test. The two test results are averaged and normalized to eliminate the influence of environmental noise and large differences in impedance magnitude on the evaluation results.

[0036] 3. By calculating the DP value, the quantitative analysis of the aging degree of oil-paper insulation can be directly achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram of a synchronous testing device for time-frequency domain response of oil-paper insulation according to the present invention;

[0038] Figure 2 It is a flow chart of an aging state evaluation method for synchronous testing of oil-paper insulation time-frequency domain response;

[0039] Figure 3 is the impedance curve on the AC side;

[0040] Figure 4 is the impedance curve on the DC side;

[0041] Figure 5 It is the curve of AC side fitting parameter A(T) and DC side fitting parameter B(T). DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0045] Specific implementation method 1: The following is combined Figure 1 The present embodiment is described. The oil-paper insulation time-frequency domain response synchronization test device described in the present embodiment includes a signal generator 1, a power amplifier 2, an AC side protection resistor 3, a DC side protection resistor 4, a high-voltage DC power supply 5, an AC micro-current acquisition module 6, a DC blocking capacitor 7, a high-voltage silicon stack 9, a DC micro-current acquisition module 10 and a host computer 11;

[0046] The host computer 11 outputs a frequency domain excitation instruction to the signal generator 1. The AC voltage signal generated by the signal generator 1 is amplified by the power amplifier 2. The amplified AC voltage signal is applied to the test product 8 via the AC side protection resistor 3. The AC signal responded by the test product 8 is collected by the AC micro-current acquisition module 6 after passing through the DC isolation capacitor 7 and fed back to the host computer 11.

[0047] The host computer 11 outputs a time domain excitation instruction to the high-voltage DC power supply 5. The DC voltage signal generated by the high-voltage DC power supply 5 is synchronously applied to the test product 8 via the DC side protection resistor 4. The DC signal responded by the test product 8 is collected by the DC micro-current acquisition module 10 after passing through the high-voltage silicon stack 9 and fed back to the host computer 11.

[0048] The host computer 11 calculates the change curve of the AC side impedance modulus and frequency and the change curve of the DC side impedance modulus and time based on the synchronously collected AC signal and DC signal, and obtains the DP value of the test product 8 based on the change curve of the AC side impedance modulus and frequency and the change curve of the DC side impedance modulus and time to achieve quantitative evaluation of the degree of transformer aging.

[0049] The frequency domain excitation instruction is an excitation signal for setting a sweep frequency range and an AC voltage amplitude, the sweep frequency range is 0.001 to 1000 Hz, the AC voltage amplitude range is 0 to 5 volts, and the peak-to-peak value of the voltage output by the excitation signal after passing through the power amplifier (2) is 0 to 2000 volts; the time domain excitation instruction is for setting a DC voltage amplitude, and the DC voltage amplitude range is 0 to 2000 volts.

[0050] The test device of this embodiment provides two parallel circuits, an AC side test circuit and a DC side test circuit, wherein the AC side test circuit is: the AC voltage signal generated by the signal generator 1 is amplified by the power amplifier 2, and then applied to the test product 8 through the AC side protection resistor 3, and the AC signal responded by the test product 8 is collected by the AC micro-current acquisition module 6 after passing through the DC blocking capacitor 7; the DC side test circuit is: the DC voltage signal generated by the high-voltage DC power supply 5 is synchronously applied to the test product 8 through the DC side protection resistor 4, and the DC signal responded by the test product 8 is collected by the DC micro-current acquisition module 10 after passing through the high-voltage silicon stack 9; the time-frequency domain synchronous sampling system uses the DC blocking capacitor 7 and the high-voltage silicon stack 9 to realize the synchronous application of AC and DC voltages on the test product 8, and collects its DC micro-current signal and AC micro-current signal in the two circuits respectively.

[0051] The AC side protection resistor 3 and the DC side protection resistor 4 are used to prevent the AC voltage source and the DC voltage source from being damaged after the test product 8 breaks down. The AC side protection resistor 3 and the DC side protection resistor 4 adopt a first set value, which is 1 megohm resistance.

[0052] The DC blocking capacitor 7 is used to prevent the DC voltage from being applied to the AC signal source; the high-voltage silicon stack 9 adopts a product with a second set value of volt withstand voltage to prevent the AC voltage from being applied to the DC high voltage side. The second set value is 20,000 volts.

[0053] Specific implementation method 2: The following is combined Figures 1 to 5 This embodiment describes an aging state assessment method for oil-paper insulation time-frequency domain response synchronization test described in this embodiment. The method is implemented based on an oil-paper insulation time-frequency domain response synchronization test device described in Embodiment 1. The method includes the following steps:

[0054] Step 1, setting the frequency domain excitation instruction including the sweep frequency range and the AC voltage amplitude, the time domain excitation instruction including the DC voltage amplitude on the DC side, and the test temperature;

[0055] The host computer can set the frequency bandwidth and voltage amplitude of the excitation signal through the program. The test frequency range is 0.001 to 1000 Hz, the voltage output range is 0 to 5 volts, and the output AC voltage effective value range after the power amplifier is 0 to 2000 volts; the high-voltage DC source output voltage range is 0 to 2000 volts.

[0056] Step 2: Perform a time-frequency domain response synchronization test on the AC side at each frequency point within the frequency sweep range, and collect the AC signal of the test product on the AC side and the DC signal of the test product on the DC side during the test at each frequency point;

[0057] In this step, synchronous acquisition is performed, and the AC and DC response currents are synchronized with the impedance under high-voltage AC and DC excitation through the DC blocking capacitor 7 and the high-voltage silicon stack 9. The DC blocking capacitor 7 is used to prevent the DC side voltage from being applied to the AC signal source; the high-voltage silicon stack 9 adopts a 20,000 volt withstand voltage grade product to prevent the AC voltage from being applied to the DC high-voltage side.

[0058] Step 3: The host computer obtains the AC impedance at the set test temperature according to the collected AC signal and the AC voltage amplitude applied to the product to be tested, and draws the AC impedance and frequency change curve; the host computer obtains the DC impedance at the set test temperature according to the collected DC signal and the DC voltage amplitude applied to the product to be tested, and draws the DC impedance and time change curve;

[0059] Drawing a DC impedance and time variation curve includes: dividing the time spent on testing the product to be tested into m test time periods, the equivalent impedance value of each test time period is the average value of the impedance of the head end test point and the impedance of the end test point in the test time period, and drawing the DC impedance and time variation curve according to the impedance value of each test time period and the time spent on testing the product to be tested.

[0060] In this step, the AC and DC impedances are calculated based on the sampled AC and DC response current signals and the applied AC and DC excitation amplitudes, and the impedance, frequency and time variation curves are obtained.

[0061] Step 4: The AC impedance and frequency variation curve and the DC impedance and time variation curve obtained by the test are both used as test curves, and the test curves are Fourier transformed to generate a transformed impedance curve. The transformed impedance modulus value in the transformed impedance curve and the original impedance modulus value in the test curve are averaged and normalized to obtain the normalized impedance modulus value and frequency variation curve of the AC side and the normalized impedance modulus value and time variation curve of the DC side;

[0062] The impedance data obtained on the DC and AC sides have a large span in magnitude, and there are differences in the data after Fourier transformation. Therefore, the DC impedance data, AC impedance data, impedance data after AC transformation, and impedance data after DC transformation obtained from the test need to be averaged and normalized to eliminate the impact of environmental noise and data magnitude on the evaluation results.

[0063] Step 5: Obtain the DP value based on the AC side normalized impedance module value and frequency change curve and the DC side normalized impedance module value and time change curve, and combine the following formula:

[0064]

[0065] Where DP is the degree of polymerization of the oil-impregnated paperboard; A(T) is the fitting parameter on the AC side, and B(T) is the fitting parameter on the DC side, which is related to the test temperature T; Z ac (f n ) is the nth test frequency point f n Normalized impedance modulus value of the AC side under, n = 1, 2,,,, N, N is the number of test frequency points, Z ac (f n ) is in ohms; Z dc (t m ) is the mth test time point t m Normalized impedance modulus value of the DC side at , m=1,2,…,M, M is the number of test time points, Z dc (t m ) is measured in ohms.

[0066] The AC side fitting parameters A(T) and the DC side fitting parameters B(T) are obtained through preliminary experiments. The specific process includes the following steps:

[0067] Step 1, set the test temperature range and interval; prepare P groups of test products with known DP values ​​(8);

[0068] Step 2: Within the set test temperature range, Q test temperatures are extracted according to the set intervals, and a time-frequency domain response synchronization test experiment is performed on the test product 8 of the P group DP value at each test temperature. The time-frequency domain response synchronization test experiment is implemented in steps 1 to 5; the overdetermined equation group is obtained by the experiment:

[0069]

[0070] In the overdetermined system, DP1, DP2, ... DP P is the DP value of the P group of test items 8, and the P DP values ​​are not equal;

[0071] A(T i ) and B(T i ) is the i-th test temperature T within the test range i AC and DC parameters, i = 1, 2, ..., Q; A (T i ) and B(T i ) is obtained by automatically optimizing the above-mentioned overdetermined equations;

[0072] Step 4: The AC parameter test data A(T1), A(T2), ..., A(T Q ) is fitted to the AC side fitting parameter A(T):

[0073] A(T)=3.45e 0.025T / 4.35+0.448

[0074] The test temperature T ranges from 10 degrees Celsius to 90 degrees Celsius, and the test temperature T interval is a third set value, and the third set value is 10 degrees Celsius.

[0075] Step 5: The DC parameter test data B(T1), B(T2), ..., B(T Q ) is fitted to the DC side fitting parameter B(T):

[0076] B(T)=0.255e 0.01T+0.468 .

[0077] Fitting curve see Figure 5 shown.

[0078] The two parameters A(T) and B(T) obtained after fitting can be directly applied to the time-frequency domain response synchronization test experiment at any test temperature to obtain the DP value, so as to achieve quantitative evaluation of the aging degree of the test product 8:

[0079] The specific test includes the following steps: in the interface of the host computer, select the test frequency range, AC voltage amplitude, and DC voltage amplitude. After starting the test, the signal generator will receive the command of the host computer and send out corresponding sinusoidal excitation signals of different frequency bands. The frequency values ​​applied in the embodiment are 1000, 470, 220, 110, 70, 40, 20, 10, 4.6, 2.2, 1, 0.46, 0.22, 0.1, 0.046, 0.022, 0.01, 0.0046, 0.0022, and 0.0001 Hz. After passing through the power amplifier, the effective value of the output voltage is 2000 volts, and the output DC voltage is 2000 volts. The AC and DC voltages are applied to the sample to be tested. The I / V conversion sampling unit is used on both the AC side and the DC side through automatic transimpedance adjustment to realize the detection of microcurrents on the AC side and the DC side. According to the applied voltage amplitude and the current values ​​at different test frequencies and at different times obtained in the test, the impedance modulus, frequency and time variation curves are calculated. Similarly, the above tests are carried out on oil-paper insulation materials with different aging degrees at different test temperatures. Finally, the functional relationship between the insulation aging degree and the test temperature and impedance modulus (different frequencies and different times) is established. The DP value can be used to achieve quantitative evaluation of the transformer aging degree.

[0080] Application Examples

[0081] The test selected a 10-year-old 35kV oil-immersed transformer as the test sample. The transformer was tested synchronously in the time-frequency domain under a test environment of 21 degrees Celsius. The comparison results between the time-frequency domain test results and the calculation results obtained after Fourier transform are as follows: Figure 3 , 4According to the calculation method of the present invention, the degree of polymerization (DP) of the insulation inside the 35kV oil-immersed transformer is 698. According to DL / T 984-2018 "Guidelines for Determining Aging of Oil-immersed Transformer Insulation", when the degree of polymerization of the insulation paperboard inside the transformer is greater than 500, the transformer insulation is in good condition and is in the early to middle stage of aging.

[0082] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A synchronous test device for time-frequency domain response of oil-paper insulation, characterized in that: It comprises a signal generator (1), a power amplifier (2), an AC side protection resistor (3), a DC side protection resistor (4), a high-voltage DC power supply (5), an AC micro-current acquisition module (6), a DC isolation capacitor (7), a high-voltage silicon stack (9), a DC micro-current acquisition module (10) and a host computer (11); The host computer (11) outputs a frequency domain excitation instruction to the signal generator (1); the AC voltage signal generated by the signal generator (1) is amplified by the power amplifier (2); the amplified AC voltage signal is applied to the test object (8) via the AC side protection resistor (3); the AC signal responded by the test object (8) is collected by the AC micro-current collection module (6) after passing through the DC isolation capacitor (7) and fed back to the host computer (11); The host computer (11) outputs a time domain excitation instruction to the high-voltage DC power supply (5); the DC voltage signal generated by the high-voltage DC power supply (5) is synchronously applied to the test object (8) via the DC side protection resistor (4); the DC signal responded by the test object (8) is collected by the DC micro-current collection module (10) after passing through the high-voltage silicon stack (9) and fed back to the host computer (11); The host computer (11) calculates the curve of the change of the AC side impedance modulus and frequency and the curve of the change of the DC side impedance modulus and time based on the synchronously collected AC signal and DC signal, and then obtains the DP value of the test product (8) based on the curve of the change of the AC side impedance modulus and frequency and the curve of the change of the DC side impedance modulus and time to achieve quantitative evaluation of the degree of transformer aging.

2. According to claim 1, a synchronous testing device for time-frequency domain response of oil-paper insulation, characterized in that: The frequency domain excitation instruction is an excitation signal for setting a sweep frequency range and an AC voltage amplitude, the sweep frequency range is 0.001 to 1000 Hz, the AC voltage amplitude range is 0 to 5 volts, and the peak-to-peak value of the voltage output by the excitation signal after passing through the power amplifier (2) is 0 to 2000 volts; the time domain excitation instruction is for setting a DC voltage amplitude, and the DC voltage amplitude range is 0 to 2000 volts.

3. According to claim 1, a synchronous testing device for time-frequency domain response of oil-paper insulation, characterized in that: The AC side protection resistor (3) and the DC side protection resistor (4) are used to prevent the AC voltage source and the DC voltage source from being damaged after the test object (8) breaks down. The AC side protection resistor (3) and the DC side protection resistor (4) adopt a first set value.

4. The oil-paper insulation time-frequency domain response synchronous testing device according to claim 1, characterized in that: The DC blocking capacitor (7) is used to prevent the DC side voltage from being applied to the AC signal source; the high-voltage silicon stack (9) uses a product with a second set value withstand voltage level to prevent the AC voltage from being applied to the DC high voltage side.

5. A method for evaluating the aging state of oil-paper insulation by synchronous testing of time-frequency domain response, the method being implemented based on a synchronous testing device for time-frequency domain response of oil-paper insulation according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1, setting the frequency domain excitation instruction including the sweep frequency range and the AC voltage amplitude, the time domain excitation instruction including the DC voltage amplitude on the DC side, and the test temperature; Step 2: Perform a time-frequency domain response synchronization test on the AC side at each frequency point within the frequency sweep range, and collect the AC signal of the test product on the AC side and the DC signal of the test product on the DC side during the test at each frequency point; Step 3: The host computer obtains the AC impedance at the set test temperature according to the collected AC signal and the AC voltage amplitude applied to the product to be tested, and draws the AC impedance and frequency change curve; the host computer obtains the DC impedance at the set test temperature according to the collected DC signal and the DC voltage amplitude applied to the product to be tested, and draws the DC impedance and time change curve; Step 4: The AC impedance and frequency variation curve and the DC impedance and time variation curve obtained by the test are both used as test curves, and the test curves are Fourier transformed to generate a transformed impedance curve. The transformed impedance modulus value in the transformed impedance curve and the original impedance modulus value in the test curve are averaged and normalized to obtain the normalized impedance modulus value and frequency variation curve of the AC side and the normalized impedance modulus value and time variation curve of the DC side; Step 5: Obtain the DP value based on the AC side normalized impedance module value and frequency change curve and the DC side normalized impedance module value and time change curve, and combine the following formula: Where DP is the degree of polymerization of the oil-impregnated paperboard; A(T) is the fitting parameter on the AC side, and B(T) is the fitting parameter on the DC side, which is related to the test temperature T; Z ac (f n ) is the nth test frequency point f n Normalized impedance modulus value of the AC side under, n = 1, 2,,,, N, N is the number of test frequency points, Z ac (f n ) is in ohms; Z dc (t m ) is the mth test time point t m Normalized impedance modulus value of the DC side at , m=1,2,…,M, M is the number of test time points, Z dc (t m ) is measured in ohms.

6. The aging state evaluation method of oil-paper insulation time-frequency domain response synchronous test according to claim 5 is characterized in that: The AC side fitting parameters A(T) and the DC side fitting parameters B(T) are obtained through preliminary experiments. The specific process includes the following steps: Step 1, set the test temperature range and interval; prepare P groups of test products with known DP values ​​(8); Step 2: within the set test temperature range, Q test temperatures are extracted according to the set intervals, and a time-frequency domain response synchronization test experiment is performed on the P group DP value of the test product (8) at each test temperature. The time-frequency domain response synchronization test experiment is implemented in steps 1 to 5. The overdetermined equation group is obtained by the experiment: In the overdetermined system, DP1, DP2, ... DP P is the DP value of the P group of test products (8), and the P DP values ​​are not equal; A(T i ) and B(T i ) is the i-th test temperature T within the test range i AC and DC parameters, i = 1, 2, ..., Q; A (T i ) and B(T i ) is obtained by automatically optimizing the above-mentioned overdetermined equations; Step 4: The AC parameter test data A(T1), A(T2), ..., A(T Q ) is fitted to the AC side fitting parameter A(T): A(T)=3.45e 0.025T / 4.35+0.448 Step 5: The DC parameter test data B(T1), B(T2), ..., B(T Q ) is fitted to the DC side fitting parameter B(T): B(T)=0.255e 0.01T+0.468 。 7. The aging state evaluation method of oil-paper insulation time-frequency domain response synchronous test according to claim 5 or 6 is characterized in that: The test temperature T ranges from 10 degrees Celsius to 90 degrees Celsius, and the test temperature T interval is a third set value.

8. The aging state evaluation method of oil-paper insulation time-frequency domain response synchronous test according to claim 5 is characterized in that: Drawing a DC impedance and time variation curve includes: dividing the time spent on testing the product to be tested into m test time periods, the equivalent impedance value of each test time period is the average value of the impedance of the head end test point and the impedance of the end test point in the test time period, and drawing the DC impedance and time variation curve according to the impedance value of each test time period and the time spent on testing the product to be tested.

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