GIS insulation defect diagnosis method and system based on test voltage fluctuation

Abstract

This invention relates to the field of high-voltage testing technology and discloses a method and system for diagnosing GIS insulation defects based on test voltage fluctuations. The method includes: S1, acquiring the voltage applied to the GIS at a sampling rate of not less than AMS / s; S2, digitizing the voltage on the GIS to obtain a set of voltage values ​​during the acquisition period; S3, obtaining a list of maximum voltage values ​​for each time period; S4, calculating the voltage change rate of the applied voltage on the GIS for each time period based on the list of maximum voltage values, wherein each instance of a voltage change rate exceeding 5% in adjacent time periods is defined as a voltage abnormal fluctuation event; S5, determining the type of voltage abnormal fluctuation event based on the waveform characteristics of the voltage fluctuation; and S6, identifying three or more voltage abnormal fluctuation events determined to be caused by partial insulation breakdown discharge. This invention can accurately detect insulation defects affecting the safe operation of GIS.

Description

Technical Field

[0001] This invention relates to the field of high voltage testing technology, and specifically to a method and system for diagnosing GIS insulation defects based on test voltage fluctuations. Background Technology

[0002] Newly built and overhauled gas-insulated switchgear (GIS) requires on-site AC withstand voltage testing to check whether the equipment was transported and installed correctly, and whether the internal insulation was damaged or degraded, ensuring that the GIS meets the requirements for commissioning.

[0003] The GIS field AC withstand voltage test is achieved through a series resonance method. If the equipment does not break down or flashover after applying the specified voltage for 1 minute, the test is considered passed. During the GIS AC withstand voltage test, if through discharge occurs due to burrs on the conductor or shell surface, foreign objects on the shell surface, or defects in the solid insulation, the series resonant withstand voltage test device will be unable to continue the test because the capacitance of the test circuit changes significantly, thus losing the resonance condition, and the test is considered failed.

[0004] Based on extensive testing experience, solid insulation components in GIS systems with surface contamination or air gap defects may experience localized, non-penetrating breakdowns during withstand voltage tests, accompanied by fluctuations in the test voltage. Because the voltage drop caused by this localized breakdown does not meet the criteria for a penetrating breakdown (series resonant withstand voltage test equipment is typically set to activate protection and stop the test if the voltage drop exceeds 30%), and the test voltage returns to normal after a short period of fluctuation, even if this occurs repeatedly, the test will still be considered passed under existing testing standards and equipment performance. These solid insulation defects, which cannot be detected and diagnosed in a timely manner during GIS AC withstand voltage tests, pose significant hidden dangers to equipment and even the power grid safety after the GIS is put into operation.

[0005] Therefore, it is necessary to design a clear, concise, safe and effective method and system for diagnosing insulation defects during AC withstand voltage tests of GIS, so as to promptly detect latent non-penetrating insulation defects inside GIS. Summary of the Invention

[0006] To address the problem in the prior art that partial breakdown discharge of solid insulation during AC withstand voltage testing of GIS cannot be accurately detected and diagnosed, and that non-penetrating solid insulation defects may not be detected in a timely manner, this invention provides a method and system for diagnosing GIS insulation defects based on test voltage fluctuations. By collecting the voltage applied to the GIS during the AC withstand voltage test, the system determines whether abnormal voltage fluctuation events occur based on the voltage drop, and detects and diagnoses GIS insulation defects based on the type and timing of the abnormal voltage fluctuation events.

[0007] This invention is achieved through the following technical solution:

[0008] A method for diagnosing GIS insulation defects based on test voltage fluctuations, comprising:

[0009] S1. Based on the GIS series resonant AC withstand voltage test circuit, the measured voltage applied to the low-voltage capacitor of the capacitor divider is acquired at a sampling rate of not less than A MS / s to obtain the voltage time-domain waveform.

[0010] S2. The measured voltage is digitized to obtain a set of voltage values ​​of the measured voltage during the acquisition period. The voltage values ​​in the set of voltage values ​​are the specific values ​​acquired at the sampling points corresponding to the sampling rate of A MS / s.

[0011] S3. Divide the voltage values ​​in the voltage value set into an average time unit of Bμs, and obtain a list of the maximum voltage values ​​for each time period, T = {T1, T2, ..., T...} i T i+1 , ..., T N}, where A MS / s*Bμs=C*10 d The number of sampling points, where C is a positive integer not less than 1, and d is a positive number;

[0012] S4. Based on the list of maximum voltage values, calculate the rate of change of the measured voltage in each time period, and obtain the rate of change list ΔT={ΔT 1～2 ΔT 2～3 , ..., ΔT i-1～i ΔT i～i+1 , ..., ΔT N-1～N}, wherein each occurrence of a voltage change rate exceeding 5% in an adjacent time period is defined as a voltage abnormal fluctuation event, and only one voltage abnormal fluctuation event is recorded within a time period of two voltage cycles;

[0013] S5. After the GIS AC withstand voltage test is completed without flashover, list all voltage abnormality fluctuation events in chronological order and determine the type of voltage abnormality fluctuation event based on the characteristics of the voltage fluctuation waveform.

[0014] S6. During the GIS AC withstand voltage test, if three or more abnormal voltage fluctuation events are identified as being caused by partial insulation breakdown discharge, and if such abnormal voltage fluctuation events still occur in the last 10 seconds of the withstand voltage test, even if no breakdown flashover occurs in the final GIS AC withstand voltage test, the GIS insulation is still diagnosed as defective, and the test is deemed unsuccessful.

[0015] As an optimization, A is set to 100 and B to 1.

[0016] As an optimization, the specific steps of S1 are as follows:

[0017] S1.1 Connect the GIS in parallel with the capacitor voltage divider;

[0018] S1.2 Acquire the voltage value applied to the low-voltage capacitor of the capacitor divider at a sampling rate of not less than A MS / s;

[0019] S1.3 Calculate the voltage across the capacitor connected in parallel with the GIS based on the voltage applied to the low-voltage capacitor of the capacitor voltage divider and the voltage division ratio of the capacitor voltage divider, thereby obtaining the voltage applied across the GIS.

[0020] S1.4 Obtain the measured voltage from the low-voltage capacitor of the capacitor divider, and obtain the voltage time-domain waveform based on the measured voltage.

[0021] As an optimization, the voltage time-domain waveform is a sine wave with frequency f and amplitude equal to the voltage value of the GIS. In the formula, L is the inductance of the test circuit and C is the capacitance of the test circuit, which mainly includes GIS and a capacitive voltage divider.

[0022] As an optimization, the expression for the voltage change rate is:

[0023]

[0024] In the formula, T i T is the maximum voltage value collected from the GIS during time period i. i+1 It is the maximum voltage value collected on the GIS during time period i+1.

[0025] As an optimization, the specific steps for S5 are as follows:

[0026] S5.1 Obtain the voltage fluctuation waveform on the GIS within the first half of the voltage cycle corresponding to the start time point of each recorded voltage abnormal fluctuation event during the test.

[0027] S5.2 Obtain the spectral distribution of the voltage fluctuation waveforms for each iteration through continuous wavelet time-frequency transformation;

[0028] S5.3 If the spectrum distribution contains a voltage fluctuation waveform with a component of not less than 30MHz, determine that the voltage fluctuation waveform of the spectrum corresponds to an abnormal voltage fluctuation event caused by partial breakdown discharge of insulation; otherwise, determine that the voltage fluctuation waveform of the spectrum corresponds to an abnormal voltage fluctuation event caused by partial breakdown discharge of non-insulation.

[0029] S5.4 Statistically analyze the voltage fluctuation events corresponding to each voltage fluctuation waveform and their corresponding occurrence times.

[0030] As an optimization, the specific steps of S5.2 are as follows:

[0031] S5.2.1. By flattening and scaling the mother wavelet ψ(t) that satisfies the zero-mean, finite energy, and allowable conditions, the voltage fluctuation waveform signal is decomposed into components ψ of different frequencies. s,u (t) is used to realize the wavelet transform of the voltage fluctuation waveform signal in each iteration. The expression is:

[0032]

[0033] In the formula, s is the translation factor, u is the scaling factor, and t is the time point of the sampled voltage fluctuation waveform signal;

[0034] S5.2.2. Perform amplitude spectrum processing on the different frequency components after wavelet transform, the expression is:

[0035]

[0036] In the formula, E(s,u) represents the amplitude spectrum of the frequency component, x(t) represents the waveform function of the voltage time-domain waveform, and C(s,u) is obtained by continuous wavelet transform of x(t);

[0037] S5.2.3 Obtain the actual frequency corresponding to the actual scale factor u.

[0038] In the formula, F c It is the wavelet center frequency, f t It is the signal sampling frequency;

[0039] S5.2.4. Based on the amplitude spectrum and corresponding frequency obtained from S5.2.2 and S5.2.3, obtain the time-frequency distribution diagram of the voltage fluctuation waveform.

[0040] This invention also discloses a GIS insulation defect diagnosis system based on test voltage fluctuations, for implementing the aforementioned GIS insulation defect diagnosis method based on test voltage fluctuations, comprising:

[0041] A voltage sampling unit is used to acquire the voltage applied to the GIS at a sampling rate of not less than AMS / s to obtain the voltage time-domain waveform.

[0042] An analog-to-digital converter (ADC) is used to convert the analog signal obtained after dividing the low-voltage capacitor measurement voltage of the capacitor divider into a digital signal.

[0043] An event extraction unit is used to calculate the rate of change of the measured voltage of the capacitor voltage divider in each time period, and to detect and extract abnormal voltage fluctuation events.

[0044] The analysis and diagnosis unit is used to judge the extracted voltage abnormal fluctuation events and diagnose whether the GIS has insulation defects based on the type and occurrence time of the voltage abnormal fluctuation events.

[0045] As an optimization, a resistor voltage divider is first used to divide the voltage across the low-voltage capacitor of the capacitor voltage divider, so that the voltage across the low-voltage capacitor is converted into a measurement voltage of 0 to 5V. Then, the voltage time-domain waveform of the measurement voltage is obtained by the opto-isolation chip, thus realizing voltage acquisition.

[0046] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0047] This invention, based on existing GIS series resonant AC withstand voltage tests, detects the transient process of test voltage drops caused by partial breakdown discharge in solid insulation. It comprehensively analyzes the number and timing of insulation degradation events, enabling timely detection of non-penetrating insulation defects. This fills the gap in existing AC withstand voltage test methods that cannot detect certain non-penetrating insulation defects in a timely manner. The method and system of this invention directly acquire, process, and analyze the measured voltage of the voltage transformer to complete the detection and diagnosis. It does not require additional high-voltage test or measurement devices, and is simple, clear, safe, accurate, and inexpensive. It can accurately detect insulation defects that affect the safe operation of GIS. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0049] Figure 1 This is a flowchart illustrating a GIS insulation defect diagnosis method based on test voltage fluctuations in an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of the partial insulation breakdown discharge and the test voltage waveforms of several cycles before and after during the AC withstand voltage test of GIS in an embodiment of the present invention.

[0051] Figure 3 This is a schematic diagram of the voltage waveform spectrum distribution of partial breakdown discharge test during the AC withstand voltage test of GIS in an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of solid insulation defects discovered by a method for diagnosing insulation defects during an AC withstand voltage test of GIS based on test voltage fluctuations, as described in an embodiment of the present invention.

[0053] Figure 5 This is a schematic diagram of the structure of an insulation defect diagnosis system for GIS AC withstand voltage test based on test voltage fluctuation, according to an embodiment of the present invention.

[0054] Figure 6 This is a schematic diagram of the GIS series resonant AC withstand voltage test circuit. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0056] Example 1 provides a method for diagnosing GIS insulation defects based on test voltage fluctuations, such as... Figure 1 As shown, it includes:

[0057] S1. Based on the GIS series resonant AC withstand voltage test circuit, the measured voltage applied to the low-voltage capacitor of the capacitor divider is acquired at a sampling rate of not less than A MS / s to obtain the voltage time-domain waveform; A is a positive number.

[0058] GIS series resonant AC withstand voltage test circuit, such as Figure 6 As shown, C1 and C2 form a capacitor voltage divider, Cx is GIS, L is the inductance of the test circuit, and the capacitor voltage detected during the test is the voltage of C2.

[0059] During the GIS AC withstand voltage test, the measured voltage of the capacitive voltage divider was acquired at a sampling rate of no less than 100 MS / s to obtain the voltage time-domain waveform. This allows for the acquisition of sufficient voltage values ​​for subsequent calculations.

[0060] Specifically:

[0061] S1.1 Connect the GIS in parallel with the capacitor voltage divider;

[0062] S1.2 Acquire the voltage value of the voltage applied to the low-voltage capacitor of the capacitor divider at a sampling rate of not less than 100MS / s;

[0063] C1 and C2 constitute the capacitor voltage divider for the test, and they appear as a single unit. During the test, the voltage across C1 and C2 is the voltage across the test sample CX. The voltage collected is the voltage across C2. The voltage division ratio is the ratio of the voltage division of C2 to C1 and C2, and the voltage across the test sample CX is calculated from this ratio.

[0064] S1.3 Calculate the voltage across the capacitor connected in parallel with the GIS based on the voltage applied to the low-voltage capacitor of the capacitor voltage divider and the voltage division ratio of the capacitor voltage divider, thereby obtaining the voltage applied across the GIS.

[0065] S1.4. Divide the voltage on the low-voltage capacitor of the capacitor divider again to obtain the measured voltage, and obtain the voltage time-domain waveform based on the measured voltage.

[0066] The capacitive voltage divider is connected in parallel with the GIS under test during the AC withstand voltage test. The voltage across the low-voltage capacitor of the capacitive voltage divider is measured, and the voltage applied to the GIS is calculated based on this voltage. During the test, the measured output voltage (the voltage across the low-voltage capacitor) is generally between tens of volts and two hundred volts. First, a resistive voltage divider is used to convert the output voltage into a 0 to 5V measurement voltage. The measurement voltage is then output through an opto-isolation chip to obtain the voltage time-domain waveform of the measurement voltage, thus realizing voltage acquisition.

[0067] The voltage time-domain waveform is approximately a sine wave with a fixed frequency f. In the formula, L represents the inductance of the test circuit, primarily determined by the reactor; C represents the capacitance of the test circuit, mainly consisting of the GIS (Gas Inductor System) and the capacitive voltage divider. According to relevant standards and GIS equipment requirements, the frequency f should be in the range of 30Hz to 300Hz.

[0068] S2. The measured voltage is digitized to obtain a set of voltage values ​​of the measured voltage during the acquisition period. The voltage values ​​in the set of voltage values ​​are the specific values ​​collected at the sampling points corresponding to the sampling rate of AMS / s; that is, the voltage values ​​in the set of voltage values ​​are the values ​​sampled at the sampling rate of 100MS / s.

[0069] S3. Divide the voltage values ​​in the voltage value set into an average time unit of Bμs, and obtain a list of the maximum voltage values ​​for each time period, T = {T1, T2, ..., T...} i T i+1 , ..., T N}, where AMS / s*Bμs=C*10 d The number of sampling points, where B and C are positive integers not less than 1, and d is a positive number;

[0070] In this embodiment, the change in the measured voltage of the capacitor voltage divider during time interval i+1 compared to the maximum voltage value during time interval i is calculated one by one, resulting in a list of the rate of change of voltage ΔT = {ΔT} for each time interval with a step size of 1μs. 1～2 ΔT 2～3 , ..., ΔT i-1～i ΔT i～i+1 , ..., ΔT N-1～N}, the voltage change rate ΔT occurs once in an adjacent time period. i～i+1 If the occurrence rate exceeds 5%, it is considered a voltage abnormality event, and only one voltage abnormality event is recorded within every two voltage cycles.

[0071] S4. Based on the list of maximum voltage values, calculate the rate of change of the measured voltage in each time period, and obtain the rate of change list ΔT={ΔT 1～2 ΔT 2～3 , ..., ΔT i-1～i ΔT i～i+1 , ..., ΔT N-1～N}, wherein each occurrence of a voltage change rate exceeding 5% in an adjacent time period is defined as a voltage abnormal fluctuation event, and only one voltage abnormal fluctuation event is recorded within a time period of two voltage cycles.

[0072] The GIS withstand voltage test uses frequency conversion to find resonance conditions, with a frequency range of 30Hz to 300Hz. One cycle may be 3.3ms-33ms, and two cycles may be 6.6ms-66ms.

[0073] During the withstand voltage test, the GIS insulation may partially break down to the reconstruction test voltage, and the abnormal fluctuation may last for one or two voltage cycles. Therefore, in this invention, starting from the moment the abnormal voltage fluctuation occurs, only one abnormal voltage fluctuation is recorded in the next two voltage cycles to avoid recording a single partial insulation breakdown as multiple occurrences.

[0074] If there are both voltage fluctuation events caused by partial insulation breakdown discharge and voltage fluctuation events caused by non-insulation partial breakdown discharge within two cycles, spectral analysis of the fluctuation signal can determine the presence of voltage fluctuation events caused by partial insulation breakdown discharge as long as there is a spectral component of not less than 30MHz (voltage fluctuations caused by power supply abnormalities usually do not have high-frequency components).

[0075] The expression for the voltage change rate is:

[0076]

[0077] In the formula, T i T is the maximum voltage value collected from the GIS during time period i. i+1 It is the maximum voltage value collected on the GIS during time period i+1, i.e., T i The maximum voltage measured by the capacitor divider during the time period i is T. i+1 It represents the maximum voltage measured by the capacitor divider during the time period i+1.

[0078] S5. After the GIS AC withstand voltage test is completed without flashover, list all voltage abnormality fluctuation events in chronological order and determine the type of voltage abnormality fluctuation event based on the characteristics of the voltage fluctuation waveform.

[0079] The specific steps are as follows:

[0080] S5.1 Obtain the voltage fluctuation waveform on the GIS within the first half of the voltage cycle corresponding to the start time point of each recorded voltage abnormal fluctuation event during the test.

[0081] S5.2 Obtain the spectral distribution of the voltage fluctuation waveforms for each iteration through continuous wavelet time-frequency transformation;

[0082] The specific steps are as follows:

[0083] S5.2.1. By flattening and scaling the mother wavelet ψ(t) that satisfies the zero-mean, finite energy, and allowable conditions, the voltage fluctuation waveform signal is decomposed into components ψ of different frequencies. s,u (t) is used to realize the wavelet transform of the voltage fluctuation waveform signal in each iteration. The expression is:

[0084]

[0085] In the formula, s is the translation factor, u is the scaling factor, and t is the time point of the sampled voltage fluctuation waveform signal;

[0086] S5.2.2. Perform amplitude spectrum processing on the different frequency components after wavelet transform, the expression is:

[0087]

[0088] In the formula, E(s,u) represents the amplitude spectrum of the frequency component, x(t) represents the waveform function of the voltage time-domain waveform, and C(s,u) is obtained by continuous wavelet transform of x(t);

[0089] The time-frequency distribution plot requires the signal amplitude of each frequency band at each time point. Figure 3 The amplitude is indicated by color and shade.

[0090] S5.2.3 Obtain the actual frequency corresponding to the actual scale factor u.

[0091] In the formula, F c It is the wavelet center frequency, f t It is the signal sampling frequency;

[0092] S5.2.4. Based on the amplitude spectrum and corresponding frequency obtained from S5.2.2 and S5.2.3, obtain the time-frequency distribution diagram of the voltage fluctuation waveform.

[0093] Figure 3 The color and shade indicate the amplitude of the signal at each time point and frequency band.

[0094] S5.3 If the spectrum distribution contains a voltage fluctuation waveform with a component of not less than 30MHz, determine that the voltage fluctuation waveform of the spectrum corresponds to an abnormal voltage fluctuation event caused by partial breakdown discharge of insulation; otherwise, determine that the voltage fluctuation waveform of the spectrum corresponds to an abnormal voltage fluctuation event caused by partial breakdown discharge of non-insulation.

[0095] For voltage fluctuation waveforms with a frequency spectrum containing a component above 30MHz, determine the corresponding voltage abnormal fluctuation event caused by partial insulation breakdown discharge; for voltage fluctuation waveforms without a frequency spectrum containing a component above 30MHz, determine the corresponding voltage abnormal fluctuation event caused by other reasons, such as voltage abnormal fluctuation event caused by power supply fluctuation.

[0096] S5.4 Statistically analyze the voltage fluctuation events corresponding to each voltage fluctuation waveform and their corresponding occurrence times.

[0097] A flashover test is automatically considered a failure. However, this invention, for GIS that does not pass the flashover test, determines the presence of non-penetrating latent insulation defects by observing voltage fluctuations during the test.

[0098] Figure 2 This is a waveform of partial insulation breakdown discharge and the test voltage for several cycles before and after during a 220kV GIS AC withstand voltage test. The voltage applied to the GIS during the withstand voltage test was 368kV, and the test frequency was 53.3Hz. The partial insulation breakdown discharge caused the test voltage to drop to its lowest value, with a half-wave abrupt change time of approximately 100ns. After about one cycle of voltage oscillation, because the solid insulation could still withstand the voltage, the test voltage was restored to 368kV, and the test continued.

[0099] Figure 3 It is obtained through continuous wavelet time-frequency transform Figure 2 The waveform's spectral distribution shows a component above 30MHz, indicating that the voltage drop was affected by rapid insulation breakdown, distinguishing it from voltage drops caused by power fluctuations. Figure 3 It can be judged Figure 2 The waveform corresponds to an abnormal voltage fluctuation event caused by partial insulation breakdown discharge.

[0100] S6. During the GIS AC withstand voltage test, if three or more abnormal voltage fluctuation events are identified as being caused by partial insulation breakdown discharge, and if such abnormal voltage fluctuation events still occur in the last 10 seconds of the withstand voltage test, even if no breakdown flashover occurs in the final GIS AC withstand voltage test, the GIS insulation is still diagnosed as defective, and the test is deemed unsuccessful.

[0101] Defective insulation tends to deteriorate over time during the test. Therefore, it is believed that an abnormal voltage fluctuation event caused by partial insulation breakdown discharge should occur at the end of the test.

[0102] Figure 4 The solid insulation defect found in step 6 was met. After the defect was found, an AC withstand voltage test was performed again. The GIS broke down and flashed after about 15 seconds. The test failed.

[0103] Example 2 of the present invention also discloses a GIS insulation defect diagnosis system based on test voltage fluctuations, such as Figure 5 As shown, a GIS insulation defect diagnosis method based on test voltage fluctuations, as described above, includes:

[0104] A voltage sampling unit is used to acquire the voltage applied to the GIS at a sampling rate of not less than AMS / s to obtain the voltage time-domain waveform; for example, the voltage sampling unit is used to acquire the voltage measured by the capacitive voltage divider at a sampling rate of not less than 100MS / s; firstly, a resistor voltage divider is used to convert the measured voltage of the capacitive voltage divider to 0 to 5V, and then the voltage is acquired after being output through an opto-isolation chip to realize the voltage acquisition of the GIS.

[0105] An analog-to-digital converter (ADC) is used to convert the analog signal obtained after dividing the low-voltage capacitor measurement voltage of the capacitor divider into a digital signal.

[0106] An event extraction unit is used to calculate the rate of change of the measured voltage of the capacitor voltage divider in each time period, and to detect and extract abnormal voltage fluctuation events.

[0107] The analysis and diagnosis unit is used to judge the extracted voltage abnormal fluctuation events and diagnose whether the GIS has insulation defects based on the type and occurrence time of the voltage abnormal fluctuation events.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for diagnosing GIS insulation defects based on test voltage fluctuations, characterized in that, include: S1. Based on the GIS series resonant AC withstand voltage test circuit, the measured voltage applied to the low-voltage capacitor of the capacitor divider is acquired at a sampling rate of not less than A MS / s to obtain the voltage time-domain waveform. S2. The measured voltage is digitized to obtain a set of voltage values ​​of the measured voltage during the acquisition period. The voltage values ​​in the set of voltage values ​​are the specific values ​​acquired at the sampling points corresponding to the sampling rate of A MS / s. S3. Divide the voltage values ​​in the voltage value set into an average time unit of B μs, and obtain a list of the maximum voltage values ​​for each time period T={T1, T2, ..., T...} i T i+1 , ..., T N }, where A MS / s*B μs= The number of sampling points, where C is a positive integer not less than 1, and d is a positive number; S4. Based on the list of maximum voltage values, calculate the rate of change of the measured voltage in each time period, and obtain the rate of change list ΔT={ΔT 1~2 ΔT 2~3 , ..., ΔT i-1~i ΔT i~i+1 , ..., ΔT N-1~N }, wherein each occurrence of a voltage change rate exceeding 5% in an adjacent time period is defined as a voltage abnormal fluctuation event, and only one voltage abnormal fluctuation event is recorded within a time period of two voltage cycles. S5. After the GIS AC withstand voltage test is completed without flashover, list all voltage abnormality fluctuation events in chronological order and determine the type of voltage abnormality fluctuation event based on the characteristics of the voltage fluctuation waveform. The specific steps are as follows: S5.1 Obtain the voltage fluctuation waveform on the GIS within the first half of the voltage cycle corresponding to the start time point of each recorded voltage abnormal fluctuation event during the test. S5.2 Obtain the spectral distribution of the voltage fluctuation waveforms for each iteration through continuous wavelet time-frequency transformation; S5.3 If the spectrum distribution contains a voltage fluctuation waveform with a component of not less than 30MHz, determine that the voltage fluctuation waveform of the spectrum corresponds to an abnormal voltage fluctuation event caused by partial breakdown discharge of insulation; otherwise, determine that the voltage fluctuation waveform of the spectrum corresponds to an abnormal voltage fluctuation event caused by partial breakdown discharge of non-insulation. S5.4 Statistically analyze the voltage fluctuation events corresponding to each voltage fluctuation waveform and their corresponding occurrence times; S6. During the GIS AC withstand voltage test, if three or more abnormal voltage fluctuation events are identified as being caused by partial insulation breakdown discharge, and if such abnormal voltage fluctuation events still occur in the last 10 seconds of the withstand voltage test, even if no breakdown flashover occurs in the final GIS AC withstand voltage test, the GIS insulation is still diagnosed as defective, and the test is deemed unsuccessful.

2. The method for diagnosing GIS insulation defects based on test voltage fluctuations according to claim 1, characterized in that, A is 100, B is 1.

3. The method for diagnosing GIS insulation defects based on test voltage fluctuations according to claim 1, characterized in that, The specific steps of S1 are as follows: S1.1 Connect the GIS in parallel with the capacitor voltage divider; S1.2 Acquire the voltage value applied to the low-voltage capacitor of the capacitor divider at a sampling rate of not less than A MS / s; S1.3 Calculate the voltage across the capacitor connected in parallel with the GIS based on the voltage applied to the low-voltage capacitor of the capacitor voltage divider and the voltage division ratio of the capacitor voltage divider, thereby obtaining the voltage applied across the GIS. S1.

4. Divide the voltage on the low-voltage capacitor of the capacitor divider again to obtain the measured voltage, and obtain the voltage time-domain waveform based on the measured voltage.

4. The method for diagnosing GIS insulation defects based on test voltage fluctuations according to claim 1, characterized in that, The voltage time-domain waveform is a sine wave with frequency f and amplitude equal to the voltage value of the GIS. In the formula, L is the inductance of the test circuit and C is the capacitance of the test circuit.

5. The method for diagnosing GIS insulation defects based on test voltage fluctuations according to claim 1, characterized in that, The expression for the voltage change rate is: ； In the formula, T i T is the maximum voltage value collected from the GIS during time period i. i+1 It is the maximum voltage value collected on the GIS during time period i+1.

6. The method for diagnosing GIS insulation defects based on test voltage fluctuations according to claim 5, characterized in that, The specific steps in S5.2 are as follows: S5.2.1, By using a mother wavelet that satisfies the conditions of zero mean, finite energy, and admissibility. By performing flattening and stretching transformations, the voltage fluctuation waveform signal is decomposed into components of different frequencies. To achieve wavelet transform of the voltage fluctuation waveform signal, the expression is: ， In the formula, s is the translation factor, u is the scaling factor, and t is the time point of the sampled voltage fluctuation waveform signal; S5.2.

2. Perform amplitude spectrum processing on the different frequency components after wavelet transform, the expression is: ; In the formula, The amplitude spectrum represents the frequency components. A waveform function representing the voltage time-domain waveform. Depend on Obtained after continuous wavelet transform; S5.2.3 Obtain the actual frequency corresponding to the actual scale factor u. ; In the formula, F c It is the wavelet center frequency, f t It is the signal sampling frequency; S5.2.

4. Based on the amplitude spectrum and corresponding frequency obtained from S5.2.2 and S5.2.3, obtain the time-frequency distribution diagram of the voltage fluctuation waveform.

7. A GIS insulation defect diagnosis system based on test voltage fluctuation, used to implement the GIS insulation defect diagnosis method based on test voltage fluctuation as described in any one of claims 1-6, characterized in that, include: A voltage sampling unit is used to acquire the voltage applied to the GIS at a sampling rate of not less than A MS / s to obtain the voltage time-domain waveform; An analog-to-digital converter (ADC) is used to convert the analog signal obtained after dividing the low-voltage capacitor measurement voltage of the capacitor divider into a digital signal. An event extraction unit is used to calculate the rate of change of the measured voltage of the capacitor voltage divider in each time period, and to detect and extract abnormal voltage fluctuation events. The analysis and diagnosis unit is used to judge the extracted voltage abnormal fluctuation events and diagnose whether the GIS has insulation defects based on the type and occurrence time of the voltage abnormal fluctuation events.

8. The GIS insulation defect diagnosis system based on test voltage fluctuation according to claim 7, characterized in that, First, a resistor voltage divider is used to divide the voltage across the low-voltage capacitor of the capacitor voltage divider, converting the voltage across the low-voltage capacitor into a measurement voltage of 0 to 5V. Then, the voltage time-domain waveform of the measurement voltage is output through an opto-isolation chip, thus realizing voltage acquisition.

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