GIS Withstand Voltage Test Breakdown Location Method and System Based on Distributed Optical Fiber

Abstract

The present invention relates to the field of breakdown location in GIS withstand voltage tests, and specifically relates to a method and system for breakdown location in GIS withstand voltage tests based on distributed optical fibers. A continuous distributed optical fiber is linearly arranged along the metal shell of the main circuit of the GIS under test. A laser light source continuously outputs optical pulse signals with a preset power, frequency, and pulse width to the starting end of the distributed optical fiber. Utilizing the principle that the vibration generated by the breakdown of the GIS will cause a change in the refractive index of the optical fiber, thereby changing the waveform of the backscattered light, the optoelectronic detection unit collects the backscattered light in real time and performs coherent averaging noise reduction processing. On the basis of constructing a reference signal of the backscattered light in the normal state, the signal processing unit timely discovers and extracts the distortion points of the backscattered light signal waveform caused by the breakdown vibration of the GIS through comparison. Finally, the fault point location module accurately reads the corresponding time unit and accurately calculates the breakdown fault point of the GIS. The present invention is applicable to breakdown location in GIS withstand voltage tests.

Description

Technical Field

[0001] The present invention relates to the field of breakdown location in the withstand voltage test of GIS (Gas Insulated Switchgear), and particularly to a method and system for breakdown location in the withstand voltage test of GIS based on distributed optical fiber. Background Art

[0002] The AC withstand voltage test is used to check whether the internal insulation strength of GIS meets the standard requirements, and it also helps to detect defects such as internal particulate foreign matters, poor conductor contact, and abnormal mechanical vibration. It is a crucial test to determine whether GIS meets the commissioning conditions. During the withstand voltage test of GIS, breakdown faults caused by equipment defects occur from time to time. In order to repair the equipment most quickly, avoid repeated pressurization as much as possible, and effectively improve the test efficiency, it is very necessary to find the breakdown point of GIS in a timely and accurate manner.

[0003] In the past ten-odd years, various types of technologies and devices for breakdown location in the withstand voltage test of GIS have been researched and developed at home and abroad. Representative ones include methods and devices such as multi-point ultrasonic amplitude location, multi-point vibration amplitude location, multi-point ultrasonic time delay location, acoustic-electric combined location, and multi-point acoustic signal location, which have promoted the improvement of the method for finding the breakdown location point in the withstand voltage test of GIS from inefficient and extensive means such as "locating by listening to sounds", repeating pressurization by changing states, detecting gas decomposition products in each gas chamber one by one, and disassembling and inspecting multiple gas chambers to scientific calculation and accurate location.

[0004] However, from a large number of on-site application experiences, the existing ultrasonic amplitude location devices, multi-point vibration amplitude location devices, and multi-point acoustic signal location devices have relatively low location accuracy, and due to reasons such as oscillation superposition or refraction and reflection of signals in the special structure of the GIS tubular cavity, there is still a relatively high possibility of misjudgment. On the one hand, the multi-point ultrasonic time delay location devices and acoustic-electric combined location devices have complex principles, time-consuming layout, and high costs. On the other hand, the layout of sensors has a great influence on the location results, and the uncertainty of the signal transmission path restricts the scientific and reasonable layout of sensors before the test, and location failure may occur due to the sensor coverage range. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method and system for breakdown location in the withstand voltage test of GIS based on distributed optical fiber, which improves the accuracy of calculating the breakdown fault point of GIS.

[0006] The present invention adopts the following technical solutions to achieve the above purpose. In the first aspect, the present invention provides a method for breakdown location in the withstand voltage test of GIS based on distributed optical fiber, including:

[0007] S1. Continuously output an optical pulse signal with a preset power, frequency, and pulse width to the distributed optical fiber through a laser light source, collect the backscattered light in real time and convert it into an electrical signal, and simultaneously perform coherent averaging noise reduction processing on the collected backscattered light signal;

[0008] S2. Divide the electrical signal converted from the backscattered light after noise reduction on average, select the maximum signal amplitude sampled during each time unit for the signal amplitude corresponding to each time unit, complete the discretization processing of the continuous signal, and obtain a list of backscattered light signal amplitudes for each time unit;

[0009] S3. Starting from the initial signal, extract multiple groups of the list of backscattered light signal amplitudes for cross-correlation analysis until it is determined that the multiple groups of signals extracted are similar. Under the unified time axis, take the average value of the amplitudes of the same time unit of multiple groups of waveforms to construct a backscattered light reference signal;

[0010] S4. During the withstand voltage test, continuously collect the backscattered light signal in real time. After a breakdown fault occurs in the GIS, extract the list of backscattered light signal amplitudes at the moment of breakdown, compare it with the backscattered light reference signal under the unified time axis, calculate the waveform distortion rate of each time unit, and extract the signals of the time units where all waveform distortion rates reach or exceed the alarm value;

[0011] S5. Extract multiple lists of backscattered light signal amplitudes after the GIS breakdown, compare them with the signals of the time units where the waveform distortion rate of the backscattered light waveform at the moment of breakdown reaches or exceeds the alarm value under the unified time axis. If it conforms to the breakdown vibration characteristics, it is judged as a waveform distortion caused by the GIS breakdown fault;

[0012] S6. Extract the maximum waveform distortion point of the backscattered light signal caused by the GIS breakdown fault, calculate the position of the GIS corresponding to the maximum waveform distortion point, and this position is the GIS breakdown fault point.

[0013] Furthermore, the method further includes:

[0014] Before the withstand voltage test, arrange the continuous distributed optical fiber linearly along the metal shell of the GIS under test. The continuous distributed optical fiber is in close contact with the metal shell. Connect the laser light source to the input end of the circulator, connect the isolation end of the circulator to the starting end of the continuous distributed optical fiber, and connect the output end of the circulator to the photoelectric detection unit.

[0015] Furthermore, the frequency of the optical pulse signal with a preset power satisfies , where c is the speed of light 3×10 8 m / s, is the refractive index of the used distributed optical fiber under normal conditions, is the straight-line length of the metal housing of the GIS main circuit for the test subject, i.e., the total length of the continuously distributed optical fiber arranged, and the pulse width of the optical pulse signal with a preset power W should satisfy , △ L is the distance resolution, and the power P should satisfy , P R is the minimum backward scattering light power that the optoelectronic detection unit can recognize, and S L is the comprehensive backward scattering coefficient considering the scattering coefficient, backward scattering factor, and distance attenuation coefficient.

[0016] Furthermore, the coherent averaging noise reduction process is to add and average multiple groups of stable backward scattering light under the unified time axis. The expression of the signal-to-noise ratio SNR after noise reduction is: ;

[0017] In the formula, M is the number of backward scattering light signals participating in the coherent averaging noise reduction process, is the average value of the amplitude coefficients of the M groups of backward scattering light signals participating in the coherent averaging noise reduction process, P r is the power of the backward scattering light signal with a unit amplitude, K is the total number of sampling points of a single backward scattering light signal, and σ is the variance of the background noise of the M groups of backward scattering light signals participating in the coherent averaging noise reduction process.

[0018] Furthermore, step S3 specifically includes:

[0019] S301. Starting from the initial signal, extract the amplitude lists of multiple groups of backward scattering light signals, and perform discrete signal cross-correlation degree R mn analysis, and the expression is: ;

[0020] In the formula, R mn is the cross-correlation degree between the m th signal and the n th signal, T i m is the amplitude of the m th signal at the i th unit time, and T i n is the amplitude of the n th signal at the i th unit time, m ≤N, n ≤N;

[0021] S302. Until the cross-correlation degree of the extracted multiple groups of backscattered light signals is not less than the set value, it is determined that the initial state signal is stable after the continuous distributed optical fiber is combined with the metal shell of the GIS main circuit under test, and a reference signal is constructed.

[0022] S303. Under the unified time axis, the amplitudes of the multiple groups of backscattered light with cross-correlation degrees not less than the set value are listed, and the average value is taken at the same time unit amplitude to construct a backscattered light reference signal. The expression of the amplitude of each time unit of the backscattered light reference signal is:

[0023] ;

[0024] In the formula, T rei is the signal amplitude of the i th time unit of the backscattered light reference signal;

[0025] S304. The constructed backscattered light reference signal is used as the initial signal for this withstand voltage test.

[0026] Furthermore, the calculation method of the waveform distortion rate is as follows:

[0027] ;

[0028] In the formula, S B1i is the signal distortion rate of the i th time unit of the first backscattered light signal collected after breakdown, and T i B1 is the signal amplitude of the i th time unit of the first backscattered light signal collected after breakdown.

[0029] Furthermore, meeting the breakdown vibration characteristics specifically includes:

[0030] If the alarm value and , then it meets the breakdown vibration characteristics;

[0031] In the formula, S Bmi is the signal distortion rate of the m th time unit of the i th backscattered light signal collected after breakdown, and S Bni is the signal distortion rate of the n th time unit of the i th backscattered light signal collected after breakdown, m is greater than n and less than or equal to the number of the amplitude list of the backscattered light signals extracted after the GIS breakdown.

[0032] Furthermore, the method for calculating the GIS position corresponding to the maximum waveform distortion point is as follows:

[0033] ;

[0034] In the formula, L is the distance between the calculated breakdown fault point and the starting end of the optical fiber, i.e., the position of the fault breakdown point, t i is the time unit corresponding to the maximum waveform distortion point of the backscattered optical signal, t N is the Nth time unit of the divided backscattered optical signal.

[0035] In a second aspect, the present invention provides a breakdown positioning system for GIS withstand voltage test based on distributed optical fiber, which is used to implement the above-mentioned breakdown positioning method for GIS withstand voltage test based on distributed optical fiber. The system includes:

[0036] An optical pulse generating module that continuously outputs an optical pulse signal with a preset power, frequency, and pulse width to the distributed optical fiber through a laser light source;

[0037] A signal acquisition module that continuously acquires the backscattered light in real time through a photoelectric detection unit and converts it into an electrical signal, and simultaneously performs coherent averaging noise reduction processing on the acquired backscattered optical signal;

[0038] A signal processing module that performs average division on the noise-reduced backscattered optical conversion signal, selects the maximum signal amplitude sampled during each time unit corresponding to the signal amplitude, completes the discretization processing of the continuous signal, and obtains a list of backscattered optical signal amplitudes for each time unit;

[0039] Starting from the initial signal, multiple groups of the backscattered optical signal amplitude lists are extracted for cross-correlation analysis until it is determined that the multiple groups of signals extracted are similar. After averaging the amplitudes of the same time unit of multiple groups of waveforms under the unified time axis, a backscattered optical reference signal is constructed;

[0040] During the withstand voltage test, the backscattered light is continuously acquired in real time. After a breakdown fault occurs in the GIS, the backscattered optical signal amplitude list at the moment of breakdown is extracted, and it is compared with the backscattered optical reference signal under the unified time axis, the waveform distortion rate of each time unit is calculated, and the signals of all time units whose waveform distortion rate reaches or exceeds the alarm value are extracted;

[0041] A fault point positioning module that extracts multiple backscattered optical signal amplitude lists after the GIS breakdown, and compares them with the signals of the time units whose waveform distortion rate of the backscattered optical waveform at the moment of breakdown reaches or exceeds the alarm value under the unified time axis. If it conforms to the breakdown vibration characteristics, it is determined as the waveform distortion caused by the GIS breakdown fault;

[0042] Extract the maximum waveform distortion point of the backscattered light signal caused by the GIS breakdown fault, and calculate the GIS position corresponding to the maximum waveform distortion point. This position is the GIS breakdown fault point.

[0043] Furthermore, after constructing the backscattered light reference signal, the waveform distortion rate alarm value set by the signal processing module makes the GIS metal shell vibrate by knocking and uses a vibration sensor to detect the vibration value of the GIS metal shell, and calculates the waveform distortion rate per unit time of the backscattered light corresponding to the vibration position with an acceleration of 5 m / s 2 and sets it as the waveform distortion rate alarm value during this GIS withstand voltage test.

[0044] The beneficial effects of the present invention are as follows:

[0045] The present invention overcomes the problems of the existing GIS withstand voltage test breakdown location methods, either having more layout points, low positioning accuracy, being easily interfered and resulting in positioning errors, or having complex principles, high costs, and the layout being restricted by the GIS structure and having a greater impact on the positioning results. Continuously distributed optical fibers are linearly arranged on the surface of the GIS main circuit metal shell. A laser light source continuously outputs optical pulse signals to the starting end of the distributed optical fibers. The photoelectric detection unit real-time collects the backscattered light signals. Using the principle that the vibration generated by the GIS breakdown will cause changes in the refractive index of the optical fiber and thus change the waveform of the backscattered light, the waveform distortion points of the backscattered light signals caused by the GIS breakdown vibration are timely discovered and extracted by comparison, the corresponding time unit is accurately read, and the GIS breakdown fault point is accurately calculated.

[0046] Before each GIS withstand voltage test, the present invention debugs and presets the optimal optical pulse signal power, frequency, and pulse width according to the actual working conditions, so as to obtain the best backscattered light resolution, anti-interference ability, and positioning accuracy. The backscattered light is real-time collected and processed by coherent averaging for noise reduction to further improve the signal-to-noise ratio of the backscattered light signal. On the basis of constructing the backscattered light reference signal in the normal state, the waveform distortion rate alarm value is scientifically set through vibration calibration, and the maximum waveform distortion point of the backscattered light signal during the GIS withstand voltage test breakdown is extracted, and then accurate positioning calculation can be carried out.

[0047] The present invention has simple layout, simple debugging, and clear criteria. The GIS breakdown positioning accuracy does not exceed 1 meter. The interference caused by external knocking on the GIS metal shell is excluded by the breakdown time, and the positioning result has high credibility. The sampling rate required for the system to collect the backscattered light signal is not high, and the computing power required for signal processing is not high. The optical fiber used as the sensor and signal transmission cable has a relatively low price, and the total length usually does not exceed 1 km, taking into account both the engineering application effect and economy. Description of the Drawings

[0048] Figure 1It is the flowchart of the breakdown location method for GIS withstand voltage test based on distributed optical fiber provided by the embodiments of the present invention;

[0049] Figure 2 It is the schematic diagram of the reference signal of the backscattered light of the distributed optical fiber and the backscattered light signal affected by the vibration of the GIS housing;

[0050] Figure 3 It is the structural block diagram of the GIS withstand voltage test breakdown location system based on distributed optical fiber provided by the embodiments of the present invention. Specific embodiments

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0052] The present invention provides a breakdown location method for GIS withstand voltage test based on distributed optical fiber, as Figure 1 shown, which specifically includes:

[0053] S1. Before the withstand voltage test, arrange the continuous distributed optical fiber linearly along the metal housing of the GIS under test. The continuous distributed optical fiber is in close contact with the metal housing. Connect the laser light source to the input end of the circulator, connect the isolation end of the circulator to the starting end of the continuous distributed optical fiber, and connect the output end of the circulator to the photoelectric detection unit.

[0054] S2. The laser light source continuously outputs optical pulse signals with a preset power, frequency, and pulse width to the distributed optical fiber through the circulator. The photoelectric detection unit collects the backscattered light in real time through the output end of the circulator at a sampling rate not lower than 200 MS / s and converts it into an electrical signal. At the same time, perform coherent averaging noise reduction processing on the collected backscattered light signal.

[0055] The optical pulse signals with preset power, frequency, and pulse width should meet the comprehensive requirements of anti-interference ability, resolution, and positioning accuracy. Specifically, the frequency of the optical pulse signal with preset power meets , where c is the speed of light 3×10 8 m / s, is the refractive index of the used distributed optical fiber under normal conditions, is the straight-line length of the metal housing of the GIS under test, that is, the total length of the arranged continuous distributed optical fiber. The pulse width of the optical pulse signal with preset power W should meet , △ L is the distance resolution, and the power P should meet , P Ris the minimum backward scattering light power that can be recognized by the optoelectronic detection unit, S L is the comprehensive backward scattering coefficient considering the scattering coefficient, backward scattering factor, and distance attenuation coefficient.

[0056] Specifically, the coherent averaging noise reduction process is to add and average multiple groups of stable backward scattering light under the unified time axis. The expression of the signal-to-noise ratio SNR after noise reduction is:

[0057] ;

[0058] In the formula, M is the number of backward scattering light signals participating in the coherent averaging noise reduction process, is the average value of the amplitude coefficients of M groups of backward scattering light signals participating in the coherent averaging noise reduction process, P r is the power of the backward scattering light signal with unit amplitude, K is the total number of sampling points of a single backward scattering light signal, and σ is the variance of the background noise of the M groups of backward scattering light signals participating in the coherent averaging noise reduction process.

[0059] S3. The converted backward scattering light signal after noise reduction is evenly divided with a time unit not greater than 10 ns. The signal amplitude corresponding to each time unit selects the maximum signal amplitude sampled during that period to complete the discretization process of the continuous signal. The N time units of the divided backward scattering light signals t ={ t 1 , t 2 ,..., t i , t i+1 ,..., t N}, and the list T of the backward scattering light signal amplitudes for each time unit = {T 1 , T 2 ,..., T i , T i+1 ,..., T N}.

[0060] S4. Starting from the initial signal, extract multiple groups of the list of the backward scattering light signal amplitudes for cross-correlation analysis until it is determined that the multiple groups of signals extracted are similar. Under the unified time axis, take the average value of the amplitudes of the same time unit of multiple groups of waveforms to construct the backward scattering light reference signal T re ={T re1 , T re2 ,..., T rei , T re（i+1） ,..., T reN};

[0061] Specifically, it includes:

[0062] S401. Starting from the initial signal, extract multiple sets of backscattered light signal amplitude lists, and perform discrete signal cross-correlation analysis under the unified time axis. The expression is as follows: R mn ;

[0063] ;

[0064] In the formula, R mn is the cross-correlation degree between the m th signal and the n th signal. T i m is the amplitude of the m th signal at the i th unit time, and T i n is the amplitude of the n th signal at the i th unit time, m ≤N, n ≤N;

[0065] S402. Until the cross-correlation degrees of the multiple sets of backscattered light signals extracted are all not less than the set value, it is determined that the initial state signal is stable after the continuous distributed optical fiber is combined with the metal shell of the GIS main circuit under test, and a reference signal is constructed;

[0066] S403. Under the unified time axis, construct a backscattered light reference signal T by taking the average value of the amplitudes of the multiple sets of backscattered light amplitude lists whose cross-correlation degrees are all not less than the set value at the same time unit amplitude. re ={T re1 , T re2 ,..., T rei , T re（i+1） ,..., T reN}. The expression for the amplitude of each time unit of the backscattered light reference signal is:

[0067] ;

[0068] In the formula, T rei is the signal amplitude of the i th time unit of the backscattered light reference signal;

[0069] S404. The constructed backscattered light reference signal is used as the initial signal for this withstand voltage test. Without being affected by external severe vibrations, the backscattered light signal monitored in real time is similar to the backscattered light reference signal T re .

[0070] During the withstand voltage test, continuously and real-time collect the backscattered light. After a breakdown fault occurs in the GIS, extract the list of amplitudes of the backscattered light signals at the moment of breakdown, compare it with the reference signal of the backscattered light under the unified time axis, calculate the waveform distortion rate for each time unit, and extract the signals of the time units where all waveform distortion rates reach or exceed the alarm value.

[0071] Specifically, the calculation method of the waveform distortion rate is as follows:

[0072] ;

[0073] In the formula, S B1i is the signal distortion rate of the i th time unit of the first backscattered light signal collected after breakdown, and T i B1 is the signal amplitude of the i th time unit of the first backscattered light signal collected after breakdown.

[0074] S6. Extract at least D lists of amplitudes of the backscattered light signals after the GIS breakdown, compare them with the signals of the time units where the waveform distortion rate of the backscattered light at the moment of breakdown reaches or exceeds the alarm value under the unified time axis. If it conforms to the breakdown vibration characteristics, it is judged as the waveform distortion caused by the GIS breakdown fault.

[0075] Specifically, conforming to the breakdown vibration characteristics specifically includes:

[0076] If the alarm value and , then it conforms to the breakdown vibration characteristics;

[0077] In the formula, S Bmi is the signal distortion rate of the m th time unit of the i th backscattered light signal collected after breakdown, and S Bni is the signal distortion rate of the n th time unit of the i th backscattered light signal collected after breakdown, m is greater than n and less than or equal to the number of the list of amplitudes of the backscattered light signals extracted after the GIS breakdown.

[0078] S7. Extract the maximum waveform distortion point of the backscattered light signal caused by the GIS breakdown fault, calculate the corresponding GIS position of the maximum waveform distortion point, and this position is the GIS breakdown fault point.

[0079] Specifically, the method for calculating the GIS position corresponding to the maximum waveform distortion point is as follows:

[0080] ;

[0081] In the formula, L is the calculated distance between the breakdown fault point and the starting end of the optical fiber, i.e., the position of the fault breakdown point. t i is the time unit corresponding to the maximum waveform distortion point of the backscattered optical signal.

[0082] As Figure 3 shown, the present invention also provides a breakdown positioning system for GIS withstand voltage test based on distributed optical fiber. The system includes:

[0083] An optical pulse generating module, which includes a laser light source and an input end of a circulator, and is used to continuously output an optical pulse signal with a preset power, frequency, and pulse width to the starting end of the continuous distributed optical fiber; on the basis of calculating the length of the distributed optical fiber, the parameters of the optical pulse signal such as power, frequency, and pulse width should be comprehensively optimized and determined according to the actual situations such as anti-interference ability, resolution, and positioning accuracy during the debugging of the positioning system.

[0084] The optical pulse generating module continuously outputs an optical pulse signal with a preset power, frequency, and pulse width to the distributed optical fiber through the laser light source;

[0085] A signal acquisition module, which uses a photoelectric detection unit to collect the backscattered optical signal in real time and convert it into an electrical signal, and at the same time performs coherent averaging noise reduction processing on the collected backscattered optical signal;

[0086] A signal processing module divides the denoised backscattered optical conversion signal evenly, selects the maximum signal amplitude sampled during each time unit for the signal amplitude corresponding to each time unit, completes the discretization processing of the continuous signal, and obtains a list of backscattered optical signal amplitudes for each time unit;

[0087] Starting from the initial signal, multiple groups of the backscattered optical signal amplitude lists are extracted for cross-correlation analysis until it is determined that the multiple groups of signals extracted are similar. After taking the average value of the amplitudes of the same time unit of multiple groups of waveforms under the unified time axis, a backscattered optical reference signal is constructed;

[0088] During the withstand voltage test, the backscattered optical signal is continuously collected in real time. After a breakdown fault occurs in the GIS, the backscattered optical signal amplitude list at the breakdown moment is extracted, and it is compared with the backscattered optical reference signal under the unified time axis, the waveform distortion rate of each time unit is calculated, and the signals of all time units whose waveform distortion rate reaches or exceeds the alarm value are extracted;

[0089] A fault point positioning module extracts multiple backscattered optical signal amplitude lists after the breakdown of the GIS, and compares them with the signals of the time units whose waveform distortion rate of the backscattered optical signal at the breakdown moment reaches or exceeds the alarm value under the unified time axis. If it conforms to the breakdown vibration characteristics, it is judged as the waveform distortion caused by the breakdown fault of the GIS.

[0090] Extract the maximum waveform distortion point of the backscattered optical signal caused by the breakdown fault of the GIS, and calculate the GIS position corresponding to the maximum waveform distortion point. This position is the GIS breakdown fault point.

[0091] Specifically, after constructing the backscattered optical reference signal, the waveform distortion rate alarm value set by the signal processing module creates vibrations in the GIS metal housing by tapping and uses a vibration sensor to detect the vibration value of the GIS metal housing, and calculates the waveform distortion rate per unit time of the backscattered light corresponding to the vibration position with an acceleration of 5 m / s 2 and sets it as the waveform distortion rate alarm value during this GIS withstand voltage test. The distributed optical fiber backscattered optical reference signal and the backscattered optical signal affected by the vibration of the GIS housing are as Figure 2 shown.

[0092] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in related fields. Any changes and variations made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A GIS withstand voltage test breakdown location method based on distributed optical fiber, characterized in that: include: S1, continuously outputting optical pulse signals of preset power, frequency and pulse width to distributed optical fibers through a laser light source, collecting backscattered light in real time and converting it into an electrical signal, and performing coherent averaging noise reduction processing on the collected backscattered light signal; S2, evenly divide the electrical signal converted from the backscattered light after noise reduction, select the maximum signal amplitude sampled during the signal amplitude corresponding to each time unit, complete the continuous signal discretization processing, and obtain a list of backscattered light signal amplitudes for each time unit; S3, starting from the initial signal, extracting multiple groups of backscattered light signal amplitude lists for cross-correlation analysis until it is determined that the extracted multiple groups of signals are similar, and taking the average of the amplitudes of the multiple groups of waveforms in the same time unit on a unified time axis to construct a backscattered light reference signal; S4. During the withstand voltage test, the backscattered light signal is continuously collected in real time. After a breakdown fault occurs in the GIS, a list of backscattered light signal amplitudes at the moment of breakdown is extracted, and the list is compared with the backscattered light reference signal under a unified time axis. The waveform distortion rate of each time unit is calculated, and the signals of all time units whose waveform distortion rates reach or exceed the alarm value are extracted; S5. Extract a list of multiple backscattered light signal amplitudes after GIS breakdown, and compare them with the signal of the time unit when the waveform distortion rate of the backscattered light at the moment of breakdown reaches or exceeds the alarm value under the unified time axis. If it meets the breakdown vibration characteristics, it is determined that the waveform distortion is caused by the GIS breakdown fault; S6. Extract the maximum waveform distortion point of the backscattered light signal caused by the GIS breakdown fault, and calculate the GIS position corresponding to the maximum waveform distortion point, which is the GIS breakdown fault point.

2. The method for GIS withstand voltage test breakdown location based on distributed optical fiber according to claim 1 is characterized in that: The method further includes: Before the voltage test, the continuously distributed optical fiber is arranged in a straight line along the metal shell of the main circuit of the tested GIS. The continuously distributed optical fiber is in close contact with the metal shell. The laser light source is connected to the input end of the circulator, the isolation end of the circulator is connected to the starting end of the continuously distributed optical fiber, and the output end of the circulator is connected to the photoelectric detection unit.

3. The GIS withstand voltage test breakdown location method based on distributed optical fiber according to claim 1 is characterized in that: Frequency of optical pulse signal with preset power satisfy , where c The speed of light is 3×10 8 m / s, is the refractive index of the distributed optical fiber used under normal conditions, is the straight length of the metal shell of the main circuit of the tested GIS, i.e. the total length of the continuously distributed optical fiber, and the pulse width of the optical pulse signal with the preset power W Should meet ,△ L is the distance resolution, the power P Should meet , P R is the minimum backscattered light power that the photoelectric detection unit can identify, S L It is the comprehensive backscattering coefficient that takes into account the scattering coefficient, backscattering factor, and distance attenuation coefficient.

4. The GIS withstand voltage test breakdown location method based on distributed optical fiber according to claim 1 is characterized in that: The coherent average noise reduction process is to add and average multiple groups of stable backscattered light under the same time axis. The signal-to-noise ratio (SNR) after noise reduction is expressed as: ; Where M is the number of backscattered light signals involved in the coherent average denoising process, is the average value of the amplitude coefficients of the backscattered light signals of group M participating in the coherent average denoising process, P r is the power of the backscattered light signal with unit amplitude, K is the total number of sampling points of a single backscattered light signal, and σ is the variance of the background noise of the M groups of backscattered light signals participating in the coherent average denoising process.

5. The GIS withstand voltage test breakdown location method based on distributed optical fiber according to claim 1 is characterized in that: Step S3 specifically includes: S301, starting from the initial signal, extract multiple groups of backscattered light signal amplitude lists, and perform discrete signal cross-correlation on a unified time axis R mn Analysis, the expression is: ； In the formula, R mn For the m The signal and n The cross-correlation of the signals, T i m For the m Signal No. i The amplitude per unit time, T i n For the n Signal No. i The amplitude per unit time, m ≤N, n ≤N; S302, until the cross-correlations of the extracted multiple groups of backscattered light signals are not less than the set value, it is determined that the initial state signal after the continuous distributed optical fiber is combined with the metal shell of the main circuit of the tested GIS is stable, and a reference signal is constructed; S303, under the same time axis, a list of multiple backscattered light amplitudes whose cross-correlations are not less than the set value is extracted, and then the average value of the amplitude in the same time unit is taken to construct a backscattered light reference signal. The amplitude expression of each time unit of the backscattered light reference signal is: ; Where, T rei is the backscattered light reference signal i The signal amplitude per time unit; S304: The constructed backscattered light reference signal is used as the initial signal for this voltage withstand test.

6. The GIS withstand voltage test breakdown location method based on distributed optical fiber according to claim 1 is characterized in that: The waveform distortion rate is calculated as follows: ; In the formula, S B1i is the first backscattered light signal collected after breakdown. i The signal distortion rate per time unit, T i B1 is the first backscattered light signal collected after the breakdown i The signal amplitude per time unit.

7. The method for GIS withstand voltage test breakdown location based on distributed optical fiber according to claim 5 is characterized in that: The breakdown vibration characteristics include: like Alarm value and , then it meets the breakdown vibration characteristics; In the formula, S Bmi The first m The backscattered light signal i The signal distortion rate per time unit, S Bni The first n The backscattered light signal i The signal distortion rate per time unit, m Greater than n and less than or equal to the number of lists of backscattered light signal amplitudes extracted after GIS breakdown.

8. The method for GIS withstand voltage test breakdown location based on distributed optical fiber according to claim 1 is characterized in that: The GIS position corresponding to the maximum waveform distortion point is calculated as follows: ; In the formula, L The calculated distance between the breakdown fault point and the starting end of the optical fiber is the fault breakdown point position. t i is the time unit corresponding to the point of maximum waveform distortion of the backscattered light signal, t N is the Nth backscattered light signal time unit divided.

9. A GIS withstand voltage test breakdown location system based on distributed optical fiber, used to implement a GIS withstand voltage test breakdown location method based on distributed optical fiber as claimed in any one of claims 1 to 8, characterized in that: The system includes: The optical pulse generation module continuously outputs optical pulse signals of preset power, frequency and pulse width to the distributed optical fiber through a laser light source; The signal acquisition module collects the backscattered light in real time through the photoelectric detection unit and converts it into an electrical signal, and at the same time performs coherent averaging noise reduction processing on the collected backscattered light signal; The signal processing module evenly divides the backscattered light conversion signal after noise reduction, selects the maximum signal amplitude sampled during the signal amplitude corresponding to each time unit, completes the continuous signal discretization processing, and obtains the backscattered light signal amplitude list of each time unit; Starting from the initial signal, extracting multiple groups of backscattered light signal amplitude lists for cross-correlation analysis until it is determined that the extracted multiple groups of signals are similar, and constructing a backscattered light reference signal after averaging the amplitudes of the multiple groups of waveforms in the same time unit on a unified time axis; During the withstand voltage test, the backscattered light is continuously collected in real time. After a breakdown fault occurs in the GIS, a list of backscattered light signal amplitudes at the moment of breakdown is extracted, which is compared with the backscattered light reference signal under a unified time axis, the waveform distortion rate of each time unit is calculated, and the signals of all time units whose waveform distortion rates reach or exceed the alarm value are extracted; The fault location module extracts a list of multiple backscattered light signal amplitudes after GIS breakdown, and compares them with the signal of the time unit when the waveform distortion rate of the backscattered light at the moment of breakdown reaches or exceeds the alarm value under the same time axis. If it meets the breakdown vibration characteristics, it is judged to be the waveform distortion caused by the GIS breakdown fault. The maximum waveform distortion point of the backscattered light signal caused by the GIS breakdown fault is extracted, and the GIS position corresponding to the maximum waveform distortion point is calculated, and the position is the GIS breakdown fault point.

10. The GIS withstand voltage test breakdown positioning system based on distributed optical fiber according to claim 9 is characterized in that: The waveform distortion rate alarm value set by the signal processing module is used to construct the backscattered light reference signal. The GIS metal shell is vibrated by knocking and the vibration sensor is used to detect the vibration value of the GIS metal shell. The vibration acceleration is calculated to be 5m / s 2 The waveform distortion rate of the backscattered light per unit time corresponding to the vibration position is set as the waveform distortion rate alarm value during this GIS withstand voltage test.

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