Deterioration State Detection System and Method for Damp Cable Joints Based on Multi-Feature Quantity Acquisition

Abstract

The present invention discloses a detection system and method for the deterioration state of a damp cable joint based on multi-feature quantity acquisition. The method includes the steps of: S1, encapsulating the cable intermediate joint in a gas sampling bag and grounding the grounding wire of the cable; S2, providing a preset test voltage for the cable through a power adjustment device and keeping it unchanged; S3, during the continuous power-on process, detecting the discharge signals of the cable body and the grounding wire through a discharge feature acquisition device and performing on-line monitoring and analysis; S4, when a discharge signal with a significant waveform change is monitored, opening the air valve of the air pump to pump air and analyzing the characteristic gas components and contents through a gas chromatograph; S5, after the acquisition is completed, identifying, extracting and analyzing the discharge signals to obtain effective discharge waveforms; S6, comprehensively analyzing the results to evaluate the deterioration state of the cable intermediate joint. The method of the present invention can effectively evaluate the deterioration state of the damp cable intermediate joint and has high reliability.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network cable fault detection, and specifically relates to a detection system and method for the deterioration state of a damp cable joint based on multi-feature quantity acquisition. Background Art

[0002] Distribution cables are one of the most important equipment in the distribution network. Due to their advantages of not occupying ground space resources, relatively high transmission capacity, and good safety performance, they have become an important part of urban and rural power supply networks, especially the distribution networks of megacities. As a connecting component of the cable line, the cable intermediate joint is one of the weak points in the current operation safety of distribution network cable lines. Research shows that due to the problems of water accumulation and dirt accumulation in the operation environment of distribution network cables, the cable intermediate joints of faulty distribution network cables generally have the defect of internal moisture, and intermittent arc grounding faults along the axial direction will occur at the XLPE-SiR insulation interface of the cable intermediate joints containing such defects. The discharge energy causes ablation damage to the insulating medium at the interface and also damages the grounding system of the line, ultimately leading to major accidents such as breakdown discharge and even fire. Therefore, it is necessary to analyze the discharge evolution process of damp distribution network cable intermediate joints, study the relationship between the discharge evolution process of damp cables and physical characteristics such as discharge waveforms and cracked gases, and provide a theoretical basis for realizing the online monitoring of the operation state of distribution network cable joints and ensuring the safety of distribution network operation.

[0003] In the existing research on the discharge of cable intermediate joints, most of them are for the simulation analysis of the electric field distortion caused by defects such as knife marks, air gaps, moisture, stress cone misalignment, and metal debris residues at the interface, and the discharge situation is judged by comparing the maximum electric field strength of the electric field distortion with the air breakdown threshold; secondly, the method of constructing artificial defects is used to carry out simulation tests to study the partial discharge situation, and the discharge situation during the breakdown process of the test slice material under different conditions is tested. The existing technology lacks an experimental analysis method for the change of the insulation performance of a true-type cable intermediate joint after being damp and the long-term evolution process of the discharge. Summary of the Invention

[0004] The first object of the present invention is to overcome the disadvantages and deficiencies existing in the prior art, and provide a detection system for the deterioration state of a damp cable joint based on multi-feature quantity acquisition. The detection system has a simple structure, is easy to operate, and has high detection accuracy.

[0005] The second object of the present invention is to provide a detection method for the deterioration state of a damp cable joint based on multi-feature quantity acquisition, which can effectively evaluate the deterioration state of a damp cable intermediate joint and has high reliability.

[0006] The object of the present invention is achieved by the following technical solutions: A deterioration state detection system for a damp cable joint based on multi-feature quantity acquisition, including a power supply adjustment device, a discharge feature acquisition device, and a characteristic gas acquisition device. The power supply adjustment device is used to connect to both ends of the cable where the cable intermediate joint is located and provide a preset test voltage. The discharge feature acquisition device is used to detect the discharge signals of the cable body and the grounding wire and analyze them.

[0007] The characteristic gas acquisition device includes a gas sampling bag, an air pump, and a gas chromatograph. The gas sampling bag is used to encapsulate the cable intermediate joint. One end of the air pump extracts test gas through a test port opened on the gas sampling bag, and the other end is connected to the gas chromatograph through a gas valve. The gas chromatograph is used to analyze the composition and content of the test gas.

[0008] Preferably, the discharge feature acquisition device includes a discharge signal collector, a high-frequency current transformer, and a medium-low-frequency current transformer. The high-frequency current transformer is used to detect the discharge signal of the cable body and transmit it to the discharge signal collector. The medium-low-frequency current transformer is used to detect the discharge signal of the grounding wire and transmit it to the discharge signal collector. The discharge signal collector is used to extract and analyze the discharge signal.

[0009] Preferably, the power supply adjustment device includes an AC power supply, a voltage regulator, and a transformer. The AC power supply is connected to both ends of the cable through the voltage regulator and the transformer in sequence. A fuse is connected in series at the output end of the AC power supply, and a current-limiting resistor is connected in series at the output end of the transformer.

[0010] Preferably, it further includes a simulated cable seepage environment device. The simulated cable seepage environment device is used to make test samples of damp cable intermediate joints. The simulated cable seepage environment device includes a constant temperature and humidity chamber and a reservoir. The constant temperature and humidity chamber is used for pre-aging treatment of cold shrinkage accessories, and the reservoir is used to soak the cable intermediate joint.

[0011] A deterioration state detection method for a damp cable joint based on multi-feature quantity acquisition, applying the above detection system, specifically includes the following steps:

[0012] S1. Encapsulate the cable intermediate joint in the gas sampling bag, leaving the cable terminal ends at both ends, and ground the grounding wire of the cable.

[0013] S2. Connect the power supply adjustment device to both ends of the cable where the cable intermediate joint is located, turn on the power supply to provide a preset test voltage and keep it unchanged.

[0014] S3. During the continuous power-on process, detect the discharge signal of the grounding wire through the medium-low-frequency transformer of the discharge feature acquisition device, detect the discharge signal of the cable body through the high-frequency transformer of the discharge feature acquisition device, and perform on-line monitoring of the discharge signal through the discharge signal collector of the discharge feature acquisition device.

[0015] S4. When a discharge signal with a significant waveform change is detected, use a suction pump to extract the test gas through the test port of the gas sampling bag, and analyze the characteristic gas components and contents in the test gas by a gas chromatograph;

[0016] S5. After the acquisition is completed, disconnect the power supply, identify, extract and analyze the discharge signals collected by the discharge signal collector to obtain effective discharge waveforms;

[0017] S6. Based on the analysis results of the characteristic gas components and contents and the discharge waveforms, evaluate the deterioration state of the cable joint.

[0018] Preferably, in step S4, the discharge signals with significant changes include single sharp pulse discharges, discharge pulse clusters and sine signals; the characteristic gas components include methane, hydrogen and carbon dioxide.

[0019] Preferably, in step S5, use Python programming to identify, extract and analyze the discharge signals collected by the discharge signal collector, which specifically includes the steps of:

[0020] S51. Data segmentation processing:

[0021] Segment the data with 1 million sampling points. In this segment, place a segmentation time window P1 with a length of 1000 sampling points for sliding sampling, and judge and record the discharge waveform;

[0022] S52. Judgment of effective discharge waveforms:

[0023] Since there is a large difference in peak values between the discharge signal and the background noise waveform, adopt the method of combining the mean-standard deviation of the discharge amplitude within the sampling time window P2 and the noise threshold to judge the discharge signal that satisfies formula (1) as an effective discharge waveform:

[0024] , formula (1),

[0025] Where: , ,

[0026] In the formula, v a , σ are respectively the mean and standard deviation of the discharge amplitude within the sampling time window P2, v i is the discharge amplitude of the i-th sampling point, n is the number of sampling points, k is a coefficient, v f is the noise threshold;

[0027] S53. Calculate the starting point and ending point of the effective discharge waveform:

[0028] The discharge amplitude v that satisfies Equation (1) is called the overlimit value. Find the first overlimit value within the sampling time window P2 and traverse forward. Take the point where the slope of the discharge waveform is 0 as the starting point of this discharge waveform;

[0029] Find the last overlimit value within the sampling time window P2 and traverse backward. Take the point where the slope of the discharge waveform is 0 as the ending point of this discharge waveform. Obtain a complete discharge waveform based on the starting point and the ending point;

[0030] S54. Calculate the macroscopic discharge waveform characteristics:

[0031] Calculate the macroscopic discharge waveform characteristics under different deterioration stages according to the discharge waveform. The macroscopic discharge waveform characteristics include discharge repetition rate, discharge pulse width, and discharge pulse amplitude.

[0032] Preferably, in step S6, the evaluation specifically includes: based on the discharge characteristics of the effective discharge waveforms collected within one power frequency cycle and the results of the characteristic gas analysis, determine whether the cable joint sample has deteriorated into the early, middle, or late stage:

[0033] The early stage meets the conditions:

[0034] The discharge characteristics include: the discharge repetition rate < 4 times / second, the average discharge pulse width is on the order of 10 -4 seconds, the discharge pulse amplitude detected by the high-frequency current transformer is less than 0.2 V, the discharge pulse amplitude detected by the medium-low frequency current transformer is less than 0.1. The results of the characteristic gas analysis include: the characteristic gas contains methane or hydrogen, and the gas content of methane or hydrogen is less than 0.001%;

[0035] The middle stage meets the conditions:

[0036] The discharge characteristics include: the discharge repetition rate is 70 - 90 times / second, the average discharge pulse width is on the order of 10 -3 seconds, the discharge pulse amplitude detected by the high-frequency current transformer is greater than 0.7 V, the range of the discharge pulse amplitude detected by the medium-low frequency current transformer is 0.09 V - 0.3 V. The results of the characteristic gas analysis include: the range of the gas content of methane or hydrogen is 0.001% - 0.005%;

[0037] The late stage meets the conditions:

[0038] The discharge characteristics include: the discharge repetition rate is less than 1.5 times / second, the average discharge pulse width is on the order of 10 -6 seconds, the discharge pulse amplitudes detected by both the high-frequency current transformer and the medium-low frequency current transformer are less than 0.2 V. The results of the characteristic gas analysis include: the gas content of methane or hydrogen is greater than 0.1%, and the gas content of carbon dioxide is greater than 1%.

[0039] Preferably, before step S1, it further includes fabricating a test sample of a damp cable joint, which specifically includes the following steps:

[0040] S01. Aging pretreatment: Place the cold shrinkable accessory in a constant temperature greenhouse for aging to simulate the stress relaxation phenomenon under the actual operation of the cable joint;

[0041] S02. Test sample fabrication: Fabricate an intermediate cable joint using the cold shrinkable accessory after aging pretreatment. The intermediate cable joint includes silicone rubber insulation, a semiconductive layer, and a stress cone;

[0042] S03. Damp treatment: Immerse the fabricated intermediate cable joint in a reservoir for several days.

[0043] Preferably, between step S02 and step S03, it further includes the following step:

[0044] Pretest of the test sample: Immerse some of the fabricated intermediate cable joints in methylene blue solution, apply different currents to the cable, and observe whether there is methylene blue solution at the interface of the XLPE-SiR composite insulation material inside the intermediate cable joint and whether there are traces of oxidation and blackening on the surface of the connecting pipe. If so, it indicates that the test sample can simulate the damp defect at the interface of the joint in a water-soaked environment.

[0045] The present invention has the following advantages and effects compared with the prior art:

[0046] (1) A method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition provided by the present invention collects multi-feature quantities including discharge signals and characteristic gases during the deterioration process of a damp intermediate cable joint in the energized state, identifies and extracts effective discharge waveforms, analyzes the composition and content of the characteristic gases. Both the discharge signal and the content of the characteristic gases have a high correlation with the deterioration state of the damp intermediate cable joint. The two feature quantities can verify each other, realizing an effective and accurate assessment of the deterioration state of the damp intermediate cable joint, with high reliability, and providing a data basis for studying the judgment of the development of insulation defects and fault diagnosis after the intermediate cable joint is damp.

[0047] (2) The test sample of the cable joint of the present invention can be a damp cable in actual operation or a fabricated simulated damp cable joint sample. By adopting the latter, it is possible to quickly and efficiently simulate cable intermediate joints with different operating years for research, and analyze the regular relationship between the discharge evolution process of the damp cable joint and physical characteristics such as discharge waveforms and cracked gases. The method for fabricating the test sample of the damp cable joint of the present invention, through aging pretreatment of the cable intermediate joint, on the one hand, can reduce the interface holding force and simulate the stress relaxation phenomenon under the actual operation of the cable joint, so that the sample is close to the actual situation of the damp defect at the joint interface; on the other hand, it can effectively shorten the time required for the test, and at the same time, it can also conduct research on cable intermediate joints with different operating years.

[0048] (3) A deterioration state detection system for a damp cable joint based on multi-characteristic quantity acquisition provided by the present invention includes a power supply adjustment device, a discharge characteristic acquisition device, and a characteristic gas acquisition device. The discharge characteristic acquisition device detects the discharge signal and identifies and extracts effective discharge waveforms, and the characteristic gas acquisition device collects and analyzes the components and contents of the characteristic gases. The detection system has a simple structure, is easy to operate, and has high detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is the equivalent circuit diagram of the deterioration state detection system for a damp cable joint based on multi-characteristic quantity acquisition of the present invention.

[0050] Figure 2 It is the structural block diagram of the deterioration state detection system for a damp cable joint based on multi-characteristic quantity acquisition of the present invention.

[0051] Figure 3 It is the flow schematic diagram of the deterioration state detection method for a damp cable joint based on multi-characteristic quantity acquisition of the present invention.

[0052] Figure 4 It is the typical discharge waveform distribution diagram of different deterioration stages in Embodiment 2 of the present invention. Among them, (a) is the early deterioration stage, (b) is the middle deterioration stage, and (c) is the late deterioration stage.

[0053] Figure 5 It is the schematic diagram of the characteristic gas content distribution in Embodiment 2 of the present invention.

[0054] Figure 6 It is the structural schematic diagram of the test sample of the damp cable joint of the present invention.

[0055] Among them, 1 is a high-frequency current transformer; 2 is the cable body section; 3 is a medium-low frequency current transformer; 4 is a copper mesh and a grounding wire; 5 is an inner sheath; 6 is a copper shielding layer; 7 is an outer semiconductive layer; 8 is a stress cone; 9 is a cross-linked polyethylene XLPE insulation; 10 is a silicone rubber SiR insulation; 11 is a protective shell; 12 is a semiconductive tape; 13 is an inner semiconductive layer; 14 is a compression joint; 15 is a copper conductor. Specific embodiments

[0056] The present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0057] Embodiment 1

[0058] As Figure 1-2 shown, a deteriorated state detection system for a damp cable joint based on multi-feature quantity acquisition includes a power supply adjustment device, a discharge feature acquisition device, and a characteristic gas acquisition device. The power supply adjustment device is used to connect the two ends of the cable where the cable intermediate joint is located and provide a preset test voltage; the discharge feature acquisition device is used to detect the discharge signal of the cable body and the grounding wire and perform analysis.

[0059] The characteristic gas acquisition device includes a gas sampling bag, an air pump, and a gas chromatograph. The gas sampling bag is used to encapsulate the cable intermediate joint. One end of the air pump extracts test gas through a test port opened in the gas sampling bag, and the other end is connected to the gas chromatograph through a gas valve. The gas chromatograph is used to analyze the composition and content of the test gas.

[0060] The discharge feature acquisition device includes a discharge signal collector, a high-frequency current transformer, and a medium-low frequency current transformer. The high-frequency current transformer is used to detect the discharge signal of the cable body and transmit it to the discharge signal collector. The medium-low frequency current transformer is used to detect the discharge signal of the grounding wire and transmit it to the discharge signal collector. The discharge signal collector is used to extract and analyze the discharge signal.

[0061] The power supply adjustment device includes an AC power supply, a voltage regulator, and a transformer. The AC power supply is connected to the two ends of the cable through the voltage regulator and the transformer in sequence; a fuse is connected in series at the output end of the AC power supply, and a current-limiting resistor is connected in series at the output end of the transformer.

[0062] It further includes a simulated cable seepage environment device. The simulated cable seepage environment device is used to make a test sample of a damp cable intermediate joint. The simulated cable seepage environment device includes a constant temperature and humidity chamber and a reservoir. The constant temperature and humidity chamber is used for cold shrinkable accessory aging pretreatment, and the reservoir is used for soaking the cable intermediate joint.

[0063] Specifically, a deterioration state detection system for a damp cable joint based on multi-feature quantity acquisition provided by the present invention includes a power supply regulating device, a discharge feature acquisition device, and a characteristic gas acquisition device. The discharge feature acquisition device detects a discharge signal and identifies and extracts an effective discharge waveform. Among them, in this embodiment, the discharge signal collector is a computer. The characteristic gas acquisition device collects and analyzes the composition and content of the characteristic gas. The detection system has a simple structure, is easy to operate, and has high detection accuracy. Among them, the composition of the characteristic gas acquisition device is as shown in Figure 1 shown. The present invention adopts a portable gas chromatograph. The injection method for detection is solid-phase microextraction injection. It uses a heated micro mechanical injector inside and a chip-type TCD, which can accurately control the intake sample.

[0064] Embodiment 2

[0065] As Figure 3 shown is a schematic flow chart of a method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition. Applying the detection system described in Embodiment 1, it specifically includes the following steps:

[0066] S1. Enclose the cable intermediate joint in a gas sampling bag, leaving the cable terminal connectors at both ends, and ground the grounding wire of the cable.

[0067] S2. Connect the power supply regulating device to both ends of the cable where the cable intermediate joint is located, and turn on the power supply to provide a preset test voltage and keep it unchanged.

[0068] S3. During the continuous power-on process, detect the discharge signal of the grounding wire through the medium-low frequency mutual inductor of the discharge feature acquisition device, detect the discharge signal of the cable body through the high-frequency mutual inductor of the discharge feature acquisition device, and perform on-line monitoring of the discharge signal through the discharge signal collector of the discharge feature acquisition device.

[0069] S4. When a discharge signal with a significant waveform change is monitored, use a suction pump to extract the test gas through the test port of the gas sampling bag.

[0070] S5. After the acquisition is completed, disconnect the power supply, analyze the composition and content of the characteristic gas in the test gas through a gas chromatograph, and at the same time identify, extract, and analyze the discharge signal collected by the discharge signal collector to obtain an effective discharge waveform.

[0071] S6. Make an assessment of the deterioration state of the cable intermediate joint according to the analysis results of the composition and content of the characteristic gas and the discharge waveform.

[0072] Specifically, a method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition provided by the present invention collects multi-features including discharge signals and characteristic gases during the deterioration process of a damp cable intermediate joint in the energized state, uses a multi-state quantity acquisition system to test the deterioration degree of the damp cable intermediate joint, and gives a method for dividing its deterioration stage, providing a means for judging the operating state of the line for the actual distribution network line operation and maintenance; the two feature quantities can verify each other, effectively and accurately evaluate the deterioration state of the damp cable intermediate joint, and have high reliability.

[0073] First, encapsulate the cable intermediate joint sample inside a gas sampling bag, leaving the terminal blocks at both ends of the joint. Install the current conduction line on both sides of the pre-treated damp cable intermediate joint sample, adjust the voltage regulator, quickly boost the test sample to the preset test voltage and keep it unchanged. In this embodiment, the test voltage is taken as 5.8 kV.

[0074] Then connect the discharge signal collector to the medium and low frequency current transformer to detect the discharge signal on the grounding wire, and at the same time connect the high frequency current transformer to collect the discharge signal on the cable body as a supplement, and observe the discharge signal at the internal interface of the cable intermediate joint online.

[0075] During the continuous power-on process, as the deterioration process of the damp cable intermediate joint progresses, multi-feature quantities are collected for the damp cable intermediate joint. Specifically, it includes:

[0076] For the discharge waveform: During the entire deterioration process of the cable, sharp pulse discharges, discharge pulse clusters, and power frequency sine signals will appear in sequence until the sine signal appears and remains for 1 minute, that is, the collection of the discharge waveform is completed.

[0077] For the characteristic gas: It is collected according to the discharge waveform situation. When a discharge signal with a significant change in waveform is collected, the significant change in the discharge signal includes a single sharp pulse discharge, a discharge pulse cluster, and a sine signal. When any of these three waveforms appears, start the air pump and open the air pump of the collection bag to collect the gas for 2 minutes, then the air pump and the air pump can be closed to complete the collection of the characteristic gas in the corresponding deterioration stage.

[0078] Complete the collection according to the expected time, disconnect the power supply, and perform data extraction and analysis. It includes passing the characteristic gas collected in different stages into a portable gas chromatograph for component and content analysis. Among them, the characteristic gas components include methane, hydrogen, and carbon dioxide. Analyze the gas content through the gas chromatograph to be used in combination with the subsequent discharge signal characteristics to judge the deterioration stage of the cable intermediate joint sample based on the multi-feature quantity analysis results. In the present invention, an air pump and a portable gas chromatograph are used for gas sampling and analysis to ensure high sensitivity of the detection;

[0079] It also includes exporting the discharge signal, and sampling and analyzing the discharge waveform by using Python programming on a computer. By integrating the two analysis results, the discharge rules and gas characteristics at different stages of the whole process of moisture deterioration of the cable joint can be clarified, and the basis for dividing the deterioration stages can be given, providing a data basis for judging the development of insulation defects and fault diagnosis after the cable joint is affected by moisture.

[0080] In step S5, use Python programming to identify, extract, and analyze the discharge signal collected by the discharge signal collector, which specifically includes the following steps:

[0081] S51. Data segmentation processing:

[0082] Segment the data into segments of 1 million sampling points. In each segment, place a sliding sampling with a segmentation time window P1 of 1000 sampling points in length, and judge and record the discharge waveform.

[0083] S52. Judgment of effective discharge waveforms:

[0084] Since there is a large difference in peak values between the discharge signal and the background noise waveform, adopt the method of combining the mean-standard deviation of the discharge amplitude within the sampling time window P2 and the noise threshold, and judge the discharge signal whose sampling value satisfies formula (1) as a valid discharge waveform:

[0085] , formula (1),

[0086] Where: , ,

[0087] In the formula, v a , σ are the mean and standard deviation of the discharge amplitude within the sampling time window P2 respectively, v i is the discharge amplitude of the i-th sampling point, n is the number of sampling points, k is a coefficient, and v f is the noise threshold;

[0088] S53. Calculate the start and end points of the effective discharge waveform:

[0089] Define the discharge amplitude v that satisfies formula (1) as the over-limit value. Find the first over-limit value within the sampling time window P2 and traverse forward, and take the point where the slope of the discharge waveform is 0 as the start point of this discharge waveform;

[0090] Find the last over-limit value within the sampling time window P2 and traverse backward, and take the point where the slope of the discharge waveform is 0 as the end point of this discharge waveform. Obtain a complete discharge waveform based on the start and end points;

[0091] S54. Calculate the macroscopic discharge waveform characteristics:

[0092] Calculate the macroscopic discharge waveform characteristics at different degradation stages based on the discharge waveform. The macroscopic discharge waveform characteristics include discharge repetition rate, discharge pulse width, and discharge pulse amplitude.

[0093] Specifically, in this embodiment, considering the large amount of data, in order to prevent the problem of program memory overrun, it is necessary to first segment the data. To prevent the segmentation position from just being in the discharge waveform and affecting the waveform data sampling, when performing data segmentation, first, a time window needs to be placed at the last 1000 sampling points of this segment, called the segmentation time window P1, which is used to judge whether there is a discharge at the segmentation point of this segment. If there is, the segmentation time window P1 continues to slide backward by 1000 sampling points, and the discharge waveform within the time window P1 is judged until there is no discharge waveform in P1.

[0094] In the judgment of the effective discharge waveform, if the sampling value exceeds k times the mean plus or minus the variance, it can be determined that there is a discharge waveform at this place. To avoid the situation of taking noise as the discharge waveform sampling due to only noise in the segmentation, a noise threshold will be defined here. v f For filtering. In this embodiment, let k take the value of 2. v f Take the value of 0.05. In this embodiment, it is set that a section of waveform needs to satisfy that the sampling value exceeds k times the mean plus or minus the variance and at the same time exceeds the noise threshold to be determined as an effective discharge once, that is, formula (1).

[0095] To sample and analyze the discharge waveform and calculate the discharge pulse width, it is necessary to perform a sliding analysis on a time window over the data segment. Here, this time window is called the sliding time window P2. If there is an overrun value within the sliding time window P2, find the first overrun value within P2 and traverse forward until a point with a waveform slope of 0 is found, which is used as the starting point of this discharge waveform, and start recording the discharge waveform from this time; P2 continues to slide backward. If there is still an overrun value within P2, record all the waveforms within P2, and continue to push P2 backward until there is no overrun value within P2, and stop sampling the discharge waveform. The time window at the place where the discharge waveform sampling stops is called P. 2a Let P 2a be the previous time window of P 2b Let P 2a and P 2b be merged into P 2c Find the last overrun value within P 2c and traverse backward until a point with a waveform slope of 0 is found, which is used as the termination point of this discharge waveform, so as to obtain a complete discharge waveform.

[0096] Based on the complete and valid discharge waveforms obtained according to the above steps, the macroscopic discharge waveform characteristics in different deterioration stages are statistically analyzed, including the discharge repetition rate, discharge pulse width, and discharge pulse amplitude. In this embodiment, the number of discharges within 1 s is defined as the discharge repetition rate, the change in the number of discharges detected within 1 s is statistically analyzed, and the average discharge repetition rate and the highest discharge repetition rate during the discharge process are calculated. For the discharge pulse width, that is, calculate the duration of each discharge pulse. For the discharge pulse amplitude, that is, calculate the voltage value at the amplitude of each discharge pulse.

[0097] In step S6, the evaluation specifically includes: based on the discharge characteristics of the valid discharge waveforms collected within one power frequency cycle and the analysis results of characteristic gases, determine whether the cable joint sample deteriorates into the early, middle, or late stage:

[0098] The early stage meets the conditions:

[0099] The discharge characteristics include: the discharge repetition rate is less than 4 times per second, the average discharge pulse width is on the order of 10 -4 seconds, the discharge pulse amplitude detected by the high-frequency current transformer is less than 0.2 V, the discharge pulse amplitude detected by the medium-low frequency current transformer is less than 0.1, and the analysis results of characteristic gases include: the characteristic gases contain methane or hydrogen, and the gas content of methane or hydrogen is less than 0.001%;

[0100] The middle stage meets the conditions:

[0101] The discharge characteristics include: the discharge repetition rate is 70 - 90 times per second, the average discharge pulse width is on the order of 10 -3 seconds, the discharge pulse amplitude detected by the high-frequency current transformer is greater than 0.7 V, the range of the discharge pulse amplitude detected by the medium-low frequency current transformer is 0.09 V - 0.3 V, and the analysis results of characteristic gases include: the range of the gas content of methane or hydrogen is 0.001% - 0.005%;

[0102] The late stage meets the conditions:

[0103] The discharge characteristics include: the discharge repetition rate is less than 1.5 times per second, the average discharge pulse width is on the order of 10 -6 seconds, the discharge pulse amplitudes detected by both the high-frequency current transformer and the medium-low frequency current transformer are less than 0.2 V, and the analysis results of characteristic gases include: the gas content of methane or hydrogen is greater than 0.1%, and the gas content of carbon dioxide is greater than 1%.

[0104] Specifically, in this embodiment, the detailed reference discharge waveforms and characteristic gas content are shown in Figure 4 and Figure 5 as shown.

[0105] Before step S1, it also includes fabricating a test sample of a damp cable joint, specifically including the steps:

[0106] S01. Aging pretreatment: Place the cold shrinkage accessory in a constant temperature greenhouse box for aging to simulate the stress relaxation phenomenon under the actual operation of the cable joint.

[0107] S02. Test sample fabrication: Use the cold shrinkage accessory after aging pretreatment to fabricate a cable intermediate joint, which includes silicone rubber insulation, a semi-conductive layer, and a stress cone.

[0108] S03. Damp treatment: Place the fabricated cable intermediate joint in a reservoir and soak it for several days.

[0109] Specifically, the test sample of the cable joint of the present invention can be an actually operating damp cable or a fabricated simulated damp cable joint sample. By adopting the latter, it is possible to quickly and efficiently simulate cable intermediate joints with different operating years for research and analyze the regular relationship between the discharge evolution process of the damp cable joint and physical characteristics such as the discharge waveform and cracked gas.

[0110] In this embodiment, first, in the aging pretreatment process, according to the technical specifications of the cold shrinkage accessory of the cable, use a constant temperature and humidity box to set the temperature at 135°C, set the aging time at 168 hours according to the test conditions, and at the same time control the temperature uniformity at ±2.5°C (that is, the difference between the maximum and minimum values of the measured average temperature of each test point in the constant temperature and humidity box within the specified time), control accuracy at ±1°C, and the heating rate ≤ 15°C / minute.

[0111] Then, after the cold shrinkage accessory completes pre-aging, install it at the test site. As Figure 6 shown in the structural schematic diagram of the test sample of the damp cable joint. After cutting off a part of the insulation and the outer shielding layer of the test cable according to the installation process requirements, slip the cold shrinkage specimen of the intermediate joint onto the outer shielding layer of one end of the cable, complete the crimping work of the cable core conductor, and install the cold shrinkage specimen of the intermediate joint according to the distance position requirements to restore the main insulation of the cable. Subsequently, use a copper mesh and a copper grounding wire to connect the copper shields at both ends of the cable to ensure the continuity of the grounding wire of the test cable. Since the external protection structures (armoring tape, epoxy resin shell, etc.) of the intermediate joint have nothing to do with the electrical insulation performance of the cable, they are not restored during the installation of the joint specimen. In addition, it should be noted that for the detection of the actual cable joint, the armoring layer does not need to be removed because the characteristic gas overflow is not affected by these structures. Among them, the cable joint samples in different groups of tests are produced in one batch, and the same aging pretreatment method is used, and the installation construction is completed by the same person.

[0112] Finally, in this embodiment, based on the analysis of the operating environment of the intermediate joint, the water immersion method in a reservoir is adopted to simulate the water seepage environment of the cable joint. The cable joint after aging pretreatment is installed and soaked in the pool for 7 days to ensure sufficient moisture absorption of the cable intermediate joint sample.

[0113] The method for fabricating a moisture-absorbed cable joint test sample of the present invention is a pre-aging means for studying the long-term evolution process of moisture absorption and discharge in cable intermediate joints. By performing aging pretreatment on the cable intermediate joint, on the one hand, the interfacial clamping force can be reduced to simulate the stress relaxation phenomenon under the actual operation of the cable joint, so that the sample is close to the actual situation of the moisture absorption defect at the joint interface; on the other hand, the test time required can be effectively shortened, and at the same time, cable intermediate joints with different operating years can be studied.

[0114] Between step S02 and step S03, the following step is further included:

[0115] Pre-test of the test sample: Immerse some of the fabricated cable intermediate joints in methylene blue solution, apply different currents to the cable, and observe whether there is methylene blue solution at the interface of the XLPE-SiR composite insulation material inside the cable intermediate joint and there are traces of oxidation and blackening on the surface of the connecting pipe. If so, it indicates that the test sample can simulate the moisture absorption defect at the joint interface in a water immersion environment.

[0116] Specifically, in this embodiment, in order to verify whether the test sample can achieve the test conditions for simulating the moisture absorption of the cable joint under the water immersion condition, a pre-test on the moisture absorption of the joint specimen is carried out. Use the aforementioned accessories after aging pretreatment and strictly fabricate the intermediate joint according to the installation process standard (silicone grease is applied at the interface). In order to more clearly observe the water vapor intrusion at the XLPE-SiR interface, immerse the installed cable joint in a water tank of methylene blue solution, with the terminal blocks at both ends of the joint above the water surface (ensuring that the solution cannot enter the joint from the cable core), and connect a large current generator to generate a load current.

[0117] During the test, three groups of samples are used, keeping other test conditions the same and only changing the load current:

[0118] The first group: The load current is zero, and it is immersed in methylene blue solution for 7 days;

[0119] The second group: Apply current to make the surface temperature reach 60 °C and keep it for 12 h, then cool for 12 h to simulate the load change during the water immersion operation of the cable, and a total of 7 cycles are carried out;

[0120] The third group: Apply current to make the surface temperature reach 60 °C and keep it for 12 h, then cool for 12 h to simulate the load change during the water immersion operation of the cable, and a total of 16 cycles are carried out.

[0121] After completing the pre-test steps for three groups of samples, clean the methylene blue solution on the outside of the connector, and after cutting open the silicone rubber on the outside of the middle connector, observe whether there is residual methylene blue solution on the surface of the metal connection pipe inside the three groups of cable connector samples and at the XLPE-SiR interface near the metal connection pipe. At the same time, observe whether there are traces of oxidation and blackening on the surface of the connection pipe. If the residual methylene blue solution at the XLPE-SiR interface can be observed and there are traces of oxidation and blackening on the surface of the connection pipe, it means that the pre-treated test sample can simulate the moisture defect at the connector interface in a soaked environment. This step can verify and ensure the actual internal state of the test sample production and the real moisture-affected cable connector, and improve the reliability of the detection method.

[0122] The above embodiments are the preferred embodiments of the present invention and do not limit the present invention. Any other changes or other equivalent replacement methods made without departing from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A detection system for the deterioration state of a damp cable joint based on multi-feature quantity acquisition, characterized in that It includes a power supply regulating device, a discharge characteristic collecting device and a characteristic gas collecting device. The power supply regulating device is used to connect the two ends of the cable where the cable intermediate joint is located and provide a preset test voltage. The discharge characteristic collecting device is used to detect the discharge signals of the cable body and the grounding wire and analyze them. The characteristic gas collecting device includes a gas sampling bag, an air pump and a gas chromatograph. The gas sampling bag is used to encapsulate the cable intermediate joint. One end of the air pump extracts the test gas through the test port opened on the gas sampling bag, and the other end is connected to the gas chromatograph through a gas valve. The gas chromatograph is used to analyze the components and contents of the test gas. The discharge characteristic collecting device includes a discharge signal collector, a high-frequency current transformer and a medium-low-frequency current transformer. The high-frequency current transformer is used to detect the discharge signal of the cable body and transmit it to the discharge signal collector. The medium-low-frequency current transformer is used to detect the discharge signal of the grounding wire and transmit it to the discharge signal collector. The discharge signal collector is used to extract and analyze the discharge signals. The power supply regulating device includes an AC power supply, a voltage regulator and a transformer. The AC power supply is sequentially connected to the two ends of the cable through the voltage regulator and the transformer. A fuse is connected in series at the output end of the AC power supply, and a current-limiting resistor is connected in series at the output end of the transformer.

2. The deterioration state detection system for a damp cable joint based on multi-feature quantity acquisition according to claim 1, wherein It also includes a simulated cable water seepage environment device, which is used to make test samples of the cable intermediate joint in a damp environment. The simulated cable water seepage environment device includes a constant temperature and humidity chamber and a reservoir. The constant temperature and humidity chamber is used for the aging pretreatment of the cold shrinkable accessories, and the reservoir is used to soak the cable intermediate joint.

3. A method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition, characterized in that, Applying the detection system according to any one of claims 1-2, specifically includes the following steps: S1. Encapsulate the cable intermediate joint in the gas sampling bag, leaving the cable terminal ends at both ends, and ground the grounding wire of the cable. S2. Connect the power supply regulating device to the two ends of the cable where the cable intermediate joint is located, turn on the power supply to provide a preset test voltage and keep it unchanged. S3. During the continuous power-on process, detect the discharge signal of the grounding wire through the medium-low-frequency current transformer of the discharge characteristic collecting device, detect the discharge signal of the cable body through the high-frequency current transformer of the discharge characteristic collecting device, and perform on-line monitoring of the discharge signals through the discharge signal collector of the discharge characteristic collecting device. S4. When a discharge signal with a significant waveform change is monitored, use the air pump to extract the test gas through the test port of the gas sampling bag, and analyze the components and contents of the characteristic gases in the test gas through the gas chromatograph. S5. After the collection is completed, disconnect the power supply, identify, extract and analyze the discharge signals collected by the discharge signal collector to obtain effective discharge waveforms. In step S5, use Python programming to identify, extract and analyze the discharge signals collected by the discharge signal collector, specifically including the steps: S51. Data segmentation processing: Segment the data with 1 million sampling points. In this segment, place a sliding sampling with a segmentation time window P1 of 1000 sampling points in length, and judge and record the discharge waveform. S52. Judgment of effective discharge waveforms: Due to the fact that there are significant peak differences between the discharge signal and the background noise waveform, the mean - standard deviation of the discharge amplitude within the sampling time window P2 combined with the noise threshold is used to determine a discharge signal whose sampling value satisfies Equation (1) as a valid discharge waveform: , formula (1), Wherein: , , where \(v\) a and \(\sigma\) are the mean and standard deviation of the discharge amplitude within the sampling time window \(P2\), respectively, \(v\) i is the discharge amplitude of the \(i\)-th sampling point, \(n\) is the number of sampling points, \(k\) is a coefficient, and \(v\) f is the noise threshold; S53. Calculate the start point and end point of the valid discharge waveform: The discharge amplitude v that satisfies Equation (1) is called the over - limit value. Find the first over - limit value within the sampling time window P2 and traverse forward. The point where the slope of the discharge waveform is 0 is taken as the start point of this discharge waveform; Find the last over - limit value within the sampling time window P2 and traverse backward. The point where the slope of the discharge waveform is 0 is taken as the end point of this discharge waveform. A complete discharge waveform is obtained based on the start point and end point; S54. Calculate the macroscopic discharge waveform characteristics: Calculate the macroscopic discharge waveform characteristics under different deterioration stages according to the discharge waveform. The macroscopic discharge waveform characteristics include discharge repetition rate, discharge pulse width, and discharge pulse amplitude; S6. Make an assessment of the deterioration state of the cable joint according to the analysis results of the characteristic gas components and content and the discharge waveform; In step S6, the assessment specifically includes: based on the discharge characteristics of the valid discharge waveforms collected within one power frequency cycle and the analysis results of the characteristic gases, determine whether the cable joint sample has deteriorated into the early, middle, or late stage: The conditions for the early stage are satisfied: The discharge characteristics include: the discharge repetition rate is less than 4 times per second, the average discharge pulse width is on the order of 10 -4 seconds, the amplitude of the discharge pulse detected by the high-frequency current transformer is less than 0.2V, and the amplitude of the discharge pulse detected by the medium-low frequency current transformer is less than 0.

1. The results of the characteristic gas analysis include: methane or hydrogen is contained in the characteristic gas, and the gas content of methane or hydrogen is less than 0.001%; The conditions for the middle stage are satisfied: The discharge characteristics include: the discharge repetition rate is 70 - 90 times per second, the average discharge pulse width is on the order of 10 -3 seconds, the amplitude of the discharge pulse detected by the high-frequency current transformer is greater than 0.7V, and the amplitude range of the discharge pulse detected by the medium- and low-frequency current transformers is 0.09 V - 0.3V. The results of the characteristic gas analysis include: the gas content range of methane or hydrogen is 0.001% - 0.005%; The conditions for the late stage are satisfied: The discharge characteristics include: the discharge repetition rate is less than 1.5 times per second, the average discharge pulse width is on the order of 10 -6 seconds, the discharge pulse amplitudes detected by the high-frequency current transformer and the medium- and low-frequency current transformers are both less than 0.2 V, and the results of the characteristic gas analysis include: the gas content of methane or hydrogen is greater than 0.1%, and the gas content of carbon dioxide is greater than 1%.

4. The method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition according to claim 3, wherein In step S4, the significantly changing discharge signals include single - spike discharges, discharge pulse clusters, and sine signals; the characteristic gas components include methane, hydrogen, and carbon dioxide.

5. The method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition according to claim 3, wherein Before step S1, it also includes making a test sample of a moisture - affected cable joint, specifically including the steps: S01. Aging pretreatment: Place the cold - shrinkable accessory in a constant - temperature greenhouse for aging to simulate the stress relaxation phenomenon under the actual operation of the cable joint; S02. Test sample production: Use the cold - shrinkable accessory after aging pretreatment to make a cable joint. This cable joint includes silicone rubber insulation, a semi - conductive layer, and a stress cone; S03. Moisture treatment: Place the made cable joint in a reservoir and soak it for several days.

6. The method for detecting the deterioration state of a damp cable joint based on multi-feature quantity acquisition according to claim 5, wherein Between step S02 and step S03, it also includes the step: Pretest of the test sample: Immerse some of the made cable joints in methylene blue solution, apply different currents to the cable, and observe whether there is methylene blue solution at the interface of the XLPE - SiR composite insulation material inside the cable joint and whether there are oxidation and blackening marks on the surface of the connecting pipe. If so, it indicates that the test sample can simulate the moisture - affected defect at the joint interface in a water - soaked environment.

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