Damp cable joint degradation state detection system and method based on multi-characteristic quantity acquisition

Abstract

The invention discloses a damp cable joint degradation state detection system and method based on multi-characteristic quantity acquisition, and the method comprises the steps: S1, packaging a cable intermediate joint in a gas sampling bag, and enabling a grounding wire of a cable to be grounded; s2, providing a preset test voltage for the cable through a power supply adjusting device and keeping the preset test voltage unchanged; s3, continuously electrifying, detecting discharge signals of the cable body and the grounding wire through a discharge characteristic acquisition device, and carrying out online monitoring and analysis; s4, opening a gas valve of a gas extracting pump to extract gas when a discharge signal with a remarkably changed waveform is monitored, and analyzing the components and content of the characteristic gas through a gas chromatograph; s5, identifying, extracting and analyzing the discharge signal after acquisition is completed to obtain an effective discharge waveform; and S6, comprehensively analyzing the result, and evaluating the degradation state of the cable intermediate joint. The method can effectively evaluate the deterioration state of the intermediate joint of the damped cable, and is high in reliability.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network cable fault detection, and in particular, relates to a system and method for detecting the deterioration state of a damp cable joint based on the collection of multiple feature quantities. Background Art

[0002] Distribution cable is one of the most important equipment in the distribution network. Due to its advantages of not occupying ground space resources, relatively high transmission capacity and good safety performance, it has become an important part of urban and rural power supply networks, especially the distribution network in megacities. As a connecting component of the cable line, the cable intermediate joint is one of the weak points in the safe operation of the current distribution network cable line. Studies have shown that due to the problem of water accumulation and pollution in the distribution network cable operation environment, the faulty distribution network cable intermediate joint generally has the defect of internal moisture, and the cable intermediate joint containing such defects will have an intermittent arc grounding fault along the axial direction at the XLPE-SiR insulation interface. The discharge energy causes ablation damage to the insulating medium at the interface, and at the same time damages the grounding system of the line, eventually leading to breakdown discharge and even fire and other major accidents. Therefore, it is necessary to analyze the discharge evolution process of the damp distribution network cable intermediate joint, and study the relationship between the discharge evolution process of the damp cable and the physical characteristics such as discharge waveform and cracking gas, so as to provide a theoretical basis for realizing the online distribution network cable joint operation status monitoring and ensuring the safety of distribution network operation.

[0003] Most of the existing research on the discharge of cable intermediate joints is to simulate and analyze the electric field distortion caused by defects such as knife marks, air gaps, moisture, stress cone dislocation, and metal debris residue at the interface, and compare the maximum field strength of the electric field distortion with the air breakdown threshold to judge the discharge situation; secondly, the simulation test is carried out by constructing artificial defects to study the partial discharge situation, and the discharge situation of the sliced ​​material during the breakdown process under different conditions is tested. The existing technology lacks an experimental analysis method for the changes in the insulation performance of the real cable intermediate joint after being damp and the long-term evolution of the discharge process. Summary of the invention

[0004] The first purpose of the present invention is to overcome the shortcomings and deficiencies in the prior art and to provide a moisture-affected cable joint degradation state detection system based on multi-feature quantity collection. 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 method for detecting the degradation state of a damp cable joint based on the collection of multiple feature quantities, which can effectively evaluate the degradation state of the damp cable intermediate joint and has high reliability.

[0006] The purpose of the present invention is achieved through the following technical solutions: a system for detecting the deterioration state of a damp cable joint based on the collection of multiple characteristic quantities, comprising a power supply regulating device, a discharge characteristic collecting device and a characteristic gas collecting device, wherein 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 and analyze the discharge signals of the cable body and the grounding wire; The characteristic gas collection device includes a gas sampling bag, an air pump and a gas chromatograph. The gas sampling bag is used to encapsulate the intermediate joint of the cable. One end of the air pump extracts the 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.

[0007] Preferably, the discharge feature acquisition device includes a discharge signal collector, a high-frequency current transformer and a medium- and 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- and low-frequency current transformer is used to detect the discharge signal of the ground wire and transmit it to the discharge signal collector. The discharge signal collector is used to extract and analyze the discharge signal.

[0008] Preferably, the power supply regulating device comprises an AC power supply, a voltage regulator and a transformer, wherein the AC power supply is connected to both ends of the cable via the voltage regulator and the transformer in sequence; a fuse is connected in series to the output end of the AC power supply, and a current-limiting resistor is connected in series to the output end of the transformer.

[0009] Preferably, it also includes a device for simulating cable water seepage environment, which is used to prepare test samples of damp cable intermediate joints. The device for simulating cable water seepage environment includes a constant temperature and humidity chamber and a water reservoir. The constant temperature and humidity chamber is used for aging pretreatment of cold shrink accessories, and the water reservoir is used for soaking cable intermediate joints.

[0010] The method for detecting the deterioration state of a damp cable joint based on the collection of multiple feature quantities, using the above-mentioned detection system, specifically includes the following steps: S1. Encapsulate the middle joint of the cable in a gas sampling bag, leaving the cable terminals at both ends, and ground the ground wire of the cable; S2. Connect the power supply regulating device to both ends of the cable where the middle joint of the cable is located, turn on the power supply to provide the preset test voltage and keep it constant; S3, during the continuous power-on process, the discharge signal of the ground wire is detected by the medium and low frequency mutual inductors of the discharge characteristic acquisition device, the discharge signal of the cable body is detected by the high frequency mutual inductor of the discharge characteristic acquisition device, and the discharge signal is monitored online by the discharge signal collector of the discharge characteristic acquisition device; S4. When a discharge signal with a significant waveform change is detected, a test gas is extracted through the test port of the gas sampling bag using a vacuum pump, and the characteristic gas components and contents in the test gas are analyzed by a gas chromatograph; S5. After the acquisition is completed, the power supply is disconnected, and the discharge signal collected by the discharge signal collector is identified, extracted and analyzed to obtain a valid discharge waveform; S6. Based on the analysis results of characteristic gas composition and content, and discharge waveform, evaluate the degradation state of the cable intermediate joint.

[0011] Preferably, in step S4, the significantly changing discharge signal includes a single sharp pulse discharge, a discharge pulse cluster and a sinusoidal signal; and the characteristic gas components include methane, hydrogen and carbon dioxide.

[0012] Preferably, in step S5, the discharge signal collected by the discharge signal collector is identified, extracted and analyzed using Python programming, which specifically includes the steps of: S51, data segmentation processing: The data is segmented into 1 million sampling points. In this segment, a segmented time window P1 with a length of 1000 sampling points is placed for sliding sampling to determine and record the discharge waveform. S52. Determination of effective discharge waveform: Since the peak value of the discharge signal is significantly different from that of the background noise waveform, the mean-standard deviation of the discharge amplitude within the sampling time window P2 is combined with the noise threshold to determine the discharge signal whose sampling value satisfies formula (1) as a valid discharge waveform: , formula (1), in: , , In the formula, v a , σ are the mean and standard deviation of the discharge amplitude in 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 the coefficient, v f is the noise threshold; S53, calculate the starting point and ending point of the effective discharge waveform: The discharge amplitude v that satisfies formula (1) is called the over-limit value. Find the first over-limit value in the sampling time window P2 and traverse forward. The point where the slope of the discharge waveform is 0 is taken as the starting point of the discharge waveform. Find the last over-limit value in the sampling time window P2 and traverse backwards, and take the point where the slope of the discharge waveform is 0 as the end point of the discharge waveform, and obtain a complete discharge waveform based on the starting point and the end point; S54. Calculate the macroscopic discharge waveform characteristics: The macroscopic discharge waveform characteristics at different degradation stages are calculated according to the discharge waveform, and the macroscopic discharge waveform characteristics include discharge repetition rate, discharge pulse width and discharge pulse amplitude.

[0013] Preferably, in step S6, the evaluation specifically includes: judging whether the degradation of the cable intermediate joint sample has entered the early, middle or late stage based on the discharge characteristics of the effective discharge waveform collected within a power frequency cycle and the characteristic gas analysis results: Early stage conditions are met: The discharge characteristics include: discharge repetition rate <4 times / second, average discharge pulse width on the order of 10 -4 seconds, the discharge pulse amplitude detected by the high-frequency current transformer is less than 0.2V, and the discharge pulse amplitude detected by the medium- and low-frequency current transformer is less than 0.1. The characteristic gas analysis results include: the characteristic gas contains methane or hydrogen, and the gas content of methane or hydrogen is less than 0.001%; The mid-term stage meets the following conditions: The discharge characteristics include: the discharge repetition rate is 70~90 times / second, and 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 0.7V, the discharge pulse amplitude detected by the medium and low frequency current transformer is in the range of 0.09 V ~ 0.3V, and the characteristic gas analysis results include: the gas content of methane or hydrogen is in the range of 0.001% ~ 0.005%; The late stage meets the following conditions: The discharge characteristics include: the discharge repetition rate is less than 1.5 times / second, and the average discharge pulse width is on the order of 10 -6 The discharge pulse amplitudes detected by the high-frequency current transformer and the medium- and low-frequency current transformer are all less than 0.2V. The characteristic gas analysis results include: the gas content of methane or hydrogen is greater than 0.1%, and the gas content of carbon dioxide is greater than 1%.

[0014] Preferably, before step S1, the method further comprises preparing a test sample of a damp cable connector, which specifically comprises the steps of: S01. Aging pretreatment: Place the shrink fittings in a constant temperature greenhouse for aging to simulate the stress relaxation phenomenon of the cable joint under actual operation; S02. Test sample preparation: Use the cold shrink accessories after aging pretreatment to prepare the cable intermediate joint, which includes silicone rubber insulation, semi-conductive layer and stress cone; S03. Moisture treatment: Place the prepared cable intermediate joint in a water reservoir and soak it for several days.

[0015] Preferably, between step S02 and step S03, the method further includes the following steps: Pre-test of test samples: soak some of the finished 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 whether there are traces of oxidation and blackening on the surface of the connecting pipe. If so, it means that the test sample can simulate the moisture defects of the joint interface in a water environment.

[0016] Compared with the prior art, the present invention has the following advantages and effects: (1) The present invention provides a method for detecting the degradation state of a damp cable joint based on the collection of multiple characteristic quantities. The method collects multiple characteristic quantities of the degradation process of the damp cable intermediate joint, including discharge signals and characteristic gases, in the power-on state, identifies and extracts effective discharge waveforms, and analyzes the composition and content of the characteristic gases. Both the discharge signal and the characteristic gas content have a high correlation with the degradation state of the damp cable intermediate joint. The two characteristic quantities can verify each other, thereby achieving effective and accurate evaluation of the degradation state of the damp cable intermediate joint with high reliability, and providing a data basis for studying the development judgment of insulation defects and fault diagnosis of the cable intermediate joint after it is damp.

[0017] (2) The cable joint test sample of the present invention can be a damp cable in actual operation, or it can be a simulated damp cable joint sample. By adopting the latter, it is possible to quickly and efficiently simulate various 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 the physical characteristics such as the discharge waveform and cracking gas. The method for preparing the damp cable joint test sample of the present invention can reduce the interface clamping force and simulate the stress relaxation phenomenon under the actual operation of the cable joint by aging the cable intermediate joint, so that the sample is close to the actual situation of the damp defect of 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.

[0018] (3) The present invention provides a system for detecting the deterioration state of a damp cable joint based on the collection of multiple characteristic quantities, including a power supply regulating device, a discharge characteristic collection device and a characteristic gas collection device. The discharge characteristic collection device detects the discharge signal and identifies and extracts the effective discharge waveform, and the characteristic gas collection device collects and analyzes the characteristic gas composition and content. The detection system has a simple structure, is easy to operate and has high detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is an equivalent circuit diagram of the system for detecting the degradation state of a damp cable joint based on the collection of multiple feature quantities of the present invention.

[0020] Figure 2 It is a structural block diagram of the system for detecting the degradation state of a damp cable joint based on the collection of multiple feature quantities of the present invention.

[0021] Figure 3 It is a flow chart of the method for detecting the degradation state of a damp cable joint based on the collection of multiple feature quantities of the present invention.

[0022] Figure 4 1 is a typical discharge waveform distribution diagram of different degradation stages in Example 2 of the present invention, where (a) is the early degradation stage, (b) is the middle degradation stage, and (c) is the late degradation stage.

[0023] Figure 5 This is a schematic diagram of the characteristic gas content distribution diagram in Example 2 of the present invention.

[0024] Figure 6 It is a schematic structural diagram of a test sample of a damp cable connector of the present invention.

[0025] Among them, 1 is a high-frequency current transformer; 2 is a cable body section; 3 is a medium- and 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 semi-conductive layer; 8 is a stress cone; 9 is cross-linked polyethylene XLPE insulation; 10 is silicone rubber SiR insulation; 11 is a protective shell; 12 is a semi-conductive tape; 13 is an inner semi-conductive layer; 14 is a crimping tube; and 15 is a copper conductor. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0027] Example 1 like Figure 1-2 As shown, the deterioration state detection system of the damp cable joint based on the collection of multiple characteristic quantities 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 signal of the cable body and the grounding wire and analyze it; The characteristic gas collection device includes a gas sampling bag, an air pump and a gas chromatograph. The gas sampling bag is used to encapsulate the intermediate joint of the cable. One end of the air pump extracts the 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.

[0028] The discharge feature acquisition device includes a discharge signal collector, a high-frequency current transformer and a medium- and 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- and low-frequency current transformer is used to detect the discharge signal of the ground wire and transmit it to the discharge signal collector. The discharge signal collector is used to extract and analyze the discharge signal.

[0029] The power supply regulating device comprises an AC power supply, a voltage regulator and a transformer. The AC power supply is connected to two ends of the cable through the voltage regulator and the transformer in sequence. A fuse is connected in series to the output end of the AC power supply, and a current-limiting resistor is connected in series to the output end of the transformer.

[0030] It also includes a device for simulating cable water seepage environment, which is used to prepare test samples of damp cable intermediate joints. The device for simulating cable water seepage environment includes a constant temperature and humidity chamber and a water reservoir. The constant temperature and humidity chamber is used for aging pretreatment of cold shrink accessories, and the water reservoir is used for soaking cable intermediate joints.

[0031] Specifically, the present invention provides a system for detecting the deterioration state of a damp cable joint based on the collection of multiple characteristic quantities, including a power supply adjustment device, a discharge characteristic collection device and a characteristic gas collection device. The discharge characteristic collection device detects the discharge signal and identifies and extracts the effective discharge waveform. In this embodiment, the discharge signal collector is a computer. The characteristic gas collection device collects and analyzes the characteristic gas composition and content. The detection system has a simple structure, is easy to operate, and has high detection accuracy. The characteristic gas collection device is composed of Figure 1 As shown, the present invention adopts a portable gas chromatograph, and the sampling method for detection is solid phase microextraction sampling. A heated micromechanical injector is used internally, and a chip-type TCD is used to accurately control the intake sample.

[0032] Example 2 like Figure 3 The figure is a flow chart of a method for detecting the deterioration state of a damp cable joint based on the collection of multiple feature quantities, and the detection system described in Example 1 is applied, specifically comprising the following steps: S1. Encapsulate the middle joint of the cable in a gas sampling bag, leaving the cable terminals at both ends, and ground the ground wire of the cable; S2. Connect the power supply regulating device to both ends of the cable where the middle joint of the cable is located, turn on the power supply to provide the preset test voltage and keep it constant; S3, during the continuous power-on process, the discharge signal of the ground wire is detected by the medium and low frequency mutual inductors of the discharge characteristic acquisition device, the discharge signal of the cable body is detected by the high frequency mutual inductor of the discharge characteristic acquisition device, and the discharge signal is monitored online by the discharge signal collector of the discharge characteristic acquisition device; S4. When a discharge signal with a significant waveform change is detected, a vacuum pump is used to extract the test gas through the test port of the gas sampling bag; S5. After the acquisition is completed, the power supply is disconnected, and the characteristic gas components and content in the test gas are analyzed by a gas chromatograph. At the same time, the discharge signal collected by the discharge signal collector is identified, extracted and analyzed to obtain an effective discharge waveform; S6. Based on the analysis results of characteristic gas composition and content, and discharge waveform, evaluate the degradation state of the cable intermediate joint.

[0033] Specifically, the present invention provides a method for detecting the degradation state of damp cable joints based on the collection of multiple characteristic quantities. The method collects multiple characteristic quantities of the degradation process of the damp cable intermediate joint in the power-on state, including discharge signals and characteristic gases, and uses a multi-state quantity collection system to test the degradation degree of the damp cable intermediate joint. A method for dividing its degradation stages is provided, thereby providing a means for judging the line operation state for actual distribution network line operation and maintenance. The two characteristic quantities can verify each other, thereby achieving effective and accurate evaluation of the degradation state of the damp cable intermediate joint, with high reliability.

[0034] First, the cable intermediate joint sample is encapsulated in the gas sampling bag, and the connection terminals at both ends of the joint are reserved. The current conduction circuit is installed on both sides of the pre-treated damp cable intermediate joint sample, and the voltage regulator is adjusted to quickly increase the voltage of the test sample to the preset test voltage and keep it unchanged. In this embodiment, the test voltage is 5.8kV; Then the discharge signal collector is connected to the medium and low frequency current transformer to detect the discharge signal on the ground wire, and the high frequency current transformer is connected to collect the discharge signal on the cable body as a supplement to observe the discharge signal of the internal interface of the cable intermediate joint online; During the continuous power-on process, as the deterioration of the damp cable intermediate joint progresses, multiple feature quantities of the damp cable intermediate joint are collected. Specifically, it includes: For the discharge waveform: during the whole process of cable degradation, sharp pulse discharge, discharge pulse cluster and industrial frequency sinusoidal signal will appear in sequence, until the sinusoidal signal appears and lasts for 1 minute, the collection of the discharge waveform is completed.

[0035] For characteristic gases: collect gas according to the discharge waveform. When a discharge signal with a significant waveform change is collected, including a single sharp pulse discharge, a discharge pulse cluster and a sine signal, when any of these three waveforms appears, start the vacuum pump and turn on the air pump of the collection bag to collect the gas for 2 minutes. Then turn off the vacuum pump and the air pump to complete the collection of characteristic gases in the corresponding degradation stage.

[0036] Complete the collection at the expected time, disconnect the power supply, and extract and analyze the data. This includes passing the characteristic gas collected at different stages into a portable gas chromatograph for component and content analysis, wherein the characteristic gas components include methane, hydrogen and carbon dioxide. The gas content is analyzed by the gas chromatograph, which is used to judge the degradation stage of the cable intermediate joint sample based on the analysis results of multiple characteristic quantities in combination with the subsequent discharge signal characteristics. In the present invention, a vacuum pump and a portable gas chromatograph are used for gas extraction and analysis to ensure that the detection has a high sensitivity; It also includes exporting discharge signals and sampling and analyzing discharge waveforms using Python programming on computers. The two analysis results are combined to clarify the discharge laws and gas characteristics at different stages of the entire process of cable intermediate joints being damp and deteriorating, and to provide a basis for dividing the degradation stages, providing a data basis for studying the development judgment of insulation defects and fault diagnosis of cable intermediate joints after being damp.

[0037] In step S5, the discharge signal collected by the discharge signal collector is identified, extracted and analyzed using Python programming, which specifically includes the following steps: S51, data segmentation processing: The data is segmented into 1 million sampling points. In this segment, a segmented time window P1 with a length of 1000 sampling points is placed for sliding sampling to determine and record the discharge waveform. S52. Determination of effective discharge waveform: Since the peak value of the discharge signal is significantly different from that of the background noise waveform, the mean-standard deviation of the discharge amplitude within the sampling time window P2 is combined with the noise threshold to determine the discharge signal whose sampling value satisfies formula (1) as a valid discharge waveform: , formula (1), in: , , In the formula, v a , σ are the mean and standard deviation of the discharge amplitude in 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 the coefficient, v f is the noise threshold; S53, calculate the starting point and ending point of the effective discharge waveform: The discharge amplitude v that satisfies formula (1) is called the over-limit value. Find the first over-limit value in the sampling time window P2 and traverse forward. The point where the slope of the discharge waveform is 0 is taken as the starting point of the discharge waveform. Find the last over-limit value in the sampling time window P2 and traverse backwards, and take the point where the slope of the discharge waveform is 0 as the end point of the discharge waveform, and obtain a complete discharge waveform based on the starting point and the end point; S54. Calculate the macroscopic discharge waveform characteristics: The macroscopic discharge waveform characteristics at different degradation stages are calculated according to the discharge waveform, and the macroscopic discharge waveform characteristics include discharge repetition rate, discharge pulse width and discharge pulse amplitude.

[0038] Specifically, in this embodiment, considering the large amount of data, in order to prevent the problem of program memory overrun, the data needs to be segmented first. In order to prevent the segmentation position from being located exactly in the discharge waveform, affecting the waveform data sampling, when segmenting the data, it is first necessary to put a time window at the last 1000 sampling points of the segment, called the segmentation time window P1, to determine whether there is a discharge at the segmentation point. If there is, the segmentation time window P1 continues to slide back 1000 sampling points to determine the discharge waveform in the time window P1 until there is no discharge waveform in P1.

[0039] In the effective discharge waveform judgment, if the sampling value exceeds the mean plus or minus the variance k times, it can be determined that there is a discharge waveform at that location. In order to avoid the situation where the noise is sampled as the discharge waveform due to the presence of only noise in the segment, a noise threshold is defined here v f In this embodiment, let k be 2. v f The value is 0.05. In this embodiment, a waveform is set to satisfy the requirement that the sampling value exceeds the mean plus or minus the variance k times and exceeds the noise threshold to be judged as a valid discharge, that is, formula (1).

[0040] In order to sample and analyze the discharge waveform and calculate the discharge pulse width, it is necessary to perform sliding analysis on the data segment in a time window, which is referred to as the sliding time window P2. If there is an over-limit value in the sliding time window P2, find the first over-limit value in P2 and traverse forward until the point with a waveform slope of 0 is found as the starting point of the discharge waveform, and record the discharge waveform from this point; P2 continues to slide backward, and if there is still an over-limit value in P2, record all waveforms in P2, and continue to push P2 backward until there is no over-limit value in P2, and stop sampling the discharge waveform. The time window where the discharge waveform sampling is stopped is called P 2a , P 2a The previous time window is called P 2b , P 2a With P 2b Merge into P 2c , find P 2c The last over-limit value in the waveform is found, and the waveform is traversed backward until a point with a waveform slope of 0 is found as the termination point of the discharge waveform, thereby obtaining a complete discharge waveform.

[0041] According to the complete effective discharge waveform obtained in the above steps, the macroscopic discharge waveform characteristics at different degradation stages are statistically analyzed, including the discharge repetition rate, discharge pulse width and discharge pulse amplitude. In this embodiment, the number of discharges within 1s is defined as the discharge repetition rate, the change in the number of discharges detected within 1 second is statistically analyzed, and the average discharge repetition rate and the highest discharge repetition rate occurring during the discharge process are calculated; for the discharge pulse width, the duration of each discharge pulse is calculated; for the discharge pulse amplitude, the voltage value at each discharge pulse amplitude is calculated.

[0042] In step S6, the evaluation specifically includes: judging whether the degradation of the cable intermediate joint sample has entered the early, middle or late stage based on the discharge characteristics of the effective discharge waveform collected within a power frequency cycle and the characteristic gas analysis results: Early stage conditions are met: The discharge characteristics include: the discharge repetition rate is less than 4 times / second, and 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 0.2V, and the discharge pulse amplitude detected by the medium- and low-frequency current transformer is less than 0.1. The characteristic gas analysis results include: the characteristic gas contains methane or hydrogen, and the gas content of methane or hydrogen is less than 0.001%; The mid-term stage meets the following conditions: The discharge characteristics include: the discharge repetition rate is 70~90 times / second, and 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 0.7V, the discharge pulse amplitude detected by the medium and low frequency current transformer is in the range of 0.09 V ~ 0.3V, and the characteristic gas analysis results include: the gas content of methane or hydrogen is in the range of 0.001% ~ 0.005%; The late stage meets the following conditions: The discharge characteristics include: the discharge repetition rate is less than 1.5 times / second, and the average discharge pulse width is on the order of 10 -6 The discharge pulse amplitudes detected by the high-frequency current transformer and the medium- and low-frequency current transformer are all less than 0.2V. The characteristic gas analysis results include: the gas content of methane or hydrogen is greater than 0.1%, and the gas content of carbon dioxide is greater than 1%.

[0043] Specifically, in this embodiment, the detailed reference discharge waveform and characteristic gas content are shown in Figure 4 and Figure 5 shown.

[0044] Before step S1, the process also includes preparing a test sample of a damp cable joint, which specifically includes the following steps: S01. Aging pretreatment: Place the cold shrink accessories in a constant temperature greenhouse for aging to simulate the stress relaxation phenomenon of the cable joint under actual operation; S02. Test sample preparation: Use the cold shrink accessories after aging pretreatment to prepare the cable intermediate joint, which includes silicone rubber insulation, semi-conductive layer and stress cone; S03. Moisture treatment: Place the prepared cable intermediate joint in a water reservoir and soak it for several days.

[0045] Specifically, the cable joint test sample of the present invention can be a damp cable in actual operation, or it can be a simulated damp cable joint sample. By adopting the latter, it is possible to quickly and efficiently simulate various 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 the physical characteristics such as the discharge waveform and cracking gas.

[0046] In this embodiment, first, in the aging pretreatment process, according to the technical specifications of the cable cold shrink accessories, a constant temperature and humidity chamber is used to set the temperature to 135°C, and the aging time is set to 168 hours according to the test conditions. At the same time, the temperature uniformity is controlled to be ±2.5°C (that is, the difference between the maximum and minimum values ​​of the measured average values ​​of the temperatures at each test point in the constant temperature and humidity chamber within the specified time), the control accuracy is ±1°C, and the heating rate is ≤15°C / minute; Then, after the cold shrink accessories have completed pre-aging, they are installed at the test site. Figure 6 The diagram shows the structure of the test sample of the damp cable joint. After the insulation and outer shielding layer of the test cable are stripped and cut off according to the installation process requirements, the intermediate joint shrinkage sample is put on the outer shielding layer of the cable at one end to complete the crimping of the cable core conductor, and the intermediate joint shrinkage sample is installed according to the distance position requirements to restore the main insulation of the cable. Subsequently, the copper shielding at both ends of the cable is connected using a copper mesh and a copper grounding wire to ensure the continuity of the grounding wire of the test cable. Since the external protective structure of the intermediate joint (armor tape, epoxy resin shell) has nothing to do with the electrical insulation performance of the cable, it is not restored during the installation of the joint sample. In addition, it should be noted that the armor layer does not need to be removed for testing the actual cable joint, because the overflow of characteristic gases is not affected by these structures. Among them, the cable joint samples in different groups of tests should be produced in one batch, and the same aging pretreatment method should be used, and the installation and construction should be completed by the same person.

[0047] Finally, in this embodiment, based on the analysis of the operating environment of the intermediate joint, a water tank soaking method is used to simulate the water seepage environment of the cable joint. The cable joint after aging pretreatment is installed and soaked in the water tank for 7 days to ensure that the cable intermediate joint sample is fully damp.

[0048] The method for preparing a test sample of a damp cable joint of the present invention is a pre-aging means for studying the long-term evolution process of moisture and discharge of a cable intermediate joint. By performing aging pretreatment on the cable intermediate joint, on the one hand, the interface holding force can be reduced, and the stress relaxation phenomenon under the actual operation of the cable joint can be simulated, so that the sample can be close to the actual situation of moisture defects on the joint interface; on the other hand, the time required for the test can be effectively shortened, and research can also be conducted on cable intermediate joints with different operating years.

[0049] Between step S02 and step S03, the following steps are also included: Pre-test of test samples: soak some of the finished 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 whether there are traces of oxidation and blackening on the surface of the connecting pipe. If so, it means that the test sample can simulate the moisture defects of the joint interface in a water environment.

[0050] Specifically, in this embodiment, in order to verify whether the test sample can achieve the test condition of simulating the moisture of the cable joint under the condition of immersion in water, a joint sample moisture pre-test is carried out. The aforementioned accessories that have been pre-treated by aging are used, and the intermediate joint (the interface is coated with silicone grease) is made in strict accordance with the installation process standards. In order to more clearly observe the water vapor intrusion at the XLPE-SiR interface, the installed cable joint is immersed in a water tank of methyl blue solution, and the terminals at both ends of the joint are higher than the water surface (to ensure that the solution cannot penetrate into the joint from the cable core), and a large current generator is connected to generate a load current.

[0051] Three groups of samples were used during the test, keeping other test conditions the same and only changing the load current: Group 1: load current is zero, immersed in methylene blue solution for 7 days; The second group: load current to make the surface temperature reach 60℃ and maintain it for 12 hours, and cool it for 12 hours to simulate the load change when the cable is immersed in water, and perform 7 cycles in total; The third group: load current until the surface temperature reaches 60℃ and maintain it for 12 hours, then cool it for 12 hours to simulate the load changes when the cable is immersed in water, for a total of 16 cycles.

[0052] After completing the pre-test steps for the three groups of samples, clean the methyl blue solution on the outside of the joint, and after cutting open the silicone rubber on the outside of the middle joint, observe whether there is residual methyl blue solution on the surface of the metal connecting tube inside the three groups of cable joint samples and at the XLPE-SiR interface near the metal connecting tube, and observe whether there are traces of oxidation and blackening on the surface of the connecting tube. If the residual methyl blue solution can be observed at the XLPE-SiR interface, and there are traces of oxidation and blackening on the surface of the connecting tube, it means that the pretreated test sample can simulate the joint interface moisture defect in a water environment. This step can verify and ensure the actual internal state of the test sample preparation and the real damp cable joint, and improve the reliability of the detection method.

[0053] The above embodiments are preferred implementations of the present invention and are not intended to limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solutions of the present invention are included in the protection scope of the present invention.

Claims

1. A moisture-affected cable joint degradation state detection system based on multi-feature quantity collection, 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 signal of the cable body and the grounding wire and analyze it; The characteristic gas collection device includes a gas sampling bag, an air pump and a gas chromatograph. The gas sampling bag is used to encapsulate the intermediate joint of the cable. One end of the air pump extracts the 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.

2. The system for detecting the degradation state of a damp cable joint based on the collection of multiple characteristic quantities according to claim 1 is characterized in that: The discharge feature acquisition device includes a discharge signal collector, a high-frequency current transformer and a medium- and 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- and low-frequency current transformer is used to detect the discharge signal of the ground wire and transmit it to the discharge signal collector. The discharge signal collector is used to extract and analyze the discharge signal.

3. The system for detecting the deterioration state of a damp cable joint based on the collection of multiple characteristic quantities according to claim 1 is characterized in that: The power supply regulating device comprises an AC power supply, a voltage regulator and a transformer. The AC power supply is connected to two ends of the cable through the voltage regulator and the transformer in sequence. A fuse is connected in series to the output end of the AC power supply, and a current-limiting resistor is connected in series to the output end of the transformer.

4. The system for detecting the degradation state of a damp cable joint based on the collection of multiple characteristic quantities according to claim 1 is characterized in that: It also includes a device for simulating cable water seepage environment, which is used to prepare test samples of damp cable intermediate joints. The device for simulating cable water seepage environment includes a constant temperature and humidity chamber and a water reservoir. The constant temperature and humidity chamber is used for aging pretreatment of cold shrink accessories, and the water reservoir is used for soaking cable intermediate joints.

5. A method for detecting the deterioration state of a damp cable joint based on the collection of multiple feature quantities, characterized in that: The detection system according to any one of claims 1 to 4 is applied, specifically comprising the following steps: S1. Encapsulate the middle joint of the cable in a gas sampling bag, leaving the cable terminals at both ends, and ground the ground wire of the cable; S2. Connect the power regulator to both ends of the cable where the middle joint of the cable is located, turn on the power supply to provide the preset test voltage and keep it constant; S3, during the continuous power-on process, the discharge signal of the ground wire is detected by the medium and low frequency mutual inductors of the discharge characteristic acquisition device, the discharge signal of the cable body is detected by the high frequency mutual inductor of the discharge characteristic acquisition device, and the discharge signal is monitored online by the discharge signal collector of the discharge characteristic acquisition device; S4. When a discharge signal with a significant waveform change is detected, a test gas is extracted through the test port of the gas sampling bag using a vacuum pump, and the characteristic gas components and contents in the test gas are analyzed by a gas chromatograph; S5. After the acquisition is completed, the power supply is disconnected, and the discharge signal collected by the discharge signal collector is identified, extracted and analyzed to obtain a valid discharge waveform; S6. Based on the analysis results of characteristic gas composition and content and discharge waveform, the degradation state of the cable intermediate joint is evaluated.

6. The method for detecting the degradation state of a damp cable joint based on multi-feature quantity collection according to claim 5 is characterized in that: In step S4, the significantly changing discharge signals include single sharp pulse discharge, discharge pulse clusters and sinusoidal signals; the characteristic gas components include methane, hydrogen and carbon dioxide.

7. The method for detecting the degradation state of a damp cable joint based on multi-feature quantity collection according to claim 5 is characterized in that: In step S5, the discharge signal collected by the discharge signal collector is identified, extracted and analyzed using Python programming, which specifically includes the following steps: S51, data segmentation processing: The data is segmented into 1 million sampling points. In this segment, a segmented time window P1 with a length of 1000 sampling points is placed for sliding sampling to determine and record the discharge waveform. S52. Determination of effective discharge waveform: Since the peak value of the discharge signal is significantly different from that of the background noise waveform, the mean-standard deviation of the discharge amplitude within the sampling time window P2 is combined with the noise threshold to determine the discharge signal whose sampling value satisfies formula (1) as a valid discharge waveform: , formula (1), in: , , In the formula, v a , σ are the mean and standard deviation of the discharge amplitude in 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 the coefficient, v f is the noise threshold; S53, calculate the starting point and ending point of the effective discharge waveform: The discharge amplitude v that satisfies formula (1) is called the over-limit value. Find the first over-limit value in the sampling time window P2 and traverse forward. The point where the slope of the discharge waveform is 0 is taken as the starting point of the discharge waveform. Find the last over-limit value in the sampling time window P2 and traverse backwards, and take the point where the slope of the discharge waveform is 0 as the end point of the discharge waveform, and obtain a complete discharge waveform based on the starting point and the end point; S54. Calculate the macroscopic discharge waveform characteristics: The macroscopic discharge waveform characteristics at different degradation stages are calculated according to the discharge waveform, and the macroscopic discharge waveform characteristics include discharge repetition rate, discharge pulse width and discharge pulse amplitude.

8. The method for detecting the degradation state of a damp cable joint based on multi-feature quantity collection according to claim 5 is characterized in that: In step S6, the evaluation specifically includes: judging whether the degradation of the cable intermediate joint sample has entered the early, middle or late stage based on the discharge characteristics of the effective discharge waveform collected within a power frequency cycle and the characteristic gas analysis results: Early stage conditions are met: The discharge characteristics include: the discharge repetition rate is less than 4 times / second, and 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 0.2V, and the discharge pulse amplitude detected by the medium- and low-frequency current transformer is less than 0.

1. The characteristic gas analysis results include: the characteristic gas contains methane or hydrogen, and the gas content of methane or hydrogen is less than 0.001%; The mid-term stage meets the following conditions: The discharge characteristics include: the discharge repetition rate is 70~90 times / second, and 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 0.7V, the discharge pulse amplitude detected by the medium and low frequency current transformer is in the range of 0.09 V ~ 0.3V, and the characteristic gas analysis results include: the gas content of methane or hydrogen is in the range of 0.001% ~ 0.005%; The late stage meets the following conditions: The discharge characteristics include: the discharge repetition rate is less than 1.5 times / second, and the average discharge pulse width is on the order of 10 -6 The discharge pulse amplitudes detected by the high-frequency current transformer and the medium- and low-frequency current transformer are all less than 0.2V. The characteristic gas analysis results include: the gas content of methane or hydrogen is greater than 0.1%, and the gas content of carbon dioxide is greater than 1%.

9. The method for detecting the degradation state of a damp cable joint based on multi-feature quantity collection according to claim 5 is characterized in that: Before step S1, the process also includes preparing a test sample of a damp cable joint, which specifically includes the following steps: S01. Aging pretreatment: Place the cold shrink accessories in a constant temperature greenhouse for aging to simulate the stress relaxation phenomenon of the cable joint under actual operation; S02. Test sample preparation: Use the cold shrink accessories after aging pretreatment to prepare the cable intermediate joint, which includes silicone rubber insulation, semi-conductive layer and stress cone; S03. Moisture treatment: Place the prepared cable intermediate joint in a water reservoir and soak it for several days.

10. The method for detecting the degradation state of a damp cable joint based on multi-feature quantity collection according to claim 9, characterized in that: Between step S02 and step S03, the following steps are also included: Pre-test of test samples: soak some of the finished 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 whether there are traces of oxidation and blackening on the surface of the connecting pipe. If so, it means that the test sample can simulate the moisture defects of the joint interface in a water environment.

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