High-voltage cable fault identification method for on-line monitoring of sheath current

Abstract

The invention relates to the field of cable fault identification, in particular to a high-voltage cable fault identification method for on-line monitoring of sheath current, which comprises the following steps of: firstly, monitoring in real time through a sheath current sensor, a fault traveling wave collector and a cable temperature sensor at key positions along a line, collecting cable line parameters, analyzing normal operation data, and determining the fault of a high-voltage cable according to the normal operation data; establishing a sheath current and temperature characteristic model, calculating the sheath current in real time and comparing the model, if the sheath current exceeds a threshold value, preliminarily judging a fault, and then calculating a fault area through traveling waves; temperature change data are obtained in a fault area, and an average temperature highest point area is found through calculation to accurately calibrate a fault position. According to the method, cable operation conditions are comprehensively mastered by multiple means, faults can be found in time, fault areas and positions can be accurately determined, fault types can be accurately judged according to multi-aspect information, the accuracy and timeliness of high-voltage cable fault recognition are effectively improved, safe and stable operation of a power system is powerfully guaranteed, and the working efficiency is improved. The operation and maintenance cost is reduced; and the cable management level is improved.

Description

Technical Field

[0001] The invention relates to the field of cable fault identification, and in particular to a high-voltage cable fault identification method for online monitoring of sheath current. Background Art

[0002] In modern power systems, high-voltage cables play a vital role and are widely used in many fields such as urban power grids and industrial production, responsible for the efficient transmission and distribution of electric energy. However, in the long-term operation of high-voltage cables, due to the influence of various complex factors, various faults are prone to occur, which poses a serious threat to the safe and stable operation of the power system.

[0003] In the existing technology, some monitoring technologies may be interfered by various factors, resulting in insufficient accuracy of monitoring data and affecting the reliability of fault diagnosis; in some cases, existing monitoring technologies may not be able to detect the occurrence of faults in a timely manner, or after detecting a fault, they cannot quickly determine the type and location of the fault, affecting the recovery speed of the power system.

[0004] Therefore, it is necessary to propose a high-voltage cable fault identification method based on online monitoring of sheath current to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a high-voltage cable fault identification method for online monitoring of sheath current, so as to solve the problem that some monitoring technologies may be interfered by various factors, resulting in insufficient accuracy of monitoring data and affecting the reliability of fault diagnosis; in some cases, existing monitoring technologies may not be able to detect the occurrence of faults in time, or after detecting a fault, the fault type and location cannot be quickly determined, affecting the recovery speed of the power system.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A high-voltage cable fault identification method for online monitoring of sheath current comprises the following steps:

[0008] S1: Real-time monitoring is carried out through high-precision sheath current sensors, fault traveling wave collectors and cable temperature sensors at key locations along the high-voltage cable. The high-precision sheath current sensors monitor the changes in sheath current in real time. The fault traveling wave collector has a high sampling frequency to accurately capture the arrival time of the fault traveling wave. The cable temperature sensor can accurately measure the cable sheath temperature and is distributed in the fault area to form multi-point monitoring;

[0009] S2: Collect the line parameters of high-voltage cables in detail, including cable length, conductor material and cross-sectional area, insulation material characteristics, sheath structure, and cable wave impedance information, and enter them into the monitoring system database;

[0010] S3: Analyze the collected normal operating sheath current and temperature data, calculate the mean, standard deviation, spectrum characteristic parameters of the sheath current, and the average level and fluctuation range characteristics of the temperature, establish a normal operating sheath current and temperature characteristic model through statistical analysis methods, and determine the typical range and variation law of the sheath current and temperature under normal conditions;

[0011] S4: Calculate the sheath current collected in real time and compare it with the sheath current characteristic model of normal operation. If the characteristic parameter of the sheath current exceeds the normal range threshold, it is preliminarily determined that the cable is faulty. By measuring the time difference between the traveling wave reaching the two ends of the cable and combining the known traveling wave speed, the approximate distance range from the fault point to one end is calculated, thereby determining the fault area.

[0012] S5: After determining the fault area, obtain the temperature change data over time in the fault area for a period of time, calculate the temperature change rate of each monitoring point and the temperature difference between adjacent monitoring points, analyze the increasing and decreasing trends of the temperature in the fault area, and obtain the average temperature values ​​of different positions in the fault area by performing weighted average calculation on the temperature of each monitoring point, and find the area with the highest average temperature. This area is the more accurate calibration range of the fault location.

[0013] Preferably, a trigger threshold of the acquisition device is set. When the traveling wave signal exceeds the threshold, the fault traveling wave collector starts to record the traveling wave data. The setting of the trigger threshold is reasonably adjusted according to the signal level during normal operation of the cable and the expected fault traveling wave signal size to ensure that the fault traveling wave can be captured in time and avoid false triggering.

[0014] Preferably, determining the fault area in step S4 includes the following steps:

[0015] S41: To ensure the accuracy of the traveling wave arrival time record, high-precision time synchronization is used to synchronize the acquisition time of the fault traveling wave collectors at both ends of the cable. The synchronization error is controlled within nanoseconds to accurately measure the time difference between the traveling wave arriving at both ends of the cable.

[0016] S42: Based on the structural parameters and physical characteristics of the cable, the theoretical propagation speed of the traveling wave in the cable is calculated using the electromagnetic field theory formula. For lossless cables, the speed of the traveling wave is Wherein, L is the inductance of the cable per unit length, and C is the capacitance of the cable per unit length. The inductance and capacitance are calculated through the material and structural parameters of the cable.

[0017] S43: According to the speed of the traveling wave and the time difference between the traveling wave and the two ends of the cable, the distance between one end of the cable and the fault point is obtained, thereby determining the scope of the fault area.

[0018] Preferably, the operating state of the cable will affect the traveling wave speed. Temperature changes will cause the physical properties of the cable material to change, affecting the traveling wave speed. By real-time monitoring of the cable temperature, a relationship curve between temperature and traveling wave speed is constructed, and the traveling wave speed is corrected in real time to reduce the impact of the cable's operating state on the traveling wave speed.

[0019] Preferably, step S5 includes the following steps:

[0020] S51: setting the data collection frequency of the temperature sensor, after the fault area is determined, capturing the dynamic change process of the temperature, increasing the collection frequency, and continuously collecting for a period of time to obtain enough temperature data samples for subsequent analysis;

[0021] S52: For each temperature monitoring point, calculate its temperature change rate. The calculation formula is: Where ΔT is the temperature difference between adjacent sampling points, and Δt is the sampling time interval;

[0022] S53: Calculate the temperature difference between adjacent temperature monitoring points, and determine the direction of temperature increase or decrease by comparing the temperature difference between adjacent monitoring points at different positions, so as to infer the approximate location of the fault point;

[0023] S54: Calculate the weighted average temperature of each monitoring point. The weight coefficient can be determined by considering the distance between the monitoring point and the possible fault point and the importance of the location of the monitoring point. The closer the monitoring point is to the possible fault point, the greater its weight coefficient is. The calculation formula is: Where T avg is the weighted average temperature, w i is the weight coefficient of the ith monitoring point, T i is the temperature of the th monitoring point, n is the total number of monitoring points, and the specific fault location in the fault area can be located more accurately through weighted average calculation.

[0024] Preferably, based on the calculated weighted average temperature value, the area where the average temperature is the highest is found, and by comparing the weighted average temperatures at different locations, the range of the area with the highest temperature is determined. This area is a more accurate calibration range of the fault location.

[0025] Preferably, the fault type is determined based on the temperature, traveling wave and fault area, and the temperature change in the fault area is observed. If the temperature rises sharply and continuously, it may be a short circuit fault; if the temperature rises slowly, it may be a chronic fault of insulation aging; the traveling wave characteristics are analyzed, and the traveling waves of different fault types behave differently; at the same time, combined with the location of the fault area, the temperature change trend, traveling wave characteristics and the location of the fault area are correlated and compared, and the fault type is determined based on the line parameters of the cable.

[0026] The technical effects and advantages of the present invention are as follows: through high-precision time synchronization and accurate calculation of traveling wave velocity, combined with the arrival time difference of traveling waves at both ends of the cable, the scope of the fault area can be accurately determined, the cable temperature can be monitored in real time and the traveling wave velocity can be corrected, the influence of the operating state on positioning can be reduced, and the temperature change rate, the temperature difference between adjacent monitoring points and the weighted average temperature can be calculated, so as to further accurately calibrate the fault location; comprehensive temperature, traveling wave and fault area information can be used to accurately determine the fault type according to line parameters, which helps to improve the accuracy and timeliness of high-voltage cable fault identification, provide strong guarantee for the safe and stable operation of the power system, reduce fault outage time, reduce operation and maintenance costs, and improve the level of cable operation management. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic structural diagram of a high-voltage cable fault identification method for online monitoring of sheath current.

[0028] Figure 2 This is a schematic diagram of the structure of the method for determining the fault area of ​​the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The embodiments of the present invention provide Figure 1-Figure 2 A high-voltage cable fault identification method for online monitoring of sheath current is shown, comprising the following steps:

[0031] S1: Real-time monitoring is carried out through high-precision sheath current sensors, fault traveling wave collectors and cable temperature sensors at key locations along the high-voltage cable. The high-precision sheath current sensors monitor the changes in sheath current in real time. The fault traveling wave collector has a high sampling frequency to accurately capture the arrival time of the fault traveling wave. The cable temperature sensor can accurately measure the cable sheath temperature and is distributed in the fault area to form multi-point monitoring;

[0032] Specifically in the embodiment, during the installation process, the sensor and the collector should be closely attached to the cable sheath to ensure a good magnetic coupling effect. In addition, the sheath current sensor is installed at key positions along the high-voltage cable, such as the cable joint, the cable terminal and the position at a certain distance in the middle of the cable line. For long-distance cable lines, a sensor is installed at a certain distance, such as every 1-2 kilometers, to ensure that the distribution of the sheath current along the cable can be fully monitored; the cable temperature sensors are distributed in the fault area to form a multi-point monitoring network. In the determined fault area, such as the area suspected of possible fault based on previous monitoring or cable line characteristics, the temperature sensors are reasonably arranged according to the cable length and structural characteristics. The sensor density is appropriately increased near the cable joint, the part of the cable body that is prone to overheating, such as the area close to the heat source or the area with large load, and other key positions to ensure that the temperature changes in the fault area can be fully and accurately monitored. For example, for a 1-kilometer-long fault area cable, 10-20 temperature sensors may be installed, and the distance between adjacent sensors varies from tens of meters to hundreds of meters according to actual conditions, forming a relatively dense temperature monitoring network.

[0033] S2: Collect the line parameters of high-voltage cables in detail, including cable length, conductor material and cross-sectional area, insulation material characteristics, sheath structure, and cable wave impedance information, and enter them into the monitoring system database;

[0034] Specifically in the embodiment, for shorter high-voltage cable lines, a direct measurement method can be used. The measurement personnel will follow the cable laying path, starting from one end of the cable, and slowly roll the distance measuring wheel or stretch the steel tape measure to the other end of the cable, and read the length value displayed on the measuring tool. During the measurement process, it is necessary to ensure that the measurement path is completely consistent with the actual direction of the cable to avoid measurement errors caused by bending, detours, etc. For longer cable lines, an indirect measurement method based on the electrical characteristics of the cable is used. Professional cable testing instruments are used to measure through the pulse reflection method. The conductor material and cross-sectional area, insulation material characteristics, sheath structure, and cable wave impedance information can all be obtained through product factory parameters.

[0035] S3: Analyze the collected normal operating sheath current and temperature data, calculate the mean, standard deviation, spectrum characteristic parameters of the sheath current, and the average level and fluctuation range characteristics of the temperature, establish a normal operating sheath current and temperature characteristic model through statistical analysis methods, and determine the typical range and variation law of the sheath current and temperature under normal conditions;

[0036] Specifically in the embodiment, according to the calculated characteristic parameters, the normal operating sheath current and temperature characteristic models are established. For the sheath current, the normal range of the mean is set to the overall mean ± a certain multiple standard deviation, that is, 6mA-14mA, and the main frequency in the spectrum characteristics should be between 45Hz-55Hz. For temperature, the normal range of the average temperature is set to 25℃-35℃, and the fluctuation range does not exceed 7℃. These ranges are used as the judgment criteria of the normal operating characteristic model;

[0037] Furthermore, the established model is verified using normal operation data from another time period, and the newly collected data is substituted into the model for judgment, and the false positive rate, that is, the proportion of normal data judged as abnormal, and the missed judgment rate, that is, the proportion of abnormal data judged as normal, are counted; if the false positive rate and missed judgment rate are high, the data is re-analyzed, and the model parameters, such as the mean range, spectrum threshold, etc., are adjusted until the accuracy of the model meets the requirements, such as the false positive rate is less than 5%, and the missed judgment rate is less than 3%. Through continuous verification and optimization, a reliable normal operation sheath current and temperature characteristic model is established to provide an accurate basis for subsequent fault judgment.

[0038] S4: Calculate the sheath current collected in real time and compare it with the sheath current characteristic model of normal operation. If the characteristic parameter of the sheath current exceeds the normal range threshold, it is preliminarily determined that the cable is faulty. By measuring the time difference between the traveling wave reaching the two ends of the cable and combining the known traveling wave speed, the approximate distance range from the fault point to one end is calculated, thereby determining the fault area.

[0039] Specifically, in the embodiment, the sheath current characteristic parameters calculated in real time are compared with the normal operating sheath current characteristic model. When setting the threshold, the measurement error and the normal operating fluctuation of the cable are considered. For example, the sheath current mean threshold is set to the standard deviation of the normal mean, and the change rate threshold is set to 2 times the normal maximum change rate. If the sheath current mean exceeds the threshold range or the change rate exceeds the threshold and lasts for a certain period of time, it is preliminarily determined that the cable is faulty.

[0040] Furthermore, for the fault traveling wave data, a comparative analysis is performed based on the pre-established downlink wave feature library for different fault types. For example, the traveling wave polarity is usually positive for a single-phase grounding fault, and may be negative or bipolar for a phase-to-phase short circuit fault. The downlink wave amplitude and rise time are also different for different fault types. By comparing the real-time collected traveling wave features with the data in the feature library, the fault type is preliminarily determined, and a comprehensive analysis is performed in combination with the judgment results of the sheath current fault.

[0041] S5: After determining the fault area, obtain the temperature change data over time in the fault area for a period of time, calculate the temperature change rate of each monitoring point and the temperature difference between adjacent monitoring points, analyze the increasing and decreasing trends of the temperature in the fault area, and obtain the average temperature values ​​of different positions in the fault area by weighted average calculation of the temperature of each monitoring point, and find the area with the highest average temperature. This area is the more accurate calibration range of the fault location;

[0042] Specifically in the embodiment, after the fault area is determined, the data of the temperature sensor in the fault area is continuously collected at a frequency of once per second for 10 minutes. The collected temperature data is preprocessed, and the Kalman filter method is used to further improve the accuracy and smoothness of the data and remove the influence of measurement noise. The rate of change of the temperature of each monitoring point is calculated using the central difference method, that is, Among them, T i is the temperature of the ith monitoring point, Δt is the sampling time interval;

[0043] Furthermore, the increasing and decreasing trends of the temperature in the fault area were analyzed, and the temperature change curve over time and the temperature distribution curve along the length of the cable were drawn. It was found from the curve that within the first 2 minutes after the fault occurred, the temperature of the monitoring point close to the cable joint rose rapidly, while the temperature of the monitoring point far from the joint rose slowly, showing a trend of decreasing from the joint to both sides; after 2-5 minutes, the temperature rise rate gradually slowed down, but the temperature at the joint was still the highest, and the overall trend was still that the temperature gradually decreased from the joint to both sides; after 5-10 minutes, the temperature tended to stabilize, and the temperature distribution gradient remained basically unchanged;

[0044] Furthermore, the weighted average temperature of each monitoring point is calculated, and the weighting coefficient is determined according to the distance between the monitoring point and the center of the fault area and the preliminarily determined fault location. The closer the monitoring point is to the center of the fault area, the larger the weighting coefficient is. After using the Gaussian weighting function to calculate the average temperature values ​​at different locations, it is found that the average temperature within the range of 0.5-1 meters from the cable joint is the highest. Therefore, the area is determined to be 0.5-1 meters away from the cable joint as a more accurate calibration range for the fault location. For further verification, the appearance of the cables in this area was checked, and it was found that the cable sheath had slight deformation and discoloration. It was preliminarily judged that the insulation damage may be caused by local overheating, which is consistent with the temperature monitoring results. At the same time, combined with the changes in the sheath current in this area, the sheath current increased significantly after the fault occurred, and a peak value appeared within the precise calibration range, which further confirmed that the fault location was in this area. The area can be subsequently inspected and repaired in detail, such as insulation resistance testing, partial discharge detection, etc., to determine the specific cause of the fault and take corresponding repair measures.

[0045] Furthermore, a trigger threshold of the acquisition device is set. When the traveling wave signal exceeds the threshold, the fault traveling wave collector starts to record the traveling wave data. The setting of the trigger threshold is reasonably adjusted according to the signal level during normal operation of the cable and the expected fault traveling wave signal size to ensure that the fault traveling wave can be captured in time and avoid false triggering.

[0046] Specifically in the embodiments, when the cable is operating normally, although there may be some weak signal fluctuations caused by factors such as electromagnetic interference, these signals usually have certain characteristics and ranges. By collecting and analyzing data for a long time, such as several days or even weeks, when the cable is operating normally, the distribution of parameters such as signal amplitude and frequency that may appear during normal operation is statistically calculated. For example, the signal amplitude during normal operation may be mainly concentrated in a lower range, and the frequency component is relatively stable. The statistical characteristics of these normal operating signals will serve as an important reference for setting the lower limit of the trigger threshold, ensuring that the trigger threshold is higher than the maximum signal level during normal operation, and avoiding false triggering of the acquisition device due to normal signal fluctuations;

[0047] Furthermore, by setting the lower limit of the trigger threshold higher than the signal level during normal operation of the cable, false triggering caused by electromagnetic interference, signal fluctuations and other factors during normal operation is effectively avoided. In a complex power system environment, there are various interference sources, such as the switching operation of adjacent equipment, lightning induction, etc. These interferences may cause short-term signal changes on the cable. If the trigger threshold is set unreasonably, these normal interference signals are easily misjudged as fault traveling waves, thereby issuing erroneous alarm information, causing the operation and maintenance personnel to perform unnecessary inspections and maintenance work, wasting manpower and material resources.

[0048] Determining the fault area in step S4 includes the following steps:

[0049] S41: To ensure the accuracy of the traveling wave arrival time record, high-precision time synchronization is used to synchronize the acquisition time of the fault traveling wave collectors at both ends of the cable. The synchronization error is controlled within nanoseconds to accurately measure the time difference between the traveling wave arriving at both ends of the cable.

[0050] S42: Based on the structural parameters and physical characteristics of the cable, the theoretical propagation speed of the traveling wave in the cable is calculated using the electromagnetic field theory formula. For lossless cables, the speed of the traveling wave is Wherein, L is the inductance of the cable per unit length, and C is the capacitance of the cable per unit length. The inductance and capacitance are calculated through the material and structural parameters of the cable.

[0051] S43: according to the speed of the traveling wave and the time difference between the traveling wave and the two ends of the cable, the distance between one end of the cable and the fault point is obtained, thereby determining the range of the fault area;

[0052] Specifically in the embodiment, when the traveling wave reaches both ends of the cable, the collector uses a high-precision counter to count the system clock pulses and record the timestamp of the arrival time of the traveling wave. By comparing the timestamps recorded by the collectors at both ends, the time difference of the traveling wave arriving at both ends of the cable is calculated;

[0053] Furthermore, for cables with multi-layer structures, such as metal shielding layers and armor layers, the influence of these additional structural layers needs to be considered when calculating inductance and capacitance. The metal shielding layer and armor layer will change the electromagnetic field distribution inside the cable, thereby affecting the inductance and capacitance values. Appropriate corrections should be made according to the specific situation or adjustments should be made using empirical coefficients to ensure that the calculated inductance and capacitance values ​​can accurately reflect the actual electrical characteristics of the cable.

[0054] Furthermore, the operating state of the cable will affect the traveling wave speed. Temperature changes will cause the physical properties of the cable material to change, affecting the traveling wave speed. By real-time monitoring of the cable temperature, a relationship curve between temperature and traveling wave speed is constructed, and the traveling wave speed is corrected in real time to reduce the impact of the operating state of the cable on the traveling wave speed.

[0055] Specifically in the embodiment, the collected traveling wave velocity data at different temperatures are sorted and analyzed. With temperature as the independent variable and traveling wave velocity as the dependent variable, a scatter plot is drawn to observe the distribution trend of the data points. Generally, temperature and traveling wave velocity present a nonlinear relationship. A suitable curve fitting method, such as the least squares method, is used to fit the scatter plot to obtain a curve equation for the relationship between temperature and traveling wave velocity. The fitted equation may be v=aT 2 +bT+c, where v is the traveling wave velocity, T is the temperature, and a, b, and c are fitting coefficients. The fitting effect is judged by analyzing the evaluation indicators of the fitting curve to ensure that the curve can accurately reflect the relationship between temperature and traveling wave velocity;

[0056] Furthermore, according to the real-time monitored cable temperature, it is substituted into the constructed temperature and traveling wave velocity relationship curve equation to calculate the corrected traveling wave velocity. Then, in the subsequent fault location calculation, the corrected traveling wave velocity is used to replace the original theoretical traveling wave velocity, thereby reducing the influence of the cable operating state on the traveling wave velocity and improving the accuracy of fault location.

[0057] Step S5 includes the following steps:

[0058] S51: setting the data collection frequency of the temperature sensor, after the fault area is determined, capturing the dynamic change process of the temperature, increasing the collection frequency, and continuously collecting for a period of time to obtain enough temperature data samples for subsequent analysis;

[0059] S52: For each temperature monitoring point, calculate its temperature change rate. The calculation formula is: Where ΔT is the temperature difference between adjacent sampling points, and Δt is the sampling time interval;

[0060] S53: Calculate the temperature difference between adjacent temperature monitoring points, and determine the direction of temperature increase or decrease by comparing the temperature difference between adjacent monitoring points at different positions, so as to infer the approximate location of the fault point;

[0061] S54: Calculate the weighted average temperature of each monitoring point. The weight coefficient can be determined by considering the distance between the monitoring point and the possible fault point and the importance of the location of the monitoring point. The closer the monitoring point is to the possible fault point, the greater its weight coefficient is. The calculation formula is: Where T avg is the weighted average temperature, w i is the weight coefficient of the ith monitoring point, T i is the temperature of the th monitoring point, n is the total number of monitoring points, and the specific fault location in the fault area can be located more accurately through weighted average calculation;

[0062] Specifically in the embodiment, when the calculated temperature difference ΔT between adjacent monitoring points is positive, it indicates that the temperature of the latter monitoring point is higher than that of the previous monitoring point, that is, the temperature is increasing; conversely, when ΔT is negative, the temperature is decreasing; by calculating the temperature difference of adjacent monitoring points at different positions along the cable line in sequence, and observing its positive and negative changes, the direction of temperature increase or decrease can be preliminarily determined.

[0063] Furthermore, after determining the direction of temperature increase and decrease, the location of the fault point is inferred based on the actual structure and laying conditions of the cable.

[0064] According to the calculated weighted average temperature value, find the area where the average temperature is the highest. By comparing the weighted average temperatures at different locations, determine the area with the highest temperature. This area is the more accurate calibration range of the fault location.

[0065] Specifically in the embodiment, before calculating the weighted average temperature, the fault area needs to be divided into several sub-areas according to the length of the cable and the distribution of monitoring points; the division principle should ensure that there are a sufficient number of monitoring points in each sub-area, and the length of the sub-area should not be too long or too short, so as to accurately reflect the temperature change trend.

[0066] Determine the fault type based on temperature, traveling wave and fault area, and observe the temperature change in the fault area. If the temperature rises sharply and continuously, it may be a short circuit fault; if the temperature rises slowly, it may be a chronic fault of insulation aging; analyze the characteristics of traveling waves, and the performance of traveling waves of different fault types is different; at the same time, combined with the location of the fault area, by correlating and comparing the temperature change trend, traveling wave characteristics and the location of the fault area, determine the fault type based on the line parameters of the cable;

[0067] Specifically in the embodiment, when the temperature rises sharply and continuously, in addition to the preliminary judgment of a short circuit fault, it is necessary to further analyze the rate and amplitude of the temperature rise; at the same time, observe the duration of the temperature rise and the final stable temperature value. If the temperature continues to rise until it reaches the allowable limit temperature of the cable material or even higher, and remains at a high level before the fault is eliminated, this further supports the judgment of a short circuit fault;

[0068] Furthermore, first, the temperature change trend, traveling wave characteristics and fault area location are analyzed independently to obtain the preliminary judgment information about the fault type. Then, the three aspects of information are correlated and compared. If there are some inconsistencies or ambiguities between the three, such as the slow rise in temperature indicates insulation aging, but the traveling wave characteristics are not typical, and the location of the fault area does not clearly point to a specific fault cause, it is necessary to collect further information, such as cable insulation resistance testing, partial discharge detection, etc., or refer to the historical experience of handling similar situations, and make judgments based on more factors to finally determine the fault type so that targeted repair measures can be taken. At the same time, in the entire judgment process, the line parameters of the cable should be fully considered. The line parameters include cable length, conductor material and cross-sectional area, insulation material characteristics, sheath structure, cable wave impedance information, etc., and their influence on temperature, traveling wave propagation and fault occurrence to ensure the accuracy of fault type judgment.

[0069] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A high voltage cable fault identification method for online monitoring of sheath current, characterized in that: The following steps are involved: S1: Real-time monitoring is carried out through high-precision sheath current sensors, fault traveling wave collectors and cable temperature sensors at key locations along the high-voltage cable. The high-precision sheath current sensors monitor the changes in sheath current in real time. The fault traveling wave collector has a high sampling frequency to accurately capture the arrival time of the fault traveling wave. The cable temperature sensor can accurately measure the cable sheath temperature and is distributed in the fault area to form multi-point monitoring; S2: Collect the line parameters of high-voltage cables in detail, including cable length, conductor material and cross-sectional area, insulation material characteristics, sheath structure, and cable wave impedance information, and enter them into the monitoring system database; S3: Analyze the collected normal operating sheath current and temperature data, calculate the mean, standard deviation, spectrum characteristic parameters of the sheath current, and the average level and fluctuation range characteristics of the temperature, establish a normal operating sheath current and temperature characteristic model through statistical analysis methods, and determine the typical range and variation law of the sheath current and temperature under normal conditions; S4: Calculate the sheath current collected in real time and compare it with the sheath current characteristic model of normal operation. If the characteristic parameter of the sheath current exceeds the normal range threshold, it is preliminarily determined that the cable is faulty. By measuring the time difference between the traveling wave reaching the two ends of the cable and combining the known traveling wave speed, the approximate distance range from the fault point to one end is calculated, thereby determining the fault area. S5: After determining the fault area, obtain the temperature change data over time in the fault area for a period of time, calculate the temperature change rate of each monitoring point and the temperature difference between adjacent monitoring points, analyze the increasing and decreasing trends of the temperature in the fault area, and obtain the average temperature values ​​of different positions in the fault area by performing weighted average calculation on the temperature of each monitoring point, and find the area with the highest average temperature. This area is the more accurate calibration range of the fault location.

2. The method for identifying high-voltage cable faults by online monitoring of sheath current according to claim 1 is characterized in that: Set the trigger threshold of the acquisition device. When the traveling wave signal exceeds the threshold, the fault traveling wave collector starts to record the traveling wave data. The trigger threshold is set based on the signal level during normal operation of the cable and the expected fault traveling wave signal size to ensure that the fault traveling wave can be captured in time and avoid false triggering.

3. The high-voltage cable fault identification method for online sheath current monitoring according to claim 1 is characterized in that: Determining the fault area in step S4 includes the following steps: S41: To ensure the accuracy of the traveling wave arrival time record, high-precision time synchronization is used to synchronize the acquisition time of the fault traveling wave collectors at both ends of the cable. The synchronization error is controlled within nanoseconds to accurately measure the time difference between the traveling wave arriving at both ends of the cable. S42: Based on the structural parameters and physical characteristics of the cable, the theoretical propagation speed of the traveling wave in the cable is calculated using the electromagnetic field theory formula. For lossless cables, the speed of the traveling wave is Wherein, L is the inductance of the cable per unit length, and C is the capacitance of the cable per unit length. The inductance and capacitance are calculated through the material and structural parameters of the cable. S43: According to the speed of the traveling wave and the time difference between the traveling wave and the two ends of the cable, the distance between one end of the cable and the fault point is obtained, thereby determining the scope of the fault area.

4. A high-voltage cable fault identification method for online monitoring of sheath current according to claim 3, characterized in that: The operating state of the cable will affect the traveling wave speed. Temperature changes will cause changes in the physical properties of the cable material, affecting the traveling wave speed. By real-time monitoring of the cable temperature, a relationship curve between temperature and traveling wave speed is constructed, and the traveling wave speed is corrected in real time to reduce the impact of the cable's operating state on the traveling wave speed.

5. The method for identifying high-voltage cable faults by online monitoring of sheath current according to claim 1 is characterized in that: The step S5 comprises the following steps: S51: setting the data collection frequency of the temperature sensor, after the fault area is determined, capturing the dynamic change process of the temperature, increasing the collection frequency, and continuously collecting for a period of time to obtain enough temperature data samples for subsequent analysis; S52: For each temperature monitoring point, calculate its temperature change rate. The calculation formula is: Where ΔT is the temperature difference between adjacent sampling points, and Δt is the sampling time interval; S53: Calculate the temperature difference between adjacent temperature monitoring points, and determine the direction of temperature increase or decrease by comparing the temperature difference between adjacent monitoring points at different positions, so as to infer the approximate location of the fault point; S54: Calculate the weighted average temperature of each monitoring point. The weight coefficient can be determined by considering the distance between the monitoring point and the possible fault point and the importance of the location of the monitoring point. The closer the monitoring point is to the possible fault point, the greater its weight coefficient is. The calculation formula is: Where T avg is the weighted average temperature, w i is the weight coefficient of the ith monitoring point, T i is the temperature of the th monitoring point, n is the total number of monitoring points, and the specific fault location in the fault area can be located more accurately through weighted average calculation.

6. A high-voltage cable fault identification method for online monitoring of sheath current according to claim 5, characterized in that: According to the calculated weighted average temperature value, find the area where the average temperature is the highest. By comparing the weighted average temperatures at different locations, determine the range of the area with the highest temperature. This area is the more accurate calibration range of the fault location.

7. The method for identifying high-voltage cable faults by online monitoring of sheath current according to claim 1 is characterized in that: Determine the fault type based on the temperature, traveling wave and fault area, observe the temperature change in the fault area, if the temperature rises sharply and continuously, it may be a short circuit fault; if the temperature rises slowly, it may be a chronic fault of insulation aging; analyze the characteristics of the traveling wave, and the performance of the traveling wave is different for different fault types; at the same time, combined with the location of the fault area, by correlating and comparing the temperature change trend, the characteristics of the traveling wave and the location of the fault area, the fault type can be determined based on the line parameters of the cable.

Images