CN116840614A - Cable line defect sensing and early warning method based on harmonic fluctuation characteristics - Google Patents
Cable line defect sensing and early warning method based on harmonic fluctuation characteristics Download PDFInfo
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Abstract
The invention belongs to the technical field of cable line defect sensing, and particularly relates to a cable line defect sensing early warning method based on harmonic fluctuation characteristics. And carrying out quantization processing on other types of information, obtaining the relative importance weight of the information to the target through fuzzy analytic hierarchy process, judging whether the relative importance weight exceeds a monitoring signal threshold value, and carrying out auxiliary judgment.
Description
Technical Field
The invention belongs to the technical field of cable line defect sensing, and particularly relates to a cable line defect sensing early warning method based on harmonic fluctuation characteristics.
Background
In the construction of a modern urban power distribution network, the characteristics of low failure rate, small maintenance, safe and reliable power supply, attractive environment and the like are greatly popularized and applied because the cable is installed underground, and the urban operation safety and stability are closely related to the operation state of the cable. However, because manual operation, the cable manufacturing process is rough, and the cable is subject to reasons such as environmental acid-base corrosion, so that partial cables enter a local ageing state in advance, and especially after a certain period of time of water inflow of a cable channel is recovered, local scratches, trepanning holes and the like of the cable easily infiltrate certain moisture, water branches are gradually formed under the action of an electric field, if the field intensity is too high, then the electric branches are formed, and finally the cable is insulated and penetrated, so that the reliability of the operation cable is greatly reduced. The design life of the cable is thirty years, and in the operation process of the cable, the local part of the cable is often defective in advance due to the influence of external force factors, and if the local defect is not removed early, the local defect can gradually evolve into a cable fault. Once the cable fails, the urban power grid is blocked, so that the production and life of people are seriously affected, and serious economic loss is caused to society. Therefore, local defects of the cable can be effectively eliminated in time, and urban safe and stable operation can be ensured.
With the rapid development of socioeconomic performance, the safe operation of power cables is becoming more and more of an issue. In the operation process of the cable, the cable is often subjected to electric leakage due to the influence of factors such as long-time high temperature, moist or corrosive environment, long service time of an insulating circuit, aging or damage of the insulating circuit, exposed wire core, low laying of the insulating circuit, collision, extrusion and other external force damage, and short-circuit fire disaster.
At present, a large amount of manpower and material resources are required to be consumed in the actual operation of the low-voltage line to carry out offline detection and maintenance on the cable, and an effective means is lacked to carry out quick investigation on the potential insulation hazards of the low-voltage line. With the gradual aging of the low-voltage line, the probability of insulation faults is increased, and technical means are introduced to effectively check hidden dangers, so that the key points are the detection and positioning of cable insulation defects and the effective evaluation of defect states. At present, most of operation and maintenance management of urban distribution cable networks have almost the same management strategy for power cables, and follow the strategies of post maintenance and regular scheduled maintenance. The method lacks the technical means of sensing and early warning of the running state of the line, cannot timely discover a plurality of insulation defects and potential faults, and cannot timely and comprehensively understand the running state and the reliability condition of the cable.
The first 10kV coaxial cable was manufactured by Vincent de Ferranti in 1890, and after 1970, the cable manufacturing industry continued to achieve new results as material technology and electrotechnical electronics continue to evolve [1]. The power cable material is widely put into a cross-linked polyethylene power cable (XLPE insulated power cable) in large and medium cities from a low-voltage street lamp power cable which is firstly made of an oil paper insulated cable, an oil filled cable and a cross-linked cable. The voltage level of the high-voltage power supply is gradually increased to 25kV, 66kV and 380kV from the initial 10kV, and then the high-voltage power supply is developed to the extra-high voltage of 500kV and above in recent years, and the voltage level reaches a qualitative leap after more than one hundred twenty years. With the continuous development of the material and voltage class of the power cable, the state evaluation method related to the material and voltage class is also continuously developed.
The invention patent with publication number of CN 215005689U discloses a monitoring device for sensing defects of a distribution cable, which comprises a protection shell, a core main board, an online power taking module, a wireless communication module, a clock module and a monitoring data receiving module, wherein the core main board, the online power taking module, the wireless communication module, the clock module and the monitoring data receiving module are arranged in the shell; the wireless communication module is connected with the core main board and is used for receiving or transmitting state cable state data; the clock module is used for providing accurate clock information for the core main board; the monitoring data receiving module is respectively connected with the core main board and a monitoring terminal arranged on the site; the monitoring terminals are arranged at two ends of the distribution cable and at the cable tap. Due to the eddy current loss and hysteresis loss in the cable, the resistance value can be increased along with the increase of harmonic frequency, and the magnetic flux compression effect generated by eddy current can lead the inductance to be reduced along with the increase of harmonic frequency. This patent does not take this into account, which necessarily leads to errors in the early warning.
Disclosure of Invention
The invention aims to provide a cable line defect sensing and early warning method based on harmonic fluctuation characteristics, which aims at solving the problems in the prior art. And carrying out quantization processing on other types of information, obtaining the relative importance weight of the information to the target through fuzzy analytic hierarchy process, judging whether the relative importance weight exceeds a monitoring signal threshold value, and carrying out auxiliary judgment.
The technical scheme of the invention is as follows:
a cable line defect perception early warning method based on harmonic fluctuation characteristics comprises the following steps:
s1: on-line monitoring a cable current transient wave recording signal to be detected, obtaining a characteristic frequency band of the transient wave recording signal, using a current transformer and a voltage transformer to sample three-phase voltage, three-phase current, zero-sequence voltage and zero-sequence current of the cable to be detected at high frequency, storing the three-phase voltage, the three-phase current, the zero-sequence voltage and the zero-sequence current as standard combo format data, sensing cable defects through fluctuation of the characteristic frequency band, and performing state evaluation on the detected cable;
s2: and meanwhile, the equipment information, the operation and maintenance information, the environment and external force influence information and the off-line test information of the cable to be monitored on line are quantized, the relative importance weight of the cable to the target is obtained through fuzzy analytic hierarchy process, whether the monitored signal threshold is exceeded or not is judged to assist in judging whether defects exist or not, and if the monitored signal threshold is exceeded, an alarm is given.
2. Specifically, in the step S1, the state evaluation is performed on the detected cable, which includes the following steps:
1) According to the sampled three-phase voltage current and zero-sequence voltage current of the cable to be tested, respectively calculating effective value phase voltage, phase current, zero-sequence voltage and zero-sequence current, and setting a starting threshold value;
2) Calculating and recording the content of each harmonic wave and the total harmonic distortion rate by taking 4 cycles as a time window;
3) Classifying different harmonic waveforms through a characteristic frequency band by using a support vector machine, and then carrying out defect identification on the cable with abnormal state;
4) Testing PD signals of the cable line, and calculating the maximum discharge capacity, the maximum voltage amplitude and the discharge times by utilizing a map;
5) After the voltage current or the total harmonic distortion rate or the content of each subharmonic or the maximum discharge capacity, the maximum voltage amplitude and the discharge times reach the starting threshold, storing the data in the first 100 cycles until the data in the last 4 cycles are recovered, and calling the recording data in the last starting step to enter the step 5);
6) The method comprises the steps of calling wave recording data during faults and harmonic distortion rate change conditions during two faults, comparing, and evaluating and early warning cable states;
7) After all the data are stored, the harmonic information showing close correlation is uploaded, and early warning information is provided.
Specifically, the starting threshold value in the step 1) is expressed as follows:u 0 the fault starting threshold is 2 times of the effective value of the phase voltage and the phase current.
Specifically, in the step S1, the cable current obtained by online measurement is subjected to fourier decomposition, assuming that the fundamental frequency of the current is ω 0 The cable current measurement i may be expressed in terms of a fourier series:
wherein n is the harmonic frequency, I n Amplitude of the nth harmonic current, ψ n The fundamental component is represented when n=1, and t is time, which is the initial phase angle of the nth harmonic current.
Specifically, classifying different harmonic waveforms by using a support vector machine through characteristic frequency bands includes the steps of classifying the duty ratio of each harmonic current under different insulation defects of a power cable, and firstly classifying the effective value I of the total current of the cable all Total harmonic current effective value I harm Solving, wherein the calculation formulas are shown as (2) to (3),
the ratio H of the individual harmonics in the total harmonic can be solved by equation (4),
the ratio N of the total harmonic component to the fundamental component can be solved by equation (5),
in the formula (5), I 1 Based on equations (2) to (5), the effective value of the fundamental current is obtained by performing simulation test on the typical insulation defect of the cable, measuring the value of the current flowing through the power cable containing the insulation defect, and analyzing the characteristics of each subharmonic component of the current in the insulation defect state of the different cable.
Specifically, the equipment information comprises names, models, operational years and voltage levels.
Specifically, the environmental and external influences comprise the external damage times, the soaking times, the temperature, the humidity and the rainfall.
In particular, the operation and maintenance information comprises overload/reload warnings, currents, tripping times and family defects.
Specifically, the off-line test information comprises an insulation resistance value, a contact resistance value, an alternating-current withstand voltage test, a direct-current resistance test and an outer sheath insulation resistance of the overvoltage protector.
In the long-term operation process of the cable line, insulation aging and faults can be generated due to various factors such as electromagnetic, mechanical stress, heat, environmental corrosion, moisture erosion and the like. The online detection and diagnosis of the high-voltage cable line at home and abroad are more studied, the research of the power distribution cable line is less, and the diagnosis and positioning after the fault of the line are biased, thus belonging to the offline fault diagnosis. The existing monitoring and positioning device can not monitor the running state of the power distribution and utilization cable line in real time, can not effectively detect and diagnose the instantaneous fault and the high-impedance fault with unobvious characteristics of the line, and further has no function of forecasting the early fault of the cable line.
In order to timely master the insulation defect and fault position of the cable line in the operation process, the cable line is monitored on line and fault positioning is carried out, on one hand, the insulation defect (hidden fault) of the cable in the operation process can be timely detected, targeted treatment measures are adopted, and the cable line fault is avoided; on the other hand, the fault is accurately positioned according to the on-line fault information and the line parameters, the fault line is repaired in time, the power supply reliability is improved, and the event upgrading is avoided.
How to realize early discovery, early investigation and early solution of cable faults becomes a key link for reducing the total amount of cable faults and improving the power supply reliability.
At present, the operation and maintenance of the cable line is mainly manual inspection, state detection and on-line monitoring, data are discretized and islanding, operation and maintenance personnel cannot effectively evaluate and master the operation state of the cable line in the inspection or maintenance process, line operation and state information data cannot be acquired through a system platform, inspection efficiency is restricted to a certain extent, inspection and detection data are scattered in various detection devices, data forms or monitoring platforms, the format lacks uniformity standardization, information interaction is difficult to realize, and the recording and storage workflow is complex. In view of the existing data conditions of cable professional management and operation and inspection businesses, data such as standing accounts, completion, inspection detection, perception monitoring, maintenance records, professional management and the like exist in multi-form images, texts and numbers, cross-data type analysis technologies are few, centralized detection and monitoring data analysis is mainly used in the existing conditions, and the correlation analysis mining capacity among state quantities is insufficient.
The invention develops core technical research from intelligent sensing of the distribution cable, forms harmonic component fluctuation sensing technology of the distribution cable line, determines application range and diagnostic criteria, solves core difficult problems of insufficient state management and control capability and inconvenient application of the distribution cable line, and develops field detection application.
The invention can reflect the insulation condition of the cable to a certain extent by the cable related index data obtained by the on-line off-line detection and the long-term on-line monitoring of the cable, but the means is single, the multi-source information of the cable is not comprehensively considered, and a cable state evaluation model of the system cannot be established to comprehensively evaluate the cable state. With the continuous improvement of the requirements of society on the power supply reliability, the off-line online test of the cable and a large amount of historical data accumulated by the long-term operation of the online monitoring system provide precious data resources for electric power staff, and the maintenance strategies of all electric power enterprises at home and abroad are changed from a planned maintenance mode to a state maintenance mode.
According to the early warning method provided by the invention, the grounding current transient wave recording signal is monitored on line, the characteristic frequency band of the transient signal is obtained, the cable defect is perceived through the fluctuation of the characteristic frequency band, and different harmonic waveforms are classified by using a support vector machine. And carrying out quantization processing on other types of information, obtaining the relative importance weight of the information to the target through fuzzy analytic hierarchy process, judging whether the relative importance weight exceeds a monitoring signal threshold value, and carrying out auxiliary judgment. The method fills the market blank, the current urban distribution cable network operation and maintenance management lacks of a line operation state sensing and early warning technical means, mass equipment management data and operation detection service data are in an off-line management state, the project study is suitable for live state sensing early warning of distribution cable lines, a distribution cable line typical ageing and degradation defect sensing technical means and an operation state evaluation criterion are established, defect identification early warning is carried out, a distribution cable state detection technical body is perfected, the safe and stable operation capacity of a distribution network can be remarkably improved, the total times of fault outage of the distribution line are reduced, the power failure range of the distribution line is reduced, and therefore economic losses are reduced, and greater economic benefits are created.
Detailed Description
The present invention will be described in detail with reference to the following embodiments.
A cable line defect perception early warning method based on harmonic fluctuation characteristics comprises the following steps:
the cable line defect perception early warning method based on harmonic fluctuation characteristics is characterized by comprising the following steps of:
s1: on-line monitoring a cable current transient wave recording signal to be detected, obtaining a characteristic frequency band of the transient wave recording signal, using a current transformer and a voltage transformer to sample three-phase voltage, three-phase current, zero-sequence voltage and zero-sequence current of the cable to be detected at high frequency, storing the three-phase voltage, the three-phase current, the zero-sequence voltage and the zero-sequence current as standard combo format data, sensing cable defects through fluctuation of the characteristic frequency band, and performing state evaluation on the detected cable;
s2: meanwhile, equipment information, operation and maintenance information, environment and external force influence information and offline test information of the cable to be monitored on line are quantized, relative importance weight of the cable to a target is obtained through fuzzy analytic hierarchy process, whether the cable exceeds a monitoring signal threshold value or not is judged to assist in judging whether defects exist, the equipment information comprises names, models, operation years and voltage grades, the environment and external force influence comprises external damage times, water immersion times, temperature, humidity and rainfall, the operation and maintenance information comprises overload/heavy load warning, current, tripping times and family defects, and the offline test information comprises an overvoltage protector insulation resistance value, a contact resistance value, an alternating-current withstand voltage test, a direct-current resistance test and an outer sheath insulation resistance.
3. Specifically, in the step S1, the state evaluation is performed on the detected cable, which includes the following steps:
1) According to the sampled three-phase voltage current and zero-sequence voltage current of the cable to be tested, respectively calculating effective value phase voltage, phase current, zero-sequence voltage and zero-sequence current, setting a starting threshold value, and the starting threshold value is expressed as follows:u 0 the fault starting threshold of the phase voltage and the phase current is 2 times of the effective value;
2) Calculating and recording the content of each harmonic wave and the total harmonic distortion rate by taking 4 cycles as a time window;
3) Classifying different harmonic waveforms through a characteristic frequency band by using a support vector machine, and then carrying out defect identification on the cable with abnormal state;
4) Testing PD signals of the cable line, and calculating the maximum discharge capacity, the maximum voltage amplitude and the discharge times by utilizing a map;
5) After the voltage current or the total harmonic distortion rate or the content of each subharmonic or the maximum discharge capacity, the maximum voltage amplitude and the discharge times reach the starting threshold, storing the data in the first 100 cycles until the data in the last 4 cycles are recovered, and calling the recording data in the last starting step to enter the step 5);
6) The method comprises the steps of calling wave recording data during faults and harmonic distortion rate change conditions during two faults, comparing, and evaluating and early warning cable states;
7) After all the data are stored, the harmonic information showing close correlation is uploaded, and early warning information is provided.
Due to the eddy current loss and hysteresis loss in the cable, the resistance value can be increased along with the increase of harmonic frequency, and the magnetic flux compression effect generated by eddy current can lead the inductance to be reduced along with the increase of harmonic frequency. In addition, the impedance value of the cable may be affected by factors such as the cable size, the cable installation method, the type of sequence of injected currents, and the like. Thus, different defect types are in different harmonicsThe impedance characteristics are different in the number, and the magnitude of harmonic current flowing through the cable core is also different. The current flowing in the core of the power cable is a function of time t and is formed by superposing a plurality of periodic current components with different frequencies, and the on-line measured cable current is subjected to Fourier decomposition in the step S1, and the fundamental frequency of the current is assumed to be omega 0 The cable current measurement i may be expressed in terms of a fourier series:
wherein n is the harmonic frequency, I n Amplitude of the nth harmonic current, ψ n The fundamental component is represented when n=1, and t is time, which is the initial phase angle of the nth harmonic current.
The method comprises classifying different harmonic waveforms through characteristic frequency bands by using a support vector machine, including the ratio of harmonic currents under different insulation defects of a power cable, and firstly, the effective value I of the total current of the cable all Total harmonic current effective value I harm Solving, wherein the calculation formulas are shown as (2) to (3),
the ratio H of the individual harmonics in the total harmonic can be solved by equation (4),
the ratio N of the total harmonic component to the fundamental component can be solved by equation (5),
in the formula (5), I 1 Based on equations (2) to (5), the effective value of the fundamental current is obtained by performing simulation test on the typical insulation defect of the cable, measuring the value of the current flowing through the power cable containing the insulation defect, and analyzing the characteristics of each subharmonic component of the current in the insulation defect state of the different cable.
Various on-line monitoring systems such as temperature, ground circulation, partial discharge and the like arranged on the cable accumulate a large amount of data for the power cable, and provide a data base for comprehensive evaluation of the state of the cable. Based on a large amount of data, carrying out state evaluation on the cable, and carrying out defect identification on the cable with abnormal state on the basis of the state evaluation result.
The invention is suitable for the live state sensing early warning and accurate detection positioning technology of the distribution cable line, establishes the accurate positioning technical means and the running state evaluation criterion of typical ageing and degradation defects of the distribution cable line, and further improves the distribution cable state detection technical system by applying three dimensions from defect identification early warning, accurate diagnosis positioning and flexible sensing. And researching a multi-dimensional and full-link risk assessment and deduction technology system of the distribution cable line, integrating big data mining and correlation analysis technology, realizing panoramic service fusion and operation and maintenance information interaction, establishing a distribution cable network operation and maintenance strategy decision based on operation risk deduction and operation and detection quality and effect assessment, and improving the differentiated accurate operation and decision guiding supporting capability of the distribution cable network. According to the invention, the harmonic signals formed by the discharge phenomenon of the insulation defects of the cable line are collected, the electric quantity harmonic characteristics of the distribution cable are captured and analyzed, and the cable state is evaluated and early-warned by comparing the typical data of the previous or historical record of the line, so that the latent faults can be found early, and the power failure loss caused by the faults is reduced.
Finally, it should be noted that the above-mentioned embodiments are only for illustrating the technical scheme of the present invention and are not limiting; while the invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that: modifications may be made to the specific embodiments of the present invention or equivalents may be substituted for part of the technical features thereof; without departing from the spirit of the invention, it is intended to cover the scope of the invention as claimed.
Claims (9)
1. The cable line defect perception early warning method based on harmonic fluctuation characteristics is characterized by comprising the following steps of:
s1: on-line monitoring a cable current transient wave recording signal to be detected, obtaining a characteristic frequency band of the transient wave recording signal, using a current transformer and a voltage transformer to sample three-phase voltage, three-phase current, zero-sequence voltage and zero-sequence current of the cable to be detected at high frequency, storing the three-phase voltage, the three-phase current, the zero-sequence voltage and the zero-sequence current as standard combo format data, sensing cable defects through fluctuation of the characteristic frequency band, and performing state evaluation on the detected cable;
s2: and meanwhile, the equipment information, the operation and maintenance information, the environment and external force influence information and the off-line test information of the cable to be monitored on line are quantized, the relative importance weight of the cable to the target is obtained through fuzzy analytic hierarchy process, whether the monitored signal threshold is exceeded or not is judged to assist in judging whether defects exist or not, and if the monitored signal threshold is exceeded, an alarm is given.
2. The method for sensing and early warning the defects of the cable line based on the harmonic fluctuation characteristics according to claim 1, wherein the step S1 of evaluating the state of the detected cable comprises the following steps:
1) According to the sampled three-phase voltage current and zero-sequence voltage current of the cable to be tested, respectively calculating effective value phase voltage, phase current, zero-sequence voltage and zero-sequence current, and setting a starting threshold value;
2) Calculating and recording the content of each harmonic wave and the total harmonic distortion rate by taking 4 cycles as a time window;
3) Classifying different harmonic waveforms through a characteristic frequency band by using a support vector machine, and then carrying out defect identification on the cable with abnormal state;
4) Testing PD signals of the cable line, and calculating the maximum discharge capacity, the maximum voltage amplitude and the discharge times by utilizing a map;
5) After the voltage current or the total harmonic distortion rate or the content of each subharmonic or the maximum discharge capacity, the maximum voltage amplitude and the discharge times reach the starting threshold, storing the data in the first 100 cycles until the data in the last 4 cycles are recovered, and calling the recording data in the last starting step to enter the step 5);
6) The method comprises the steps of calling wave recording data during faults and harmonic distortion rate change conditions during two faults, comparing, and evaluating and early warning cable states;
7) After all the data are stored, the harmonic information showing close correlation is uploaded, and early warning information is provided.
3. The method for detecting and warning defects of a cable line based on harmonic fluctuation characteristics according to claim 2, wherein the starting threshold value in the step 1) is expressed as follows:u 0 the fault starting threshold is 2 times of the effective value of the phase voltage and the phase current.
4. The method for sensing and early warning defects of a cable line based on harmonic fluctuation characteristics according to claim 1, wherein in the step S1, fourier decomposition is performed on the cable current obtained by online measurement, and the fundamental frequency of the current is assumed to be ω 0 The cable current measurement i may be expressed in terms of a fourier series:
wherein n is the harmonic frequency, I n Amplitude of the nth harmonic current, ψ n The fundamental component is represented when n=1, and t is time, which is the initial phase angle of the nth harmonic current.
5. Harmonic fluctuation feature-based according to claim 2The cable line defect sensing and early warning method is characterized in that the step 3) of classifying different harmonic waveforms through a characteristic frequency band by using a support vector machine comprises the steps of classifying the duty ratio of each subharmonic current under different insulation defects of a power cable, and firstly classifying the effective value I of the total current of the cable all Total harmonic current effective value I harm Solving, wherein the calculation formulas are shown as (2) to (3),
the ratio H of the individual harmonics in the total harmonic can be solved by equation (4),
the ratio N of the total harmonic component to the fundamental component can be solved by equation (5),
in the formula (5), I 1 Based on equations (2) to (5), the effective value of the fundamental current is obtained by performing simulation test on the typical insulation defect of the cable, measuring the value of the current flowing through the power cable containing the insulation defect, and analyzing the characteristics of each subharmonic component of the current in the insulation defect state of the different cable.
6. The method for sensing and early warning of defects of a cable line based on harmonic fluctuation characteristics according to claim 1, wherein the equipment information comprises names, models, operational years and voltage levels.
7. The method for sensing and early warning the defects of the cable line based on the harmonic fluctuation characteristics according to claim 1, wherein the environmental and external influences comprise the external damage times, the water immersion times, the temperature, the humidity and the rainfall.
8. The method for sensing and early warning defects of a cable line based on harmonic fluctuation characteristics according to claim 1, wherein the operation and maintenance information comprises overload/heavy load warning, current, tripping times and family defects.
9. The method for sensing and early warning the defects of the cable line based on the harmonic fluctuation characteristics according to claim 1, wherein the offline test information comprises an insulation resistance value of an overvoltage protector, a contact resistance value, an alternating current withstand voltage test, a direct current resistance test and an insulation resistance of an outer sheath.
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| CN117686783A (en) * | 2023-12-12 | 2024-03-12 | 武汉朗德电气有限公司 | High-voltage cable grounding current on-line monitoring device based on load dynamic management |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117686783A (en) * | 2023-12-12 | 2024-03-12 | 武汉朗德电气有限公司 | High-voltage cable grounding current on-line monitoring device based on load dynamic management |
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