CN113075501B - Cable fault positioning method and system based on impedance spectrum periodic characteristics - Google Patents

Cable fault positioning method and system based on impedance spectrum periodic characteristics Download PDF

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CN113075501B
CN113075501B CN202110329715.1A CN202110329715A CN113075501B CN 113075501 B CN113075501 B CN 113075501B CN 202110329715 A CN202110329715 A CN 202110329715A CN 113075501 B CN113075501 B CN 113075501B
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cable
fault
impedance spectrum
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CN113075501A (en
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张丹丹
莫石
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Huazhong University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

Abstract

The invention discloses a cable fault positioning method and system based on impedance spectrum periodic characteristics, belonging to the field of cable fault positioning and comprising the following steps: acquiring the average phase velocity of a cable to be detected, and measuring the impedance spectrum of the cable to be detected; extracting equivalent frequency division contained in the impedance spectrum, calculating a period corresponding to each equivalent frequency division, wherein the minimum period corresponds to the tail end of the cable, and each of the other periods corresponds to a cable fault section; and when the number of the periods is more than 1, the cable to be detected has faults, the position of the corresponding cable fault section is calculated based on each period except the minimum period, and the distance between any cable fault section and the head end of the cable is equal to the ratio of the average phase velocity of 1/2 to the corresponding period of any cable fault section. The fault position on the cable is associated with the periodic characteristics of the cable impedance spectrum to obtain the position of the cable fault, the influence of a peak is avoided, the cable fault can be accurately positioned, high voltage does not need to be applied in the positioning process, discharging does not need to be performed, a measuring circuit is simple, and the cable is not damaged.

Description

Cable fault positioning method and system based on impedance spectrum periodic characteristics
Technical Field
The invention belongs to the field of cable fault positioning, and particularly relates to a cable fault positioning method and system based on impedance spectrum periodic characteristics.
Background
The phenomena of electromagnetic loss increase, electric field distortion, temperature rise and the like can occur at the local defect position of the cable. If the local defects can not be found in time, branch aging can be further generated, and finally, the defects are developed into penetrating insulation defects, such as short-circuit defects and high-resistance defects, so that power supply interruption and power accidents are caused. If a certain technology can be adopted to realize the detection and the positioning of the local defects of the cable and eliminate the defects in time, the defects of the cable can be avoided. Therefore, the research significance of the detection and positioning technology of the local defects of the cable is great, the cable defects and power failure accidents can be prevented, and the safe and stable operation of an electrical system is guaranteed.
The traditional off-line measurement technology can be used for detecting the overall insulation state of the cable but cannot realize the defect positioning of the cable if parameters such as insulation resistance, dielectric loss factor, voltage withstanding value, and elongation at break of an insulating material of the cable are tested. With the development of the cable local defect detection technology, a series of practical methods for cable local defect positioning make breakthrough research progress, including an impedance method, a temperature online monitoring technology, a local discharge detection technology and an impedance spectrum technology.
The impedance method can position the high-resistance defect, but is greatly influenced by the interference of a power frequency electric field and the nonlinearity of a defect point electric arc, and the measurement error is large. For cables with voltage class of 110kv and above, the temperature online monitoring technology directly connects optical fibers into the cables, and the defects of the cables are located by monitoring the temperature and stress of the cables, but the cost is high. In the partial discharge detection technology, due to the problems of serious signal attenuation, large noise interference, large dispersion and the like, the identification of a partial discharge signal becomes very difficult. The existing impedance spectrum technology needs cables with the same length and the same model for comparison, and interference peaks exist in an obtained cable state diagnosis curve, so that defect positioning errors are caused.
Disclosure of Invention
Aiming at the defects and the improvement requirements of the prior art, the invention provides a cable fault positioning method and a cable fault positioning system based on impedance spectrum periodic characteristics, and aims to correlate the fault position on a cable with the periodic characteristics of the impedance spectrum of the cable, obtain a positioning curve of the cable fault and realize accurate and lossless cable fault positioning.
To achieve the above object, according to one aspect of the present invention, there is provided a cable fault location method based on impedance spectrum periodic characteristics, including: s1, acquiring the average phase velocity of the cable to be detected, and measuring the impedance spectrum of the cable to be detected; s2, extracting equivalent frequency division contained in the impedance spectrum, and calculating a period corresponding to each equivalent frequency division, wherein the minimum period corresponds to the tail end of the cable, and each of the rest periods corresponds to a cable fault section; and S3, when the number of the periods is more than 1, faults exist in the cable to be detected, and the position of the corresponding cable fault section is calculated based on each period except the minimum period, wherein the distance from any cable fault section to the head end of the cable is equal to the ratio of the average phase speed of 1/2 to the corresponding period of any cable fault section.
Further, S1 is preceded by: and determining the frequency range of impedance spectrum measurement based on the length of the cable to be detected, so that the bandwidth of the impedance spectrum measurement is the maximum value under the condition of meeting the constraint condition.
Further, the constraint conditions are:
wherein, Δ f is the bandwidth of the impedance spectrum measurement, N is the total number of sampling points of the impedance spectrum measurement, N is the number of sampling points in each period, v1And l is the wave speed, and l is the length of the cable to be detected.
Further, the obtaining of the average phase velocity of the cable to be detected in S1 includes: respectively measuring impedance spectrums in the frequency range when the end part of the fault-free cable is open-circuited or short-circuited, wherein the type of the fault-free cable is the same as that of the cable to be detected; and calculating the average phase velocity of the cable to be detected in the frequency range according to the impedance spectrum of the fault-free cable.
Figure BDA0002994508820000021
Further, the average phase velocity is:
v2＝2πf/β
γ＝α+iβ
Figure BDA0002994508820000031
wherein v is2Is the average phase velocity, f is the frequency point within the frequency range, β is the phase shift coefficient, γ is the propagation constant, α is the attenuation constant, ZscAs short-circuit impedance, ZopFor open circuit impedance, l' is the length of the faultless cable.
Further, the impedance spectrum of the cable to be detected is derived as follows:
Figure BDA0002994508820000032
Figure BDA0002994508820000033
Figure BDA0002994508820000034
Figure BDA0002994508820000035
wherein Z isl-x-dFor the impedance from the end of the faulty section to the end of the cable, Zl-xFor the impedance from the head end of the fault section to the tail end of the cable, ZxInput impedance, Z, measured for the head end of the cablecCharacteristic impedance for fault-free section, ZdIs the characteristic impedance of the fault section, ΓLIs the load reflection coefficient, Γ1For the reflection coefficient at the end of the fault section, Γ2Is the reflection coefficient, gamma, at the head end of the fault sectioncPropagation constant, gamma, for faultless sectionsdIs the propagation constant of the fault section, l is the length of the cable to be detected, x is the length from the head end of the fault section to the head end of the cable, d is the length of the fault section, alpha is the attenuation constant, v2F is the frequency point in the frequency range.
Further, the cable to be detected is a multi-core cable, and the measuring the impedance spectrum of the cable to be detected in S1 includes: and forming a loop based on two-phase core wires in the multi-core cable, and connecting two ends of the loop to measure the impedance spectrum of the loop.
Further, the cable to be detected is a single-core coaxial cable, and the measuring the impedance spectrum of the cable to be detected in S1 includes: based on a loop formed by a cable core wire and a metal shielding layer in the single-core coaxial cable, two ends of the loop are connected to measure an impedance spectrum of the loop.
Further, when the number of the cycles is 1, there is no fault in the cable to be detected.
According to another aspect of the present invention, there is provided a cable fault location system based on impedance spectrum period characteristics, comprising: the acquisition and measurement module is used for acquiring the average phase velocity of the cable to be detected and measuring the impedance spectrum of the cable to be detected; the calculation module is used for extracting equivalent frequency division contained in the impedance spectrum, calculating a period corresponding to each equivalent frequency division, wherein the minimum period corresponds to the tail end of the cable, and each of the rest periods corresponds to a cable fault section; and the fault positioning module is used for judging that a fault exists in the cable to be detected when the number of the periods is greater than 1, and calculating the position of the corresponding cable fault section based on each period except the minimum period, wherein the distance from any cable fault section to the head end of the cable is equal to 1/2, and the ratio of the average phase velocity to the period corresponding to any cable fault section.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) calculating the impedance from the tail end of a local fault section to the tail end of a cable and the impedance from the head end of the local fault section to the tail end of the cable by an iterative method to obtain a fault cable impedance spectrum model, analyzing and finding that the impedance spectrum calculation model comprises a reflection coefficient of a local fault part, wherein the reflection coefficient comprises a period factor, and the period of the period factor is related to the position of the local fault section; in addition, the positioning method does not need to apply high voltage or discharge, has simple measuring circuit and no damage to the cable, can prevent cable defects and power failure accidents, and ensures the safe and stable operation of an electrical system;
(2) the frequency range of the impedance spectrum measurement is set according to the length of the cable to be detected, so that the bandwidth of the impedance spectrum measurement is the maximum value under the condition that the constraint condition is met, the position dead zone of the cable measurement is inversely proportional to the bandwidth, the larger the bandwidth is, the smaller the position dead zone of the cable measurement is, and the precision and the accuracy of the cable local fault positioning are further improved.
Drawings
Fig. 1 is a flowchart of a cable fault location method based on impedance spectrum period characteristics according to an embodiment of the present invention;
fig. 2A is a schematic diagram of an impedance spectrum measurement loop of a multi-core cable according to an embodiment of the present invention;
fig. 2B is a schematic diagram of a single-core coaxial cable impedance spectrum measurement circuit according to an embodiment of the present invention;
fig. 3A is a schematic model diagram of a multi-core fault cable according to an embodiment of the present invention;
fig. 3B is a schematic model diagram of a single-core coaxial fault cable according to an embodiment of the present invention;
FIG. 4A is an impedance magnitude spectrum of an experimental cable provided by an embodiment of the present invention;
FIG. 4B is an impedance phase spectrum of an experimental cable provided by an embodiment of the present invention;
FIG. 5 is a cable fault location curve provided by an embodiment of the present invention;
fig. 6 is a block diagram of a cable fault location system based on impedance spectrum period characteristics according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Fig. 1 is a flowchart of a cable fault location method based on impedance spectrum period characteristics according to an embodiment of the present invention. Referring to fig. 1, a cable fault location method based on impedance spectrum period characteristics (hereinafter, referred to as a cable fault location method) in this embodiment is described in detail with reference to fig. 2A to 5. Referring to fig. 1, the cable fault location method includes operations S1-S3.
In operation S1, an average phase velocity of the cable to be detected is obtained, and an impedance spectrum of the cable to be detected is measured.
According to the embodiment of the present invention, before performing operation S1, the method further includes: and determining the frequency range of the impedance spectrum measurement based on the length of the cable to be detected, so that the bandwidth of the impedance spectrum measurement is the maximum value under the condition of meeting the constraint condition.
Through a large number of simulation and experimental researches, it is found that, with the cable fault positioning method in the embodiment, a smoother graph can be obtained only by at least 8 sampling points in each period if a better cable local fault positioning effect is to be obtained. During the experiment, the sampling points in each period are 16, 32 and 64.
The period of the impedance spectrum is TfV/2l, therefore, the bandwidth constraint is:
Figure BDA0002994508820000061
where Δ f is the bandwidth of the impedance spectroscopy measurement, and Δ f ═ fup-flow，fupAnd flowRespectively the upper and lower limits of the frequency range of the impedance spectrum measurement, N is the total number of sampling points of the impedance spectrum measurement, N is the number of sampling points in each period, v1And l is the wave speed and the length of the cable to be detected.
At the same time, a complete cycle is required to locate the fault location. The closer the fault is to the measurement point, the longer the period of the impedance spectrum. Let x be0Is a dead zone of the cable head end, and the bandwidth delta f is v1/2x0The larger the frequency range of the impedance spectrum measurement is, the smaller the dead zone is. Thus, it is possible to provideThe bandwidth of the impedance spectrum measurement should be as wide as possible under the condition that the above constraint conditions are satisfied.
In operation S1, the obtaining the average phase velocity of the cable to be detected includes: respectively measuring impedance spectrums in the determined frequency range when the end part of the fault-free cable is open or short-circuited, wherein the type of the fault-free cable is the same as that of the cable to be detected; and calculating the average phase velocity of the cable to be detected in the determined frequency range according to the impedance spectrum of the fault-free cable. The length of the fault-free cable is any length.
As can be seen from the transmission line theory, the open-circuit impedance and the short-circuit impedance of the end of the fault-free cable (i.e. the healthy cable) are:
Figure BDA0002994508820000071
Figure BDA0002994508820000072
wherein Z isopIs open circuit impedance, ZscAs short-circuit impedance, ZcFor characteristic impedance, γ is the propagation constant and l' is the length of the fault-free cable. Based on the expression of the open-circuit impedance and the short-circuit impedance, the characteristic impedance Z can be knowncAnd the propagation constants γ are:
Figure BDA0002994508820000073
Figure BDA0002994508820000074
in practical application, only the open-circuit impedance Z of the tail end of the fault-free cable with any suppression length needs to be testedopAnd short circuit impedance ZscObtaining the characteristic impedance Z of the cable by reverse extrapolationcAnd a propagation constant γ, and the attenuation constant α and the phase shift coefficient β of the cable can be calculated from the expression γ of the propagation constant γ ═ α + i β. And the phase velocity is equal to 2 π f/β, therebyThe phase velocity in the measuring frequency range can be calculated, and the average value of the phase velocities of the corresponding frequencies of all the sampling points is taken as the average phase velocity in the measuring range.
Operation S2 is performed to extract the equivalent frequency divisions included in the impedance spectrum, and calculate a period corresponding to each equivalent frequency division, where the minimum period corresponds to the end of the cable, and each of the remaining periods corresponds to a cable fault section.
The cable impedance spectrum is measured by a precise impedance analyzer, and when the cable impedance spectrum is measured, a lead with a certain length is used for connecting a cable measuring end with a port of the impedance analyzer, and the other end of the cable is controlled to be open-circuited, short-circuited or connected with a load.
Specifically, when the cable to be detected is a multi-core cable, a loop is formed based on two-phase core wires in the multi-core cable, and both ends of the loop formed by the two-phase cable are connected to measure an impedance spectrum of the cable, as shown in fig. 2A. When the cable to be detected is a single-core coaxial cable, a loop is formed based on a cable core wire and a metal shielding layer in the single-core coaxial cable, and two ends of the loop formed by the cable core wire and the metal shielding layer are connected to measure an impedance spectrum of the cable, as shown in fig. 2B.
Referring to the multi-core faulty cable model shown in fig. 3A and the single-core coaxial faulty cable model shown in fig. 3B, the principle of extracting the impedance spectrum period characteristics in operation S2 is as follows: based on the chain equivalent circuit principle of the transmission line and the calculation idea of the input impedance of the coaxial cable based on the iterative method, a calculation formula of the input impedance of the cable containing the local defects can be deduced.
Respectively calculating the impedance Z from the end of the fault section to the end of the cablel-x-dImpedance Z from head end of fault section to tail end of cablel-xInput impedance Z measured from the head end of the cablex：
Figure BDA0002994508820000081
Figure BDA0002994508820000082
Figure BDA0002994508820000083
Figure BDA0002994508820000084
Figure BDA0002994508820000085
Figure BDA0002994508820000086
Wherein Z iscCharacteristic impedance for fault-free section, ZdIs the characteristic impedance of the fault section, ΓLIs the load reflection coefficient, Γ1For the reflection coefficient at the end of the fault section, Γ2Is the reflection coefficient, gamma, at the head end of the fault sectioncPropagation constant, gamma, for faultless sectionsdIs the propagation constant of the fault section, l is the length of the cable to be detected, x is the length from the head end of the fault section to the head end of the cable, d is the length of the fault section, alpha is the attenuation constant, v2F is the frequency point in the frequency range. In the calculation of gamma1Impedance Z from end of faulty section to end of cablel-x-dConsidered as an equivalent load; in the calculation of gamma2Impedance Z from head end of faulty section to tail end of cablel-xConsidered as an equivalent load.
According to the calculation model of the input impedance of the defective cable, the calculation model of the impedance of the defective cable comprises the reflection coefficient of the fault position
Figure BDA0002994508820000087
The reflection coefficient includes a period factor
Figure BDA0002994508820000088
Converting beta to omega/v2Substituting the period factor can obtain:
Figure BDA0002994508820000089
period factor
Figure BDA0002994508820000091
Period T offIs 0.5v2V, the period being related to the location x of the faulty section of the cable, v2Is the phase velocity of the electrical signal in the cable, i.e. the above-mentioned average phase velocity.
In operation S2, the equivalent frequency division included in the impedance spectrum may be extracted by fast fourier transform, and the period T of the frequency of the impedance spectrum may be determinedf，TfWhich contains the location and status information of the failed segment. The fast Fourier transform curve is F ═ FFT (Z)l)，ZlExtracting the peak frequency f in the FFT curve for the impedance amplitude or phase spectrum at the head end of a cable of length lp. Then T can be obtainedf＝1/fp。
And operation S3, when the number of the periods is larger than 1, detecting that a fault exists in the cable, and calculating the position of the corresponding cable fault section based on each period except the minimum period, wherein the distance from any cable fault section to the cable head end is equal to the ratio of the average phase velocity of 1/2 to the corresponding period of any cable fault section.
Based on the impedance spectrum period TfAverage phase velocity v in cable2And the fault section position x2/2TfAnd acquiring the position of the fault section. It should be noted that, when there is no fault in the cable to be detected, the number of cycles obtained in operation S2 is one, and correspondingly, the ratio obtained in operation S3 is one; when N faults exist in the cable to be detected, N is larger than or equal to 1, the number of the cycles obtained in operation S2 is N +1, and correspondingly, the ratio obtained in operation S3 is N + 1.
Firstly, judging whether a fault exists in the cable to be detected according to the number of equivalent frequency divisions contained in the impedance spectrum, and if the number of the equivalent frequency divisions is 1, the fault does not exist in the cable to be detected. If the number of the equivalent frequency division is larger than 1, faults exist in the cable to be detected, the number of the fault sections is the difference between the number of the ratio and 1, then the period corresponding to each frequency division is calculated, wherein the minimum period corresponds to the position of the tail end of the cable to be detected, and the rest periods correspond to the positions of the fault sections one by one.
In order to verify the effectiveness of the cable fault positioning method in the embodiment of the invention, a low-voltage cable with the model number of VLV-0.6/1kV3 x 10 is taken as a research object, and a positioning experiment is carried out on insulation breakage defects on the cable. The total length of the experimental cable is 20m, the insulation breakage defect is located at 7.5m, and the defect length is 0.1 m.
Selecting an experimental impedance spectrum with a measuring frequency interval of [6MHz and 120MHz ] and a sampling number of 1600, sampling at equal intervals, controlling the short circuit at the tail end of the cable during measurement, and obtaining an impedance amplitude spectrum of the cable as shown in figure 4A and an impedance phase spectrum of the cable as shown in figure 4B. And measuring the tail end open-circuit short-circuit impedance spectrum of the healthy cable of the same model to obtain the average phase velocity of the VLV-0.6/1kV 3X 10 cable at [6MHz and 120MHz ] as 2.2X 108 m/s. The defect position is obtained by processing the impedance phase spectrum, as shown in fig. 5. As can be seen from fig. 5, the maximum value of the localization function f (x) corresponds to a spatial position of 7.62m, the central position of the actual defect cross-section is 7.50m, and the error is 0.12 m. Experimental results show that the cable fault positioning method can effectively position the cable fault position and realize accurate and lossless cable fault positioning
Fig. 6 is a block diagram of a cable fault location system based on impedance spectrum period characteristics according to an embodiment of the present invention. Referring to fig. 6, the cable fault location system 600 based on the impedance spectrum period characteristics includes an acquisition and measurement module 610, a calculation module 620 and a fault location module 630.
The acquisition and measurement module 610 performs, for example, operation S1 for acquiring an average phase velocity of the cable to be detected and measuring an impedance spectrum of the cable to be detected.
The calculating module 620 performs operation S2, for example, to extract equivalent frequency divisions included in the impedance spectrum, and calculate a period corresponding to each equivalent frequency division, where the minimum period corresponds to the end of the cable, and each of the remaining periods corresponds to a cable fault section.
The fault locating module 630, for example, performs operation S3, where the fault locating module is configured to determine that a fault exists in the cable to be detected when the number of cycles is greater than 1, and calculate a position of a corresponding cable fault section based on each cycle other than the minimum cycle, where a distance from any cable fault section to the cable head end is equal to a ratio of the average phase velocity 1/2 to the corresponding cycle of the any cable fault section.
The cable fault location system 600 based on impedance spectrum period characteristics is used for executing the cable fault location method based on impedance spectrum period characteristics in the embodiments shown in fig. 1-5. For details, please refer to the cable fault location method based on the impedance spectrum period characteristic in the embodiments shown in fig. 1 to fig. 5, which will not be described herein again.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A cable fault positioning method based on impedance spectrum periodic characteristics is characterized by comprising the following steps:
s1, acquiring the average phase velocity of the cable to be detected, and measuring the impedance spectrum of the cable to be detected;
s2, extracting equivalent frequency division contained in the impedance spectrum, and calculating a period corresponding to each equivalent frequency division, wherein the minimum period corresponds to the tail end of the cable, and each of the rest periods corresponds to a cable fault section;
and S3, when the number of the periods is more than 1, faults exist in the cable to be detected, and the position of the corresponding cable fault section is calculated based on each period except the minimum period, wherein the distance from any cable fault section to the head end of the cable is equal to the ratio of the average phase speed of 1/2 to the corresponding period of any cable fault section.
2. The method for cable fault location based on impedance spectrum periodic characteristics as claimed in claim 1, wherein said S1 is preceded by: and determining the frequency range of impedance spectrum measurement based on the length of the cable to be detected, so that the bandwidth of the impedance spectrum measurement is the maximum value under the condition of meeting the constraint condition.
3. The method for cable fault location based on impedance spectrum periodic characteristics according to claim 2, wherein the constraint conditions are:
Figure FDA0003316287420000011
wherein, Δ f is the bandwidth of the impedance spectrum measurement, N is the total number of sampling points of the impedance spectrum measurement, N is the number of sampling points in each period, v1And l is the wave speed, and l is the length of the cable to be detected.
4. The cable fault location method based on impedance spectrum periodic characteristics as claimed in claim 2, wherein the step of obtaining the average phase velocity of the cable to be detected in the step S1 includes:
respectively measuring impedance spectrums in the frequency range when the end part of the fault-free cable is open-circuited or short-circuited, wherein the type of the fault-free cable is the same as that of the cable to be detected;
and calculating the average phase velocity of the cable to be detected in the frequency range according to the impedance spectrum of the fault-free cable.
5. The method for cable fault location based on impedance spectrum periodic characteristics of claim 4, wherein the average phase velocity is:
v2＝2πf/β
γ＝α+iβ
Figure FDA0003316287420000021
wherein v is2Is the average phase velocity, f is the frequency point within the frequency range, β is the phase shift coefficient, γ is the propagation constant, α is the attenuation constant, ZscAs short-circuit impedance, ZopFor open circuit impedance, l' is the length of the faultless cable.
6. The cable fault location method based on impedance spectrum periodic characteristics as claimed in claim 2, wherein the impedance spectrum of the cable to be detected is calculated by:
Figure FDA0003316287420000022
Figure FDA0003316287420000023
Figure FDA0003316287420000024
Figure FDA0003316287420000025
wherein Z isl-x-dFor the impedance from the end of the faulty section to the end of the cable, Zl-xFor the impedance from the head end of the fault section to the tail end of the cable, ZxInput impedance, Z, measured for the head end of the cablecCharacteristic impedance for fault-free section, ZdIs the characteristic impedance of the fault section, ΓLIs the load reflection coefficient, Γ1For the reflection coefficient at the end of the fault section, Γ2Is the reflection coefficient, gamma, at the head end of the fault sectioncPropagation constant, gamma, for faultless sectionsdIs the propagation constant of the fault section, l is the length of the cable to be detected, x is the length from the head end of the fault section to the head end of the cable, d is the length of the fault section, alpha is the attenuation constant, v2F is the frequency point in the frequency range.
7. The cable fault location method based on impedance spectrum periodic characteristics as claimed in claim 1, wherein the cable to be detected is a multi-core cable, and the measuring the impedance spectrum of the cable to be detected in S1 includes:
and forming a loop based on two-phase core wires in the multi-core cable, and connecting two ends of the loop to measure the impedance spectrum of the loop.
8. The cable fault location method based on impedance spectrum periodic characteristics according to claim 1, wherein the cable to be detected is a single-core coaxial cable, and the measuring the impedance spectrum of the cable to be detected in S1 includes:
based on a loop formed by a cable core wire and a metal shielding layer in the single-core coaxial cable, two ends of the loop are connected to measure an impedance spectrum of the loop.
9. The method for locating the cable fault based on the impedance spectrum periodic characteristics according to any one of claims 1 to 8, wherein when the number of the periods is 1, no fault exists in the cable to be detected.
10. A cable fault location system based on impedance spectrum periodic characteristics, comprising:
the acquisition and measurement module is used for acquiring the average phase velocity of the cable to be detected and measuring the impedance spectrum of the cable to be detected;
the calculation module is used for extracting equivalent frequency division contained in the impedance spectrum, calculating a period corresponding to each equivalent frequency division, wherein the minimum period corresponds to the tail end of the cable, and each of the rest periods corresponds to a cable fault section;
and the fault positioning module is used for judging that a fault exists in the cable to be detected when the number of the periods is greater than 1, and calculating the position of the corresponding cable fault section based on each period except the minimum period, wherein the distance from any cable fault section to the head end of the cable is equal to 1/2, and the ratio of the average phase velocity to the period corresponding to any cable fault section.
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