Weak current cable fault positioning method and system

Abstract

The present application relates to a kind of weak electric cable fault location method and system, method includes: by real-time monitoring axial stress variation preliminary locking fault area, in target section injection low-frequency pulse signal and analysis reflected waveform characteristics, extract the waveform distortion characteristics in reflected signal;Based on amplitude attenuation and time delay relationship dynamic adjustment output impedance, if dynamic adjustment output impedance cannot make the output impedance of the low-frequency pulse signal injected and the impedance variation trend of cable synchronization, then marked as impedance mismatch point;After identifying impedance mismatch point, by multi-band signal attenuation difference degree analysis excludes other interference, determine fault point position;System is used to realize the above method.The method and system combine stress monitoring and electrical signal detection, significantly shorten detection range, improve positioning accuracy and detection accuracy, suitable for complex environment under weak electric cable fault diagnosis.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weak current cable fault positioning, in particular to a weak current cable fault positioning method and system. BACKGROUND

[0002] With the rapid development of modern communication and power systems, weak current cables (such as communication cables, control cables, etc.) are widely used in various complex environments. Since weak current cables are usually laid underground, in pipes or hidden spaces, they are easily affected by factors such as mechanical stress, environmental corrosion, temperature changes, etc., and are prone to insulation aging, partial damage, loose joints and other faults. If these faults are not detected and located in time, they may lead to a decrease in signal transmission quality, a decrease in system stability, and even more serious communication interruptions or power accidents. Therefore, the fault detection and positioning technology of weak current cables has become the focus of the industry.

[0003] Currently, traditional cable fault detection methods mainly include time domain reflectometry (TDR), frequency domain reflectometry (FDR), impedance analysis, etc. Time domain reflectometry locates fault points by injecting pulse signals into the cable and analyzing the reflected waveform, but this method has low sensitivity to high resistance faults and weak defects, and is easily disturbed by noise. Frequency domain reflectometry improves detection accuracy by analyzing the reflected signal characteristics at different frequencies, but it is still difficult to distinguish between signal changes caused by cable natural attenuation and real faults. Impedance analysis can detect cable impedance abnormalities, but in dynamic load or complex laying environment, the real-time and accuracy of impedance matching adjustment are insufficient, which may lead to misjudgment. In addition, most existing technologies rely on offline detection or periodic inspection, which cannot monitor the cable state in real time, leading to delayed fault discovery and affecting system reliability. SUMMARY

[0004] To overcome the defects of offline detection lag, serious signal attenuation in long distance detection, and easy misjudgment in weak current cable fault positioning in the prior art, the present application provides a weak current cable fault positioning method and system, which preliminarily locates the fault section by real-time stress monitoring to shorten the detection range, and combines dynamic impedance matching and multi-band attenuation analysis to achieve early warning, accurate positioning and significantly improve detection accuracy.

[0005] To solve the above technical problems, the present application provides a weak current cable fault positioning method, comprising the following steps:

[0006] When the weak current cable is working normally, the axial stress distribution change of the weak current cable is monitored in real time, and the section where the stress distribution characteristics change significantly is identified as the fault area to be detected;

[0007] Inject a low-frequency pulse signal into a weak electric cable in a fault detection area, collect a reflected signal on the weak electric cable, and extract a waveform distortion feature in the reflected signal;

[0008] Based on the extracted waveform distortion feature, an impedance mismatch amount is calculated, an output impedance of the low-frequency pulse signal is dynamically adjusted, and if the dynamic adjustment of the output impedance cannot make the output impedance of the injected low-frequency pulse signal synchronous with an impedance change trend of the cable, the impedance mismatch point is marked;

[0009] At the impedance mismatch point, different frequency band detection signals are injected, the attenuation rates of the signals in different frequency bands are collected, the attenuation difference degrees of the impedance mismatch point in different frequency bands are calculated, and the position with the largest change in the attenuation difference degree is determined as the final fault point.

[0010] In an embodiment of the present application, the process of real-time monitoring of the axial stress distribution change of the weak electric cable includes the following steps:

[0011] If the weak electric cable is integrated with an optical communication unit, a distributed optical fiber sensing technology can be used to establish a strain-stress conversion model to convert the strain distribution into the axial stress distribution, so as to realize the detection of the stress distribution change;

[0012] If the weak electric cable does not have an optical communication unit, a plurality of stress sensing units are arranged at equal intervals along the axial direction of the weak electric cable, stress data are synchronously collected by the stress sensing units, the data of adjacent sensing units are differentially calculated, the change trend of the stress data is analyzed, and an abnormal fluctuation area is identified.

[0013] In an embodiment of the present application, the frequency range of the low-frequency pulse signal is 1 kHz-10 kHz, the pulse width is 50-200 μs, the interval time between adjacent pulses is not less than 5 times the pulse width, and the low-frequency pulse signal is injected into the fault detection area through a coupler.

[0014] In an embodiment of the present application, the waveform distortion feature includes an amplitude attenuation mutation point and a time delay abnormal point, and based on the extracted waveform distortion feature, the process of calculating the impedance mismatch amount includes:

[0015] A standard waveform template of the reflected signal is established;

[0016] The amplitude attenuation mutation point and the time delay abnormal point are compared and identified according to the standard waveform template;

[0017] The amplitude ratio and the phase difference of the reflected signal and the incident signal are calculated at the amplitude attenuation mutation point and the time delay abnormal point, respectively;

[0018] The mismatch degree of the reflected signal is determined in combination with the amplitude ratio and the phase difference, a corresponding relationship table of the mismatch degree and the impedance mismatch amount is established, and is used to guide the adjustment of the impedance mismatch amount.

[0019] In an embodiment of the present application, the process of identifying amplitude decay mutation points and time delay anomaly points according to the standard waveform template includes:

[0020] Segmenting the reflected signal in time domain, and calculating the standard deviation of the amplitude of each segment of the signal;

[0021] If the standard deviation of the amplitude of a segment exceeds 20% of the average value of the same segment of the standard waveform template, it is marked as an amplitude decay mutation point;

[0022] If the time delay difference of the same segment exceeds 10% of the propagation delay of the standard waveform template, it is marked as a time delay anomaly point.

[0023] In an embodiment of the present application, if dynamic adjustment of the output impedance still cannot match the trend of the impedance change of the cable, before marking the impedance mismatch point, the electromagnetic field distribution near the impedance mismatch point is further detected, and if local electromagnetic field anomaly enhancement is detected, it is determined that the impedance mismatch point is likely caused by external interference. The shielding layer excitation signal is applied to the weak current cable to enhance the electromagnetic shielding effectiveness of the outer shielding layer of the cable, suppress the influence of external interference on the low-frequency pulse signal, and then perform dynamic impedance adjustment. If the trend of the impedance change of the cable still cannot be matched, the impedance mismatch point is marked.

[0024] In an embodiment of the present application, at the impedance mismatch point, a plurality of preset frequency bands are sequentially injected, wherein the plurality of frequency bands cover the low frequency to high frequency range, and the adjacent frequency bands have a partially overlapping frequency band.

[0025] In an embodiment of the present application, the process of calculating the attenuation difference degree of the impedance mismatch point at different frequency bands and determining the position with the largest attenuation difference degree change as the final fault point includes:

[0026] Arranging the attenuation rates of each frequency band in order from low to high, calculating the attenuation rate change amount between adjacent frequency bands, and calculating the average value of all adjacent frequency band attenuation rate change amounts as a reference benchmark;

[0027] Screening out adjacent frequency band combinations with attenuation rate change amounts exceeding the reference benchmark, and calculating the attenuation difference degree at the center frequency point corresponding to the frequency band combination, wherein the attenuation difference degree is the difference between the high-frequency side attenuation rate and the low-frequency side attenuation rate at the center frequency point;

[0028] Comparing the attenuation difference degrees at each impedance mismatch point along the axial direction of the weak current cable, and determining the position with the largest attenuation difference degree change as the final fault point.

[0029] In an embodiment of the present application, when the weak current cable is a multi-branch topology structure, the following steps are performed:

[0030] Before identifying the fault area to be detected, a topological identification signal is injected into the weak current cable, a cable branch topological graph is constructed according to the reflection time delay characteristics of each branch node, and the position information of each branch node is recorded;

[0031] When monitoring the change of the axial stress distribution, the stress of each branch section is analyzed independently in combination with the topological graph, if the change degree of the stress distribution characteristics of a branch exceeds the set multiple of the average change level of the main cable, the branch section is preferentially marked as the fault area to be detected;

[0032] When the low-frequency pulse signal is injected, the pulse width is adjusted according to the electrical length of the branch where the fault area is located, so that the energy of the pulse signal is concentrated in the branch section, and the interference of the reflection signals of other branches is reduced;

[0033] When the impedance mismatch point is detected, whether the mismatch point is located at the branch node is judged in combination with the topological graph, if yes, a directional detection signal is injected into the branch node, the reflection signal intensity difference of each branch is compared, and the false fault point caused by the impedance mutation of the branch is excluded;

[0034] When the final fault point is determined, if the position with the largest attenuation difference degree is located near the branch node, the frequency domain impedance spectrum scanning is performed on all branches connected to the node, the branch with the most significant impedance spectrum mutation is selected as the fault branch, and the final fault point is accurately positioned on the branch.

[0035] To solve the above technical problems, the application further provides a weak current cable fault positioning system, comprising:

[0036] A stress monitoring module is used for monitoring the change of the axial stress distribution of the weak current cable in real time when the weak current cable is working normally, and identifying a section with significant change of stress distribution characteristics as a fault area to be detected;

[0037] A signal processing module is used for injecting a low-frequency pulse signal into the fault area to be detected, collecting reflection signals on the weak current cable, and extracting waveform distortion characteristics in the reflection signals;

[0038] An impedance analysis module is used for calculating the impedance mismatch amount based on the extracted waveform distortion characteristics, and dynamically adjusting the output impedance of the low-frequency pulse signal, if the dynamic adjustment of the output impedance cannot make the output impedance of the injected low-frequency pulse signal synchronous with the impedance change trend of the cable, the impedance mismatch point is marked;

[0039] A fault diagnosis module is used for injecting detection signals of different frequency bands into the impedance mismatch point respectively, collecting the attenuation rates of the signals of different frequency bands, calculating the attenuation difference degrees of the impedance mismatch point under different frequency bands, and determining the position with the largest change of the attenuation difference degrees as the final fault point.

[0040] The above technical solutions of the present application have the following advantages compared with the prior art:

[0041] 1. By pre-locking the suspicious section through stress distribution changes, the subsequent electrical signal detection range is shortened, greatly reducing the detection time and system power consumption. This "rough screening and then precise measurement" strategy significantly improves the overall detection efficiency.

[0042] 2. Enhance early fault identification capability: stress monitoring can capture the characteristic changes in the early stage of mechanical damage, realize early warning of faults, and make up for the defects of traditional electrical signal detection methods that are not sensitive to early faults.

[0043] 3. Improve positioning accuracy: multi-stage verification mechanism (stress anomaly → impedance mismatch → multi-frequency band confirmation) effectively reduces the false alarm rate, especially suitable for high resistance fault detection in complex environments.

[0044] 4. Reduce operation and maintenance costs: precise section positioning avoids full-line detection and blind excavation, reducing maintenance workload, and early detection of faults can avoid greater losses caused by fault expansion.

[0045] 5. Adapt to complex working conditions: dynamic impedance adjustment mechanism enables the method to adapt to load fluctuations and environmental influences, showing better stability in industrial field applications.

[0046] The weak current cable fault positioning method and system of the present application combines mechanical stress monitoring with electrical characteristic analysis, providing a new technical route for weak current cable fault detection, especially suitable for long-distance and complex environment cable operation and maintenance scenarios, and has important engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to make the content of the present application easier to be clearly understood, the following further describes the present application in detail according to specific embodiments of the present application and in conjunction with the drawings, in which:

[0048] Figure 1 is a step flowchart of the weak current cable fault positioning method of the present application;

[0049] Figure 2 is a step flowchart of the weak current cable fault positioning method of the present application applied to a multi-branch topology structure;

[0050] Figure 3 is a structural framework diagram of the weak current cable fault positioning system of the present application. DETAILED DESCRIPTION

[0051] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting the present application.

[0052] Referring to Figure 1 As shown in the figure, the application discloses a weak current cable fault positioning method, comprising the following steps:

[0053] S10, when the weak current cable is working normally, the axial stress distribution change of the weak current cable is monitored in real time, and a section where the stress distribution characteristics change significantly is identified as a to-be-detected fault area;

[0054] Firstly, the stress distribution change is introduced into the cable fault positioning, and by identifying the section where the stress characteristics change significantly, the potential mechanical damage or structural deterioration area can be quickly locked, compared with the traditional method of simply relying on electrical signal detection, early warning of the fault can be realized through stress monitoring, the potential fault risk area can be found earlier, and the traditional method of blind detection on the whole cable length is avoided.

[0055] S20, a low-frequency pulse signal is injected into the to-be-detected fault area of the weak current cable, a reflected signal on the weak current cable is collected, and a waveform distortion feature in the reflected signal is extracted;

[0056] After the to-be-detected fault area is determined, the low-frequency pulse signal is injected only in the target section, instead of full-line detection, which greatly shortens the action range of the detection signal, reduces the signal attenuation and interference in long-distance transmission on the one hand, improves the signal quality, and significantly reduces the time and energy consumption required for detection on the other hand; the injection of the low-frequency pulse signal is mainly aimed at the problem of serious attenuation of high-frequency signals in long-distance cable detection, and the low-frequency signal has better penetration and anti-interference ability, and can obtain more reliable reflected waveform.

[0057] By analyzing the waveform distortion feature of the reflected signal, the possible fault position can be preliminarily judged, and compared with the traditional TDR method, the cooperative detection mechanism of "stress positioning + electrical signal verification" makes the fault positioning process more efficient and reliable.

[0058] S30, based on the extracted waveform distortion feature, the impedance mismatch amount is calculated, the output impedance of the low-frequency pulse signal is dynamically adjusted, and if the dynamic adjustment of the output impedance cannot make the output impedance of the injected low-frequency pulse signal synchronous with the impedance change trend of the cable, the impedance mismatch point is marked;

[0059] Further, based on the extracted waveform distortion features, the method adopts a dynamic impedance adjustment mechanism to adapt to the dynamic changes of cable impedance by calculating the impedance mismatch amount in real time and adjusting the output impedance, thereby solving the problem of inaccurate impedance matching in complex environments. During the dynamic impedance adjustment process, if the reflected signal after dynamic adjustment of impedance is stable, it means that the corresponding waveform distortion feature may be a false fault condition caused by environmental interference or other interference, and it will not be identified. If the impedance matching is adjusted dynamically for several times, some points still cannot make the reflected signal stable, and these points are marked as suspected fault points, thereby effectively solving the poor adaptability problem of traditional impedance analysis method in complex environments.

[0060] S40, injecting detection signals of different frequency bands at the impedance mismatch point respectively, collecting the attenuation rates of signals of each frequency band, calculating the attenuation difference degrees of the impedance mismatch point under different frequency bands, and determining the position with the largest attenuation difference degree change as the final fault point;

[0061] Different types of cable faults (such as insulation aging, partial damage or loose joints, etc.) have significant differences in the attenuation characteristics of signals of different frequencies, while the influence of normal cable impedance changes or environmental interference on signals of each frequency band is relatively uniform. By injecting detection signals of multiple frequency bands at the impedance mismatch point respectively, and accurately measuring the attenuation rates of signals of each frequency band, the "frequency response fingerprint" of the fault point can be constructed.

[0062] Specifically, when the detection signal encounters a real fault point, due to the abnormal physical structure at the fault point (such as changes in dielectric loss, sudden changes in conductor cross-sectional area, etc.), electromagnetic waves of different frequency bands will exhibit nonlinear attenuation characteristics. For example, high-frequency signals are more sensitive to conductor surface damage, while low-frequency signals can better reflect deep insulation degradation; by calculating the difference degree index of the attenuation rates of each frequency band, the fault feature signal can be effectively amplified, while the interference caused by the inherent attenuation of the line and environmental noise is suppressed.

[0063] This decision mechanism based on multi-frequency band feature fusion not only improves the recognition ability of complex faults, but also effectively avoids the misjudgment problem that is prone to occur when single frequency band detection is used.

[0064] In practical applications, according to the application position and scene of the weak current cable, two different schemes can be used to realize stress detection: for the cable integrated with an optical communication unit, the Brillouin scattering frequency shift or Rayleigh scattering strain data is input into a strain-stress conversion model by using a distributed optical fiber sensing technology. Due to the mechanical coupling between the optical fiber and the cable sheath, the strain distribution can accurately reflect the axial stress change. This continuous distributed monitoring has a millimeter-level spatial resolution and can accurately locate the stress concentration section; for the cable without an optical communication unit, a discrete stress sensor array is used. The data of adjacent units are synchronously collected by the equally spaced MEMS stress sensors. The differential calculation of the adjacent unit data can eliminate the common mode interference such as ambient temperature. When the differential value of a certain section exceeds the threshold value, it indicates that there is an abnormal stress gradient in the region. This design not only avoids the missing detection problem of traditional point sensors, but also amplifies the local abnormal signal through the differential algorithm.

[0065] Both of the above stress detection schemes can effectively identify the section with sudden change of stress distribution characteristics, and provide an accurate target area for subsequent fault location. The detection logic of mechanical anomaly first and electrical fault later significantly improves the timeliness of fault warning.

[0066] Specifically, in order to achieve optimal signal propagation characteristics and reflection signal analysis capability in the fault location process, in the embodiment, based on the transmission characteristics of the weak current cable, the frequency range is set to 1 kHz-10 kHz: this frequency band can not only penetrate the distributed capacitance and inductance of the cable, avoid excessive attenuation of high-frequency signals due to skin effect, but also maintain sufficient wavelength resolution (the wavelength is about tens to hundreds of meters in typical weak current cables), to ensure that the reflected signal can accurately reflect the position information of the impedance mutation point; the design of pulse width of 50-200 μs balances the time resolution and energy accumulation. A wider pulse can carry higher energy to improve the signal-to-noise ratio, but too wide pulse width will cause the overlap of the reflection signals of adjacent sections, so this range can ensure the distinguishability of the reflection signal of the fault point, and avoid the aliasing of adjacent reflection waveforms.

[0067] Further, the requirement that the interval time between adjacent pulses is not less than 5 times the pulse width is to ensure that all reflection signals of the previous pulse are completely attenuated before the next pulse is injected, to prevent mutual interference of multi-pulse reflection signals. If the interval time is too short, the residual reflection of the previous pulse will be superimposed with the reflection of the subsequent pulse, resulting in waveform distortion and distortion of feature extraction. The setting of 5 times the pulse width takes into account the attenuation characteristics of the cable, to ensure that the reflection signal has enough time to attenuate below the noise level, so as to ensure that the reflection signal collected after each pulse injection is the independent response of the current pulse, and to improve the accuracy of impedance mismatch point detection.

[0068] Further, the design of the signal injection through the coupler solves the impedance matching problem between the signal source and the cable. The coupler can realize impedance transition between the signal source and the cable, reduce signal reflection loss when directly injected, isolate possible DC components or high-voltage interference between the signal source and the cable, and protect the detection equipment. In addition, the high-pass or band-pass characteristics of the coupler can also filter out power frequency interference, ensuring the purity of low-frequency pulse signals, so that the distortion components in the reflected signal are only caused by cable impedance changes, not external noise interference.

[0069] Specifically, the waveform distortion features are specifically defined as amplitude attenuation mutation points and time delay abnormal points, which accurately capture abnormal information in the reflected signal from two dimensions of time domain and amplitude domain, so as to more accurately identify the position and degree of cable impedance mismatch; wherein: the amplitude attenuation mutation point reflects the energy loss of the signal in the propagation process due to impedance discontinuity, for example, conductor breakage, poor contact or insulation deterioration and other faults will cause the signal amplitude to drop sharply; and the time delay abnormal point reflects the difference in signal propagation speed caused by medium change or local deformation, such as cable extrusion, water ingress or local aging, which will cause the equivalent dielectric constant of the signal propagation path to change, thereby changing the transmission delay of the signal; by monitoring both features at the same time, false positives caused by single feature detection (such as relying solely on amplitude attenuation may misjudge normal impedance matching points as fault points) can be avoided, and the robustness of fault location can be improved.

[0070] Further, based on the extracted waveform distortion features, the process of calculating the impedance mismatch amount includes the following steps:

[0071] First, a standard waveform template of the reflected signal needs to be established, which is usually based on the reflection characteristics of the cable in the normal state, including typical amplitude attenuation curve and propagation time delay characteristics.

[0072] In the fault detection stage, the actual collected reflected signal is compared with the template to identify the region where the amplitude suddenly drops (amplitude attenuation mutation point) and the position where the signal arrival time abnormally lags (time delay abnormal point); the identification of these two feature points is not carried out in isolation, but is verified by each other - for example, if the amplitude suddenly drops and the time delay increases at the same time, it is likely that the conductor is broken with local medium change; if only the time delay is abnormal and the amplitude changes gently, it may indicate that the cable sheath is deformed but the conductor remains connected.

[0073] Specifically, the process of identifying amplitude decay mutation points and time delay abnormal points based on the standard waveform template includes: time-domain segmentation of the reflected signal, which is usually based on pulse width and cable propagation speed to ensure that each segment corresponds to a specific interval on the physical cable; such segmentation processing makes the fault location have spatial resolution and can convert global waveform analysis into local anomaly detection. Then, the standard deviation of the signal amplitude is calculated in each segment, rather than simply comparing the instantaneous value, because the standard deviation can reflect the fluctuation intensity and overall energy change of the signal, avoiding the interference of accidental noise of a single sampling point. Finally, threshold limitation is performed, when the standard deviation of a certain segment exceeds 20% of the average value of the corresponding segment of the standard template, it indicates that the signal amplitude of the segment is significantly unstable, which may be caused by the reflection superposition caused by impedance mutation, so it is marked as an amplitude decay mutation point; this threshold setting considers both the natural fluctuation of the signal of the normal cable (usually <10%) and ensures that the real fault characteristics (such as reflection amplitude change caused by conductor breakage, usually >30%) can be captured.

[0074] For the detection of time delay abnormal points, the time difference of signal arrival in the same segment is compared with the propagation delay of the standard template, and the propagation delay of the standard template reflects the theoretical transmission speed of the signal in the intact cable, and the time delay difference of the actual signal exceeding 10% is determined to be abnormal, and this threshold can effectively identify the change of propagation speed caused by medium change (such as moisture absorption of the insulation layer, local deformation). For example, water in the cable will cause the local dielectric constant to increase, making the signal propagation speed decrease by 5%-15%, and the sheath extrusion may increase the delay by 8%-12%, and the 10% threshold covers the time delay change range caused by typical faults.

[0075] Next, the amplitude ratio and phase difference of the reflected signal and the incident signal are calculated at the identified distortion points, respectively, the amplitude ratio directly reflects the loss degree of signal energy, and the phase difference reflects the change of equivalent electrical length of signal propagation path; the combination of these two parameters can more comprehensively describe the nature of impedance mismatch: pure resistive mismatch (such as increased contact resistance) mainly manifests as amplitude change, while reactive mismatch (such as abnormal distributed capacitance or inductance) more significantly affects the phase.

[0076] By establishing a correspondence table between mismatch degree and impedance mismatch amount, abstract waveform distortion can be converted into specific impedance change quantitative indicators, which is usually generated based on the reflection coefficient formula in the transmission line theory and experimental calibration data, so that the output impedance can be adjusted dynamically and effectively.

[0077] In this embodiment, through multi-dimensional signal feature fusion, the single amplitude detection of traditional time domain reflectometry (TDR) is upgraded to amplitude and phase joint analysis. Amplitude attenuation discontinuity points are mainly used for positioning obvious impedance discontinuity points (such as open circuit or short circuit), and time delay anomaly points are more sensitive to distributed faults (such as uniform aging or damp of cable). The synergistic effect of the two enables the system to distinguish different types of faults: for example, local corrosion of the conductor may manifest as gradual amplitude decline accompanied by slight time delay increase, while damage to the insulation layer may cause amplitude discontinuity but no change in time delay. In addition, the introduction of the mismatch degree corresponding relationship table enables the impedance adjustment process to change from empirical trial and error to precise matching under theoretical guidance, significantly improving the efficiency and success rate of dynamic impedance matching and providing more reliable input data for subsequent multi-frequency band attenuation difference analysis.

[0078] In actual engineering environment, the surrounding electromagnetic field environment will cause great interference to impedance matching. When dynamic adjustment of output impedance cannot be synchronized with the trend of cable impedance change, there are two possibilities: one is real impedance mismatch caused by physical damage of the cable itself, and the other is equivalent impedance change caused by interference current induced by external strong electromagnetic field (such as adjacent power line coupling, radio frequency equipment radiation); if all impedance mismatch points are marked as fault points without distinction, it will lead to high false positive rate.

[0079] In this embodiment, by detecting electromagnetic field distribution, the influence of the interference source can be identified from the physical mechanism - the electromagnetic field distribution of the real fault point usually presents the characteristic of inward gathering (such as electric field concentration at the conductor breakage), while the external interference shows abnormal enhancement of field strength outward radiation. This auxiliary judgment based on field distribution significantly improves the accuracy of fault location.

[0080] The specific implementation process is as follows: first, after the failure of dynamic impedance adjustment, start the near-field detection module to scan the electromagnetic field around the impedance mismatch point, use the combination of non-contact magnetic field probe (such as Hall sensor) and electric field probe (such as flat panel antenna) to measure 3D field strength distribution and calculate its gradient change; when detecting that the local field strength exceeds 30% of the typical value of the cable during normal operation and shows outward diffusion distribution, it is determined that external interference is dominant, at this time, the shielding layer excitation signal (usually high frequency signal of 100 kHz-1 MHz, amplitude is 5%-10% of the working voltage of the cable) is applied, through the skin effect, uniform eddy current distribution is formed in the outer shielding layer, so that the transfer impedance of the shielding layer is reduced by 40%-60%, thereby suppressing the coupling of external interference to low frequency pulse signal.

[0081] The key of this process is the selection of the frequency of the excitation signal: too low frequency will result in insufficient excitation of the shielding layer, and too high frequency may cause parasitic resonance of the cable, so it needs to be adjusted adaptively according to the conductive characteristics of the shielding layer material (such as copper braid or aluminum foil), and after the shielding enhancement is completed, the dynamic impedance adjustment is re-performed, if the impedance matching degree is improved to above the threshold, the fault is excluded; if it still cannot be matched, it can be confirmed that this point is the real impedance mismatch point.

[0082] In this embodiment, when the final fault point is determined by injecting probe signals of different frequency bands, multiple frequency bands covering the low frequency to high frequency range are set, and a partially overlapping frequency band design is adopted, which can establish a fault feature fingerprint library of the full frequency band, thereby realizing accurate identification of different types of faults; among them: low frequency signals (such as 1-10kHz) can penetrate the distributed parameter network of the cable, mainly reflecting the lumped parameter faults such as conductor continuity; the middle frequency signal (such as 10-100kHz) is sensitive to uniform aging of the insulation layer; the high frequency signal (such as 100kHz-1MHz) can capture local discharge, sheath damage and other distributed defects; this wide frequency coverage ensures that whether the fault is a concentrated impedance mutation or a distributed parameter gradual change, it can be effectively excited by at least one frequency band of the probe signal, and the partial overlap of adjacent frequency bands (such as 5-15kHz and 10-20kHz with 5kHz overlap) realizes seamless connection of frequency domain detection, avoiding feature omission caused by frequency band gaps, and ensuring data continuity during frequency band switching through response consistency verification in the overlap area.

[0083] Specifically, the process of injecting probe signals of different frequency bands is: generating a sequence of probe signals arranged by frequency gradient from the signal generator, the center frequency of each frequency band is distributed according to logarithmic law (such as 1kHz, 3kHz, 10kHz, 30kHz, etc.), this non-linear distribution conforms to the sensitivity law of cable fault characteristics with frequency change - higher density sampling is needed in the low frequency area to distinguish conductor defects, and the interval can be appropriately relaxed in the high frequency area due to the skin effect; the signal injection adopts a combination of continuous wave (CW) and pulse modulation: CW mode is used for measuring steady-state attenuation rate, and pulse mode is used for obtaining time domain reflection characteristics.

[0084] Combined with the actual working condition, the weak current cable will produce overall aging caused uniform attenuation in long-term operation, and this background change will mask the characteristics of the local fault point, therefore, when calculating the attenuation difference of the impedance mismatch point under different frequency bands, this embodiment proposes a reference comparison method of attenuation rate change amount of adjacent frequency bands, which essentially builds a dynamic detection threshold adaptive to the current cable state - the reference reflects the overall attenuation characteristics of the cable, and the frequency band combination that significantly exceeds the reference indicates the existence of local abnormalities.

[0085] Specifically, in the process of calculating the attenuation difference degree of the impedance mismatch point at different frequency bands, the attenuation rate data of each frequency band is pre-processed first, and the attenuation rate change amount between adjacent frequency bands is calculated after sorting by frequency from low to high. This differential processing eliminates the common basic attenuation component of each frequency band and highlights the frequency response mutation characteristics unique to the fault point. For example, a uniformly aged cable may show a 30% increase in attenuation rate across all frequency bands, and the change amount between adjacent frequency bands will remain stable; while a cable with local insulation defects will show abnormal changes at a specific frequency band (such as at a frequency corresponding to the defect resonance frequency). By statistically establishing a reference benchmark for the average value of all adjacent change amounts, an adaptive threshold based on the current state of the cable is actually constructed. When the change amount of a certain group of adjacent frequency bands exceeds the benchmark value, it indicates that there is non-uniform attenuation in that frequency band interval. At this time, the attenuation difference degree (attenuation rate difference between high and low frequency sides) at the center frequency point of the frequency band combination is extracted. This parameter can quantify the sensitivity difference of the fault point to signals of different frequencies. Finally, by comparing the difference degree change range of each impedance mismatch point in the axial direction, the spatial precise positioning of the fault point is realized.

[0086] This relative value comparison strategy makes the fault detection independent of the initial state of the cable, and can maintain consistent detection sensitivity for cables of different batches or service life.

[0087] In actual engineering environment, the layout of weak current cable is mostly multi-branch topology structure, therefore, in order to improve the practicability of the fault positioning method of the present application, on the basis of the above embodiment, referring to the method for positioning fault of weak current cable with multi-branch topology structure as shown in the figure, the present application further provides a method for positioning fault of weak current cable with multi-branch topology structure, comprising the following steps: Figure 2

[0088] S11, before identifying the fault area to be detected, a topology identification signal is injected into the weak current cable, a cable branch topology graph is constructed according to the reflection time delay characteristics of each branch node, and the position information of each branch node is recorded;

[0089] The cable branch topology graph constructed by the topology identification signal provides a spatial reference framework for all subsequent detection steps. This logical sequence of mapping first and then detecting makes the fault positioning in complex networks traceable. The topology identification signal usually adopts a narrow pulse with a fast rising edge (such as a 50ns pulse width). The reflection time delay difference caused by impedance discontinuity at each branch node is used to reconstruct the network structure through the time domain reflectometry (TDR) principle. The spatial resolution can reach 0.5% of the cable length, ensuring that branch nodes with a spacing of only a few meters can be distinguished.

[0090] ​S21, when monitoring the change of axial stress distribution, independently analyzing the stress of each branch section in combination with the topology graph, if the stress distribution characteristic change degree of a branch exceeds the set multiple of the average change level of the trunk cable, the branch section is marked as a to-be-detected fault area;

[0091] Convert the overall stress analysis to a topology-based subarea evaluation. When the stress change of a branch exceeds the set multiple (usually 3-5 times) of the average level of the trunk, it indicates that the branch may be subjected to abnormal mechanical stress (such as pulling or extrusion). This subarea threshold strategy effectively avoids the masking effect of the stress of the trunk cable on the weak change of the branch. For example, in a multi-camera wiring of a security system, a sudden increase in stress of a branch may be a sign that the cable is injured by an object, while the stress change of the cable in the trunk slot is relatively flat. By independently analyzing the stress of each branch, the system can detect potential fault points at an early stage.

[0092] S31, when injecting a low-frequency pulse signal, adjusting the pulse width according to the electrical length of the branch where the fault area is located, so that the energy of the pulse signal is concentrated in the branch section, reducing the interference of the reflection signals of other branches;

[0093] According to the electrical length of the branch where the fault area is located (provided by the topology graph), the pulse width is dynamically set to match the electrical length of the branch (usually 1.2-1.5 times the round-trip delay of the branch), so that the signal energy is concentrated in the target branch, and the superimposed reflection of the pulse in other branches is avoided. For example, for a 20-meter-long branch, a 200ns pulse (corresponding to an electrical length of about 40 meters) is selected to ensure that the signal completely covers the branch without significantly penetrating into adjacent branches. This parameter optimization makes the detection results of each branch in a bus-type or tree-type topology not interfere with each other.

[0094] S41, when detecting an impedance mismatch point, combining the topology graph to determine whether the mismatch point is located at a branch node, if so, injecting a directional detection signal into the branch node, and comparing the reflection signal intensity difference of each branch to exclude false fault points caused by sudden changes in branch impedance;

[0095] The fault discrimination at the node adopts a directional probing signal technology, the signal has specific spectral characteristics (such as band-limited pseudo-random code), by comparing the correlation coefficient and energy ratio of the reflection signals of each branch, the real fault branch can be accurately identified; when the impedance mismatch point is located at the node, the traditional method is difficult to distinguish whether the node connector is aging or the branch cable is faulty, the present scheme injects a directional signal (its frequency characteristics are designed for the different frequency responses of the connector and the cable) into the node, and makes a judgment according to the proportional relationship between the connector characteristic resonance peak (usually appearing at 10-30MHz) and the cable attenuation characteristics. For example, the oxidation of the connector will produce obvious resonance at high frequency band, and the branch cable fracture will show enhanced reflection in the full frequency band.

[0096] S51, when the position with the largest attenuation difference is located near the branch node in the final determination of the fault point, frequency domain impedance spectrum scanning is performed on all branches connected to the node, the branch with the most obvious impedance spectrum mutation is selected as the fault branch, and the final fault point is accurately positioned on the branch;

[0097] The frequency domain impedance spectrum scanning in the final fault confirmation stage draws the impedance-frequency curve of each branch by applying a sweep signal of 0.1-10MHz, and the real fault branch will have an impedance mutation at a specific frequency point (such as an abrupt change in capacitive reactance at 1MHz near the insulation damage point), while the normal branch will maintain a smooth curve.

[0098] Through the above method, the application scenario of the weak current cable fault positioning disclosed by the present application is expanded to the actual topological network structure, and through the intelligent topological adaptation mechanism, the method has the ability to handle complex cable networks in real scenarios.

[0099] In order to realize the fault positioning method of the above two embodiments, the present application also provides a weak current cable fault positioning system for realizing the above method, referring to Figure 3 , the system comprises:

[0100] A stress monitoring module is configured to monitor the axial stress distribution change of the weak current cable in real time when the weak current cable is working normally, and identify a section with a significant change in stress distribution characteristics as a to-be-detected fault area;

[0101] A signal processing module is configured to inject a low-frequency pulse signal into the to-be-detected fault area, collect the reflection signal on the weak current cable, and extract the waveform distortion characteristics in the reflection signal;

[0102] An impedance analysis module is configured to calculate the impedance mismatch amount based on the extracted waveform distortion characteristics, and dynamically adjust the output impedance of the low-frequency pulse signal, and if the dynamic adjustment of the output impedance cannot make the output impedance of the injected low-frequency pulse signal synchronous with the impedance change trend of the cable, it is marked as an impedance mismatch point;

[0103] The fault diagnosis module is configured to inject detection signals of different frequency bands at the impedance mismatch point respectively, collect the attenuation rates of the signals of different frequency bands, calculate the attenuation difference degrees of the impedance mismatch point under different frequency bands, and determine the position with the largest change in the attenuation difference degree as the final fault point.

[0104] Specifically, the system further comprises a topology identification module configured to inject a topology identification signal to the weak current cable, construct a cable branch topology graph according to the reflection time delay characteristics of each branch node, and record the position information of each branch node, so as to realize the fault positioning of the weak current cable in the complex topology network through the topology identification module.

[0105] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer usable storage media containing computer usable program codes (including but not limited to disk storage, CD-ROM, optical storage, etc.).

[0106] Obviously, the above embodiments are only examples for clearly illustrating the present application, and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for locating a fault in a low voltage cable, characterized by: The method comprises the following steps: Real-time monitoring of the axial stress distribution change of the weak current cable, identifying the section where the stress distribution characteristics change significantly as the fault detection area; Injecting a low-frequency pulse signal into the weak current cable at the fault detection area, collecting the reflected signal on the weak current cable, and extracting the waveform distortion characteristics of the reflected signal; Based on the extracted waveform distortion characteristics, calculating the impedance mismatch amount, dynamically adjusting the output impedance of the low-frequency pulse signal, and if the dynamic adjustment of the output impedance cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, marking it as an impedance mismatch point; At the impedance mismatch point, injecting detection signals of different frequency bands respectively, collecting the attenuation rates of signals of each frequency band, calculating the attenuation difference degree of the impedance mismatch point at different frequency bands, and determining the position with the largest change in attenuation difference degree as the final fault point.

2. The low voltage cable fault locating method of claim 1, wherein: The process of real-time monitoring of the axial stress distribution change of the weak current cable comprises the following steps: If the weak current cable is integrated with an optical communication unit, a distributed optical fiber sensing technology can be used to establish a strain-stress conversion model to convert strain distribution into axial stress distribution, realizing the detection of stress distribution change; If the weak current cable does not have an optical communication unit, multiple stress sensing units are arranged at equal intervals along the axial direction of the weak current cable, stress data is synchronously collected by the stress sensing units, differential calculation is performed on the data of adjacent sensing units, the change trend of the stress data is analyzed, and the abnormal fluctuation area is identified.

3. The low voltage cable fault locating method of claim 1, wherein: The frequency range of the low-frequency pulse signal is 1kHz-10kHz, the pulse width is 50-200μs, the interval time between adjacent pulses is not less than 5 times the pulse width, and the low-frequency pulse signal is injected into the fault detection area through a coupler.

4. The low voltage cable fault locating method of claim 1, wherein: The waveform distortion characteristics include amplitude attenuation mutation points and time delay abnormal points, and the process of calculating the impedance mismatch amount based on the extracted waveform distortion characteristics comprises: Establishing a standard waveform template of the reflected signal; Comparing and identifying the amplitude attenuation mutation points and the time delay abnormal points according to the standard waveform template; Calculating the amplitude ratio and phase difference of the reflected signal and the incident signal at the amplitude attenuation mutation points and the time delay abnormal points respectively; Determining the mismatch degree of the reflected signal in combination with the amplitude ratio and the phase difference, establishing a corresponding relationship table between the mismatch degree and the impedance mismatch amount, and using it to guide the adjustment of the impedance mismatch amount.

5. The low voltage cable fault location method of claim 4, wherein: The process of comparing and identifying the amplitude attenuation mutation points and the time delay abnormal points according to the standard waveform template comprises: Segmenting the reflected signal in time domain, and calculating the standard deviation of the amplitude of each segment; If the standard deviation of the amplitude of a segment exceeds 20% of the average value of the same segment of the standard waveform template, it is marked as an amplitude attenuation mutation point; If the time delay difference of the same segment exceeds 10% of the propagation delay of the standard waveform template, it is marked as a time delay abnormal point.

6. The low voltage cable fault locating method of claim 1, wherein: If the dynamic adjustment of the output impedance still cannot match the impedance variation trend of the cable, before marking the impedance mismatch point, the electromagnetic field distribution near the impedance mismatch point is further detected, and if local electromagnetic field abnormally enhances, it is determined that the impedance mismatch point is possibly caused by external interference. The shielding layer excitation signal is applied to the weak current cable to enhance the electromagnetic shielding effectiveness of the outer shielding layer of the cable and suppress the influence of external interference on the low-frequency pulse signal. Then, the dynamic impedance adjustment is performed again. If the impedance variation trend of the cable still cannot be matched, the impedance mismatch point is marked.

7. The weak current cable fault positioning method according to claim 1, characterized in that: At the impedance mismatch point, a plurality of preset frequency bands of detection signals are sequentially injected, wherein the plurality of frequency bands cover a low frequency to a high frequency range, and adjacent frequency bands have a partially overlapping frequency band.

8. The low voltage cable fault locating method of claim 1, wherein: The attenuation difference degree of the impedance mismatch point at different frequency bands is calculated, and the position with the largest attenuation difference degree change is determined as the final fault point. The attenuation rates of each frequency band are arranged in order from low to high, the attenuation rate change amount between adjacent frequency bands is calculated, and the average value of the attenuation rate change amount of all adjacent frequency bands is calculated as a reference benchmark. The adjacent frequency band combination whose attenuation rate change amount exceeds the reference benchmark is screened out, the attenuation difference degree at the center frequency point corresponding to the frequency band combination is calculated, and the attenuation difference degree is the difference between the high-frequency side attenuation rate and the low-frequency side attenuation rate at the center frequency point. Along the axial direction of the weak current cable, the attenuation difference degrees at each impedance mismatch point are compared, and the position with the largest attenuation difference degree change is determined as the final fault point.

9. The low voltage cable fault locating method of claim 1, wherein: When the weak current cable is of a multi-branch topology structure, the following steps are performed: Before identifying the to-be-detected fault region, a topology identification signal is injected into the weak current cable, a cable branch topology graph is constructed according to the reflection time delay characteristics of each branch node, and the position information of each branch node is recorded; When monitoring the axial stress distribution change, each branch section is independently analyzed in combination with the topology graph, and if the stress distribution characteristic change degree of a certain branch exceeds the set multiple of the average change level of the main cable, the branch section is preferentially marked as the to-be-detected fault region; When injecting the low-frequency pulse signal, the pulse width is adjusted according to the electrical length of the branch where the fault region is located, so that the energy of the pulse signal is concentrated in the branch section, and the interference of other branch reflection signals is reduced; When the impedance mismatch point is detected, whether the mismatch point is located at a branch node is judged in combination with the topology graph, if yes, a directional detection signal is injected into the branch node, and by comparing the reflection signal intensity difference of each branch, a false fault point caused by branch impedance mutation is excluded; When the final fault point is determined, if the position with the largest attenuation difference degree change is located near a branch node, all branches connected to the node are subjected to frequency domain impedance spectrum scanning, the branch with the most significant impedance spectrum mutation is selected as the fault branch, and the final fault point is accurately positioned on the branch.

10. A low voltage cable fault location system characterized by: The stress monitoring module is configured to monitor the axial stress distribution change of the weak current cable in real time when the weak current cable is normally working, and identify a section with a significantly changed stress distribution characteristic as a to-be-detected fault region. ​ The signal processing module is configured to inject a low-frequency pulse signal into the to-be-detected fault area, collect a reflected signal on the weak current cable, and extract a waveform distortion feature in the reflected signal. The impedance analysis module is configured to calculate an impedance mismatch amount based on the extracted waveform distortion feature, dynamically adjust an output impedance of the low-frequency pulse signal, and mark an impedance mismatch point if the dynamically adjusted output impedance cannot synchronize the output impedance of the injected low-frequency pulse signal with an impedance change trend of the cable. The fault diagnosis module is configured to inject detection signals of different frequency bands into the impedance mismatch point respectively, collect attenuation rates of the signals of different frequency bands, calculate an attenuation difference degree of the impedance mismatch point at different frequency bands, and determine a position with the largest change in the attenuation difference degree as a final fault point.

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