Weak current cable fault positioning method and system

Abstract

The invention relates to a weak current cable fault positioning method and system, and the method comprises the steps: preliminarily locking a fault region through monitoring the axial stress change in real time, injecting a low-frequency pulse signal in a target section, analyzing the reflection waveform characteristics, and extracting the waveform distortion characteristics in a reflection signal; dynamically adjusting the output impedance based on the amplitude attenuation and time delay relationship, and if the dynamically adjusted output impedance cannot enable the output impedance of the injected low-frequency pulse signal to be synchronous with the impedance change trend of the cable, marking as an impedance mismatch point; after an impedance mismatch point is identified, other interferences are eliminated through multi-band signal attenuation difference analysis, and the position of a fault point is determined; the system is used for implementing the method. According to the method and system, stress monitoring and electric signal detection are combined, the detection range is remarkably shortened, the positioning precision and the detection accuracy are improved, and the method and system are suitable for weak current cable fault diagnosis in a complex environment.

Description

Technical Field

[0001] The present invention relates to the technical field of weak-current cable fault locating technology, and in particular to a weak-current cable fault locating method and system. Background Art

[0002] With the rapid development of modern communications and power systems, weak-current cables (such as communication cables and control cables) are widely used in various complex environments. Since weak-current cables are often laid underground, in pipelines, or in hidden spaces, they are subject to long-term mechanical stress, environmental corrosion, temperature fluctuations, and other factors, making them prone to faults such as insulation aging, localized damage, and loose joints. If these faults are not detected and located promptly, they can lead to decreased signal transmission quality, reduced system stability, and even more serious communication outages or power outages. Therefore, fault detection and location technology for weak-current cables has become a key focus of the industry.

[0003] At present, traditional cable fault detection methods mainly include time domain reflectometry (TDR), frequency domain reflectometry (FDR), impedance analysis, etc. Time domain reflectometry locates the fault point by injecting a pulse signal into the cable and analyzing the reflected waveform, but this method has low detection sensitivity for high-resistance faults and weak defects and is easily affected by noise interference. Frequency domain reflectometry improves detection accuracy by analyzing the characteristics of reflected signals at different frequencies, but it is still difficult to distinguish between signal changes caused by natural cable attenuation and real faults. Impedance analysis can detect cable impedance anomalies, but under dynamic loads or complex laying environments, the real-time and accuracy of impedance matching adjustment are insufficient, which can easily lead to misjudgment. In addition, most existing technologies rely on offline detection or periodic inspections, and are unable to monitor cable status in real time, resulting in delayed fault detection and affecting system reliability. Summary of the Invention

[0004] To this end, the technical problem to be solved by the present invention is to overcome the defects of offline detection lag, severe attenuation of long-distance detection signals, and easy misjudgment in the existing technology of weak current cable fault location, and provide a weak current cable fault location method and system, which preliminarily locks the fault section through real-time stress monitoring to shorten the detection range, and combines dynamic impedance matching and multi-band attenuation analysis to achieve early warning, precise positioning and significantly improve detection accuracy.

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

[0006] When the weak-current cable is operating normally, the axial stress distribution changes of the weak-current cable are 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 the fault area to be detected on the weak-current cable, collect the reflected signal on the weak-current cable, and extract the waveform distortion characteristics in the reflected signal;

[0008] Based on the extracted waveform distortion characteristics, the impedance mismatch is calculated and the output impedance of the low-frequency pulse signal is dynamically adjusted. If the dynamic output impedance adjustment cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, it is marked as an impedance mismatch point.

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

[0010] In one embodiment of the present invention, the process of real-time monitoring of axial stress distribution changes of weak current cables includes the following steps:

[0011] If an optical communication unit is integrated into the weak current cable, distributed optical fiber sensing technology can be used to establish a strain-stress conversion model to convert the strain distribution into axial stress distribution, thereby detecting changes in stress distribution.

[0012] If there is no optical communication unit in the weak-current cable, multiple stress sensing units are arranged at equal intervals along the axial direction of the weak-current cable. Stress data is collected synchronously through the stress sensing units, and differential calculation is performed on the data of adjacent sensing units to analyze the changing trend of the stress data and identify abnormal fluctuation areas.

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

[0014] In one embodiment of the present invention, the waveform distortion features include: amplitude attenuation mutation points and time delay abnormal points. Based on the extracted waveform distortion features, the process of calculating the impedance mismatch includes:

[0015] Establish a standard waveform template for the reflected signal;

[0016] According to the standard waveform template, compare and identify the amplitude attenuation mutation points and time delay abnormal points;

[0017] Calculate the amplitude ratio and phase difference between the reflected signal and the incident signal 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, and a corresponding relationship table between the mismatch degree and the impedance mismatch amount is established to guide the adjustment of the impedance mismatch amount.

[0019] In one embodiment of the present invention, the process of comparing and identifying amplitude attenuation mutation points and time delay abnormal points based on the standard waveform template includes:

[0020] Segment the reflected signal in the time domain and calculate the standard deviation of the signal amplitude in each segment;

[0021] If the standard deviation of the amplitude of a certain 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;

[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 one embodiment of the present invention, if the dynamic adjustment of the output impedance still cannot match the cable impedance change trend, before marking it as an impedance mismatch point, the electromagnetic field distribution near the impedance mismatch point is further detected. If an abnormal enhancement of the local electromagnetic field is detected, it is determined that the impedance mismatch point may be caused by external interference. First, a shielding layer excitation signal is applied to the low-voltage cable to enhance the electromagnetic shielding effectiveness of the cable outer shielding layer and suppress the influence of external interference on the low-frequency pulse signal. Then, dynamic impedance adjustment is performed. If it still cannot match the cable impedance change trend, it is marked as an impedance mismatch point.

[0024] In one embodiment of the present invention, detection signals of a plurality of preset frequency bands are sequentially injected at the impedance mismatch point, wherein the plurality of frequency bands cover a range from low frequency to high frequency, and adjacent frequency bands are set to have partially overlapping frequency bands.

[0025] In one embodiment of the present invention, the process of calculating the attenuation difference of the impedance mismatch point in different frequency bands and determining the location with the largest attenuation difference change as the final fault point includes:

[0026] Arrange the attenuation rates of each frequency band in ascending order, calculate the change in attenuation rates between adjacent frequency bands, and calculate the average value of the change in attenuation rates of all adjacent frequency bands as a reference benchmark;

[0027] Screening out adjacent frequency band combinations whose attenuation rate changes exceed the reference benchmark, and calculating the attenuation difference at the center frequency point corresponding to the frequency band combination, where the attenuation difference is the difference between the attenuation rate on the high-frequency side and the attenuation rate on the low-frequency side at the center frequency point;

[0028] Along the axial direction of the weak current cable, the attenuation differences at each impedance mismatch point are compared, and the location with the largest change in attenuation difference is determined as the final fault point.

[0029] In one embodiment of the present invention, when the weak current cable has a multi-branch topology, the following steps are performed:

[0030] Before identifying the fault area to be detected, a topology identification signal is first injected into the weak current cable. A cable branch topology map is constructed based on the reflection delay characteristics of each branch node, and the location information of each branch node is recorded.

[0031] When monitoring changes in axial stress distribution, independent stress analysis is performed on each branch section in combination with the topological map. If the degree of change in the stress distribution characteristics of a branch exceeds a set multiple of the average change level of the trunk cable, the branch section is preferentially marked as a fault area to be detected;

[0032] When injecting a low-frequency pulse signal, 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 reflected signals from other branches is reduced;

[0033] When an impedance mismatch point is detected, the topology map is used to determine whether the mismatch point is located at a branch node. If so, a directional detection signal is injected into the branch node. By comparing the difference in reflected signal strength between branches, false fault points caused by sudden changes in branch impedance are eliminated.

[0034] When the fault point is finally determined, if the location with the largest attenuation difference is near a branch node, a frequency domain impedance spectrum scan 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 located on this branch.

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

[0036] The stress monitoring module is used to monitor the axial stress distribution changes of the weak-current cables in real time when the cables are operating normally, and identify the sections where the stress distribution characteristics have changed significantly as the fault areas to be detected;

[0037] A signal processing module is used to inject a low-frequency pulse signal into the fault area to be detected, collect the reflected signal on the weak current cable, and extract the waveform distortion characteristics in the reflected signal;

[0038] The impedance analysis module is used to calculate the impedance mismatch based on the extracted waveform distortion characteristics and dynamically adjust the output impedance of the low-frequency pulse signal. If the dynamic output impedance adjustment cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, it is marked as an impedance mismatch point;

[0039] The fault diagnosis module is used to inject detection signals of different frequency bands at the impedance mismatch point, collect the attenuation rate of the signal in each frequency band, calculate the attenuation difference of the impedance mismatch point in different frequency bands, and determine the position with the largest attenuation difference change as the final fault point.

[0040] The above technical solution of the present invention has the following advantages over the prior art:

[0041] 1. Pre-locating suspicious areas through stress distribution changes shortens the scope of subsequent electrical signal detection, significantly reducing detection time and system power consumption. This "coarse screening first, then fine testing" strategy significantly improves overall detection efficiency.

[0042] 2. Enhanced early fault identification capabilities: Stress monitoring can capture characteristic changes in the early stages of mechanical damage, enabling early warning of faults and making up for the defect of traditional electrical signal detection methods that are insensitive to early faults.

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

[0044] 4. Reduce operation and maintenance costs: Accurate section positioning avoids full-line inspection and blind excavation, which can reduce maintenance workload. At the same time, early detection of faults can avoid greater losses caused by the expansion of faults.

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

[0046] The weak-current cable fault location method and system of the present invention combines mechanical stress monitoring with electrical characteristic analysis, providing a new technical route for weak-current cable fault detection. It is particularly suitable for cable operation and maintenance scenarios over long distances and in complex environments, and has important engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0048] Figure 1 It is a flowchart of the steps of the weak current cable fault location method of the present invention;

[0049] Figure 2 This is a flowchart of the steps of applying the weak current cable fault location method of the present invention to a multi-branch topology structure;

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

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0052] Reference Figure 1 As shown, the present invention discloses a method for locating a weak current cable fault, comprising the following steps:

[0053] S10. When the weak-current cable is operating normally, monitor the axial stress distribution changes of the weak-current cable in real time, and identify the section where the stress distribution characteristics change significantly as the fault area to be detected;

[0054] First, stress distribution changes are introduced into cable fault location. By identifying sections where stress characteristics change significantly, potential mechanical damage or structural deterioration areas can be quickly identified. Compared with traditional methods that rely solely on electrical signal detection, stress monitoring can achieve early warning of faults and detect potential fault risk areas earlier. At the same time, it provides a precise target area for subsequent electrical signal detection, avoiding the disadvantage of traditional methods that require blind detection along the entire cable length.

[0055] S20, injecting a low-frequency pulse signal into the fault area to be detected of the weak-current cable, collecting the reflected signal on the weak-current cable, and extracting the waveform distortion characteristics in the reflected signal;

[0056] After determining the fault area to be detected, low-frequency pulse signals are injected only in the target section instead of detecting the entire line. This improvement significantly shortens the range of the detection signal. On the one hand, it reduces the attenuation and interference of the signal during long-distance transmission and improves the signal quality. On the other hand, it significantly reduces the time and energy consumption required for detection. The injection of low-frequency pulse signals is mainly aimed at the problem of severe attenuation of high-frequency signals during long-distance cable detection. Low-frequency signals have better penetration and anti-interference capabilities, and can obtain more reliable reflected waveforms.

[0057] By analyzing the waveform distortion characteristics of the reflected signal, the possible fault location can be preliminarily determined. Compared with traditional TDR methods, this collaborative detection mechanism of "stress location + electrical signal verification" makes the fault location process more efficient and reliable.

[0058] S30. Calculate the impedance mismatch based on the extracted waveform distortion characteristics and dynamically adjust the output impedance of the low-frequency pulse signal. If the dynamic output impedance adjustment cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, it is marked as an impedance mismatch point.

[0059] Furthermore, based on the extracted waveform distortion features, the method adopts a dynamic impedance adjustment mechanism. By calculating the impedance mismatch in real time and adjusting the output impedance, it can adapt to the dynamic changes of the cable impedance and solve the problem of inaccurate impedance matching in complex environments. In the process of dynamic impedance adjustment, if the reflected signal is stable after the dynamic impedance adjustment, it means that the corresponding waveform distortion feature may be a false fault caused by environmental interference or other interference, and it will not be identified. If the impedance matching is adjusted dynamically multiple times, some points still cannot stabilize the reflected signal. These points are marked as suspected fault points, which effectively solves the problem of poor adaptability of traditional impedance analysis methods in complex environments.

[0060] S40, injecting detection signals of different frequency bands at the impedance mismatch point, collecting the attenuation rate of the signal in each frequency band, calculating the attenuation difference of the impedance mismatch point in different frequency bands, and determining the location with the largest attenuation difference change as the final fault point;

[0061] Different types of cable faults (such as insulation aging, localized damage, or loose connectors) have significantly different attenuation characteristics for signals at different frequencies. However, normal cable impedance variations or environmental interference have a relatively uniform impact on signals across all frequency bands. By injecting probe signals at multiple frequency bands at the impedance mismatch point and accurately measuring the attenuation rate of the signal in each frequency band, a "frequency response fingerprint" of the fault point can be constructed.

[0062] Specifically, when the detection signal encounters a real fault point, electromagnetic waves in different frequency bands will exhibit nonlinear attenuation characteristics due to physical structural anomalies at the fault site (such as changes in dielectric loss or sudden changes in conductor cross-sectional area). For example, high-frequency signals are more sensitive to surface damage, while low-frequency signals are more sensitive to deep-seated insulation degradation. By calculating the differential attenuation rate index for each frequency band, the fault signature signal can be effectively amplified while suppressing interference from inherent line attenuation and environmental noise.

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

[0064] In practical applications, two different schemes can be used to achieve stress detection according to the application location and scenario of low-voltage cables: for cables with integrated optical communication units, distributed optical fiber sensing technology is used to input Brillouin scattering frequency shift or Rayleigh scattering strain data into the strain-stress conversion model. 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 millimeter-level spatial resolution and can accurately locate the stress concentration section; for cables without optical communication units, a discrete stress sensing array is used. MEMS stress sensors arranged at equal intervals are used to synchronously collect data. Differential calculation of adjacent unit data can eliminate common-mode interference such as ambient temperature. When the differential value of a certain section exceeds the threshold, it indicates that there is an abnormal stress gradient in the area. This design not only avoids the problem of missed detection by traditional point sensors, but also amplifies local abnormal signals through differential algorithms.

[0065] Both of the above-mentioned stress detection schemes can effectively identify sections with sudden changes in stress distribution characteristics, providing precise target areas for subsequent fault location. This detection logic of mechanical anomalies first and electrical faults later significantly improves the timeliness of fault warning.

[0066] Specifically, in order to achieve optimal signal propagation characteristics and reflected signal analysis capabilities during the fault location process, in this embodiment, based on the transmission characteristics of the low-voltage cable, the frequency range is set to 1kHz-10kHz: this frequency band can not only penetrate the distributed capacitive reactance and inductive reactance of the cable, avoiding excessive attenuation of high-frequency signals due to the skin effect, but also maintain sufficient wavelength resolution (the wavelength in a typical low-voltage cable is about tens to hundreds of meters), ensuring that the reflected signal can accurately reflect the location information of the impedance mutation point; the pulse width of 50-200μs is designed to strike a balance between time resolution and energy accumulation. Wider pulses can carry higher energy to improve the signal-to-noise ratio, but too wide will cause overlapping of close-range reflected signals. Therefore, this range can both ensure the identifiability of the reflected signal at the fault point and avoid aliasing of adjacent reflected waveforms.

[0067] Furthermore, the requirement that the interval between adjacent pulses be no less than five times the pulse width ensures that all reflected signals from the previous pulse have completely decayed before the next pulse is injected, preventing interference between multiple pulse reflections. If the interval is too short, residual reflections from the previous pulse will overlap with reflections from subsequent pulses, leading to distortion in waveform feature extraction. The five times pulse width setting takes into account the attenuation characteristics of the cable, ensuring that reflected signals have sufficient time to decay below the noise level. This ensures that the reflected signals collected after each pulse injection are independent responses to the current pulse, improving the accuracy of impedance mismatch point detection.

[0068] Furthermore, the impedance matching problem between the signal source and the cable is solved through the design of the coupler injection signal. The coupler can realize the impedance transition between the signal source and the cable, reduce the signal reflection loss during direct injection, and at the same time isolate the DC component or high-voltage interference that may exist in the signal source and the cable, thereby protecting the detection equipment; moreover, the high-pass or band-pass characteristics of the coupler can also filter out power frequency interference, ensuring the purity of the low-frequency pulse signal, so that the distortion component in the reflected signal is only caused by the change in cable impedance, rather than external noise interference.

[0069] Specifically, the waveform distortion features are specifically defined as amplitude attenuation mutation points and time delay anomaly points, accurately capturing abnormal information in the reflected signal from both the time domain and amplitude domain dimensions, thereby more accurately identifying the location and degree of cable impedance mismatch. Among them: the amplitude attenuation mutation point reflects the energy loss caused by impedance discontinuity during signal propagation. For example, faults such as conductor breakage, poor contact or insulation deterioration will cause the signal amplitude to drop sharply; and the time delay anomaly point reflects the difference in signal propagation speed caused by medium changes or local deformation. For example, cable extrusion, water ingress or local aging will cause the equivalent dielectric constant of the signal propagation path to change, thereby changing the signal transmission delay. By simultaneously monitoring these two features, the misjudgment caused by single feature detection can be avoided (for example, relying solely on amplitude attenuation may misjudge a normal impedance matching point as a fault point), thereby improving the robustness of fault location.

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

[0071] First, a standard waveform template for the reflected signal needs to be established. This template is usually based on the reflection characteristics of the cable under normal conditions, including typical amplitude attenuation curves and propagation delay characteristics.

[0072] During the fault detection phase, the actual collected reflected signal is compared with the template to identify areas where the amplitude suddenly drops (amplitude attenuation mutation points) and locations where the signal arrival time is abnormally delayed (time delay anomaly points). The identification of these two characteristic points is not performed in isolation, but rather they verify each other. For example, if a sudden drop in amplitude and an increase in time delay occur simultaneously at a certain location, it is very likely that the conductor is broken with a local dielectric change. If only the time delay is abnormal and the amplitude changes smoothly, it may indicate that the cable sheath is deformed but the conductor remains connected.

[0073] Specifically, the process of comparing and identifying amplitude attenuation mutation points and time delay anomalies based on a standard waveform template involves segmenting the reflected signal in the time domain. This segmentation is typically based on pulse width and cable propagation velocity, ensuring that each segment corresponds to a specific area on the physical cable. This segmentation provides spatial resolution for fault location, transforming global waveform analysis into localized anomaly detection. Next, the standard deviation of the signal amplitude is calculated within each segment, rather than simply comparing instantaneous values. This is because the standard deviation reflects both the severity of signal fluctuations and overall energy variations, avoiding occasional noise interference from a single sampling point. Finally, a threshold is applied. When the standard deviation of a segment exceeds 20% of the average value of the corresponding segment in the standard template, it indicates significant signal amplitude instability, likely caused by reflection superposition caused by impedance mutations, and is therefore marked as an amplitude attenuation mutation point. This threshold setting accounts for the natural signal fluctuations of a normal cable (typically <10%) while ensuring that true fault characteristics are captured (e.g., reflection amplitude changes caused by a conductor break are typically >30%).

[0074] Time delay anomalies are detected by comparing the arrival time difference of signals in the same segment with the propagation delay of a standard template. The propagation delay of the standard template reflects the theoretical transmission speed of the signal in an intact cable. An anomaly is detected when the actual signal delay difference exceeds 10%. This threshold effectively identifies propagation speed changes caused by dielectric changes (such as moisture in the insulation layer or local deformation). For example, water ingress in a cable can increase the local dielectric constant, reducing signal propagation speed by 5%-15%, while sheath extrusion can increase delay by 8%-12%. The 10% threshold precisely covers the range of time delay variations caused by typical faults.

[0075] Next, the amplitude ratio and phase difference between the reflected signal and the incident signal are calculated at the identified distortion point. The amplitude ratio directly reflects the degree of signal energy loss, while the phase difference reflects the change in the equivalent electrical length of the signal propagation path. The combination of these two parameters can more comprehensively describe the nature of the impedance mismatch: purely resistive mismatch (such as increased contact resistance) is mainly manifested as an amplitude change, while reactive mismatch (such as abnormal distributed capacitance or inductance) has a more significant impact on the phase.

[0076] By establishing a corresponding relationship table between mismatch degree and impedance mismatch amount, the abstract waveform distortion can be converted into a specific quantitative indicator of impedance change. This relationship table is usually generated based on the reflection coefficient formula in transmission line theory and experimental calibration data, so that the dynamic adjustment of output impedance can be targeted.

[0077] In this embodiment, the single amplitude detection of the traditional time domain reflectometry (TDR) is upgraded to a joint amplitude and phase analysis through the fusion of multi-dimensional signal features. The amplitude attenuation mutation point is mainly used to locate obvious impedance discontinuities (such as open circuits or short circuits), while the time delay anomaly point is more sensitive to distributed faults (such as uniform aging or moisture of cables). 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 a gradual decrease in amplitude accompanied by a slight increase in time delay, while damage to the insulation layer may cause a sudden change in amplitude but unchanged time delay. In addition, the introduction of the mismatch correspondence table transforms the impedance adjustment process from empirical trial 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-band attenuation difference analysis.

[0078] In actual engineering environments, the surrounding electromagnetic field environment can cause significant interference to impedance matching. When the dynamically adjusted output impedance cannot keep pace with the cable impedance change trend, there are two possibilities: one is the actual impedance mismatch caused by physical damage to the cable itself, and the other is the equivalent impedance change caused by local interference current induced by strong external electromagnetic fields (such as coupling from adjacent power lines and radiation from radio frequency equipment). If all impedance mismatch points are indiscriminately marked as fault points, the misjudgment rate will increase.

[0079] In this embodiment, by detecting the electromagnetic field distribution, the influence of the interference source can be identified from a physical mechanism perspective. The electromagnetic field distribution of the actual fault point usually shows an inward-aggregating characteristic (such as the electric field concentration at the conductor break), while external interference is manifested as an abnormally enhanced outward-radiating field intensity. 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 dynamic impedance adjustment fails, the near-field detection module is started to scan the electromagnetic field around the impedance mismatch point, and a combination of a non-contact magnetic field probe (such as a Hall sensor) and an electric field probe (such as a flat antenna) is used to measure the 3D field strength distribution and calculate its gradient change; when the local field strength is detected to exceed 30% of the typical value when the cable is working normally and is distributed outward, it is determined that external interference is dominant. At this time, a shielding layer excitation signal (usually a high-frequency signal of 100kHz-1 MHz, with an amplitude of 5%-10% of the cable working voltage) is applied, and a uniform eddy current distribution is formed in the outer shielding layer through the skin effect, which reduces the transfer impedance of the shielding layer by 40%-60%, thereby suppressing the coupling of external interference to the low-frequency pulse signal.

[0081] The key to this process lies in the selection of the excitation signal frequency: a frequency that is too low will lead to insufficient excitation of the shielding layer, while a frequency that is too high may cause parasitic resonance of the cable. Therefore, it is necessary to adaptively adjust according to the conductive properties of the shielding layer material (such as copper braid or aluminum foil layer). After the shielding enhancement is completed, dynamic impedance adjustment is performed again. If the impedance matching degree is improved to above the threshold, the fault mark is removed; if it still cannot be matched, it can be confirmed that the point is the real impedance mismatch point.

[0082] In this embodiment, when injecting detection signals of different frequency bands to determine the final fault point, multiple frequency bands are set to cover the low-frequency to high-frequency range, and a partially overlapping frequency band design is adopted. This allows the establishment of a full-band fault feature fingerprint library, thereby accurately identifying different types of faults. Specifically, low-frequency signals (such as 1-10 kHz) can penetrate the distributed parameter network of the cable and mainly reflect lumped parameter faults such as conductor continuity. Medium-frequency signals (such as 10-100 kHz) are sensitive to uniform aging of the insulation layer. High-frequency signals (such as 100 kHz-1 MHz) can capture distributed defects such as partial discharge and sheath damage. This wideband coverage ensures that whether the fault manifests as a centralized impedance mutation or a distributed parameter gradient, it can be effectively stimulated by the detection signal of at least one frequency band. The setting of partially overlapping frequency bands in adjacent frequency bands (such as the 5 kHz overlap of 5-15 kHz and 10-20 kHz) achieves seamless frequency domain detection, avoiding feature omissions caused by frequency band gaps and ensuring data continuity during frequency band switching through response consistency verification in the overlapping area.

[0083] Specifically, the process of injecting detection signals in different frequency bands is as follows: the signal generator generates a sequence of detection signals arranged according to a frequency gradient, and the center frequency of each frequency band is distributed according to a logarithmic law (such as 1kHz, 3kHz, 10kHz, 30kHz, etc.). This nonlinear distribution conforms to the sensitivity of cable fault characteristics to frequency changes - higher density sampling is required in the low-frequency region to distinguish conductor defects, while the interval can be appropriately relaxed in the high-frequency region due to the skin effect; the signal is injected using a combination of swept continuous wave (CW) and pulse modulation: the CW mode is used to measure the steady-state attenuation rate, and the pulse mode is used to obtain time-domain reflection characteristics.

[0084] Based on the analysis of actual working conditions, weak-current cables will produce uniform attenuation due to overall aging during long-term operation. This background change will mask the characteristics of local fault points. Therefore, when calculating the attenuation difference of the impedance mismatch point in different frequency bands, this embodiment proposes a benchmark comparison method for the change in attenuation rate of adjacent frequency bands. In essence, it constructs a dynamic detection threshold that is adaptive to the current cable status - the reference benchmark reflects the overall attenuation characteristics of the cable, and the frequency band combination that significantly exceeds the benchmark indicates the presence of local abnormalities.

[0085] Specifically, when calculating the attenuation differential of an impedance mismatch point across different frequency bands, the attenuation rate data for each frequency band is preprocessed and sorted by frequency from low to high. The attenuation rate variation between adjacent frequency bands is then calculated. This differential processing eliminates the fundamental attenuation component shared across all frequency bands, highlighting the frequency response mutation characteristic of the fault point. For example, a uniformly aged cable may exhibit a 30% year-over-year increase in attenuation across all frequency bands, while the variation in adjacent frequency bands will remain stable. However, a cable with a localized insulation defect may exhibit abnormal variations in specific frequency bands (such as at the multiple of the defect resonant frequency). By calculating the average of all adjacent variations to establish a reference baseline, an adaptive threshold is constructed based on the current state of the cable. When the variation in a group of adjacent frequency bands exceeds the baseline, it indicates non-uniform attenuation within that frequency band. The attenuation differential (the difference between the high- and low-frequency attenuation rates) at the center frequency of this frequency band combination is then extracted. This parameter quantifies the fault point's sensitivity to signals at different frequencies. Ultimately, by axially comparing the magnitude of the differential variation across each impedance mismatch point, the fault point can be precisely located spatially.

[0086] This relative value comparison strategy ensures that fault detection is not affected by the initial condition of the cable, and maintains consistent detection sensitivity even for cables from different batches or years of use.

[0087] In actual engineering environments, the layout of weak current cables is mostly a multi-branch topology. Therefore, in order to improve the practicality of the fault location method of the present invention, based on the above embodiment, reference is made to Figure 2 As shown, the present invention also provides a fault location method when the weak current cable has a multi-branch topology structure, comprising the following steps:

[0088] S11. Before identifying the fault area to be detected, inject a topology identification signal into the weak current cable, construct a cable branch topology map based on the reflection delay characteristics of each branch node, and record the location information of each branch node;

[0089] The cable branch topology map constructed using the topology identification signal provides a spatial reference framework for all subsequent detection steps. This logical sequence of first mapping and then detection makes fault location in complex networks traceable. The topology identification signal typically uses a narrow pulse with a fast rising edge (such as a 50ns pulse width). It utilizes the reflection delay differences caused by impedance discontinuities at each branch node to reconstruct the network structure using the principle of time domain reflectometry (TDR). Its spatial resolution can reach 0.5% of the cable length, ensuring that branch nodes only a few meters apart can be distinguished.

[0090] S21. When monitoring changes in axial stress distribution, perform independent stress analysis on each branch section in combination with the topological map. If the degree of change in the stress distribution characteristics of a branch exceeds a set multiple of the average change level of the trunk cable, then prioritize marking the branch section as a fault area to be detected.

[0091] By converting overall stress analysis into a topology-based zoning assessment, when the stress change in a branch exceeds a set multiple (usually 3-5 times) of the average trunk level, it indicates that the branch may be experiencing abnormal mechanical stress (such as pulling or squeezing). This zoning threshold strategy effectively prevents the trunk cable stress from masking subtle changes in the branch. For example, in the wiring of multiple cameras in a security system, a sudden increase in stress in a branch may be a precursor to the cable being crushed by an object, while the stress changes in the cables within the trunk cable duct are relatively gradual. By independently analyzing the stress of each branch, the system can identify potential fault points at an early stage.

[0092] S31. When injecting a low-frequency pulse signal, adjust 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 and the interference of reflected signals from other branches is reduced;

[0093] The pulse width is dynamically set based on the electrical length of the branch where the fault is located (provided by the topology map), matching the branch's electrical length (typically 1.2-1.5 times the branch's round-trip delay). This ensures that signal energy is concentrated on the target branch while preventing overly wide pulses from causing superimposed reflections in other branches. For example, for a 20-meter branch, selecting a pulse width of 200ns (corresponding to an electrical length of approximately 40 meters) ensures complete signal coverage without significant penetration into adjacent branches. This parameter optimization ensures that detection results from each branch do not interfere with each other in bus or tree topologies.

[0094] S41. When an impedance mismatch point is detected, determine whether the mismatch point is located at a branch node based on the topology map. If so, inject a directional detection signal into the branch node and eliminate false fault points caused by sudden changes in branch impedance by comparing the difference in reflected signal strength between the branches.

[0095] Fault identification at nodes utilizes directional detection signal technology. This signal has specific spectral characteristics (such as a band-limited pseudo-random code). By comparing the correlation coefficient and energy ratio of the reflected signals from each branch, the actual faulty branch can be accurately identified. When the impedance mismatch point is located at a node, traditional methods have difficulty distinguishing between aging node connectors and branch cable faults. This solution injects a directional signal (with frequency characteristics designed to account for the different frequency responses of connectors and cables) into the node and makes a judgment based on the proportional relationship between the connector's characteristic resonance peak (typically occurring in the 10-30MHz range) and the cable attenuation characteristics in the reflected signal. For example, connector oxidation will produce significant resonance at high frequencies, while a broken branch cable will manifest as increased reflection across the entire frequency band.

[0096] S51. When the fault point is finally determined, if the location with the largest attenuation difference is near a branch node, perform a frequency domain impedance spectrum scan on all branches connected to the node, select the branch with the most significant impedance spectrum mutation as the fault branch, and accurately locate the final fault point on this branch;

[0097] In the final fault confirmation stage, the frequency domain impedance spectrum scan draws the impedance-frequency curve of each branch by applying a 0.1-10MHz sweep frequency signal. The real fault branch will have an impedance mutation at a specific frequency point (for example, the insulation damage point will show a sudden drop in capacitive reactance near 1MHz), while the normal branch maintains a smooth curve.

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

[0099] In order to implement the fault location methods of the above two embodiments, the present invention also provides a weak current cable fault location system for implementing the above methods, referring to Figure 3 As shown, the system includes:

[0100] The stress monitoring module is used to monitor the axial stress distribution changes of the weak-current cables in real time when the cables are operating normally, and identify the sections where the stress distribution characteristics have changed significantly as the fault areas to be detected;

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

[0102] The impedance analysis module is used to calculate the impedance mismatch based on the extracted waveform distortion characteristics and dynamically adjust the output impedance of the low-frequency pulse signal. If the dynamic output impedance adjustment cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, it is marked as an impedance mismatch point;

[0103] The fault diagnosis module is used to inject detection signals of different frequency bands at the impedance mismatch point, collect the attenuation rate of the signal in each frequency band, calculate the attenuation difference of the impedance mismatch point in different frequency bands, and determine the position with the largest attenuation difference change as the final fault point.

[0104] Specifically, the system also includes: a topology identification module, which is used to inject a topology identification signal into the weak-current cable, construct a cable branch topology map based on the reflection delay characteristics of each branch node, and record the location information of each branch node. The topology identification module is used to realize the fault location of the weak-current cable in a complex topology network.

[0105] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0106] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for locating a weak current cable fault, characterized by: The following steps are involved: When the weak-current cable is operating normally, the axial stress distribution changes of the weak-current cable are monitored in real time, and the section where the stress distribution characteristics change significantly is identified as the fault area to be detected; Inject a low-frequency pulse signal into the fault area to be detected on the weak-current cable, collect the reflected signal on the weak-current cable, and extract the waveform distortion characteristics in the reflected signal; Based on the extracted waveform distortion characteristics, the impedance mismatch is calculated and the output impedance of the low-frequency pulse signal is dynamically adjusted. If the dynamic output impedance adjustment cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, it is marked as an impedance mismatch point. At the impedance mismatch point, detection signals of different frequency bands are injected respectively, the attenuation rate of the signal in each frequency band is collected, the attenuation difference of the impedance mismatch point in different frequency bands is calculated, and the position with the largest attenuation difference change is determined as the final fault point.

2. The method for locating a weak current cable fault according to claim 1, wherein: The process of real-time monitoring of axial stress distribution changes in weak current cables includes the following steps: If an optical communication unit is integrated into the weak current cable, distributed optical fiber sensing technology can be used to establish a strain-stress conversion model to convert the strain distribution into axial stress distribution, thereby detecting changes in stress distribution. If there is no optical communication unit in the weak-current cable, multiple stress sensing units are arranged at equal intervals along the axial direction of the weak-current cable. Stress data is collected synchronously through the stress sensing units, and differential calculation is performed on the data of adjacent sensing units to analyze the changing trend of the stress data and identify abnormal fluctuation areas.

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

4. The method for locating a weak current cable fault according to claim 1, wherein: The waveform distortion features include: amplitude attenuation mutation points and time delay abnormal points. Based on the extracted waveform distortion features, the process of calculating the impedance mismatch includes: Establish a standard waveform template for the reflected signal; According to the standard waveform template, compare and identify the amplitude attenuation mutation points and time delay abnormal points; Calculate the amplitude ratio and phase difference between the reflected signal and the incident signal at the amplitude attenuation mutation point and the time delay abnormal point respectively; The mismatch degree of the reflected signal is determined in combination with the amplitude ratio and the phase difference, and a corresponding relationship table between the mismatch degree and the impedance mismatch amount is established to guide the adjustment of the impedance mismatch amount.

5. The method for locating a weak current cable fault according to claim 4, characterized in that: The process of comparing and identifying amplitude attenuation mutation points and time delay abnormal points based on the standard waveform template includes: Segment the reflected signal in the time domain and calculate the standard deviation of the signal amplitude in each segment; If the standard deviation of the amplitude of a certain 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 anomaly point.

6. The method for locating a weak current cable fault according to claim 1, wherein: If the dynamic adjustment of the output impedance still cannot match the cable impedance change trend, before marking it as an impedance mismatch point, further detect the electromagnetic field distribution near the impedance mismatch point. If an abnormal enhancement of the local electromagnetic field is detected, it is determined that the impedance mismatch point may be caused by external interference. First, apply a shielding layer excitation signal to the low-voltage cable to enhance the electromagnetic shielding effectiveness of the cable outer shielding layer and suppress the influence of external interference on the low-frequency pulse signal. Then perform dynamic impedance adjustment. If it still cannot match the cable impedance change trend, it is marked as an impedance mismatch point.

7. The method for locating a weak current cable fault according to claim 1, wherein: At the impedance mismatch point, detection signals of multiple preset frequency bands are injected in sequence, wherein the multiple frequency bands cover the range from low frequency to high frequency, and adjacent frequency bands are set to have partially overlapping frequency bands.

8. The method for locating a weak current cable fault according to claim 1, wherein: The process of calculating the attenuation difference of the impedance mismatch point in different frequency bands and determining the location with the largest attenuation difference as the final fault point includes: Arrange the attenuation rates of each frequency band in ascending order, calculate the change in attenuation rates between adjacent frequency bands, and calculate the average value of the change in attenuation rates of all adjacent frequency bands as a reference benchmark; Screening out adjacent frequency band combinations whose attenuation rate changes exceed the reference benchmark, and calculating the attenuation difference at the center frequency point corresponding to the frequency band combination, where the attenuation difference is the difference between the attenuation rate on the high-frequency side and the attenuation rate on the low-frequency side at the center frequency point; Along the axial direction of the weak current cable, the attenuation differences at each impedance mismatch point are compared, and the location with the largest change in attenuation difference is determined as the final fault point.

9. The method for locating a weak current cable fault according to claim 1, wherein: When the weak current cable has a multi-branch topology, perform the following steps: Before identifying the fault area to be detected, a topology identification signal is first injected into the weak current cable. A cable branch topology map is constructed based on the reflection delay characteristics of each branch node, and the location information of each branch node is recorded. When monitoring changes in axial stress distribution, independent stress analysis is performed on each branch section in combination with the topological map. If the degree of change in the stress distribution characteristics of a branch exceeds a set multiple of the average change level of the trunk cable, the branch section is preferentially marked as a fault area to be detected; When injecting a low-frequency pulse signal, 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 reflected signals from other branches is reduced; When an impedance mismatch point is detected, the topology map is used to determine whether the mismatch point is located at a branch node. If so, a directional detection signal is injected into the branch node. By comparing the difference in reflected signal strength between branches, false fault points caused by sudden changes in branch impedance are eliminated. When the fault point is finally determined, if the location with the largest attenuation difference is near a branch node, a frequency domain impedance spectrum scan 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 located on this branch.

10. A weak current cable fault location system, characterized by: include: The stress monitoring module is used to monitor the axial stress distribution changes of the weak-current cables in real time when the cables are operating normally, and identify the sections where the stress distribution characteristics have changed significantly as the fault areas to be detected; A signal processing module is used to inject a low-frequency pulse signal into the fault area to be detected, collect the reflected signal on the weak current cable, and extract the waveform distortion characteristics in the reflected signal; The impedance analysis module is used to calculate the impedance mismatch based on the extracted waveform distortion characteristics and dynamically adjust the output impedance of the low-frequency pulse signal. If the dynamic output impedance adjustment cannot synchronize the output impedance of the injected low-frequency pulse signal with the impedance change trend of the cable, it is marked as an impedance mismatch point; The fault diagnosis module is used to inject detection signals of different frequency bands at the impedance mismatch point, collect the attenuation rate of the signal in each frequency band, calculate the attenuation difference of the impedance mismatch point in different frequency bands, and determine the position with the largest attenuation difference change as the final fault point.

Images