A cable fault locating method and system for a weak current system

Abstract

This invention discloses a method and system for locating cable faults in low-voltage systems, belonging to the field of low-voltage system fault detection technology. The method includes: applying multiple sets of coded electrical signals of different frequencies to the low-voltage cable under test, and simultaneously acquiring the response voltage sequences at the ends and beginnings of each cable; constructing a distortion correlation matrix reflecting the topology of the low-voltage system based on the transmission distortion sequences of all cables; performing eigenvalue decomposition on the distortion correlation matrix, extracting the principal feature vector, and determining the cable branch where the fault is located based on the position index of each element in the principal feature vector; calculating the time difference between the occurrence time of the first overshoot peak in the transmission distortion sequence of the fault branch and the excitation time, and combining this with the preset propagation speed of the electrical signal in that branch to obtain the precise distance to the fault point. This solution enables automatic identification of faulty branches and precise location of fault points in complex low-voltage topologies without the need for individual cable inspection.

Description

Technical Field

[0001] This invention relates to the field of fault detection technology for low-voltage systems, specifically to a method and system for locating cable faults in low-voltage systems. Background Technology

[0002] Low-voltage systems are widely used in building automation, security monitoring, fire alarms, and communication networks. Their cables are typically laid out in star, tree, or bus topologies, resulting in a large number of cables with concealed paths. When faults such as open circuits, short circuits, or insulation degradation occur, the system loses partial or complete functionality, making troubleshooting and repair time-consuming and labor-intensive. For locating these cable faults, manual segmented measurement has long been relied upon, using multimeters, time-domain reflectometers, or insulation resistance testers to disconnect sections of the line for tracing. This working method requires technicians to enter conduits, cable trays, or suspended ceilings to operate, testing each cable individually until the faulty branch and its specific location are found.

[0003] Time-domain reflectometers inject a single pulse into the cable and observe the reflected echo. However, in multi-branch low-voltage networks, each branch node generates reflections, resulting in multiple superimposed pulses in the echo waveform, making interpretation extremely difficult and unable to directly determine which branch the fault is located in. Frequency-domain reflectometry obtains frequency response data through frequency sweeping and then performs inverse Fourier transform to obtain time-domain information, but it is also plagued by the aliasing problem of multipath reflections. Some methods only collect single-end response data of the cable when applying the test signal. The obtained signal distortion characteristics are mixed with the cross-influence of multiple factors such as excitation source variation, line attenuation, and end impedance, making the waveform characteristics characterizing the fault location blurred, and the positioning accuracy sensitive to noise.

[0004] Regarding the core technical challenges, the reflected signals from multi-branch cables in complex topologies are superimposed on each other, requiring a discrimination mechanism that can automatically identify the branch where the fault is located from the system-level response. Another challenge is that fault information in data acquired by single-end or asynchronous acquisition is submerged in the combined effects of overall system attenuation and load changes, lacking a signal characterization method that can isolate the distortion components caused by the abnormal transmission path and highlight the morphological changes of the injected signal itself. Summary of the Invention

[0005] The purpose of this invention is to provide a cable fault location method and system for low-voltage systems, so that in low-voltage networks with multi-branch topology, the faulty cable branch can be directly identified without manual inspection of each cable, and the component reflecting only the abnormal transmission path can be extracted from the response signal to calculate the precise distance of the fault point.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a cable fault location method for low-voltage systems, comprising: Multiple sets of coded electrical signals of different frequencies are applied to the low-voltage cables under test, and the response voltage sequences at the beginning and end of each cable are collected simultaneously. The response voltage sequences at the beginning and end of each cable are then differentially analyzed point-by-point to generate a transmission distortion sequence for each cable. Based on the transmission distortion sequences of all cables, a distortion correlation matrix reflecting the topology of the low-voltage system is constructed. The distortion correlation matrix is ​​then subjected to eigenvalue decomposition to extract the principal feature vector, and the cable branch where the fault is located is determined based on the position index of each element in the principal feature vector. Based on the transmission distortion sequence corresponding to the faulty cable branch, the time difference between the occurrence time of the first overshoot peak in the transmission distortion sequence and the application time of the excitation signal is calculated. This time difference is multiplied by the preset propagation speed of the electrical signal in that branch cable to obtain the precise distance to the fault point.

[0007] As a technical solution of this invention, when multiple sets of coded electrical signals of different frequencies are applied to the low-voltage cable under test, a signal generator sequentially generates multiple single-frequency sine wave signals. Each single-frequency sine wave signal has the same duration and its frequency is arranged in an arithmetic progression. All single-frequency sine wave signals are sequentially combined into a complete coded electrical signal sequence. This coded electrical signal sequence is then amplified and simultaneously injected into the beginning and end of all cables under test in the low-voltage system. A voltage sampler is placed at both the beginning and end of each cable. All voltage samplers are triggered by the same clock source and collect voltage values ​​at a fixed sampling rate during the duration of each single-frequency sine wave signal, forming the beginning-end response voltage sequence and the end-end response voltage sequence for each cable. Preferably, a zero-level guard interval is inserted between two adjacent single-frequency sine wave signals. The duration of the guard interval is at least one sampling period to avoid crosstalk between signals affecting the independence of each frequency response. Therefore, multi-frequency coded excitation can fully stimulate the cable's response to different fault characteristics, providing rich frequency domain information for subsequent analysis and enhancing the detection capability of various cable faults in the low-voltage system.

[0008] Preferably, when generating the transmission distortion sequence for each low-voltage cable, for each low-voltage cable, the voltage value in the first-end response voltage sequence acquired at the same sampling time is subtracted from the voltage value in the last-end response voltage sequence to obtain the difference value at that sampling time. All difference values ​​are arranged in chronological order to form an initial difference sequence. Each difference value in the initial difference sequence is divided by the corresponding voltage value in the first-end response voltage sequence of the cable to obtain a normalized difference value. All normalized difference values ​​are arranged in chronological order to generate the transmission distortion sequence for that low-voltage cable. The normalized transmission distortion sequence eliminates common interference, signal amplitude fluctuations, and system deviations, making the transmission distortion characteristics caused by faults more prominent, which helps improve the sensitivity of fault identification.

[0009] When constructing the distortion correlation matrix, the topology of the low-voltage system is obtained, with each cable branch treated as a node and the connection points between cable branches as edges. For each node, its corresponding transmission distortion sequence is subjected to a Fourier transform to obtain a frequency domain distortion vector. The cosine similarity between the frequency domain distortion vectors of every two nodes is calculated, and the calculated cosine similarity is used as the matrix element value at the corresponding row and column position in the distortion correlation matrix, where the number of rows and columns of the distortion correlation matrix is ​​equal to the total number of nodes. Preferably, before calculating the cosine similarity, the amplitude of the frequency domain distortion vector of each node is normalized so that the magnitude of each vector is 1, thereby eliminating interference caused by signal energy differences and focusing only on the morphological similarity of the distorted waveforms. The distortion correlation matrix constructed through the similarity of frequency domain distortion features can effectively characterize the transmission distortion correlation between various cable branches of the low-voltage system caused by faults, providing a reliable data foundation for determining faulty branches using spectral analysis methods.

[0010] When performing eigenvalue decomposition on the distorted correlation matrix, a power-law iterative decomposition is performed to extract the eigenvector corresponding to the largest eigenvalue as the principal eigenvector. The element with the largest value in the principal eigenvector is found, and its position index in the vector is determined as the principal fault node index. The cable branch corresponding to the principal fault node index is determined as the cable branch where the fault occurs. Since the distortion characteristics of the fault branch are the main contributing components in the correlation matrix, the branch most significantly affected by the fault can be quickly and accurately located by extracting the principal eigenvector, avoiding the computational overhead of comparing each branch one by one.

[0011] When calculating the occurrence time of the first overshoot peak, a first-order differential operation is performed on the transmission distortion sequence corresponding to the cable branch where the fault is located to obtain a differential distortion sequence. Zeros whose signs change from positive to negative are sequentially searched in the differential distortion sequence, and the sampling time corresponding to the first zero that satisfies this condition is recorded as a candidate peak time. The voltage value of the candidate peak time is extracted from the transmission distortion sequence. If this voltage value exceeds twice the average of all voltage values ​​in the transmission distortion sequence, the candidate peak time is determined as the occurrence time of the first overshoot peak; otherwise, the next zero whose sign changes from positive to negative is searched, and this step is repeated. The number of sampling intervals between the occurrence time of the first overshoot peak and the application time of the excitation signal is calculated, and the number of sampling intervals is multiplied by the sampling period to obtain the time difference. Preferably, when searching for zeros whose signs change from positive to negative in the differential distortion sequence, if a change from positive to negative is detected in three consecutive sampling points, only the zero corresponding to the middle sampling point is retained as a candidate peak time, thereby eliminating misjudgments caused by multiple zero crossings. Through the overshoot peak identification and confirmation mechanism, the start time of the reflected wave at the fault point can be accurately extracted, providing a robust time reference for accurate distance calculation.

[0012] Before calculating the precise distance to the fault location, the process includes: obtaining the cable model of the cable branch where the fault is located; retrieving the nominal wave velocity of the cable from a pre-stored cable parameter library based on the cable model; obtaining the ambient temperature value of the cable branch; and linearly correcting the nominal wave velocity based on the ambient temperature value to obtain the actual propagation speed. The correction factor is one-thousandth of the wave velocity change per degree Celsius of temperature change. Calculating the fault distance using the temperature-corrected wave velocity effectively compensates for the influence of ambient temperature on signal propagation speed, improving ranging accuracy. Furthermore, the precise distance to the fault location is compared with the total length of the cable branch where the fault is located. If the precise distance to the fault location is less than the total length, the fault type is determined to be a single-point open circuit fault, and the precise distance to the fault location is used as the final location output. If the precise distance to the fault location is equal to the total length, the fault type is determined to be an end-of-circuit fault, and the total length is used as the final location output. By comparing the fault distance with the total branch length, not only can the precise location of the fault be given, but also the two typical fault types of single-point open circuit and end-of-circuit open circuit can be automatically distinguished, providing maintenance personnel with more specific diagnostic information.

[0013] As a further preferred solution, after outputting the final location result, based on the topology identifier of the cable branch where the fault is located, the physical routing diagram of that branch is retrieved from the design drawing database of the low-voltage system. The precise distance from the beginning of the branch to the fault point is marked on the physical routing diagram in coordinate form, generating a routing diagram with fault markings. The routing diagram and the fault type determination result are encapsulated into a fault report and sent to the monitoring terminal via the communication interface. To ensure reliable transmission of the fault report, the fault report is compressed before transmission. The compression method involves run-length encoding of consecutive identical pixels in the routing diagram and converting the fault type determination result into binary marker bytes. The compressed data is split into multiple data packets according to a preset communication protocol, each data packet containing a data sequence number and a checksum field. All data packets are sent sequentially through the communication interface, and after sending each data packet, the system waits for confirmation from the monitoring terminal. If no confirmation is received within a specified time, the data packet is retransmitted. In this way, after a fault occurs in the cable of the low-voltage system, a visual fault location diagram can be automatically generated and reliably delivered to the monitoring terminal through compression and confirmation retransmission mechanism, so that remote operation and maintenance personnel can intuitively grasp the fault location and significantly improve the efficiency of fault response and handling.

[0014] This invention also provides a cable fault location system for low-voltage systems, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of the cable fault location method for low-voltage systems described above. This system integrates functions such as encoded excitation, multi-channel synchronous acquisition, distortion correlation matrix construction, eigenvalue decomposition branch location, overshoot peak time extraction, and temperature-compensated ranging. It can automatically and accurately determine cable fault points in complex low-voltage system topologies and supports the visualization and reliable remote transmission of fault reports.

[0015] The technical effects and advantages provided by the present invention in the above technical solution are as follows: By synchronously acquiring response voltages at both ends of the low-voltage cable and performing point-by-point differential calculations, a transmission distortion sequence is generated. Under the same coded electrical signal excitation, the response difference between the beginning and end ends stems solely from the distortion experienced by the signal during propagation along the cable; the waveform changes of the injected signal itself are canceled out in the differential calculation. The resulting transmission distortion sequence eliminates the influence of excitation source fluctuations and end-load differences, retaining only information such as reflection and attenuation anomalies introduced by the fault point. Fault analysis based on this sequence avoids the problem of confusion between the excitation signal's own morphological changes and transmission path anomalies in traditional single-ended measurements, making the distortion characteristics caused by the fault clearer and more independent.

[0016] After frequency domain transformation of the transmission distortion sequences of all cables, the cosine similarity between nodes is calculated to construct a distortion correlation matrix, and the principal eigenvector is extracted through eigenvalue decomposition. Due to reflections and impedance discontinuities, the distribution pattern of the frequency domain distortion vector of a faulty branch deviates significantly from that of a normal branch. This deviation is manifested in the prominent values ​​of corresponding elements in the principal eigenvector. The faulty branch is directly located using the position index of the largest element in the principal eigenvector, without relying on pre-set thresholds or standard waveform libraries for matching, and unaffected by interference from reflected signals from other normal branches in the network. This technique enables automatic identification of the specific cable branch where the fault occurs in complex multi-branch interconnected topologies, eliminating the need for individual cable disconnection testing. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a flowchart of a cable fault location method for low-voltage systems; Figure 2This is a flowchart of the transmission distortion sequence generation process; Figure 3 This is a flowchart of the method for locating faulty cable branches in a low-voltage system; Figure 4 This is a schematic diagram of the main feature vector for locating cable faults in a low-voltage system. Figure 5 This is a schematic diagram of the transmission distortion sequence and its differential distortion sequence of a faulty cable. Figure 6 This is a diagram showing the physical routing of the fault location. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] See Figure 1 This invention provides a cable fault location method for low-voltage systems, comprising the following steps: applying multiple sets of coded electrical signals of different frequencies to the low-voltage cable under test, and simultaneously acquiring the response voltage sequences at the ends and beginnings of each low-voltage cable; performing point-by-point differential operations on the beginning-end response voltage sequence and the end response voltage sequence corresponding to each low-voltage cable to generate a transmission distortion sequence for each low-voltage cable; constructing a distortion correlation matrix reflecting the topology of the low-voltage system based on the transmission distortion sequences of all low-voltage cables; performing eigenvalue decomposition on the distortion correlation matrix, extracting the principal feature vector, and determining the cable branch where the fault is located based on the position index of each element in the principal feature vector; calculating the time difference between the occurrence time of the first overshoot peak in the transmission distortion sequence and the application time of the excitation signal based on the transmission distortion sequence corresponding to the cable branch where the fault is located, and multiplying the time difference by the preset propagation speed of the electrical signal in the cable branch to obtain the precise distance of the fault point.

[0021] Example 1: In practice, a signal generator sequentially generates multiple single-frequency sine wave signals. Each single-frequency sine wave signal has the same duration, and the frequencies of all single-frequency sine wave signals are arranged in an arithmetic progression. Let the total number of single-frequency sine wave signals be... , No. The frequency of a single-frequency sine wave signal Determined by the following formula:

[0022] in, This indicates the starting frequency of the first single-frequency sine wave signal. This represents the frequency step size between two adjacent single-frequency sine wave signals. This is the sequence number of the single-frequency sine wave signal. Pick Starting frequency Set as the lower limit frequency of the operating frequency band for low-voltage cables, frequency step size The bandwidth of the low-voltage cable operating frequency band divided by the total number of single-frequency sine wave signals. This ensures that the frequencies of all single-frequency sine wave signals cover the entire operating frequency band of the low-voltage cable. The duration of each single-frequency sine wave signal is denoted as . , The value is determined based on the settling time required for the response at the end of the low-voltage cable to reach a steady state, ensuring that the voltage sampler can acquire sufficient stable waveform data during the duration of each single-frequency sine wave signal.

[0023] Signal generators according to serial number from Increment to The output frequencies are in the following order: A single-frequency sine wave signal, each single-frequency sine wave signal lasts... Duration. Between two adjacent single-frequency sine wave signals, the signal generator outputs a zero-level signal, forming a zero-level guard interval. The duration of the zero-level guard interval is set to be equal to one sampling period, denoted as . Sampling period A fixed sampling rate shared by all voltage samplers The reciprocal of.

[0024] All sequentially generated single-frequency sinusoidal signals and zero-level guard intervals are concatenated in time sequence to form a complete coded electrical signal sequence. This coded signal sequence is input to a power amplifier, whose gain is set according to the required excitation voltage amplitude of the low-voltage cable, ensuring that the voltage amplitude of the coded signal sequence output by the power amplifier reaches the preset value. After power amplification, the coded signal sequence is simultaneously injected between the starting conductors of all cables under test and the reference ground in the low-voltage system through a signal distribution network.

[0025] A first voltage sampler is placed at the beginning of each cable under test, and a second voltage sampler is placed at the end of each cable under test. All first and second voltage samplers are triggered by a clock signal provided by the same clock source. The clock source generates a frequency of... A square wave clock is distributed to each voltage sampler via a transmission line of equal length, ensuring strict synchronization of the sampling times of all voltage samplers. Fixed sampling rate. The set value is the highest frequency in the encoded electrical signal sequence. 20 times, of which equal to the The frequency of a single-frequency sine wave signal .

[0026] Each voltage sampler operates at a fixed sampling rate during the duration of each single-frequency sine wave signal. Analog-to-digital conversion is performed to acquire instantaneous voltage values, which are then converted into digital values ​​for storage. For any cable under test, the first voltage sampler at the cable's head end acquires all digital voltage values ​​during the entire duration of the coded electrical signal sequence, arranged in chronological order of sampling time, forming the head end response voltage sequence of the cable under test. Similarly, the second voltage sampler at the cable's tail end acquires all digital voltage values ​​during the entire duration of the coded electrical signal sequence, arranged in chronological order of sampling time, forming the tail end response voltage sequence of the cable under test. This acquisition and arrangement process is performed on all cables under test in the low-voltage system to obtain the head end response voltage sequence and tail end response voltage sequence for each cable under test.

[0027] Example 2: In specific implementation, please refer to Figure 2 For each low-voltage cable under test, the following processing is performed to generate the transmission distortion sequence of the low-voltage cable under test.

[0028] Obtain the head-end and tail-end response voltage sequences of the low-voltage cable under test. Both sequences contain the same number of sampled voltage values; let the total number of sampled voltage values ​​be denoted as . , Equal to fixed sampling rate The total number of sampling points is obtained by multiplying the total duration of the encoded electrical signal sequence. Based on the sampling time sequence, the first sampling point in the first-end response voltage sequence is... The voltage value at each sampling time is denoted as The first voltage in the terminal response voltage sequence The voltage value at each sampling time is denoted as ,in For sampling sequence number, Pick .

[0029] For each sampling number The first-end response voltage value at the same sampling time With end response voltage value Perform a subtraction operation to obtain the difference value at that sampling time. The calculation method is According to sampling sequence number from to The order will be all Each difference value Arrange them to form the initial difference sequence.

[0030] For each difference value in the initial difference sequence ,use Divide by the first-end response voltage value with the same sampling number as the difference value. The normalized difference value is obtained. Normalized difference Determined by the following formula:

[0031] in, Indicates the th in the transmission distortion sequence The value at each sampling location Indicates the first-end response voltage sequence Each sampled voltage value, Indicates the first voltage in the terminal response voltage sequence Each sampled voltage value, For sampling sequence number, Pick .

[0032] when When the voltage value is zero, the normalized difference value Set it directly to zero. (This will change the entire list.) Normalized difference values According to sampling sequence number from to The sequence formed by arranging the data in chronological order is the transmission distortion sequence of the low-voltage cable under test. This process is repeated for each low-voltage cable under test in the low-voltage system to obtain the transmission distortion sequence corresponding to each cable.

[0033] Example 3: In specific implementation, please refer to Figure 3 Obtain the topology diagram of the low-voltage system. The topology diagram is stored in a graph data structure. Each node in the graph data structure represents a cable branch, and the node identifier uses the topology identifier of the cable branch in the low-voltage system design drawings. Each edge in the graph data structure represents a connection point between two cable branches; the cable branches corresponding to the two nodes connected by an edge are physically directly connected. The total number of nodes in the topology diagram is denoted as... All nodes are numbered sequentially as follows .

[0034] For the number is For the cable branch corresponding to the node, obtain the transmission distortion sequence of that cable branch, where Pick Perform a Discrete Fourier Transform on the distorted transmission sequence, with the number of transform points set to the length of the distorted transmission sequence. The discrete Fourier transform yields a value of length [missing value]. A complex sequence, where each complex number represents the amplitude and phase of the transmission distortion sequence of that cable branch at the corresponding frequency point. Take the first... The complex components constitute the frequency domain distortion vector, denoted as . . The setting value satisfies positive integers, The specific values ​​are determined based on the frequency resolution corresponding to the operating frequency band of the low-voltage cable, so that the frequency domain distortion vector... The frequency range it covers covers the frequencies of all single-frequency sine wave signals in the encoded electrical signal sequence.

[0035] For the frequency domain distortion vector corresponding to each node Amplitude normalization is performed. This is done by calculating the frequency domain distortion vector. Length of the module , module length Frequency domain distortion vector The arithmetic square root of the sum of the squares of the magnitudes of all complex components. The frequency domain distortion vector. Divide each complex component in by its modulus This yields the normalized frequency domain distortion vector, whose magnitude is... When the modulus is long When the value is zero, the normalized frequency domain distortion vector is directly taken as the zero vector.

[0036] For any two nodes, their numbers are denoted as follows: and The corresponding normalized frequency domain distortion vectors are denoted as follows: and Calculate the normalized frequency domain distortion vector. With the normalized frequency domain distortion vector Cosine similarity between cosine similarity Determined by the following formula:

[0037] in, Indicates the number is The nodes and their numbers are The cosine similarity between nodes. Indicates the number is The normalized frequency domain distortion vector corresponding to the node. Indicates the number is The conjugate transpose of the normalized frequency domain distortion vector corresponding to the node. This represents the vector dot product operation. Represents the normalized frequency domain distortion vector The length of the mold, Represents the normalized frequency domain distortion vector The magnitude of the normalized frequency domain distortion vector is... cosine similarity The actual calculation is equivalent to and The inner product of.

[0038] The calculated cosine similarity As the first in the distorted correlation matrix Line number The matrix element values ​​of the column. For all numbered combinations... Calculate the cosine similarity and fill in the matrix elements, where Pick , Pick The result after filling all matrix elements. OK The column matrix is ​​the distorted incidence matrix, and the distorted incidence matrix is ​​the first column matrix. Line number Column element corresponding node number With node number Similarity metric between them.

[0039] Perform power-law iterative decomposition on the distorted incidence matrix. The power-law iterative decomposition process is as follows: initialize a matrix of length... random nonzero vector Each component of the vector takes an interval A random real number within the range. In the... In the next iteration, the distorted correlation matrix is ​​multiplied by the vector. Obtain vector Then the vector Normalize each component by dividing it by its maximum magnitude to obtain the vector. .vector Proceed to the next iteration. When the vector with vector The iteration terminates when the Euclidean distance is less than a preset convergence threshold. The vector at the time of iteration termination... This refers to the extracted main feature vector. The preset convergence threshold is set to... This setting is determined based on the precision of floating-point arithmetic and the size of the matrix, ensuring that the exponentiation iteration reaches a stable state within a finite number of iterations.

[0040] In the principal feature vector, each component is examined one by one to find the component with the largest value. The index of the position of this component with the largest value in the principal feature vector is determined as the index of the principal fault node, and the position index is taken as the ordinal number of the component in the vector. , The range of values ​​is Index the primary fault node. The corresponding cable branch, i.e., the one numbered in the topology connection diagram. The cable branch represented by the node is identified as the cable branch where the fault occurs.

[0041] See Figure 4 The horizontal axis in the figure represents the index of the node in the low-voltage system topology connection diagram. The value ranges from 0 to 600, and the vertical axis represents the component value of the corresponding node in the principal feature vector. The curve represents the change curve of the principal feature vector component values ​​extracted by power iterative decomposition of the distorted correlation matrix. The overall curve shows a low amplitude fluctuation trend, and most of the principal feature vector component values ​​are concentrated in the range close to zero, indicating that, except for a few nodes, the similarity features of other nodes are low.

[0042] At node index approximately 300, a significant peak suddenly appears in the principal feature vector component value, with an amplitude close to 1, much higher than the amplitudes of other node component values, clearly distinguishing it from background noise. The node identifier corresponding to this peak is the index of the principal fault node. This indicates the branch of the cable where the fault is located.

[0043] This figure reflects the results obtained in Example 3 by constructing a distortion correlation matrix through frequency domain distortion vector normalization and cosine similarity calculation, and then extracting the main feature vector using the power iteration method. The clear appearance of the peak indicates that the transmission distortion caused by the fault is prominent in the frequency domain feature set of the corresponding node, achieving accurate identification of the faulty node. This result provides accurate fault branch basis for fault location and distance measurement in subsequent examples.

[0044] Example 4: In practice, the transmission distortion sequence corresponding to the cable branch where the fault is located, as determined by the fault location process, is obtained. The transmission distortion sequence includes data arranged in chronological order of sampling time. The normalized difference value, denoted as the i-th... The normalized difference value corresponding to each sampling point is A first-order difference operation is performed on the transmission distortion sequence. Starting from the second sampling point, the normalized difference value of each subsequent sampling point is subtracted from the normalized difference value of the previous sampling point. The result is used as an element of the differential distortion sequence. The length of the differential distortion sequence is... , record the The difference is ,in Pick .

[0045] In the differential distortion sequence, sequentially search for the zero points where the sign changes from positive to negative. The search method involves checking the signs of two adjacent difference values ​​sequentially; if the sign of the zero point changes from positive to negative... Each difference value The sign of is positive and the first Each difference value If the sign of the difference is negative, the time between the sampling positions corresponding to the two difference values ​​is considered a zero point where the sign changes from positive to negative, and the sampling time corresponding to the zero point is recorded as the candidate peak time. During the pairwise checking process, if a zero point where the sign changes from positive to negative is detected in the interval of three consecutive sampling points, then the sampling point is considered a candidate peak time. , , If all adjacent difference pairs satisfy the condition of the first being positive and the second being negative, then only the sampling point in the middle position will be included. The corresponding zero point is retained as a candidate peak time, while the other two zero points are discarded. In this way, moving from the beginning of the differential distortion sequence to the end, the sampling time of the first zero point encountered after merging and retention is recorded as the current candidate peak time.

[0046] Extract the normalized difference value corresponding to the current candidate peak time from the transmission distortion sequence. Calculate all of the transmitted distortion sequences. The arithmetic mean of the normalized differences is the sum of all normalized differences divided by 1. Get the mean .like Greater than If so, the current candidate peak time is determined as the time when the first overshoot peak occurs. Not greater than If the current candidate peak time is not found, the search continues from the zero point position in the differential distortion sequence to find the next zero point where the sign changes from positive to negative, obtains a new candidate peak time, and repeats the comparison and judgment steps described in this paragraph until the occurrence time of the first overshoot peak is determined.

[0047] The excitation signal application time is determined by the start time of the coded electrical signal sequence being amplified and simultaneously injected into the heads of all cables under test in the low-voltage system, corresponding to the sampling sequence number. Calculate the sampling number and sampling sequence number corresponding to the occurrence time of the first overshoot peak. The number of sampling intervals between them, denoted as . Number of sampling intervals Multiply by the sampling period To obtain the time difference .

[0048] Obtain the cable type of the cable branch where the fault occurs. The cable type is extracted from the cable list in the low-voltage system design drawings or from the on-site cable identification. Based on the cable type, retrieve a matching record from a pre-stored cable parameter database. The cable parameter database is stored in a relational table format, with each record containing a cable type field and a nominal wave velocity field. Read the nominal wave velocity corresponding to the cable type and denote it as... .

[0049] Temperature sensors are installed at designated locations in the environment where the low-voltage system is located. These sensors are connected to the processing unit via an analog-to-digital converter interface to collect real-time ambient temperature values ​​around the cable branch where the fault occurs, denoted as [missing information]. Obtain the current ambient temperature value output by the temperature sensor. And obtain the nominal temperature of the cable model recorded in the parameter database. nominal temperature Nominal wave velocity The reference temperature for measurement.

[0050] The nominal wave velocity is linearly corrected based on the ambient temperature value, and the correction factor is set to a value of [value missing]. The correction factor per degree Celsius is set based on the publicly available parameters of the temperature coefficient of the dielectric constant of commonly used insulating materials for low-voltage cables. Within the normal temperature range, the relative change rate of wave velocity is approximately one-thousandth per degree Celsius. The linear correction process calculates the actual propagation speed as follows: If the ambient temperature value With nominal temperature If they are different, then the relative change in velocity is , If the ambient temperature value equal to nominal temperature ,but .

[0051] time difference The actual propagation speed of the electrical signal in the branch cable where the fault is located Multiply to obtain the precise distance to the fault point. Determined by the following formula:

[0052] in, This indicates the precise distance from the fault point to the beginning of the cable branch, in meters. This represents the time difference between the occurrence of the first overshoot peak and the application of the excitation signal, expressed in seconds. This indicates the actual propagation speed of the electrical signal in the cable branch after temperature correction, in meters per second.

[0053] See Figure 5 The horizontal axis in the figure represents the sampling sequence number. The value ranges from 0 to 600. The left vertical axis represents the normalized difference value of the transmission distortion sequence, and the right vertical axis represents the difference value of the differential distortion sequence. The solid curve represents the transmission distortion sequence corresponding to the cable branch where the fault is located, and the dashed curve represents the differential distortion sequence obtained after the transmission distortion sequence has undergone first-order differential operation.

[0054] As shown in the figure, within the sampling sequence number range of approximately 400 to 450, the transmission distortion sequence exhibits a significant overshoot peak. The normalized difference value rapidly rises to a peak of approximately 0.6 before quickly falling back to near zero, displaying a sharp peak shape. The sampling time corresponding to this peak is the time when the first overshoot peak occurs. The differential distortion sequence also exhibits significant sign changes and peak fluctuations in this range, reflecting the rapid changing trend of the normalized difference value in the transmission distortion sequence.

[0055] Before the peak occurs (sampling numbers 0 to 390), the normalized difference value of the transmission distortion sequence remains at a low level with small fluctuations. The differential distortion sequence fluctuates relatively smoothly, without any obvious zero-points where the sign changes from positive to negative. After the peak occurs (sampling numbers 450 to 600), the normalized difference value drops rapidly and tends to stabilize. The fluctuation amplitude of the differential distortion sequence decreases, exhibiting a state of spurious noise.

[0056] This figure fully illustrates the process in Example 4 of performing first-order differential calculations based on the transmission distortion sequence of the cable branch where the fault occurred to identify the first overshoot peak. By observing the peak value of the solid curve and its corresponding sampling number, combined with the sign change of the dashed curve, the moment when the first overshoot peak occurs can be accurately determined, thus providing a basis for subsequent calculation of the precise time difference of the fault point's distance. Provide evidence.

[0057] Example 5: In practice, the precise distance to the fault point obtained from the fault location process is acquired, and the total length of the cable branch where the fault occurs is retrieved from the low-voltage system's design drawing database. This database contains a cable branch attribute table, which records the correspondence between the topology identifier of each cable branch and its total length. The total length of the cable branch where the fault occurs is obtained by retrieving its topology identifier from the cable branch attribute table.

[0058] The precise distance to the fault point is compared with the total length of the cable branch where the fault occurs. If the precise distance to the fault point is less than the total length of the cable branch, the fault type is determined to be a single-point open circuit fault, and the precise distance to the fault point is used as the final location output. If the precise distance to the fault point is equal to the total length of the cable branch, the fault type is determined to be an end-of-circuit fault, and the total length of the cable branch is used as the final location output.

[0059] Based on the topology identifier of the cable branch where the fault occurs, the physical routing diagram corresponding to the cable branch where the fault occurs is retrieved from the design drawing database of the low-voltage system. The physical routing diagram is stored in vector graphic data format. The vector graphic data contains a series of ordered coordinate points that constitute the path of the cable branch where the fault occurs. Each coordinate point consists of an abscissa value and a ordinate value. The coordinate points are connected in sequence to form the physical route of the cable branch where the fault occurs.

[0060] Mark the fault location on the physical routing map. Starting from the coordinates of the first end of the cable branch where the fault occurs, accumulate the path length sequentially along the coordinates on the physical routing map. When the accumulated path length first reaches the value output by the final location, determine the coordinates corresponding to that location as the fault marker coordinates. Overlay a fault marker symbol on the physical routing map at the fault marker coordinates. The fault marker symbol uses a red cross shape, and add the numerical text of the final location output next to the fault marker symbol to generate a routing diagram with fault markers.

[0061] The fault report is encapsulated by the fault-marked routing diagram and the fault type determination result. The fault report consists of a header and a body. The header includes a report generation timestamp and the topology identifier of the cable branch where the fault occurred. The body includes the fault type determination result field, the final location output field, and the routing diagram image data field. The fault type determination result field takes the value of either the string "single-point open circuit fault" or the string "end-of-line open circuit fault".

[0062] The fault report is compressed. During compression, the routing diagram image data field is extracted from the fault report. This image data is converted to bitmap format. The bitmap image is scanned row by row, and the number of pixels with consecutive identical color values ​​in each row is counted. The number of pixels with consecutive identical color values ​​and their color values ​​are grouped into a run-length encoded tuple. All run-length encoded tuples are arranged sequentially to form the compressed image data. The fault type determination result is converted into binary marker bytes. When the fault type determination result is a single-point circuit breaker fault, the binary marker byte value is 0x01; when the fault type determination result is an end-point circuit breaker fault, the binary marker byte value is 0x02. The remaining fields of the fault report retain their original text format and are reassembled with the compressed image data and binary marker bytes to form the compressed fault report data block.

[0063] The compressed fault report data block is split into multiple data packets according to a preset communication protocol. The preset protocol specifies a maximum payload length of 1024 bytes for a single data packet. Each data packet consists of a header, payload, and checksum. The header contains a sequence number field and a total number field. The sequence number field is an unsigned integer, starting from 0 and incrementing sequentially. The total number field is filled with the total number of data packets transmitted. The payload field loads a fragment of the compressed fault report data block. The checksum field uses a 16-bit cyclic redundancy check algorithm to calculate the checksum value for all bytes in the header and payload.

[0064] All data packets are sent sequentially according to their sequence numbers via the communication interface. The communication interface uses an Ethernet physical layer interface, and the data packets are sent in TCP message format. After sending each data packet, a timer is started to wait for an acknowledgment, with a timer duration set to 500 milliseconds. If the communication interface receives an acknowledgment message from the monitoring terminal within 500 milliseconds, and the sequence number in the acknowledgment message matches the sequence number of the sent data packet, the timer is stopped and the next data packet is sent. If the timer times out and no acknowledgment message is received, the current data packet is retransmitted, and the retransmission counter is incremented by 1. If the retransmission counter value exceeds 3, the fault report sending process is terminated, and a communication failure event is logged.

[0065] See Figure 6In the graph, the horizontal axis represents the physical coordinate of the cable branch where the fault occurred, in meters; the vertical axis represents the physical coordinate, in meters. The curve depicts the physical route of the cable branch where the fault occurred as a continuous broken line. This route is formed by connecting a series of ordered coordinate points, reflecting the actual route and spatial layout of the cable. The curve exhibits a periodic fluctuation trend, extending horizontally from 0 meters to 50 meters, and vertically varying between approximately -0.6 meters and 0.6 meters, reflecting the undulation and curvature of the line in space.

[0066] The coordinates of the fault point are marked with an "×" symbol in the figure. This mark is located at approximately 33 meters on the horizontal axis and approximately -0.4 meters on the vertical axis, clearly indicating the specific location of the fault on the physical route. As described in Example 5, the marked location is determined by accumulating the path length sequentially along the physical route from the starting coordinates until the accumulated length reaches the precise distance to the fault point.

[0067] This diagram clearly shows the intuitive representation of fault location results on the physical routing map, assisting in the generation of routing diagram image data in the fault report and the spatial correspondence between the fault type determination results, which facilitates subsequent on-site maintenance and fault troubleshooting.

[0068] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for locating cable faults in low-voltage systems, characterized in that, Includes the following steps: Multiple single-frequency sine wave signals are generated sequentially by a signal generator. Each single-frequency sine wave signal has the same duration and its frequency is arranged in an arithmetic progression. All single-frequency sine wave signals are then combined into a complete coded electrical signal sequence. The encoded electrical signal sequence is amplified and simultaneously injected into the beginning of all cables under test in the low-voltage system, and the response voltage sequence at the beginning and end of each low-voltage cable is collected synchronously. Perform point-by-point differential operation on the head response voltage sequence and the tail response voltage sequence corresponding to each low-voltage cable to generate the transmission distortion sequence of each low-voltage cable. Based on the transmission distortion sequences of all low-voltage cables, a distortion correlation matrix reflecting the topology of the low-voltage system is constructed, including: Obtain the topology diagram of the low-voltage system, treating each cable branch as a node and the connection points between cable branches as edges; For each node, perform a Fourier transform on its corresponding transmission distortion sequence to obtain the frequency domain distortion vector; Calculate the cosine similarity between the frequency domain distortion vectors of every two nodes, and use the calculated cosine similarity as the matrix element value at the corresponding row and column position in the distortion correlation matrix, where the number of rows and columns of the distortion correlation matrix are equal to the total number of nodes. Perform power-law iterative decomposition on the distorted correlation matrix and extract the eigenvector corresponding to the largest eigenvalue as the principal eigenvector; Find the element with the largest value in the main feature vector, and determine the index of the position of this element in the vector as the index of the main fault node; The cable branch corresponding to the main fault node index is identified as the cable branch where the fault occurs. Perform a first-order difference operation on the transmission distortion sequence corresponding to the cable branch where the fault is located to obtain the differential distortion sequence; In the differential distortion sequence, find the zeros whose signs change from positive to negative in turn, and record the sampling time corresponding to the first zero that meets the condition as the candidate peak time. Extract the voltage value at the candidate peak moment in the transmission distortion sequence. If the voltage value exceeds twice the average of all voltage values ​​in the transmission distortion sequence, then the candidate peak moment is determined as the moment when the first overshoot peak occurs. Otherwise, continue to search for the next zero point where the sign changes from positive to negative and repeat this step. Calculate the number of sampling intervals between the occurrence of the first overshoot peak and the application of the excitation signal. Multiply the number of sampling intervals by the sampling period to obtain the time difference. Multiply this time difference by the preset propagation speed of the electrical signal in the branch cable to obtain the precise distance of the fault point.

2. The cable fault location method for low-voltage systems according to claim 1, characterized in that, The step of synchronously acquiring the response voltage sequence at the end and beginning of each low-voltage cable further includes: A voltage sampler is placed at the beginning and end of each cable. All voltage samplers are triggered by the same clock source and collect voltage values ​​at a fixed sampling rate during the duration of each single-frequency sine wave signal, forming the beginning response voltage sequence and the end response voltage sequence of each cable respectively.

3. The cable fault location method for low-voltage systems according to claim 2, characterized in that, When combining all single-frequency sine wave signals into a complete coded electrical signal sequence, a zero-level guard interval is inserted between two adjacent single-frequency sine wave signals, and the duration of the guard interval is at least one sampling period.

4. The cable fault location method for low-voltage systems according to claim 3, characterized in that, The step of performing point-by-point differential operations on the head-end response voltage sequence and the tail-end response voltage sequence corresponding to each low-voltage cable to generate the transmission distortion sequence of each low-voltage cable further includes: For each low-voltage cable, the voltage value in the first-end response voltage sequence obtained at the same sampling time is subtracted from the voltage value in the last-end response voltage sequence to obtain the difference value at that sampling time. Arrange all difference values ​​in the order of sampling time to form the initial difference sequence; Divide each differential value in the initial differential sequence by the corresponding voltage value in the response voltage sequence at the cable head end to obtain the normalized differential value. Arrange all the normalized differential values ​​in chronological order to generate the transmission distortion sequence of the low-voltage cable.

5. A cable fault location method for low-voltage systems according to claim 4, characterized in that, Before calculating the cosine similarity between the frequency domain distortion vectors of every two nodes, the amplitude of the frequency domain distortion vector of each node is normalized so that the magnitude of each vector is 1.

6. A cable fault location method for low-voltage systems according to claim 5, characterized in that, When searching for zeros in the differential distortion sequence where the sign changes from positive to negative, if the sign changes from positive to negative in three consecutive sampling points, only the zero corresponding to the middle sampling point is retained as the candidate peak time.

7. A cable fault location system for low-voltage systems, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the cable fault location method for low-voltage systems as described in any one of claims 1 to 6.

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