Defect locating method and device of power cable, terminal and storage medium

Abstract

The application provides a defect positioning method and device of a power cable, a terminal and a storage medium. The method comprises the following steps: measuring the head-end impedance spectrum of the to-be-measured cable, and calculating the head-end reflection coefficient of the to-be-measured cable according to the head-end impedance spectrum; taking a Gaussian signal as an incident signal for measuring the to-be-measured cable, and calculating the target frequency domain signal of the reflection signal according to the incident signal and the head-end reflection coefficient; performing inverse fast Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflection signal; and calculating the reflection peak barycenter position of the target time domain signal according to the target time domain signal, wherein the reflection peak barycenter position is the defect position of the to-be-measured cable. The application can improve the accuracy of local defect identification and more accurately obtain the positioning of the cable defect.

Description

Technical Field

[0001] This invention relates to the field of cable defect location technology, and in particular to a method, device, terminal and storage medium for locating defects in power cables. Background Technology

[0002] The power industry is a crucial foundational energy sector for national economic development. Due to the advantages of power cables—small footprint, reliable power supply, and simple operation and maintenance—their application in power transmission is becoming increasingly widespread, and cable lines have become the main arteries of urban power transmission. Currently, my country experiences over ten thousand cable defects and faults annually. Sudden faults or operation with defects can easily lead to large-scale power outages, fires, and other serious accidents, with power restoration times generally exceeding 24 hours or even longer, posing a significant challenge to the high reliability requirements of urban power grids. Furthermore, cables in actual operation are affected by multiple environmental factors such as heat and mechanical forces, which may induce permanent faults due to localized latent defects such as insulation deterioration or damage. Once a cable fault occurs, it can lead to the shutdown or even loss of control of large electrical systems, causing severe economic losses and social impact.

[0003] Existing methods for locating local defects in power cable insulation typically involve directly performing an inverse Fourier transform on the real or imaginary part of the impedance spectrum to pinpoint the defect. However, this method ignores the impedance mismatch between the instrument and the cable, which exacerbates the reflection phenomenon at the beginning of the cable, thereby reducing the accuracy and resolution of the local defect location and resulting in significant errors in the local defect location results. Summary of the Invention

[0004] This invention provides a method, apparatus, terminal, and storage medium for locating defects in power cables, in order to solve the problem of inaccurate local defect location in power cables in the prior art.

[0005] In a first aspect, embodiments of the present invention provide a method for locating defects in power cables, comprising:

[0006] The impedance spectrum at the beginning of the cable under test is measured, and the reflection coefficient at the beginning of the cable under test is calculated from the impedance spectrum at the beginning.

[0007] A Gaussian signal is used as the incident signal for measuring the cable under test. The target frequency domain signal of the reflected signal is calculated based on the incident signal and the reflection coefficient at the beginning of the cable.

[0008] Perform an inverse fast Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflected signal;

[0009] Based on the target time-domain signal, the centroid position of the reflection peak of the target time-domain signal is calculated, and the centroid position of the reflection peak is the defect location of the cable under test.

[0010] In one possible implementation, the head-end reflection coefficient of the cable under test is obtained by calculating the head-end impedance spectrum, including:

[0011] The first-end reflection coefficient of the cable under test is obtained by performing impedance transformation on the first-end impedance spectrum.

[0012] The formula for impedance transformation is as follows:

[0013] Where Γ V (0) represents the reflection coefficient at the beginning of the cable under test, Z(0) represents the impedance at the beginning of the cable under test, Z i ε represents the surge impedance of the cable under test, ε0 represents the vacuum permittivity, and ε r The relative permittivity of the cable under test is represented by μ0, and the permeability in vacuum is represented by r. s r represents the outer diameter of the copper shielding layer of the cable under test. c This indicates the outer diameter of the cable core to be tested.

[0014] In one possible implementation, calculating the target frequency domain signal of the reflected signal based on the incident signal and the head-end reflection coefficient includes:

[0015] The incident signal is subjected to a fast Fourier transform to obtain a first frequency domain signal;

[0016] The first-end reflection coefficient is subjected to negative frequency domain conjugate extension processing to obtain the processed first-end reflection coefficient.

[0017] The first frequency domain signal is multiplied by the processed first-end reflection coefficient to obtain the target frequency domain signal of the reflected signal.

[0018] In one possible implementation, performing a fast Fourier transform on the incident signal to obtain a first frequency domain signal includes:

[0019] according to The first frequency domain signal is obtained;

[0020] Among them, S i (ω) represents the first frequency domain signal, S i (t) represents the incident signal, FFT[.] represents the Fast Fourier Transform function, b represents the time delay constant of the incident signal, c represents the pulse width constant of the incident signal, and t represents time.

[0021] In one possible implementation, calculating the centroid position of the reflection peak of the target time-domain signal based on the target time-domain signal includes:

[0022] Based on the target time-domain signal, determine the abscissa value of the centroid of the reflection peak in the target time-domain signal;

[0023] The position of the centroid of the reflection peak is obtained based on the abscissa of the centroid of the reflection peak and the propagation speed of the electromagnetic wave in the cable under test.

[0024] In one possible implementation, determining the abscissa value of the centroid of the reflection peak in the target time-domain signal based on the target time-domain signal includes:

[0025] according to Determine the abscissa value of the centroid of the reflection peak;

[0026] Where z' represents the x-coordinate of the centroid of the reflection peak, x i S represents the x-coordinate value of each point in the reflection peak. r (x i ) represents the amplitude coordinate value of each point in the reflection peak, m represents the number of points in the reflection peak, and i represents a constant.

[0027] In one possible implementation, the location of the centroid of the reflection peak of the target time-domain signal is obtained based on the abscissa value of the centroid of the reflection peak and the propagation speed of the electromagnetic wave in the cable under test, including:

[0028] The position of the centroid of the reflection peak is obtained by multiplying the abscissa of the centroid of the reflection peak by the propagation speed of the electromagnetic wave in the cable under test.

[0029] Secondly, embodiments of the present invention provide a defect location device for power cables, comprising:

[0030] The measurement and calculation module is used to measure the impedance spectrum at the beginning of the cable under test and calculate the reflection coefficient at the beginning of the cable under test based on the impedance spectrum.

[0031] The calculation module is used to use a Gaussian signal as the incident signal for measuring the cable under test, and to calculate the target frequency domain signal of the reflected signal based on the incident signal and the reflection coefficient at the beginning.

[0032] The transformation module is used to perform a fast inverse Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflected signal;

[0033] The positioning module is used to calculate the centroid position of the reflection peak of the target time domain signal based on the target time domain signal, wherein the centroid position of the reflection peak is the defect location of the cable under test.

[0034] Thirdly, embodiments of the present invention provide a terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method described in the first aspect or any possible implementation thereof.

[0035] Fourthly, embodiments of the present invention provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the method described in the first aspect or any possible implementation thereof.

[0036] This invention provides a method, apparatus, terminal, and storage medium for locating defects in power cables. The method involves measuring the impedance spectrum of the cable under test at its initial end and calculating its initial reflection coefficient. A Gaussian signal is used as the incident signal for measuring the cable. Based on the incident signal and the initial reflection coefficient, a target frequency domain signal of the reflected signal is calculated. An inverse fast Fourier transform (IFFT) is performed on the target frequency domain signal to obtain a target time domain signal of the reflected signal. The centroid position of the reflection peak of the target time domain signal is calculated, and this centroid position is identified as the defect location of the cable under test. This invention uses an impedance transformation formula to calculate the initial reflection coefficient of the cable under test and obtains the frequency and time domain signals of the cable under test through simulated Gaussian signals, IFFT, and quasi-IFFT, thus suppressing initial reflection and spectral leakage. Furthermore, determining the defect location of the cable under test by using the centroid position of the reflection peak overcomes the problem of inaccurate local defect location in current technologies, improves the accuracy of local defect identification, and provides a more accurate location of cable defects. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart illustrating the implementation of a defect location method for power cables provided in an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the connection between the network analyzer and the cable under test provided in an embodiment of the present invention;

[0040] Figure 3 This is the Smith chart of the first-end impedance spectrum provided in the embodiment of the present invention;

[0041] Figure 4 This is a reflection coefficient spectrum diagram provided in an embodiment of the present invention;

[0042] Figure 5 This is a spectrum diagram of the first frequency domain signal provided in an embodiment of the present invention;

[0043] Figure 6 This is a time-domain diagram of the target time-domain signal of the reflected signal provided in an embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram of the structure of a defect location device for power cables provided in an embodiment of the present invention;

[0045] Figure 8 This is a schematic diagram of the terminal provided in an embodiment of the present invention. Detailed Implementation

[0046] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0048] The cable under test can be considered as a cascade of infinitely many transmission line elements with a length of Δz. Assuming that the distributed parameters at all points in the cable under test are equal, the impedance at each point in the cable under test can be obtained by establishing differential equations based on Kirchhoff's laws.

[0049] Optional, according to Obtain the impedance at each point in the cable under test;

[0050] Where z represents any point in the cable under test, Z(z) represents the impedance at each point in the cable under test, and Z... c Γ represents the characteristic impedance of the cable under test. V (z) represents the reflection coefficient at each point in the cable under test, Γ V (l1) represents the reflection coefficient at the load end of the cable under test, l1 represents the position of the load end of the cable under test, k represents the propagation constant of the cable under test, and j represents the imaginary unit.

[0051] Z c And k can be calculated from the distribution parameters;

[0052] Optional, according to To calculate Zc and k;

[0053] Where R represents the resistance per unit length of the cable under test, L represents the inductance per unit length of the cable under test, G represents the conductance per unit length of the cable under test, C represents the capacitance per unit length of the cable under test, ω1 represents the frequency of the incident wave, α represents the real part of the propagation constant, and β represents the imaginary part of the propagation constant.

[0054] When a local defect exists in the cable under test, the distribution parameters at the defect location will change. In this case, the impedance at the test end can be solved recursively, defining the test end and the load end of the cable under test, with the recursion proceeding from the load end to the test end.

[0055] The impedance expression for the test terminal is:

[0056] Where n represents any point in the cable under test from the load end to the test end, Z(n) represents the impedance at that point, and Γ V (n+1) represents the reflection coefficient after recursion at this point, Z c Z(n) represents the characteristic impedance at that point, and Z(n+1) represents the recursive impedance at that point.

[0057] The impedance expression at the test end shows that the impedance at each point in the cable under test (UTP) depends only on the distributed parameters of the cable. When a local defect exists in the UTP, the electromagnetic signal relationship at that point changes, resulting in a change in the distributed parameters. Therefore, when a local defect exists in the UTP and defect localization is required, impedance spectroscopy can be used to analyze the UTP.

[0058] Figure 1 The following is a detailed flowchart of a defect location method for power cables provided in an embodiment of the present invention:

[0059] Step 101: Measure the impedance spectrum at the beginning of the cable under test, and calculate the reflection coefficient at the beginning of the cable under test based on the impedance spectrum.

[0060] Optionally, the impedance spectrum at the beginning of the cable under test can be measured using the S11 mode of a network analyzer.

[0061] A network analyzer is a comprehensive microwave measurement instrument that can perform scanning measurements over a wide bandwidth to determine network parameters. In this embodiment, the test frequency of the network analyzer can be set to 100kHz to 100MHz, and the sampling interval can be set to 10kHz.

[0062] The S11 mode includes the S11 parameter, which represents the ratio of the reflected wave to the incident wave of the incident signal.

[0063] like Figure 2The diagram shows the connection between the network analyzer and the cable under test. One end of the cable under test is connected to the measurement port of the network analyzer via an alligator clip. The conductor of the cable under test is connected to the measurement port of the network analyzer via alligator clip 1, and the grounding shield of the cable under test is connected to the measurement port of the network analyzer via alligator clip 2. The other end of the cable under test is open.

[0064] like Figure 3 The Smith chart of the first-end impedance spectrum shown can be seen. Figure 3 In the middle, as the frequency increases, the circumference continues to expand, which indicates that the impedance spectrum at the beginning shows a trend of decaying oscillation.

[0065] In one possible implementation, the head-end reflection coefficient of the cable under test is obtained by calculating the head-end impedance spectrum, including:

[0066] The reflection coefficient at the beginning of the cable under test is obtained by performing impedance transformation on the impedance spectrum at the beginning.

[0067] The formula for impedance transformation is:

[0068] Where Γ V (0) represents the reflection coefficient at the beginning of the cable under test, Z(0) represents the impedance at the beginning of the cable under test, Z i ε represents the surge impedance of the cable under test, ε0 represents the vacuum permittivity, and ε r The relative permittivity of the cable under test is represented by μ0, and the permeability in vacuum is represented by r. s r represents the outer diameter of the copper shielding layer of the cable under test. c This indicates the outer diameter of the cable core to be tested.

[0069] The head-end reflection coefficient represents the ratio of the reflected wave to the incident wave at the test point, which is the transfer function of the cable system.

[0070] Optionally, the reflection coefficient at the beginning of the cable under test, calculated using impedance transformation, can reduce the reflection phenomenon at the beginning of the cable and improve the accuracy and resolution of positioning.

[0071] See Figure 4 The spectrum of the reflection coefficient is shown below. The horizontal axis represents the test frequency, and the vertical axis represents the amplitude of the reflection coefficient, in dB. Figure 4 It can be seen that as the test frequency increases, the amplitude of the reflection coefficient shows an increasing trend.

[0072] Step 102: Use a Gaussian signal as the incident signal for measuring the cable under test. Calculate the target frequency domain signal of the reflected signal based on the incident signal and the reflection coefficient at the beginning of the cable.

[0073] Optionally, using a Gaussian signal as the incident signal can effectively suppress reflections at the beginning of the cable under test and spectral leakage.

[0074] In one possible implementation, the target frequency domain signal of the reflected signal is calculated based on the incident signal and the head-end reflection coefficient, including:

[0075] Perform a fast Fourier transform on the incident signal to obtain the first frequency domain signal;

[0076] The Fast Fourier Transform (FFT) is a general term for efficient and fast computation methods that use computers to calculate the Discrete Fourier Transform, involving the conversion of signals from the time domain to the frequency domain.

[0077] Optional, according to The first frequency domain signal is obtained;

[0078] Among them, S i (ω) represents the first frequency domain signal, S i (t) represents the incident signal, FFT[.] represents the Fast Fourier Transform function, b represents the time delay constant of the incident signal, c represents the pulse width constant of the incident signal, and t represents time.

[0079] See Figure 5 The spectrum of the first frequency domain signal is shown, where the horizontal axis represents the frequency of the first frequency domain signal and the vertical axis represents the amplitude of the first frequency domain signal. Figure 5 It can be seen that the amplitude of the first frequency domain signal first increases and then decreases with the increase of frequency, and there is a maximum amplitude value around 0MHz.

[0080] Optionally, the value of b is not limited in this embodiment; for example, b can be 1 × 10⁻⁶. -6 1.5×10 -6 wait.

[0081] After the above calculations, the expression for the first frequency domain signal is obtained as follows:

[0082] Where ω represents the frequency of the first frequency domain signal, f s This represents the sampling frequency of the first frequency domain signal.

[0083] As can be seen from the expression of the first frequency domain signal, its amplitude-frequency characteristics are only related to the pulse width constant of the incident signal and are independent of the time delay constant of the incident signal. If c is too small, the first frequency domain signal will still have a large component at the upper frequency limit, causing spectral leakage during the time-frequency domain transformation. Conversely, if c is too large, the pulse width of the first frequency domain signal will be too large, affecting the positioning accuracy and resolution.

[0084] In one possible implementation, to prevent spectrum leakage, it can be based on Calculate the value of c.

[0085] Where, ω u This indicates the upper frequency limit of the signal in the first frequency domain.

[0086] In this embodiment, the test frequency of the network analyzer can be set to 100kHz to 100MHz, ω u The value can be 100MHz, therefore, c is 4.833 × 10⁻⁶. -9 .

[0087] The negative frequency domain conjugate extension of the first-end reflection coefficient is performed to obtain the processed first-end reflection coefficient.

[0088] After the incident signal undergoes a Fast Fourier Transform, the resulting first frequency domain signal is conjugate symmetric. If two numbers are conjugate, it means that the two numbers have the same amplitude but different phases.

[0089] Optionally, performing negative frequency domain conjugate extension processing on the front-end reflection coefficient may include:

[0090] S1: Periodically extend the reflection coefficient at the front end;

[0091] S2: Reverse the reflection coefficient at the front end;

[0092] S3: Take the principal value interval;

[0093] S4: Take the conjugate to obtain the first-end reflection coefficient after negative frequency domain conjugate extension processing.

[0094] Multiply the first frequency domain signal by the processed first-end reflection coefficient to obtain the target frequency domain signal of the reflected signal;

[0095] According to S r (ω)=S i (ω)Γ V (0) * Obtain the target frequency domain signal of the reflected signal;

[0096] Among them, S r (ω) represents the target frequency domain signal of the reflected signal, Γ V (0) * It represents the first-end reflection coefficient after conjugate extension in the negative frequency domain.

[0097] Step 103: Perform an inverse fast Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflected signal.

[0098] Optional, according to S r (t) = abs[IFFT(S r (ω))] yields the target time-domain signal of the reflected signal;

[0099] Among them, S r (t) represents the target time-domain signal of the reflected signal, IFFT[.] represents the inverse fast Fourier transform function, and abs[.] represents the absolute value function.

[0100] The inverse fast Fourier transform involves a conversion from the frequency domain to the time domain. The abs function returns the absolute value of a signal, which is unsigned.

[0101] See Figure 6 The diagram shows the time-domain plot of the target time-domain signal of the reflected signal. The horizontal axis represents the transmission time of the target time-domain signal in nanoseconds (ns), and the vertical axis represents the amplitude of the target time-domain signal. Figure 6 It can be observed that there are test blind zones at the beginning and end of the target time-domain signal, and multiple reflection peaks are generated as the frequency increases. The amplitude of the reflection peaks first increases and then decreases, and this trend continues until the test blind zone is reached. Among all the reflection peaks, there are two reflection peaks with larger amplitudes, indicating the location of local defects. Because the expression of the first frequency domain signal is negatively correlated with the pulse width constant of the incident signal, the target time-domain signal obtained by operating on the first frequency domain signal and then performing an inverse fast Fourier transform is positively correlated with the pulse width constant of the incident signal. Therefore, the length of the test blind zone is determined by the pulse width constant of the incident signal, and the pulse width constant of the incident signal is positively correlated with the length of the test blind zone.

[0102] Step 104: Calculate the centroid position of the reflection peak of the target time domain signal based on the target time domain signal. The centroid position of the reflection peak is the defect location of the cable under test.

[0103] The most common method for locating the centroid of the reflection peak is the peak method, which selects a single peak point or the center point of two peaks as the location basis. However, due to the large sampling interval of the measurement signal, there will be a large offset between the position of the test peak and the actual peak, so the peak method has a large error.

[0104] In one possible implementation, based on the target time-domain signal and Determining the abscissa value of the centroid of the reflection peak in the target time domain signal reduces the impact of a single measurement data point on the overall signal;

[0105] Where z' represents the x-coordinate of the centroid of the reflection peak, x i S represents the x-coordinate value of each point in the reflection peak. r (x i ) represents the amplitude coordinate value of each point in the reflection peak, m represents the number of points in the reflection peak, and i represents a constant.

[0106] The position of the centroid of the reflection peak is obtained by multiplying the x-coordinate of the centroid of the reflection peak by the propagation speed of the electromagnetic wave in the cable under test.

[0107] In one possible implementation, to analyze the positioning error of the present invention, this embodiment uses a YJLV-1×35-8.7 / 15kV XLPE cable as the cable under test, with a length of 20m. A local wear defect is introduced at a position 9.1m from the beginning of the cable. The network analyzer test frequency is set to 100kHz~100MHz, and the sampling interval is 10kHz. The peak method and the present invention are used to locate the defect respectively. The positioning accuracy analysis of the semiconducting layer and insulation wear is shown in Table 1. Table 1 lists the peak positions measured by the peak method. The midpoint of the peak is obtained based on the peak position and is used as the defect positioning result of the peak method. Table 1 also lists the center of gravity position measured by the present invention. The center of gravity is obtained based on the center of gravity position and is used as the defect positioning result of the present invention.

[0108] according to Calculate the positioning error corresponding to the two methods;

[0109] Where E represents the positioning error, l s This indicates the defect location result obtained from the measurement, l m The value indicates the actual location of the defect, and l indicates the total length of the cable under test.

[0110] Table 1. Analysis of Cable Wear Defect Location Accuracy

[0111]

[0112] As shown in Table 1, the positioning error of the present invention is significantly lower than that of the peak method, and the positioning error of the present invention decreases with the increase of wear, reaching 0.1% in the case of cable insulation damage.

[0113] This invention provides a method for locating defects in power cables. The method involves measuring the impedance spectrum at the beginning of the cable under test and calculating its reflection coefficient. A Gaussian signal is used as the incident signal for measuring the cable. Based on the incident signal and the reflection coefficient, the target frequency domain signal of the reflected signal is calculated. An inverse fast Fourier transform is performed on the target frequency domain signal to obtain the target time domain signal of the reflected signal. The centroid position of the reflection peak is calculated based on the target time domain signal, and this centroid position is identified as the defect location in the cable under test. This invention uses impedance transformation formulas to calculate the reflection coefficient at the beginning of the cable under test. It then obtains the frequency and time domain signals of the cable under test through simulated Gaussian signals, fast Fourier transform, and fast Fourier pseudo-transform, suppressing beginning-end reflection and spectral leakage. Simultaneously, it innovatively selects the centroid position of the reflection peak as the positioning basis to obtain the centroid position of the reflection peak of the target time domain signal. The defect location of the cable under test is then determined by the centroid position of the reflection peak, overcoming the problem of inaccurate local defect location in current technologies, improving the accuracy of local defect identification, and more accurately locating cable defects.

[0114] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0115] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0116] Figure 7 A schematic diagram of a defect location device for power cables according to an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below:

[0117] like Figure 7 As shown, a defect location device 7 for power cables includes: a measurement module 71, a calculation module 72, a transformation module 73, and a location module 74;

[0118] Measurement module 71 is used to measure the impedance spectrum at the beginning of the cable under test;

[0119] Calculation module 72 is used to calculate the first-end reflection coefficient of the cable under test by calculating the impedance spectrum at the first end;

[0120] The calculation module 72 is also used to use a Gaussian signal as the incident signal for measuring the cable under test, and to calculate the target frequency domain signal of the reflected signal based on the incident signal and the reflection coefficient at the beginning.

[0121] Transformation module 73 is used to perform inverse fast Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflected signal;

[0122] The positioning module 74 is used to calculate the centroid position of the reflection peak of the target time domain signal based on the target time domain signal. The centroid position of the reflection peak is the defect location of the cable under test.

[0123] In one possible implementation, the calculation module 72 calculates the head-end reflection coefficient of the cable under test by analyzing the head-end impedance spectrum, for the purpose of:

[0124] The reflection coefficient at the beginning of the cable under test is obtained by performing impedance transformation on the impedance spectrum at the beginning.

[0125] The formula for impedance transformation is:

[0126] Where Γ V (0) represents the reflection coefficient at the beginning of the cable under test, Z(0) represents the impedance at the beginning of the cable under test, Z i ε represents the surge impedance of the cable under test, ε0 represents the vacuum permittivity, and ε r The relative permittivity of the cable under test is represented by μ0, and the permeability in vacuum is represented by r. s r represents the outer diameter of the copper shielding layer of the cable under test. c This indicates the outer diameter of the cable core to be tested.

[0127] In one possible implementation, the calculation module 72 calculates the target frequency domain signal of the reflected signal based on the incident signal and the head-end reflection coefficient, for use in:

[0128] Perform a fast Fourier transform on the incident signal to obtain the first frequency domain signal;

[0129] The negative frequency domain conjugate extension of the first-end reflection coefficient is performed to obtain the processed first-end reflection coefficient.

[0130] The target frequency domain signal of the reflected signal is obtained by multiplying the first frequency domain signal with the processed first-end reflection coefficient.

[0131] Calculation module 72 performs a fast Fourier transform on the incident signal to obtain a first frequency domain signal, which is used for:

[0132] according to The first frequency domain signal is obtained;

[0133] Among them, S i (ω) represents the first frequency domain signal, S i (t) represents the incident signal, FFT[.] represents the Fast Fourier Transform function, b represents the time delay constant of the incident signal, c represents the pulse width constant of the incident signal, and t represents time.

[0134] In one possible implementation, the positioning module 74 calculates the centroid position of the reflection peak of the target time-domain signal based on the target time-domain signal, for the purpose of:

[0135] Based on the target time-domain signal, determine the abscissa value of the centroid of the reflection peak in the target time-domain signal;

[0136] The position of the centroid of the reflection peak is obtained by using the abscissa of the centroid of the reflection peak and the propagation speed of the electromagnetic wave in the cable under test.

[0137] The positioning module 74 determines the abscissa value of the centroid of the reflection peak in the target time domain signal based on the target time domain signal, for the purpose of:

[0138] according to Determine the x-coordinate of the centroid of the reflection peak;

[0139] Where z' represents the x-coordinate of the centroid of the reflection peak, x i S represents the x-coordinate value of each point in the reflection peak. r (x i ) represents the amplitude coordinate value of each point in the reflection peak, m represents the number of points in the reflection peak, and i represents a constant.

[0140] The positioning module 74 obtains the position of the centroid of the reflection peak of the target time-domain signal based on the abscissa value of the centroid of the reflection peak and the propagation speed of the electromagnetic wave in the cable under test, for the purpose of:

[0141] The position of the centroid of the reflection peak is obtained by multiplying the x-coordinate of the centroid of the reflection peak by the propagation speed of the electromagnetic wave in the cable under test.

[0142] This invention provides a defect location device for power cables. It measures the impedance spectrum at the beginning of the cable under test and calculates the reflection coefficient at the beginning of the cable. A Gaussian signal is used as the incident signal for measuring the cable. Based on the incident signal and the reflection coefficient at the beginning of the cable, the target frequency domain signal of the reflected signal is calculated. An inverse fast Fourier transform is performed on the target frequency domain signal to obtain the target time domain signal of the reflected signal. Based on the target time domain signal, the centroid position of the reflection peak of the target time domain signal is calculated, and the centroid position of the reflection peak is the defect location of the cable under test. This invention uses impedance transformation formulas to calculate the reflection coefficient at the beginning of the cable under test. It then obtains the frequency and time domain signals of the cable under test through simulated Gaussian signals, fast Fourier transform, and fast Fourier pseudo-transform, suppressing beginning-end reflection and spectral leakage. Simultaneously, it innovatively selects the centroid position of the reflection peak as the positioning basis to obtain the centroid position of the reflection peak of the target time domain signal. The defect location of the cable under test is then determined by the centroid position of the reflection peak, overcoming the problem of inaccurate local defect location in current technologies, improving the accuracy of local defect identification, and more accurately locating cable defects.

[0143] Figure 8 This is a schematic diagram of a terminal provided in an embodiment of the present invention. Figure 8 As shown, the terminal 8 in this embodiment includes a processor 80, a memory 81, and a computer program 82 stored in the memory 81 and executable on the processor 80. When the processor 80 executes the computer program 82, it implements the steps in the aforementioned embodiments of the defect location methods for power cables, for example... Figure 1 Steps 101 to 104 are shown. Alternatively, when processor 80 executes computer program 82, it implements the functions of each module / unit in the above-described device embodiments, for example... Figure 7 The functions of modules / units 71 to 74 shown.

[0144] For example, computer program 82 can be divided into one or more modules / units, one or more of which are stored in memory 81 and executed by processor 80 to complete the present invention. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 82 in terminal 8. For example, computer program 82 can be divided into... Figure 7 Modules / units 71 to 74 are shown.

[0145] Terminal 8 may include, but is not limited to, a processor 80 and a memory 81. Those skilled in the art will understand that... Figure 8 This is merely an example of terminal 8 and does not constitute a limitation on terminal 8. It may include more or fewer components than shown, or combine certain components, or different components. For example, the terminal may also include input / output devices, network access devices, buses, etc.

[0146] The processor 80 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0147] The memory 81 can be an internal storage unit of the terminal 8, such as a hard disk or RAM. The memory 81 can also be an external storage device of the terminal 8, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory 81 can include both internal and external storage units of the terminal 8. The memory 81 is used to store computer programs and other programs and data required by the terminal. The memory 81 can also be used to temporarily store data that has been output or will be output.

[0148] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0149] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0150] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0151] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0152] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0153] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0154] If integrated modules / units are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the above-described embodiments of the defect location methods for power cables. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0155] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for locating defects in power cables, characterized in that, include: The impedance spectrum at the beginning of the cable under test is measured, and the reflection coefficient at the beginning of the cable under test is calculated from the impedance spectrum at the beginning. A Gaussian signal is used as the incident signal for measuring the cable under test. The target frequency domain signal of the reflected signal is calculated based on the incident signal and the reflection coefficient at the beginning of the cable. Perform an inverse fast Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflected signal; Based on the target time-domain signal, calculate the centroid position of the reflection peak of the target time-domain signal, where the centroid position of the reflection peak is the defect location of the cable under test; The step of calculating the centroid position of the reflection peak of the target time-domain signal based on the target time-domain signal includes: according to Determine the abscissa value of the centroid of the reflection peak; in, The x-coordinate value represents the centroid of the reflection peak. This represents the x-coordinate value of each point in the reflection peak. This represents the amplitude coordinates of each point in the reflection peak. m Indicates the number of points of reflection peaks. i Represents a constant; The position of the centroid of the reflection peak is obtained by multiplying the abscissa of the centroid of the reflection peak by the propagation speed of the electromagnetic wave in the cable under test.

2. The defect location method for power cables according to claim 1, characterized in that, The reflection coefficient at the beginning of the cable under test is obtained by calculating the impedance spectrum at the beginning of the cable, including: The first-end reflection coefficient of the cable under test is obtained by performing impedance transformation on the first-end impedance spectrum. The formula for impedance transformation is as follows: ; in This represents the reflection coefficient at the beginning of the cable under test. This indicates the impedance at the beginning of the cable under test. This represents the surge impedance of the cable under test. Represents the vacuum permittivity. This represents the relative permittivity of the cable under test. Indicates the permeability in a vacuum. This indicates the outer diameter of the copper shielding layer of the cable under test. This indicates the outer diameter of the cable core to be tested.

3. The defect location method for power cables according to claim 1, characterized in that, Based on the incident signal and the first-end reflection coefficient, the target frequency domain signal of the reflected signal is calculated, including: The incident signal is subjected to a fast Fourier transform to obtain a first frequency domain signal; The first-end reflection coefficient is subjected to negative frequency domain conjugate extension processing to obtain the processed first-end reflection coefficient. The first frequency domain signal is multiplied by the processed first-end reflection coefficient to obtain the target frequency domain signal of the reflected signal.

4. The defect location method for power cables according to claim 3, characterized in that, The step of performing a fast Fourier transform on the incident signal to obtain a first frequency domain signal includes: according to The first frequency domain signal is obtained; in, Indicates the first frequency domain signal. Indicates the incident signal. FFT [.] denotes the Fast Fourier Transform function. b The time delay constant represents the incident signal. c The pulse width constant represents the incident signal. t Indicates time.

5. A defect location device for power cables, characterized in that, include: The measurement module is used to measure the impedance spectrum at the beginning of the cable under test. The calculation module is used to calculate the reflection coefficient of the cable under test by calculating the impedance spectrum at the first end; The calculation module is also used to use a Gaussian signal as the incident signal for measuring the cable under test, and to calculate the target frequency domain signal of the reflected signal based on the incident signal and the first-end reflection coefficient. The transformation module is used to perform a fast inverse Fourier transform on the target frequency domain signal to obtain the target time domain signal of the reflected signal; The positioning module is used to calculate the centroid position of the reflection peak of the target time domain signal based on the target time domain signal, wherein the centroid position of the reflection peak is the defect location of the cable under test. The step of calculating the centroid position of the reflection peak of the target time-domain signal based on the target time-domain signal includes: based on Determine the abscissa value of the centroid of the reflection peak; wherein, The x-coordinate value represents the centroid of the reflection peak. This represents the x-coordinate value of each point in the reflection peak. This represents the amplitude coordinates of each point in the reflection peak. m Indicates the number of points of reflection peaks. i The value represents a constant; the position of the centroid of the reflection peak is obtained by multiplying the x-coordinate of the centroid of the reflection peak by the propagation speed of the electromagnetic wave in the cable under test.

6. A terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1 to 4.

7. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 4.

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