Method for detecting defects in a cable, detection system and computer-readable storage medium

Abstract

The application discloses a cable defect detection method, a detection system and a computer readable storage medium. The detection method comprises the following steps: applying a pulse voltage at a head end of a cable; determining a first time length required for a signal generated by the pulse voltage to travel back and forth between the head end of the cable and a tail end of the cable once; taking a time point when the pulse voltage is injected into the head end of the cable as a starting point, and obtaining voltage signals and current signals of the head end of the cable corresponding to a second time length as target signals, wherein the second time length is n times of the first time length, and 1 > n > 0; determining an equivalent impedance spectrum of the target signals, and positioning a defect position according to a relationship among a frequency of a defect frequency component of the equivalent impedance spectrum, a length from a detection position to the head end of the cable and a relative dielectric constant of a main insulation of the cable. In this way, the frequency component caused by the reflection of the defect position can be improved, and the sensitivity of defect positioning can be improved.

Description

Technical Field

[0001] This application relates to the field of electrical engineering technology, and in particular to a method, system and computer-readable storage medium for detecting cable defects. Background Technology

[0002] Cross-linked polyethylene (XLPE) cables, with their excellent insulation performance and mechanical strength, have gradually become a core component of urban power grid transmission systems. However, complex operating conditions and construction errors can easily lead to cable structural damage. These hidden dangers may evolve into insulation faults during long-term operation, subsequently causing sudden power outages and resulting in cascading economic losses. Currently, frequency-domain reflectometry (FDR) has proven highly effective in detecting and locating internal cable defects. In FDR, broadband impedance spectrum (BIS) locates cable defects by analyzing the impedance spectrum components caused by defects. The mainstream BIS methods currently include Fast Fourier Transform (FFT) and Integral Transform (IT). Both FFT and IT are affected by the frequency components caused by reflections from the cable ends in the impedance spectrum. Excessively high end-positioning peaks indirectly weaken the defect location peaks, reducing the sensitivity of defect location. Summary of the Invention

[0003] This application provides a method, system, and computer-readable storage medium for detecting cable defects, in order to solve at least some of the problems in the related art.

[0004] This application provides a method for detecting cable defects, the method comprising: A pulse voltage is applied to the beginning of the cable; Based on the length of the cable and the relative permittivity of the main insulation of the cable, determine the first duration required for the signal generated by the pulse voltage to travel back and forth once between the beginning and end of the cable; Starting from the moment when the pulse voltage is injected into the beginning of the cable, the voltage and current signals at the beginning of the cable corresponding to the second duration are obtained as the target signal, wherein the second duration is n times the first duration, 1>n>0; Determine the equivalent impedance spectrum of the target signal, wherein the equivalent impedance spectrum includes the impedance corresponding to each frequency point of the target signal in a first frequency sequence; The defect location is determined by the relationship between the frequency of the defect frequency component in the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable.

[0005] Optionally, locating the defect based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable includes: Based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable, the detection location sequence is converted into a defect frequency component sequence. Determine the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum; If the defect component at a certain frequency point in the defect frequency component sequence is greater than a set threshold, the detection position corresponding to that frequency point in the defect frequency component sequence is determined as the defect position.

[0006] Optional, 0.98 ≥ n ≥ 0.95.

[0007] Optionally, the value of the second duration includes two values, and obtaining the voltage signal and current signal at the cable end corresponding to the second duration as the target signal includes: The voltage signal and the current signal of the second duration are respectively acquired as the target signal; Determining the defect component corresponding to each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum includes: Determine the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum in the two target signals of the second duration; The detection method further includes: The defect component of each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum of the target signal corresponding to the defect frequency component sequence corresponding to the smaller of the two second durations is subtracted from the defect component of each frequency point in the equivalent impedance spectrum of the target signal corresponding to the defect frequency component sequence corresponding to the smaller of the two second durations. The defect component of each frequency point in the equivalent impedance spectrum of the target signal corresponding to the defect frequency component sequence ... The defect location in the cable segment is determined based on the defect component, between the location corresponding to the smaller of the two second durations and the location corresponding to the larger of the two second durations.

[0008] Optionally, applying a pulse voltage to the beginning of the cable includes: The period of the pulse voltage and the pulse width of the pulse voltage are determined; wherein the period of the pulse voltage is 10 times to 200 times the first duration, and the pulse width of the pulse voltage is 1 / 200 to 1 / 20 of the first duration.

[0009] Optionally, determining the equivalent impedance spectrum of the target signal, wherein the equivalent impedance spectrum includes the impedance corresponding to each frequency point of the target signal in the first frequency sequence, including: The first frequency sequence is established based on the period and pulse width of the pulse voltage, and the first frequency sequence includes multiple frequency points; The voltage components at multiple frequency points in the voltage signal are calculated using a digital phase-locked loop algorithm. The digital phase-locked loop algorithm is used to calculate the current components at multiple frequency points in the current signal; Based on the voltage component and the current component, the impedance corresponding to each frequency point of the target signal in the first frequency sequence is determined.

[0010] Optionally, the starting frequency of the first frequency sequence is 100 / T, the frequency step size of the first frequency sequence is 1 / T, and the ending frequency of the first frequency sequence is 1 / (2τ), where T is the period of the pulse voltage and τ is the pulse width of the pulse voltage.

[0011] Optionally, converting the detection position sequence into a defect frequency component sequence based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable includes: The detection position sequence of the cable is determined based on the cable length and the defect detection step size; The relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable is based on... The detection location sequence is converted into a defect frequency component sequence; where F is the frequency of the defect frequency component of the equivalent impedance spectrum, L is the length of the detection location from the beginning of the cable, and εr is the relative permittivity of the main insulation of the cable.

[0012] This application also provides a cable defect detection system, the detection system including a memory, a processor and a program stored in the memory and executable on the processor, wherein the processor executes the program to implement a cable defect detection method.

[0013] In another aspect, this application provides a computer-readable storage medium on which a program is stored, which, when executed, implements a method for detecting cable defects.

[0014] Compared with related technologies, the cable defect detection method provided in this application applies a pulse voltage to the cable's beginning end; based on the cable length and the relative permittivity of the cable's main insulation, it determines the first time required for the signal generated by the pulse voltage to travel back and forth once between the cable's beginning and end; taking the moment the pulse voltage is injected into the cable's beginning end as the starting point, it acquires the voltage and current signals at the cable's beginning end corresponding to a second time duration as the target signal, where the second time duration is n times the first time duration, 1 > n > 0. Thus, the second time duration is shorter than the first time duration, and the target signal does not include the voltage and current signals reflected from the cable's end to its beginning end. Consequently, the equivalent impedance spectrum of the target signal also does not include the equivalent impedance portion formed by the voltage and current signals reflected from the cable's end to its beginning end. This avoids the frequency components caused by reflections from the cable's end in the equivalent impedance spectrum weakening the frequency components caused by reflections at the defect location, thereby improving the sensitivity of defect location. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] Figure 1 This is a schematic flowchart illustrating a cable defect detection method according to one embodiment of this application.

[0017] Figure 2 for Figure 1 The flowchart of one embodiment of step 15 is shown.

[0018] Figure 3 This is a schematic diagram of a cable defect detection method according to another embodiment of this application.

[0019] Figure 4 for Figure 1 The flowchart illustrates one embodiment of step 14 in the cable defect detection method shown.

[0020] Figure 5 This is a schematic diagram of the voltage and current signals obtained using the cable defect detection method provided in the embodiments of this application.

[0021] Figure 6 This is a schematic diagram of the equivalent impedance spectrum determined using the cable defect detection method provided in the embodiments of this application.

[0022] Figure 7 This is a diagram showing the detection results using the cable defect detection method provided in this application.

[0023] Figure 8This is a structural block diagram of a cable defect detection system provided in an embodiment of this application. Detailed Implementation

[0024] This application provides a method, system, and computer-readable storage medium for detecting cable defects. The method, system, and storage medium are described in detail below with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] Please refer to Figure 1 , Figure 1 This is a schematic flowchart of a cable defect detection method 10 according to an embodiment of this application. Figure 1 As shown, the cable defect detection method 10 provided in this application embodiment includes steps 11 to 15.

[0026] Step 11: Apply a pulse voltage to the beginning of the cable; Step 12: Based on the cable length and the relative permittivity of the cable's main insulation, determine the first time required for the signal generated by the pulse voltage to travel back and forth once between the beginning and end of the cable. Step 13: Starting from the moment when the pulse voltage is injected into the beginning of the cable, obtain the voltage and current signals at the beginning of the cable corresponding to the second duration as the target signal, wherein the second duration is n times the first duration, 1>n>0; Step 14: Determine the equivalent impedance spectrum of the target signal, wherein the equivalent impedance spectrum includes the impedance corresponding to each frequency point of the target signal in the first frequency sequence; Step 15: Locate the defect location based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable.

[0027] The cable defect detection method provided in this application involves applying a pulse voltage to the cable's beginning end; determining the first time required for the signal generated by the pulse voltage to travel back and forth between the cable's beginning and end based on the cable's length and the relative permittivity of its main insulation; and acquiring the voltage and current signals at the cable's beginning end corresponding to a second time duration as the target signal, starting from the moment the pulse voltage is injected into the cable's beginning end. The second time duration is n times the first time duration, where 1 > n > 0. Since the second time duration is shorter than the first time duration, the target signal does not include the voltage and current signals reflected from the cable's end to its beginning end. Consequently, the equivalent impedance spectrum of the target signal also does not include the equivalent impedance portion formed by the voltage and current signals reflected from the cable's end to its beginning end. This avoids the defect component caused by reflection from the cable's end in the equivalent impedance spectrum weakening the defect component at the defect location, thus improving the sensitivity of defect localization.

[0028] In some embodiments, step 12, starting from the moment the pulse voltage is injected into the cable's head end, acquires the voltage and current signals at the cable's head end corresponding to a second duration as the target signal, wherein the second duration is n times the first duration, 1 > n > 0, and includes: The voltage and current signals at the cable head end are acquired, and the voltage and current signals at the cable head end corresponding to a second duration are extracted as the target signal. The second duration is n times the first duration, where 1 > n > 0. In this way, a voltage and current signal greater than or equal to the first duration can be acquired at the cable head end first. After acquiring the voltage and current signals greater than or equal to the first duration, the voltage and current signals at the cable head end corresponding to the second duration are extracted as the target signal. This facilitates control over the duration of the target signal and improves the accuracy of target signal acquisition.

[0029] Please refer to Figure 2 , Figure 2 for Figure 1 The flowchart illustrates one embodiment of step 15. (See attached diagram.) Figure 2 As shown, step 15 locates the defect location based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable. This includes steps 151 to 153.

[0030] Step 151: Based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable, the detection location sequence is converted into a defect frequency component sequence. Step 152: Determine the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum; Step 153: If the defect component at a certain frequency point in the defect frequency component sequence is greater than a set threshold, determine the detection position corresponding to that frequency point in the defect frequency component sequence as the defect position.

[0031] Step 151 transforms the continuous sequence of cable detection locations into a unique sequence of corresponding defect frequency components by physically correlating the frequency of the defect frequency components in the equivalent impedance spectrum, the distance from the detection location to the beginning of the cable, and the relative permittivity of the main insulation. This establishes a mapping relationship between the frequency of the defect frequency components in the equivalent impedance spectrum and the distance from the detection location to the beginning of the cable. Therefore, when a frequency anomaly in the defect frequency components of the equivalent impedance spectrum is determined, the distance from the beginning of the cable can be determined based on the mapping relationship between the frequency of the defect frequency components and the distance from the detection location to the beginning of the cable, thus determining the location of the cable defect.

[0032] Step 152 determines the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum. This allows for analysis of the curve trend and peak positions formed by the defect components at each frequency point in the equivalent impedance spectrum by plotting points. Based on the judgment condition in step 153, if the defect component at a certain frequency point in the defect frequency component sequence is greater than a set threshold, the detection position corresponding to that frequency point in the defect frequency component sequence is determined as the defect location, using that frequency point as the medium. Thus, by analyzing the equivalent impedance spectrum of the target signal, the defect location is determined, achieving cable defect detection and localization. Furthermore, the target signal does not include voltage and current signals reflected from the cable end to the cable beginning; therefore, the equivalent impedance spectrum of the target signal also does not include the equivalent impedance portion formed by voltage and current signals reflected from the cable end to the cable beginning. This avoids the defect component caused by cable end reflection in the equivalent impedance spectrum weakening the defect component at the defect location, improving the sensitivity of defect localization.

[0033] In some embodiments, 0.98 ≥ n ≥ 0.95. A larger value for n allows for better detection of voltage and current signals generated by defects near the cable end, improving the completeness of cable inspection. However, if n is too large, the acquisition of the target signal must be precise to avoid the reflected signal from the cable end being included in the target signal due to imprecise control of the second duration, thus affecting the accuracy of cable inspection.

[0034] In some embodiments, target signals corresponding to two second durations can be acquired separately. For example, the first second duration can be set to 0.95 times the first duration to avoid introducing reflected signals from the cable end and improve the accuracy of cable detection. The second second duration can be set to 0.99 times or even 0.999 times the first duration to improve the completeness of cable detection. It is also possible to analyze whether there are defects between the cable segments at the cable positions corresponding to the first and second second durations. If there are no defects, the specific location of the cable defect can be located based on the target signal corresponding to the first second duration.

[0035] In some embodiments, the target signal corresponding to the second duration and the target signal corresponding to the first duration can be acquired separately. For example, the second duration can be set to 0.95 times the first duration to avoid introducing reflected signals from the cable end and improve the accuracy of cable detection. The target signal of the first duration can improve the completeness of cable detection and can analyze whether there are defects in the cable segment between the cable position corresponding to the first duration and the cable end. If there are no defects, the specific location of the cable defect can be located based on the target signal corresponding to the first second duration. If there are defects in the cable segment between the cable position corresponding to the first duration and the cable end, the value of the second duration can be gradually increased, and the target signal corresponding to the second duration can be detected again.

[0036] Please refer to Figure 3 , Figure 3 This is a schematic flowchart illustrating a cable defect detection method according to another embodiment of this application. Figure 3 In the illustrated embodiment, the second duration includes two values. Step 13 acquires the voltage and current signals at the cable head end corresponding to the second duration as target signals, including step 131. Step 131: Acquire the voltage and current signals for the two second durations as target signals respectively.

[0037] Step 152 determines the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum, including step 1521.

[0038] Step 1521: Determine the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum in the two target signals of the second duration.

[0039] The detection method also includes steps 16 and 17.

[0040] Step 16: Take the defect component of each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the larger of the two second time durations, and subtract the defect component of each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the smaller of the two second time durations, to determine the defect component of each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the smaller of the two second time durations and the position corresponding to the larger of the two second time durations. Step 17: Determine the location of the defect in the cable segment between the location corresponding to the smaller of the two second durations and the location corresponding to the larger of the two second durations, based on the defect component.

[0041] The location corresponding to the first second duration can be determined based on the first second duration, and the location corresponding to the second second duration can be determined based on the second second duration. The cable segment between the locations corresponding to the first and second second durations can then be determined. Specifically, if the first second duration is 0 and the second second duration is 0.1 times the first duration, the cable segment between the locations corresponding to the first and second second durations is the cable segment from the cable head to 0.1 times the cable length; if the first second duration is 0.1 times the first duration and the second second duration is 0.2 times the first duration, the cable segment between the locations corresponding to the first and second second durations is the cable segment between 0.1 times and 0.2 times the cable length.

[0042] In step 16, by analyzing the target signals corresponding to the first and second time durations, the defect components at each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the first and second time durations are obtained, respectively. The defect components at each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the second time duration are subtracted from the defect components at each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the first and second time durations, thus determining the defect components at each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the cable segment between the positions corresponding to the first and second time durations.

[0043] In step 17, the defect location in the cable segment between the first and second time durations is determined based on the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum of the target signal between the first and second time durations.

[0044] In this way, the cable can be segmented, and defects in each segment can be located one by one. This not only avoids the attenuation of the defect component caused by reflection from the cable end to the defect component at the defect location, but also avoids the mutual interference between defect components from different cable segments, improving the detection and location accuracy of smaller defects. For example, there may be a serious defect between 0.4 and 0.5 times the cable length, and a minor defect between 0.3 and 0.4 times the cable length. Without segmented defect location, the serious defect between 0.4 and 0.5 times the cable length will have a larger defect component, while the minor defect between 0.3 and 0.4 times the cable length will have a smaller defect component. The larger defect component will attenuate the smaller defect component, potentially making the minor defect between 0.3 and 0.4 times the cable length difficult to detect or causing inaccurate location. By employing a segmented defect location method, defects can be located separately for cable segments between 0.3 and 0.4 times the cable length, and for cable segments between 0.4 and 0.5 times the cable length. This method avoids the weakening effect of severe defects between 0.4 and 0.5 times the cable length on minor defects between 0.3 and 0.4 times the cable length, thereby improving the location accuracy of minor defects between 0.3 and 0.4 times the cable length.

[0045] In some implementations, a pulse voltage is applied to the beginning of the cable, including: The period and pulse width of the pulse voltage are determined; wherein the period of the pulse voltage is 10 times to 200 times the first duration, and the pulse width is 1 / 200 to 1 / 20 of the first duration. In the embodiments of this application, T1 Where T1 is the first duration and L1 is the length of the cable. Let be the relative permittivity of the cable's main insulation. The period of the pulse voltage is 100 times the first duration, and the pulse width is 1 / 100th of the first duration. That is, , Where T is the period of the pulse voltage and τ is the pulse width of the pulse voltage.

[0046] T1 reflects the time it takes for the signal to travel completely round trip in the cable. The period T needs to be much larger than T1 to ensure that the reflected signal of the previous pulse, including defect reflections and end reflections, has fully propagated before the next pulse is injected. This avoids the superposition of the reflected signal of the previous pulse with the incident signal of the next pulse, which would cause distortion in subsequent voltage / current signal acquisition. In this patent embodiment, T=100T1. This value satisfies the basic requirement of avoiding signal superposition while also balancing detection efficiency.

[0047] The pulse width determines the frequency bandwidth of the pulse signal. The relationship between τ and T1 is needed to ensure that the pulse's frequency bandwidth covers the effective range of the defective frequency component sequence, while avoiding insufficient signal energy due to an excessively narrow pulse width and reduced frequency resolution due to an excessively wide pulse width. In this embodiment, τ = T1 / 100, a value that balances signal energy and frequency resolution.

[0048] Please refer to Figure 4 , Figure 4 for Figure 1 The flowchart illustrates one embodiment of step 14 in the cable defect detection method shown. Figure 4 As shown, step 14 determines the equivalent impedance spectrum of the target signal, wherein the equivalent impedance spectrum includes the impedance corresponding to each frequency point of the target signal in the first frequency sequence, including steps 141 to 144.

[0049] Step 141: Establish a first frequency sequence based on the period and pulse width of the pulse voltage. The first frequency sequence includes multiple frequency points. In some specific embodiments, the starting frequency point of the first frequency sequence is 100 / T, the frequency step size of the first frequency sequence is 1 / T, and the ending frequency point of the first frequency sequence is 1 / (2τ), where T is the period of the pulse voltage and τ is the pulse width of the pulse voltage.

[0050] Traditional broadband impedance spectroscopy (BIS) methods often use fixed frequency sequences (such as preset fixed frequency points of 10Hz~10kHz), which can easily lead to a mismatch between the frequency range and the defect signal. If the frequency range is too narrow, it will miss the near-end defect signal in the high-frequency band; if the frequency range is too wide, it will introduce noise in irrelevant frequency bands, increasing the subsequent calculation load.

[0051] Step 141 constructs a first frequency sequence based on the period (T) and pulse width (τ) of the pulse voltage, with a starting frequency of 100 / T, a frequency step of 1 / T, and a ending frequency of 1 / (2τ). This allows for a deep binding between the frequency range and the characteristics of the pulse signal. The ending frequency 1 / (2τ) corresponds to the highest effective frequency of the pulse signal. According to the Fourier transform principle, the pulse width τ determines the frequency bandwidth of the pulse, and 1 / (2τ) is the upper limit of the bandwidth, ensuring that the frequency sequence completely covers the range of defect frequency components that the pulse signal can excite, avoiding the omission of high-frequency defect signals. The starting frequency 100 / T is associated with the signal propagation characteristics through the period T. T is much larger than the first duration T1, ensuring that the low-frequency band covers the low-frequency signals of distant defects, achieving full coverage of the effective frequency band without dead zones.

[0052] By setting a frequency step size to ensure frequency resolution, a step size of 1 / T can match the interval between adjacent frequency points with the pulse period, avoiding the overlap of adjacent defect frequency components due to an excessively large step size, or the data redundancy and low computational efficiency due to an excessively small step size, thus balancing resolution and computational efficiency.

[0053] Step 142: Use a digital phase-locked loop algorithm to calculate the voltage components of the voltage signal at multiple frequency points; Step 143: Use a digital phase-locked loop algorithm to calculate the current components of the current signal at multiple frequency points; Step 144: Determine the impedance corresponding to each frequency point of the target signal in the first frequency sequence based on the voltage and current components.

[0054] Steps 142 to 143 use a digital phase-locked loop (PLL) algorithm to extract voltage and current components respectively. The PLL algorithm locks each frequency point in the first frequency sequence by comparing the phase of the reference signal with the target signal, and extracts only the signal component that has the same frequency and phase correlation with that frequency point, while filtering out noise at other frequencies.

[0055] In step 144, the voltage and current components at the same frequency point are extracted to calculate the impedance. In this patent application, the impedance is calculated by extracting the voltage and current components at the same frequency point. The impedance at each frequency point is calculated from the voltage and current components at that frequency point, avoiding the frequency mismatch error caused by using the voltage component of frequency A and the current component of frequency B to calculate the impedance. This ensures that the impedance value at each frequency point truly reflects the equivalent impedance characteristics of the cable at that frequency, improves the accuracy of the equivalent impedance spectrum of the target signal, and further enhances the accuracy of defect location using the equivalent impedance spectrum.

[0056] In some embodiments, the detection position sequence is converted into a defect frequency component sequence based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the cable's beginning, and the relative permittivity of the cable's main insulation. This includes: The cable detection position sequence is determined based on the cable length and the defect detection step size. Specifically, the starting length of the detection position sequence is 0, and the ending length is m times the cable length, where 1.3 > m > 1. In this way, the cable detection position sequence covers the entire cable, and the defect frequency component sequence obtained from the cable detection position sequence can also cover the entire cable. The step size can be set according to actual conditions; a smaller step size results in higher defect location accuracy, while a larger step size results in faster defect location speed. An appropriate step size can be set according to the defect location requirements.

[0057] Based on the relationship between the frequency of the defect frequency component in the equivalent impedance spectrum, the length of the detection location from the cable's beginning, and the relative permittivity of the cable's main insulation. The detection location sequence is converted into a defect frequency component sequence; where F is the frequency of the defect frequency component in the equivalent impedance spectrum, L is the length of the detection location from the cable's beginning, and εr is the relative permittivity of the cable's main insulation. This establishes a mapping relationship between the detection location sequence and the defect frequency component sequence, facilitating the location of the defect when the amplitude of the defect frequency component in the equivalent impedance spectrum at a certain frequency point in the defect frequency component sequence exceeds a set value, or when the amplitude of a certain frequency point is significantly greater than the amplitude of adjacent frequency points.

[0058] In some embodiments, determining the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum includes: using a digital phase-locked loop algorithm to calculate the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum. This can improve the calculation accuracy of the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum.

[0059] To verify the effectiveness of the cable defect detection method provided in this application embodiment, a 100m long YJV-8.7 / 15kV 1×25 cable with a main insulation relative permittivity of 3.25 was measured on-site. A weak defect was placed at 23m from the cable end, and a slightly weaker defect was placed at 33m. A pulse with a period of 0.1ms and a pulse width of 10ns was applied to the cable end. Figure 5 This is a schematic diagram of the voltage and current signals obtained using the cable defect detection method provided in this application. A time period of 0-1200 ns is extracted for equivalent impedance spectrum extraction. Figure 6 This is a schematic diagram of the equivalent impedance spectrum determined using the cable defect detection method provided in the embodiments of this application.

[0060] Please refer to Figure 7 , Figure 7 This diagram illustrates the detection results using the cable defect detection method provided in this application. The blue line represents the detection results using the TMIS (Total Measurement Information System) method provided in this application; the red line represents the detection results using the Fast Fourier Transform (FFT) method; and the yellow line represents the detection results using the Integral Transform (IT) method. The defect impedance spectra used for the FFT and IT methods are obtained through measurement. The reference healthy impedance spectrum for the IT method is obtained by measuring the impedance spectrum of the same cable before manufacturing the defect. Figure 7 It can be seen that both the TMIS method and the IT method can accurately locate two defects, while the FFT method can only vaguely locate weak defects and cannot identify weak defects at all.

[0061] Experimental results show that the FFT method has limited sensitivity and is difficult to detect weak defects. This is because the FFT method generates a significant spike near the cable end, and for weak defects, the spectral leakage from this end peak can mask the peak associated with the defect. Although the IT method mitigates the influence of the end peak to some extent by subtracting the reference healthy spectrum, its impact is still significant. If the defect severity is further reduced, the end peak in the IT method's localization results may also mask the defect peak. In contrast, the cable defect detection method (TMIS) provided in this application does not have this problem, demonstrating its superiority in locating weak defects.

[0062] Please refer to Figure 8 , Figure 8 This is a structural block diagram of a cable defect detection system 3 provided in an embodiment of this application. The detection system 3 includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements a cable defect detection method.

[0063] exist Figure 8 In the illustrated embodiment, the cable defect detection system 3 may include a computer-readable storage medium 32, which may store a program that can be invoked by a processor 31, and may include a non-volatile storage medium. In some embodiments, the cable defect detection system 3 may include memory 33 and an interface 34. In some embodiments, the cable defect detection system 3 may also include other hardware depending on the actual application.

[0064] This application, in another aspect, provides a computer-readable storage medium on which a program is stored, which, when executed, implements a cable defect detection method 10. In some embodiments, it may take the form of a computer program product implemented on one or more computer-readable storage media 32 (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing program code. The computer-readable storage medium 32 includes permanent and non-permanent, removable and non-removable media, and information storage can be implemented using any method or technology. The information may be computer-readable instructions, data structures, program modules, or other data. Examples of computer-readable storage media 32 include, but are not limited to: phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, read-only optical disc read-only memory (CD-ROM), digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transfer medium, which can be used to store information accessible by a computing device.

[0065] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0066] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for detecting cable defects, characterized in that, The detection method includes: A pulse voltage is applied to the beginning of the cable; Based on the length of the cable and the relative permittivity of the main insulation of the cable, determine the first duration required for the signal generated by the pulse voltage to travel back and forth once between the beginning and end of the cable; Starting from the moment when the pulse voltage is injected into the beginning of the cable, the voltage and current signals at the beginning of the cable corresponding to the second duration are obtained as target signals, wherein the second duration is n times the first duration, 1>n>0; the value of the second duration includes two values, and obtaining the voltage and current signals at the beginning of the cable corresponding to the second duration as target signals includes: obtaining the voltage signal and the current signal of the second duration respectively as the target signals; The equivalent impedance spectrum of the target signal is determined, wherein the equivalent impedance spectrum includes the impedance corresponding to each frequency point of the target signal in a first frequency sequence; wherein the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum of the target signal in two second durations is determined. The defect location is determined based on the relationship between the frequency of the defect frequency component in the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the cable's main insulation. Specifically, the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum of the target signal corresponding to the larger of the two second durations is subtracted from the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum of the target signal corresponding to the smaller of the two second durations. This determines the defect component at each frequency point in the defect frequency component sequence of the equivalent impedance spectrum of the target signal corresponding to the cable segment between the position corresponding to the smaller of the two second durations and the position corresponding to the larger of the two second durations. The defect location in the cable segment between the position corresponding to the smaller of the two second durations and the position corresponding to the larger of the two second durations is then determined based on the defect component.

2. The method for detecting cable defects according to claim 1, characterized in that, The method of locating the defect location based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable includes: Based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable, the detection location sequence is converted into a defect frequency component sequence. Determine the defect component at each frequency point in the defect frequency component sequence corresponding to the equivalent impedance spectrum; If the defect component at a certain frequency point in the defect frequency component sequence is greater than a set threshold, the detection position corresponding to that frequency point in the defect frequency component sequence is determined as the defect position.

3. The method for detecting cable defects according to claim 1, characterized in that, 0.98≥n≥0.95。 4. The method for detecting cable defects according to claim 1, characterized in that, Applying a pulse voltage to the beginning of the cable includes: The period of the pulse voltage and the pulse width of the pulse voltage are determined; wherein the period of the pulse voltage is 10 times to 200 times the first duration, and the pulse width of the pulse voltage is 1 / 200 to 1 / 20 of the first duration.

5. The method for detecting cable defects according to claim 1, characterized in that, The step of determining the equivalent impedance spectrum of the target signal, wherein the equivalent impedance spectrum includes the impedance corresponding to each frequency point of the target signal in the first frequency sequence, including: The first frequency sequence is established based on the period and pulse width of the pulse voltage, and the first frequency sequence includes multiple frequency points; The voltage components at multiple frequency points in the voltage signal are calculated using a digital phase-locked loop algorithm. The digital phase-locked loop algorithm is used to calculate the current components at multiple frequency points in the current signal; Based on the voltage component and the current component, the impedance corresponding to each frequency point of the target signal in the first frequency sequence is determined.

6. The method for detecting cable defects according to claim 5, characterized in that, The starting frequency of the first frequency sequence is 100 / T, the frequency step size of the first frequency sequence is 1 / T, and the ending frequency of the first frequency sequence is 1 / (2τ), where T is the period of the pulse voltage and τ is the pulse width of the pulse voltage.

7. The method for detecting cable defects according to claim 2, characterized in that, The step of converting the detection position sequence into a defect frequency component sequence based on the relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection position from the beginning of the cable, and the relative permittivity of the main insulation of the cable includes: The detection position sequence of the cable is determined based on the cable length and the defect detection step size; The relationship between the frequency of the defect frequency component of the equivalent impedance spectrum, the length of the detection location from the beginning of the cable, and the relative permittivity of the main insulation of the cable is based on... The detection location sequence is converted into a defect frequency component sequence; where F is the frequency of the defect frequency component of the equivalent impedance spectrum, L is the length of the detection location from the beginning of the cable, and εr is the relative permittivity of the main insulation of the cable.

8. A cable defect detection system, characterized in that, The detection system includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the cable defect detection method as described in any one of claims 1-7.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a program that, when executed, implements the cable defect detection method as described in any one of claims 1-7.

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