Cable defect detection method and system based on impedance spectrum imaginary part resonance peak shift

Abstract

This invention discloses a cable defect detection method and system based on the resonant peak shift of the imaginary part of the impedance spectrum. The method includes: measuring the input impedance at the cable end to obtain a data sequence of the imaginary part of the input impedance changing with frequency; preprocessing the data sequence to obtain a measured resonant peak frequency sequence; obtaining a theoretical resonant peak frequency sequence; calculating the frequency shift and peak shift coefficient of each order resonant peak based on the measured and theoretical resonant peak frequency sequences; determining whether there is a unidirectional frequency shift trend, and if so, determining whether there is a latent defect in the cable; performing a frequency domain transformation on the data sequence to obtain the reflection positioning spectrum along the cable length, and calculating the location of the latent defect; determining the type, severity, and spatial scale of the latent defect, and outputting the latent defect detection result. This invention can promptly and accurately detect potential insulation performance problems without damaging the cable, improving the reliability and safety of cable operation.

Description

Technical Field

[0001] This invention belongs to the field of power cable condition detection and fault diagnosis technology, and relates to a cable defect detection method and system based on the offset of the imaginary part resonance peak of the impedance spectrum. Background Technology

[0002] DC power cables may develop latent insulation defects during long-term operation due to manufacturing processes, construction damage, and operating environment, such as insulation deterioration due to moisture, water treeing, or other types of localized insulation aging. These defects are difficult to detect in their early stages, and if not repaired in time, they may develop into serious faults, threatening the safe operation of the power grid. Traditional cable testing methods, such as polarization / depolarization current method (PDC) and time domain reflection method (TDR), are insufficient in locating defects such as localized moisture in the cable body, and cannot detect subtle defects in the cable body in a timely manner. For example, the TDR method has limited high-frequency components in the injected pulse and severe signal dispersion in the cable, making it difficult to locate weak defects in the cable body.

[0003] In recent years, input impedance spectral analysis based on frequency domain reflection (FDR) has attracted attention. Studies have shown that the input impedance spectrum at the cable end contains rich information about transmission characteristics, which can be used for fault location and type identification. Existing literature has proposed methods for diagnosing cable fault types (such as open circuit, short circuit, high impedance, and low impedance faults) and achieving precise location using input impedance spectroscopy. Simultaneously, some studies have applied this frequency domain impedance method to detect cable moisture defects: locating the moisture-affected area by analyzing changes in electrical parameters caused by moisture. These methods demonstrate that broadband impedance spectroscopy testing has high sensitivity and can detect minute defects that are easily overlooked by traditional methods.

[0004] However, mature methods are still lacking for early non-destructive diagnosis of latent insulation defects in cables (such as initial water treeing and slight dampness). While the aforementioned frequency domain methods can locate localized defects with strong impedance discontinuities, their sensitivity to detecting extremely weak changes in dielectric parameters caused by latent defects such as initial water treeing and dampness is limited and needs improvement. Therefore, a novel method is urgently needed to quantify subtle changes in spectral characteristics to achieve early identification and location of latent defects in DC cables. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a cable defect detection method and system based on the shift of the imaginary resonant peak of the impedance spectrum. By quantitatively modeling the phenomenon of the drift of the imaginary resonant peak of the cable input impedance spectrum, the spectral change characteristics caused by latent insulation defects are extracted. This enables highly sensitive detection and precise location of early latent defects inside the cable, such as micro-dampness and water tree aging. It can promptly and accurately detect potential insulation performance problems without damaging the cable, thereby improving the reliability and safety of cable operation.

[0006] The present invention adopts the following technical solution.

[0007] The first aspect of this invention proposes a cable defect detection method based on the shift of the imaginary part resonance peak of the impedance spectrum, comprising: A sweep frequency signal is injected into a DC cable and the input impedance at the cable end is measured to obtain a data sequence of the imaginary part of the input impedance as a function of frequency; the data sequence is preprocessed to obtain a measured resonant peak frequency sequence; and the theoretical resonant peak frequency sequence of the cable under defect-free conditions is obtained. Based on the measured resonant peak frequency sequence and the theoretical resonant peak frequency sequence, calculate the frequency shift and peak shift coefficient of each order of resonant peak; Based on the frequency shift of each order resonance peak, it is determined whether there is a unidirectional frequency shift trend. If so, the resonance migration coherence quantum factor is calculated to determine whether there is a latent defect in the cable. If a latent defect exists, the data sequence is frequency domain transformed to obtain the reflection location spectrum along the cable length. The location of the latent defect is calculated based on the reflection location spectrum. The type, severity, and spatial scale of the latent defect are determined according to the frequency shift and peak shift coefficient, and the latent defect detection result is output.

[0008] Preferably, the step of injecting a sweep frequency signal into the DC cable and measuring the input impedance at the cable's head end to obtain a data sequence showing the change of the imaginary part of the input impedance with frequency specifically includes: A wideband impedance testing device is connected to one end of the DC cable under test. A sweep frequency signal within a set range is injected into the cable, and the input impedance at the beginning of the cable is measured step by step. The data sequence of the imaginary part of the input impedance changing with frequency is recorded.

[0009] Preferably, the acquisition of the theoretical resonant peak frequency sequence of the cable under defect-free conditions is specifically as follows: (1) When the cable dielectric material parameters are known, the theoretical resonant peak frequency sequence can be calculated according to the following formula:

[0010] in, The propagation speed of electromagnetic waves in the cable is obtained based on the cable dielectric material parameters. L n is the cable length; n is the resonance order; For the theoretical first n The frequency of the first resonant peak; (2) When the parameters of the cable dielectric material are unknown, the measured resonant peak frequency sequence of the same type of defect-free cable is used as the theoretical resonant peak frequency sequence.

[0011] Preferably, the step of determining whether there is a unidirectional frequency shift trend based on the frequency shift of each order resonance peak includes: Based on the positive and negative values ​​of the frequency offset, the frequency offset direction of each order resonance peak is analyzed. If the frequency offset direction of resonance peaks exceeding a preset number or a set proportion is consistent, it is determined that there is a frequency offset trend in the same direction.

[0012] Preferably, the formula for calculating the resonant migration coherence quantum factor is as follows:

[0013] in, The resonant migration coherence quantum factor; N This represents the total order of the resonance peaks; For modal sensitivity weights; This represents the frequency offset of the nth-order resonant peak. This represents the average frequency shift of each order of resonant peak. The standard deviation factor of the baseline background noise; This is a unit step function; it takes the value 1 when the value inside the parentheses is greater than or equal to 0, and 0 otherwise. As a direction indicator factor; This is the consistency threshold.

[0014] Preferably, the presence of latent defects in the cable is determined based on the resonant migration coherence quantum factor, as follows: If the resonant migration coherence quantum factor exceeds the preset confidence threshold, the cable is determined to have a latent defect; otherwise, it is determined to be random noise or non-systematic fluctuation, and the detection process ends.

[0015] Preferably, determining the type, severity, and spatial scale of latent defects based on the frequency offset and peak shift coefficient specifically includes: (1) Analyze the frequency shift direction of the resonance peak based on the frequency shift, and determine the type of latent defect based on the frequency shift direction of the resonance peak: if the frequency shift corresponding to the same frequency shift trend is negative, it means that the frequency of the resonance peak shifts to the left, and the latent defect type is capacitive; if the frequency shift corresponding to the same frequency shift trend is positive, it means that the frequency of the resonance peak shifts to the right, and the latent defect type is inductive. (2) Determine the severity of latent defects based on the magnitude of the peak shift coefficient: If the average value of the peak shift coefficient of each order resonance peak corresponding to the same frequency shift trend is higher than the preset threshold, the severity of latent defects is at the maintenance level; otherwise, the severity of latent defects is at the monitoring level. (3) By comparing the peak shift coefficients of different order resonance peaks, the spatial scale of latent defects can be determined: if the difference between the peak shift coefficients of low-order resonance peaks and high-order resonance peaks in the same frequency shift trend exceeds the set value, the latent defect is determined to be a large spatial size defect; otherwise, the latent defect is determined to be a small spatial size defect; where high order refers to order greater than or equal to 10, and low order refers to order greater than or equal to 1 and less than or equal to 5.

[0016] Preferably, the method further includes: after determining that the cable has latent defects, performing the following degradation analysis: 1) Calculate the change in effective dielectric constant of the insulating medium at the defect location based on the following dielectric loss co-inversion equation:

[0017] in, This represents the change in the effective dielectric constant of the insulating medium at the defect location. This is the cable structure proportionality factor; This refers to the cable length. The speed at which electromagnetic waves propagate in a cable; N This represents the total order of the resonance peaks; This represents the frequency offset of the nth-order resonant peak. Here is the loss coupling coefficient; This represents the relative change in the quality factor of the measured nth-order resonance peak. 2) According to The calculation results determine the stage of defect deterioration: if If the calculation results show an order-of-magnitude increase and the correlation coefficient with the relative change of the quality factor shows a logarithmic growth trend not less than the preset value, then it is determined that the defect has entered the rapid deterioration period. 3) Based on the various orders in the aforementioned dielectric loss cooperative inversion equation right The contribution of a defect is used to determine its degradation type: if the ratio of the contribution of a higher-order term to that of a lower-order term is greater than the set ratio, the defect is determined to be a point degradation with high localization; otherwise, it is determined to be segmental aging. Here, n≥10 corresponds to a higher-order term, and 1≤n≤5 corresponds to a lower-order term.

[0018] A second aspect of this invention proposes a cable defect detection system based on the shift of the imaginary part resonance peak of the impedance spectrum, comprising: The data acquisition and processing module is used to inject a sweep frequency signal into the DC cable and measure the input impedance at the cable head end to obtain a data sequence of the imaginary part of the input impedance changing with frequency; to preprocess the data sequence to obtain the measured resonant peak frequency sequence; and to obtain the theoretical resonant peak frequency sequence of the cable under defect-free conditions. The latent defect judgment module is used to calculate the frequency shift and peak shift coefficient of each order resonance peak based on the measured resonance peak frequency sequence and the theoretical resonance peak frequency sequence; to judge whether there is a unidirectional frequency shift trend based on the frequency shift of each order resonance peak; if so, to calculate the resonance migration coherence quantum factor and to judge whether there is a latent defect in the cable; if there is a latent defect, to enter the latent defect detection module. The latent defect detection module is used to perform frequency domain transformation on the data sequence to obtain the reflection location spectrum along the cable length, calculate the location of the latent defect based on the reflection location spectrum, determine the type, severity and spatial scale of the latent defect according to the frequency offset and peak shift coefficient, and output the latent defect detection result.

[0019] A third aspect of the present invention provides a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0020] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0021] Compared with the prior art, the beneficial effects of the present invention include at least the following: This invention obtains a data sequence of the imaginary part of the input impedance as a function of frequency by measuring the input impedance at the beginning of the cable. This data sequence yields the measured resonant peak frequency sequence, which is then compared with the theoretical resonant peak frequency sequence to calculate the resonant peak migration quantification index. This enables the detection of latent defects in DC cables. The process only requires applying a sweep frequency signal to one end of the cable and measuring the impedance response. It causes no mechanical or electrical damage to the cable itself, making it a true online non-destructive testing method. The voltage and current amplitudes during the test are very small, which will not accelerate defect deterioration and is suitable for condition assessment of operating cables.

[0022] This invention utilizes subtle changes in the imaginary part of the input impedance spectrum to detect latent defects that are difficult to detect using traditional methods such as TDR. Simulation and experimental results show that when a local defect in a cable causes a change in capacitance per unit length exceeding approximately 5% or the defect length exceeds 5 cm, this invention can reliably identify the presence of the defect. For such defects, this invention has high identification sensitivity and can effectively detect weak signs of insulation degradation.

[0023] The resonance peak migration quantization index proposed in this invention is the frequency shift of each order resonance peak. With peak shift coefficient This enables the digital characterization of spectral variations. Specifically, it involves monitoring the resonant frequency shift. By analyzing the frequency shift direction of the resonance peak, the type of latent defect can be determined, and the electrical properties of the defect can be identified; Peak shift coefficient obtained by normalization It facilitates the setting of thresholds for automatic judgment of the severity of latent defects and the assistance in judging the spatial scale of defects, thus facilitating condition monitoring and preventive maintenance.

[0024] This invention introduces a resonant migration coherence quantum factor to determine the presence of latent defects in cables. It utilizes modal sensitivity weighting to achieve multimodal information fusion, and reflects the cable's high-frequency sensitivity to minute defects through high-order weight compensation. By integrating information from all order resonance peaks, it improves detection sensitivity and accuracy. Based on a unit step function, it achieves quantitative verification of the consistency of offset directions at each order, solving the problem of false frequency offset caused by system thermal drift or measurement noise in field testing. It can effectively distinguish between latent defects with physical consistency inside the cable and measurement random noise or non-systematic fluctuations, ensuring the reliability of the test results.

[0025] The present invention has a resonant frequency offset. Based on this, by analyzing the direction of resonance peak shift, the electrical nature (capacitive or inductive) of defects can be distinguished. For example, it can be determined whether the defect is due to moisture in the dielectric (capacitive, increasing capacitance) or due to material damage (inductive, decreasing capacitance). The defect type information provided by this invention helps in precise repair, allowing for the development of different repair and handling strategies for different types of defects.

[0026] This invention performs frequency domain transformation on data sequences where the imaginary part of the input impedance varies with frequency, and performs spectral domain positioning based on the principle of frequency domain reflection. This allows for precise location of internal defects without cutting the cable. Compared to traditional methods, this invention significantly improves positioning accuracy, with an error of less than 0.4% for locating cable faults; for defects such as cable dampness, the positioning error can be controlled within 5%, providing maintenance personnel with accurate fault locations and greatly reducing troubleshooting time.

[0027] This invention also establishes a dielectric loss cooperative inversion equation that characterizes the mapping relationship between the resonant peak characteristics and the evolution of physical parameters at the defect. It not only considers the frequency shift, but also introduces the relative change in the quality factor of the measured resonant peak to reflect the broadening effect of the imaginary part of the impedance peak. Furthermore, it corrects the nonlinear contribution of conductivity change to frequency drift through the loss coupling coefficient, which can accurately calculate the change in the effective dielectric constant of the insulating medium at the defect location, so as to effectively assess the defect degradation.

[0028] In summary, this invention, by measuring frequency domain impedance and analyzing the imaginary part of the input impedance spectrum, can detect latent insulation defects in DC cables early, quantitatively, accurately, and non-destructively, providing a scientific basis for cable condition-based maintenance decisions and possessing significant engineering application value. Attached Figure Description

[0029] Figure 1 This is an equivalent model for the distributed parameters of a defective cable.

[0030] Figure 2 This is a flowchart of a cable defect detection method based on the shift of the imaginary part resonance peak of the impedance spectrum. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0032] Embodiment 1 of this invention provides a cable defect detection method based on the shift of the imaginary resonant peak of the impedance spectrum. Based on the principle of frequency domain reflection, it identifies and locates potential defects in the insulation of DC cables by analyzing the imaginary part characteristics of the input impedance spectrum at the cable's head end, overcoming the shortcomings of existing technologies in detecting minute insulation defects. Specifically, the method is as follows: This invention employs a distributed parameter equivalent model of cables to characterize the transmission characteristics of cables in different frequency domains, such as... Figure 1 As shown, the resistance R0, inductance L0, conductance G0, and capacitance C0 are uniformly distributed along the cable. Local defects can manifest as localized changes in these parameters. For example, moisture-induced insulation defects can cause an increase in the dielectric constant of that section, i.e., an increase in capacitance C0 per unit length, while having a smaller impact on L0 and R0.

[0033] According to transmission line theory, the characteristic impedance of a cable and transmission constant They are respectively:

[0034]

[0035] in =2πf is the angular frequency. α It is the attenuation constant. β It is the phase constant, the wave propagation speed in the cable. In the high-frequency band v It is approximately a constant and is related to the dielectric constant and magnetic permeability.

[0036] For a defect-free cable of length L, its end load impedance is: Z L The reflection coefficient of the reflected wave at the end voltage is defined as: .

[0037] If the end is open, that is ,but If the end is short-circuited, that is ,but Characteristic impedance mismatch can also introduce reflections inside the cable.

[0038] For a cable that is open at one end and has no internal defects, its input impedance at the beginning is... Transmission line theory can be used to deduce that: .

[0039] In the case of an open circuit After simplifying the above formula It is a frequency function containing an imaginary part, that is, it exhibits inductive reactance or capacitive reactance characteristics, and its imaginary part exhibits periodic oscillations.

[0040] If we further approximate the loss at high frequencies to be negligible ,but , .

[0041] At this point, the analytical expression for the imaginary part of the input impedance is: Or utilize Equivalent representation as .

[0042] The above expression reveals the conditions for the appearance of resonance peaks: when When a certain value is met, the imaginary part of the input impedance exhibits an extreme value or even an infinite region (under ideal lossless conditions).

[0043] Depend on It can be seen that the imaginary peak of the resonance corresponds to , n =1,2,3…, that is, when the cable length is an integer multiple of half the propagation wavelength: .

[0044] These frequencies f n These are the resonant peak frequencies of the imaginary part of the impedance spectrum. In the open-circuit case, these peak frequencies correspond to the half-wavelength resonance condition of the cable length. The interval between adjacent peak frequencies is approximately... This is inversely proportional to the cable length. When a latent defect exists at a certain point in the cable body, it can be equivalent to introducing an impedance discontinuity at that point. For example, location... A localized damp section of insulation was observed, with a length of [length missing]. .

[0045] Compared to the intact section, the relative permittivity of the dielectric in the damp section increases, leading to a greater capacitance in that section. ,in The capacitance parameters are for the intact segment. This reduces the characteristic impedance of the local segment. Thus in position This results in a capacitive impedance discontinuity. Similarly, if local defects reduce the dielectric constant (such as local insulation material defects, dielectric cracks, etc. leading to equivalent dielectric loss), the dielectric constant will also decrease. (decrease), then This results in a discontinuity due to sensory defects.

[0046] The interfaces at both ends of the defect will produce reflections, denoted as at . Reflectance at location and in Reflectance at location .

[0047] For capacitive defects ( Increase (decrease), have The phase of the reflected wave is reversed relative to the incident wave. ; For the deficiency of emotion ( Decrease (increase) The reflected waves are in the same phase and direction.

[0048] The input impedance of a defective cable can be calculated through segmented transmission line analysis. In short, the cable can be considered as three segments connected in series: From the beginning to the source of the defect intact segments and defective segments to and the remaining intact segment after the defect to the end l .

[0049] By solving the transmission matrix segment by segment, the total input impedance can be obtained. For containing , and end The comprehensive function. The complex derivation formulas are not given here; only the following points will be noted: The existence of local defects makes The imaginary part has changed from a single one The form changes to a superposition of multiple sine terms, reflecting the multiple reflection interference effect.

[0050] Specifically, the defect introduces a length that is longer than the original length. Shorter reflection paths (such as round trip) and These paths, corresponding to new frequency characteristics, will modulate the original resonant modes. This results in a resonant peak shift phenomenon: originally equidistant resonant peaks shift their frequency positions under defect disturbances. For example, for capacitive defects (such as moisture, water trees, etc., which increase local capacitance), the electrical length is effectively lengthened, and the overall resonant frequency shifts to the left and decreases; the more severe the defect (e.g., increased moisture content leading to...), the more pronounced the shift. The more the value increases, the more pronounced the leftward shift of the spectrum. Conversely, for inductive defects (such as reduced capacitance due to decreased local insulation quality), the resonant frequency shifts to the right and increases. This pattern has been verified in simulations and experiments: capacitive defects cause the overall input impedance spectrum to shift to the left and the frequencies of each resonant point to decrease; inductive defects cause the spectral lines to shift to the right and the resonant frequencies to increase. Therefore, by detecting the shift of the imaginary resonant peak of the input impedance spectrum, the presence and nature of defects can be identified.

[0051] Peak shift can be quantitatively described using the resonance condition equation. For example, the resonance of a single defect in a lossless condition approximately satisfies: ,in This represents the additional phase term introduced by the defect, which varies with frequency and depends on the amplitude and phase of the defect reflection coefficient.

[0052] when It is negative (capacitive defect). For the phase delay effect, to satisfy resonance f It decreases compared to when there are no defects; conversely, when... Positive (sensory deficiency) The phase lead effect causes resonance f Increase.

[0053] Solving the above equations yields the new frequencies of the resonance peaks of each order. Its relative offset is defined as follows: Resonance peak mobility For the first n Order resonance peak, ,in For frequencies of the same order in an intact cable, This represents the frequency at which defects exist.

[0054] To facilitate quantitative comparison, a peak shift coefficient or offset rate can be defined: , is used to represent the relative percentage of the resonant peak frequency shift.

[0055] Regarding capacitive defects, Negative values ​​(peak shifted to the left) (A positive value indicates the offset magnitude); for sensory defects, It is a positive value (peak shifted to the right).

[0056] This invention can select the first-order resonance peak ( n offset of =1) As a quantitative indicator characterizing the severity of latent defects; the more severe the defect, the higher the severity. The larger the peak shift, the better. If necessary, averaging multiple peak shifts can also be used to improve robustness.

[0057] like Figure 2 As shown, this invention utilizes the aforementioned spectral model to achieve non-destructive testing of latent defects in cables through the following steps: S1: Inject a sweep frequency signal into the DC cable and measure the input impedance at the cable end to obtain a data sequence showing the change of the imaginary part of the input impedance with frequency. ; More preferably, a broadband impedance testing device is connected to one end of the DC cable under test, and a sweep frequency signal in the range of 150kHz to 100MHz is injected into the cable to gradually measure the input impedance at the cable's beginning. Within this frequency band, multiple-order resonant responses can be excited over a length of tens to hundreds of meters of the cable. The key focus is on recording the data sequence of the imaginary part of the input impedance as a function of frequency. .

[0058] S2: For the data sequence Preprocessing was performed to obtain the measured resonant peak frequency sequence; and the theoretical resonant peak frequency sequence of the cable under defect-free conditions was also obtained. ; More preferably, the acquired impedance spectrum data is subjected to necessary smoothing and noise reduction processing to eliminate the influence of high-frequency measurement noise.

[0059] Based on the known parameters of the cable (length) L (Based on parameters such as dielectric material, etc.) or by referring to data from similar defect-free cables, calculate the theoretical resonant peak frequency under ideal conditions. f n The sequence serves as a benchmark. If a reference is lacking, an ideal formula can be used. First, estimate the reference resonant interval. That is: (1) When the cable dielectric material parameters are known, the theoretical resonant peak frequency sequence can be calculated according to the following formula:

[0060] in, The wave propagation speed in the cable (the propagation speed of electromagnetic waves in the cable) is obtained based on the cable dielectric material parameters. L n is the cable length; n is the resonance order; For the theoretical first n The frequency of the first resonant peak; (2) When the parameters of the cable dielectric material are unknown, the measured resonant peak frequency sequence of a defect-free cable of the same type is used as the theoretical resonant peak frequency sequence. .

[0061] S3: Based on the measured resonant peak frequency sequence and the theoretical resonant peak frequency sequence Calculate the frequency shift of each order resonance peak With peak shift coefficient ; Frequency shift based on each order of resonant peak Determine if there is a frequency shift trend in the same direction. If so, determine the frequency shift based on the resonant peaks of each order. Calculate the resonant migration coherence quantum factor To determine whether the cable has latent defects, if it is determined that the cable has latent defects, proceed to S4; More preferably, after processing Search for local peak points on the curve and record the positions of each resonance peak. and amplitude. Compare these peak frequencies with the reference. Compare and calculate the peak value. offset and peak shift coefficient If multiple peaks are found to exhibit a significant and unidirectional shift trend (e.g., all moving towards lower frequencies), it is preliminarily determined that the cable has a corresponding type of potential defect.

[0062] In this embodiment, based on the measured resonant peak frequency sequence and the theoretical resonant peak frequency sequence Calculate the frequency shift of each order resonance peak With peak shift coefficient ,include: Search for local peak points on the measured resonant peak frequency sequence curve. and the theoretical resonant peak frequency sequence By comparison, the frequency shifts of the resonance peaks of each order were obtained. ; according to and Calculate peak shift coefficient ; in, For the actual measurement n Order resonance peak frequency, For the theoretical first n The frequency of the first resonant peak.

[0063] Frequency shift based on each order of resonant peak Determining whether there is a same-direction frequency shift trend includes: Based on frequency offset The positive and negative cases are analyzed to determine the frequency shift direction of each order resonance peak. If the frequency shift direction of multiple order resonance peaks exceeds a preset number or a set proportion, it is determined that there is a unidirectional frequency shift trend. Here, a quick judgment is made on the overall general direction of the frequency shift, for example, 80% of the peaks show a unidirectional shift. Then, the shift direction of each peak is considered individually in the following text. The consistency of the shift direction of all peaks is analyzed comprehensively to obtain the multimodal resonance migration coherence quantum factor.

[0064] Specifically, to address the issue of spurious frequency shifts caused by system thermal drift or measurement noise during field testing, this invention proposes a quantitative index for determining the existence of defects: the resonant migration coherence quantum factor. :

[0065] in, N The total number of effective resonance peaks selected for analysis; n is the resonance order; The modal sensitivity weights are used to compensate for the high-frequency sensitivity of the cable to minute defects through higher-order weights. This is a unit step function; it takes the value 1 when the value inside the parentheses is greater than or equal to 0, and 0 otherwise. As a direction indicator factor; The preset consistency threshold is set between 0.7 and 0.9, meaning that when 70%-90% of the resonance peaks are in the same direction, the system considers them to have physical consistency and continues to execute the detection process.

[0066] Specifically, direction indicator factor Determined based on the direction of the same-direction frequency offset trend: If the frequency shift trend is positive, that is... N Frequency shift of most of the resonant peaks If positive, then the direction indicator factor Take 1; If the frequency shift trend is negative, that is... N Frequency shift of most of the resonant peaks If it is negative, then the direction indicator factor is... Pick 1.

[0067] The system acquires the frequency shift of each order resonance peak. Subsequently, the order of resonance peaks with the same offset direction was counted as a percentage of the total number of orders analyzed. proportion ; If this ratio is not less than the preset consistency threshold ( The preferred value range is 0.7-0.9, and it is usually greater than or equal to the set ratio used when judging the same-direction frequency shift trend. If so, the spectral shift is judged to have physical consistency, and the directional consistency coefficient is determined to be... = The value is 1.

[0068] If the consistency ratio is lower than the threshold ,but If the value is 0, the system determines that the measurement result is random noise or non-systematic fluctuation and directly terminates the detection process.

[0069] The coherent Gaussian kernel function measures the deviation of peak shift at each order from the average migration. ( That is, the frequency shift of each order resonance peak. The degree of the mean; the Gaussian kernel function The physical essence of this is to measure the dispersion of peak shifts of each order relative to the average level. If the shifts of all peaks have high coherence, then... As the kernel value approaches 0, the kernel function value approaches 1, thus increasing the quantum factor. The value.

[0070] The standard deviation factor of the baseline background noise:

[0071] in, This indicates the number of times a defect-free cable (or the same cable in a defect-free state) is repeatedly measured; For the first i In the measurement, the first n Measured frequency values ​​of the order resonance peak; For the first n The order resonance peak at M The average frequency value in this measurement.

[0072] The system substitutes the frequency shifts of each order resonance peak into the formula for the coherence quantum factor of multimode resonance migration. ,include: like If the value exceeds a preset confidence threshold, it is determined to be a latent defect with physical consistency inside the cable, excluding random environmental interference; if If the preset confidence threshold is not exceeded, it is determined to be random noise or non-systematic fluctuation, and the detection process ends.

[0073] S4: For the data sequence A frequency domain transformation is performed to obtain the reflection location spectrum along the cable length, and the location of latent defects is calculated based on the reflection location spectrum; More preferably, the imaginary part of the input impedance is treated as a frequency domain signal, and its spatial distribution information is obtained through spectral domain transformation. Specifically, this can be achieved by... Perform a Discrete Fourier Transform (DFT) or a better Windowed Fourier Transform (WFT) to obtain the reflection location spectrum along the cable length. On the obtained location spectrum, the defect location... and end This will correspond to a distinct reflection peak. The delay (or frequency) corresponding to the location peak will be calculated. And combine this with the known wave speed (the speed at which electromagnetic waves propagate in a cable). The distance from the defect to the test end (cable head end) can be calculated: ,in The round-trip propagation time of the defect reflection (the delay corresponding to the reflection peak on the reflection localization spectrum) is inversely proportional to the frequency domain peak position. This allows for the determination of the location of latent defects. When necessary, this invention employs a high-resolution window function to reduce spectral leakage errors and improve localization accuracy.

[0074] S5: Based on the frequency offset With peak shift coefficient Determine the type, severity, and spatial scale of latent defects, and output the latent defect detection results.

[0075] More preferably, the nature and severity of the defect are comprehensively evaluated by combining the resonance peak shift index and the location results. If the peak frequency shifts to the left and the reflection coefficient... A negative peak shift indicates a capacitive defect (possibly due to moisture, water trees, etc.); conversely, a rightward peak shift corresponds to an inductive defect (material aging or shielding damage, etc.). Peak Shift Coefficient The size reflects the degree of defect; if it exceeds a preset threshold (e.g.) This indicates that the defect has reached a detectable level. Comparing the peak shifts of different orders can also help determine the spatial scale of the defect: larger defects will affect the positions of lower and higher order peaks, while very small defects will have a more significant impact on higher order short wavelength components.

[0076] Finally, the defect detection results are output, including the determined defect location, type (capacitive / sensitive), and quantified severity index. If If the indicators show minor defects (below the threshold), subsequent periodic monitoring can be arranged; if the indicators significantly exceed the limits, it indicates a high potential risk of failure, and cable repair or replacement or remedial measures should be arranged in a timely manner.

[0077] In this embodiment, based on the frequency offset With peak shift coefficient Determining the type, severity, and spatial scale of latent defects includes: (1) Based on frequency offset Analyze the frequency shift direction of the resonance peak, and determine the type of latent defect based on the frequency shift direction of the resonance peak: If the frequency shift trend corresponds to the frequency shift amount A negative value indicates that the frequency of the resonance peak shifts to the left, and the latent defect type is capacitive. If the frequency shift trend corresponds to the frequency shift amount If the value is positive, it indicates that the frequency of the resonance peak shifts to the right, and the latent defect type is inductive. Understandably, a single latent defect can cause a unidirectional change in the equivalent electrical parameters of a cable, resulting in a general unidirectional shift of the quantized resonant peaks of the imaginary part of the impedance spectrum across multiple orders: capacitive defects correspond to an increase in equivalent electrical length and a decrease in the overall resonant frequency to the left, while inductive defects correspond to a decrease in equivalent electrical length and a increase in the overall resonant frequency to the right. Therefore, under the condition of correct peak matching, the multi-order frequency shifts... The signs should remain consistent, and there should be no necessary alternation between positive and negative signs or abrupt changes in type. Furthermore, in step S3, this method explicitly uses the consistent frequency shift direction of multiple-order resonant peaks exceeding a preset number or a set proportion as a criterion for the same-direction trend. Only when this same-direction migration trend is satisfied will the subsequent defect type determination proceed.

[0078] (2) Based on the peak shift coefficient The size determines the severity of latent defects: If the corresponding frequency shift trend is in the same direction If the average value is higher than the preset threshold, then the severity of the latent defect is the maintenance level. If the corresponding frequency shift trend is in the same direction If the mean value is not higher than the preset threshold, then the severity of the latent defect is the monitoring level. (3) By comparing the peak shift coefficients of different order resonant peaks in the same frequency shift trend. Spatial scale for aiding in the assessment of defects: If the peak shift coefficients of lower-order resonance peaks and higher-order resonance peaks If the difference exceeds the set value, the latent defect is determined to be a large-space size defect, where the lower-order preferred value is 1≤n≤5 and the higher-order preferred value is n≥10; Otherwise, the latent defect is determined to be a small-space-size defect.

[0079] This invention further establishes a mapping relationship between the characteristics of the resonance peak and the evolution of physical parameters at the defect using perturbation theory. Latent defects (such as moisture) not only cause phase delay but also lead to energy dissipation due to increased dielectric loss angle. Therefore, a dielectric loss cooperative inversion equation is proposed to quantitatively assess the degree of local aging:

[0080] in, The change in the effective dielectric constant of the insulating medium at the defect location is the direct target of the inversion equation, which directly reflects the evolution of the physical properties of the insulating medium. This is a cable structure proportionality coefficient, which is related to the cable radius and the thickness of the shielding layer; ,in R The outer radius of the insulation layer, r The outer radius of the conductor shielding layer.

[0081] This refers to the cable length. The propagation speed of electromagnetic waves in a cable; propagation characteristic parameters and This determines the conditions under which resonance occurs; N The total number of effective resonance peaks; n is the resonance order; This is a frequency sensitivity correction factor used to balance the response weights of different order resonances under dispersion effects; For the actual measurement n The relative change in the quality factor of the order resonance peak, i.e. This reflects the broadening effect of the imaginary part peak shape of the impedance, where To measure the quality factor of the nth order resonance peak, It is the quality factor of the theoretical nth order resonance peak.

[0082] This is the loss coupling coefficient, used to correct the nonlinear contribution of conductivity changes to frequency drift (for cross-linked polyethylene insulated DC cables commonly used in power systems). The value of is typically between 0.05 and 0.25. Increased dielectric loss leads to energy dissipation at the resonance peak. Capture the characteristic changes caused by this loss; This is used to ensure that the dielectric constant can still be accurately inverted even when losses are high.

[0083] like The calculation results show an order-of-magnitude increase, and are consistent with... If a strong logarithmic growth trend is observed (a correlation coefficient of not less than 0.85 can be selected as a reference), then the defect has entered a period of rapid deterioration.

[0084] By comparing the different orders in the formula The contribution distribution of the weights indicates that if the local dielectric change inverted by the higher-order terms is much greater than that of the lower-order terms, the defect is judged to be a highly localized point-like degradation (initial puncture or microbubble). For example, if there is a 5mm bubble defect in the insulation of a cable, the phase shift caused by the defect is extremely small because its half wavelength is much larger than the defect size, and the local sensitivity of high-frequency signals is extremely high. The local effective dielectric constant inverted by the defect may reach 3-5 times the reference value. Otherwise, it is judged to be segmental aging (localized damp area).

[0085] Among them, each level The contribution of the weights is reflected in the dielectric loss cooperative inversion equation. right (specifically) ) contributions.

[0086] The local dielectric change derived from higher-order terms, i.e., the change corresponding to higher-order terms such as n≥10. In total The percentage of contribution.

[0087] The final system will A health score, normalized to 0-100, serves as the sole digital criterion for cable condition inspection or immediate replacement. For example, a health score of 85-100 indicates that the cable is in good condition and can be monitored and inspected online according to the usual schedule; 60-85 indicates that the inspection cycle needs to be shortened and the evolution trend of defects needs to be tracked; 40-60 indicates that the cable needs targeted power outage inspection or local repair of the defect location; and below 40 indicates an extremely high risk of breakdown, requiring immediate replacement or emergency power outage.

[0088] Embodiment 2 of the present invention provides a cable defect detection system based on the resonant peak shift of the imaginary part of the impedance spectrum, comprising: The data acquisition and processing module is used to inject a sweep frequency signal into the DC cable and measure the input impedance at the cable end to obtain a data sequence of the imaginary part of the input impedance as a function of frequency. ; for the data sequence Preprocessing was performed to obtain the measured resonant peak frequency sequence; and the theoretical resonant peak frequency sequence of the cable under defect-free conditions was also obtained. ; The latent defect detection module is used to determine the latent defect based on the measured resonant peak frequency sequence and the theoretical resonant peak frequency sequence. Calculate the frequency shift of each order resonance peak With peak shift coefficient Frequency shift based on each order resonance peak Determine if there is a frequency shift trend in the same direction. If so, determine the frequency shift based on the resonant peaks of each order. Calculate the resonant migration coherence quantum factor To determine whether the cable has latent defects, if it is determined that the cable has latent defects, it will proceed to the latent defect detection module. The latent defect detection module is used to analyze the data sequence. A frequency domain transformation is performed to obtain the reflection location spectrum along the cable length. The location of latent defects is calculated based on this reflection location spectrum; and the frequency offset is then used to determine the location. With peak shift coefficient Determine the type, severity, and spatial scale of latent defects, and output the latent defect detection results.

[0089] More preferably, the data acquisition and processing module is equipped with a reference spectrum generation unit, which can generate a theoretical resonant frequency sequence based on the known cable length L and wave velocity v: ; The latent defect detection module uses the local processor to call the extreme value search algorithm to extract the measured imaginary part. Local extreme points f' n and with f n In comparison, the resonance offset data Δ is formed. f n The local computing core includes a resonance peak mobility coefficient generation unit, used to calculate the following offset indices: The K n Used to identify the presence of defects and determine the type of defect. K n >0 and f' n < f n (This is a defect in tolerance; conversely, it is a defect in intuition.)

[0090] The latent defect detection module will process the imaginary part data obtained by the data acquisition and processing module. The data is further input to an FFT transform unit, which maps the spectrum to a positional reflection spectrum and identifies the reflection peak delay. Combined with wave speed v Calculate the location of the defect: ,in, This is the distance from the defect to the beginning of the cable; The wave velocity in the cable; This is the time delay corresponding to the reflection peak on the reflection localization spectrum.

[0091] The latent defect detection module can also be used to perform the following degradation analysis on defects: 1) Calculate the change in effective dielectric constant of the insulating medium at the defect location based on the following dielectric loss co-inversion equation:

[0092] in, This represents the change in the effective dielectric constant of the insulating medium at the defect location. This is the cable structure proportionality factor; This refers to the cable length. The speed at which electromagnetic waves propagate in a cable; N The total number of effective resonance peaks; n is the resonance order; This is a frequency sensitivity correction factor used to balance the response weights of different order resonances under dispersion effects; For the actual measurement n The relative change in the quality factor of the order resonance peak, i.e. This reflects the broadening effect of the imaginary part peak shape of the impedance, where To measure the quality factor of the nth order resonance peak, It is the quality factor of the theoretical nth order resonance peak.

[0093] is the loss coupling coefficient.

[0094] 2) According to The calculation results determine the stage of defect deterioration: like The calculation results show an order-of-magnitude increase, and are consistent with... If a strong logarithmic growth trend is observed, it can be determined that the defect has entered a period of rapid deterioration. 3) Based on the various orders in the aforementioned dielectric loss cooperative inversion equation The contribution distribution of weights determines the type of defect degradation. By comparing the different orders in the dielectric loss cooperative inversion equation If the local dielectric change derived from higher-order terms is much greater than that from lower-order terms, the defect is determined to be a highly localized point-like degradation (initial puncture or microbubble); otherwise, it is determined to be segmental aging (localized damp areas).

[0095] 4) A health score, normalized to 0-100, serves as the sole digital criterion for determining cable condition and whether it should be replaced immediately.

[0096] Embodiment 3 of the present invention provides a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0097] Embodiment 4 of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0098] Compared with the prior art, the beneficial effects of the present invention include at least the following: This invention obtains a data sequence of the imaginary part of the input impedance as a function of frequency by measuring the input impedance at the beginning of the cable. This data sequence yields the measured resonant peak frequency sequence, which is then compared with the theoretical resonant peak frequency sequence to calculate the resonant peak migration quantification index. This enables the detection of latent defects in DC cables. The process only requires applying a sweep frequency signal to one end of the cable and measuring the impedance response. It causes no mechanical or electrical damage to the cable itself, making it a true online non-destructive testing method. The voltage and current amplitudes during the test are very small, which will not accelerate defect deterioration and is suitable for condition assessment of operating cables.

[0099] This invention utilizes subtle changes in the imaginary part of the input impedance spectrum to detect latent defects that are difficult to detect using traditional methods such as TDR. Simulation and experimental results show that when a local defect in a cable causes a change in capacitance per unit length exceeding approximately 5% or the defect length exceeds 5 cm, this invention can reliably identify the presence of the defect. For such defects, this invention has high identification sensitivity and can effectively detect weak signs of insulation degradation.

[0100] The resonance peak migration quantization index proposed in this invention is the frequency shift of each order resonance peak. With peak shift coefficient This enables the digital characterization of spectral variations. Specifically, it involves monitoring the resonant frequency shift. It can quantitatively assess the development trend of defects; for example, the increase in insulation moisture over time will lead to a peak shift coefficient. Gradually increasing in size facilitates condition monitoring and preventative maintenance. Specifically, the resonant frequency offset... It is mainly used to characterize the polarity direction of spectral shift, thereby pinpointing the electrical properties of defects. The specific correlation is as follows: If A negative value indicates that the resonance peak shifts to lower frequencies due to increased local capacitance, which is identified as a capacitive defect; if If the value is positive, it is judged as a deficiency in emotional perception. Furthermore, Peak shift coefficients generated after normalization This is then used to further quantify the severity of the defect. Peak shift coefficient It facilitates the setting of thresholds for automatic judgment of the severity of latent defects and assists in judging the spatial scale of defects.

[0101] This invention introduces a resonant migration coherence quantum factor to determine the presence of latent defects in cables. It utilizes modal sensitivity weighting to achieve multimodal information fusion, and reflects the cable's high-frequency sensitivity to minute defects through high-order weight compensation. By integrating information from all order resonance peaks, it improves detection sensitivity and accuracy. Based on a unit step function, it achieves quantitative verification of the consistency of offset directions at each order, solving the problem of false frequency offset caused by system thermal drift or measurement noise in field testing. It can effectively distinguish between latent defects with physical consistency inside the cable and measurement random noise or non-systematic fluctuations, ensuring the reliability of the test results.

[0102] The present invention has a resonant frequency offset. Based on this, by analyzing the direction of resonance peak shift, the electrical nature (capacitive or inductive) of defects can be distinguished. For example, it can be determined whether the defect is due to moisture in the dielectric (capacitive, increasing capacitance) or due to material damage (inductive, decreasing capacitance). The defect type information provided by this invention helps in precise repair, allowing for the development of different repair and handling strategies for different types of defects.

[0103] This invention performs frequency domain transformation on data sequences where the imaginary part of the input impedance varies with frequency, and performs spectral domain positioning based on the principle of frequency domain reflection. This allows for precise location of internal defects without cutting the cable. Compared to traditional methods, this invention significantly improves positioning accuracy, with an error of less than 0.4% for locating cable faults; for defects such as cable dampness, the positioning error can be controlled within 5%, providing maintenance personnel with accurate fault locations and greatly reducing troubleshooting time.

[0104] This invention also establishes a dielectric loss cooperative inversion equation that characterizes the mapping relationship between the resonant peak characteristics and the evolution of physical parameters at the defect. It not only considers the frequency shift, but also introduces the relative change in the quality factor of the measured resonant peak to reflect the broadening effect of the imaginary part of the impedance peak. Furthermore, it corrects the nonlinear contribution of conductivity change to frequency drift through the loss coupling coefficient, which can accurately calculate the change in the effective dielectric constant of the insulating medium at the defect location, so as to effectively assess the defect degradation.

[0105] In summary, this invention, by measuring frequency domain impedance and analyzing the imaginary part of the input impedance spectrum, can detect latent insulation defects in DC cables early, quantitatively, accurately, and non-destructively, providing a scientific basis for cable condition-based maintenance decisions and possessing significant engineering application value.

[0106] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0107] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0108] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0109] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for detecting defects in a cable based on the shift of the resonance peak of the imaginary part of the impedance spectrum, characterized in that, The method includes: A sweep frequency signal is injected into a DC cable and the input impedance at the cable end is measured to obtain a data sequence of the imaginary part of the input impedance as a function of frequency; the data sequence is preprocessed to obtain a measured resonant peak frequency sequence; and the theoretical resonant peak frequency sequence of the cable under defect-free conditions is obtained. Based on the measured resonant peak frequency sequence and the theoretical resonant peak frequency sequence, calculate the frequency shift and peak shift coefficient of each order of resonant peak; Based on the frequency shift of each order resonance peak, it is determined whether there is a unidirectional frequency shift trend. If so, the resonance migration coherence quantum factor is calculated to determine whether there is a latent defect in the cable. If a latent defect exists, the data sequence is frequency domain transformed to obtain the reflection location spectrum along the cable length. The location of the latent defect is calculated based on the reflection location spectrum. The type, severity, and spatial scale of the latent defect are determined according to the frequency shift and peak shift coefficient, and the latent defect detection result is output.

2. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The process of injecting a sweep frequency signal into the DC cable and measuring the input impedance at the cable's head end to obtain a data sequence showing the imaginary part of the input impedance changing with frequency specifically includes: A wideband impedance testing device is connected to one end of the DC cable under test. A sweep frequency signal within a set range is injected into the cable, and the input impedance at the beginning of the cable is measured step by step. The data sequence of the imaginary part of the input impedance changing with frequency is recorded.

3. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The theoretical resonant peak frequency sequence of the cable under defect-free conditions is obtained as follows: (1) When the cable dielectric material parameters are known, the theoretical resonant peak frequency sequence can be calculated according to the following formula: in, The propagation speed of electromagnetic waves in the cable is obtained based on the cable dielectric material parameters. L n is the cable length; n is the resonance order; For the theoretical first n The frequency of the first resonant peak; (2) When the parameters of the cable dielectric material are unknown, the measured resonant peak frequency sequence of the same type of defect-free cable is used as the theoretical resonant peak frequency sequence.

4. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The determination of whether there is a unidirectional frequency shift trend based on the frequency shift of each order resonance peak includes: Based on the positive and negative values ​​of the frequency offset, the frequency offset direction of each order resonance peak is analyzed. If the frequency offset direction of resonance peaks exceeding a preset number or a set proportion is consistent, it is determined that there is a frequency offset trend in the same direction.

5. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The formula for calculating the resonant migration coherence quantum factor is as follows: in, The resonant migration coherence quantum factor; N This represents the total order of the resonance peaks; For modal sensitivity weights; This represents the frequency offset of the nth-order resonant peak. This represents the average frequency shift of each order of resonant peak. The standard deviation factor of the baseline background noise; This is a unit step function; it takes the value 1 when the value inside the parentheses is greater than or equal to 0, and 0 otherwise. As a direction indicator factor; This is the consistency threshold.

6. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The presence of latent defects in a cable is determined based on the resonant migration coherence quantum factor, as follows: If the resonant migration coherence quantum factor exceeds the preset confidence threshold, the cable is determined to have a latent defect; otherwise, it is determined to be random noise or non-systematic fluctuation, and the detection process ends.

7. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The latent defect type, severity, and spatial scale are determined based on the frequency offset and peak shift coefficient, specifically including: (1) Analyze the frequency shift direction of the resonance peak based on the frequency shift, and determine the type of latent defect based on the frequency shift direction of the resonance peak: if the frequency shift corresponding to the same frequency shift trend is negative, it means that the frequency of the resonance peak shifts to the left, and the latent defect type is capacitive; if the frequency shift corresponding to the same frequency shift trend is positive, it means that the frequency of the resonance peak shifts to the right, and the latent defect type is inductive. (2) Determine the severity of latent defects based on the magnitude of the peak shift coefficient: If the average value of the peak shift coefficient of each order resonance peak corresponding to the same frequency shift trend is higher than the preset threshold, the severity of latent defects is at the maintenance level; otherwise, the severity of latent defects is at the monitoring level. (3) By comparing the peak shift coefficients of different order resonance peaks, the spatial scale of latent defects can be determined: if the difference between the peak shift coefficients of low-order resonance peaks and high-order resonance peaks in the same frequency shift trend exceeds the set value, the latent defect is determined to be a large spatial size defect; otherwise, the latent defect is determined to be a small spatial size defect; where high order refers to order greater than or equal to 10, and low order refers to order greater than or equal to 1 and less than or equal to 5.

8. The cable defect detection method based on the resonant peak shift of the imaginary part of the impedance spectrum according to claim 1, characterized in that: The method further includes: after determining that the cable has latent defects, performing the following degradation analysis: 1) Calculate the change in effective dielectric constant of the insulating medium at the defect location based on the following dielectric loss co-inversion equation: in, This represents the change in the effective dielectric constant of the insulating medium at the defect location. This is the cable structure proportionality factor; This refers to the cable length. The speed at which electromagnetic waves propagate in a cable; N This represents the total order of the resonance peaks; This represents the frequency offset of the nth-order resonant peak. Here is the loss coupling coefficient; This represents the relative change in the quality factor of the measured nth-order resonance peak. 2) According to The calculation results determine the stage of defect deterioration: if If the calculation results show an order-of-magnitude increase and the correlation coefficient with the relative change of the quality factor shows a logarithmic growth trend not less than the preset value, then the defect has entered a rapid deterioration period. 3) Based on the various orders in the aforementioned dielectric loss cooperative inversion equation right The contribution of the defect is used to determine the type of degradation: if the ratio of the contribution of higher-order terms to the contribution of lower-order terms is greater than the set ratio, the defect is determined to be point degradation with high localization; otherwise, it is determined to be segmental aging. Among them, n≥10 corresponds to higher-order terms, and 1≤n≤5 corresponds to lower-order terms.

9. A cable defect detection system based on the shift of the resonance peak of the imaginary part of the impedance spectrum, operating the method of any of claims 1-8, characterized in that, The system includes: The data acquisition and processing module is used to inject a sweep frequency signal into the DC cable and measure the input impedance at the cable head end to obtain a data sequence of the imaginary part of the input impedance changing with frequency; to preprocess the data sequence to obtain the measured resonant peak frequency sequence; and to obtain the theoretical resonant peak frequency sequence of the cable under defect-free conditions. The latent defect judgment module is used to calculate the frequency shift and peak shift coefficient of each order resonance peak based on the measured resonance peak frequency sequence and the theoretical resonance peak frequency sequence; to judge whether there is a unidirectional frequency shift trend based on the frequency shift of each order resonance peak; if so, to calculate the resonance migration coherence quantum factor and to judge whether there is a latent defect in the cable; if there is a latent defect, to enter the latent defect detection module. The latent defect detection module is used to perform frequency domain transformation on the data sequence to obtain the reflection location spectrum along the cable length, calculate the location of the latent defect based on the reflection location spectrum, determine the type, severity and spatial scale of the latent defect according to the frequency offset and peak shift coefficient, and output the latent defect detection result.

10. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-8.

11. A computer readable storage medium having stored thereon a computer program, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-8.

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