A method and system for cable impedance spectroscopy defect localization

Abstract

The application discloses a kind of cable impedance spectrum defect positioning method and system, belong to cable defect positioning technical field, method includes: using impedance analyzer measurement cable to be measured, obtain the head end input impedance spectrum of cable to be measured, and compare with the head end input impedance spectrum of healthy cable, judge whether the cable to be measured exists defect;If there is defect, a plurality of temperature data in the circumferential direction of intermediate joint are acquired, and the temperature difference of peak value and valley value temperature data is used to determine whether the cable to be measured has aged, if it does not occur aging, then using the head end input impedance spectrum of the cable to be measured obtained, directly using frequency domain reflection method to carry out cable defect positioning, if it occurs aging, then according to aging degree compensation the head end input impedance spectrum of the cable to be measured obtained, and based on the head end input impedance spectrum after compensation using frequency domain reflection method to carry out cable defect positioning.The application can weaken the interference of uneven aging on defect positioning, realize the accurate positioning of cable defect.

Description

Technical Field

[0001] This invention belongs to the field of cable defect location technology, specifically relating to a method and system for locating cable impedance spectrum defects. Background Technology

[0002] Currently, with the continuous increase in the number of urban power distribution network cables put into operation and their service life, defect location of cross-linked polyethylene (XLPE) cables has gradually become a research focus in the power industry. At present, cable defect location technologies mainly include impedance methods, partial discharge methods, and reflection methods. Due to the drawbacks of impedance methods and partial discharge methods, such as large errors, low sensitivity, cumbersome measurement procedures, and significant susceptibility to external signals, reflection methods are commonly used in practical engineering for cable defect detection.

[0003] The reflection method often refers to the frequency domain reflection method, which involves inputting a low-voltage, high-frequency signal into the cable, measuring the cable's broadband impedance spectrum, and then using relevant algorithms to transform the impedance spectrum function from the broadband domain to the time domain. This allows us to obtain a graph showing the relationship between the cable's internal impedance matching and its length. The point where the impedance mismatch is most severe is the specific location of the cable defect.

[0004] However, in actual distribution network cables, under the influence of electric field force in long-term high-voltage environments (10kV and above), they are prone to aging. This aging is often uneven and widespread, which leads to a large amount of useless impedance mismatch information in the impedance spectrum function obtained by the frequency domain reflection method. This causes the local defects that actually exist to be obscured, seriously affecting the accurate location of cable defects by operation and maintenance personnel. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method and system for locating cable impedance spectrum defects, which can reduce the interference of uneven aging on defect location and achieve accurate location of cable defects.

[0006] This invention provides the following technical solution: Firstly, a method for locating defects in cable impedance spectrum is provided, including: The impedance analyzer is used to measure the input impedance spectrum of the cable under test, and the spectrum is compared with the input impedance spectrum of the cable under test to determine whether there is a defect in the cable under test. If a defect is found, several temperature data points are collected around the intermediate joint. The temperature difference between the peak and valley values ​​is used to determine whether the cable under test has aged. If no aging has occurred, the frequency domain reflection method is used directly to locate the cable defect using the obtained input impedance spectrum at the beginning of the cable under test. If aging has occurred, the input impedance spectrum at the beginning of the cable under test is compensated according to the degree of aging, and the frequency domain reflection method is used to locate the cable defect based on the compensated input impedance spectrum at the beginning of the cable.

[0007] Optionally, the step of collecting several temperature data points around the intermediate joint and using the temperature difference between the peak and valley values ​​to determine whether the cable under test has aged is specifically as follows: Temperature data of the intermediate joint is collected by six temperature sensors that are evenly surrounded around the circumference of the intermediate joint of the cable under test. The three harmonic Fourier model was used to fit the temperature data collected multiple times to obtain the peak and valley temperatures of the intermediate joint surface, and the maximum temperature difference of the intermediate joint was obtained. Determine whether the maximum temperature difference of the intermediate joint of the cable under test exceeds the set threshold. If it does, aging has occurred; otherwise, no aging has occurred.

[0008] Alternatively, the curve fitting can take the form of: ; in, Position and angle variables temperature, The DC component, For the order of harmonics, and The first k The sine and cosine coefficients of the subharmonic.

[0009] Optionally, the input impedance spectrum at the beginning of the cable under test obtained based on the aging degree compensation is specifically obtained in the following manner: ; in, The impedance value of the cable under test after aging compensation. The frequency point in the input impedance spectrum of the cable under test. f The corresponding impedance value, This is the aging temperature rise compensation coefficient. The maximum temperature difference at the intermediate joint of the cable under test. This is a temperature coefficient function pre-fitted using aging data.

[0010] Optionally, the input impedance spectrum of the first end of the healthy cable is obtained through transmission line theory. Specifically, the healthy cable is equivalent to a distributed parameter model, and the distributed parameters are modeled to obtain the distributed parameters of the healthy cable. Then, the input impedance of the first end of the healthy cable is obtained by the ratio of voltage and current at any position from the first end of the cable.

[0011] Secondly, a cable impedance spectrum defect location system is provided, comprising: An impedance analyzer is used to measure the cable under test and obtain the input impedance spectrum at the beginning of the cable. The defect detection module is used to compare the input impedance spectrum of the first end of the cable under test with that of a healthy cable to determine whether there is a defect in the cable under test. The aging judgment module is used to collect several temperature data points on the circumference of the intermediate joint when there are defects in the cable under test, and to use the temperature difference between the peak and valley temperature data to determine whether the cable under test has aged. The defect location module is used to locate cable defects directly using the frequency domain reflection method when no aging has occurred, by utilizing the obtained input impedance spectrum of the cable under test at the beginning of the test. When aging has occurred, the module compensates the obtained input impedance spectrum of the cable under test at the beginning of the test according to the degree of aging, and then uses the frequency domain reflection method to locate cable defects based on the compensated input impedance spectrum at the beginning of the test.

[0012] Optionally, the aging determination module includes: Temperature sensors, six of which are evenly arranged around the circumference of the intermediate joint of the cable under test; The data acquisition submodule is used to acquire temperature data of the intermediate joint; The temperature difference acquisition module is used to perform curve fitting on the temperature data collected multiple times using the three harmonic Fourier model to obtain the surface peak and valley temperatures of the intermediate joint, and to obtain the maximum temperature difference of the intermediate joint. The aging determination submodule is used to determine whether the maximum temperature difference of the intermediate joint of the cable under test exceeds the set threshold. If it does, aging occurs; otherwise, no aging occurs.

[0013] Thirdly, a computer device is provided, including a processor and a memory; wherein, when the processor executes a computer program stored in the memory, it implements the steps of the cable impedance spectrum defect location method according to any one of the first aspects.

[0014] Fourthly, a computer-readable storage medium is provided for storing a computer program; when the computer program is executed by a processor, it implements the steps of the cable impedance spectrum defect location method according to any one of the first aspects.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention determines the uneven aging of the cable by measuring the temperature difference at the intermediate joint of the cable under test. Then, it compensates for the input impedance spectrum at the beginning of the cable based on the degree of uneven aging. Finally, it obtains the precise defect location using frequency domain impedance spectroscopy. The compensated input impedance spectrum at the beginning of the cable under test eliminates a large amount of useless impedance mismatch information, preventing the actual defects in the cable from being obscured. This effectively reduces the interference of uneven aging on cable defect location and achieves precise defect location. The cable impedance spectrum defect location method of this invention is highly practical; operators only need to connect the detection equipment at the distribution node to quickly generate a defect location report, significantly improving inspection efficiency. By detecting and accurately locating potential defects early, it can prevent the escalation of faults, reduce maintenance costs, and thus significantly enhance the stability of the power distribution network. Attached Figure Description

[0016] Figure 1 This is a flowchart of the cable impedance spectrum defect location method of the present invention; Figure 2 This is the circuit diagram of the equivalent distributed parameters of the healthy cable of the present invention; Figure 3 This is a schematic diagram showing the arrangement of the six temperature sensor probes of the present invention; Figure 4 This is a radial temperature distribution diagram of a cable with uneven aging defects and without defects, according to the present invention. Figure 5 This is a flowchart of the present invention for determining whether a cable exhibits uneven aging; Figure 6 This is a radial temperature distribution diagram under different current conditions according to the present invention; Figure 7 This is the impedance spectrum of the defect-free, healthy cable of the present invention; Figure 8 This is the impedance spectrum of the defective cable under test according to the present invention; Figure 9 This is the fitting curve of the surface temperature of the cable under test according to the present invention; Figure 10 This is the impedance spectrum of the cable under test after aging compensation according to the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be used to limit the scope of protection of the present invention. It should be noted that the term "comprising" and any variations thereof in the specification, claims and the above-mentioned drawings of the present invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or devices.

[0018] Example 1 like Figure 1 As shown, a method for locating defects in cable impedance spectrum is provided, including: Step S1: Use an impedance analyzer to measure the cable under test and obtain the input impedance spectrum at the beginning of the cable under test.

[0019] The structure of the impedance analyzer can refer to existing technology, and the measurement method of the impedance analyzer for the cable under test can also refer to existing technology.

[0020] Step S2: Compare the input impedance spectrum of the cable under test with that of a healthy cable to determine if the cable under test has a defect. If the cable under test has no defect, the defect location process ends. If a defect exists, collect several temperature data points around the intermediate joint and use the temperature difference between the peak and valley values ​​to determine if the cable under test has aged. If no aging has occurred, use the obtained input impedance spectrum of the cable under test to directly locate the defect using the frequency domain reflection method. If aging has occurred, compensate the obtained input impedance spectrum of the cable under test according to the degree of aging, and use the frequency domain reflection method to locate the defect based on the compensated input impedance spectrum.

[0021] In this embodiment, the method of comparing the input impedance spectrum of the cable under test with that of a healthy cable to determine whether the cable under test has a defect can refer to existing technologies. Generally, it is as follows: directly determine whether the impedance spectra are consistent. If they are consistent, the cable under test does not have a defect. If they are inconsistent, the cable under test has a defect.

[0022] The input impedance spectrum at the beginning of the healthy cable is obtained through transmission line theory. Specifically, the healthy cable is equivalent to a distributed parameter model, and the distributed parameters are modeled to obtain the distributed parameters of the healthy cable. Then, the input impedance at the beginning of the healthy cable is obtained by the ratio of voltage and current at any position from the beginning of the cable.

[0023] More specifically, according to transmission line theory, under high-frequency conditions, a cable should be equivalent to a distributed parameter model, and its distributed parameter equivalent circuit is as follows: Figure 2As shown in the figure, , , , These represent the distributed resistance, distributed inductance, distributed capacitance, and distributed conductance of the cable per unit length. d x This refers to a tiny unit of a cable.

[0024] At high frequencies, the various distribution values ​​of a cable can be calculated from relevant parameters such as the cable's actual material, structure, and dimensions. The distribution parameters per unit length of cable can be approximated as: ; ; ; ; in, The angular frequency of the input signal. ; Permeability of free space; and These are the cable core radius and the inner radius of the metal shielding layer, respectively. and These are the conductivity of the cable core and the conductivity of the metal shielding layer, respectively. The dielectric constant of the insulating layer; The conductivity of the insulating layer.

[0025] With a total length of l In a cable, the end where the signal input is located is designated as the beginning (origin), and the load end is designated as the end (terminus). The cable can be positioned at any point from the beginning. x voltage at and current It can be represented as: ; ; In the formula: and These are the incident voltage and the reflected voltage, respectively. The propagation coefficient of the cable; The characteristic impedance of a healthy cable.

[0026] The propagation coefficient and characteristic impedance of a cable are determined by its type and structure, and can be obtained by the following formula: ; ; ; In the formula: is the attenuation constant, representing the attenuation characteristics of the wave; is the phase constant, representing the phase shift characteristics of the wave; This refers to the speed at which electromagnetic waves propagate in the cable. The frequency of the incident signal; The wavelength of the electromagnetic wave in the cable.

[0027] In step S2, such as Figure 5 As shown, the determination of whether the cable under test has aged is as follows: Step a: Collect temperature data of the intermediate joint by using six temperature sensors that are evenly arranged around the circumference of the intermediate joint of the cable under test.

[0028] The six temperature sensors are arranged around the cable under test as follows: Figure 3 As shown, the cable cores are distributed symmetrically in three phases, and simulation results indicate that thermal defects can cause abnormal temperature rises in approximately one-sixth of the circumferential area of ​​the joint's outer surface. Based on this, six temperature measurement points are evenly distributed at 60° intervals along the circumference to achieve full-area monitoring of the circumferential thermal gradient characteristics. Simultaneously, six evenly distributed temperature data points are collected, and cable aging is assessed based on the severity of the temperature rise.

[0029] Specifically, the intermediate joint of a three-core cable is a crucial connecting element in power transmission and distribution systems, and its operating condition affects the stability of power transmission. Intermediate joints operate under high current and high voltage conditions for extended periods, making them highly susceptible to localized overheating due to electrothermal coupling, which gradually leads to uneven aging of the cable itself. Therefore, monitoring the condition of cable intermediate joints is an important measure to ensure the safe operation of power systems, helping to detect potential problems early, reduce the risk of failure, and improve system reliability.

[0030] The steady-state temperature field analysis of cable joints can be reduced to the problem of heat conduction modeling in a multi-physics coupled system. The heat source distribution induced by the Joule heating effect of the conductor material constitutes the non-homogeneous term of the temperature field governing equation, while the nonlinear modulation of the material's conductivity by the temperature field forms a two-way coupling mechanism between the electromagnetic and thermal fields.

[0031] The governing equations for the temperature field are derived based on Fourier's law and the law of conservation of energy, and their expression in rectangular coordinates is as follows: ; in, Density, unit: kg / m³ 3 ; Specific heat capacity, unit: J / (kg·℃); Thermal conductivity; Heat generated by a current-carrying conductor. Convective heat dissipation mainly includes three parts: heat conduction, heat convection, and heat radiation.

[0032] The outer surface of the cable joint can be considered to be in direct contact with the air. According to the convection heat dissipation formula, we know that: ; in, h This is the air heat transfer coefficient, which is usually taken as 10; n Indicates the direction along the normal; For external surface temperature, The initial ambient temperature is expressed in Kelvin (K).

[0033] A finite element simulation model of a cable joint with insulation aging was established in COMSOL software. Under a room temperature of 20℃, the temperature of the cable joint during normal operation was obtained. Figure 4 As shown, Figure 4 Figures (a) and (b) show the temperature distribution of a cable joint with insulation aging and a normal, healthy cable, respectively. Figure 4 As can be seen, the temperature rise of the aging phase of the cable joint with insulation aging is obvious compared with that of a normal healthy cable. Therefore, the aging condition of the three-phase cable can be judged by monitoring the temperature rise of the cable joint.

[0034] Step b: Use the three harmonic Fourier model to perform curve fitting on the temperature data collected multiple times to obtain the peak and valley temperatures of the intermediate joint surface, and obtain the maximum temperature difference of the intermediate joint.

[0035] Fourier series demonstrates significant advantages in modeling surface temperature distribution on cable joints. Based on orthogonality and harmonic decomposition principles, it can strictly satisfy periodic boundary conditions and approximate nonlinear temperature distribution characteristics (such as local extrema and multi-peak morphology) with high fidelity by superimposing sine and cosine basis functions of different frequencies. Multiple simulation data fitting experiments revealed that the third harmonic Fourier model showed the best fit, with the curve fitting form as follows: ; in, Position and angle variables temperature, The DC component, For the order of harmonics, and The first k The sine and cosine coefficients of the subharmonic.

[0036] Plot the fitted function curve. Ideally, the fitted curve should have three peaks within a 360° period. If not, analyze the curve based on the principle that the temperature will not change abruptly, determine the core position, change the probe position to measure a new set of temperature data, and refit the Fourier function until the three peaks of the temperature within the period are found.

[0037] In this embodiment, the feasibility of the method for identifying heat generation due to crimping defects in cable intermediate joints was also determined through simulation. A simulation model of the cable intermediate joint was built based on finite element theory to simulate the radial temperature distribution on the outer surface of the joint corresponding to the center of the splice pipe with a single-phase moderate heat generation defect under different current conditions. Figure 6 As shown, Figure 6 Figures (a), (b), and (c) show the radial temperature distribution under current conditions of 200A, 300A, and 400A, respectively. Figure 6 It can be seen that the current condition only affects the magnitude of the maximum radial temperature difference, and does not affect the relationship between the maximum radial temperature difference under the heat-generating defect and the maximum radial temperature difference under normal conditions. The severity of the defect can be judged by the ratio of the maximum radial temperature difference under the heat-generating defect to the maximum radial temperature difference under normal conditions.

[0038] Step c: Determine whether the maximum temperature difference of the intermediate joint of the cable under test exceeds the set threshold. If it does, aging has occurred; otherwise, no aging has occurred. The set threshold can be determined based on expert experience.

[0039] In step S2, the input impedance spectrum of the cable under test obtained based on the aging degree compensation is specifically as follows: ; in, The impedance value of the cable under test after aging compensation. The frequency point in the input impedance spectrum of the cable under test. f The corresponding impedance value, This is the aging temperature rise compensation coefficient. The maximum temperature difference at the intermediate joint of the cable under test. This is a temperature coefficient function pre-fitted using aging data.

[0040] Temperature coefficient It is a function determined through experimental calibration, and its specific form is related to the cable's insulation material (such as XLPE) and aging type. In one specific implementation, By different aging levels (corresponding to different A broadband impedance spectrum test was performed on a cable sample, and the test data was fitted to an Nth-order polynomial to determine: ; In the formula, , and All of these are fitting coefficients obtained through experimental calibration, and under normal circumstances... n For 2-4, This refers to frequency, measured in MHz.

[0041] Aging causes a large number of highly polar carbonyl and hydroxyl groups to appear inside the XLPE insulation layer of the cable. These newly added permanent dipoles will exhibit significant orientation polarization under the influence of an external electric field, significantly increasing the dielectric constant of the cable. The dielectric constant, in turn, affects the distributed capacitance of the cable, thereby affecting the characteristic impedance and propagation coefficient, leading to impedance mismatch in the cable impedance spectrum and affecting the location of actual defects.

[0042] In this embodiment, the frequency domain reflection method for cable defect location can refer to existing technology. Specifically, when no aging has occurred, an inverse Fourier transform is performed on the input impedance spectrum of the first end of the cable under test, or when aging has occurred, an inverse Fourier transform is performed on the compensated input impedance spectrum of the first end. The inverse Fourier transform is used to obtain a time domain reflection map, and the location of the defect point is read from the map.

[0043] Example 2 Provide a specific application example.

[0044] Taking a 10kV XLPE cable as the research object, a cable model with a total length of 100m was built on the Matlab platform. Its basic parameters are shown in Table 1. The lower frequency limit was set to 10kHz, the upper frequency limit to 60MHz, and the cable end was left open-circuited. The results are as follows: Figure 7 The impedance spectrum of the healthy cable is shown.

[0045] Table 1 Basic simulation parameters of the cable

[0046] Subsequently, a localized damage defect with a length of 0.15m was created at a distance of 70m. Uneven aging was then randomly distributed throughout the cable at other locations, with varying degrees of aging. The input impedance spectrum at the beginning of the cable under test obtained at this point is as follows: Figure 8 As shown.

[0047] Temperature data at 0° (360°), 60° (420°), 120°, 180°, 240°, and 300° (46.26℃, 46.34℃, 47.85℃, 46.24℃, 46.21℃, and 45.26℃) were selected and expanded to the third harmonic using Fourier series. The fitting results are as follows: Figure 9 As shown, the peak surface temperature of the joint obtained through fitting is 47.9℃, with an error of only 0.1% compared to the simulated peak temperature of 47.85℃; the lowest surface temperature is 45.18℃, with an error of only 0.2% compared to the simulated peak temperature of 45.26℃, indicating good fitting performance. The maximum temperature difference obtained from the fitted curve is 2.72℃, which differs from the simulated maximum temperature difference of 2.59℃ by 0.13℃, representing an error of 5%. Based on the maximum temperature difference of 0.76℃ under normal, defect-free conditions, it can be inferred that the cable is aging.

[0048] The maximum temperature difference of 2.72℃ obtained from the fitted curve was used... To correct the input impedance spectrum at the beginning of the cable, the frequency domain reflection method is used to locate the cable defect. The defect location results in Matlab are as follows: Figure 10 As shown in the simulation results, the compensated cable defect location results only exhibit significant peaks at the cable start, the defect location at 69.5257m, and the cable end at 100.132m. The number and amplitude of interference peaks at other locations are greatly reduced, and the waveform becomes relatively stable, which is beneficial for inspection personnel to accurately determine the location of cable defects. Therefore, the method proposed in this invention has significant practical value.

[0049] Table 2 Comparison of positioning results before and after compensation

[0050] As shown in Table 2, the compensated cable not only has better positioning accuracy, but also has better performance in terms of resolution (the ratio of amplitude at the defect to amplitude at the end).

[0051] Example 3 A cable impedance spectrum defect location system is provided, comprising: Impedance analyzer is used to measure the cable under test and obtain the input impedance spectrum at the beginning of the cable under test; The defect detection module is used to compare the input impedance spectrum of the first end of the cable under test with that of a healthy cable to determine whether there is a defect in the cable under test. The aging judgment module is used to collect several temperature data points on the circumference of the intermediate joint when there are defects in the cable under test, and to use the temperature difference between the peak and valley temperature data to determine whether the cable under test has aged. The defect location module is used to locate cable defects directly using the frequency domain reflection method when no aging has occurred, by utilizing the obtained input impedance spectrum of the cable under test at the beginning of the test. When aging has occurred, the module compensates the obtained input impedance spectrum of the cable under test at the beginning of the test according to the degree of aging, and then uses the frequency domain reflection method to locate cable defects based on the compensated input impedance spectrum at the beginning of the test.

[0052] Furthermore, the aging judgment module includes: Temperature sensors, six of which are evenly arranged around the circumference of the intermediate joint of the cable under test; The data acquisition submodule is used to acquire temperature data of the intermediate joint; The temperature difference acquisition module is used to perform curve fitting on the temperature data collected multiple times using the three harmonic Fourier model to obtain the surface peak and valley temperatures of the intermediate joint, and to obtain the maximum temperature difference of the intermediate joint. The aging determination submodule is used to determine whether the maximum temperature difference of the intermediate joint of the cable under test exceeds the set threshold. If it does, aging occurs; otherwise, no aging occurs.

[0053] Example 4 The present invention provides a computer device, including a processor and a memory; wherein, when the processor executes a computer program stored in the memory, it implements the steps of the above-described cable impedance spectrum defect location method.

[0054] For more detailed information on the above methods, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0055] Example 5 The present invention provides a computer-readable storage medium for storing a computer program; when the computer program is executed by a processor, it implements the steps of the above-described cable impedance spectrum defect location method.

[0056] For more detailed information on the above methods, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0057] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The systems, devices, and storage media disclosed in the embodiments are described simply because they correspond to the methods disclosed in the embodiments; relevant details can be found in the method section.

[0058] Those skilled in the art will clearly understand that the techniques in the embodiments of the present invention can be implemented using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or certain parts of the embodiments of the present invention.

[0059] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for locating defects in cable impedance spectrum, characterized in that, include: The impedance analyzer is used to measure the input impedance spectrum of the cable under test, and the spectrum is compared with the input impedance spectrum of the cable under test to determine whether there is a defect in the cable under test. If a defect exists, collect several temperature data points around the intermediate joint and use the temperature difference between the peak and valley values ​​to determine whether the cable under test has aged. If no aging has occurred, use the obtained input impedance spectrum at the beginning of the cable under test and directly use the frequency domain reflection method to locate the cable defect. If aging has occurred, compensate the obtained input impedance spectrum at the beginning of the cable under test according to the degree of aging, and use the frequency domain reflection method to locate the cable defect based on the compensated input impedance spectrum at the beginning of the cable. The process involves collecting several temperature data points around the intermediate joint and using the temperature difference between the peak and valley values ​​to determine whether the cable under test has aged. Temperature data of the intermediate joint is collected by six temperature sensors that are evenly surrounded around the circumference of the intermediate joint of the cable under test. The three harmonic Fourier model was used to fit the temperature data collected multiple times to obtain the peak and valley temperatures of the intermediate joint surface, and the maximum temperature difference of the intermediate joint was obtained. Determine whether the maximum temperature difference of the intermediate joint of the cable under test exceeds the set threshold. If it does, aging has occurred; otherwise, no aging has occurred. The specific method for obtaining the input impedance spectrum at the beginning of the cable under test based on aging compensation is as follows: ； in, The impedance value of the cable under test after aging compensation. The frequency point in the input impedance spectrum of the cable under test. The corresponding impedance value, This is the aging temperature rise compensation coefficient. The maximum temperature difference at the intermediate joint of the cable under test. This is a temperature coefficient function pre-fitted using aging data.

2. The cable impedance spectrum defect location method according to claim 1, characterized in that, The curve fitting takes the form of: ； in, Position and angle variables temperature, The DC component, For the order of harmonics, and The first The sine and cosine coefficients of the subharmonic.

3. The cable impedance spectrum defect location method according to claim 1, characterized in that, The input impedance spectrum at the beginning of the healthy cable is obtained through transmission line theory. Specifically, the healthy cable is equivalent to a distributed parameter model, and the distributed parameters are modeled to obtain the distributed parameters of the healthy cable. Then, the input impedance at the beginning of the healthy cable is obtained by the ratio of voltage and current at any position from the beginning of the cable.

4. A cable impedance spectrum defect location system, comprising the steps of the cable impedance spectrum defect location method according to any one of claims 1-3, characterized in that, include: Impedance analyzer is used to measure the cable under test and obtain the input impedance spectrum at the beginning of the cable under test; The defect detection module is used to compare the input impedance spectrum of the first end of the cable under test with that of a healthy cable to determine whether there is a defect in the cable under test. The aging judgment module is used to collect several temperature data points on the circumference of the intermediate joint when there are defects in the cable under test, and to use the temperature difference between the peak and valley temperature data to determine whether the cable under test has aged. The defect location module is used to locate cable defects directly using the frequency domain reflection method by utilizing the obtained input impedance spectrum of the cable under test before aging occurs. When aging occurs, the input impedance spectrum of the cable under test is obtained by compensation according to the degree of aging, and the defect location of the cable is performed by frequency domain reflection method based on the compensated input impedance spectrum of the cable.

5. The cable impedance spectrum defect location system according to claim 4, characterized in that, The aging judgment module includes: Temperature sensors, six of which are evenly arranged around the circumference of the intermediate joint of the cable under test; The data acquisition submodule is used to acquire temperature data of the intermediate joint; The temperature difference acquisition module is used to perform curve fitting on the temperature data collected multiple times using the three harmonic Fourier model to obtain the surface peak and valley temperatures of the intermediate joint, and to obtain the maximum temperature difference of the intermediate joint. The aging determination submodule is used to determine whether the maximum temperature difference of the intermediate joint of the cable under test exceeds the set threshold. If it does, aging occurs; otherwise, no aging occurs.

6. A computer device, characterized in that, It includes a processor and a memory; wherein, when the processor executes the computer program stored in the memory, it implements the steps of the cable impedance spectrum defect location method according to any one of claims 1-3.

7. A computer-readable storage medium, characterized in that, Used to store computer programs; when the computer programs are executed by a processor, they implement the steps of the cable impedance spectrum defect location method according to any one of claims 1-3.

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