A method for cable defect location and related devices

Abstract

The present invention belongs to the technical field of cable defect detection, and particularly relates to a cable defect positioning method and related device. The cable defect positioning method includes the following steps: obtaining the reflection coefficient of the cable to be measured; determining the attenuation constant in the reflection coefficient, compensating the attenuation constant through deconvolution operation to obtain a compensated defect positioning function; based on the compensated defect positioning function, obtaining an impulse response function that can reflect the true change in wave impedance; performing integral processing on the impulse response function to obtain a step response positioning spectrum of the difference between the wave impedance of each segment corresponding to the cable to be measured and the normal wave impedance, and positioning the defects of the cable to be measured based on the step response positioning spectrum. Through the step response conversion algorithm, the changes in the wave impedance of each segment of the cable can be accurately revealed, overcoming the problem in the prior art that only focuses on defect positioning while ignoring the comprehensive analysis of wave impedance characteristics.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable defect detection, and particularly relates to a cable defect location method and related device. Background Art

[0002] Distribution cables can be regarded as the main arteries of the power grid and have been widely used in the construction of modern power grids. However, due to the complex operating environment and the action of various stresses such as electricity, heat, and machinery during long-term operation, cables are extremely prone to defects such as thermal aging, water tree aging, mechanical damage, and partial discharge, which may further lead to cable failures and even power outages. Therefore, the development of accurate cable defect location and diagnosis technologies is of great significance for improving the safe and reliable operation of power systems.

[0003] In the prior art, time domain reflectometry (TDR) or frequency domain reflectometry (FDR) is usually used for cable defect location. The existing traveling wave reflection method mainly focuses on the location of cable defects. This method can only reveal specific positions where the wave impedance in the cable changes significantly, and fails to comprehensively present the true wave impedance characteristics of each position in the cable, thus limiting the comprehensive evaluation of the cable wave impedance distribution.

[0004] Secondly, although the prior art can effectively locate cable defects, it mainly focuses on defect location and ignores the qualitative analysis of the deterioration degree at any position in the cable. Therefore, it lacks the ability to comprehensively evaluate the overall health status of the cable.

[0005] In addition, the prior art relies on the fast Fourier transform to extract defect location information from the frequency domain reflection coefficient. However, due to the attenuation of high-frequency signals during propagation, the pulse amplitude in the obtained defect location curve cannot accurately reflect the change amount of the cable wave impedance. Therefore, the cable defect location method in the prior art has a low accuracy. Summary of the Invention

[0006] The purpose of the present invention is to provide a cable defect location method and related device, which solve the problems of low accuracy of the cable defect location method and inability to comprehensively evaluate the cable state.

[0007] The present invention is realized through the following technical solutions:

[0008] The present invention discloses a cable defect location method, including the following steps:

[0009] S1. Obtain the reflection coefficient of the cable to be measured;

[0010] S2. Determine the attenuation constant in the reflection coefficient, and compensate the attenuation constant through deconvolution operation to obtain a compensated defect location function;

[0011] S3. Based on the compensated defect location function, obtain an impulse response function that can reflect the true change in wave impedance;

[0012] S4. Perform integral processing on the impulse response function to obtain a step response location spectrum of the difference between the wave impedance of each section of the cable under test and the normal wave impedance, and locate the defects of the cable under test based on the step response location spectrum.

[0013] Further, in S2, the attenuation constant in the reflection coefficient is determined specifically by the following formula:

[0014] ;

[0015] where is the attenuation constant; k is the fitting coefficient; f is the electromagnetic wave signal frequency;

[0016] The fitting coefficient is determined according to the reflection coefficient, specifically:

[0017] By linearly fitting the upper boundary of the envelope of the reflection coefficient in the frequency domain, the absolute value of the slope of the envelope upper boundary fitting function is obtained, and then the fitting coefficient is obtained k。

[0018] Further, in S2, the process of compensating the attenuation constant through deconvolution operation to obtain a compensated defect location function specifically includes the following steps:

[0019] Perform a fast Fourier transform on the real part of the reflection coefficient to obtain a defect location spectrum, and the specific expression is;

[0020] ;

[0021] where is the reflection coefficient;

[0022] Perform a fast Fourier transform on the attenuation term and perform deconvolution operation with the defect location spectrum to obtain the compensated defect location function;

[0023] The compensated defect location function is:

[0024] ;

[0025] where T ( x ) is the compensated defect location function; * -1is the deconvolution operator; F ( x ) is the defect location spectrum; is the attenuation constant; x is the distance between the defect location in the cable under test and the head end of the cable under test; is the attenuation term, and FFT() is the fast Fourier transform.

[0026] Further, in S3, the expression of the impulse response function is:

[0027] ;

[0028] wherein, P ( x ) is the impulse response function; T ( x ) is the compensated defect location function.

[0029] Further, the expression of the impulse response function is derived based on the correction formula of wave impedance;

[0030] The correction formula is constructed based on the relationship between the reflection coefficient and the wave impedance, and the expression is;

[0031] ;

[0032] wherein, M is the amplitude of the reflection coefficient, C ( M ) is the wave impedance difference.

[0033] Further, in S4, the impulse response function is integrated to obtain the step response location spectrum of the difference between the wave impedance of each section corresponding to the cable under test and the normal wave impedance, specifically:

[0034] ;

[0035] wherein, D ( x ) is the step response location spectrum of the difference between the wave impedance of each section corresponding to the cable under test and the normal wave impedance; P ( x ) is the impulse response function; x is the distance between the defect location in the cable under test and the head end of the cable under test.

[0036] The present invention also discloses a cable defect location system, including:

[0037] A data acquisition module, configured to acquire the reflection coefficient of the cable under test;

[0038] An attenuation constant calculation module, configured to determine the attenuation constant in the reflection coefficient;

[0039] A compensation module, configured to compensate the attenuation constant through deconvolution operation to obtain a compensated defect location function;

[0040] An impulse response processing module, configured to obtain an impulse response function that can reflect the true change in wave impedance based on the compensated defect location function;

[0041] A step response location processing module, configured to perform integral processing on the impulse response function to obtain a step response location spectrum of the difference between the wave impedance of each section corresponding to the cable to be measured and the normal wave impedance, and perform defect location on the cable to be measured based on the step response location spectrum.

[0042] The present invention also discloses a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the cable defect location method are implemented.

[0043] The present invention also discloses a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, the steps of the cable defect location method are implemented.

[0044] The present invention also discloses a computer program product, including computer program / instructions, and when the computer program / instructions are executed by a processor, the steps of the cable defect location method are implemented.

[0045] Compared with the prior art, the present invention has the following beneficial technical effects:

[0046] The present invention discloses a cable defect location method. First, the reflection coefficient of the cable to be measured is obtained. By measuring the reflection coefficient, relevant information about signal reflection in the cable can be obtained, and signal reflection is closely related to the characteristics of the cable and the presence of defects. Since the signal will attenuate as the transmission distance increases during the signal transmission process of the cable, which will affect the judgment of the defect degree of the cable, the present invention compensates the attenuation constant through deconvolution operation, which can eliminate or reduce the influence of signal attenuation on the measurement result, obtain a compensated defect location function, and make the subsequent analysis based on this defect location function more accurately reflect the actual situation of the cable, effectively improving the accuracy of defect location and avoiding misjudgment of the defect position caused by signal attenuation. The change in wave impedance is one of the important characteristics of the cable with defects. By compensating the attenuation constant, the location spectrum can more accurately present the true change in wave impedance.

[0047] Finally, integral processing is performed on the impulse response function. Integral processing can further highlight the characteristics of wave impedance changes, convert the impulse response into a step response form that is easier to analyze and understand. In this way, the difference between the wave impedance of each section in the cable and the normal wave impedance can be determined more accurately, so as to accurately locate the defect position of the cable. Compared with the analysis based only on the impulse response, this method can provide more detailed and accurate information, improving the reliability and effectiveness of cable defect location.

[0048] In summary, through a series of measurements, compensations, and analysis processes, this cable defect location method can effectively improve the accuracy and reliability of cable defect location, accurately determine the position of cable defects, and provide strong technical support for cable maintenance and troubleshooting. Brief Description of the Drawings

[0049] Figure 1 It is a flowchart of a cable defect location method of the present invention;

[0050] Figure 2 It is a schematic diagram of an equivalent model of cable distribution parameters of the present invention;

[0051] Figure 3 It is a schematic diagram of a cable model with local defects of the present invention;

[0052] Figure 4 It is a schematic diagram of a single-core cross-linked polyethylene distribution cable model of the present invention;

[0053] 1. Core wire; 2. Inner semiconductive layer; 3. Insulation layer; 4. Outer semiconductive layer; 5. Copper tape shielding layer; 6. Sheath;

[0054] Figure 5 It is a schematic diagram of the step response characteristic curves of normal and defect cables with different aging degrees of the present invention;

[0055] Figure 6 It is a schematic diagram of the step response characteristic curve of a diffusely damp-defected cable of the present invention;

[0056] Figure 7 It is a schematic diagram of the step response characteristic curve of a cable with an outer shield damaged defect of the present invention;

[0057] Figure 8 It is a schematic diagram of the step response characteristic curves of different wave impedance cable combinations of the present invention;

[0058] Figure 9 It is a schematic diagram of the step response curve of an immersed and aged cable in a certain city of the present invention;

[0059] Figure 10 It is a test result diagram of very low frequency partial discharge of the present invention;

[0060] Figure 11 This is the step response curve of a shielded damaged cable of the present invention;

[0061] Figure 12 This is the partial discharge test result diagram of the present invention;

[0062] Figure 13 This is the block diagram of a cable defect location system of the present invention;

[0063] Figure 14 This is the schematic diagram of a computer device of the present invention. Detailed implementation manners

[0064] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further detailed description is given in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0065] The components described and shown in the drawings and embodiments of the present invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the claimed present invention, but only represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0066] It should be noted that the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that a process, element, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes the elements inherent to the process, element, method, article or device.

[0067] The features and performance of the present invention are further described in detail in the following embodiments.

[0068] Embodiment 1

[0069] As Figure 1 shown, the present invention provides a cable defect location method, including the following steps:

[0070] S1. Obtain the reflection coefficient of the cable to be measured;

[0071] S2. Determine the attenuation constant in the reflection coefficient, and compensate the attenuation constant through deconvolution operation to obtain a compensated defect location function;

[0072] S3. Obtain an impulse response function that can reflect the true change in wave impedance based on the compensated defect location function;

[0073] S4. Integrate the impulse response function to obtain a step response location spectrum of the difference between the wave impedance of each section of the cable under test and the normal wave impedance, and locate the defects in the cable under test based on the step response location spectrum.

[0074] By determining the attenuation constant in the reflection coefficient and performing deconvolution operation compensation, the present invention can effectively eliminate the attenuation effect of the test signal during transmission in the cable, thus avoiding the problem of deviation or even failure in the positioning result in the prior art; obtaining an impulse response function that can reflect the true change in wave impedance based on the compensated defect location function, and then integrating the impulse response function to obtain a step response location spectrum can locate multiple sections of defects simultaneously, overcoming the defect in the prior art that multiple sections of defects cannot be located simultaneously, which is beneficial to applications in the actual environment; obtaining an impulse response function based on the compensated defect location function and converting the impulse response into a step response location spectrum can more accurately determine the difference between the wave impedance of each section in the cable and the normal wave impedance, thereby more accurately locating and analyzing local defects in the cable.

[0075] Embodiment 2

[0076] Based on Embodiment 1, S1 is introduced.

[0077] In S1, the network analyzer method can be specifically used to measure the cable under test to obtain the reflection coefficient.

[0078] According to the transmission line theory, when the wavelength of the electromagnetic wave propagating in the transmission line is much smaller than the physical length of the transmission line, the model of the transmission line needs to be represented by distributed parameters.

[0079] Figure 2 Shown is a schematic diagram of an equivalent model of the distributed parameters of a cable provided by the present invention. As a classic long line, a coaxial power cable can establish an equivalent model of the distributed parameters of the cable to describe the transmission characteristics of electromagnetic waves in the cable. Figure 2 In the figure: R is the resistance per unit length of the cable, L is the inductance per unit length of the cable, G is the conductance per unit length of the cable, C are the capacitances per unit length of the cable respectively, and ∆z is the unit length.

[0080] Due to the existence of high-frequency reverse current between the core wire and the metal shielding layer of the coaxial cable, according to the skin effect and proximity effect, the distributed parameters of the cable will change with the change of the electromagnetic wave frequency, and can be expressed as:

[0081] (1)

[0082] In Equation (1), , is the electromagnetic wave frequency, is the pi, is the angular frequency; is the permeability of free space; and are the radius of the cable core and the inner radius of the metal shielding layer, respectively; and are the resistivity of the cable core and the resistivity of the metal shielding layer, respectively; k 1 , k 2 , k 3 are the shielding layer breakage coefficient, the breakage mutual inductance coefficient and the breakage capacitance coefficient, respectively. The above coefficients of a normal cable are all 1; , are the relative permittivity of the cable insulation material and the permittivity of free space, respectively.

[0083] When the sinusoidal steady state condition is satisfied, for a cable with a length of , at any position the voltage and the current can be expressed as:

[0084] (2)

[0085] In Equation (2), is the incident voltage wave on the load side, is the reflected voltage wave on the load side; and are the propagation constant and the characteristic impedance of the cable, respectively.

[0086] and are both characteristic parameters of the transmission line, and the two are determined by the distributed parameters of the transmission line itself. The propagation constant can be written as , where is the attenuation constant, is the phase shift constant. For a microwave low-loss transmission line, the characteristic impedance can be approximated as .

[0087] For a normal cable with a length of , when the impedance connected to the end of the cable is of the load, the reflection coefficient at any position is:

[0088] (3)

[0089] In Equation (3): and are the propagation constant and characteristic impedance of the normal cable, respectively.

[0090] Figure 3 is a schematic diagram of a cable model with local defects, as Figure 3 shown. When there are local defects in a certain section of the cable, is the distance from the head end of the defective part to the head end of the cable, is the distance from the tail end of the defective part to the head end of the cable.

[0091] According to Equation (3), the reflection coefficient at the end of the cable is:[[]]

[0092] (4)

[0093] From the cable to the equivalent characteristic impedance and at the reflection coefficient are respectively expressed as:[[]]

[0094] (5)

[0095] (6)

[0096] In Equation (6), is the characteristic impedance of the defective part of the cable.

[0097] Similarly, from the cable to the equivalent characteristic impedance and at the reflection coefficient are respectively expressed as:[[]]

[0098] (7)

[0099] (8)

[0100] In Equation (7), is the propagation constant of the defective part of the cable.

[0101] If the impedance at the head end of the cable is matched, combining Equations (3) to (8) can obtain the expression of the reflection coefficient at the head end of the cable:[[]]

[0102] (9)

[0103] In the formula, α is the attenuation constant; β is the phase constant, is the reflection coefficient at the cable head end.

[0104] For the convenience of subsequent expressions, hereinafter, l a is denoted as x .

[0105] The derivation process of formula (9) is to illustrate the theoretical demonstration that positioning information can be extracted from the reflection coefficient.

[0106] Embodiment 3

[0107] Mainly introduce S2, determine the attenuation constant in the reflection coefficient α , and compensate the attenuation constant through deconvolution operation to obtain the compensated defect positioning function. Specifically, the process is as follows:

[0108] The calculation expression of the attenuation constant is:

[0109] (10)

[0110] Wherein, is the attenuation constant; k is the fitting coefficient; is the electromagnetic wave frequency.

[0111] By linearly fitting the upper boundary of the envelope of the reflection coefficient in the frequency domain, the absolute value of the slope of the envelope upper boundary fitting function is obtained, and then the fitting coefficient k is obtained.

[0112] Specifically, in the attenuation term α is variable, and its value is affected by the frequency change. For power cables, as the frequency of high-frequency electromagnetic waves increases, the attenuation factor increases significantly. Considering that within the test frequency band of long cables (<1000 MHz), the attenuation constant has an approximate linear relationship with the electromagnetic wave frequency, the attenuation constant can be expressed as shown in the above formula (10).

[0113] Specifically, after performing a fast Fourier transform on the real part of the reflection coefficient measured by S1, a defect positioning spectrum is obtained, and the expression is:

[0114] (11)

[0115] Furthermore, due to the influence of the attenuation constant, the amplitude of the defect positioning spectrum is not equal to the amplitude of the reflection coefficient. To compensate for the influence of the attenuation constant, the attenuation term can be subjected to a fast Fourier transform and deconvolution operation with the defect positioning spectrum F (x ) to obtain the compensated defect positioning function T (x ):

[0116] (12)

[0117] Among them, T ( x ) is the compensated defect location function; * -1 is the deconvolution operator; F ( x ) is the defect location spectrum; is the attenuation constant; x is the distance between the defect position in the cable under test and the head end of the cable under test; is the attenuation term. The Fast Fourier Transform (FFT) is an efficient algorithm for calculating the discrete Fourier transform.

[0118] Example 4

[0119] On the basis of Example 3, S3 is mainly introduced. Based on the compensated defect location function, an impulse response function that can reflect the true change in wave impedance is obtained. The expression of the impulse response function is derived based on the correction formula of wave impedance.

[0120] Based on the relationship between the reflection coefficient and the difference in wave impedance, a correction formula is constructed. The specific process is as follows:

[0121] According to Equations (6) and (8), the difference in the wave impedance of the cable at the defect position and the wave impedance in the normal state can be expressed as:

[0122] (13)

[0123] Among them, is the characteristic impedance of the defective part of the cable; is the characteristic impedance of the normal cable; M is the amplitude of the reflection coefficient; is the difference in wave impedance.

[0124] Then, the correction formula constructed based on the relationship between the reflection coefficient and the wave impedance has the following expression:

[0125] ;

[0126] Among them, M is the amplitude of the reflection coefficient; C ( M ) is the difference in wave impedance.

[0127] According to the correction formula, the impulse response function that can reflect the true change in wave impedance is obtained, and its expression is:

[0128] (14)

[0129] Wherein, P ( x ) is the adjusted impulse response function; T ( x ) is the compensated defect location function; x is the distance between the defect position in the cable under test and the head end of the cable under test.

[0130] Embodiment 5

[0131] Based on Embodiment 4, S4 is mainly introduced: performing integral processing on the impulse response function to obtain the step response localization spectrum of the difference between the wave impedance of each segment corresponding to the cable under test and the normal wave impedance, so as to realize the defect localization of the cable under test based on the step response localization spectrum.

[0132] In an embodiment of the present application, the impulse response localization spectrum obtained through integral transformation can reveal the jump characteristics of the wave impedance. Further integrating the impulse response can obtain the cumulative effect of the wave impedance change amount in the spatial domain, that is, the step response localization spectrum reflecting the difference between the wave impedance of each segment of the cable and the normal wave impedance D ( x ).

[0133] (15)

[0134] Wherein, D ( x ) is the step response localization spectrum of the difference between the wave impedance of each segment of the cable under test and the normal wave impedance; P ( x ) is the impulse response function.

[0135] Through the step response conversion algorithm, the change of the wave impedance of each segment of the cable can be accurately revealed, overcoming the problem that the prior art only focuses on defect localization and ignores the comprehensive analysis of wave impedance characteristics. Compared with the traditional frequency domain reflection technology, the present invention can more precisely reflect the spatial distribution of the cable wave impedance and the wave impedance change amount, providing a more comprehensive cable health status assessment. Secondly, in view of the attenuation effect of high-frequency signals in long cables, the present invention effectively compensates the influence of the attenuation constant through deconvolution operation, overcoming the problem that the amplitude of the defect localization spectrum in the prior frequency domain reflection technology cannot quantitatively reflect the degree of wave impedance change due to signal attenuation. In addition, through the step response conversion algorithm, the present invention can not only locate the defect, but also quantitatively analyze the deterioration degree of each segment of the cable, providing a reliable basis for cable maintenance and fault prediction.

[0136] For the above cable defect localization method, the present invention proposes corresponding simulation verification.

[0137] To verify the feasibility of the step - response conversion algorithm in identifying cable faults, a simulation model of a 10 kV single - core cross - linked polyethylene distribution cable as shown below is built on the MATLAB (Matrix Laboratory) platform. As Figure 4 shown, the cable structure mainly includes a core wire 1, an inner semi - conductive layer 2, an insulating layer 3, an outer semi - conductive layer 4, a copper tape shielding layer 5, and a sheath 6. The insulating layer 3 is made of cross - linked polyethylene. The simulation parameters are shown in Table 1. Figure 4 As shown, the cable structure mainly includes a core wire 1, an inner semi - conductive layer 2, an insulating layer 3, an outer semi - conductive layer 4, a copper tape shielding layer 5, and a sheath 6. The insulating layer 3 is made of cross - linked polyethylene. The simulation parameters are shown in Table 1.

[0138] Table 1

[0139]

[0140] Based on the common faults of cross - linked polyethylene distribution cables, 4 types of simulation are set, namely: different degrees of local aging, diffusive moisture ingress, damaged shielding layer, and different combinations of cables with different wave impedances.

[0141] (a) Cables with different degrees of local aging

[0142] According to the Cole - Cole equation, by setting different fitting parameters, simulations of cable local aging defects with different degrees can be achieved. The Cole - Cole equation was proposed by American scientists Kenneth S. Cole and Robert H. Cole and is used to describe the relationship between the complex dielectric constant of a dielectric and the frequency under the action of an alternating electric field, which can more accurately reflect the relaxation characteristics of the actual dielectric. The expression is:

[0143] (16)

[0144] In the formula, the complex dielectric constant of the cable; A , B , P are fitting parameters respectively; is the real part of the complex dielectric constant; is the imaginary part of the complex dielectric constant; is the vacuum dielectric constant; is the imaginary unit; is the angular frequency.

[0145] Set the simulation parameters of local aging defects as shown in Table 2.

[0146] Table 2

[0147]

[0148] Figure 5Schematic diagram of the step response characteristics curve of defective cables with different aging degrees provided for the verification example of the present invention. The step response characteristics curves of three defective cables with different aging degrees and a normal cable control group with an open end are obtained by simulation as shown in Figure 5 shown. It can be seen from the simulation results that both the step response and the impulse response can accurately locate the end of the cable, and obvious peaks appear at the defect. Since the polarity and amplitude of the real part of the reflection coefficient are determined by the relative magnitude between the wave impedance of the defective part of the cable and the wave impedance of the normal cable, when the wave impedance of the defective part is greater than the normal wave impedance, the step response peak is positive; when the wave impedance of the defective part is less than the normal wave impedance, the step response peak is negative. The magnitude of the peak is proportional to the difference between the wave impedances.

[0149] For thermal aging, the relative permittivity at the defect location is higher than that of the normal cable, resulting in a decrease in wave impedance. Therefore, the step response curve dips downward at the defect, and the valley value decreases as the degree of thermal aging increases.

[0150] (b) Simulation of diffusely damp cables

[0151] Moisture ingress is one of the main reasons for the insulation deterioration of cross-linked polyethylene power cables. Due to the hydrophilicity of the cross-linked polyethylene material, water molecules will enter the pores inside the material, and then a large number of water-containing micropores are formed, transforming the original solid dielectric into a solid-liquid composite dielectric. The relative permittivity of water is much larger than that of cross-linked polyethylene, so the relative permittivity of the damp part of the cable is greater than the normal value.

[0152] Based on the above principle, a diffusely damp cable model can be built by setting different relative permittivity values. The simulation parameters are shown in Table 3.

[0153] Table 3

[0154]

[0155] The step response characteristics curve of the damp cable with an open end obtained by simulation is as shown in Figure 6 shown. It can be seen from Figure 6 that as the relative permittivity increases, the distributed capacitance of the cable increases and the wave impedance decreases. Therefore, a negative peak appears in the step response in the damp curve. It can also be seen from Figure 6 that due to the characteristics of diffuse moisture ingress, the degree of moisture ingress at the moisture intrusion point of the cable is the heaviest, and as the moisture diffuses, the degree of moisture ingress on both sides of the intrusion point gradually decreases. Therefore, the rise of the step response is relatively gentle.

[0156] (c) Simulation of shield-damaged cables

[0157] The outer shielding layer is an important guarantee for the uniform distribution of the electric field in the cable. Damage to the outer shielding layer may cause the electric field to concentrate in certain areas, thereby accelerating the aging of the insulating layer or triggering partial discharge, and even leading to the breakdown of the cable insulation.

[0158] The simulation model parameters of the cable with damaged outer shielding are shown in Table 4. Among them k 1 and k 2 and k 3 are the shielding layer damage coefficient, the damaged mutual inductance coefficient, and the damaged capacitance coefficient respectively. For a normal cable, the above coefficients are all 1.

[0159] Table 4

[0160]

[0161] As Figure 7 shown, the schematic diagram of the step response characteristic curve of the cable with damaged outer shielding provided by the verification example of the present invention. The step response can more accurately reflect the defect location. Different from aging and moisture absorption, for a cable with damaged outer shielding, due to the increase in distributed reactance and the decrease in distributed conductance, the wave impedance is larger than that in the normal case. Therefore, the defect shows a positive value in the step response.

[0162] (d) Combination of cables with different wave impedances

[0163] The case where two cables with characteristic impedances of 50Ω and 70Ω respectively and both with a length of 80m are connected is simulated, and the step response characteristic curve of the combined cable is as Figure 8 shown. It can be seen from Figure 8 that the step response of the combined cable is in a stepped shape. Since the characteristic impedance of the second cable is greater than that of the first one, the step response curve rises at the 80m joint and the next peak does not appear until the end of the cable, which conforms to the simulation setting that the test wave enters the cable with a larger impedance from the cable with a smaller impedance.

[0164] Considering that the effectiveness of the step response conversion algorithm cannot be verified on long-distance power cables in the laboratory environment, the verification example of the present invention conducts on-site detection of the actually operated cables, measures the reflection coefficient spectra of the moisture-absorbed cables and the cables with damaged outer shielding respectively, and verifies the defect location based on the step response conversion algorithm.

[0165] 1) Cable moisture absorption and aging cases and analysis

[0166] The step response method is used to test a three-phase 20kV immersed and aged cable with a length of 1019m in a certain city. The step response test results of the cable are as Figure 9As shown. By observing the curve, it can be seen that the overall difference in the three-phase curves is not significant, but local fluctuations occur in the area near 360 m. The step response shows a decrease in the wave impedance of phase B. Considering that moisture ingress will cause a decrease in the wave impedance of the defective cable, it is preliminarily determined that this section of the cable has moisture-induced aging.

[0167] In order to further verify the cause of the deterioration of phase B cable, in this experiment, the cable trench was also opened for visual inspection of the cable and very low frequency partial discharge test at 2 times the rated voltage. Figure 10 A very low frequency partial discharge test result diagram provided by the present invention is as Figure 10 shown. In this section of the cable, obvious moisture-induced aging discoloration occurred, and a discharge pulse with a maximum of 820 pC occurred at 358 m, which is consistent with the test results of the step response and pulse response. The positioning error is within 0.2%.

[0168] 2) Shield breakage cases and analysis

[0169] The step response test results of a 5100 m three-phase cable with shield breakage are as Figure 11 shown.

[0170] According to the position of the separation point of the step response curve, it can be known that there is a joint in this cable near 1284 m. In addition, the step response curve of phase C cable shows an abnormal rising trend faster than the other two phases near the joint, which conforms to the characteristics of shield breakage.

[0171] Due to the breakage of the outer shield layer, the distributed capacitance of the cable and the relative permittivity of the insulation decrease, resulting in an increase in the wave impedance. According to the capacitor voltage division principle, the internal voltage of the cable section with an increased wave impedance is greater than that of the normal part. Therefore, there is usually a certain probability of abnormal partial discharge in the cable with shield breakage.

[0172] In order to verify the deterioration of this section of the cable, a handheld partial discharge tester was used to detect the partial discharge of this section of the cable, and it was found that the partial discharge signal could be clearly captured. Figure 12 A partial discharge test result diagram provided by the present invention is as Figure 12 shown. The cable defect location technology based on the step response conversion algorithm can accurately locate the cable defect location by reflecting the change amount of the cable wave impedance, and the positioning error in the detection of long cables is within 0.2%. The degree of cable deterioration is reflected by the amplitude of the curve. The experiment verifies the effectiveness and reliability of the method in the verification example of the present invention, and proves that it can provide reliable technical support for cable condition monitoring and preventive maintenance in the power system in practical applications.

[0173] As Figure 13 shown, the present invention also discloses a cable defect location system, including:

[0174] A data acquisition module for acquiring the reflection coefficient of a cable under test;

[0175] An attenuation constant calculation module for determining the attenuation constant in the reflection coefficient;

[0176] A compensation module for compensating the attenuation constant through deconvolution operation to obtain a compensated defect location function;

[0177] A pulse response processing module for obtaining a pulse response function that can reflect the true change in wave impedance based on the compensated defect location function;

[0178] A step response location processing module for performing integral processing on the pulse response function to obtain a step response location spectrum of the difference between the wave impedance of each segment of the cable under test and the normal wave impedance, and locating the defects of the cable under test based on the step response location spectrum.

[0179] Figure 14 This is a schematic structural diagram of a computer device for cable defect location provided by the present invention. The cable defect location device includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to: acquire the reflection coefficient measured for the cable under test; determine the attenuation constant in the reflection coefficient, compensate the attenuation constant through deconvolution operation to obtain a compensated defect location function; obtain a pulse response function that can reflect the true change in wave impedance based on the compensated defect location function; perform integral processing on the pulse response function to obtain a step response location spectrum of the difference between the wave impedance of each segment of the cable under test and the normal wave impedance, and locate the defects of the cable under test based on the step response location spectrum.

[0180] The present invention also provides a non-volatile computer storage medium storing computer-executable instructions, and the computer-executable instructions are set to: acquire the reflection coefficient measured for the cable under test; determine the attenuation constant in the reflection coefficient, compensate the attenuation constant through deconvolution operation to obtain a compensated defect location function; obtain a pulse response function that can reflect the true change in wave impedance based on the compensated defect location function; perform integral processing on the pulse response function to obtain a step response location spectrum of the difference between the wave impedance of each segment of the cable under test and the normal wave impedance, and locate the defects of the cable under test based on the step response location spectrum.

[0181] Each embodiment in this application is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the embodiments of devices, equipment, and non-volatile computer storage media, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, reference can be made to the corresponding descriptions in the method embodiments.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that it is still possible to modify the specific implementation manners of the present invention or make equivalent replacements. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A cable defect location method, characterized in that: The following steps are involved: S1. Obtain the reflection coefficient of the cable to be tested; S2, determining an attenuation constant in the reflection coefficient, and compensating the attenuation constant by a deconvolution operation to obtain a compensated defect location function; S3, based on the compensated defect location function, obtain an impulse response function that can reflect the actual change of wave impedance; S4, integrating the impulse response function to obtain a step response positioning spectrum of the difference between each wave impedance of the cable to be tested and the normal wave impedance, and locating the defects of the cable to be tested based on the step response positioning spectrum; In S2, the attenuation constant is compensated by deconvolution operation to obtain a compensated defect location function. The process includes: Perform fast Fourier transform on the real part of the reflection coefficient to obtain the defect location spectrum, the specific expression is: ； in, is the reflection coefficient; Performing a fast Fourier transform on the attenuation term and performing a deconvolution operation with the defect location spectrum to obtain the compensated defect location function; The defect location function after compensation is: ； in, T ( x ) is the defect location function after compensation; * -1 is the deconvolution operator; F ( x ) is the defect location spectrum; is the attenuation constant; x is the distance between the defect position in the cable to be tested and the head end of the cable to be tested; is the attenuation term, FFT() is the fast Fourier transform; In S3, the expression of the impulse response function is: ； in, P ( x ) is the impulse response function; T ( x ) is the defect location function after compensation; The expression of the impulse response function is derived based on the correction formula of wave impedance; The correction formula is constructed based on the relationship between the reflection coefficient and the wave impedance, and the expression is: ； in, M is the magnitude of the reflection coefficient, C ( M ) is the wave impedance difference.

2. A cable defect location method according to claim 1, characterized in that: In S2, the attenuation constant in the reflection coefficient is determined using the following formula: ; in, is the attenuation constant; k is the fitting coefficient; f is the frequency of electromagnetic wave signal; The fitting coefficient is determined based on the reflection coefficient, specifically: By linearly fitting the upper boundary of the envelope of the reflection coefficient in the frequency domain, the absolute value of the slope of the fitting function on the upper boundary of the envelope is obtained, and the fitting coefficient is obtained. k .

3. A cable defect location method according to claim 1, characterized in that: In S4, the impulse response function is integrated to obtain a step response positioning spectrum of the difference between each wave impedance of the cable to be tested and the normal wave impedance, which is specifically: ； in, D ( x ) is the step response positioning spectrum of the difference between each wave impedance of the cable to be tested and the normal wave impedance; P ( x ) is the impulse response function; x It is the distance between the defect position in the cable to be tested and the beginning of the cable to be tested.

4. A cable defect location system for implementing the cable defect location method according to any one of claims 1 to 3, characterized in that: include: A data acquisition module, used to obtain the reflection coefficient of the cable to be tested; An attenuation constant calculation module, used to determine the attenuation constant in the reflection coefficient; A compensation module, used for compensating the attenuation constant by deconvolution operation to obtain a compensated defect location function; An impulse response processing module is used to obtain an impulse response function that can reflect the actual change of wave impedance based on the compensated defect location function; The step response positioning processing module is used to integrate the impulse response function to obtain a step response positioning spectrum of the difference between each wave impedance section corresponding to the cable to be tested and the normal wave impedance, and locate the defects of the cable to be tested based on the step response positioning spectrum.

5. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the cable defect locating method according to any one of claims 1 to 3 are implemented.

6. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the cable defect locating method according to any one of claims 1 to 3 are implemented.

7. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the cable defect location method according to any one of claims 1 to 3 are implemented.

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