Cable shielding layer damage degree assessment method, system and device and storage medium

Abstract

The invention discloses a cable shielding layer damage degree evaluation method, which comprises the following steps of: according to a transmission line theory, enabling a cable under high frequency to be equivalent to a distributed parameter model, establishing a corresponding defect sample library by simulating metal shielding layer damage of different degrees of the cable, and calculating to obtain a broadband impedance spectrum of the cable containing defects under a simulation condition; processing the broadband impedance spectrum to obtain positioning spectrum data containing defect positioning peaks; and performing function fitting on the positioning spectrum data to obtain a damage degree evaluation function of the metal shielding layer. By adopting the method, the damage degree and the damage position of the metal shielding layer of the cable can be quickly and accurately evaluated; when a power grid is maintained and repaired, manpower and material resources can be saved and fault detection time can be shortened by using the method.

Description

Technical Field

[0001] The present invention relates to the field of power cable defect detection, and in particular to a method, system, device and storage medium for evaluating the degree of damage of a cable shielding layer. Background Art

[0002] As an important infrastructure in modern society, cross-linked polyethylene (XLPE) cables are widely used in power transmission projects. During long-term operation, cables are easily affected by environmental factors, which leads to gradual degradation of insulation performance, thereby increasing the possibility of failure. In order to ensure the safety and reliability of power supply, extend the service life of cables, improve the working efficiency of power systems, and reduce economic losses, regular cable fault detection must be carried out.

[0003] At present, the main method for cable fault detection is cable defect location, and the main methods are time domain reflectometry (TDR) and frequency domain reflectometry (FDR). The TDR method locates the defect position by inputting a pulse signal based on the time delay difference of the received reflected wave. Since there are few high-frequency signals in TDR, the accuracy of defect location by this method is poor and it is easily interfered. The FDR method introduces more high-frequency signals, which makes it have a higher resolution for defect location and thus achieves precise positioning; and the high-frequency signal is less affected by environmental interference. This method mainly uses broadband impedance spectroscopy (BIS) and reflection coefficient spectrum (RCS), and processes them through some transformation methods to obtain the required positioning spectrum to achieve accurate positioning of cable defects.

[0004] In the prior art, there are methods of creating local cable faults by changing the complex dielectric constant through simulation or heating the fixed position of the cable through designed experiments. The defect location can be obtained more accurately in the positioning spectrum and the degree of aging of the defect can be reflected. However, it is impossible to detect and locate cable shielding defects of different severity. Summary of the invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the background technology, the first purpose of the present invention is to disclose a method for evaluating the degree of damage of a cable shielding layer;

[0006] The second object is to disclose a cable shield damage assessment system;

[0007] The third object is to disclose a device for assessing the degree of damage to a cable shielding layer;

[0008] A fourth objective is to disclose a storage medium for evaluating the degree of damage to a cable shielding layer.

[0009] Technical solution: The cable shielding layer damage assessment method disclosed in the present invention comprises the following steps:

[0010] S1. According to the transmission line theory, the cable at high frequency is equivalent to a distributed parameter model. By simulating the damage of the metal shielding layer of the cable to different degrees, a corresponding defect sample library is established, and the broadband impedance spectrum of the defective cable under simulation is calculated;

[0011] S2. Processing the broadband impedance spectrum to obtain positioning spectrum data containing defect positioning peaks;

[0012] S3. Function fitting is performed on the positioning spectrum data to obtain a damage degree assessment function for the metal shielding layer.

[0013] Among them, in S1, different metal shielding layer damages are simulated by changing the local cable parameter settings at the fault point.

[0014] Furthermore, the broadband impedance spectrum of the defective cable in S1 is calculated as follows:

[0015] The starting positions of cable defects are l a To b , Z 0h , γ h are the characteristic impedance and propagation constant of normal cables, Z 0d , γ d are the characteristic impedance and propagation constant at the cable defect, respectively;

[0016] Broadband impedance spectrum Z of defective cable d (f):

[0017]

[0018]

[0019]

[0020]

[0021]

[0022] In the formula, Z la (f), Z lb (f) is the cable at the defect starting point l a , l b The broadband impedance spectrum of la , Γ lb is the cable at the defect starting point l a , l b The reflection coefficient.

[0023] Furthermore, in S2, by performing Fourier transform on the broadband impedance spectrum and adding a Taylor window function to suppress its spectrum leakage, the frequency domain data is converted into spatial domain data to obtain a positioning spectrum containing defect positioning peaks.

[0024] Furthermore, in S2, by adjusting the simulation parameters, a sample database of simulated cable defect location spectra with different degrees of shielding layer damage is established.

[0025] Furthermore, in S3, a polynomial function is fitted between the normalized amplitude at the defect abnormal peak in the positioning spectrum data and the damage degree of the cable metal shielding layer to obtain a cable metal shielding layer damage degree evaluation function.

[0026] Furthermore, S3 specifically includes:

[0027] Record the abnormal peak value of the positioning spectrum corresponding to the degree of damage, the abnormal peak value is the independent variable, and the degree of damage is the dependent variable;

[0028] The polynomial order required for fitting is determined, the fitting equation is constructed, the residual sum of squares between the data points and the fitting curve is optimized, the polynomial fitting coefficients are solved, and the metal shielding layer damage degree evaluation function is obtained.

[0029] The present invention also discloses a cable shielding layer damage assessment system, comprising:

[0030] The simulation modeling module is used to simulate and establish a sample database of cable defect location spectra with different degrees of shielding layer damage, and fit the cable metal shielding layer damage degree estimation function;

[0031] Data acquisition module, used to obtain the impedance data of the cable head end within a certain frequency band;

[0032] The feature extraction module processes the impedance data of the first end of the cable to obtain the cable defect location and the abnormal peak of the positioning spectrum;

[0033] The defect estimation module obtains the damage degree of the cable metal shielding layer by bringing the extracted abnormal peak into the fitted damage degree estimation function.

[0034] The present invention also discloses a cable shielding layer damage assessment device, comprising: one or more processors;

[0035] A storage device for storing one or more programs and resource data;

[0036] When the one or more programs are executed by one or more processors, the one or more processors implement the above-mentioned cable shielding layer damage degree assessment method.

[0037] The present invention also discloses a storage medium for evaluating the degree of damage of a cable shielding layer, on which a computer program is stored. When the program is executed by a processor, the method for evaluating the degree of damage of a cable shielding layer is implemented.

[0038] Beneficial effects: Compared with the prior art, the present invention provides a non-destructive cable defect detection method, which can quickly and accurately evaluate the degree of damage and the location of the cable metal shielding layer; during power grid maintenance and repair, the use of this method can save manpower and material resources and shorten fault detection time. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of the method of the present invention;

[0040] Figure 2 A model diagram of a cable transmission line with local defects in Example 1;

[0041] Figure 3 It is the positioning spectrum in Example 1;

[0042] Figure 4 The simulation and experimental results and fitting curves in Example 1 are shown. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0044] Example 1

[0045] like Figure 1 The cable shield damage assessment method shown includes the following steps:

[0046] S1. According to the transmission line theory, the cable at high frequency is equivalent to a distributed parameter model. By changing the local cable parameter settings at the fault point, the metal shielding layer of the simulated cable is damaged to different degrees, and a corresponding defect sample library is established. The broadband impedance spectrum of the defective cable under simulation conditions is calculated.

[0047] The defects of the cable will cause the distribution parameters at the local defect to change. The present invention uses the following model to describe the signal transmission characteristics of the defective cable, such as Figure 2 As shown in the figure, R0, L0, G0, and C0 represent the resistance, inductance, conductance, and capacitance of the cable per unit length. The broadband impedance spectrum of the defective cable is obtained by simulation using the FDR method.

[0048] The starting positions of cable defects are l a To b , Z 0h , γ h are the characteristic impedance and propagation constant of normal cables, Z 0d , γ dare the characteristic impedance and propagation constant at the cable defect, respectively;

[0049] Broadband impedance spectrum Z of defective cable d (f):

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] In the formula, Z la (f), Z lb (f) is the cable at the defect starting point l a , l b The broadband impedance spectrum of la , Γ lb is the cable at the defect starting point l a , l b The reflection coefficient.

[0056] S2. By performing Fourier transform on the broadband impedance spectrum and adding Taylor window function to suppress its spectrum leakage, the frequency domain data is converted into spatial domain data to obtain a positioning spectrum containing defect positioning peaks; by adjusting the simulation parameters, a sample database of defect positioning spectra of simulated cables with different degrees of shielding layer damage is established.

[0057] S3. Perform polynomial function fitting on the normalized amplitude at the defect abnormal peak in the positioning spectrum data and the damage degree of the cable metal shielding layer to obtain a cable metal shielding layer damage degree evaluation function, which specifically includes:

[0058] The abnormal peak of the positioning spectrum corresponding to the degree of damage is recorded, with the abnormal peak as the independent variable and the degree of damage as the dependent variable; the polynomial order required for fitting is determined, the fitting equation is constructed, the residual sum of squares between the data points and the fitting curve is optimized, the polynomial fitting coefficient is solved, and the metal shielding layer damage degree evaluation function is obtained.

[0059] The power cables simulated in this embodiment are 10m and 20m copper core cross-linked polyethylene (XLPE) cables, named as cables 1 and 2 respectively. The measured data is a 13.40m copper core cross-linked polyethylene cable, named as cable 3. The defect of cable 1 is 6.00m away from the head end of the cable; the defects of cables 2 and 3 are 3.40m away from the head end of the cable. The wideband impedance spectrum of cable 3 is tested by sweep frequency of impedance analyzer. The lower limit of the sweep frequency signal is 0.1MHz, the upper limit of the frequency is 300MHz, and the number of sampling points is 801.

[0060] According to Figure 1 the above method shown is implemented as follows:

[0061] For the simulation of different degrees of damage to the metal shielding layer. Since the local damage of the metal shielding layer of the cable will cause the physical entity part of this section of the cable to be missing and the physical coaxial structure to change, resulting in a decrease in the capacitance of the relevant defective section. Therefore, different degrees of damage to the metal shielding layer can be simulated by changing the capacitance at the defective part of the cable, that is, making the capacitance per unit length C d = kC (0 < k < 1), where C is the capacitance per unit length of the intact cable. The smaller k is, the more serious the damage to the metal shielding layer.

[0062] Separate defect sample libraries of different degrees of damage to the metal shielding layer of Cable No. 1 and Cable No. 2 are simulated and established. In the sample library, the proportion coefficients x of the damage degree of the metal shielding layer of different samples are x = [0.99 0.95 0.90 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.35 0.25]. The broadband impedance spectrum Z d (f) of the cable with defects under the simulation conditions is calculated.

[0063] Connect the impedance analyzer to the head end of Cable No. 3, and keep the other end as the tail end in an open state. The two clamping fixtures at both ends of the impedance analyzer are respectively connected to the cable core and the grounded copper shielding layer to obtain the broadband impedance spectrum Z d (f) of the real cable. The degrees of damage to the copper shielding layer of Cable No. 3 during the experiment are 35%, 55%, and 75% respectively.

[0064] Perform Fourier transform on Z d (f), and add a Taylor window function to suppress its spectral leakage. Convert the frequency-domain data Z d (f) to spatial-domain data Z d (z).

[0065] For the convenience of observation, Figure 3 only partially exemplified is the positioning spectrogram of the cable with different degrees of damage to the copper shielding layer (Cable No. 1) obtained, as Figure 3 shown. It can be seen from the figure that the abnormal peak is located at 6.08 m, and the positioning result differs from the actual defect position by 0.08 m. The maximum error precision of the defect positioning result is only 0.8%, indicating that this method can accurately locate the defect position. And from Figure 3 it can be known that as the degree of damage to the copper shielding layer increases, the abnormal peak value increases.

[0066] The defect data obtained from the simulated coaxial cable No. 1 is used as the data set to be fitted, which is two-dimensional data (x, y), where the normalized amplitude x of the abnormal peak of the positioning spectrum is the independent variable, and the degree of damage of the copper shielding layer y is the corresponding dependent variable value.

[0067] The order of the polynomial function required for the selected fit is 3.

[0068] Construct the fitting equation, which is in the form of:

[0069] f(x)=a0+a1x+a2x 2 +a3x 3

[0070] Where a0, a1, a2, a3 are the polynomial coefficients that need to be determined.

[0071] The least square fitting method is used to minimize the residual sum of squares between the data points and the fitting curve, and then the polynomial coefficients a0, a1, a2, a3 are solved to obtain the metal shielding layer damage evaluation function f(x).

[0072] After using the simulated coaxial cable No. 1 to obtain the metal shielding layer damage evaluation function f(x), the simulated coaxial cable No. 2 was simulated and analyzed first, and then the real cable No. 3 was tested. The results are as follows: Figure 4 shown. Figure 4 In the figure, the red solid line is the fitting function f(x) curve obtained by using the simulated coaxial cable No. 1; the blue dotted line is the simulation experiment result of the simulated coaxial cable No. 2, that is, the variation curve of the damage degree of the metal shielding layer with the normalized amplitude of the abnormal peak under the simulation condition; the green circle represents the measured experimental result of the real cable No. 3, that is, the damage degree of the metal shielding layer and its corresponding normalized amplitude of the abnormal peak under the actual measurement condition. Figure 4 The metal shielding layer damage degree assessment function is more accurate in assessing the damage degree of the metal shielding layer. x h 、x l are the upper and lower limits of the normalized amplitude, y2 and y1 are the actual damage degree of the copper shielding layer of the simulated cable and the damage degree of the copper shielding layer evaluated by the damage degree evaluation function f(x), respectively. The difference between the fitting curve and the simulation data can be evaluated. The experimental results show that the sum of squares of the residuals between the fitting curve (red realization) and the simulation structure (blue dotted line) is 0.0263. The amplitude of the measured data is substituted into the damage degree evaluation function of the metal shielding layer, and the damage degrees evaluated are 34.14%, 57.66%, and 78.30%, respectively, corresponding to the actual damage degrees of 35%, 55%, and 75%, respectively. The average error between the evaluation value and the actual value of the damage degree is 2.27%.

[0073] Example 2

[0074] The present invention also provides a cable shielding layer damage assessment system, comprising:

[0075] The simulation modeling module is used to simulate and establish a sample database of cable defect location spectra with different degrees of shielding layer damage, and fit the cable metal shielding layer damage degree estimation function;

[0076] Data acquisition module, used to obtain the impedance data of the cable head end within a certain frequency band;

[0077] The feature extraction module processes the impedance data of the first end of the cable to obtain the cable defect location and the abnormal peak of the positioning spectrum;

[0078] The defect estimation module obtains the damage degree of the cable metal shielding layer by bringing the extracted abnormal peak into the fitted damage degree estimation function.

[0079] Example 3

[0080] The present invention also provides a cable shielding layer damage assessment device, comprising: one or more processors;

[0081] A storage device for storing one or more programs and resource data;

[0082] When the one or more programs are executed by one or more processors, the one or more processors implement the above-mentioned cable shielding layer damage degree assessment method.

[0083] Example 4

[0084] The present invention also provides a storage medium for evaluating the degree of damage of a cable shielding layer, on which a computer program is stored. When the program is executed by a processor, the above-mentioned method for evaluating the degree of damage of a cable shielding layer is implemented.

[0085] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods or computer program products. Therefore, the present application may adopt the form of a complete software embodiment or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0086] The present application is described with reference to the flowcharts of the methods and computer program products according to the embodiments of the present application. It should be understood that each process in the flowchart can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the process in the flowchart. Figure 1 A device that specifies the functions of a process or multiple processes.

[0087] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A function specified in a process or multiple processes.

[0088] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 The steps of a specified function in a process or multiple processes.

[0089] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A method for evaluating the degree of damage to a cable shielding layer, characterized in that: The following steps are involved: S1. According to the transmission line theory, the cable at high frequency is equivalent to a distributed parameter model. By simulating the damage of the metal shielding layer of the cable to different degrees, a corresponding defect sample library is established, and the broadband impedance spectrum of the defective cable under simulation is calculated; S2. Processing the broadband impedance spectrum to obtain positioning spectrum data containing defect positioning peaks; S3. Function fitting is performed on the positioning spectrum data to obtain a damage degree assessment function for the metal shielding layer.

2. The cable shielding layer damage assessment method according to claim 1, characterized in that: In S1, different metal shielding layer damages are simulated by changing the local cable parameter settings at the fault point.

3. The cable shielding layer damage assessment method according to claim 1, characterized in that: The broadband impedance spectrum calculation method of the defective cable in S1 is as follows: The starting positions of cable defects are l a To b , Z 0h , γ h are the characteristic impedance and propagation constant of normal cables, Z 0d , γ d are the characteristic impedance and propagation constant at the cable defect, respectively; Broadband impedance spectrum Z of defective cable d (f): In the formula, Z la (f), Z lb (f) is the cable at the defect starting point l a , l b The broadband impedance spectrum of la , Γ lb The cable is at the defect starting point l a , l b The reflection coefficient.

4. The cable shielding layer damage assessment method according to claim 1, characterized in that: In S2, the broadband impedance spectrum is Fourier transformed, and the Taylor window function is added to suppress its spectrum leakage, and the frequency domain data is converted into spatial domain data to obtain a positioning spectrum containing defect positioning peaks.

5. The cable shielding layer damage assessment method according to claim 1, characterized in that: In S2, by adjusting the simulation parameters, a sample database of defect location spectra of simulated cables with different degrees of shielding layer damage is established.

6. The cable shielding layer damage assessment method according to claim 1, characterized in that: In S3, a polynomial function is fitted between the normalized amplitude at the defect abnormal peak in the positioning spectrum data and the damage degree of the cable metal shielding layer to obtain a cable metal shielding layer damage degree evaluation function.

7. The cable shielding layer damage assessment method according to claim 1, characterized in that: S3 specifically includes: Record the abnormal peak value of the positioning spectrum corresponding to the degree of damage, the abnormal peak value is the independent variable, and the degree of damage is the dependent variable; The polynomial order required for fitting is determined, the fitting equation is constructed, the residual sum of squares between the data points and the fitting curve is optimized, the polynomial fitting coefficients are solved, and the metal shielding layer damage degree evaluation function is obtained.

8. A cable shield damage assessment system, characterized in that: include: The simulation modeling module is used to simulate and establish a sample database of cable defect location spectra with different degrees of shielding layer damage, and fit the cable metal shielding layer damage degree estimation function; Data acquisition module, used to obtain the impedance data of the cable head end within a certain frequency band; The feature extraction module processes the impedance data of the first end of the cable to obtain the cable defect location and the abnormal peak of the positioning spectrum; The defect estimation module obtains the damage degree of the cable metal shielding layer by bringing the extracted abnormal peak into the fitted damage degree estimation function.

9. A cable shield damage assessment device, characterized in that: include: one or more processors; A storage device for storing one or more programs and resource data; When the one or more programs are executed by one or more processors, the one or more processors implement the cable shielding layer damage degree assessment method as described in any one of claims 1 to 7.

10. A storage medium for evaluating the degree of damage of a cable shielding layer, characterized in that: A computer program is stored thereon, and when the program is executed by a processor, the method for evaluating the degree of damage of a cable shielding layer as claimed in any one of claims 1 to 7 is implemented.

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