Cable multi-joint defect mixed positioning method and device based on broadband impedance spectrum

Abstract

The method comprises the following steps: building a test platform, connecting the cable to be measured to an impedance analyzer; selecting a suitable frequency band as the working frequency band of the impedance analyzer for measurement, and transmitting the broadband impedance spectrum to the host computer; processing the obtained broadband impedance spectrum data to obtain a positioning spectrum, so that the defect and joint position can be obtained. The mixed positioning device comprises: an impedance measurement module for obtaining the impedance data of the cable head end in a certain frequency band; a data transmission module for transmitting the cable head end impedance data obtained by the impedance measurement module to the data processing host computer when the impedance data is detected; and a data processing module for obtaining a positioning spectrum by processing the cable head end impedance data, and obtaining the cable joint and defect position. The present application can efficiently and accurately locate the positions of multiple joints and defects of the cable, and realize non-destructive positioning of the cable joints and defects.

Description

Technical Field

[0001] This invention belongs to the field of power cable defect detection, and relates to a method and device for hybrid location of cable multi-joint defects based on broadband impedance spectrum. Background Technology

[0002] Cross-linked polyethylene (XLPE) cables are becoming increasingly important in modern power systems due to their excellent electrical and mechanical properties, and are widely used in power transmission projects. During long-term operation, cables are susceptible to environmental factors, leading to gradual degradation of insulation performance and the appearance of localized defects. To reduce cable maintenance time and costs, it is necessary to locate and inspect the defective parts of the cable.

[0003] Because cables can reach lengths of several kilometers, traditional manual maintenance methods are time-consuming and labor-intensive. To reduce the time and cost of cable maintenance, two non-destructive cable defect location techniques are currently mainly used: Time Domain Reflectometry (TDR) and Frequency Domain Reflectometry (FDR). Both methods utilize the information contained in the reflected signals to diagnose impedance discontinuities in the cable line, thus revealing the location of the cable defect. The TDR method locates the defect by injecting a pulse signal and analyzing the time delay difference of the received reflected wave. However, the reflected signal from the defect is weak, making precise location difficult. The FDR method estimates the defect location by analyzing the broadband impedance spectrum (BIS) or the reflection coefficient spectrum (RCS). Due to the introduction of more high-frequency signals, it achieves higher location accuracy.

[0004] Existing technologies can pinpoint individual defects in cables with relatively high accuracy. However, in actual power supply lines, due to their long lengths, multiple joints are often present in the cables. The presence of multiple joints can interfere with the detection and location of cable defects. Therefore, considering the characteristics of actual power supply lines, researching a hybrid location method and device for multiple cable joint defects based on broadband impedance spectrum is an urgent problem to be solved in power supply line inspection. Summary of the Invention

[0005] To address the current problem of mixed location of defects in multiple cable joints, this invention proposes a method and device for mixed location of defects in multiple cable joints based on broadband impedance spectroscopy (BIS). This method can efficiently and accurately locate the positions of multiple cable joints and defects, achieving non-destructive location of cable joints and defects.

[0006] The technical solution adopted in this invention is as follows:

[0007] A hybrid defect location method for multiple cable joints based on broadband impedance spectrum includes the following steps:

[0008] Step 1: Set up the test platform and connect the cable under test to the impedance analyzer;

[0009] Step 2: Select a suitable frequency band as the operating frequency band of the impedance analyzer for measurement, and transmit the broadband impedance spectrum to the host computer;

[0010] Step 3: Process the obtained broadband impedance spectrum data to obtain the location spectrum, which can be used to determine the location of defects and joints.

[0011] Step 2 includes the following steps:

[0012] Step 2.1: Select a suitable frequency band and sampling step size as the operating frequency band of the impedance analyzer for measurement.

[0013] The conditions for determining the test step size Δf (Hz) of the impedance analyzer are shown in equation (1):

[0014]

[0015] In equation (1), v is the propagation speed of electromagnetic waves in the cable, in m / s; l is the actual length of the cable being measured, in m; Δf is the frequency domain measurement step size;

[0016] Step 2.2: The host computer obtains the broadband impedance spectrum data measured by the impedance analyzer through the data transmission module.

[0017] Step 3 includes the following steps:

[0018] Step 3.1: Perform Taylor windowing on the broadband impedance spectrum Z0(f): Z0(f)*taylorwin(w)=Z w (f), to obtain Z w (f);

[0019] Step 3.2: Process the broadband impedance spectrum data using linear frequency-modulated Z-transform to obtain the localization spectrum Z0(x);

[0020] Linear frequency modulated Z-transform can sample at any frequency band on the unit circle of the Z-plane, effectively removing interference from redundant data. Its sampling point z... k Represented as Equation (2):

[0021] z k =AW -k (k=0,1…,M-1) (2);

[0022] Where k is z k The counting variable, M, is the total number of sampling points. Let A0 be the starting position, A0 be the radius, and θ0 be the phase angle; The sampling path is defined by W0, the stretching factor is defined by W0, and the angle between sampling points is defined by φ0. When A and W0 are both set to 1, it is considered as sampling the unit circle into M equal parts.

[0023] That is, by controlling the start and end sampling points and sampling phase difference of the linear frequency modulated Z-transform, the windowed impedance spectrum data Z-transform can be transformed. w (f) Transform into any desired localization spectrum Z0(x):

[0024]

[0025] In the formula, n is the counting variable of Z0(f), and * indicates taking the conjugate of the complex number. The location spectrum can be obtained by plotting the Z0(x) curve.

[0026] Step 3.3: By locating the abnormal peaks in the positioning spectrum, the cable joint and defect locations can be determined.

[0027] A cable multi-joint defect hybrid location device based on broadband impedance spectrum includes:

[0028] Impedance measurement module is used to acquire cable end impedance data within a certain frequency band;

[0029] The data transmission module transmits the cable end impedance data obtained by the impedance measurement module to the data processing host computer in the built-in format when impedance data is detected.

[0030] The data processing module is a host computer that stores computer programs. It processes the impedance data at the beginning of the cable to obtain a location spectrum and the location of the cable joint and defect.

[0031] This invention provides a method and apparatus for hybrid location of defects in multiple cable joints based on broadband impedance spectrum, with the following technical advantages:

[0032] 1) The cable defect location method of the present invention can achieve non-destructive location of cable joints and defects;

[0033] 2) The method of the present invention can efficiently and accurately locate the positions of multiple joints and defects in a power supply line containing multiple joints.

[0034] 3) This invention uses linear frequency-modulated Z-transform to process broadband impedance spectrum data, which can process the impedance data into a positioning spectrum of arbitrary range and improve positioning accuracy. Attached Figure Description

[0035] Figure 1 This is a flowchart of the method of the present invention.

[0036] Figure 2This is a diagram showing the location of joints and defects in an 823m 10kV XLPE coaxial copper core cable.

[0037] Figure 3 Location spectrum of 823m 10kV XLPE coaxial copper core cable.

[0038] Figure 4 This is a diagram showing the location of the connector and defects in a 146m radio frequency coaxial communication cable.

[0039] Figure 5 Location spectrum of a 146m radio frequency coaxial communication cable.

[0040] Figure 6 This is a schematic diagram of the structure of a cable multi-joint defect mixed positioning device according to the present invention. Detailed Implementation

[0041] The multi-joint defect hybrid location method based on broadband impedance spectrum includes the following steps:

[0042] Step S1: Set up the test platform, calibrate the measurement error of the impedance analyzer, and connect the first end of the cable under test to the impedance analyzer;

[0043] Step S2: Select a suitable frequency band as the working frequency band of the impedance analyzer for measurement, and transmit the broadband impedance spectrum to the host computer.

[0044] Step S3: The obtained broadband impedance spectrum data is processed to obtain the location spectrum, from which the location of defects and joints can be determined.

[0045] Preferably, step S1 specifically includes:

[0046] Step S1.1: Set up the test platform, calibrate the impedance analyzer to eliminate its measurement errors, and complete the preliminary preparations for data transmission between the impedance analyzer and the host computer.

[0047] Step S1.2: Connect the first end of the coaxial cable under test to the impedance analyzer, and keep the end in an open circuit state for testing; connect the test terminals of the impedance analyzer to the cable core and the metal shielding layer of the cable respectively to measure its broadband impedance spectrum Z0(f).

[0048] Preferably, step S2 specifically includes:

[0049] Step S2.1: Select a suitable frequency band and sampling step size as the operating frequency band of the impedance analyzer for measurement.

[0050] The conditions for determining the test step size Δf (Hz) of the impedance analyzer are shown in equation (1):

[0051]

[0052] In the above formula, v (m / s) is the propagation speed of electromagnetic waves in the cable, and l (m) is the actual length of the cable being measured.

[0053] Step S2.2: The host computer obtains the broadband impedance spectrum data measured by the impedance analyzer through the data transmission module.

[0054] Preferably, step S3 specifically includes:

[0055] Step S3.1: Perform Taylor windowing on the broadband impedance spectrum Z0(f) to obtain Z w (f).

[0056] Step S3.2: Since the input impedance spectrum can be expressed as a function of frequency, it can be processed using Fourier transform to obtain spatial domain location spectrum data reflecting the defect data. Because traditional Fourier transform has limitations in practical applications and contains a large amount of redundant data interfering with the location results, this invention uses linear frequency modulated Z-transform to process the broadband impedance spectrum data to obtain the location spectrum Z0(x).

[0057] The linear frequency modulated Z-transform is a transformation method that can sample any frequency band on the unit circle of the Z-plane, effectively removing interference from redundant data. Its sampling points can be expressed by equations (2) to (4):

[0058] z k =AW -k (k=0,1…,M-1) (2)

[0059]

[0060] Where M is the total number of sampling points, A is the starting position, A0 is the radius, θ0 is the phase angle, W0 is the extension rate, and φ0 is the angle between the sampling points. In this invention, A and W0 are both set to 1, which is considered as sampling the unit circle into M equal parts.

[0061] By controlling the start and end sampling points and sampling phase difference of the linear frequency modulated Z-transform, the windowed impedance spectrum data can be Z-transformed. w (f) Transform it into any desired localization spectrum Z0(x). Plotting the Z0(x) curve will yield the localization spectrum.

[0062] Step S3.3: By locating the abnormal peaks in the positioning spectrum, the cable joint and defect location can be determined.

[0063] Example 1:

[0064] This example demonstrates a test locating one joint and one shielding defect in an 823m 10kV XLPE copper core cable. The locations of the joint and defect are as follows: Figure 2 As shown. The implementation process of this embodiment is as follows. Figure 1 As shown, a multi-joint defect hybrid localization method based on broadband impedance spectrum includes the following steps:

[0065] A1.1: Set up a test platform, calibrate the impedance analyzer to eliminate its measurement errors, and complete the preliminary preparations for data transmission between the impedance analyzer and the host computer.

[0066] A1.2: Connect the first end of the 10kV XLPE coaxial copper core cable to the impedance analyzer, and keep the end in an open circuit state for testing. Connect the test terminals of the impedance analyzer to the copper core and the metal shielding layer of the cable respectively to measure its broadband impedance spectrum Z0(f).

[0067] A2.1: Select the frequency band from 0.1MHz to 75MHz as the operating frequency band of the impedance analyzer for measurement, with 2400 frequency domain measurement points.

[0068] A2.2: The host computer reads the broadband impedance spectrum data measured by the impedance analyzer through the data transmission module.

[0069] A3.1: The impedance spectral number Z0(f) is processed using the Taylor window function to obtain Z w (f) is used to improve the effect of subsequent transformations.

[0070] A3.2: By analyzing Z w (f) Perform linear frequency modulation Z-transform to obtain the positioning spectrum Z0(x), i.e., obtain the positioning spectrum, as shown in the figure. Figure 3 As shown. By Figure 3 As can be seen, the abnormal peaks are located at 419.91m and 619.75m respectively. The actual locations of the copper shielding layer and the connector are 420m and 620m, respectively, corresponding to absolute positioning errors of 0.09m and 0.25m, and relative errors of 0.01% and 0.03%. The absolute error is the absolute value of the distance difference between the positioned location and the actual location, and the relative error is defined as the ratio of the absolute error to the total length of the cable being measured.

[0071] Example 2:

[0072] This embodiment is a test locating eight joints and one copper shielding defect on a 146m RF coaxial communication cable. The locations of the joints and defects are as follows: Figure 4 As shown. The implementation process of this embodiment is as follows. Figure 1 As shown, a multi-joint defect hybrid localization method based on broadband impedance spectrum includes the following steps:

[0073] B1.1: Set up a test platform, calibrate the impedance analyzer to eliminate its measurement errors, and complete the preliminary preparations for data transmission between the impedance analyzer and the host computer.

[0074] B1.2: Connect the first end of the 146m RF coaxial communication cable to the impedance analyzer, and keep the end in an open circuit state for testing. Connect the test terminals of the impedance analyzer to the copper core and the metal shielding layer of the cable respectively to measure its broadband impedance spectrum Z0(f).

[0075] B2.1: Select the frequency band from 0.1MHz to 60MHz as the operating frequency band of the impedance analyzer for measurement, with 1600 frequency domain measurement points.

[0076] B2.2: The host computer reads the broadband impedance spectrum data measured by the impedance analyzer through the data transmission module.

[0077] B3.1: The impedance spectral number Z0(f) is processed using the Taylor window function to obtain Z w (f) is used to improve the effect of subsequent transformations.

[0078] B3.2: By analyzing Z w (f) Perform linear frequency modulated Z-transform to obtain the localization spectrum Z0(x), the result is as follows Figure 5 As shown. Figure 5 The abnormal peaks are clearly visible at 16.51m, 39.78m, 55.74m, 69.00m, 80.64m, 96.34m, 116.36m, 126.37m, 140.17m, and 152.35m. Table 1 shows the location results and error analysis of eight joints and one shielding layer defect. As can be seen from Table 1, the absolute error of the location of each joint and defect does not exceed 0.40m, and the relative error does not exceed 0.3%.

[0079] The two embodiments above demonstrate that the multi-joint defect hybrid location method based on broadband impedance spectrum proposed in this invention can achieve good defect location results when multiple joints and defects coexist.

[0080] Table 1. Positioning Results and Error Analysis

[0081]

[0082] Example 3:

[0083] The present invention also provides a mixed location device for defects in multiple cable joints, such as... Figure 6 As shown, it includes:

[0084] The impedance measurement module is a HIOKI IM7581 impedance analyzer loaded with a HIOKI IM9202 test fixture, used to acquire cable end impedance data within a certain frequency band.

[0085] The data transmission module is a data transmission device that uses an Ethernet interface and an RJ-45 interface to store the cable end impedance data obtained by the impedance measurement module in the module's built-in data format and transmit it to the data processing host computer.

[0086] The data processing module is a host computer that stores computer programs. It processes the impedance data at the beginning of the cable to obtain a location spectrum and the location of cable joints and defects.

Claims

1. A hybrid defect location method for multiple cable joints based on broadband impedance spectrum, characterized in that... Includes the following steps: Step 1: Set up the test platform and connect the cable under test to the impedance analyzer; Step 2: Select a suitable frequency band as the operating frequency band of the impedance analyzer for measurement, and transmit the broadband impedance spectrum to the host computer; Step 3: Process the obtained broadband impedance spectrum data to obtain the location spectrum, which can be used to determine the location of defects and joints. Step 3 includes the following steps: Step 3.1: Broadband impedance spectrum Perform Taylor window addition processing: ,get ; Step 3.2: Process the broadband impedance spectrum data using linear frequency-modulated Z-transform to obtain the localization spectrum. ; Linear frequency modulated Z-transform can sample at any frequency band on the unit circle of the Z-plane, effectively removing interference from redundant data; its sampling points Represented as Equation (2): in, for The counting variable, The total number of sampling points. Starting position For radius, Phase angle; For the sampling path, For elongation, The sampling points are divided into equal angles; and A value of 1 is considered as an application of the unit circle. Equal sampling; That is, by controlling the start and end sampling points and sampling phase difference of the linear frequency modulated Z-transform, the windowed impedance spectrum data can be processed. Transform into any desired localization spectrum : ； In the formula, for The counting variable, To take the conjugate of a complex number; The location spectrum can be obtained by plotting the curve. Step 3.3: By locating the abnormal peaks in the positioning spectrum, the cable joint and defect locations can be determined.

2. The method for hybrid location of cable joint defects based on broadband impedance spectrum according to claim 1, characterized in that: Step 2 includes the following steps: Step 2.1: Select a suitable frequency band and sampling step size as the operating frequency band of the impedance analyzer for measurement; Test step size of impedance analyzer The conditions for taking the value are shown in equation (1): (1)； In equation (1), The speed of electromagnetic waves in a cable, measured in m / s; The actual length of the cable measured, in units of: ; For frequency domain measurement step size; Step 2.2: The host computer obtains the broadband impedance spectrum data measured by the impedance analyzer through the data transmission module.

3. A positioning device for implementing the hybrid positioning method for cable multi-joint defects based on broadband impedance spectrum as described in claim 1 or 2, characterized in that... include: Impedance measurement module is used to acquire cable end impedance data within a certain frequency band; The data transmission module transmits the cable end impedance data obtained by the impedance measurement module to the data processing host computer in the built-in format when impedance data is detected. The data processing module is a host computer that stores computer programs. It processes the impedance data at the beginning of the cable to obtain a location spectrum and the location of the cable joint and defect.

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