Cable multi-joint defect hybrid positioning method and device based on broadband impedance spectroscopy

Abstract

The invention discloses a cable multi-joint defect hybrid positioning method and device based on broadband impedance spectroscopy, and the method comprises the steps: building a test platform, and connecting a tested cable with an impedance analyzer; selecting a proper frequency band as a working frequency band of the impedance analyzer for measurement, and transmitting a broadband impedance spectrum to an upper computer; and processing the acquired broadband impedance spectrum data to obtain a positioning spectrogram, so that the positions of defects and joints can be obtained. The hybrid positioning device comprises an impedance measurement module used for acquiring cable head end impedance data in a certain frequency band; the data transmission module is used for transmitting the impedance data of the head end of the cable obtained by the impedance measurement module to a data processing upper computer when the impedance data is detected; and the data processing module is used for processing the head end impedance data of the cable to obtain a positioning spectrogram, and obtaining cable joints and defect positions. According to the invention, the positions of a plurality of joints and defects of the cable can be efficiently and accurately positioned, and lossless positioning of the cable joints and the defects is realized.

Description

Technical Field

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

[0002] Cross-linked polyethylene (XLPE) cables have become increasingly important in modern power systems due to their excellent electrical and mechanical properties and are widely used in power transmission projects. Cables are easily affected by environmental factors during long-term operation, which causes the insulation performance to gradually deteriorate, resulting in local defects in the cables. In order to reduce the time and cost of cable maintenance, it is necessary to locate and detect the defective parts of the cables.

[0003] Because the length of the cable may reach several thousand meters, the traditional manual maintenance method is time-consuming and labor-intensive. In order to reduce the time and cost of cable maintenance, two non-destructive cable defect location technology methods, time domain reflectometry (TDR) and frequency domain reflectometry (FDR), are currently used. Both methods are based on the fact that when the signal encounters a structure with mismatched characteristic impedance in the cable transmission line, it will be reflected at the characteristic impedance mutation. The impedance discontinuity in the cable line is diagnosed by using the information contained in the reflected signal to reflect the defect location of the cable. The time domain reflectometry (TDR) method locates the defect location by injecting a pulse signal and analyzing the time delay difference of the received reflected wave. However, the reflected signal from the defect part of the time domain reflectometry (TDR) is weak, making it difficult to accurately locate. The frequency domain reflectometry (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 has higher positioning accuracy.

[0004] Existing technologies can locate single defects in cables relatively accurately. However, in actual power supply lines, there are often multiple joints on the cables because the lines are very long. The presence of multiple joints will interfere with the detection and location of cable defects. In view of the characteristics of actual power supply lines, studying a hybrid location method and device for cable multi-joint defects based on broadband impedance spectroscopy is an urgent problem to be solved in power supply line detection. Summary of the invention

[0005] In view of the current problem of mixed positioning of multiple joint defects in cables, the present invention proposes a mixed positioning method and device for multiple joint defects in cables based on broadband impedance spectrum (BIS), which can efficiently and accurately locate the positions of multiple joints and defects of cables, and realize lossless positioning of cable joints and defects.

[0006] The technical solution adopted by the present invention is:

[0007] The hybrid positioning method for cable multi-joint defects based on broadband impedance spectroscopy includes the following steps:

[0008] Step 1: Build a test platform and connect the cable to be tested to the impedance analyzer;

[0009] Step 2: 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;

[0010] Step 3: Process the acquired broadband impedance spectrum data to obtain a positioning spectrum, from which the defect and joint locations can be obtained.

[0011] The step 2 comprises 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 test step length Δf (Hz) of the impedance analyzer is given by equation (1):

[0014]

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

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

[0017] The step 3 comprises the following steps:

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

[0019] Step 3.2: Use linear frequency modulation Z transform to process the broadband impedance spectrum data to obtain the positioning spectrum Z0(x);

[0020] The linear frequency modulation Z transform can sample any frequency band on the unit circle of the Z plane and effectively remove the interference of redundant data. k It is expressed as formula (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, is the starting point, A0 is the radius, θ0 is the phase angle; is the sampling path, W0 is the stretching rate, φ0 is the equal division angle between sampling points; A and W0 are taken as 1, which is regarded as sampling the unit circle in M ​​equal divisions.

[0023] That is, the impedance spectrum data Z after windowing can be transformed by controlling the start and end sampling points and sampling phase difference of the linear frequency modulation Z transform. w (f) Transformed into any desired positioning spectrum Z0(x):

[0024]

[0025] Where n is the counting variable of Z0(f), and * represents taking the complex conjugate. The positioning spectrum can be obtained by plotting the Z0(x) curve.

[0026] Step 3.3: By locating the position of the abnormal peak in the spectrum, the cable joint and defect position can be located.

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

[0028] Impedance measurement module, used to obtain the impedance data of the cable head end within a certain frequency band;

[0029] A data transmission module, when the impedance data is detected, transmits the impedance data of the cable head end obtained by the impedance measurement module to the data processing host computer in a format built into the data transmission module;

[0030] The data processing module is a host computer storing a computer program, which processes the impedance data of the cable head end to obtain a positioning spectrum, and obtains the cable joint and defect position.

[0031] The present invention provides a hybrid cable multi-joint defect location method and device based on broadband impedance spectroscopy, and the technical effects are as follows:

[0032] 1) The cable defect locating method of the present invention can realize non-destructive locating 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 of cables on a power supply line containing multiple joints.

[0034] 3) The present invention uses linear frequency modulation Z transform to process broadband impedance spectrum data, which can process the impedance data into a positioning spectrum in any range and improve the positioning accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The figure is a flow chart of the method of the present invention.

[0036] Figure 2This is a 823m 10kV XLPE coaxial copper core cable joint and defect location diagram.

[0037] Figure 3 This is the positioning spectrum of 823m 10kV XLPE coaxial copper core cable.

[0038] Figure 4 This is a diagram of the connectors and defect locations of a 146m RF coaxial communication cable.

[0039] Figure 5 This is the positioning spectrum of the 146m RF coaxial communication cable.

[0040] Figure 6 It is a structural schematic diagram of a hybrid positioning device for multiple cable joint defects of the present invention. DETAILED DESCRIPTION

[0041] The hybrid positioning method of multiple joint defects based on broadband impedance spectroscopy includes the following steps:

[0042] Step S1: Building a test platform, calibrating the measurement error of the impedance analyzer, and connecting the first end of the tested cable 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: Processing the acquired broadband impedance spectrum data to obtain a positioning spectrum, thereby obtaining the defect and joint locations.

[0045] Preferably, step S1 specifically comprises:

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

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

[0048] Preferably, step S2 specifically comprises:

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

[0050] The test step length Δf (Hz) of the impedance analyzer is given by 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 measured cable.

[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 comprises:

[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 by Fourier transform to obtain spatial domain positioning spectrum data reflecting the defect data. Since the traditional Fourier transform has limitations in practical application and there is a large amount of redundant data interfering with the positioning result, the present invention uses linear frequency modulation Z transform to process the broadband impedance spectrum data to obtain the positioning spectrum Z0(x).

[0057] The linear frequency modulation Z transform can sample any frequency band on the unit circle of the Z plane, which can effectively remove the interference of redundant data. Its sampling points can be expressed as equations (2) to (4):

[0058] z k =AW -k (k=0,1…,M-1) (2)

[0059]

[0060] Wherein, M is the total number of sampling points, A is the starting point position, A0 is the radius, θ0 is the phase angle, W0 is the stretch rate, and φ0 is the angle between the sampling points. In the present invention, A and W0 are set to 1, which is regarded as sampling the unit circle in M ​​equal parts.

[0061] The impedance spectrum data Z after windowing can be transformed by controlling the start and end sampling points and sampling phase difference of the linear frequency modulation Z transform. w (f) is converted into any desired localization spectrum Z0(x). The localization spectrum can be obtained by plotting the Z0(x) curve.

[0062] Step S3.3: By locating the position of the abnormal peak in the spectrum, the cable joint and the defect position can be located.

[0063] Embodiment 1:

[0064] This example is a 10kV XLPE copper core cable with a length of 823m and a 1 joint and 1 shield layer damage location test. The joint and defect locations are as follows: Figure 2 The implementation process of this embodiment is as follows. Figure 1 As shown, a hybrid positioning method for multiple joint defects based on broadband impedance spectroscopy includes the following steps:

[0065] A1.1: Build 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.

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

[0067] A2.1: Select the frequency range of 0.1MHz to 75MHz as the working frequency range of the impedance analyzer for measurement, and the number of frequency domain measurement points is 2400.

[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: Use the Taylor window function to process the impedance spectrum Z0(f) to obtain Z w (f) to improve its subsequent transformation effect.

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

[0071] Embodiment 2:

[0072] This example is a 146m RF coaxial communication cable with 8 joints and 1 copper shielding layer damage location test. Figure 4 The implementation process of this embodiment is as follows. Figure 1 As shown, a hybrid positioning method for multiple joint defects based on broadband impedance spectroscopy includes the following steps:

[0073] B1.1: Build 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.

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

[0075] B2.1: Select the frequency band of 0.1MHz to 60MHz as the working frequency band of the impedance analyzer for measurement, and the number of frequency domain measurement points is 1600.

[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: Use the Taylor window function to process the impedance spectrum Z0(f) to obtain Z w (f) to improve its subsequent transformation effect.

[0078] B3.2: Through Z w (f) Perform linear frequency modulation Z transform to obtain the positioning spectrum Z0(x). The result is as follows: Figure 5 shown. Figure 5 It can be clearly seen that the abnormal peaks are located at 16.51m, 39.78m, 55.74m, 69.00m, 80.64m, 96.34m, 116.36m, 126.37m, 140.17m, and 152.35m. Table 1 gives the positioning results and error analysis of 8 joints and 1 shielding layer defect. It can be seen from Table 1 that the absolute positioning error of each joint and defect does not exceed 0.40m, and the relative error does not exceed 0.3%.

[0079] The above two embodiments show that the multi-joint defect hybrid location method based on broadband impedance spectroscopy proposed by the present invention can achieve good defect location effect when multiple joints and defects coexist.

[0080] Table 1 Positioning results and error analysis

[0081]

[0082] Embodiment 3:

[0083] The present invention also provides a hybrid cable multi-joint defect positioning device, such as Figure 6 As shown, including:

[0084] The impedance measurement module is a Hioki IM7581 impedance analyzer loaded with a Hioki IM9202 test fixture, which is used to obtain the impedance data of the cable head end within a certain frequency band;

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

[0086] The data processing module is a host computer storing a computer program, which processes the impedance data of the first end of the cable to obtain a positioning spectrum, and obtains the cable joint and defect position.

Claims

1. A hybrid cable multi-joint defect location method based on broadband impedance spectroscopy, characterized by The following steps are involved: Step 1: Build a test platform and connect the cable to be tested to the impedance analyzer; Step 2: 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; Step 3: Process the acquired broadband impedance spectrum data to obtain a positioning spectrum, from which the defect and joint locations can be obtained.

2. According to claim 1, the hybrid cable multi-joint defect location method based on broadband impedance spectroscopy is characterized by: The step 2 comprises the following steps: Step 2.1: Select a suitable frequency band and sampling step size as the working frequency band of the impedance analyzer for measurement; The test step length Δf (Hz) of the impedance analyzer is given by equation (1): In formula (1), v is the propagation speed of electromagnetic waves in the cable, unit: m / s; l is the actual length of the measured cable, unit: m; Δf is the frequency domain measurement step; Step 2.2: The host computer obtains the broadband impedance spectrum data measured by the impedance analyzer through the data transmission module.

3. According to claim 1, the hybrid cable multi-joint defect location method based on broadband impedance spectroscopy is characterized by: The step 3 comprises the following steps: Step 3.1: Perform Taylor windowing on the broadband impedance spectrum Z0(f): Z0(f)*taylorwin(w)=Z w (f), we get Z w (f); Step 3.2: Use linear frequency modulation Z transform to process the broadband impedance spectrum data to obtain the positioning spectrum Z0(x); Linear frequency modulation Z transform can sample any frequency band on the unit circle of the Z plane and effectively remove the interference of redundant data; its sampling point z k It is expressed as formula (2): z k =AW -k (k=0,1…,M-1) (2); Where k is z k The counting variable, M is the total number of sampling points, is the starting point, A0 is the radius, θ0 is the phase angle; is the sampling path, W0 is the stretching rate, φ0 is the angle between sampling points; A and W0 are set to 1, which is regarded as sampling the unit circle in M ​​equal parts; That is, the impedance spectrum data Z after windowing can be transformed by controlling the start and end sampling points and sampling phase difference of the linear frequency modulation Z transform. w (f) Transformed into any desired positioning spectrum Z0(x): Where n is the counting variable of Z0(f), and * represents taking the conjugate of the complex number; the positioning spectrum can be obtained by plotting the Z0(x) curve; Step 3.3: By locating the position of the abnormal peak in the spectrum, the cable joint and defect position can be located.

4. A hybrid cable multi-joint defect location device based on broadband impedance spectroscopy, characterized in that include: Impedance measurement module, used to obtain the impedance data of the cable head end within a certain frequency band; A data transmission module, when the impedance data is detected, transmits the impedance data of the cable head end obtained by the impedance measurement module to the data processing host computer in a format built into the data transmission module; The data processing module is a host computer storing a computer program, which processes the impedance data of the cable head end to obtain a positioning spectrum, and obtains the cable joint and defect position.

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