Cable defect positioning method under frequency point missing condition

Abstract

The invention relates to a cable defect positioning method under the condition of frequency point deficiency, and belongs to the technical field of high voltage. According to the method, a new voltage signal is obtained by delaying a measured voltage signal in a time domain for a preset time, and the new voltage signal is subtracted from an original voltage signal to obtain a cable pulse response with a smaller pulse width, so that a cable impedance spectrum with a wider range is obtained, and the cable impedance spectrum is applied to a fast Fourier transform algorithm in a frequency domain reflection method. And hidden danger defects in the cable can be accurately positioned. According to the method, the problem that the cable defect positioning precision is reduced due to frequency point deficiency under the equipment limiting condition is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high voltage, and particularly relates to a method for locating cable defects in the case of missing frequency points. Background Art

[0002] As the backbone network for urban power transmission, power cables have become the core facilities in modern power grid construction due to the advantages of saving space through underground laying and maintaining urban aesthetics. With the advancement of urbanization and the shortage of land resources, their application scale has been continuously expanding, undertaking the important function of ensuring stable power supply. However, during long-term operation, cables are vulnerable to factors such as construction damage, chemical corrosion, and insulation aging, which can lead to defects such as abnormal grounding circulation and local overheating. In severe cases, it may cause line damage or even power grid paralysis. Since cables are buried deep underground and defects often occur in the internal structural layer, traditional detection means are difficult to accurately locate potential hazards. Developing efficient detection technologies is of crucial significance for timely identifying problems such as partial discharge and abnormal temperature rise. It can not only prevent major power accidents and reduce operation and maintenance costs, but also be an important support for ensuring power supply reliability and extending the cable lifespan, directly affecting the safe operation of urban infrastructure and social and economic stability.

[0003] Currently, the research focus in the field of cable detection is on the application innovation of the electromagnetic wave propagation theory, and fault identification and location are carried out based on the reflection and attenuation characteristics of electromagnetic signals by defect points in the transmission line. Under this technical framework, the core principle of the frequency domain analysis method is to achieve fault detection by analyzing the broadband impedance characteristic spectrum of the cable system. This method deconstructs and analyzes the reflected signal in the frequency domain. Since it adopts an equal-weight processing strategy for the entire frequency band and contains rich high-frequency components, it can effectively extract the microscopic defect characteristics of the cable and theoretically has high detection sensitivity and spatial resolution.

[0004] At the engineering implementation level, compared with the swept-frequency sine wave injection scheme that requires expensive impedance analyzers, the detection system based on pulse excitation shows significant cost advantages. The pulse signal itself has broadband spectral characteristics. By combining the fast Fourier transform technology to perform spectral analysis on the time-domain response, the broadband impedance characteristics of the cable system can be efficiently obtained (specific reference patent: "Impedance Spectrum Measurement Method, Device, Equipment and Medium Based on Voltage Measurement", application number 2024104267091). This technical path not only reduces the equipment investment cost but also ensures the accuracy requirements for impedance spectrum measurement.

[0005] Although the current detection technology based on frequency domain reflection has significant advantages in micro-damage identification, its application has obvious technical constraints. The implementation of this method relies on high-specification detection equipment, and its core is to construct a high-resolution impedance spectrum through dense frequency point sampling to achieve precise positioning. However, there are key limitations in actual engineering: the pulse signal generating device is restricted by physical characteristics, and the time domain width of its output pulse directly affects the spectral integrity, which will cause the loss of data at specific frequency points. This spectral discontinuity phenomenon will directly weaken the calculation accuracy of the system for the cable defect location. Summary of the Invention

[0006] The object of the present invention is to provide a method for cable defect location in the case of missing frequency points, which uses the method of time domain signal misalignment subtraction to solve the problem of incomplete frequency points.

[0007] To achieve the above object, the technical solution of the present invention is: a method for cable defect location in the case of missing frequency points, by delaying the measured voltage signal by a predetermined time in the time domain to obtain a new voltage signal, and subtracting it from the original voltage signal to obtain a cable pulse response with a smaller pulse width, and then obtaining a wider cable impedance spectrum to further accurately locate the hidden defects in the cable.

[0008] Further, the obtained wider cable impedance spectrum is applied to the fast Fourier transform algorithm in the frequency domain reflection method to accurately locate the hidden defects in the cable.

[0009] Further, the specific implementation steps of the method are as follows:

[0010] Step 1: Obtain the voltage signal of the cable section to be measured, perform Fourier transform on it to obtain a cable impedance spectrum with missing frequency points, and determine that the number of missing frequency points in the selected frequency range is N;

[0011] Step 2: Delay the sampled voltage signal by time t in the time domain to obtain a new voltage signal, and subtract it from the original voltage signal to obtain the misalignment subtracted signal to update the cable impedance spectrum and obtain a cable impedance spectrum without missing frequency points in the selected frequency range;

[0012] Step 3: Perform fast Fourier transform on the real part of the updated cable impedance spectrum to obtain the corresponding frequency points f cable (n) and the amplitude spectrum X cable (n) corresponding to each frequency point, and then obtain the positioning calculation result of the cable defect.

[0013] Further, in step 1, the method for obtaining the voltage signal of the cable section to be measured is: injecting a pulse signal with a pulse width of τ into the cable section to be measured and sampling the corresponding voltage signal.

[0014] Further, in step two, the delay time t is expressed as follows:

[0015]

[0016] m = 1, 2, 3,......; if there are still missing frequency points in the updated cable impedance spectrum, then increase m until there are no missing frequency points in the selected frequency range.

[0017] Further, in step three, the frequency point f cable (n) satisfies

[0018]

[0019] where n = 1, 2, 3,......, f l is the lower limit frequency of the cable impedance spectrum, and f h is the upper limit frequency of the cable impedance spectrum.

[0020] Further, the positioning calculation result of the cable defect is obtained based on the following formula:

[0021]

[0022] where x represents the distance between the positioning point and the starting end of the cable, satisfying 0 ≤ x ≤ L, L is the total length of the cable; v is the electromagnetic wave propagation speed.

[0023] Further, v is determined by the medium characteristics:

[0024]

[0025] where c is the speed of light, and ε r is the relative permittivity of the main insulation of the cable.

[0026] The present invention also provides a cable defect positioning system in the case of missing frequency points, including a memory, a processor, and computer program instructions stored on the memory and capable of being run by the processor. When the processor runs the computer program instructions, the method steps described above can be implemented.

[0027] The present invention also provides a computer-readable storage medium, on which computer program instructions capable of being run by the processor are stored. When the processor runs the computer program instructions, the method steps described above can be implemented.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. By shifting the original voltage signal backward in the time domain to obtain a delayed voltage signal and subtracting the two to get the cable response under a smaller pulse width excitation, the frequency components missing in the original cable broadband impedance spectrum are obtained, improving the defect location accuracy in the case of missing frequency points;

[0030] 2. Using the completed impedance spectrum reduces the requirements for equipment in on-site applications, reducing the testing and diagnosis costs while ensuring the location accuracy. Description of the Drawings

[0031] Figure 1 It is a flowchart for completing the cable broadband impedance spectrum;

[0032] Figure 2 is the original voltage signal;

[0033] Figure 3 is the misaligned subtraction voltage signal;

[0034] Figure 4 is the measured impedance spectrum;

[0035] Figure 5 is the completed impedance spectrum;

[0036] Figure 6 is the fast Fourier transform result of the measured impedance spectrum;

[0037] Figure 7 is the fast Fourier transform result of the completed impedance spectrum. Detailed Implementation Manner

[0038] The technical solution of the present invention will be specifically described below in conjunction with the drawings.

[0039] The present invention provides a method for locating cable defects in the case of missing frequency points. By delaying the measured voltage signal in the time domain by a predetermined time to obtain a new voltage signal and subtracting it from the original voltage signal, a cable pulse response with a smaller pulse width is obtained, and then a wider range of cable impedance spectrum is obtained, which is applied to the fast Fourier transform algorithm in the frequency domain reflectometry to accurately locate the hidden defects in the cable.

[0040] The following is the specific implementation process of the present invention.

[0041] The hardware configuration of the experimental system includes a pulse generating device (amplitude A, pulse width τ) and a data acquisition unit (sampling frequency S, recording duration T). After performing a fast Fourier transform on the obtained time-domain pulse signal, the frequency point distribution of its discrete spectrum follows the formula

[0042]

[0043] where the total number of sampling points N = ST, and the analytical formula of the corresponding amplitude spectrum is

[0044] |X(f n )| = Aτ·sinc(πτf n )

[0045] When the condition is satisfied, the sinc(πτf n ) function exhibits periodic zero-crossing characteristics, resulting in a significant attenuation of the corresponding frequency point amplitude |X(f n )| to a near-zero state.

[0046] From the characteristics of the broadband impedance spectrum, it is known that for cables of the same model, the smaller the cable length, the larger the period of the broadband impedance spectrum. Therefore, in the short-distance cable detection scenario, to achieve accurate defect identification, it is necessary to increase the high-frequency coverage of the spectrum analysis. However, when the upper limit of the target frequency exceeds , there will be a frequency point missing phenomenon in the cable impedance spectrum, which will ultimately cause a systematic error in the calculation of the defect position and seriously affect the spatial resolution of the fault location.

[0047] Based on the above analysis, a cable defect location method in the case of missing frequency points, that is, an impedance spectrum completion scheme based on the time-domain signal misalignment subtraction method, is as Figure 1 shown.

[0048] Step 1: Inject a pulse signal with a pulse width of τ into the cable segment to be measured, sample the corresponding voltage signal, perform Fourier transform on it to obtain the cable impedance spectrum with missing frequency points, and determine that the number of missing frequency points in the selected frequency range is N.

[0049] Step 2: Delay the sampled voltage signal in the time domain by time t to obtain a new voltage signal, and subtract it from the original signal, which is equivalent to reducing the pulse width of the signal. Update the cable impedance spectrum using the newly obtained misalignment-subtracted signal, where if there are still missing frequency points in the impedance spectrum, increase m until there are no missing frequency points in the selected frequency range.

[0050] Step 3: Perform a fast Fourier transform on the real part of the completed cable impedance spectrum to obtain the corresponding frequency points f cable (n) and the amplitude spectrum X cable (n) corresponding to each frequency point. The frequency points f cable (n) satisfy

[0051]

[0052] where f l is the lower limit frequency of the impedance spectrum, and f h is the upper limit frequency of the impedance spectrum. The location calculation result of the cable defect can be obtained according to the following formula:

[0053]

[0054] Among them, x represents the distance between the positioning point and the starting end of the cable, satisfying 0 ≤ x ≤ L, where L is the total length of the cable; v is the propagation speed of the electromagnetic wave, which is determined by the medium characteristics:

[0055]

[0056] Among them, c is the speed of light, and ε r is the relative permittivity of the main insulation of the cable.

[0057] The following shows a test example of applying the above method to a 100m long RG58 coaxial cable, where there is a defect at 50m of the cable. Rigol DG2052 and Pico Scope 2408B are used as measuring instruments. The original voltage signal is as Figure 2 shown, and the signal obtained by subtracting the original voltage signals with a phase shift is as Figure 3 shown. The measured impedance spectrum obtained from the original voltage signal is as Figure 4 shown, and the completed impedance spectrum obtained from the voltage signal with phase shift subtraction is as Figure 5 shown. The measured impedance spectrum and the completed impedance spectrum are subjected to fast Fourier transform analysis, and the obtained results are as Figure 6 , Figure 7 shown.

[0058] From Figure 6 , Figure 7 it can be seen that Figure 7 there are only spikes at 50m and 100m, which respectively represent the defect position and the cable end position, while Figure 6 there are multiple false peak interferences in the non-target area. This spectrum leakage phenomenon will cause misjudgment of the defect position. The defect location result calculated using the completed impedance spectrum has higher accuracy. The present invention effectively solves the problem of missing frequency points through the completed impedance spectrum, and improves the accuracy and accuracy of defect location.

[0059] The present invention also provides a cable defect location system in the case of missing frequency points, including a memory, a processor, and computer program instructions stored on the memory and capable of being run by the processor. When the processor runs the computer program instructions, the method steps as described in any of the above can be implemented.

[0060] The present invention also provides a computer-readable storage medium, on which computer program instructions capable of being run by the processor are stored. When the processor runs the computer program instructions, the method steps as described in any of the above can be implemented.

[0061] The above are the preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention in terms of the functions and effects produced shall fall within the protection scope of the present invention.

Claims

1. A method for cable defect location in the case of frequency point loss, characterized in that A new voltage signal is obtained by delaying the measured voltage signal by a predetermined time in the time domain, and subtracting it from the original voltage signal to obtain a cable pulse response with a smaller pulse width, thereby obtaining a cable impedance spectrum with a wider range, and further accurately locating potential defects in the cable.

2. The cable defect location method in case of frequency point loss according to claim 1, characterized in that, The obtained cable impedance spectrum with a wider range is applied to the fast Fourier transform algorithm in the frequency domain reflectometry method to accurately locate potential defects in the cable.

3. A method for cable defect location in the case of frequency point loss according to claim 1, characterized in that, The specific implementation steps of the method are as follows: Step 1: Obtain the voltage signal of the cable segment to be measured, perform Fourier transform on it to obtain a cable impedance spectrum with missing frequency points, and determine that the number of missing frequency points in the selected frequency range is N. Step 2: Delay the sampled voltage signal by time t in the time domain to obtain a new voltage signal, and subtract it from the original voltage signal to obtain the signal after staggered subtraction, so as to update the cable impedance spectrum and obtain a cable impedance spectrum without missing frequency points in the selected frequency range. Step 3: Perform a fast Fourier transform on the real part of the updated cable impedance spectrum to obtain the corresponding frequency point f cable (n) and the amplitude spectrum X corresponding to each frequency point cable (n), and then obtain the positioning calculation result of the cable defect.

4. A method for cable defect location in the case of missing frequency points according to claim 3, characterized in that In Step 1, the method for obtaining the voltage signal of the cable segment to be measured is: injecting a pulse signal with a pulse width of τ into the cable segment to be measured and sampling the corresponding voltage signal.

5. A method for cable defect location in the case of missing frequency points according to claim 3, characterized in that In Step 2, the delay time t is expressed as follows: m = 1, 2, 3,......; if there are still missing frequency points in the updated cable impedance spectrum, increase m until there are no missing frequency points in the selected frequency range.

6. A method for cable defect location in the case of frequency point loss according to claim 3, characterized in that In step 3, the frequency point f cable (n) satisfies where n = 1, 2, 3,......, f l is the lower limit frequency of the cable impedance spectrum, and f h is the upper limit frequency of the cable impedance spectrum.

7. A method for cable defect location in the case of frequency point loss according to claim 6, characterized in that The positioning calculation result of the cable defect is obtained based on the following formula: where x represents the distance between the positioning point and the beginning end of the cable, satisfying 0 ≤ x ≤ L, L is the total length of the cable; v is the electromagnetic wave propagation rate.

8. A method for cable defect location in the case of frequency point loss according to claim 7, characterized in that v is determined by the medium characteristics: where c is the speed of light, and ε r is the relative permittivity of the main insulation of the cable.

9. A cable defect location system in the case of frequency point loss, characterized in that, It includes a memory, a processor, and computer program instructions stored on the memory and capable of being run by the processor. When the processor runs the computer program instructions, it can implement the method steps described in any one of claims 1-8.

10. A computer-readable storage medium, on which computer program instructions capable of being run by the processor are stored. When the processor runs the computer program instructions, it can implement the method steps described in any one of claims 1-8.

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