Cable defect detection system and method

Abstract

The invention discloses a cable defect detection system and method. The system comprises a frequency-adjustable sine wave generator, the output end of the sine wave generator is connected to a voltage signal amplifier, the output end of the voltage signal amplifier is respectively connected to a power divider and a first capacitive voltage divider, the output end of the power divider is connected to a coupler and a reference cable, the other end of the reference cable is connected to a first three-way joint, the output end of the coupler is respectively connected to a high-voltage cable to be detected and the first three-way joint, the first three-way joint is electrically connected to a second capacitive voltage divider, the output end of the second capacitive voltage divider is connected to a first channel of a signal acquisition and analysis system, the output end of the first capacitive voltage divider is connected to a second three-way joint, the second three-way joint is respectively electrically connected to a first low-voltage cable and a second low-voltage cable, the other ends of the first low-voltage cable and the second low-voltage cable are both connected to a third three-way joint, and the third three-way joint is electrically connected to a second channel of the signal acquisition and analysis system. The invention realizes the detection of defects at different positions of the cable.

Description

Technical Field

[0001] The present invention relates to the field of electrical equipment sensing and detection, and in particular to a cable defect detection system and method. Background Art

[0002] Cables are an important part of the power grid system. Due to differences in cable quality, operating environment, and service life, some cables may have some defects. Therefore, cable defect detection is of great significance to ensure the safe and reliable operation of the power grid.

[0003] At present, there are two main methods for detecting cable defects in smart power plants: time domain reflectometry (TDR) and frequency domain reflectometry (FDR).

[0004] Time Domain Reflectometry (TDR): Also known as pulse echo technology, it is one of the most widely used cable fault location technologies. A high-frequency pulse is sent into the cable core, the pulse propagates through the cable, and is reflected forward at the end of the cable or at any break. At the short-circuit point, the pulse is negatively reflected. Changes in the cable structure caused by the fault will change the impedance, causing part of the incident wave to be reflected back to the sending end. Since it needs to detect through reflected waves, TDR technology is only applicable to low-resistance short-circuit faults or high-resistance open-circuit faults, and cannot monitor strains or disturbances that do not cause cable shorts or breaks.

[0005] Frequency Domain Reflectometry (FDR): FDR is a cable fault detection and location method based on frequency domain signals. It is used to detect insulation damage that affects the local capacitance and impedance of the cable. FDR sends a variable frequency signal and calculates the line impedance based on the frequency. When the transmitted signal encounters an impedance change caused by a change in insulation type, seams, or insulation degradation, a reflected signal is returned. The size of the reflected signal determines the relative severity of the identified impedance change.

[0006] Although the traditional FDR method has a better cable defect detection effect, its positioning accuracy is insufficient in practical applications. Therefore, it is necessary to conduct further research on cable defect detection solutions to improve the accuracy of defect detection. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a cable defect detection system and method, which realizes the detection of defects at different positions of the cable, measures and grasps the nonlinear characteristics of the power supply by setting a reference cable loop, and solves the cable defect positioning error caused by the nonlinearity of the power supply through interpolation calculation based on the nonlinear results.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a cable defect detection system, comprising a frequency-adjustable sine wave generator, the output end of the sine wave generator is connected to a voltage signal amplifier, the output end of the voltage signal amplifier is respectively connected to a power divider and a first capacitive voltage divider, the output end of the power divider is connected to a coupler and a reference cable, the other end of the reference cable is connected to a first three-way connector, the output end of the coupler is respectively connected to a high-voltage cable to be detected and a first three-way connector, the first three-way connector is electrically connected to a second capacitive voltage divider, the output end of the second capacitive voltage divider is connected to a first channel of a signal acquisition and analysis system, the output end of the first capacitive voltage divider is connected to a second three-way connector, the second three-way connector is respectively electrically connected to a first low-voltage cable and a second low-voltage cable, the other ends of the first low-voltage cable and the second low-voltage cable are both connected to a third three-way connector, and the third three-way connector is electrically connected to a second channel of a signal acquisition and analysis system.

[0009] A further improvement of the technical solution of the present invention is that the length difference between the first low-voltage cable and the second low-voltage cable is more than 6 times the length of the high-voltage cable to be detected.

[0010] A further improvement of the technical solution of the present invention is: a cable defect detection method, comprising the following steps:

[0011] S1. Use a frequency-adjustable sine wave generator to output a sine wave with the same amplitude and continuously changing frequency, and amplify the sine signal through a voltage signal amplifier;

[0012] S2, the sinusoidal signal output by the voltage signal amplifier is divided into two parts after passing through the power divider, one part of the sinusoidal signal enters the high-voltage cable to be detected through the coupler, and the reflected signal of the high-voltage cable to be detected beats with the electrical signal in the reference cable, and the beat result is transmitted to the first channel of the signal acquisition and analysis system through the first three-way connector and the second capacitive voltage divider;

[0013] S3, the sinusoidal signal output by the voltage signal amplifier enters the first low-voltage cable and the second low-voltage cable after passing through the first capacitive voltage divider, the frequency band of the first capacitive voltage divider is wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable and the second low-voltage cable, the sinusoidal wave signals of the first low-voltage cable and the second low-voltage cable reaching the third three-way connector at the same time have different frequencies, forming a beat frequency, and transmitted to the second channel of the signal acquisition and analysis system;

[0014] S4, adjusting the beat frequency result of the detected high-voltage cable on the first channel of the signal acquisition and analysis system by performing an inversion compensation algorithm on the beat frequency result obtained by the second channel of the signal acquisition and analysis system;

[0015] S5. The frequency of the beat signal between the high-voltage cable to be tested and the reference cable is positively correlated with the position of the high-voltage cable to be tested. The beat signals of different frequencies are extracted by segmentation through the filter to reflect the signal reflection situation at the corresponding position of the high-voltage cable to be tested. If the high-voltage cable to be tested has insulation defects, the corresponding beat signal will increase significantly.

[0016] A further improvement of the technical solution of the present invention is that: the process of step S4 is: if the frequency band of the second capacitive voltage divider in step S2 is wider than the beat frequency band of the reflected signal of the detected high-voltage cable and the electrical signal in the reference cable, and the frequency band of the first capacitive voltage divider in step S3 is wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable and the second low-voltage cable, then an inversion compensation algorithm is performed on the beat frequency result obtained by the second channel of the signal acquisition and analysis system;

[0017] If the frequency band of the second capacitor voltage divider in step S2 is not wider than the beat frequency band of the reflected signal of the detected high-voltage cable and the electrical signal in the reference cable, and the frequency band of the first capacitor voltage divider is not wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable and the second low-voltage cable, then the frequency response results of the first capacitor voltage divider and the second capacitor voltage divider are used with the beat frequency results obtained by the second channel of the signal acquisition and analysis system to perform Vina deconvolution calculation, and the beat frequency results after frequency band compensation are obtained to perform an inversion compensation algorithm.

[0018] A further improvement of the technical solution of the present invention is that the beat frequency results obtained by the first channel and the second channel of the signal acquisition and analysis system in step S4 are converted into digital signals by a high-speed A / D converter for data analysis.

[0019] A further improvement of the technical solution of the present invention is that the specific steps of the inversion compensation algorithm in step S4 are:

[0020] S41. First, perform Hilbert transform on the beat frequency result obtained by the second channel of the signal acquisition and analysis system. The formula is as follows:

[0021]

[0022] Obtaining the change of the frequency of the beat frequency signal of the first low-voltage cable and the second low-voltage cable over time, wherein the change of the frequency over time can reflect the nonlinearity of the power supply;

[0023] S42, adjusting the beat frequency result of the high-voltage cable to be detected on the first channel of the signal acquisition and analysis system by using the KNN interpolation algorithm to adjust the beat frequency result of the beat frequency signal of the first low-voltage cable and the second low-voltage cable in step S41 over time.

[0024] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0025] 1. The present invention can obtain the health status of different positions of long-distance cable lines, laying the foundation for intelligent cable transmission lines that realize panoramic cable information perception and data analysis;

[0026] 2. The present invention realizes the detection of defects at different positions of the cable. By setting a reference cable loop, the nonlinear characteristics of the power supply are measured and grasped. Through interpolation calculation based on the nonlinear results, the cable defect positioning error caused by the nonlinearity of the power supply is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the connection of the system of the present invention;

[0028] Among them, 1. sine wave generator, 2. voltage signal amplifier, 3. power divider, 4. first capacitive voltage divider, 5. coupler, 6. reference cable, 7. first three-way connector, 8. high-voltage cable to be detected, 9. second capacitive voltage divider, 10. signal acquisition and analysis system, 11. second three-way connector, 12. first low-voltage cable, 13. second low-voltage cable, 14. third three-way connector. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with embodiments:

[0030] like Figure 1 As shown, a cable defect detection system includes a frequency-adjustable sine wave generator 1, the output end of the sine wave generator 1 is connected to a voltage signal amplifier 2, the output end of the voltage signal amplifier 2 is respectively connected to a power divider 3 and a first capacitive voltage divider 4, the output end of the power divider 3 is connected to a coupler 5 and a reference cable 6, the other end of the reference cable 6 is connected to a first three-way connector 7, the output end of the coupler 5 is respectively connected to a high-voltage cable 8 to be detected and the first three-way connector 7, the first three-way connector 7 is electrically connected to a second capacitive voltage divider 9, the output end of the second capacitive voltage divider 9 is connected to a first channel of a signal acquisition and analysis system 10, the output end of the first capacitive voltage divider 4 is connected to a second three-way connector 11, the second three-way connector 11 is respectively electrically connected to a first low-voltage cable 12 and a second low-voltage cable 13, and the length difference between the first low-voltage cable 12 and the second low-voltage cable 13 is more than 6 times the length of the high-voltage cable 8 to be detected.

[0031] The other ends of the first low-voltage cable 12 and the second low-voltage cable 13 are both connected to a third three-way connector 14 , and the third three-way connector 14 is electrically connected to a second channel of the signal acquisition and analysis system 10 .

[0032] Method of use: A cable defect detection method, comprising the following steps:

[0033] S1, using a frequency-adjustable sine wave generator 1 to output a sine wave with the same amplitude and continuously changing frequency, and amplifying the sine signal to several hundred volts through a voltage signal amplifier 2;

[0034] S2, the sinusoidal signal output by the voltage signal amplifier 2 is divided into two parts after passing through the power divider 3, one part of the sinusoidal signal enters the high-voltage cable to be detected 8 through the coupler 5, and the reflected signal of the high-voltage cable to be detected 8 beats with the electrical signal in the reference cable 6, and the beat result is transmitted to the first channel of the signal acquisition and analysis system 10 through the first three-way connector 7 and the second capacitive voltage divider 9;

[0035] S3, the sinusoidal signal output by the voltage signal amplifier 2 enters the first low-voltage cable 12 and the second low-voltage cable 13 after passing through the first capacitive voltage divider 4, the frequency band of the first capacitive voltage divider 4 is wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable 12 and the second low-voltage cable 13, the sinusoidal wave signals of the first low-voltage cable 12 and the second low-voltage cable 13 reaching the third three-way connector 14 at the same time have different frequencies, forming a beat frequency, and transmitted to the second channel of the signal acquisition and analysis system 10;

[0036] S4, if the frequency band of the second capacitive voltage divider 9 in step S2 is wider than the beat frequency band of the reflected signal of the detected high-voltage cable 8 and the electrical signal in the reference cable 6, and the frequency band of the first capacitive voltage divider 4 in step S3 is wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable 12 and the second low-voltage cable 13, then the inversion compensation algorithm is performed on the beat frequency result obtained by the second channel of the signal acquisition and analysis system 10;

[0037] If the frequency band of the second capacitor voltage divider 9 in step S2 is not wider than the beat frequency band of the reflected signal of the detected high-voltage cable 8 and the electrical signal in the reference cable 6, and the frequency band of the first capacitor voltage divider 4 is not wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable 12 and the second low-voltage cable 13, then the frequency response results of the first capacitor voltage divider 4 and the second capacitor voltage divider 9 are used with the beat frequency results obtained by the second channel of the signal acquisition and analysis system 10 to perform Vina deconvolution calculation, and the beat frequency results after band compensation are obtained to perform an inversion compensation algorithm, and the beat frequency results of the detected high-voltage cable 8 on the first channel of the signal acquisition and analysis system 10 are adjusted by the inversion compensation algorithm, and the beat frequency results obtained by the first channel and the second channel of the signal acquisition and analysis system 10 are converted into digital signals by a high-speed A / D converter for data analysis;

[0038] The specific steps of the inversion compensation algorithm are:

[0039] S41, firstly, perform Hilbert transform on the beat frequency result obtained by the second channel of the signal acquisition and analysis system 10, and the formula is as follows:

[0040]

[0041] The variation of the frequency of the beat frequency signals of the first low-voltage cable 12 and the second low-voltage cable 13 over time is approximately a straight line, but there is a slight bend, reflecting the nonlinearity of the power supply;

[0042] S42, adjusting the beat frequency result of the high-voltage cable 8 to be detected on the first channel of the signal acquisition and analysis system 10 by using the KNN interpolation algorithm based on the result of the change of the beat frequency signal of the first low-voltage cable 12 and the second low-voltage cable 13 over time in step S41.

[0043] S5. The frequency of the beat signal between the high-voltage cable 8 to be detected and the reference cable 6 is positively correlated with the position of the high-voltage cable 8 to be detected. The beat signals of different frequencies are extracted by segmented filters to reflect the signal reflection situation at the corresponding position of the high-voltage cable 8 to be detected. If the high-voltage cable 8 to be detected has insulation defects, the corresponding beat signal will increase significantly.

[0044] The premise that the frequency of the beat signal between the high-voltage cable 8 to be detected and the reference cable 6 is positively correlated with the position of the high-voltage cable 8 to be detected in the present invention is that the frequency of the sine wave output by the voltage signal amplifier 2 changes linearly. However, in actual situations, this power supply has a large nonlinearity, resulting in very poor spatial resolution of the defect detection result.

[0045] Therefore, in order to solve the problem of power supply nonlinearity, the present invention connects the first capacitive voltage divider 4 to the output of the voltage signal amplifier 2 to reduce the signal amplitude. Secondly, the first low-voltage cable 12 and the second low-voltage cable 13 are respectively connected through the second three-way connector 11, and the first low-voltage cable 12 and the second low-voltage cable 13 have different lengths. The first low-voltage cable 12 and the second low-voltage cable 13 then enter the second channel of the signal acquisition and analysis system 10 through the third three-way connector 14.

[0046] In order to solve the problem of power supply nonlinearity, an inversion compensation algorithm needs to be used on the basis of the above hardware. This inversion compensation algorithm can effectively improve the spatial resolution of defect detection.

[0047] The present invention realizes the detection of defects at different positions of the cable, measures and grasps the nonlinear characteristics of the power supply by setting a reference cable loop, and solves the cable defect positioning error caused by the nonlinearity of the power supply through interpolation calculation based on the nonlinear result.

Claims

1. A cable defect detection system, characterized in that: The invention comprises a frequency-adjustable sine wave generator (1), wherein the output end of the sine wave generator (1) is connected to a voltage signal amplifier (2), the output end of the voltage signal amplifier (2) is respectively connected to a power divider (3) and a first capacitive voltage divider (4), the output end of the power divider (3) is connected to a coupler (5) and a reference cable (6), the other end of the reference cable (6) is connected to a first three-way connector (7), the output end of the coupler (5) is respectively connected to a high-voltage cable to be detected (8) and the first three-way connector (7), the first three-way connector (7) is electrically connected to the first three-way connector (8), and the output end of the coupler (5) is respectively connected to a high-voltage cable to be detected (8) and the first three-way connector (7). Two capacitive voltage dividers (9), the output end of the second capacitive voltage divider (9) is connected to the first channel of the signal acquisition and analysis system (10), the output end of the first capacitive voltage divider (4) is connected to the second three-way connector (11), the second three-way connector (11) is respectively electrically connected to the first low-voltage cable (12) and the second low-voltage cable (13), the other ends of the first low-voltage cable (12) and the second low-voltage cable (13) are both connected to the third three-way connector (14), and the third three-way connector (14) is electrically connected to the second channel of the signal acquisition and analysis system (10); The cable defect detection method using the cable defect detection system comprises the following steps: S1, using a frequency-adjustable sine wave generator (1) to output a sine wave with a constant amplitude and a continuously changing frequency, and amplifying the sine signal through a voltage signal amplifier (2); S2, the sinusoidal signal output by the voltage signal amplifier (2) is divided into two parts after passing through the power divider (3), one part of the sinusoidal signal enters the high-voltage cable to be detected (8) through the coupler (5), and the reflected signal of the high-voltage cable to be detected (8) beats with the electrical signal in the reference cable (6), and the beat result is transmitted to the first channel of the signal acquisition and analysis system (10) through the first three-way connector (7) and the second capacitive voltage divider (9); S3, the sinusoidal signal output by the voltage signal amplifier (2) enters the first low-voltage cable (12) and the second low-voltage cable (13) after passing through the first capacitive voltage divider (4), the frequency band of the first capacitive voltage divider (4) is wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable (12) and the second low-voltage cable (13), the sinusoidal wave signals of the first low-voltage cable (12) and the second low-voltage cable (13) reaching the third three-way connector (14) at the same time have different frequencies, forming a beat frequency, and transmitted to the second channel of the signal acquisition and analysis system (10); S4, adjusting the beat frequency result of the detected high-voltage cable (8) on the first channel of the signal acquisition and analysis system (10) by performing an inverse compensation algorithm on the beat frequency result obtained by the second channel of the signal acquisition and analysis system (10); the specific steps of the inverse compensation algorithm are: S41, firstly, the beat frequency result obtained by the second channel of the signal acquisition and analysis system (10) is subjected to Hilbert transform, and the formula is as follows: Obtaining the change in frequency of the beat frequency signals of the first low-voltage cable (12) and the second low-voltage cable (13) over time; S42, adjusting the beat frequency result of the high-voltage cable (8) to be detected on the first channel of the signal acquisition and analysis system (10) by using a KNN interpolation algorithm to adjust the beat frequency result of the beat frequency signal of the first low-voltage cable (12) and the second low-voltage cable (13) over time in step S41; S5. The frequency of the beat signal between the high-voltage cable (8) to be detected and the reference cable (6) is positively correlated with the position of the high-voltage cable (8) to be detected. Beat signals of different frequencies are extracted in segments through a filter to reflect the signal reflection situation at the corresponding position of the high-voltage cable (8) to be detected. If the high-voltage cable (8) to be detected has an insulation defect, the corresponding beat signal will increase significantly.

2. A cable defect detection system according to claim 1, characterized in that: The difference in length between the first low-voltage cable (12) and the second low-voltage cable (13) is more than 6 times the length of the high-voltage cable (8) to be detected.

3. A cable defect detection system according to claim 1, characterized in that: The process of step S4 is as follows: if the frequency band of the second capacitive voltage divider (9) in step S2 is wider than the beat frequency band of the reflected signal of the detected high-voltage cable (8) and the electrical signal in the reference cable (6), and the frequency band of the first capacitive voltage divider (4) in step S3 is wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable (12) and the second low-voltage cable (13), then an inversion compensation algorithm is performed on the beat frequency result obtained by the second channel of the signal acquisition and analysis system (10); If the frequency band of the second capacitor voltage divider (9) in step S2 is not wider than the beat frequency band of the reflected signal of the detected high-voltage cable (8) and the electrical signal in the reference cable (6), and the frequency band of the first capacitor voltage divider (4) is not wider than the beat frequency band of the sinusoidal wave signal of the first low-voltage cable (12) and the second low-voltage cable (13), then the frequency response results of the first capacitor voltage divider (4) and the second capacitor voltage divider (9) are used with the beat frequency results obtained by the second channel of the signal acquisition and analysis system (10) to perform Vina deconvolution calculation, and the beat frequency results after frequency band compensation are obtained to perform an inversion compensation algorithm.

4. A cable defect detection system according to claim 1, characterized in that: In step S4, the beat frequency results obtained by the first channel and the second channel of the signal acquisition and analysis system (10) are converted into digital signals by a high-speed A / D converter for data analysis.

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