A cable defect detection system and method based on pulse sine wave

Abstract

The invention discloses a cable defect detection system and method based on pulsed sine waves. The system comprises a sine wave generator with a fixed frequency. The output end of the sine wave generator is connected to a high-frequency voltage amplifier. The output end of the high-frequency voltage amplifier is connected to a high-frequency switch. The output ends of the high-frequency switch are respectively connected to a coupler and a controller. The output ends of the coupler are respectively connected to a high-voltage cable to be detected and a three-way joint. A bare wire is between the high-frequency voltage amplifier and the high-frequency switch. A spatial stray capacitance is formed between a flat electrode and the bare wire. The flat electrode is respectively connected to a high-frequency capacitor and a high-frequency cable. The flat electrode and the high-frequency capacitor form a high-frequency voltage divider. The output end of the three-way joint is connected to a signal acquisition and analysis system. The invention amplifies the detection signal, realizes the detection of defects at different positions of the cable, and improves the signal detection sensitivity of small defects.

Description

Technical Field

[0001] The present invention relates to the field of electrical equipment sensing detection, and in particular to a pulse sine wave-based 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] Currently, there are two main methods for detecting cable defects: time domain reflectometry (TDR) and frequency domain reflectometry (FDR).

[0004] 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.

[0005] 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 small defects that do not cause cable shorts or breaks.

[0006] The reason why the traditional TDR method cannot detect small defects is that the amplitude change of the reflected signal caused by small defects is small. Therefore, it is necessary to conduct further research on cable defect detection schemes to improve the signal detection sensitivity of small defects. 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 based on pulsed sine waves, which amplifies the detection signal, realizes the detection of defects at different positions of the cable, and improves the signal detection sensitivity of small defects.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a cable defect detection system based on pulsed sine waves, including a sine wave generator with a fixed frequency, the output end of the sine wave generator is connected to a high-frequency voltage amplifier, the output end of the high-frequency voltage amplifier is connected to a high-frequency switch, the output ends of the high-frequency switch are respectively connected to a coupler and a controller, the output ends of the coupler are respectively connected to a high-voltage cable to be detected and a three-way connector, there is a bare wire between the high-frequency voltage amplifier and the high-frequency switch, a spatial stray capacitance is formed between a flat electrode and the bare wire, the flat electrode is respectively connected to a high-frequency capacitor and a high-frequency cable, the flat electrode and the high-frequency capacitor form a high-frequency voltage divider, and the output end of the three-way connector is connected to a signal acquisition and analysis system.

[0009] A further improvement of the technical solution of the present invention is that the high-frequency cable is less than 0.5 meters.

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

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

[0012] S2, adjust the voltage from a continuous sine wave to a sine wave of frequency F with a conduction time of T nanoseconds through a high-frequency switch;

[0013] S3, a sine wave of frequency F lasting T nanoseconds is input to the cable to be tested through the coupler, and the reflected signal of the cable to be tested returns to the coupler and enters the three-way connector;

[0014] S4. The voltage dividing ratio of the high-frequency voltage divider is adjusted by adjusting the distance between the flat electrode and the bare wire. The continuous signal output by the high-frequency voltage divider enters the three-way connector through the high-frequency cable;

[0015] S5. The output result of the high-frequency voltage divider in step S4 interferes with the reflected signal of the cable to be detected in step S3. The reflected signal of the F frequency in the reflected signal of the cable to be detected is amplified by the continuous signal output by the high-frequency voltage divider, and the amplified signal is collected and processed by the signal acquisition and analysis system.

[0016] A further improvement of the technical solution of the present invention is that in step S2, T nanoseconds includes more than 3 cycles of a sine wave with a frequency of F.

[0017] A further improvement of the technical solution of the present invention is that in step S4, the flat plate electrode is circular and its diameter is less than 1 / 20 of the wavelength corresponding to the F frequency.

[0018] A further improvement of the technical solution of the present invention is that the specific steps of collecting and processing the signal in step S5 by the signal collection and analysis system are:

[0019] Step S51: The signal collected by the signal acquisition and analysis system is filtered by a bandpass filter with a center frequency of F to eliminate interference from other frequency signals and improve the signal-to-noise ratio;

[0020] Step S52, obtaining the envelope of a sine wave with a frequency of F through Hilbert transform of the result;

[0021] Step S53, subtracting the envelope result obtained in step S52 from the envelope when the cable is in good condition, and performing threshold analysis on the subtraction result;

[0022] Step S54: Perform position correspondence analysis on the results exceeding the threshold value to obtain the position of the defect.

[0023] A further improvement of the technical solution of the present invention is that the signal collected by the signal collection and analysis system in step S51 is converted into a digital signal by a high-speed A / D converter for data analysis.

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

[0025] The reason why the traditional TDR method cannot detect small defects is that the amplitude change of the reflected signal caused by small defects is small. The cable defect detection system and method based on pulsed sine waves of the present invention amplifies the detection signal, realizes the detection of defects at different positions of the cable, improves the signal detection sensitivity of small defects, and can obtain the health status of different positions of long-distance cable lines, laying the foundation for realizing intelligent cable transmission lines with panoramic cable information perception and data analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the connection of the system of the present invention;

[0027] Among them, 1. sine wave generator, 2. high-frequency voltage amplifier, 3. high-frequency switch, 4. coupler, 5. high-voltage cable to be detected, 6. flat electrode, 7. spatial stray capacitance, 8. high-frequency capacitor, 9. high-frequency cable, 10. three-way connector, 11. signal acquisition and analysis system, 12. controller. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with embodiments:

[0029] like Figure 1As shown, a cable defect detection system based on pulsed sine wave includes a sine wave generator 1 with a fixed frequency. The output end of the sine wave generator 1 is connected to a high-frequency voltage amplifier 2 to amplify the signal to tens of kilovolts. The output end of the high-frequency voltage amplifier 2 is connected to a high-frequency switch 3. The output ends of the high-frequency switch 3 are respectively connected to a coupler 4 and a controller 12. The output end of the coupler 4 is respectively connected to a high-voltage cable 5 to be detected and a three-way connector 10. There is a bare wire between the high-frequency voltage amplifier 2 and the high-frequency switch 3. A spatial stray capacitor 7 is formed between the flat electrode 6 and the bare wire. The flat electrode 6 is respectively connected to a high-frequency capacitor 8 and a high-frequency cable 9. The high-frequency cable 9 is less than 0.5 meters to avoid distortion of the high-frequency signal. The flat electrode 6 and the high-frequency capacitor 8 form a high-frequency voltage divider. The output end of the three-way connector 10 is connected to a signal acquisition and analysis system 11.

[0030] A method for detecting cable defects based on pulsed sine waves comprises the following steps:

[0031] S1, use a fixed frequency sine wave generator 1 to output a sine wave with the same amplitude and frequency F, and amplify the sine signal through a high frequency voltage amplifier 2;

[0032] S2, adjusting the voltage from a continuous sine wave to a sine wave of frequency F with an on-time of T nanoseconds through a high-frequency switch 3, wherein the on-time T nanoseconds includes more than 3 cycles of the sine wave of frequency F, and the on-time T nanoseconds is adjusted by the controller 12 through the high-frequency switch. The longer the on-time, the larger the response signal and the lower the spatial resolution, while the shorter the on-time, the smaller the response signal and the higher the spatial resolution;

[0033] S3, a sine wave of frequency F lasting T nanoseconds is input to the cable to be detected 5 through the coupler 4, and the reflected signal of the cable to be detected 5 returns to the coupler 4 and then enters the three-way connector 10;

[0034] S4, adjust the voltage divider ratio of the high-frequency voltage divider by adjusting the distance between the flat electrode 6 and the bare wire. The final voltage divider ratio should make the voltage entering the signal acquisition and analysis system 11 slightly lower than its maximum measurable voltage. Too low a voltage will weaken the ability to detect small defects, and too high a voltage will damage the signal acquisition and analysis system 11. The continuous signal output by the high-frequency voltage divider enters the three-way connector 10 through the high-frequency cable 9, where the flat electrode 6 is circular and its diameter is less than 1 / 20 of the wavelength corresponding to the F frequency;

[0035] S5. The output result of the high-frequency voltage divider in step S4 interferes with the reflected signal of the cable 5 to be detected in step S3. The reflected signal of the cable 5 to be detected includes signals of frequency F and other frequencies. The reflected signal of frequency F will be significantly amplified by the continuous signal output by the high-frequency voltage divider, while signals of other frequencies will not. The amplified signal is collected and processed by the signal acquisition and analysis system 11.

[0036] The specific steps of signal acquisition and analysis system 11 acquisition and processing are:

[0037] Step S51: The signal collected by the signal collection and analysis system 11 is filtered by a bandpass filter with a center frequency of F to eliminate interference from other frequency signals and improve the signal-to-noise ratio;

[0038] Step S52, obtaining the envelope of a sine wave with a frequency of F through Hilbert transform of the result;

[0039] Step S53, subtracting the envelope result obtained in step S52 from the envelope when the cable is in good condition, and performing threshold analysis on the subtraction result;

[0040] Step S54: Perform position correspondence analysis on the results exceeding the threshold value to obtain the position of the defect.

[0041] The signals collected by the signal acquisition and analysis system 11 are converted into digital signals through a high-speed A / D converter for data analysis, and the cable defect location processing algorithm based on pulse sine waves is solidified inside the FPGA of the signal acquisition and analysis system 11.

Claims

1. A cable defect detection system based on pulsed sine wave, characterized in that: The invention comprises a sine wave generator (1) with a fixed frequency, wherein the output end of the sine wave generator (1) is connected to a high-frequency voltage amplifier (2), the output end of the high-frequency voltage amplifier (2) is connected to a high-frequency switch (3), the output end of the high-frequency switch (3) is respectively connected to a coupler (4) and a controller (12), the output end of the coupler (4) is respectively connected to a high-voltage cable (5) to be detected and a three-way connector (10), a bare wire is provided between the high-frequency voltage amplifier (2) and the high-frequency switch (3), a flat plate electrode (6) is respectively connected to a high-frequency capacitor (8) and a high-frequency cable (9), the high-frequency cable (9) is connected to the three-way connector (10), a spatial stray capacitor (7) formed between the flat plate electrode (6) and the bare wire and the high-frequency capacitor (8) form a high-frequency voltage divider, and the output end of the three-way connector (10) is connected to a signal acquisition and analysis system (11).

2. A cable defect detection system based on pulsed sine wave according to claim 1, characterized in that: The high-frequency cable (9) is less than 0.5 meters.

3. A cable defect detection method based on pulsed sine wave, characterized in that: The cable defect detection system according to claim 1 is adopted, and the specific method comprises the following steps: S1, use a fixed frequency sine wave generator (1) with the same output amplitude and frequency F The sine wave is amplified by a high-frequency voltage amplifier (2); S2, adjusts the voltage from a continuous sine wave to a sine wave of frequency F with a conduction time of T nanoseconds through a high-frequency switch (3); S3, a sinusoidal wave of frequency F lasting T nanoseconds is input to the cable to be detected (5) through the coupler (4), and the reflected signal of the cable to be detected (5) returns to the coupler (4) and then enters the three-way connector (10); S4, adjusting the voltage divider ratio of the high-frequency voltage divider by adjusting the distance between the flat electrode (6) and the bare wire, and the continuous signal output by the high-frequency voltage divider enters the three-way connector (10) through the high-frequency cable (9); S5. The output result of the high-frequency voltage divider in step S4 interferes with the reflected signal of the cable to be detected (5) in step S3. The reflected signal of the F frequency in the reflected signal of the cable to be detected (5) is amplified by the continuous signal output by the high-frequency voltage divider, and the amplified signal is collected and processed by the signal collection and analysis system (11).

4. A method for detecting cable defects based on pulsed sine waves according to claim 3, characterized in that: In step S2, T nanoseconds includes more than 3 cycles of a sine wave with a frequency of F.

5. The cable defect detection method based on pulsed sine wave according to claim 3 is characterized in that: In step S4, the flat plate electrode (6) is circular and has a diameter smaller than 1 / 20 of the wavelength corresponding to the F frequency.

6. A method for detecting cable defects based on pulsed sine waves according to claim 3, characterized in that: The specific steps of signal acquisition and processing by the signal acquisition and analysis system (11) in step S5 are: Step S51: The signal collected by the signal collection and analysis system (11) is filtered by a bandpass filter with a center frequency of F to eliminate interference from other frequency signals and improve the signal-to-noise ratio; Step S52, obtaining the envelope of a sine wave with a frequency of F through Hilbert transform of the result; Step S53, subtracting the envelope result obtained in step S52 from the envelope when the cable is in good condition, and performing threshold analysis on the subtraction result; Step S54: Perform position correspondence analysis on the results exceeding the threshold value to obtain the position of the defect.

7. A method for detecting cable defects based on pulsed sine waves according to claim 6, characterized in that: In step S51, the signal collected by the signal collection and analysis system (11) is converted into a digital signal by a high-speed A / D converter for data analysis.

Images