A device and method for detecting soft defects in the insulation of power distribution cables.

Abstract

This invention belongs to the field of power equipment fault detection and diagnosis, and discloses a device and method for detecting soft defects in the insulation of power distribution cables. The device uses a high-voltage DC power supply to boost the low voltage of a lithium battery pack, stores energy through an RC charging circuit while limiting the current, and then triggers a power electronic switch via a control and drive circuit to release a high-voltage pulse to the matching resistor and the cable under test. Simultaneously, a dynamic measurement circuit automatically switches the voltage division ratio according to the settings during measurement. A data acquisition card collects reflected signals, which are then analyzed and located by a host computer. This device significantly improves the detection sensitivity of weak reflected signals, solves the problem of missed detection of soft defects in insulation caused by the low reflection amplitude in traditional TDR technology, and achieves high-precision location of soft defects in cable insulation. It also possesses advantages such as controllable energy storage, dynamic adaptation, and strong anti-interference capabilities.

Description

Technical Field

[0001] This invention belongs to the field of power equipment fault detection and diagnosis, and specifically relates to a device and method for detecting soft defects in the insulation of power distribution cable lines. Background Technology

[0002] With the continuous advancement of urbanization, cities are placing increasingly higher demands on infrastructure construction. Among these, the urban power distribution system, as a core infrastructure ensuring urban energy supply, directly impacts the normal order of urban production and daily life. Power distribution cables, due to their significant advantages such as compact structure, aesthetically pleasing installation, and high reliability, are widely used in urban power distribution systems. However, some power distribution cable lines operate in harsh environments for extended periods, making their insulation layers prone to gradual defects. If these defects are not addressed promptly, they can develop into cable faults, leading to power outages. Therefore, early detection and location of soft defects in cable insulation are crucial for ensuring the safe operation of lines and improving power supply reliability.

[0003] Currently, Time Domain Reflectometry (TDR) is a mature cable fault detection and location technology widely used in the industry. This technology is based on the difference in characteristic impedance between the fault location and the intact location of the cable. When a pulse is injected into the cable, a reflected pulse is generated at the location of the abrupt change in characteristic impedance. The cable fault is detected and located by measuring the reflected pulse. However, for soft insulation defects in distribution cables, the characteristic impedance of the soft insulation defect changes very little compared to the intact cable. This results in a weak amplitude of the reflected pulse generated after pulse injection, making it difficult for existing TDR technology to effectively capture this reflected signal, thus hindering accurate detection and location of soft insulation defects in distribution cables.

[0004] It is evident that existing testing methods for power distribution cables are insufficient for detecting and locating soft defects in the insulation of power distribution cables. Summary of the Invention

[0005] This invention provides a device and method for detecting soft defects in the insulation of power distribution cables. Using this detection device, different voltage division ratios can be set according to the intensity of the pulse reflection signal to effectively capture the reflection signal, thereby achieving accurate detection and location of soft defects in the insulation of power distribution cables.

[0006] To achieve the above objectives, the present invention employs the following technical content:

[0007] A device for detecting soft defects in the insulation of power distribution cable lines includes: a high-voltage DC power supply, an RC charging circuit, a power electronic switch circuit, a dynamic measurement circuit, a lithium battery pack, a matching resistor, a control and drive circuit, a data acquisition card, and a host computer.

[0008] The input terminal of the high-voltage DC power supply is connected to the lithium battery pack, and the output terminal is connected to the input terminal of the RC charging circuit; the output terminal of the RC charging circuit is connected to the input terminal of the power electronic switch circuit; the output terminal of the power electronic switch circuit is connected to the input terminal of the matching resistor; the output terminal of the matching resistor is connected to the input terminal of the power distribution cable under test; the input terminal of the dynamic measurement circuit is connected to the output terminal of the matching resistor, and the output terminal of the dynamic measurement circuit is connected to the input terminal of the data acquisition card; the host computer is connected to the input terminal of the control and drive circuit and the output terminal of the data acquisition card.

[0009] High-voltage DC power supplies are used to boost the low voltage input to a lithium battery pack to a high voltage.

[0010] RC charging circuits are used to limit charging current and store electrical energy output from high-voltage DC power supplies.

[0011] Power electronic switching circuits are used to control the timing of energy release in RC charging circuits in order to inject high-voltage pulses into the power distribution cable under test.

[0012] The control and drive circuit is used to control the on / off state of the power electronic switch circuit and the switching on / off state of the dynamic measurement circuit according to the commands output by the host computer.

[0013] The dynamic measurement circuit is used to switch different voltage division ratios according to the pulse intensity;

[0014] The data acquisition card is used to acquire the pulse reflection signal of the power distribution cable under test, so as to locate the location of soft defects in the line insulation based on the pulse reflection signal.

[0015] Furthermore, the RC charging circuit includes a charging resistor and an energy storage capacitor connected in series; the charging resistor is a high-voltage glass glaze resistor; the energy storage capacitor is a high-voltage non-inductive film capacitor; wherein, the high-voltage DC power supply adjusts the DC voltage of the lithium battery pack to an adjustable high-voltage DC voltage, and charges the energy storage capacitor through the RC charging circuit.

[0016] Furthermore, the power electronic switching circuit adopts a switch matrix circuit, which includes multiple sets of switch units with identical structures. These multiple sets of switch units are connected in series and parallel to form the switch matrix circuit. Each switch unit includes an RCD snubber circuit and a MOSFET switch connected in parallel. The RCD snubber circuit includes a discharge resistor, a buffer capacitor, and a diode group. The discharge resistor and the buffer capacitor are connected in series, and the diode group is connected in parallel with the discharge resistor. The positive terminal of the diode group is connected to the drain of the MOSFET switch, and the negative terminal of the diode group is connected to the discharge resistor and the buffer capacitor.

[0017] Furthermore, the diode group includes multiple fast recovery diodes with identical structures; the multiple fast recovery diodes are connected in series in the same direction.

[0018] Furthermore, the dynamic measurement circuit includes multiple cascaded voltage divider units.

[0019] Furthermore, the dynamic measurement circuit includes three voltage divider units: a first voltage divider unit, a second voltage divider unit, and a third voltage divider unit; the first voltage divider unit, the second voltage divider unit, and the third voltage divider unit are cascaded.

[0020] The first voltage divider unit includes a first high-voltage arm resistor, a first high-voltage arm resistor, a first low-voltage arm resistor, and a GaN switch pair; wherein, the first high-voltage arm resistor and the first high-voltage arm resistor are connected in series, the GaN switch pair and the first low-voltage arm resistor are connected in series, and the series branch of the first high-voltage arm resistor, the GaN switch pair, and the first low-voltage arm resistor is connected in parallel.

[0021] The second voltage divider unit includes a second high-voltage arm resistor, a second high-voltage arm resistor, a second low-voltage arm resistor, and a GaN switch pair; wherein, the second high-voltage arm resistor and the second high-voltage arm resistor are connected in series, the GaN switch pair and the second low-voltage arm resistor are connected in series, and the series branch of the second high-voltage arm resistor and the GaN switch pair and the second low-voltage arm resistor is connected in parallel.

[0022] The third voltage divider unit includes a third high-voltage arm resistor, a third high-voltage arm resistor, a third low-voltage arm resistor, and a GaN switch pair; wherein, the third high-voltage arm resistor and the third high-voltage arm resistor are connected in series, the GaN switch pair and the third low-voltage arm resistor are connected in series, and the series branch of the third high-voltage arm resistor, the GaN switch pair, and the third low-voltage arm resistor is connected in parallel.

[0023] Furthermore, among the three voltage divider units, when the GaN switch pair corresponding to a voltage divider unit is turned on, the voltage divider unit corresponding to the GaN switch pair is engaged, and the output voltage amplitude of the voltage divider unit is 1 / 10 of the input voltage amplitude; when the GaN switch pair of a voltage divider unit is turned off, the voltage divider unit corresponding to the GaN switch pair is disconnected, and the output voltage amplitude of the voltage divider unit is equal to the input voltage amplitude; when no voltage divider unit is engaged, the voltage division ratio of the dynamic measurement circuit is 1:1; when the first voltage divider unit is engaged alone, the voltage division ratio of the dynamic measurement circuit is 10:1; when the first and second voltage divider units are engaged simultaneously, the voltage division ratio of the dynamic measurement circuit is 100:1; when the first, second, and third voltage divider units are engaged simultaneously, the voltage division ratio of the dynamic measurement circuit is 1000:1.

[0024] Furthermore, the control and drive circuit includes an FPGA controller, a lithium battery, and a multi-channel drive circuit; wherein, the lithium battery is connected to the multi-channel drive circuit and supplies power to the multi-channel drive circuit; the FPGA controller controls each drive circuit respectively.

[0025] Each drive circuit has the same structure, including an opto-isolation module, a drive isolation power supply, and a drive module. The opto-isolation module is connected to the output of the FPGA controller and converts the electrical signal at the output to an electro-optical / optical-electrical signal to provide a control signal for the drive module. The lithium battery is connected to the drive module through the drive isolation power supply. The output of the drive module is connected to the power electronic switching circuit and the dynamic measurement circuit, respectively.

[0026] A detection method for a device for detecting soft defects in the insulation of power distribution cables, applied to a host computer, comprising:

[0027] Pulse injection setup steps: Generate a pulse injection command by setting the injection pulse width and pulse injection mode;

[0028] Dynamic measurement setup steps: Generate a dynamic measurement setup command by setting the switching time of dynamic measurement and the voltage division ratio at each switching time;

[0029] Command transmission steps: Through the control and drive circuit, pulse injection commands and dynamic measurement setting commands are sent to the power electronic switching circuit and the dynamic measurement circuit;

[0030] Acquisition steps: Acquire pulse reflection signals using a data acquisition card;

[0031] The iterative process involves repeatedly executing the pulse injection setting step, the dynamic measurement setting step, the command sending step, and the acquisition step until a clear and complete pulse reflection signal is acquired. The clear and complete pulse reflection signal is then output as the final measurement result. This final measurement result is used to locate the position of soft defects in the line insulation.

[0032] Furthermore, after the cyclic step, the following steps are also included:

[0033] The arrival time of each reflected pulse is obtained using the threshold method;

[0034] The reflection position of the tested power distribution cable line is calculated based on the arrival time of the pulse reflection.

[0035] Based on the line design drawings of the power distribution cable under test, the intermediate joints and the end of the line are excluded from all the reflection positions of the power distribution cable under test. The remaining reflection positions of the power distribution cable under test are taken as the locations of soft defects in the line insulation.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This invention provides a device for detecting soft defects in the insulation of power distribution cables. A high-voltage DC power supply boosts the low voltage of a lithium battery pack, stores the energy through an RC charging circuit, and limits the current. A control and drive circuit then triggers a power electronic switch to release a high-voltage pulse to a matching resistor and the cable under test. Simultaneously, a dynamic measurement circuit automatically switches the voltage division ratio according to the measurement settings. A data acquisition card collects the reflected signal, which is then analyzed and located by a host computer. Although the impedance change of soft defects is weak, the high-voltage pulse can excite a more significant reflected signal. The RC charging circuit ensures concentrated release of pulse energy, the dynamic measurement circuit balances the capture of both strong and weak signals through voltage division ratio switching, and the matching resistor reduces signal distortion. This device significantly improves the detection sensitivity of weak reflected signals, solves the problem of missed detection of soft defects in insulation caused by the low reflection amplitude in traditional TDR technology, achieves high-precision location of soft defects in cable insulation, and also has advantages such as controllable energy storage, dynamic adaptation, and strong anti-interference capabilities.

[0038] This invention also provides a detection method for a device used to detect soft defects in the insulation of power distribution cables. Based on the aforementioned device, this method executes the detection process via a host computer: setting the pulse width and injection mode to generate an injection command; configuring the switching time and voltage division ratio of the dynamic measurement circuit to generate a measurement command; sending the command to the power electronic switch and dynamic measurement circuit via a control drive circuit; and acquiring the reflected signal via a data acquisition card and iteratively optimizing until a clear signal is obtained. Although the impedance change of soft defects is weak, high-voltage pulse injection can excite a more significant reflected signal; the dynamic voltage division ratio adjustment can flexibly switch the measurement sensitivity, avoiding saturation distortion caused by strong emission pulses, while ensuring effective capture of weak reflected signals; the cyclic acquisition mechanism optimizes the signal-to-noise ratio through parameter iteration and suppresses environmental interference. This method solves the problem of missed detection of soft defects in insulation caused by low reflection amplitude and signal overlap in traditional TDR systems, significantly improving positioning accuracy and reliability, and possessing strong anti-interference capabilities. Attached Figure Description

[0039] Figure 1 A schematic diagram of the overall structure of a device for detecting soft defects in the insulation of power distribution cable lines, provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the control and drive circuit provided in an embodiment of the present invention;

[0041] Figure 3 A flowchart illustrating a detection method for a device for detecting soft defects in the insulation of power distribution cable lines, provided in an embodiment of the present invention;

[0042] Figure 4 A flowchart of the detection data analysis process provided in an embodiment of the present invention.

[0043] Figure label:

[0044] 1. Charging resistor; 2. Energy storage capacitor; 3. Discharging resistor; 4. Buffer capacitor; 5. Diode group; 6. MOSFET switch; 7. First high-voltage arm resistor; 8. First high-voltage arm resistor; 9. GaN switch pair; 10. First low-voltage arm resistor; 11. Second high-voltage arm resistor; 12. Second high-voltage arm resistor; 13. Second low-voltage arm resistor; 14. Third high-voltage arm resistor; 15. Third high-voltage arm resistor; 16. Third low-voltage arm resistor; 17. FPGA controller; 18. Lithium battery; 19. Opto-isolation module; 20. Driver isolation power supply; 21. Driver module. Detailed Implementation

[0045] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0048] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0049] The terms “first”, “second”, etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0050] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0051] As mentioned in the background section, for soft defects in the insulation of power distribution cables, the characteristic impedance changes little compared to intact cables, and the amplitude of the reflected pulse after pulse injection is small. Existing TDR technology is difficult to capture and measure, thus making it impossible to detect and locate soft defects in the insulation of power distribution cables.

[0052] To address the aforementioned problems, this embodiment provides a detection device for soft defects in the insulation of power distribution cables. This device incorporates a high-voltage pulse injection source with adjustable pulse width to inject high-intensity pulses into the power distribution cable, thereby increasing the intensity of the reflected pulses. Simultaneously, a dynamic measurement circuit is designed, capable of rapidly switching the voltage division ratio during pulse measurement. A low voltage division ratio circuit is activated when measuring low pulses to ensure the sensitivity of the measurement results, while a high voltage division ratio circuit is activated when measuring high pulses to ensure that the measurement results do not exceed the measurement range. This achieves high-sensitivity measurement of reflected pulses of varying intensities. Further analysis and calculation of the reflected pulses are then performed to determine and locate soft defects in the power distribution cable insulation. This device achieves high-sensitivity detection of reflected pulses for soft defects in power distribution cable insulation, providing a new technical solution for the high-sensitivity detection and location of soft defects in power distribution cable insulation, and possesses significant engineering practical value.

[0053] like Figure 1 As shown, A represents a high-voltage DC power supply, B represents an RC charging circuit, C represents a power electronic switch circuit, D represents a dynamic measurement circuit, E represents a lithium battery pack, F represents a matching resistor, G represents a control and drive circuit, H represents a data acquisition card, and K represents a host computer.

[0054] like Figure 1 As shown in the figure, this embodiment provides a high-sensitivity detection and location device for soft defects in the insulation of power distribution cable lines, including: a high-voltage DC power supply A, an RC charging circuit B, a power electronic switching circuit C, a dynamic measurement circuit D, a lithium battery pack E, a matching resistor F, a control and drive circuit G, a data acquisition card H, and a host computer K. The specific connection method is as follows:

[0055] The input terminal of the high-voltage DC power supply A is connected to the lithium battery pack E, and the output terminal is connected to the input terminal of the RC charging circuit B; the output terminal of the RC charging circuit B is connected to the input terminal of the power electronic switch circuit C; the output terminal of the power electronic switch circuit C is connected to the input terminal of the matching resistor F; the output terminal of the matching resistor F is connected to the input terminal of the cable under test; the input terminal of the dynamic measurement circuit D is connected to the output terminal of the matching resistor F, and the output terminal of the dynamic measurement circuit D is connected to the input terminal of the data acquisition card H; the host computer K is connected to the input terminal of the control and drive circuit G and the output terminal of the data acquisition card H.

[0056] In this embodiment, the high-voltage DC power supply A has a power of 5W and a rated output current of 1mA. It can adjust the 15V DC voltage of the lithium battery pack E to an adjustable DC high voltage of 0~5kV, and charge the energy storage capacitor 2 through the RC charging circuit. The RC charging circuit B consists of a charging resistor 1 and the energy storage capacitor 2 connected in series. The charging resistor 1 in the RC charging circuit B is a high-voltage glass enamel resistor with a resistance of 5MΩ; the energy storage capacitor 2 is a high-voltage non-inductive film capacitor with a rated voltage of 10kV and a capacitance of 0.33uF.

[0057] In this embodiment, the power electronic switching circuit C is a switching matrix circuit composed of four identical switching units I connected in series and parallel. Each switching unit I consists of an RCD snubber circuit and a MOSFET switch 6 connected in parallel. The RCD snubber circuit comprises a discharge resistor 3, a buffer capacitor 4, and a diode group 5. The discharge resistor 3 and the buffer capacitor 4 are connected in series, and the diode group 5 is connected in parallel with the discharge resistor 3. The anode of the diode group 5 is connected to the drain of the MOSFET switch 6, and the cathode of the diode group 5 is connected to the discharge resistor 3 and the buffer capacitor 4. Discharge resistor 3 is a high-voltage glass glaze resistor with a resistance of 50Ω; buffer capacitor 4 is a high-voltage ceramic capacitor with a rated voltage of 10kV and a capacitance of 1nF; diode group 5 consists of three identical ultra-fast recovery diodes connected in series in the same direction, each diode has a reverse breakdown voltage of 1.2kV, a rated average forward current of 32A, a forward voltage drop of 1.7V, and a reverse blocking recovery time of 32ns; the MOSFEET switch has a withstand voltage of 3.3kV, a maximum pulse current of 100A in 3μs, and a gate control voltage range of -5V to +20V.

[0058] The RC charging circuit employs a combination of high-voltage glass-glazed resistors and non-inductive film capacitors, using a series structure to limit charging current and store energy. The high voltage withstand capability of the glass-glazed resistors ensures stable operation under high-voltage conditions, while the low parasitic inductance of the non-inductive film capacitors reduces energy loss during high-frequency pulse injection, thus guaranteeing the integrity and amplitude of the pulse signal. This design optimizes charging efficiency and avoids signal distortion caused by component parasitic parameters, providing high-quality raw data for subsequent reflected signal analysis.

[0059] The power electronic switching circuit employs a modular switching matrix design, combining multiple parallel RCD snubber circuits with MOSFETs to achieve rapid on / off control of high-voltage pulses. The fast recovery diodes and buffer capacitors in the RCD circuits effectively suppress voltage spikes during switch turn-off, reducing electromagnetic interference. The multi-unit series-parallel structure improves overall voltage withstand capability and reduces thermal stress on individual components by distributing current paths, thereby enhancing system reliability and lifespan. This design is particularly suitable for precise pulse triggering in high-voltage, high-current scenarios.

[0060] In this embodiment, the dynamic measurement circuit D is composed of a first voltage divider unit J1, a second voltage divider unit J2, and a third voltage divider unit J3 cascaded together. The first voltage divider unit J1 is composed of a first high-voltage arm resistor 7, a first high-voltage arm resistor 8, a first low-voltage arm resistor 10, and a GaN switch pair 9. The first high-voltage arm resistor 7 and the first high-voltage arm resistor 8 are connected in series, the GaN switch pair 9 and the first low-voltage arm resistor 10 are connected in series, and the series branch of the first high-voltage arm resistor 8 and the GaN switch pair 9 and the first low-voltage arm resistor 10 is connected in parallel.

[0061] The second voltage divider unit J2 is composed of a second high-voltage arm resistor 11, a second high-voltage arm resistor 12, a second low-voltage arm resistor 13, and a GaN switch pair 9; wherein, the second high-voltage arm resistor 11 and the second high-voltage arm resistor 12 are connected in series, the GaN switch pair 9 and the second low-voltage arm resistor 13 are connected in series, and the series branch of the second high-voltage arm resistor 12 and the GaN switch pair 9 and the second low-voltage arm resistor 13 is connected in parallel.

[0062] The third voltage divider unit J3 consists of a third high-voltage arm resistor 14, a third high-voltage arm resistor 15, a third low-voltage arm resistor 16, and a GaN switch pair 9. The third high-voltage arm resistor 14 and the third high-voltage arm resistor 15 are connected in series, the GaN switch pair 9 and the third low-voltage arm resistor 16 are connected in series, and the series branch of the third high-voltage arm resistor 15 and the GaN switch pair 9 and the third low-voltage arm resistor 16 is connected in parallel.

[0063] In this embodiment, the first high-voltage arm resistor 7 of the first voltage divider unit J1 is a high-voltage glass enamel resistor with a resistance of 200Ω and a power of 3W; the first high-voltage arm resistor 8 is a metal oxide film resistor with a resistance of 1MΩ; the first low-voltage arm resistor 10 is a metal oxide film resistor with a resistance of 22Ω and a power of 3W; the switch pair 9 is composed of two GaN switch transistors of the same type connected in series at their source terminals. The second high-voltage arm resistor 11 of the second voltage divider unit J2 is a metal oxide film resistor with a resistance of 200Ω and a power of 3W; the second high-voltage arm resistor 12 is a metal oxide film resistor with a resistance of 1MΩ; the second low-voltage arm resistor 13 is a metal oxide film resistor with a resistance of 22Ω and a power of 3W. The third high-voltage arm resistor 14 of the third voltage divider unit J3 is a metal oxide film resistor with a resistance of 200Ω and a power of 3W; the third high-voltage arm resistor 15 is a high-voltage arm resistor with a resistance of 1MΩ; the third low-voltage arm resistor 16 is a metal oxide film resistor with a resistance of 22Ω and a power of 3W.

[0064] In this embodiment, the dynamic measurement circuit D can achieve different voltage division ratios by switching different voltage divider units, enabling highly sensitive measurement of pulses of different intensities. Under the parameter settings of the components described above, when the GaN switch pair 9 of the first voltage divider unit J1 is turned on, the first voltage divider unit J1 is engaged, and the output voltage amplitude of the first voltage divider unit J1 is 1 / 10 of the input voltage amplitude; when the GaN switch pair 9 of the first voltage divider unit J1 is turned off, the first voltage divider unit J1 is disengaged, and the output voltage amplitude of the first voltage divider unit J1 is approximately equal to the input voltage amplitude. The second voltage divider unit J2 and the third voltage divider unit J3 operate in the same manner as the first voltage divider unit J1. Therefore, when no voltage divider unit is engaged, the voltage division ratio of the dynamic measurement circuit D is 1:1. When the first voltage divider unit J1 is engaged alone, the voltage division ratio of the dynamic measurement circuit D is 10:1. When the first voltage divider unit J1 and the second voltage divider unit J2 are engaged simultaneously, the voltage division ratio of the dynamic measurement circuit D is 100:1. When the first voltage divider unit J1, the second voltage divider unit J2, and the third voltage divider unit J3 are engaged simultaneously, the voltage division ratio of the dynamic measurement circuit D is 1000:1.

[0065] The three-stage voltage divider unit of the dynamic measurement circuit achieves dynamic switching of the voltage division ratio through GaN switches, utilizing the high-frequency characteristics of gallium nitride devices to quickly respond to reflected signals of varying intensities. The voltage divider units employ a cascaded structure, combining different voltage division ratios (e.g., 10:1 to 1000:1) to capture the complete waveform of strong reflected pulses while amplifying the detailed features of weak signals. The low on-resistance and high-speed switching characteristics of the GaN switches further reduce signal path loss and delay, ensuring measurement accuracy and real-time performance.

[0066] like Figure 2 As shown, the structure of the control and drive circuit G consists of an FPGA controller 17, a lithium battery 18, and seven drive circuits Q1 to Q7.

[0067] The FPGA controller 17 includes seven output ports P1 to P7, each controlling one of the seven drive circuits. A lithium battery 18 powers these seven drive circuits, which are identical in structure, consisting of an opto-isolation module 19, a drive isolation power supply 20, and a drive module 21. The lithium battery 18 outputs 15V. The opto-isolation module 19 converts the electrical signals from the FPGA output ports P1 to P7 into electro-optical / optical-electrical signals, providing control signals to the drive module 21. The drive isolation power supply 20 has an input voltage of 4.5~36V and a dual output voltage of +20V / -5V. The drive module 21 is a bipolar drive module with a maximum input voltage range of +25V / -8V and a maximum drive current of 10A.

[0068] The control logic of the control and drive circuit G is as follows: The output ports (P1~P4) of the FPGA controller 17 control the four sets of switching units I in the power electronic switching circuit C, respectively. The control timing of the output ports P1~P4 is consistent. After receiving the command from the host computer K to inject the pulse width and mode, the FPGA controller 17 controls the on / off duration of the power electronic switching circuit C, thereby generating high-voltage pulses of different widths. The output ports P5~P7 of the FPGA controller 17 control the on / off of the GaN switch pair transistors 9 in the voltage divider units J1, J2, and J3 of the dynamic measurement circuit D, respectively. After receiving the dynamic measurement command from the host computer K, the FPGA controller 17 controls the switching of different voltage divider units according to the timing in the command, thereby changing the voltage division ratio of the dynamic measurement circuit D and realizing the measurement of signals of different intensities.

[0069] Meanwhile, during pulse measurement, to protect the data acquisition card H from damage by strong pulses, the first voltage divider unit J1, the second voltage divider unit J2, and the third voltage divider unit J3 of the dynamic measurement circuit D are all engaged during pulse injection, that is, the voltage division ratio of the dynamic measurement circuit D is 1000:1; the switching time is 100ns before pulse injection and 100ns after pulse injection.

[0070] In this embodiment, the control and drive circuits work in conjunction with the FPGA and multiple isolated drives to achieve precise synchronization between high-voltage pulse injection and dynamic measurement. The design of the opto-isolation module and independent drive power supply effectively isolates the high-voltage side from the low-voltage control loop, avoiding ground interference; the parallel processing capability of the FPGA supports millisecond-level timing control of the switching matrix and voltage divider unit, ensuring strict matching of pulse generation, signal acquisition, and voltage divider ratio switching, thereby improving the time resolution of defect location.

[0071] In this embodiment, the host computer K and the FPGA controller 17 communicate using a serial port protocol. Functions include: injecting pulse width and injection pulse mode, setting the switching time and voltage division ratio for dynamic measurement, and lower-level computer identification.

[0072] This embodiment also provides a detection method for a high-sensitivity detection and location device for soft defects in the insulation of power distribution cables, applied to a host computer K. The specific operation steps are as follows:

[0073] Pulse injection steps: Generate a pulse injection command by setting the injection pulse width and pulse injection mode;

[0074] Dynamic measurement setup steps: Generate a dynamic measurement setup command by setting the switching time of dynamic measurement and the voltage division ratio at each switching time;

[0075] Command transmission steps: Through the control and drive circuit, pulse injection commands and dynamic measurement setting commands are sent to the power electronic switching circuit and the dynamic measurement circuit;

[0076] Acquisition steps: Acquire pulse reflection signals using a data acquisition card;

[0077] The cyclical steps are as follows: the pulse injection step, the dynamic measurement setting step, the command sending step, and the acquisition step are repeatedly executed until a clear and complete pulse reflection signal is acquired, and the clear and complete pulse reflection signal is output as the final measurement result; the final measurement result is used to locate the position of soft defects in the line insulation.

[0078] like Figure 3 As shown, the specific steps include:

[0079] S11: Set the injection pulse width;

[0080] S12: Set the switching time of dynamic measurement and the voltage division ratio at each switching time to form a dynamic measurement setting command;

[0081] S13: Send dynamic measurement setting commands to the dynamic measurement circuit through the control and drive circuit;

[0082] S14: Set the pulse injection mode; including single pulse injection mode and periodic pulse injection mode; the injection pulse width and pulse injection mode form the pulse injection command;

[0083] S15: Sends pulse injection commands to the power electronic switching circuit via the control and drive circuit;

[0084] S16: Acquire pulse reflection signal;

[0085] S17: Determine whether the dynamic measurement settings for this round are reasonable based on the collected pulse reflection signals;

[0086] S18: Repeat steps S12, S13, S14, S15 and S16 until the acquired pulse reflection signal can clearly and completely reflect the characteristics of the pulse reflection signal, complete the signal measurement, and output the measurement result.

[0087] S19: Analyze the measurement results, determine the soft defects in the internal insulation of the cable, and locate the defects.

[0088] It should be noted that in steps S11, S12, S13, S14, and S15, the pulse injection setting step and the dynamic measurement setting step can be performed in any order or simultaneously.

[0089] like Figure 4 As shown, after obtaining the test data of the power distribution cable, the following steps can be used to determine and locate soft defects inside the cable:

[0090] S21: Determine the arrival time of each pulse reflection using the threshold method;

[0091] S22: Calculate the reflection position based on the arrival time of the pulse reflection;

[0092] S22: Based on the circuit design drawings of the power distribution cable under test, excluding the locations of intermediate joints and the end of the circuit, the remaining locations can be identified as locations where there are soft insulation defects in the cable circuit.

[0093] Therefore, the present invention provides a detection device for soft defects in the insulation of power distribution cable lines, which has the following advantages compared with existing detection methods:

[0094] This testing device includes a high-voltage DC power supply, an RC charging circuit, a power electronic switching circuit, a dynamic measurement circuit, a lithium battery pack, matching resistors, a control and drive circuit, a data acquisition card, and a host computer. The high-voltage DC power supply boosts the low voltage input to the lithium battery to a high voltage, which is then used to charge the energy storage capacitor via the charging resistor in the RC charging circuit. The host computer sends control commands to the control and drive circuit via a serial port. The control and drive circuit controls the power electronic switching circuit to turn on and off, releasing the energy in the energy storage capacitor and injecting a high-voltage pulse into the power distribution cable line. Simultaneously, the control and drive circuit controls the switching of the dynamic measurement circuit. Different voltage division ratios are set according to the intensity of different reflected pulses to achieve high-sensitivity measurement of the reflected pulses. Further analysis of the measurement results enables high-sensitivity detection and location of soft defects in the insulation of power distribution cables.

[0095] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A device for detecting soft defects in the insulation of power distribution cable lines, characterized in that, include: High voltage DC power supply, RC charging circuit, power electronic switching circuit, dynamic measurement circuit, lithium battery pack, matching resistor, control and drive circuit, data acquisition card and host computer; The input terminal of the high-voltage DC power supply is connected to the lithium battery pack, and the output terminal is connected to the input terminal of the RC charging circuit; the output terminal of the RC charging circuit is connected to the input terminal of the power electronic switch circuit; the output terminal of the power electronic switch circuit is connected to the input terminal of the matching resistor; the output terminal of the matching resistor is connected to the input terminal of the power distribution cable under test; the input terminal of the dynamic measurement circuit is connected to the output terminal of the matching resistor, and the output terminal of the dynamic measurement circuit is connected to the input terminal of the data acquisition card; the host computer is connected to the input terminal of the control and drive circuit and the output terminal of the data acquisition card. High-voltage DC power supplies are used to boost the low voltage input to a lithium battery pack to a high voltage. RC charging circuits are used to limit charging current and store electrical energy output from high-voltage DC power supplies. Power electronic switching circuits are used to control the timing of energy release in RC charging circuits in order to inject high-voltage pulses into the power distribution cable under test. The control and drive circuit is used to control the on / off state of the power electronic switch circuit and the switching on / off state of the dynamic measurement circuit according to the commands output by the host computer. The dynamic measurement circuit is used to switch different voltage division ratios according to the pulse intensity; The data acquisition card is used to acquire the pulse reflection signal of the power distribution cable under test, so as to locate the location of soft defects in the line insulation based on the pulse reflection signal; The dynamic measurement circuit includes three voltage divider units: a first voltage divider unit, a second voltage divider unit, and a third voltage divider unit; the first voltage divider unit, the second voltage divider unit, and the third voltage divider unit are cascaded. The first voltage divider unit includes a first high-voltage arm resistor (7), a first high-voltage arm resistor (8), a first low-voltage arm resistor (10), and a GaN switch pair (9); wherein the first high-voltage arm resistor (7) and the first high-voltage arm resistor (8) are connected in series, the GaN switch pair (9) and the first low-voltage arm resistor (10) are connected in series, and the series branch of the first high-voltage arm resistor (8) and the GaN switch pair (9) and the first low-voltage arm resistor (10) is connected in parallel; The second voltage divider unit includes a second high-voltage arm resistor (11), a second high-voltage arm resistor (12), a second low-voltage arm resistor (13), and a GaN switch pair (9); wherein the second high-voltage arm resistor (11) and the second high-voltage arm resistor (12) are connected in series, the GaN switch pair (9) and the second low-voltage arm resistor (13) are connected in series, and the series branch of the second high-voltage arm resistor (12) and the GaN switch pair (9) and the second low-voltage arm resistor (13) is connected in parallel; The third voltage divider unit includes a third high-voltage arm resistor (14), a third high-voltage arm resistor (15), a third low-voltage arm resistor (16), and a GaN switch pair (9); wherein the third high-voltage arm resistor (14) and the third high-voltage arm resistor (15) are connected in series, the GaN switch pair (9) and the third low-voltage arm resistor (16) are connected in series, and the series branch of the third high-voltage arm resistor (15) and the GaN switch pair (9) and the third low-voltage arm resistor (16) is connected in parallel.

2. The detection device for soft defects in the insulation of power distribution cable lines according to claim 1, characterized in that, The RC charging circuit includes a charging resistor (1) and an energy storage capacitor (2) connected in series; the charging resistor (1) is a high-voltage glass glaze resistor; the energy storage capacitor (2) is a high-voltage non-inductive film capacitor; wherein, the high-voltage DC power supply adjusts the DC voltage of the lithium battery pack to an adjustable DC high voltage, and charges the energy storage capacitor (2) through the RC charging circuit.

3. The detection device for soft defects in the insulation of power distribution cable lines according to claim 1, characterized in that, The power electronic switching circuit adopts a switching matrix circuit, which includes multiple sets of switching units with the same structure. The multiple sets of switching units are connected in series and parallel to form a switching matrix circuit. The switching unit includes an RCD absorption circuit and a MOSFET switching transistor (6) connected in parallel. The RCD absorption circuit includes a discharge resistor (3), a buffer capacitor (4), and a diode group (5). The discharge resistor (3) is connected in series with the buffer capacitor (4), and the diode group (5) is connected in parallel with the discharge resistor (3). The positive terminal of the diode group (5) is connected to the drain of the MOSFET switching transistor (6), and the negative terminal of the diode group (5) is connected to the discharge resistor (3) and the buffer capacitor (4).

4. The detection device for soft defects in the insulation of power distribution cable lines according to claim 3, characterized in that, The diode group (5) includes multiple fast recovery diodes with the same structure; the multiple fast recovery diodes are connected in series in the same direction.

5. The detection device for soft defects in the insulation of power distribution cable lines according to claim 1, characterized in that, In the three voltage divider units, when the GaN switch pair (9) corresponding to a voltage divider unit is turned on, the voltage divider unit corresponding to the GaN switch pair (9) is engaged, and the output voltage amplitude of the voltage divider unit is 1 / 10 of the input voltage amplitude; when the GaN switch pair (9) of a voltage divider unit is turned off, the voltage divider unit corresponding to the GaN switch pair (9) is disconnected, and the output voltage amplitude of the voltage divider unit is equal to the input voltage amplitude; when no voltage divider unit is engaged, the voltage division ratio of the dynamic measurement circuit is 1:1; when the first voltage divider unit is engaged alone, the voltage division ratio of the dynamic measurement circuit is 10:1; when the first voltage divider unit and the second voltage divider unit are engaged simultaneously, the voltage division ratio of the dynamic measurement circuit is 100:1; when the first voltage divider unit, the second voltage divider unit, and the third voltage divider unit are engaged simultaneously, the voltage division ratio of the dynamic measurement circuit is 1000:

1.

6. The detection device for soft defects in the insulation of power distribution cable lines according to claim 1, characterized in that, The control and drive circuit includes an FPGA controller (17), a lithium battery (18), and a multi-channel drive circuit; wherein, the lithium battery (18) is connected to the multi-channel drive circuit and supplies power to the multi-channel drive circuit; the FPGA controller (17) controls each drive circuit respectively. Each drive circuit has the same structure, including an opto-isolation module (19), a drive isolation power supply (20), and a drive module (21). The opto-isolation module (19) is connected to the output of the FPGA controller (17) and provides control signals to the drive module (21) after the electrical signal at the output is converted from electrical to optical / optical to electrical. The lithium battery (18) is connected to the drive module (21) through the drive isolation power supply (20). The output of the drive module (21) is connected to the power electronic switch circuit and the dynamic measurement circuit, respectively.

7. A detection method for a device for detecting soft defects in the insulation of power distribution cable lines, applied to a host computer, characterized in that, The detection device for soft defects in the insulation of power distribution cable lines according to any one of claims 1-6 includes: Pulse injection setup steps: Generate a pulse injection command by setting the injection pulse width and pulse injection mode; Dynamic measurement setup steps: Generate a dynamic measurement setup command by setting the switching time of dynamic measurement and the voltage division ratio at each switching time; Command transmission steps: Through the control and drive circuit, pulse injection commands and dynamic measurement setting commands are sent to the power electronic switching circuit and the dynamic measurement circuit; Acquisition steps: Acquire pulse reflection signals using a data acquisition card; The iterative process involves repeatedly executing the pulse injection setting step, the dynamic measurement setting step, the command sending step, and the acquisition step until a clear and complete pulse reflection signal is acquired. The clear and complete pulse reflection signal is then output as the final measurement result. This final measurement result is used to locate the position of soft defects in the line insulation.

8. The detection method of the device for detecting soft defects in the insulation of power distribution cable lines according to claim 7, characterized in that, Following the cyclical step, the following is also included: The arrival time of each reflected pulse is obtained using the threshold method; The reflection position of the tested power distribution cable line is calculated based on the arrival time of the pulse reflection. Based on the line design drawings of the power distribution cable under test, the intermediate joints and the end of the line are excluded from all the reflection positions of the power distribution cable under test. The remaining reflection positions of the power distribution cable under test are taken as the locations of soft defects in the line insulation.

Images