Cable fault location system and method based on dc pre-arc and low voltage pulse reflection

Abstract

The application relates to a cable fault positioning system and method based on a direct current pre-arc and low-voltage pulse reflection, and relates to the technical field of power cable fault detection. The existing high-voltage pulse method is prone to damaging the cable, the waveform recognition degree is poor, the cable fault point cannot be positioned, and the problem of repeated positioning cannot be solved. A direct current voltage is applied to the cable to be detected, and the current generated after the cable to be detected receives the direct current voltage is detected in real time. When it is detected that the current is greater than or equal to a preset current value for a preset time, it is determined that a fault occurs. At this time, the ball gap is controlled to be turned on, so that the pulse signal generated by the impulse voltage generator is transmitted to the cable to be detected through the turned-on ball gap. The time when the pulse signal is reflected by the fault point of the cable to be detected and the propagation speed of the pulse signal in the cable to be detected are collected, and the fault point position is calculated. The application is used for positioning the cable fault position.

Description

Technical Field

[0001] This invention relates to the field of power cable fault detection technology. Background Technology

[0002] Currently, the location of faults in cross-linked polyethylene insulated cables is primarily achieved using the traveling wave detection principle. For low-resistance and open-circuit faults, low-voltage pulse reflection can obtain clearly characteristic and highly distinguishable detection waveforms. However, in actual emergency repairs, high-resistance and flashover faults account for a high proportion. When using traditional high-voltage pulse reflection and secondary pulse methods, the resistance at the fault point is not constant, causing the reflection coefficient to change and become unstable. This results in a chaotic and disordered waveform signal containing both reflected pulse signals and noise. Therefore, identifying the reflected pulse signals and their timing is difficult, making it challenging to guarantee the accuracy of fault location.

[0003] Among them, according to Figure 2 This explains why the reflection coefficient is unstable and the reflected wave is difficult to distinguish when high-resistance faults and flashover faults account for a high proportion of cable faults. In actual cable lines, the resistance at the fault point can be equivalent to... The cables on both sides of the fault point are respectively connected with a impedance equal to the wave impedance. Replace it with a resistor, fault resistor Wave impedance of the second cable segment Connected in parallel, forming the load of the first section of the cable, the equivalent impedance at the fault point is: Reflection coefficient: By analyzing the electromagnetic wave reflection coefficient of actual cable lines, we can obtain the following: (1) When a low-resistance fault occurs in the cable, The reflection coefficient is very small, close to 1, and the pulse current applied to detect the fault undergoes total reflection, resulting in a clear and stable reflected signal from the fault point. (2) When the cable experiences a high-resistance or flashover fault, The amplitude is large and fluctuates greatly. At this time, the reflection coefficient is small and extremely unstable. The pulse signal reflected from the fault point is not obvious and is not easy to distinguish. It is easily affected by external interference. Therefore, it is impossible to locate the cable fault point.

[0004] To improve waveform quality and fault detection accuracy, existing technologies often optimize detection by increasing pulse voltage amplitude or applying AC high voltage. However, this approach has significant technical drawbacks: under high voltage, weakly insulating parts inside the cable are easily damaged by breakdown. As the pressurization time increases, the overall insulation damage to the cable continues to worsen, easily inducing secondary faults. The superposition of multiple faults causes severe distortion of the reflected pulse waveform and mutual interference between signals, making it impossible to effectively identify the reflected pulse signal corresponding to the fault location and its timing. Furthermore, this type of high-voltage detection continuously damages the cable itself, preventing repeated testing and severely limiting the reliability and accuracy of fault location.

[0005] In summary, the existing high-voltage pulse method is prone to damaging cables, and the reflected pulse signals have poor identification, resulting in poor accuracy in locating cable fault points. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of existing high-voltage pulse methods, which are prone to damaging cables and have poor identification of reflected pulse signals, resulting in poor accuracy in locating cable fault points. This invention proposes a cable fault location system and method based on DC pre-ignition arc and low-voltage pulse reflection.

[0007] A cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection, the system comprising a DC high-voltage generator, an impulse voltage generator, a detection unit, and a ball gap. Controllers and signal acquisition devices;

[0008] A DC high voltage generator is used to simultaneously apply DC voltage to the cable under test and an impulse voltage generator.

[0009] The detection unit is used to detect the current generated by the cable under test after receiving DC voltage in real time and send it to the controller.

[0010] The controller determines a fault when it detects that the current is greater than or equal to a preset current value for a continuous preset time period, and then controls the ball gap accordingly. The circuit is turned on, allowing the pulse signal emitted by the impulse voltage generator after receiving the DC voltage to pass through the conductive ball gap. Transmitted to the cable under test;

[0011] The signal acquisition device is used to acquire the time of the reflected pulse signal at the fault point of the cable under test, the time of the incident pulse signal of the cable under test, and the propagation speed of the pulse signal in the cable under test, and to calculate the location of the fault point.

[0012] Preferably, the preset current value is 50mA.

[0013] Preferably, the location of the fault point is represented as follows:

[0014] ,

[0015] In the formula, The distance from one end of the cable under test to the fault point. The length of the cable to be measured is... The propagation speed of the pulse signal in the cable under test. The moment when the reflected pulse signal is at the fault point of the cable under test. The moment of the incident pulse signal on the cable under test. The propagation speed of the pulse signal in the cable under test. , The inductance per unit length of the cable under test is denoted as . The capacitance per unit length of the cable under test. The relative permeability of the medium surrounding the cable core is given. The relative permittivity of the medium surrounding the core of the cable under test is given by the given information. It is the speed of light.

[0016] The beneficial effects of this invention are:

[0017] This invention employs a detection scheme combining DC pre-ignition arc and low-voltage pulse reflection. First, a DC voltage is applied to the cable under test, creating a continuous and stable DC arc path at the high-resistance or flashover fault points. No noise is generated under DC arcing. Then, a low-voltage pulse signal is applied to the cable. The reflected signal is solely the reflected pulse signal without any noise. The location of the cable fault point calculated using the reflected pulse signal is more accurate. Therefore, this invention can actively transform the unstable resistance of the cable fault point into a stable low-resistance fault state. Without increasing cable damage, the low-voltage pulse signal is superimposed to obtain a noise-free, reflected pulse signal and its timing. This completely solves the technical problems of large impedance fluctuations at the fault point, chaotic reflected waveforms, blurred characteristic signals, difficulty in identification, and low positioning accuracy in traditional detection methods. It achieves non-destructive, efficient, high-precision, and repeatable rapid positioning of high-resistance and flashover faults in cross-linked polyethylene insulated cables.

[0018] This invention relies on DC high-voltage stable arc control combined with low-voltage pulse detection to avoid the drawbacks of excessive voltage boosting in traditional high-voltage pulse and AC high-voltage detection methods. It effectively prevents secondary breakdown and damage to weak areas of cable insulation, avoids the generation of new fault hazards, significantly reduces damage to the cable body during the detection process, supports repeated fault testing, and significantly improves detection stability and applicability.

[0019] This invention designs a DC high voltage generating circuit and an impulse signal generating circuit, which can output DC high voltage and standard impulse pulse signals with low ripple coefficient and high stability. The system has high integration and reliable operation, and is suitable for on-site cable operation and maintenance conditions.

[0020] This invention presents a non-destructive, efficient, and precise detection solution for high resistance and flashover faults in cross-linked polyethylene cables. It effectively overcomes the shortcomings of existing technologies and has strong practical application value and promotion significance. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of cable fault location using the traveling wave method.

[0022] Figure 2 The circuit diagram for the equivalent surge impedance of a cable fault;

[0023] Figure 3 This is a schematic diagram of a cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection.

[0024] Figure 4 This is the schematic diagram of the superposition circuit;

[0025] Figure 5 This is the circuit schematic of a DC high-voltage generator;

[0026] Figure 6 This is the circuit diagram of an impulse voltage generator. Detailed Implementation

[0027] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0029] Example 1:

[0030] Combination Figure 3 and Figure 4 This embodiment describes a cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection. The system includes a DC high-voltage generator 1, an impulse voltage generator 2, a detection unit, and a ball gap. 3. Controller and signal acquisition device;

[0031] DC high voltage generator 1 is used to simultaneously apply DC voltage to the cable under test and impulse voltage generator 2;

[0032] The detection unit is used to detect the current generated by the cable under test after receiving DC voltage in real time and send it to the controller.

[0033] The controller determines a fault when it detects that the current is greater than or equal to a preset current value for a continuous preset time period, and then controls the ball gap accordingly. The circuit is turned on, allowing the pulse signal emitted by the impulse voltage generator 2 after receiving the DC voltage to pass through the conductive ball gap. Transmitted to the cable under test;

[0034] Signal acquisition device 3 is used to acquire the time of the reflected pulse signal at the fault point of the cable under test, the time of the incident pulse signal of the cable under test, and the propagation speed of the pulse signal in the cable under test, and to calculate the location of the fault point.

[0035] Furthermore, the system also includes a protective resistor. ,

[0036] Protective resistor It is connected in series between the output of the voltage multiplier rectifier unit and the cable under test.

[0037] Further limiting, the preset current value is 50mA.

[0038] Specifically, such as Figure 3 and 4 As shown, the purpose of applying a DC voltage to the cable under test is to create a continuous and stable arcing path at the high-resistance or flashover fault point, transforming the equivalent impedance of the fault point from a high-resistance and unstable state to a low-resistance and constant state. Furthermore, when the current is detected to be greater than or equal to a preset current value for a continuous preset time, a fault is determined to have occurred. Conversely, when the current is less than the preset current value, it indicates that the cable is not faulty, because the current is too small to trigger a reflected pulse signal from the resistor under test. Therefore, the fault status of the cable under test can be determined based on the current value.

[0039] spherical gap g d It is positioned between the pulse signal input terminal and the cable under test, and is used for controlled ignition when maintaining a stable arcing state at the fault point, so that the pulse signal can pass through.

[0040] Protective resistor Used to limit arcing current and protect high-voltage components; matching resistor It is connected between the beginning of the cable under test and ground to suppress signal wave reflection at the beginning of the cable under test.

[0041] DC high voltage (DC voltage) in the spherical gap g d Before ignition, the current should always be applied to the cable under test to ensure that the fault point remains in an arcing state. Since the current to maintain the arc should not be less than 50mA, the protective resistor R... dSelect 100kΩ. When the fault ignition arc is stable, apply g to the ball gap. d When an ignition pulse is applied, the pulse current acts on the low-resistance fault that is in an arcing state, and the fault can be accurately located by reflecting the signal.

[0042] Further defined, the DC high voltage generator 1 includes a power frequency power supply 1-1, a full-bridge rectifier unit 1-2, a half-bridge inverter unit 1-3, an LCC filter unit 1-4, a high-frequency transformer 1-5, a voltage multiplier rectifier unit 1-6, and a drive unit 1-7;

[0043] The power frequency power supply 1-1 is used to output AC power and transmit it to the full-bridge rectifier unit 1-2;

[0044] Full-bridge rectifier unit 1-2 is used to rectify AC power into DC power and transmit it to half-bridge inverter unit 1-3;

[0045] Half-bridge inverter unit 1-3 is used to invert DC power into high-frequency AC power and transmit it to LCC filter unit 1-4;

[0046] LCC filter units 1-4 are used to filter high-frequency AC power and output the processed high-frequency AC power to high-frequency transformer 1-5.

[0047] High-frequency transformers 1-5 are used to convert the processed high-frequency AC power into voltage and output the converted high-frequency voltage to the voltage doubler rectifier unit 1-6.

[0048] Voltage doubler rectifier units 1-6 are used to boost the transformed high-frequency voltage and output a stable DC voltage.

[0049] Drive units 1-7 are used to drive half-bridge inverter units 1-3.

[0050] Furthermore, the DC high voltage generator also includes protection units 1-8;

[0051] Protection unit 1-8 is connected between drive unit 1-7 and voltage doubler rectifier unit 1-6, and is used to provide circuit protection for drive unit 1-7 and voltage doubler rectifier unit 1-6.

[0052] Specifically, such as Figure 5 The DC high-voltage generator circuit shown can output a stable DC high voltage of up to 10kV with a ripple factor not exceeding 1%, meeting relevant standard requirements. In the circuit, ~ It is a rectifier diode. , It is a field-effect transistor (MOSFET). , It is a freewheeling diode. , It is a high-voltage rectifier silicon stack. , This is a high-voltage filter capacitor. For filtering capacitors, For filtering inductors, and Together, they form an LCC filter circuit.

[0053] Figure 5 The main control circuit controls ~ It acquires high-voltage output signals and adjusts the pulse frequency and duty cycle of the PWM wave of the power transistor in the full-bridge inverter circuit to achieve high-voltage output regulation, resonant soft-switching control, and overvoltage, overcurrent, and short-circuit fault protection.

[0054] Further specifying, the impulse voltage generator 2 includes a resistor. ,resistance ,resistance ,resistance ,resistance and capacitor - ;

[0055] The DC voltage output terminal of the voltage multiplier rectifier unit (1-6) is connected to a resistor. One end, resistor The other end is simultaneously connected to one end of the spherical gap and the capacitor. One end;

[0056] Grounding terminal and resistor of voltage multiplier rectifier unit (1-6) One end of each resistor is connected to the power supply ground. The other end is also connected to a resistor One end and the other end of the sphere gap, resistance The other end is also connected to a capacitor The other end, resistor one end and capacitor One end, resistor The other end is connected to one end of the cable under test, the grounding terminal of the cable under test, and the capacitance. The other end and resistor One end of each resistor is connected to the power supply ground. The other end is connected to the other end of the cable to be tested.

[0057] Specifically, such as Figure 6 The shown impulse signal generator circuit generates an amplitude of 10kV and a wavefront time T. f The half-wave time is 0.5µs, and the half-wave time is T. t For a 2µs impulse voltage wave, select a capacitor (main capacitor). It is 1nF, capacitor (impact capacitor). It is 0.1nf; through the wavefront time T f and half-wave time T t Calculation yields: Resistance (wavefront resistance) A 1.7kΩ resistor (tail resistor) was selected. 2.6kΩ was selected.

[0058] The impact signal generator outputs an impact pulse voltage when triggered by the controller, which is used to locate and detect fault points that have formed a stable arcing channel.

[0059] To further define the location of the fault, it is represented as follows:

[0060] ,

[0061] In the formula, The distance from one end of the cable under test to the fault point. The length of the cable to be measured is... The propagation speed of the pulse signal in the cable under test. The moment when the reflected pulse signal is at the fault point of the cable under test. The moment of the incident pulse signal on the cable under test. The propagation speed of the pulse signal in the cable under test. , The inductance per unit length of the cable under test is denoted as . The capacitance per unit length of the cable to be tested. The relative permeability of the medium surrounding the cable core is given. The relative permittivity of the medium surrounding the core of the cable under test is given by the given information. It is the speed of light.

[0062] Specifically, Figure 1 It shows and .

[0063] The cable fault location method proposed in this embodiment, which combines DC pre-ignition arc with low-voltage pulse reflection, utilizes the speed of light... =3 10 8 In addition to obtaining the propagation speed, the wave impedance of the traveling wave in the cable is: m / s. Because the impedance at the fault point is mismatched with the impedance of the cable itself, electromagnetic waves will be refracted and reflected at the fault point. The location of the fault point can be determined by the reflection of the pulse wave at the fault point; the degree of reflection can be measured by the reflection coefficient. In other words, in the formula, This is the reflected voltage. The incident voltage, The equivalent impedance at the fault point.

[0064] Example 2:

[0065] A cable fault location method based on DC pre-ignition arc and low-voltage pulse reflection, wherein the method is implemented based on a cable fault location system using DC pre-ignition arc and low-voltage pulse reflection, the method comprising:

[0066] A DC voltage is applied to the cable under test, and the current generated by the cable after receiving the DC voltage is detected in real time. When the detected current is greater than or equal to a preset current value for a preset time, a fault is determined to have occurred, and the ball gap is controlled. Turning on the signal allows the pulse signal to pass through the conductive ball gap. The signal is transmitted to the cable under test; the timing of the pulse signal reflected from the fault point of the cable under test and the propagation speed of the pulse signal in the cable under test are collected, and the location of the fault point is calculated.

[0067] Working principle:

[0068] During on-site testing, the test terminal of this device is first reliably connected to the cross-linked polyethylene insulated cable line to be inspected. Wiring insulation checks and grounding protection are then completed to ensure a safe and reliable testing process. After the system is connected to the power frequency AC power supply, the power frequency voltage sequentially passes through a full-bridge rectifier, a half-bridge inverter, and an LCC filter circuit to output a low-ripple, high-quality high-frequency AC voltage. This voltage is then boosted by a voltage doubler rectifier unit to stably output a maximum of 10kV DC high voltage, controlling the DC output ripple factor to be less than 1%, meeting the requirements for high-voltage arcing operation.

[0069] The principle of cable fault location is as follows Figure 3 As shown, the power frequency power supply sequentially passes through a full-bridge rectifier unit, a half-bridge inverter unit, and an LCC filter unit to output high-quality high-frequency AC power. This high-frequency AC power is then processed by a voltage doubler rectifier unit to obtain a stable and ideal high-voltage DC power. The output high-voltage DC power is divided into two paths: one path is directly applied to the cable under test, utilizing the DC voltage regulation characteristics to continuously act on the high-resistance or flashover fault points of the cable. Under the continuous action of the high-voltage DC power, the flashover fault and high-resistance fault locations, which originally had high insulation resistance and unstable discharge, gradually form a continuous and stable arcing channel. The equivalent contact resistance of the fault point is significantly reduced and remains constant, stabilizing the randomly fluctuating high-resistance fault condition into a low-resistance fault state with a fixed resistance value that is easy to detect, eliminating the waveform distortion problem caused by random changes in fault impedance.

[0070] Another DC high-voltage circuit serves as the power supply for the impulse signal generator, providing a stable operating voltage for the pulse generation circuit. Once the arc ignition state following the cable fault is fully stable and the arc continues to burn reliably, the ball gap ignition circuit is activated, triggering the impulse signal generator to output a standard impulse pulse voltage. The impulse voltage amplitude is set to 10kV, and the wavefront time T is controlled. f=0.5 μs, half-wave time T t =2 μs; the circuit selection includes main capacitor C1=1 nF, voltage divider capacitor C2=0.1 nF, and matching wavefront resistor R. f =1.7 kΩ, wave tail resistance R t =2.6 kΩ, ensuring that the output pulse waveform is standardized and the parameters are stable.

[0071] A low-voltage pulse signal and a DC arc voltage are coupled through a superposition circuit and applied to the cable under test. The pulse traveling wave propagates uniformly along the cable line, generating a clear and stable reflected signal at the fault point due to impedance mismatch. The device's built-in signal acquisition module captures the incident pulse and the reflected pulse at the fault point in real time, accurately records the pulse round-trip propagation time, calculates the traveling wave propagation speed by combining the inductance and capacitance parameters per unit length of the cable, and then accurately calculates the actual distance between the fault point and the test end using a fault location formula, thus completing the precise fault location.

[0072] A 50Ω matching resistor R is configured in the circuit. m Effectively suppresses reflection interference from the cable's head end; a 100kΩ protective resistor is installed in the high-voltage circuit. The system strictly ensures that the arcing current is not less than 50mA to maintain long-term stable arc combustion, while limiting overcurrent in the circuit to prevent high-voltage components from breaking down and being damaged. The entire testing process adopts a "DC low-voltage arcing + weak pulse detection" mode, which does not require the application of large-amplitude instantaneous high voltage, and will not cause breakdown or irreversible damage to the intact insulation area of ​​the cable. It can perform repeated testing on the same cable line and repeatedly verify the fault location, improving the accuracy of on-site maintenance.

[0073] After completing the fault location and detection, the pulse generation circuit is shut down in sequence, the DC high voltage is slowly reduced and cut off, and the test wiring is removed after the equipment is fully discharged, thus completing the single cable fault detection process.

[0074] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection, characterized in that, The system includes a DC high voltage generator (1), an impulse voltage generator (2), a detection unit, and a ball gap. , controller and signal acquisition device (3); A DC high voltage generator (1) is used to simultaneously apply DC voltage to the cable under test and the impulse voltage generator (2); The detection unit is used to detect the current generated by the cable under test after receiving DC voltage in real time and send it to the controller. The controller determines a fault when it detects that the current is greater than or equal to a preset current value for a continuous preset time period, and then controls the ball gap accordingly. The circuit is turned on, allowing the pulse signal emitted by the impulse voltage generator (2) after receiving the DC voltage to pass through the conductive ball gap. Transmitted to the cable under test; The signal acquisition device (3) is used to acquire the time of the reflected pulse signal at the fault point of the cable under test, the time of the incident pulse signal of the cable under test, and the propagation speed of the pulse signal in the cable under test, and to calculate the location of the fault point.

2. The cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection according to claim 1, characterized in that, The preset current value is 50mA.

3. The cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection according to claim 2, characterized in that, The DC high voltage generator (1) includes a power frequency power supply (1-1), a full-bridge rectifier unit (1-2), a half-bridge inverter unit (1-3), an LCC filter unit (1-4), a high-frequency transformer (1-5), a voltage multiplier rectifier unit (1-6), and a drive unit (1-7). The power frequency power supply (1-1) is used to output AC power and transmit it to the full-bridge rectifier unit (1-2). The full-bridge rectifier unit (1-2) is used to rectify AC power into DC power and transmit it to the half-bridge inverter unit (1-3). The half-bridge inverter unit (1-3) is used to invert DC power into high-frequency AC power and transmit it to the LCC filter unit (1-4). The LCC filter unit (1-4) is used to filter the high-frequency AC power and output the processed high-frequency AC power to the high-frequency transformer (1-5). The high-frequency transformer (1-5) is used to convert the processed high-frequency AC power into voltage and output the converted high-frequency voltage to the voltage doubler rectifier unit (1-6). The voltage doubler rectifier unit (1-6) is used to boost the transformed high-frequency voltage and output a stable DC voltage; The drive unit (1-7) is used to drive the half-bridge inverter unit (1-3) to work.

4. The cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection according to claim 3, characterized in that, The DC high voltage generator also includes protection units (1-8); The protection unit (1-8) is connected between the drive unit (1-7) and the voltage doubler rectifier unit (1-6) to provide circuit protection for the drive unit (1-7) and the voltage doubler rectifier unit (1-6).

5. The cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection according to claim 4, characterized in that, The impulse voltage generator (2) includes resistors ,resistance ,resistance ,resistance ,resistance and capacitor - ; The output terminal of the voltage multiplier rectifier unit (1-6) is connected to a resistor. One end, resistor The other end is connected to both the end of the spherical gap and the capacitor. One end; Grounding terminal and resistor of voltage multiplier rectifier unit (1-6) One end of each resistor is connected to the power supply ground. The other end is also connected to a resistor One end and the other end of the sphere gap, resistance The other end is also connected to a capacitor The other end, resistor one end and capacitor One end, resistor The other end is connected to one end of the cable under test, the grounding terminal of the cable under test, and the capacitance. The other end and resistor One end of each resistor is connected to the power supply ground. The other end is connected to the other end of the cable to be tested.

6. The cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection according to claim 2 or 5, characterized in that, The system also includes a protective resistor. , Protective resistor Connected in series between the output terminal (1-6) of the voltage multiplier rectifier unit and the cable under test.

7. The cable fault location system based on DC pre-ignition arc and low-voltage pulse reflection according to claim 6, characterized in that, The location of the fault is indicated as follows: ， In the formula, The distance from one end of the cable under test to the fault point. The length of the cable to be measured is... The propagation speed of the pulse signal in the cable under test. The moment when the reflected pulse signal is at the fault point of the cable under test. The moment of the incident pulse signal on the cable under test. The propagation speed of the pulse signal in the cable under test. , The inductance per unit length of the cable under test is... The capacitance per unit length of the cable to be tested. The relative permeability of the medium surrounding the cable core is given. The relative permittivity of the medium surrounding the core of the cable under test is given by the given information. It is the speed of light.

8. A cable fault location method based on DC pre-burning arc and low-voltage pulse reflection, wherein the method is implemented based on the cable fault location system based on DC pre-burning arc and low-voltage pulse reflection as described in claim 6, characterized in that, The method includes: A DC voltage is applied to the cable under test, and the current generated by the cable after receiving the DC voltage is detected in real time. When the detected current is greater than or equal to a preset current value for a preset time, the ball gap is controlled. Turning on the signal allows the pulse signal to pass through the conductive ball gap. The signal is transmitted to the cable under test; the timing of the pulse signal reflected from the fault point of the cable under test and the propagation speed of the pulse signal in the cable under test are collected, and the location of the fault point is calculated.

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