High-voltage direct flash pre-positioning method for cable fault

Abstract

The invention provides a high-voltage direct flash pre-positioning method for a cable fault, and belongs to the technical field of cable fault detection, and the method comprises the following steps: 1, carrying out the preliminary diagnosis and preprocessing of a faulty cable, 2, applying a high-voltage direct current to the faulty cable, and carrying out the information collection, 3, analyzing the collected waveform, calculating the fault distance, and carrying out the calculation of the fault distance. And 4, verifying the position of the fault point again by adopting an acoustic-magnetic synchronization method. According to the handheld phase acquisition sensor, phase deviation is compared through human body induction, the positioning problem of a complex burying environment is solved, the high-resistance fault positioning efficiency is remarkably improved by optimizing signal acquisition and safety control of a traditional direct flash method and combining an intelligent analysis means, and the handheld phase acquisition sensor is suitable for high-voltage cable systems such as electric power and railways. And a voltage sampling method (divider resistance) and a current sampling method (linear current coupler) are supported, and different cable impedance characteristics are adapted.

Description

Technical Field

[0001] The present invention relates to the technical field of cable fault detection, and in particular to a high-voltage direct flash pre-location method for cable faults. Background Art

[0002] A high-voltage generator applies a DC high voltage to the faulty cable. When the voltage reaches the insulation breakdown threshold at the fault point, a flashover discharge occurs, creating a low-resistance short circuit. The fault point then acts as a "short circuit." The fault distance is calculated using the time difference between the round-trip reflection of the radio wave between the fault point and the test end, combined with the cable's wave velocity.

[0003] Existing high-voltage direct flashovers include the DC high-voltage flashover method and the impulse high-voltage flashover method. The DC high-voltage flashover method directly applies DC high voltage to the faulty cable until the fault point flashes over. It is suitable for high-resistance flashover faults with high insulation resistance and high voltage breakdown. The high-voltage power supply is connected to the cable fault through a ball gap, and the ball gap controls the discharge moment. The ball gap needs to be adjusted manually, and the discharge energy is difficult to control, which may damage the cable or equipment. The impulse high-voltage flashover method applies an impulse high voltage to the cable through the ball gap through an energy storage capacitor, and uses a pulse current to break down the fault point. It is suitable for leakage high-resistance faults with low insulation resistance and continuous leakage current. The equipment of this method is complex, and care must be taken to prevent overvoltage from damaging the instrument. Therefore, it is necessary to design a high-voltage direct flash pre-location method for cable faults. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-voltage direct flash pre-location method for cable faults to solve the technical problems mentioned in the background technology.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for pre-locating high-voltage direct flash of a cable fault, the method comprising the following steps:

[0007] Step 1: Preliminary diagnosis and pretreatment of the faulty cable;

[0008] Step 2: Apply high-voltage DC current to the faulty cable and collect information;

[0009] Step 3: Analyze the collected waveform and calculate the fault distance;

[0010] Step 4: Use the acoustic-magnetic synchronization method to verify the fault point location again.

[0011] Furthermore, the specific process of step 1 is: use a multimeter to measure the resistance of the fault cable relative to the ground, confirm that the resistance of the fault cable is greater than 100 kΩ, and then discharge the cable for more than 5 minutes to avoid residual charge interference.

[0012] Furthermore, wear 10kV insulating gloves and goggles, hang high-voltage operation warning signs at both ends of the cable, disconnect the cable from the grid, and use a tester to confirm that there is no voltage. The test points include connectors and terminals. Set the multimeter to the resistance range with a range of ≥200kΩ. Connect the red test lead to the faulty phase conductor and the black test lead to the ground terminal of the cable armor layer. If it is a three-phase cable, short-circuit the non-faulty phases and ground them uniformly to avoid induced voltage. The reading should be stable >100kΩ. If it fluctuates, record the minimum value. If the resistance is 90-100kΩ, use the flashover method instead. If it is <10kΩ, burn through it first to reduce the resistance.

[0013] Use a discharge rod, connect the grounding end of the discharge rod to the grounding pile, maintain reliable grounding, hold the insulating rod, and touch the discharge tip to the cable conductor phase by phase, in the order of phase A → phase B → phase C → armor layer. The single-phase discharge time is ≥1 minute, repeat 3 rounds, and the total time is >5 minutes. After discharge, let it stand for 2 minutes, use a high-voltage tester to retest each phase to ensure there is no residual voltage, and use the voltage range of the multimeter to confirm that the voltage between the conductor and the ground is <5V.

[0014] Furthermore, the specific process of step 2 is as follows: the positive pole of the high-voltage generator is connected to the fault phase, the negative pole is grounded to the cable armor layer, the voltage is slowly increased at a rate of 1 kV / s, and the leakage current is monitored. If the current suddenly increases by more than 10 mA, it is stopped immediately. When the voltage rises to the fault point breakdown threshold, a discharge arc is generated, triggering the oscilloscope to record the traveling wave signal.

[0015] Furthermore, the specific process of step 3 is as follows: applying a DC voltage to the faulty cable to cause the fault point to discharge and flashover, and then recording and measuring the time t required for the current traveling wave signal generated by the fault point to travel back and forth between the test end and the fault point. Then, based on the transmission speed V of the traveling wave in the cable, the fault distance can be calculated. The direct flash method is mainly used to test high-resistance faults caused by flashover in power cables, and can also be used to test leakage high-resistance faults with extremely high resistance but lower resistance than that of intact phases.

[0016] The cubic spline interpolation algorithm is used to accurately calibrate the inflection point of the reflected wave, reduce manual interpretation errors, automatically match the cable type database, and call the corresponding wave velocity v value.

[0017] Furthermore, the specific process of step 4 is as follows: applying an impact high voltage to the faulty cable through a high-voltage generator to generate a stable discharge at the fault point, detecting a crisp sound of discharge in the ball gap and a large spark, or confirming the discharge pulse through an oscilloscope, arranging the piezoelectric ceramic pickup and the fluxgate sensor orthogonally on the ground directly above the cable, with a spacing of about 0.5-1 meters, ensuring that the two collect signals synchronously, using the pulse magnetic field signal generated at the moment of high-voltage discharge to trigger the instrument to synchronously sample, automatically starting sound signal collection when a sudden change in the magnetic field is detected by the magnetic field sensor, and collecting sound signals at the same time, the mechanical vibration sound of the discharge at the fault point, manifested as a popping pulse waveform and a pulse magnetic field waveform generated by the discharge current, are stored in the instrument memory;

[0018] Time difference calculation: The time difference Δt between the magnetic field signal and the sound signal is calculated by the instrument software. The formula is: Δt = t m -t s , where t m is the arrival time of the magnetic field signal, t s For the sound signal arrival time and distance estimation, the horizontal distance between the fault point and the sensor is calculated based on the speed of sound in air: L = Δt × 340 / 2. For mobile positioning, move the sensor along the cable path to find the point where the acoustic and magnetic time difference Δt is the smallest. The corresponding point is directly above the fault point.

[0019] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0020] The handheld phase acquisition sensor of the present invention solves the positioning problem in complex buried environments by comparing phase offsets through human body induction. By optimizing the signal acquisition and safety control of the traditional direct flash method and combining it with intelligent analysis methods, it significantly improves the efficiency of high-resistance fault positioning. It is suitable for high-voltage cable systems such as power and railways, supports voltage sampling methods (voltage divider resistors) and current sampling methods (linear current couplers), and adapts to different cable impedance characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and by way of preferred embodiments. However, it should be noted that many of the details listed in this specification are merely provided to help the reader gain a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be practiced even without these specific details.

[0023] like Figure 1 As shown, a high-voltage direct flash pre-location method for cable faults comprises the following steps:

[0024] Step 1: Preliminary diagnosis and pretreatment of the faulty cable. Use a multimeter to measure the resistance of the faulty phase relative to ground and confirm that the resistance of the faulty cable is >100kΩ. Then discharge the cable for >5 minutes to avoid residual charge interference. Wear 10kV insulating gloves and goggles, hang high-voltage operation warning signs at both ends of the cable, disconnect the cable from the grid, and use a tester to confirm that there is no voltage. The test points include connectors and terminals. Set the multimeter to the resistance range with a range ≥200kΩ. Connect the red test lead to the conductor of the faulty phase and the black test lead to the ground terminal of the cable armor layer. If it is a three-phase cable, short-circuit the non-faulty phases and ground them uniformly to avoid induced voltage. The reading should be stable >100kΩ. If there is fluctuation, record the minimum value. If the resistance is 90–100kΩ, use the flashover method instead. If it is <10kΩ, burn through the resistance first to reduce the resistance.

[0025] Use a discharge rod, connect the grounding end of the discharge rod to the grounding pile, maintain reliable grounding, hold the insulating rod, and touch the discharge tip to the cable conductor phase by phase, in the order of phase A → phase B → phase C → armor layer. The single-phase discharge time is ≥1 minute, repeat 3 rounds, and the total time is >5 minutes. After discharge, let it stand for 2 minutes, use a high-voltage tester to retest each phase to ensure there is no residual voltage, and use the voltage range of the multimeter to confirm that the voltage between the conductor and the ground is <5V.

[0026] Step 2: Apply a high-voltage DC current to the faulty cable and collect information. Connect the positive terminal of the high-voltage generator to the faulty phase, and the negative terminal to grounding the cable armor. Ramp the voltage up slowly at 1 kV / s, monitoring the leakage current. If the current suddenly increases by more than 10 mA, stop immediately. When the voltage reaches the fault point breakdown threshold, a discharge arc is generated, triggering an oscilloscope to record the traveling wave signal.

[0027] Step 3: Analyze the collected waveforms and calculate the fault distance. A DC voltage is applied to the faulty cable, causing a flashover. The time t required for the current traveling wave signal generated by the fault point to travel back and forth between the test terminal and the fault point is then recorded and measured. The fault distance can then be calculated based on the transmission velocity V of the traveling wave in the cable. The direct flash method is primarily used to test for flashover-induced high-resistance faults in power cables. It can also be used to test for leaky high-resistance faults with exceptionally high resistance but lower resistance than intact phases.

[0028] The cubic spline interpolation algorithm is used to accurately calibrate the inflection point of the reflected wave, reduce manual interpretation errors, automatically match the cable type database, and call the corresponding wave velocity v value.

[0029] Step 4: Use the acoustic-magnetic synchronization method to re-verify the fault point location. A high-voltage generator is used to apply a high voltage impulse to the faulty cable, causing a stable discharge at the fault point. A crisp sound and large sparks are detected in the ball gap discharge, or the discharge pulse is confirmed using an oscilloscope. The piezoelectric ceramic pickup and fluxgate sensor are placed orthogonally on the ground directly above the cable, approximately 0.5-1 meter apart, ensuring synchronous signal acquisition. The pulsed magnetic field signal generated by the instantaneous high-voltage discharge triggers the instrument's synchronous sampling. When the magnetic field sensor detects a sudden change in the magnetic field, it automatically starts sound signal acquisition. The sound signal, the mechanical vibration sound of the fault point discharge, manifested as a popping pulse waveform, and the pulsed magnetic field waveform generated by the discharge current are simultaneously collected and stored in the instrument's memory.

[0030] Time difference calculation: The time difference Δt between the magnetic field signal and the sound signal is calculated by the instrument software. The formula is: Δt = t m -t s , where t m is the arrival time of the magnetic field signal, t s For the sound signal arrival time and distance estimation, the horizontal distance between the fault point and the sensor is calculated based on the speed of sound in air: L = Δt × 340 / 2. For mobile positioning, move the sensor along the cable path to find the point where the acoustic and magnetic time difference Δt is the smallest. The corresponding point is directly above the fault point.

[0031] Matters not covered by the present invention are known technologies.

[0032] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for pre-locating high-voltage direct flash of a cable fault, characterized by: The method comprises the following steps: Step 1: Preliminary diagnosis and pretreatment of the faulty cable; Step 2: Apply high-voltage DC current to the faulty cable and collect information; Step 3: Analyze the collected waveform and calculate the fault distance; Step 4: Use the acoustic-magnetic synchronization method to verify the fault point location again.

2. A method for pre-locating a high-voltage direct flash of a cable fault according to claim 1, characterized in that: The specific process of step 1 is as follows: Use a multimeter to measure the resistance of the fault cable relative to ground and confirm that the resistance of the faulty cable is greater than 100 kΩ. Then discharge the cable for more than 5 minutes to avoid residual charge interference.

3. A method for pre-locating a high-voltage direct flash of a cable fault according to claim 21, characterized in that: Wear 10kV insulating gloves and goggles, hang high-voltage operation warning signs at both ends of the cable, disconnect the cable from the grid, and use a tester to confirm there is no voltage. The test points include connectors and terminals. Set the multimeter to the resistance range with a range ≥ 200kΩ. Connect the red test lead to the faulty phase conductor and the black test lead to the ground terminal of the cable armor layer. If it is a three-phase cable, short-circuit the non-faulty phases and ground them uniformly to avoid induced voltage. The reading should be stable > 100kΩ. If it fluctuates, record the minimum value. If the resistance is 90-100kΩ, use the flashover method instead. If it is <10kΩ, burn through it first to reduce the resistance. Use a discharge rod, connect the grounding end of the discharge rod to the grounding pile, maintain reliable grounding, hold the insulating rod, and touch the discharge tip to the cable conductor phase by phase, in the order of phase A → phase B → phase C → armor layer. The single-phase discharge time is ≥1 minute, repeat 3 rounds, and the total time is >5 minutes. After discharge, let it stand for 2 minutes, use a high-voltage tester to retest each phase to ensure there is no residual voltage, and use the voltage range of the multimeter to confirm that the voltage between the conductor and the ground is <5V.

4. The method for pre-locating a high-voltage direct flash of a cable fault according to claim 1, characterized in that: The specific process of step 2 is as follows: the positive pole of the high-voltage generator is connected to the fault phase, the negative pole is grounded to the cable armor layer, the voltage is slowly increased at a rate of 1 kV / s, and the leakage current is monitored. If the current suddenly increases by more than 10 mA, it is stopped immediately. When the voltage rises to the fault point breakdown threshold, a discharge arc is generated, triggering the oscilloscope to record the traveling wave signal.

5. The method for pre-locating a high-voltage direct flash of a cable fault according to claim 1, characterized in that: The specific process of step 3 is as follows: a DC voltage is applied to the faulty cable to cause a flashover at the fault point. The time t required for the current traveling wave signal generated by the fault point to travel back and forth between the test end and the fault point is then recorded and measured. The fault distance can then be calculated based on the transmission speed V of the traveling wave in the cable. The direct flash method is mainly used to test high-resistance flashover faults in power cables. It can also be used to test leakage high-resistance faults with extremely high resistance but lower resistance than the intact phase. The cubic spline interpolation algorithm is used to accurately calibrate the inflection point of the reflected wave, reduce manual interpretation errors, automatically match the cable type database, and call the corresponding wave velocity v value.

6. A method for pre-locating high-voltage direct flash of a cable fault according to claim 1, characterized in that: The specific process of step 4 is as follows: a high-voltage generator is used to apply an impact high voltage to the faulty cable to generate a stable discharge at the fault point. A crisp sound and large sparks are detected in the ball gap discharge, or the discharge pulse is confirmed by an oscilloscope. The piezoelectric ceramic pickup and the fluxgate sensor are orthogonally arranged on the ground directly above the cable, with a spacing of about 0.5-1 meters. The two are ensured to collect signals synchronously. The pulse magnetic field signal generated at the moment of high-voltage discharge is used to trigger the instrument to synchronously sample. When a sudden change in the magnetic field is detected by the magnetic field sensor, the sound signal collection is automatically started. At the same time, the sound signal, the mechanical vibration sound of the fault point discharge, which is manifested as a popping pulse waveform and the pulse magnetic field waveform generated by the discharge current, are collected and stored in the instrument memory. Time difference calculation: The time difference Δt between the magnetic field signal and the sound signal is calculated by the instrument software. The formula is: Δt = t m -t s , where t m is the arrival time of the magnetic field signal, t s The arrival time of the sound signal and the distance estimation are used to calculate the horizontal distance between the fault point and the sensor according to the speed of sound propagation in the air: L = Δt × 340 / 2, mobile positioning, move the sensor along the cable path, find the point where the acoustic and magnetic time difference Δt is the smallest, and the corresponding point is directly above the fault point.

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