How to deal with cable failure? Sichuan monitoring system company
Failure judgment method
The method to determine the type of cable fault is to measure the insulation resistance of each phase at one end of the line with an insulation resistance meter. The type of failure is generally determined based on the following:
(1) When the insulation resistance of one or more cores of the cable to ground is measured, or the insulation resistance between the core and the core is less than 100 kiloohms, it is a low-resistance ground or short-circuit fault.
(2) When the insulation resistance of one or more cores of the cable to the ground is measured, or the insulation resistance between the core and the core is much lower than the normal value, but higher than 100 kiloohms, it is a high resistance ground fault.
(3) When the insulation resistance of one or more cores of the cable to ground is high or normal, a continuity test of the conductor shall be performed to check whether there is a disconnection. If it is, it is a disconnection fault.
(4) When one or more conductors of the test cable are discontinuous and grounded by resistance, it is broken and ground fault.
(5) Flashover faults often occur in preventive withstand voltage tests, and most of them occur at the cable terminals and intermediate joints. Flashovers sometimes occur multiple times in a row, with intervals ranging from a few seconds to a few minutes.
Test method for failure
The instruments and equipment used in the past include QF1-A cable detector, DLG-1 type flash tester, cable path meter and fault pinpointer. The currently popular test method is flash test, which includes flash and direct flash. The flash method is commonly used. The flash test has high accuracy, simple operation, and safety and reliability. Its equipment is mainly composed of two parts, namely the high voltage generating device and the current pulse meter. The high voltage generating device is used to generate DC high voltage or shock high voltage, which is applied to the faulty cable to force the faulty point to discharge and generate a reflected signal. The current pulse meter is used to pick up the reflected signal to measure the fault distance or directly measure the open circuit, short circuit or low resistance fault with low voltage pulses.
Test method based on fault point resistance
(1) When the fault point resistance is equal to infinity, it is easy to find open circuit faults by low-voltage pulse measurement. Generally, pure open circuit faults are not common. Usually, open circuit faults are relatively high-phase or phase-to-phase high-impedance faults, and relatively ground or phase-to-phase Low resistance faults coexist. ,
(2) When the fault point resistance is equal to zero, it is easy to find the short-circuit fault by low-voltage pulse measurement, but it is rarely encountered in actual work.
(3) When the fault point resistance is greater than zero and less than 100 kiloohms, it is easy to find low resistance faults by low voltage pulse measurement.
(4) Flashover faults can be measured by the direct flash method. Such faults generally exist inside the joint. The resistance at the fault point is greater than 100 kiloohms, but the value changes greatly, and each measurement is uncertain.
(5) The high-impedance fault can be measured by the flash method, and the resistance at the fault point is greater than 100 kiloohms and the value is determined. Generally, when the test current is greater than 15 milliamps, the test waveform is repetitive and can overlap, and at the same time a waveform has one emission, three reflections, and the pulse amplitude gradually decreases, the measured distance is the distance from the fault point to the cable test end; Test the distance from the point of failure to the opposite end of the cable.
The above is how to deal with the cable faults that Sichuan Monitoring System Co. analyzes for you. Are the customers who have read it clear? If you have any needs, please contact us.