Methods for diagnosing power cable faults

Generally speaking, power cables mainly have faults such as wire breakage, grounding or short circuit faults, wire breakage and grounding faults, and flashover faults. We can determine the type of fault in power cables based on the following methods. Here, an insulation resistance meter is needed. For wires and cables, place the insulation resistance meter at one end of the line to measure the insulation resistance of each phase.

(1) When one or several conductors of the shake test cable are discontinuous and grounded through a resistor, it can be determined as a broken wire and grounding fault.

(2) When the insulation resistance of one or several cores of a cable to ground is measured by shaking, or when the insulation resistance between cores is much lower than the normal value but higher than 100 kiloohms, it is a high resistance grounding fault.

Power Cable

(3) When the insulation resistance of one or several cores of the shake test cable to ground is high or normal, a conductor continuity test should be conducted to check for wire breakage. If there is, it is a wire breakage fault.

(4) When the insulation resistance of one or several cores of a cable to ground or between cores is less than 100 kiloohms, it is a low resistance grounding or short circuit fault.

(5) Flashover faults often occur during preventive voltage withstand tests, and the locations of occurrence are mostly at cable terminals and intermediate joints. Flashing sometimes occurs multiple times in a row, with intervals ranging from a few seconds to a few minutes between each occurrence.

The instruments and equipment used in the past include QF1-A cable detector, DLG-1 flash tester, cable routing instrument, and fault locator. The currently popular testing method is the flash test method, which includes both impulse and direct flashes, with the impulse test being the most commonly used. The flash test has high accuracy and simple operation,. The equipment mainly consists of two parts, namely the high-voltage generator and the current pulse meter. High voltage generator is used to generate direct current high voltage or impulse high voltage, which is applied to the faulty cable to force the fault point to discharge and generate a reflected signal. Current pulse meter is used to pick up reflected signals to measure fault distance or directly measure open circuit, short circuit or low resistance faults with low-voltage pulses.