10kV cable fault location

In the city's power grid, a 386-meter-long 10kV power cable suddenly malfunctioned. One end connects to a ring main unit, and the other to a distribution cabinet; it's buried deep underground. Preliminary tests by on-site personnel showed that the insulation of phase B was only 0.04MΩ, while the insulation of the other phases was intact. Where exactly was the fault? Did they have to excavate the entire 386-meter length?

Insulation test: An XHMR-5000V insulation resistance tester was used to perform a phase-to-ground insulation test on phase B. At 5000V, the resistance was 0.04MΩ (270V), while the other phases reached GΩ after 15 seconds. The conclusion is that phase B is faulty to ground.

Total length verification: First, using the XHGG502 cable fault tester, the total length of the cable was measured to be approximately 386.5 meters using the low-voltage pulse method.

For the B-phase ground fault, we used the high-voltage flashover method for coarse measurement. After connecting the XHHV535-4Z high-voltage pulse generator, the voltage steadily increased to 10kV. As the time relay precisely closed the gap, the instrument clearly captured the standard reflected waveform at the moment the fault broke down. The waveform showed the cable fault distance to be 164.1 meters. The fault range was suddenly reduced from 386.5 meters to this small area.

Since the route was partially known and guided by cable stakes, we primarily relied on a 503 locator for precise positioning. Proceeding along the route to the 164.1-meter mark, we applied high voltage again when we reached the vicinity of the construction site. When the voltage reached approximately 10kV, a clear, rhythmic discharge sound emanated from underground! The source of the sound was precisely near the roughly measured distance. Upon closer inspection, we found that the cable had been exposed due to previous construction work, and the fault point was clearly breached and exposed to the air.