Case 1: Single-phase ground fault detection.
Line address: Shanghai voltage level: 10kv
Insulation Type: Oil-impregnated paper insulation Cable length: 6926m As shown in Figure 7-1, the cable is directly buried and has five connectors in the middle. When the cable fails during operation, the insulation resistance is measured with a megohmmeter in the substation, phase A is , phase B is 5K, and phase C is , so it is determined that the cable has a single-phase high-resistance grounding fault.
GDBN-G60 high-voltage signal generator, C2000 power cable fault rangefinder, D30 cable fault fixed-point instrument, megohmmeter, multimeter, etc.
At the substation end, the total length of the cable is measured to be 692m after adjusting the wave speed to 162m s between phase A and B by the low-voltage pulse method, as shown in Figure 7-2, which is consistent with the data at the substation end, and the waveform shown in Figure 7-3 is measured by the pulse current method between phase B and the metal sheath, and the fault distance is 617m; After checking the data, it was found that the fault point may be near the No. 4 intermediate joint, and the fault point was found between the No. 3 and No. 4 intermediate joints through the acousto-magnetic synchronization legal point of the T-502 fault pointer. Check the cause and find that the fault point is on the cable body, which may be damage during cable laying, deterioration of insulation after long operation, and finally lead to grounding fault.
At the beginning of the flash flash of phase B, the discharge is not sufficient, the flash pulse current waveform is atypical, it is difficult to accurately measure the distance, and the cause may be caused by water vapor at the fault point. After flashing a few times and the temperature of the fault point rises, the discharge is sufficient, and the pulse current waveform is easy to analyze.