800V cable fault detection (photovoltaic field)

Basic information on site

1. The cable is a 800V low-voltage cable, and the laying method is direct burial.

2. The total length of the cable is about 200 meters.

3. The fault phenomenon is that the circuit breaker cannot supply power.

4. The cable path is clear.

5. The two ends of the cable are located at one end in the box transformer and the other end in the junction box.

Instruments used

1. Insulation resistance tester (XHMR-5000V).

2. Cable fault tester (XHGG502).

3. Precision point finder (XHDD503).

4. High voltage power supply (XHHV-510-12).

5. Mobile power supply (1000W).

6. Operation box test transformer (5-50) and three-leg capacitor.

Fault nature

Use the 2.5KV gear of the insulation resistance tester to test, and measure the insulation resistance of A-ground, B-ground, C-ground, A-B, B-C, and A-C respectively. It is found that the resistance of B relative to ground is 0Ω (5V), and the others are all above GΩ. It is preliminarily judged that there is a leakage fault between B and ground.

Cable length

Test length is 190 meters

1. Full-length waveform of low-voltage pulse method

Rough measurement method of fault distance

Using the high voltage flashover method

Rough measurement of high voltage flashover waveform (once)

Rough measurement of high voltage flashover waveform (secondary acquisition adjustment)

Rough measurement method:

1.First, the low-voltage pulse method is used to detect the total length of the cable, which is 190 meters.

2.The high-voltage flashover method is used to perform a rough fault measurement on the cable. When the voltage rises to 9kV, the discharge is sufficient. The analysis of the high-voltage flashover waveform shows that the fault distance is about 118 meters.

Fault finding and precise positioning

Use the cable fault pinpointer to accurately locate within the rough measurement range.

1. There is a fault discharge sound at about 110 meters.

2. After repeated comparison and positioning, it is finally accurately located at about 119 meters.

3. The following figure is a real picture of the excavation of the fault point.

4. This fault is caused by external force damaging the cable.

Fault Test Summary

• The voltage of low-voltage cables cannot be raised too high, which will result in low discharge energy at the fault point, so the fixed point needs to be determined carefully and patiently.
• If the outer skin of the low-voltage cable is damaged and the resistance is low, try to retest with step voltage.
• To eliminate armor discharge, you can take methods such as disconnecting the armor layer.