Armor Layer Short Circuit Fault

A photovoltaic power plant in Shaanxi Province, which should have been operating at its peak during the summer, was brought to a standstill by a strike from a critical cable. A YJV 3*120-800V armored low-voltage cable, like the power plant's "artery," was 1335 meters long, buried deep underground, connecting the photovoltaic panels to the transformer substation. When a low-resistance short circuit occurred in the armor layer (insulation resistance 0MΩ, armor resistance only 3Ω) between phases B, power generation losses accumulated every hour, making emergency repairs imperative! Have your cables ever experienced a similar "problem"?

Step 1: Determine the type of fault

Using the 1000V range of the XHMR-5kV insulation resistance tester, the insulation resistance of phases A, B, and C, as well as all phase-to-phase and phase-to-ground insulation, was measured. Phases A and C both showed resistance above 1 GΩ, while phase B showed 0 MΩ, with phase-to-phase insulation above 1 GΩ. A subsequent multimeter test of the armor layer on phase B showed a resistance of 3 Ω.

Step 2:Test cable length

Step 3:Coarse detection of cable faults

1. Using a low-voltage pulse test on phase B of the photovoltaic area, a short-circuit waveform was obtained, and it was roughly determined that the fault point was about 30 meters away from the test end.

2. Then, use the high-voltage flashover method to roughly measure the fault distance in the photovoltaic area and confirm it again.

Step 4: Precise Positioning

The cable path on site is clear. Main insulation fault location: acoustic method and acoustic-magnetic time-of-flight method.

1. Use an integrated XHHV512-12L high-voltage pulse generator to apply a high-voltage pulse to the faulty phase.

2. Use a 503E locator to pinpoint the fault within the coarse measurement range, using acoustic method and acoustic-magnetic time-of-flight method.

3. Finally, the fault point was found 30 meters away from the test end.

Summary and Sharing

1. For locating low-voltage cable faults, the pulse voltage should not be too high compared to high voltage, as this will reduce the discharge energy at the fault point, resulting in a very quiet discharge sound and making precise location more difficult. The solution is to increase the capacitance of the high-voltage source, thereby increasing the discharge energy at the fault point and amplifying the discharge sound.

2. Low-voltage faults require repeated verification using multiple testing methods to prevent misdiagnosis due to armor-to-ground discharge. For the faults mentioned above, we used the low-voltage pulse method, high-voltage flashover method, acoustic method, and acoustomagnetic time-of-flight method.