2024-10-31
Low voltage cable near-end fault detection
1. On-site situation
The cable is V V (polyethylene copper core cable) 380V, 3+2. One end of the cable has been removed and wrapped, but it is inconvenient to enter inside, so high voltage is added from the other end. The neutral wire grounding of the test end cable has been removed.
2.testing equipment used
(1) Insulation test tool: XHMR-5000V insulation resistance tester
(2) Rough test equipment: XHGG502 cable fault pre-locator
(3) Path finding: XHGX507 pipeline locator
(4) High voltage source: XHHV512-10 high voltage pulse generator
(5) Precision test equipment: XHDD503 cable fault locator
3. Testing Process
(1) Insulation test:
The cable insulation resistance tester was used at 500V to measure the voltage between phase A and ground, which was 500V and the insulation was 0.9MΩ; the voltage between phase B and ground was 217V and the insulation was 0.03MΩ; the voltage between phase C and ground was 504V and the insulation was 284MΩ; the voltage between neutral line and ground was 500V and the insulation was 2.8MΩ; the insulation between phases was above 10MΩ, and the preliminary judgment was that the fault was between phase B and ground.
Phase B insulation test
(2) Rough measurement
Use the low-voltage pulse method of XHGG502 tester to measure the length of the A, B, and C three-phase to ground and the neutral line test cables, all of which are 850 meters.
(3) High voltage detection
1. Use XHGG510-12L to apply a high voltage pulse signal to phase B.
2. Use the high voltage flashover method of XHGG502 cable fault tester to collect waveforms, and the 10kV fault point is brokendown.
3. The waveform is displayed as a near-end fault waveform.
4. Analyze the waveform - detect that the rough fault distance is about 15m.
(4) High-voltage flashover waveform analysis
From the waveform, it can be seen that this trend belongs to the waveform of a near-end fault. If a near-end fault is selected, it can be seen that the distance is 31m, and then divided by 2, the rough distance of the fault point can be obtained to be about 15m.
(5) Fault location
Use the 503 cable fault locator to roughly measure the fault distance to about 15 meters for location, listen to the discharge sound at the fault point, and finally find the fault point at 10 meters and start excavation.
4. Summary
This fault is a near-end fault, which is close to the test end. The sound of the generator and the high-voltage power supply may cover the discharge sound of the fault point. You can move the generator farther away and listen carefully to the discharge sound nearby. The high-voltage power supply discharges electricity every few seconds, so count a few seconds in your mind to see if they are consistent, and then combine the ground vibration to determine the location of the fault point.
