In the intricate network of underground cables beneath the city, accurate fault location means faster restoration of power supply. Recently, we completed a 10kV cable fault detection project, where the fault was located at a hidden intermediate joint.
| End positions |
The starting point is at the distribution cabinet, and the ending point is at the substation. |
| On-site situation |
The route is clear, following the drainage ditch along the edge of the road.
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| Insulation resistance |
The three-phase resistance to ground is low. |
| Using the instrument |
1. XHGG502 Cable Fault Tester
2. XHMR-5kV Insulation Resistance Tester
3. XHHV535-4Z Rod-type High-Voltage Pulse Generator
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The three phases of the cable were tested using the 5kV range of the XHMR-5kV insulation resistance tester: the resistance between phase A and ground was approximately 1.2 MΩ, the resistance between phase B and ground was 0.5 MΩ, and the insulation of phase C was normal. Based on this, a fault was determined in phases A and B.
We then used the low-voltage pulse method of the XHGG502 cable fault tester to test the cable. The test results showed that the total length of the cable was approximately 2700.2 meters.
To determine the location of the cable fault, the waveform was acquired using the high-voltage flashover method of the XHGG502 cable fault tester, which indicated that the fault point was approximately 2000.5 meters from the testing end.
Using the XHHV535-4Z high-voltage pulse generator, phase B was energized. Initially, the voltage was increased to 20kV without breakdown, but when the voltage reached 22kV, discharge occurred at the fault point.
Because the cable was laid in a trench, the discharge sound could be heard at the manhole cover approximately 2000m away. After descending into the manhole for confirmation, the fault point was identified as a joint failure. Since the insulation of phase A was also low, high voltage was applied to phase A for further testing, and the same joint discharged again, indicating that the fault points of both phases were in the same location.
In this test, waveform analysis using the high-voltage flashover method presented some difficulties. Interference was present at the site, requiring the identification of periodic discharge signals from the later part of the waveform. This reminds us that:
Waveform analysis requires practical experience.
On-site interference needs to be appropriately handled.
Using multiple methods in combination can improve localization accuracy.
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