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Project Overview

XZH TEST completed an on-site cable fault detection project for a 10kV cross-linked polyethylene (XLPE) insulated power cable in Denver, Colorado, USA. The three-phase cable (phases A, B and C) was completely disconnected at both ends before testing to ensure a safe and isolated test environment.

Fault Detection Process

1. The cable was discharged and verified de-energized, then both cable ends were disconnected and kept suspended and isolated.
2. Insulation resistance between all phases and to ground was measured using a 2500V insulation tester. The C-phase-to-ground insulation measured 1.73MΩ, indicating a high-resistance fault.
3. After identifying the faulted phase, the 502A detector was used to measure phase-to-ground and phase-to-phase distances. The instrument was set to pulse mode, the dielectric velocity was selected for the cable material, and length selection was performed. After sampling, the waveform was captured and auto-measured to compare phase-to-ground and phase-to-phase distances and determine the cable length.
4. The low-voltage pulse method measured the full cable length but could not locate the fault distance. The 535/4Z high-voltage surge generator was applied to break down the fault point. No breakdown occurred up to 20kV. The 60Q burn-through bridge was then used on phase C to increase leakage current beyond 100mA and reduce the fault resistance. Finally, high-voltage surge discharge was applied to the faulted phase to capture the fault waveform and determine the fault distance.

Fault Nature

Using the 2.5kV electronic insulation tester to measure phase-to-phase and phase-to-ground insulation resistance, the C-phase-to-ground resistance read 0MΩ (0V), while a multimeter measured 1.9kΩ; all other readings exceeded GΩ. This is classified as a leakage-type high-resistance fault.

Test Results

Waveform analysis:

1. The low-voltage pulse waveform measured a full cable length of 473m with no short-circuit or open-circuit fault.
2. The impulse flashover method raised the voltage to 15kV, where the fault point formed a flashover discharge, confirming the fault distance at 377m.

Precise Pinpointing

During precise fault location, it was essential to first trace the cable route. Using the 503E instrument within the range before and after the measured distance, the probe was moved no more than one meter at a time directly above the cable. The strongest signal directly above the fault point indicated the exact fault location.

Conclusion & Key Takeaways

1. Accurately tracing the cable route is essential before pinpointing; any route deviation means the pinpointing instrument receives no signal, so the cable path must be located first.
2. For high-resistance faults, burning through the faulted phase first can significantly save time.
3. After locating the fault, wait for excavation while continuing to apply voltage to the faulted cable, in case nearby cable sheaths are damaged and other cables are mistaken for the faulted one. Only proceed after final confirmation.

About XZH TEST

XZH TEST provides professional electrical testing solutions and cable fault detection equipment for power utilities, industrial facilities, and electrical engineering contractors worldwide.