آخرین مورد شرکت در مورد Xi'an Xu&Hui Electromechanical Technology Co., Ltd. گواهینامه

Project Overview

Background

The tested cable is a 26/35 kV medium-voltage power cable (YJV 3×300) running between a substation and a box-type transformer at a solar PV plant in Japan. The cable is direct-buried, about 7,800 m long, and has several intermediate joints whose exact burial positions were not documented. After many years in service, the circuit tripped suddenly and could not be restored, so a complete cable fault detection and location service was requested.

Fault Verification

Routine insulation checks at 5 kV showed all three phases above the GΩ range, yet phase B failed the voltage-withstand test. A further insulation resistance survey with the electronic megohmmeter at the 5 kV range covering A-ground, B-ground, C-ground and all phase-to-phase combinations found that phase B measured only 0.5 MΩ to ground, while every other combination remained above GΩ. The fault was therefore classified as a leakage-type high-resistance fault on phase B.

Cable Length Measurement

The marked cable length was 7,800 m. Low-voltage pulse testing returned a measured length of 7,732.4 m, which confirmed the total route length before fault location began.

Rough Fault Location

Three methods were combined to estimate the fault distance from the test end:

• Low-voltage pulse method: the waveform showed only the full cable length, with no clear fault reflection on this high-resistance fault.
• High-voltage flashover method: analysis of the flashover waveform placed the fault at about 2,539 m from the test end.
• Bridge method: measurement indicated the fault at about 2,555 m from the test end, in close agreement with the flashover result.

The flashover and bridge results agreed well, narrowing the fault zone to roughly 2.3–2.6 km from the test end. Typical waveform charts recorded during rough location included the low-voltage pulse test chart, the high-voltage flashover test chart, and the bridge method test chart.

Cable Route Tracing

The exact cable route on site was not clearly documented, and the alignment was complex, running through farmland. The Model 507C cable locator was therefore used to re-trace the route and mark the position of the cable above ground before precise pinpointing.

Precise Fault Location

Impulse high voltage was raised to 36 kV to generate a detectable discharge at the fault point. Within the suspected zone of 2,300–2,600 m, the team walked directly above the marked route using the Model 503 pinpointer (acoustic method) and the Model 503E pinpointer (acoustic-magnetic time difference method). The fault point was finally confirmed at about 2,500 m from the test end, and excavation confirmed a water-ingress joint fault.

Test Summary & Key Takeaways

• For joint water-ingress faults, the discharge under impulse high voltage can be irregular, which makes the high-voltage flashover waveform difficult to obtain. The waveform should therefore be monitored continuously and interpreted with care during testing.
• When the flashover waveform cannot be obtained reliably on a joint water-ingress fault, the bridge method is an effective alternative for rough fault distance estimation.
• Combining flashover, bridge, route tracing and acoustic pinpointing methods delivers a reliable result on long, high-resistance buried cable faults.