최근 회사 사건 Xi'an Xu&Hui Electromechanical Technology Co., Ltd. 인증서

Project Overview

Background

The tested cable is an 800 V armored low-voltage power cable (YJV 3×120) running from the PV panel array side to the box-type transformer side of a solar plant in Weinan, Shaanxi. The cable is about 1,335 m long and is direct-buried along a known route. When abnormal operation was reported on the circuit, the plant requested a complete cable fault detection and location service.

Fault Verification

Insulation resistance was first measured with an electronic megohmmeter at the 1000 V range, covering all phase-to-phase and phase-to-ground combinations. Phases A and C both measured above 1 GΩ, while phase B measured 0 MΩ; all phase-to-phase readings were above 1 GΩ. A multimeter check between phase B and the cable armor gave 3 Ω. The initial diagnosis was therefore a phase B short circuit to the armor layer.

Cable Length Measurement

A low-voltage pulse test on the A-C phase loop produced the full-length waveform (Fig. 1), giving a measured cable length of 1,333.1 m, which matched the marked length of 1,335 m.

Rough Fault Location

Two complementary methods were combined to estimate the fault distance from the PV-side test end:

• Low-voltage pulse method: the healthy-phase waveform confirmed the full cable length of about 1,300 m, and the faulty-phase short-circuit waveform indicated the fault at roughly 30 m from the test end.
• High-voltage flashover method: applied from the PV side to verify the near-end fault distance (L = S/N) indicated by the pulse test.

The recorded waveforms included the low-voltage pulse full-length waveform (A-C phase), the low-voltage pulse test waveform from the PV side, and the high-voltage flashover waveform from the PV side. Both methods agreed on a fault zone approximately 30 m from the test end.

Precise Fault Location

Because the cable route was clearly known, no route tracing was needed. The Model 512-12 integrated impulse unit with large capacitance applied impulse high voltage to the faulty phase. Within the suspected 30 m zone, the Model 503 pinpointer (acoustic method) and the Model 503E pinpointer (acoustic-magnetic time difference method) were used to trace the discharge, and the Model 507C cable locator was applied in audio-frequency mode for final pinpointing. The fault point was finally confirmed at approximately 30 m from the test end.

Test Summary & Key Takeaways

• For low-voltage cables, the impulse test voltage cannot be raised as high as for high-voltage cables. The resulting low discharge energy makes the discharge sound very weak and increases the difficulty of precise pinpointing. The solution is to increase the capacitance of the high-voltage source, which raises the discharge energy at the fault point and makes the discharge sound stronger.
• Low-voltage cable faults should be cross-verified with multiple test methods to avoid misjudgment caused by armor-to-ground discharge. In this job, the low-voltage pulse method, high-voltage flashover method, audio-frequency method, acoustic method, and acoustic-magnetic time difference method were combined to achieve a reliable result.