latest company case about Xi'an Xu&Hui Electromechanical Technology Co., Ltd. Certifications

Project Background

During the commissioning of the 35kV collector line (Line 35F4) at the Jiayu Gulang Huanghuatan 300MW PV power station, the cable failed its AC withstand voltage test. The cable, connecting Box Transformer No. 08 to tower BJ1 (overhead line transition), experienced a flashover protection trip at 52kV after approximately 50 minutes of testing. Upon re-energization, the voltage could not rise above 7kV, confirming a flashover breakdown on Phase A. With the project on a tight commissioning schedule, rapid fault location and repair were critical to avoid delays in grid connection.

The cable route spanned 940 meters of direct-buried installation with two intermediate joints and terminal joints accessible via dedicated inspection pits. Pre-fault insulation measured R15S: 387GΩ and R60S: 869GΩ (absorption ratio 2.25). Post-flashover readings dropped to 2GΩ with absorption ratio of 1.

Equipment Deployed

Testing Process

Step 1 — Insulation Diagnosis & Fault Nature Assessment

Using the XHMR-5kV insulation resistance tester, the team confirmed pre-fault insulation at 2.25 absorption ratio and post-flashover readings at 2GΩ with absorption ratio of 1.0, indicating a high-voltage flashover fault requiring elevated test voltage to trigger breakdown.

Step 2 — Cable Length Measurement & Joint Identification

The 502 TDR tester in low-voltage pulse mode measured the full cable length at 940 meters, revealing joint reflections at approximately 300m and 600m — closely matching field-provided pit locations and narrowing the suspected fault zone.

Step 3 — Burn-Through Treatment

The team deployed the 60Q burn-through bridge, applying a sustained 4kV/10mA current for approximately 10 minutes. Voltage dropped to 0.3kV while current rose above 300mA, confirming the fault point was successfully converted to a stable low-resistance channel suitable for HV flashover testing.

Step 4 — High-Voltage Flashover Pre-Location

With the fault channel established, the team configured the 5-50 test transformer with the 40/6 pulse energy storage capacitor for high-voltage flashover testing. The high-voltage output was routed through the discharge ball gap to the faulted phase, with the capacitor ground connected to the cable copper braid shield. The 502 TDR captured flashover waveforms, and analysis determined the fault distance at 317.7 meters from the test terminal.

Step 5 — Precise Acoustic-Magnetic Pinpointing

The 503D acoustic-magnetic pinpointer was deployed near the 317m mark. Joint pits at 300m and 600m yielded no discharge sounds, confirming the fault was not at either joint. At 320m, distinct discharge sounds were detected — faint due to sandy soil dispersal. No visible external damage was found upon excavation, but re-energization revealed localized cable vibration at a specific point. The fault was identified as a factory-made single-phase joint within the cable body, not a field-installed joint.

Step 6 — Repair & Verification

After repair, the XHBP-1056/528 variable-frequency series resonant AC withstand test set was used for verification. The cable successfully withstood 52kV AC for 60 minutes, confirming the repair was complete.

Key Results

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