800V Solar Farm Cable Fault Detection Case in Ninh Thuan, Vietnam

Project Overview

Background

On August 27, 2026, the XZH field service team was called to a solar power plant in Ninh Thuan Province, Vietnam, where an 800V three-core armored aluminum cable running between a combiner box and a box-type transformer had developed a phase-to-earth fault. The cable is laid directly underground and forms part of the photovoltaic power collection system. Site information indicated that the route had been re-laid during Phase II construction, which raised a strong suspicion of external mechanical damage.

Step 1: Fault Diagnosis by Insulation Test

Using an electronic megohmmeter at the 2.5kV range, the team measured the insulation resistance of A-E, B-E, C-E, A-B, B-C and A-C respectively. The B-E reading was 0Ω (5V), while all other readings remained above GΩ. A solid B-phase-to-earth fault was therefore confirmed before any further testing was carried out.

Step 2: Fault Pre-Location

The cable fault locator (Model 502) first applied the low-voltage pulse method and measured the total cable length at 190 m. The high-voltage flashover method was then adopted for fault distance measurement: when the output voltage was raised to 9kV, the fault discharged fully and repeatedly, and the pre-located fault distance was calculated at 120 m from the test end.

Step 3: Fault Pinpointing

Because the insulation resistance at the fault was zero, the team removed the armor grounding at one end before applying the test voltage again. The discharge sound at the fault point then became clearly audible. Walking along the cable route around the 120 m position with the acoustic pinpointer (Model 503), the discharge sound was heard directly in the pre-located zone. A shallow dig exposed the cable and visually confirmed the exact fault point — without the need for full trench excavation.

Cause of the Fault

The fault was caused by external mechanical damage during Phase II construction: the cable route was re-laid by the Phase II contractor, and Phase I and Phase II of the plant belong to different owners. The impact crushed the cable and damaged the B-phase insulation, leading to a direct phase-to-earth leakage.

Instruments Used

Technical Summary

This case demonstrates the complete XZH cable fault testing workflow for photovoltaic plants: insulation diagnosis, full-length measurement, HV flashover pre-location, acoustic pinpointing and on-site confirmation — helping solar farm operators restore power quickly with minimum excavation.

For cable fault testing services or cable fault locator instruments, please contact the XZH team for a quotation.