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800V Solar Farm Cable Fault Detection Case in Ninh Thuan Vietnam: 190m Route 120m Fault Pinpointed

2026-09-08

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

Project Overview

Item	Detail
Project	800V cable fault detection at a solar power plant in Ninh Thuan Province, Vietnam
Test Date	August 27, 2026
Test Team	XZH cable fault testing engineers
Cable Type	800V three-core armored aluminum cable, direct-buried
Cable Route	190 m in total; one end terminated at the combiner box and the other end at the box-type transformer
Fault Symptom	B-phase single-phase-to-earth leakage fault

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.

Test Result: 190 m cable route measured by low-voltage pulse; 120 m fault distance pre-located by 9kV HV flashover; fault point pinpointed acoustically and confirmed by shallow excavation — the complete locate-trace-pinpoint workflow was finished on site in one visit.

Instruments Used

Item	Detail
Electronic megohmmeter	Insulation resistance diagnosis at the 2.5kV range (B-E = 0Ω, others >GΩ)
XHGG502	Low-voltage pulse full-length measurement and HV flashover fault distance pre-location
XHDD503	Acoustic pinpointing along the pre-located zone
XHGX507	Carried for route confirmation; route markers were available so tracing was not required
XHHV512-12L	9kV flashover excitation of the fault
Portable power supply	On-site powering of the test instruments

Technical Summary

Why removing the armor grounding at one end makes the discharge sound louder: the insulation layer of low-voltage cables is thin. Once the cable breaks down, the discharge energy is conducted through the armor directly to the ground bars at both ends. When the armor grounding at one end is removed, the leakage energy at the fault point can only return through the single remaining ground bar and leak to earth at the fault itself — so the discharge sound at the fault point becomes significantly stronger and easier to pinpoint.

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.