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Campus Underground Cable Fault Location — XHDD-503 Pinpointer at Linyou Middle School, China

2026-07-13

Project Overview

On August 28, 2023, our engineering team was dispatched to Linyou County Middle School in Baoji, Shaanxi Province, China, to diagnose and pinpoint critical underground power cable faults that had caused a complete power outage to the teaching building.

Customer Background

Linyou County Middle School is a public educational institution with a campus-wide underground power distribution network. The faulty cable — a YJV 4×75mm², 380/440V low-voltage power cable spanning 300 meters from the transformer distribution room to the teaching building distribution box — served as the primary power supply for the entire teaching building.

The Challenge

Parameter	Finding
Cable Type	YJV 4×75mm², 380/440V
Total Length	300 meters
Phase-to-Phase Insulation	0Ω (short circuit)
Phase-to-Ground Insulation	0Ω (ground fault)
Fault Type	Phase-to-phase short circuit with ground fault
Cable Joint Location	270m mark (cable well)

The school required same-day fault pinpointing to minimize disruption to classes. Minimal excavation was critical to protect the campus grounds, and the presence of other buried utilities demanded precise, non-destructive fault location.

Our Solution & Equipment

We deployed a complete four-stage fault location workflow using XZH TEST equipment:

Stage	Equipment	Model	Function
1. Insulation Testing	Digital Megohmmeter	XHMR-5kV	500V range — measured phase-to-phase & phase-to-ground resistance
2. HV Pulse Generation	HV Pulse Generator	XHHV535-2L	Applied 6–7kV impulse voltage to create flashover at fault points
3. Fault Pre-location	Cable Fault Tester	XHGG-502	Low-voltage pulse & high-voltage pulse waveform analysis for distance measurement
4. Precise Pinpointing	Cable Fault Pinpointer	XHDD-503 & XHDD-503D	Acoustic-magnetic synchronization method for <0.1m accurate fault location

Implementation Process

Insulation Assessment: Using the XHMR-5kV at 500V, we confirmed all three phases had 0Ω insulation to ground and between phases, confirming a short-circuit ground fault.
Path Verification: Cable route was clearly marked with indicator posts. The cable joint at 270m was identified and noted.
Rough Pre-location: The XHHV535-2L applied 6kV impulse voltage to the faulty cable, creating controlled flashover discharge. The XHGG-502 captured both low-voltage and high-voltage pulse waveforms, showing two fault distances: 120 meters and 170 meters.
Precise Pinpointing: Voltage was increased to 7kV for clearer acoustic discharge signals. Using the XHDD-503 and XHDD-503D cable fault pinpointers with acoustic-magnetic synchronization, our engineers precisely located both fault points by identifying the minimum time difference between electromagnetic and acoustic signals. Both locations were marked for excavation.
Excavation Confirmation: Targeted excavation at the marked positions confirmed both fault locations, with deviation under 0.1m.

On-site wiring: HV pulse generator connected to faulty cable for discharge testing

Project Results

Result	Detail
Faults Located	2 (120m and 170m positions)
Pinpointing Accuracy	<0.1m (acoustic-magnetic synchronization)
Total Duration	Same-day completion (on-site testing to final pinpointing)
Excavation Scope	Minimal — only two marked positions
Safety Record	Zero incidents, zero false digs, zero injuries

Conclusion

This project demonstrates XZH TEST's comprehensive cable fault location capabilities in time-sensitive campus environments. The four-stage methodology — from insulation testing through rough pre-location to acoustic-magnetic precise pinpointing with the XHDD-503 series — delivered accurate, efficient fault location with minimal disruption. The dual use of XHDD-503 and XHDD-503D pinpointers at two independent fault locations validated the instrument's reliability in complex, real-world field conditions. With same-day pinpointing and sub-0.1m accuracy, the school was able to restore power quickly while preserving campus infrastructure integrity.