Known as the stethoscope and navigator of cable maintenance
The Cable Fault Tester is the core device used in power system operation and maintenance for quickly locating fault points in underground or overhead cables, known as the “stethoscope” and “navigator” of cable maintenance.
It is not just a single instrument but typically a comprehensive testing system. Following the logic of “coarse detection first, then precise pinpointing,” it helps maintenance personnel accurately locate cable short circuits, open circuits, or leakage points without digging up the ground.
I can break down the working principle, core components, and operational workflow of this system for you in detail.
Core Working Principle: From “Coarse Detection” to “Precise Location”
Cable fault testing is generally divided into two stages: distance measurement (coarse detection) and path pinpointing (precise detection).
. Distance Measurement (Coarse Detection): Knowing how far the fault is
This step determines the approximate distance from the test end to the fault point (e.g., 1500 meters from the test end).
Low-Voltage Pulse Method (Radar Method):
Principle: A low-voltage pulse is transmitted into the cable. When the pulse encounters an impedance discontinuity point (such as a break or short circuit), it reflects back. The instrument calculates the distance by measuring the time difference between the transmitted and reflected waves (
Application: Open circuits, low-resistance short circuits (resistance <100Ω).
High-Voltage Flashover Method (Impulse Flashover/Direct Flashover):
Principle: For high-resistance faults (such as minor insulation damage with high resistance), low-voltage pulses cannot reflect. In this case, high voltage (e.g., 15kV-35kV) must be applied to break down the fault point, generating arc discharge that triggers traveling wave reflection, thereby measuring the distance.
Application: High-resistance leakage and high-resistance flashover faults (the most common type of fault in power cables).
Secondary/Tertiary Pulse Method:
This is the mainstream technology in modern high-end instruments. It uses high-voltage pulses to break down the fault point while simultaneously transmitting low-voltage pulses. By comparing the waveform differences “before breakdown” and “after breakdown,” high-resistance faults can be identified with exceptional clarity, solving the pain point of difficult waveform interpretation in traditional flashover methods.
. Path and Pinpointing (Precise Detection): Knowing where the fault is
Coarse detection only tells you “there is a fault at 1500 meters,” but the cable is buried underground. Where exactly on the surface is it located? This requires pinpointing.
Path Detection: Using the principle of electromagnetic induction, a specific frequency signal is applied to the cable, and a receiver scans the ground surface to map the cable route and burial depth.
Acoustic-Magnetic Synchronous Pinpointing Method:
Principle: This is currently the most mainstream method. The instrument applies high-voltage pulses to the cable, and when the fault point breaks down, it emits a “pop” discharge sound (acoustic wave) and generates electromagnetic waves.
Operation: The pinpointing instrument receives both signals simultaneously at the ground surface. Electromagnetic waves travel extremely fast (arriving instantaneously), while acoustic waves travel slowly (propagating through soil). The instrument calculates the time difference between the two, or the operator directly listens through headphones for the loudest sound point, to lock in the precise location of the fault point (with an error controlled within 0.2 meters).
