Cable fault tester instrument sends low-voltage pulse signals to cables
Cable fault tester (also commonly referred to as cable fault detector or cable fault locator) is a professional device specifically used to detect fault locations in various types of lines such as power cables and communication cables. It is like a "stethoscope" and "CT scanner" for the cable system, capable of quickly and accurately pinpointing fault points in underground or concealed lines without blind excavation.
⚙️ Core Working Principle
Cable fault testers typically adopt a two-step strategy of "first rough distance measurement (pre-location), then precise pinpointing," with the core principle mainly based on traveling wave reflection and acoustic-magnetic synchronization technology:
Pre-location (distance measurement): Find out roughly which section the fault point is in
Low-voltage pulse reflection method (TDR): The instrument sends low-voltage pulse signals to the cable. When the signal encounters impedance discontinuities such as open circuits or short circuits, reflections occur. By measuring the time difference between the transmitted wave and the reflected wave, combined with the wave speed of the cable, the distance to the fault point is automatically calculated. This method is very effective for open circuits and low-resistance short circuits.
High-voltage flashover method (impulse flash method/direct flash method): For high-resistance or flashover faults caused by insulation aging, water ingress, etc., the instrument applies high voltage to cause instantaneous breakdown discharge at the fault point, generating traveling wave signals. The distance is calculated by capturing the reflection time of this transient traveling wave.
Secondary/multiple pulse method (modern mainstream): This is currently the most advanced distance measurement technology. It utilizes the moment of high-voltage breakdown at the fault point to emit low-voltage pulses for collection. By comparing the waveform differences before and after breakdown, it can extremely intuitively and accurately lock onto the location of high-resistance faults, with strong anti-interference capability.
Precise pinpointing: Find the exact location of the fault point on the ground
Acoustic-magnetic synchronization method: At the moment of high-voltage breakdown at the fault point, the fault point emits a "pop" discharge sound (acoustic wave) accompanied by electromagnetic waves. The pinpointing instrument receives these two signals on the ground through probes, and uses the time difference between the arrival of sound and electromagnetic waves, as well as the intensity of the sound, to precisely lock onto the position directly above the fault point (with an error typically within 0.2 meters).
Step voltage method: Mainly used for outer sheath damage or low-resistance grounding faults in directly buried cables. By injecting a signal between the fault phase and the earth, the fault location is determined by measuring the abrupt change point of step voltage on the ground.
