Cable fault locator working principle

A cable fault tester is a professional instrument used to locate fault points in power cables, communication cables, or control cables. It is widely applied in fields such as power systems, rail transit, municipal engineering, and petrochemicals. The working principle of the cable fault tester is primarily based on the following methods:

1. Low Voltage Pulse Reflection Method (TDR)

A low-voltage electrical pulse is injected into the cable. When the pulse propagates to points of impedance discontinuity-such as breakpoints, short-circuit points, or joints-reflected echoes are generated. The instrument calculates the distance to the fault point by measuring the time difference between the transmitted pulse and the reflected pulse, combined with the known propagation speed of the pulse in the cable.

2. Impulse High-Voltage Flashover Method

A high voltage (DC or impulse voltage) is applied to the cable to cause instantaneous breakdown and arc discharge at high-resistance or flashover fault points. The sudden change in current or voltage during discharge excites traveling waves that propagate and reflect along the cable. The tester captures the reflection time of the traveling wave and uses the relationship between wave velocity and time to determine the fault distance. This method is often combined with acoustic-magnetic synchronization technology for pinpointing.

3. Bridge Method

Using the principle of DC bridge balance, the fault point position is calculated by comparing the resistance ratio between the fault phase and a reference phase (or an intact section of the cable), based on the known total length of the cable. This method is suitable for low-resistance grounding or short-circuit faults, with the other end of the cable connected to form a complete circuit.

Summary of Applications

Among the three principles:

The low-voltage pulse method is used for non-destructive distance measurement of low-resistance and wire breakage faults.

The high-voltage flashover method is used for excitation and location of high-resistance and flashover faults.

The bridge method serves as a high-precision auxiliary means for low-resistance faults.

Modern cable fault testers typically integrate multiple principles to meet the detection needs of various fault types.