Cable fault location

While paper-impregnated cables are particularly susceptible to external chemical and thermal influences, in high-voltage PE or XLPE cables the polyethylene insulation of the conductor is affected, leading to partial breakdowns and cracks that “eat away” the insulation.

The elapsed time multiplied by the diffusion speed v/2 gives the distance to the source of the fault.

The waves are unable to pass the fault because of the arc produced by the short circuit, so they are therefore reflected back again as with the pulse reflection method, which due to the burning short circuit results in a reversal of polarity.

[1] Murray loop test employs the principle of wheatstone bridge for locating the fault.

One end of the faulted cable is connected through a pair of resistors to the voltage source.

Then the distance to the fault location is calculated by solving the bridge equation.

If the fault resistance is high, the sensitivity of the Murray bridge is reduced and the Varley loop may be more suitable.

A Burn Down Instrument has a Voltage Generator connected via Transformer and allows individual control of output voltage and current, a vital step for burning down High Impedance Faults.

In 20 years that followed, over 2000 fault location vehicles were manufactured, more than half of which were intended for the former USSR.

These methods of cable fault location quickly became established in Western Europe as well.