Cable Fault Locating

Cable Fault Locating uses a device installed on a conductor to determine if the current exceeds the indicators current rating. Cable Fault Locating involves the use of the magnetic field induced by load current to find the fault.

Cable fault locating uses an arc-reflection system, which is considered the best technology available for locating failures in medium to high-voltage cables.
An arc-reflection system is the combination of high-voltage impulse generator (also know as a thumper) and a TDR system.

A TDR system is basically a high frequency, low-voltage pulse generator in combination with an oscilloscope. The TDR pulse is sent down the cable and the voltage reflection (echo) from the cable is recorded as a waveform. The method behind arc-reflection technology is to thump the de-energized cable to produce an arc at the fault point and simultaneously send a TDR pulse down the cable to reflect off of the arc.

The time it takes for the TDR pulse to travel down the cable to the arc and return is used to calculate the distance to the arc (fault). Arc-reflection systems work best on shielded cable because a low-resistive return path is needed for the TDR pulse to see the arc. Good results are typical with Mine Power Feeder (MPF), miner and trailing cables.

When it comes to cable fault locating, it is noted that the introduction of cables with solid dielectric insulation and of modern splicing technology has imposed new standards and restrictions on cable testing and cable fault locating. The arbitrary use of high voltages and energies during DC, AC, and impulse testing of in-service power cables with solid dielectric insulation frequently programs the cables with defects which become faults after the cables are returned to service. The inadequacy of DC testing in determining the cables AC breakdown strength, the danger of programming the cables with faults when DC and impulse testing at unnecessarily high voltages, and the advantages of very low frequency (VLF) testing and arc reflection methods (ARM) in locating cable defects and faults are presented. BY establishing cable fault locating and cable testing guidelines for cable with solid dielectric insulation, which incorporate current research and available technology, utilities can realize substantial savings in cable replacement, cable rehabilitation, and work force budgets.