An effective way to reduce cable failures

Tony Walker, applications engineer for HV cable diagnostics and fault location at Megger, discusses the benefits of partial discharge (PD) testing.

An effective way to reduce cable failures

Faults on underground power cables are almost always disruptive and costly to fix. So there’s a very big incentive to minimise the risk of such faults occurring. One of the most effective ways of doing this is to use partial discharge (PD) testing and mapping, partial discharge activity is an indication of incipient insulation faults and is widely regarded as one of the best ‘early warning’ indicators of deterioration in medium and high voltage insulation.

PD diagnostics has therefore become a well-established method of quality control for new assets, as well as condition assessment of service-aged systems. PD testing looks for the characteristic electromagnetic signature produced by small electrical discharges in air gaps, voids and cavities in cable insulation, and in joints and splices. These discharges typically start long before these problems develop into a fault, so detecting them early gives time for action to be taken to avert outright failure.

A large percentage of failures on new cables are attributable to poor installation work. So PD testing during the commissioning of new installations can reveal many of the issues, such as improper or incomplete stripping of insulation, improper shrinking of insulating sleeves, or nicks and cuts in the insulation and other poor workmanship.

Regular PD testing on in-service cables provides useful data that can be trended or compared with data from similar cables to flag up changes that need further investigation.

While no test method can reveal every incipient fault, PD testing is undoubtedly the best form of “insurance” against cable faults that’s currently available. And, considered in the light of the financial impact of a typical cable fault, it’s insurance well worth buying.

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