Effect of trapped charges on cable SVL failure

The ATP-EMTP programme is used to model a cable circuit with high SVL failure rate. This paper presents results of the investigation. It will be shown that although the SVLs should withstand the surges for normal switching and external fault conditions, but their energy absorption rating is exceeded if the cable is energised while it has high level of trapped charges with opposite polarity to switching voltages. The operational switching log confirmed that the cables with high SVL failures are those which were used as a means of voltage control during light load conditions and that when they are switched daily for this purpose there is no discharge path for the charge drainage. Short and long term remedies are proposed to resolve the issues.