On-site Diagnostic Tests on Polymer Insulated Cables Using Depolarization Current Measurements

Amodified technique of depolarization current measurements encompassing monitoring of high speed depolarization processes was used to perform diagnostic tests on polymeric cable insulation operating under diverse environmental conditions and voltage levels. The high frequency characteristics were compared with those of the slower depolarization processes commonly obtain during on-site tests. Both the high and low frequency measurements showed a consistent correlation with the operating conditions of the cable insulation. It was observed that the low frequency characteristics were dependent on the duration of the dc poling time but only if the insulation was deteriorated, especially with water trees. Unaged and relatively new insulation did not show such behavior. The majority of the field tests were performed with a relatively low dc voltage of only 1 kV or less and under very adverse environmental conditions, with temperatures as low as ¿30°C.