Depolarization Current Measurements on Field-Aged XLPE Cable Insulation

Abstract

Laboratory tests on field aged and unaged cables were performed using DC depolarization current measurements. Aged cables with water trees showed high dielectric losses and depolarization currents as compared with the reference, unaged cable. Both the area under the depolarization current waveform and dielectric loss factor, tandelta, increased with DC poling and the applied AC voltage, respectively. A new indicator of the insulation aging derived from the measured current is proposed to rate the degree of aging of cable insulation. This indicator increases with the poling field, and a DC poling voltage less than 50% of the nominal peak value of the cable operating voltage is sufficient to obtain reliable values. The cable insulation aging indicator could be a useful tool for monitoring the operating condition of cables in service and help utilities to develop cable replacement programs based on the actual state of the cable insulation conditions.