PARTIAL DISCHARGES DUE TO ELECTRICAL TREEING IN POLYMERS - PHASE-RESOLVED AND TIME-SEQUENCE OBSERVATION AND ANALYSIS

We have investigated the partial discharge (PD) due to electrical tree ing degradation in low-density polyethylene (LDPE), ethylene-vinyl ace tate copolymer (RIA) and ethylene-acrylic acid copolymer (EAA) by a co mputer-aided partial discharge measurement system which allowed us to obtain phase-resolved PD pulse data. The experimental results revealed that the PD magnitude was strongly affected by the instantaneous appl ied voltage and that the occurrence of a PD was determined by the time derivative of the applied voltage (dv/dt). The PD pulse-sequence anal ysis revealed the following: (i) a PD occurs in a discharge path which consists of a tree trunk and branches extending from the trunk; (ii) in each discharge path at most one PD occurs per half cycle. Based on these facts, a model of PDs due to electrical treeing was proposed. Th e influences of applied voltage and frequency were investigated by app lying a triangular voltage. The number and average magnitude of PDs in creased linearly with applied voltage whereas the PD charge per cycle increased quadratically. These results are in good agreement with the model.