PD patterns and PD current shapes of a void in LDPE

Partial Discharges (PDs) cause the degradation of insulating materials and govern the lifetime of high-voltage power apparatus and cables. Therefore, it is important to understand the PD behaviors in the aging process. In this paper, partial discharges and their current shapes of low-density polyethylene (LDPE) with a void were measured. The PD (φ-q-n) pattern and the current shape changed remarkably with time and were related to each other. They depended not only upon the size and shape of a void but also the degree of PD degradation. They changed with time from Stage 1 (initial stage) to Stage 5 (final stage) via Stage 2, 3 and 4. The PD current shape and PD magnitude gave us information about the mechanisms of PD, streamer-like discharge and Townsend-like discharge. The PD current shape was calculated by computer simulation. Parameters which affect the current shape were discussed. Such changes in PD characteristics will be applicable to the insulation diagnosis