Characteristics of partial discharge on high-density polyethylene insulation under AC and DC voltages

The majority of insulation system failures in electrical grids are caused by partial discharge (PD) activity. Continuous PD activity gradually degrades the quality of insulation, potentially resulting in total breakdown. This study investigates PD activity in high-density polyethylene (HDPE) insulation, detected through the observation and measurement of PD charge using the CIGRE Method II electrode system. The objective is to analyze PD behavior in HDPE cable insulation containing cavity-type defects under alternating current (AC) and direct current (DC). The samples consist of three layers of HDPE sheets, each 1 mm thick, with an artificial circular cavity of 1 cm in diameter embedded in the middle layer. This configuration enables detailed analysis of insulation damage and degradation. The results show that HDPE performs better under DC voltage compared to AC. This is evidenced by the average PD inception voltage (Vin) under DC conditions reaching 15.5 kV, higher than the 11.8 kV observed under AC, as well as a significantly longer PD inception time (Tin) under DC conditions. Although the PD charge magnitude is nearly the same under both voltage types, the higher voltage required to trigger PD under DC indicates that HDPE exhibits superior insulation resistance to DC voltage.