Partial discharge characteristics of oil impregnated insulation system with an oil gap under continuous AC voltage application

The fundamental partial discharge characteristics of an oil-impregnated insulation system with an oil gap were investigated in this study, in addition to the effects of the oil gap conditions such as size, depth, location, and volume on the partial discharge inception electric field (PDIEF). We initially assumed the oil gap to be a defect of oil-filled (OF) cable systems. A breakdown occurred at the oil gap in all test samples. We then selected one of the oil gap conditions that gave the lowest PDIEF, and we investigated its time transition of partial discharge characteristics under a continuous alternating current (AC) voltage application. As a result, partial discharges continued with the AC voltage that was lower than that of the partial discharge inception, and the test sample broke down after approximately 16 days. Partial discharges occurred near the timing of the zero crossing of the applied voltage. Their characteristics such as charge magnitude and number did not increase, and partial discharges with larger magnitudes began at the timing closer to the peaks of the AC voltage.