Partial Discharge Inception Voltage of an Oil Gap between Polypropylene Films and the Effect of a Small Amount of Gas

Film power capacitors are made out of laminated polypropylene (PP) films and aluminium foil electrodes, which are then impregnated with insulating oil. Partial discharge (PD) occur within voids, or around the edge of electrode, resulting in the deterioration of the PP film, and ultimately, to dielectric breakdown. In this study, we used an oil gap electrode system, wherein an oil gap or oil-air gap was formed between the PP films. Thereby investigated the PD characteristics. Partial discharge inception voltage (PDIV), PD light emission, and discharge amplitude-number of PDs-phase which PD occurred (φ-q-n) patterns were observed under the application of AC voltage. The PD characteristics of oil gap electrode changed sequential. It showed that PD in the oil gap generated the oil-decomposed-gas voids initially, before further PD occurred within these gas voids. The PDIV of the oil-air gap electrode was lower than that of the oil gap electrode, despite the oil being moved via dielectrophoresis and PD in the gas region being partially suppressed.