Analysis of creeping discharges on oil-impregnated pressboard under combined AC and DC voltages

This paper presents a comparative analysis of the creeping discharge characteristics on mineral oil-impregnated pressboard (OIP) under combined AC and DC voltages. The creeping discharge behavior at various voltage levels to failure were analyzed using partial discharge (PD) measurements, camera observations, and electric field simulations. It was found that the creeping discharge distribution was significantly influenced by the DC component, and it was difficult to induce failure even on OIP with high moisture under combined AC and DC voltage. The flashover along the free-oil boundary layer above the OIP during creeping discharge occurred much more easily under combined AC and DC than under AC voltage, and the quality of the oil was important to avoid flashover. These differences were attributed to the combined influence of the electric field distribution under DC and space charge accumulation.