Surface flashover studies on precompressed pressboard insulation under superimposed AC/DC voltages

The scale down models of pre-compressed mineral oil insulation system have been studied under surface flashover of the surface of insulation. The experimental investigations have been dealt with for conventional AC, DC and superimposed voltages of AC/DC at different electrode gap distances. Two types of models using cylindrical embedded electrodes and stuck electrodes on the surface are employed. The studies relating to different conditions of the insulation system namely dry pressboard, impregnated pressboard in air medium, impregnated pressboard in oil medium are detailed. The surface flashover voltages under AC, DC and superimposed voltages have predominant effect on small electrode gaps causing sufficient damage to the surface of insulation. The time to failure of insulation due to discharges are presented. The discharges are more severe on dry pressboard as compared to oil impregnated pressboard