Influence of oil-flow to the breakdown characteristics of oil-pressboard insulation in converter transformer under compound electrical field

Taken a composited insulation system of oil and pressboard filled in two parallel tabulate electrodes as research object, the oil-flow electrification experiment was carried out without applied voltage and under DC voltage. The relationship between leakage current and velocity was measured. The electric-field caused by oil-flow electrification was calculated. The breakdown characteristics experiment of the composited insulation system was carried out at different velocity, stressed by AC voltage, DC voltage and AC plus DC voltages with different AC voltage content. The result shows that, as the velocity increases, the breakdown voltage of the oil-pressboard composited insulation system may decrease and the electric-field caused by oil-flow electrification may increase. The oil-flow electrification will increase under DC electrification than that without applied voltage.