Influence of hydrostatic pressure on creeping discharge characteristics over solid/liquid insulating interfaces under AC and DC voltages

This study deals with the influence of hydrostatic pressure on discharges propagating at solid/liquid insulating interface submitted to a divergent electric field under AC and DC voltages. The investigated insulator samples are of phenoplast resin (bakelite) and the considered liquid is mineral oil. The experimental results show that the hydrostatic pressure and the waveform, amplitude and polarity of voltage greatly influence the characteristic parameters of creepage discharges. The stopping (or final) length, Lf, which is the maximum extension of these discharges increases with voltage; it is reduced when applying a hydrostatic pressure. Lf increases quasi-linearly with the voltage and decreases quasi-linearly when the hydrostatic pressure is increased, whatever the voltage waveform. These results are of great interest especially for design and dimensioning of insulation systems in high voltage oil-filled apparatus and especially non-breathing components.