Influence of hydrostatic pressure on morphology and final length of creeping discharges over solid/liquid interfaces under impulse voltages

This paper is aimed at the influence of hydrostatic pressure on the morphology and final length of creeping discharges propagating over solid / liquid insulating surfaces in a point-plane electrode arrangement submitted to lightning impulse voltages. Three types of solid insulators (namely polycarbonate, phenoplast resin (Bakelite) and glass), immersed in mineral oil are tested. It is shown that the length of branches constituting the discharges are reduced when the hydrostatic pressure is increased whatever the polarity of the voltage. The final length of discharges L_f increases quasi-linearly with the voltage and decreases when the hydrostatic pressure is increased for both positive and negative polarities as observed elsewhere under AC and DC. On the other hand, for given voltage and pressure, L_f increases with the dielectric constant of solid materials indicating the important role of the capacitive effects in the propagation mechanism.