Evidencing of the Capacitive Effects on the Development of Creeping Discharges at Solid/Fluid Interfaces

The present paper reports on the evidencing of the capacitive effects on the characteristic parameters of the surface discharges propagating over different types of insulators immersed in gases or dielectric liquids, in a point-plane electrode arrangement submitted to different types of voltage waveforms namely AC, DC and lightning impulse voltages. These effects are highlighted through the influence of thickness and dielectric constant of insulators. The investigated insulators are circular samples of different thicknesses issued of various materials of different dielectric constants (namely, PTFE, glass, epoxy, Phenoplast resin (Bakelite) and pressboard); and the considered fluids are mineral oil, vegetable oil, and gases. It is shown that the lengths of discharges and surface density of their branches increase when the thickness of insulator is reduced and/or the dielectric constant of insulator is increased what clearly evidences the role of capacitive effects.