Relationship between the physicochemical properties of materials and the fractal dimension of creeping discharges propagating at solid/fluid interfaces

TLDR: In this article, the main parameters that affect fractal dimension D of creeping discharges propagating over different types of insulators immersed in gases at different pressures or in dielectric liquids, in a point-plane electrode arrangement are analyzed.

Abstract: The present paper is aimed at the main parameters that affect the fractal dimension D of creeping discharges propagating over different types of insulators immersed in gases at different pressures or in dielectric liquids, in a point-plane electrode arrangement. Especially, the dielectric constant, thickness of insulators, gas pressure, type of liquids (mineral and vegetable oils) and the type of voltage waveforms (lightning impulse voltage or DC) are analyzed. The considered insulators are circular samples of different thicknesses made of different materials (namely, glass, epoxy resin, PTFE, phenolplast resin and pressboard). The fractal dimension D of the observed discharge patterns is determined by the box counting method. It is shown that D depends on the thickness (e) and the dielectric constant of insulator (s), gas and its pressure or type of liquid. In a given gas or liquid, D decreases when e increases and it increases with s this dependency of D upon e and e indicates the important role of the electric field and capacitive effect in the propagation mechanism. Also, D decreases when the gas pressure is increased; and D is higher with lightning impulse voltage than with DC voltage. However, in liquids, D decreases when increasing the dielectric constant of liquid. These results evidence the existence of a relation between the fractal dimension and the physicochemical parameters of both materials constituting the insulating mixed structure.