Fractal analysis of creeping discharge patterns propagating at solid/liquid interfaces-influence of the nature and geometry of solid insulators

The paper deals with the fractal analysis of the creeping discharge propagating over different solid insulators immersed in mineral oil under negative impulse voltage using a point-plane electrode arrangement. The fractal dimension is estimated thanks to the box counting method. We observed that the creeping discharges propagate radially. Their shape and length depend on the physical and geometrical properties of solid insulators. It´s shown that the discharge patterns observed over the investigated solid materials present a fractal dimension D which depend upon the thickness of the solid samples (e) and the type of insulator. D decreases when e increases and it increases with the dielectric constant of insulator. D is the highest for glass and the lowest for polycarbonate; it is in between for phenoplast resin. These results suggest the possible implication of capacitive effects on the propagation phenomena of creeping discharges and the existence of a relation between the fractal dimension and the physical parameters.