Relation between discharge initiation points and electrical field nonuniformity on electrode surface

Relations between electrical field nonuniformity and distribution of discharge initiation sites on electrode surfaces were investigated. A discharge initiation probability at some sites was associated with the local strength of electrical field. The multifractal analysis of the discharge initiation points distribution reveals that the sites where the discharge initiation probability is highest are not the maximum local field points. The discharge initiation is more probable at the sites forming a fractal set on the electrode surface. This was verified for the transformer oil impulse breakdown in cone-plane geometry. The multifractal dimension spectrum of the field distribution was changed by a cone angle variation (90-180°). The distribution of discharge initiation sites on the cone surface and breakdown and time lag are measured. The threshold angle, which corresponds to transition of the discharge initiation sites from the cone tip to the lateral surface was determined as 135°. A relation between the local electrical field strength and the probability of the discharge initiation was obtained. It was showed that breakdown probability determination of the complicated electrode system demands the evaluation of the local field distribution of the whole electrode surface