Empirical model of a high voltage insulator under nonuniform pollution

Experimental results on the influence of the dry zone length and its position, with respect to the electrodes, on the leakage current and the arc length are used to determine an empirical model. The tests are conducted on a plane experimental model under AC voltage. Two configurations of the pollution layer are considered: (i) at the high voltage electrode side; and (ii) at the ground electrode side. Different conductivities of the wet layer are used. By adopting some simplified assumptions some of which being based on the experimental results, the authors propose a simple empirical model. This latter gives the expression of the whole impedance between the electrodes, from which they deduce the transferred voltage on the dry zone, whatever the configuration of the pollution. The obtained results show that the empirical model gives very correct results in the case of a linear system. Beyond this latter, the model is convenient no longer because of the probable decrease of the apparent impedance of the dry zone when the system becomes critical