A numerical model using surface charges for the calculation of electric fields and leakage currents on polluted insulator surfaces

The pollution on the surface of an insulator is asymmetric though the insulators, in general, are axisymmetric. A pollution layer of wet or dry type has an enhancement effect on the distribution of the electric potential, field and leakage current on the surface of the high-voltage (HV) outdoor insulators. In the present work, a numerical method for the computation of the electric potential, field and surface leakage current on the surface of the polluted HV insulators is developed. The method is based on the surface charge simulation (SCSM) and discrete charge simulation techniques when the simulation charges are complex at a given frequency. The method takes into account surface as well as volume conductivities in addition to the effect of the dry band or wet pollution. Due to the conductivity of the insulation a complex permittivity of the insulating material has to be regarded. The surface pollution on the insulators, in general, is asymmetric and is simulated by small or big patches of dry band or wet pollution. Therefore, the field configuration has to be three-dimensional. Special emphasis is laid on the extreme local field variation at the boundary between dry and wet surface patches. As an example, the method is applied to a polluted cylindrical insulator supporting a HV electrode above the ground plane.