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# FABEAD82d01 - erical Model Using Surface Charges for the...

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erical Model Using Surface Charges for the Calculation of Electric Fields and Leakage Currents on Polluted Insulator Surfaces A. Ahmed and H. Singer Department of Theoretical Electrical Engineering Technical University Hamburg-Harburg Harburger SchloBstr. 20 2 1079 Hamburg, GERMANY Abstract The pollution on the surface of an insulator is asymmetric though the insulators, in general, are axi- symmetric. A pollution layer of wet or dry type has an cnhancement 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 where 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. Introduction The insulation system of a high voltage equipment has to withstand high electric stress for decades. An inherently critical zone of these equipments is the interface between the solid insulator and the surrounding. Hence, the study of the fundamental phenomena in electrically stressed interfaces is of crucial importance to enable the design of high voltage and clean conditions the electric field follows the rules of the electrostatic field and can be simulated correspondingly. Increasing surface conductivity due to conductive contamination leads to increase in surface equipments which satisfy the requirements. Under dry P. K. Mukherjee Department of Electrical Engineering Jadavpur University Calcutta INDIA leakage current which can initiate a heat conduction process occurring on the insulator surface. The nature and severity of the surface contamination can vary over a wide range [l]. If a random spot dries out first, for a smooth cylinder, the current density around it will be increased causing even higher heat to evaporate the moisture. The dry spot will grow laterally, that is perpendicular to current flow [2], until it covers a whole circle around the surface of a cylindrical insulator. The formation of a dry-band zone, which may eventually cause a flashover of the insulator, can be viewed as the final result of such a process [3]. Several computational techniques have been

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