Charging of Solid Elements of High-Voltage Insulation by Corona in Gas

Paper i proceeding, 2011

Solid dielectric coatings and barriers embedded in gaseous medium form hybrid insulation where gas phase has much lower ability to withstand electrical discharges than solid materials. In the most common case of systems with non-uniform electric fields, corona discharge may be initiated in gas and exist until the applied voltage and corresponding field strength are high enough. Corona acts as a source of electrical charges, which can be deposited on surfaces of solid elements. The accumulated charges produce their own field, which being superimposed with the external one may alter the entire field distribution in the insulation and may affect its performance [1, 2]. In the present paper, corona charging of solid dielectric surfaces is analyzed by means of computer simulations focusing on the dynamic behavior of electric fields in the considered system. The model describes glow mode of corona discharge and treats gas-solid interfaces as barriers for charge carriers. Being verified against static characteristics of corona discharges in a rod-plane system, the model is further utilized for analyzing impulse coronas in different electrode arrangements. The results of the computer simulations yield dynamics of space charges in gas gaps and surface charges on gas-solid interfaces as well as corresponding variations of electric field distributions in the entire system. The obtained results are employed to elucidate regularities in flashover characteristics registered in experiments. It is shown that charging of surfaces of solid elements of the insulation may be essential for enhancement of its performance, as in the case of dielectric barriers. Surface charging, however, could be undesirable under certain conditions. The analysis of insulation systems accounting for the corona charging allows improved design evaluation of high voltage equipment. Anticipated new sustainable solutions with low environmental impact will benefit from the understanding of the discussed effects.