Role of surface charging in the performance of polymeric high voltage insulation systems

Environmental concerns, being one of today's driving forces in the development of future transmission and distribution of electric power, enforce a strong demand for minimizing the use of some types of insulating materials in high voltage insulation. In this context, use of gas mixtures and solid coatings/barriers in insulation systems offers interesting and yet unexplored possibilities. Among diverse concepts, air insulated systems with conducting parts covered by thick dielectric coatings — so called hybrid insulation systems — are considered. Processes of electric charge deposition and relaxation on the solid coating surfaces yield an enhanced electric withstand, which arises in this system from a conditioning effect by charges generated in the gas phase. The system exhibits both adaptive and dynamic features and the future task in its development foresees selecting solid materials able to resist the associated discharge activity and, at the same time, provide required electrical properties. This presentation demonstrates and explains the principle features of hybrid insulation system, including phenomena in its gaseous and solid parts, by comparing experimental results with process simulations. Further, dynamics of the decay of electric charge deposited on thick dielectric coatings is analyzed and, finally, the influence of the deposited charge on electric withstand ability along dielectric surfaces is discussed.