Lightning Impulse Flashover Characteristics of Glass Insulator String with RTV Coating

Insulator plays the vital role in the high voltage transmission lines, including glass insulator, porcelain insulator, and silicone rubber (SR) based composite insulator. In addition, glass/porcelain insulator with SR coating is the most efficient approach to integrate the advantages of both organic and inorganic materials, and has been widely used worldwide. However, the significant performance degradation of steep-front impulse withstand ability of glass/porcelain insulator after coating has sparked widespread concern among researchers and engineers. Previous research has tried to illustrate the breakdown mechanism, while the tests are based on single pieces of insulators. Thus, in this paper, the lightning flashover tests on insulator strings with and without coating are carried out. The flashover processes are recorded and analyzed, which further verifies the influence of coating on the surface arc development. Then, based on the results, the recommending revisions towards the current test standards on coated insulators are proposed. It not only examines the possible defects in dielectrics, but also takes into account the distortion of flashover process introduced by the coating.