DC-toughened glass insulators pre-coated with RTV silicone rubber — Field returns from aged samples installed on HVDC lines

RTV silicone rubber coating on ceramic insulators has been used for at least two decades in order to solve critical problems related to pollution in harsh environments. In Italy the experience on AC 380 kV transmission lines started ten years ago; today this kind of insulators is considered as an attractive solution to solve problems of flashovers in highly polluted areas. Recently a trial installation started on HVDC Terna's lines. The first tests performed on an insulator string sampled after more than 2 years have shown that RTV pre-coated insulators seem to be a valid alternative to ceramic insulators in highly polluted environment even if further investigations are needed in order to better understand their behavior under DC stress.