Surface charge accumulate and decay of direct-fluorinated RTV silicone rubber

Room temperature vulcanized (RTV) silicone rubber (SiR) is a kind of basic insulating material and is widely used to coat porcelain and glass high voltage insulators. In HVDC transmission lines, electric corona could take place even on well-designed hardware and insulators, which could make charge accumulate on the surface of insulators and inject into the surface. However, with the disadvantage of organic polymer, its corona-resistance property is not good enough, which makes insulation early degradation occur frequently. The existence of surface charge has a great effect on degradation characteristic and is the main reason leading to flashover. Fluorination as change the chemical component in surface layer of polymers should bring the corresponding change in electrical properties of the insulators´ surface layer thus influence the surface charge accumulation and decay. This paper focuses on the effect of fluorination time on the accumulation and decay behaviors of surface charge. Samples were fluorinated in a reaction vessel at about 298K (25 °C) using a F₂/N₂ mixture with 12% F₂ by volume and 0.05 MPa (500 mbar) for respectively 5, 10 and 15 minutes. Surface charge accumulation test were performed at room temperature with a relative humidity of ~ 40%. Obtained results show the dependence of the surface potential upon the fluorination time of samples, varying as a function of the electrode polarity. It is indicated that the surface fluorination can significantly suppress surface charge accumulation and improve the decay rate of the surface charge.