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

Abstract

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. In these lines, corona discharge even occurs on well-designed hardware and insulators, which can inject charge into the insulator surface. The existence of surface charge has a marked effect on insulation degradation and plays an important role during the development of the surface flashover. Direct-fluorination is a method to change the chemical component, which could induce the corresponding changes in electrical properties of the surface layer, thus influencing the charge injection. This paper tries to study the effect of fluorination time on surface charge accumulation and decay of room temperature vulcanized (RTV) SiR. The samples were fluorinated in a laboratory vessel at 298 K (25°C) using a F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture with 12% F2 by volume at 0.05 MPa (500 mbar) for 5, 10, 15, and 20 minutes. The sample surface chemical composition was analyzed by means of ATR-IR. The behavior of surface potential under dc voltage was recorded at room temperature with a relative humidity of ~40%. Obtained results show a dependence of the surface potential and the dissipation time upon the fluorination time, varying with the charging time. It is suggested that the direct fluorination can significantly suppress the accumulation and accelerate the decay of the surface charge.