Influence of ultraviolet radiation on insulation properties of silicone rubber for cable accessories and mechanism analysis

UV ray is an unavoidable environmental factor in the operation of outdoor cable accessories, which is easy to cause the cable accessories flashover and breakdown faults. In this paper, the changes of insulation properties of silicone rubber (SiR) after UV radiation treatment were studied from the aspects of microstructure, dielectric properties, surface properties and discharge properties. Combined with the analysis of molecular chain damage and surface trap, the influence mechanism of UV radiation on the insulation properties of SiR was revealed. The experimental results show that the dielectric constant of SiR after UV radiation treatment first decreases and then increases, it decreases to 3.06 at 240 h and increases to 3.93 at 1000 h. UV radiation can reduce the surface resistance of SiR, it decreases by 48% after 1000 h radiation. With the extension of UV radiation time, the surface trap level corresponding to the peak of the trap density is about 0.95 eV, the trap density decreases to 2.32 x 1022 eV-1 m-3 at 240 h. Short-term UV radiation can promote the secondary cross-linking of SiR, resulting in the increase of flashover voltage from 6.32 to 7.64 kV. Long-term radiation can destroy the molecular chain structure, resulting in a slight decrease in the flashover voltage. With the extension of UV radiation time, the breakdown strength decreases by about 14% at 1000 h. This work has guiding significance for the radiation performance and life evaluation of cable accessories.