Abstract
Outdoor HV polymer insulating materials could be aged by acid rain so that the insulator surface becomes rough, and hydrophobicity changes. The tracking and discharge may then occur, leading to insulation breakdown or flashover. In this paper, the relation of hydrophobicity and surface roughness of hlgh temperature vulcanizing silicone rubber (HTV SR) insulator aged in artificial acid rain is investigated. The experimental phenomena of variation, degradation and recovery of hydropbobicity of silicone rubber insulator before and after aging are discussed from a fractal theoretical point of view, The rough surface of whether a virgin or aged insulator presents the appearance of a fractal surface. Research results show that due to fractal phenomenon, the hydrophobicity of the moderately roughened virgin sample may increase with the surface roughness. After aging in acid rain, the insulator surface becomes rougher, and the hydrophobic groups in surface layer are wom away. The fractal surface of the aged insulator for lack of hydrophobic materials may become hydrophilic so that surface hydrophobicity degrades. In the following dry condition, the hydrophobic polymer liquid bulk diffuses and migrates to surface layer. The fractal surface of the aged insulator with the supplement of hydrophoblc polymer liquid may become more hydrophobic. The degraded hydrophobicity is therefore restored to some extent.This research shows that the outstanding performances of silicone rubber insulator are available to outdoor application in severe environmental stress.
