Ageing and degradation mechanisms of silicone polymers used for outdoor electrical insulation

Silicone is an organic material largely used in outdoor electrical insulation. Performances and results have shown to be largely depending upon chemistry and applications. It is used either in the form of silicone rubber moulded over a fiberglass core in composite insulators or as a coating over ceramic insulators in overhead line or substation applications. Corona activity has been identified in the last fifteen to twenty years as a major threat for silicone rubber, and besides the erosion pattern often visible in such cases there are other signs of degradation of the polymer. Progressively, experts have pointed out the necessity to be more stringent in the evaluation of maximum acceptable stress levels allowed on silicone housings [1]. Among the typical degradation seen on the housing…