Review of aging and recovery of silicone rubber insulation for outdoor use

This paper surveys the properties which give silicone rubber its distinctive and highly desirable performance characteristics for use as outdoor insulation. The methods of assessing these properties are discussed and this is followed by a detailed survey of what is known of aging and recovery mechanisms. Corona is identified as the principle electrical aging agent and evidence is presented for irreversible loss of polymer as a result of aging. However, the surface recovery mechanisms are robust and, provided there is an adequate resting period, the hydrophobic properties recover. This supports the view, from service experience, that there is no substantial evidence to show that normal aging, unless it results in the exposure of the glass fiber core, detracts from the performance of insulators.