Study of surface degradation of HTV silicone rubber under thermal and ultraviolet exposures

Polymeric insulators are widely used in electrical power system in particular transmission and distribution lines. Silicon rubber is a high performance polymeric material with superior insulation property and physical properties such as light weight. This paper presents the effects of ultra violet radiation and heat on the aging of silicon rubber and estimates the lifetime of insulators made of this material based on chemical bounds percentage at different exposure times. Experimental works were performed on samples collected from a 22KV silicone rubber insulator. The specimens were subjected to accelerated aging cycles using an Accelerated Weathering Tester (QUV) at 50°C and UVA exposure of 340nm at the irradiation intensity of 0.68W/m² for up to 3000 hours. A series of tests were conducted on the samples using instruments that measure different aspects of aging. The degradation was examined using a Scanning Electron Microscope (SEM) and a Fourier Transforms Infrared Spectroscopy (ATR-FTIR). In addition, the color change of the specimens was measured by CHROMA Meter (CR-300). In this paper, we show that the remaining service life of the insulators can be estimated using the chemical measurements and color factors by making comparisons between new, aged and totally damaged specimens. The 3D scatterplot for the obtained data show a clear trend and timeline on how a new specimen degrades over time and eventually leads to complete failure. This information provided by the 3D scatterplot could be used to estimate the remaining life of silicone rubber insulators.