An experimental investigation on the degradation characteristic of the outdoor silicone rubber insulator due to sulfate and nitrate ions

Since 1960, polymer insulator has been employed as an outdoor insulator for high voltage ascribed to its excellent aging characteristics compared to those of ceramic insulator. However, in spite of various investigations related to the polymer insulator, its aging mechanism due to acid rain have not been well elucidated. In this paper, aging characteristics of outdoor silicone rubber insulator resulting from the acid rain have been investigated with regards to sulfuric and nitric solutions. For this purpose, silicone rubber was aged by being immersed in the sulfuric and nitric solutions with different level of pH (5.6, 4.0, 2.5, 1.5) during 1500 hours and various tests were performed such as tracking, contact angle, tanδ, breakdown voltage, SEM, EDS, FT-IR. Regarding the effect of the acidity of nitric solution, the surface of test samples were slightly damaged up to pH 2.5 and ruined at pH 1.5. However, in case of sulfuric solution, the degree of the surface degradation was observed to be consistently increased. And thus, for the former, it could be expected that there is certain critical value between pH 1.5 and pH 2.5, which likely could induce serious surface degradation For both cases, it was observed that the hydrophobicity and tracking resistance of the silicone rubber insulator are well retained regardless of the acidity of the solution