Electrical performance of RTV silicone rubber coatings after exposure to an acidic environment

Room Temperature Vulcanizing Silicone Rubber (RTV SR) coatings are used for improving the contamination performance of ceramic insulators, especially in substations. Recently, some concern has been expressed regarding the electrical performance of RTV SR coatings under acid rain conditions. In the present study, four different formulations of RTV SR coatings were applied to porcelain slabs. The coated slabs were subjected to three types of acids, namely nitric, sulfuric and oxalic, with pH=2 and pH=4, for different durations up to 1 week. Tracking and erosion tests were performed using a modified version of the ASTM D-2303 Inclined Plane Test. The contamination withstand capability of 34.5 kV RTV coated post insulators was determined using the clean fog test procedure, before and after acid exposure. Bare porcelain was used for obtaining reference data. A slight reduction of the hydrophobicity was observed for the RTV SR coatings exposed to acids. Their tracking and erosion resistance was not compromised. In addition, the contamination withstand capability imparted by the coatings to the bare porcelain surface, was reduced due to acid exposure, but, the values were still higher than those obtained with bare porcelain.