Influence of thickness, substrate type, amount of silicone fluid and solvent type on the electrical performance of RTV silicone rubber coatings

Room temperature vulcanizing (RTV) silicone rubber coating is increasingly being used by power utilities to overcome the contamination problems encountered in ceramic and glass insulators under wet conditions. The formulation of the RTV coating system is currently undergoing an intensive development in an effort to optimize its performance and in particular to extend its lifetime. While there are many forms of RTV, those used for insulator coating purposes invariably use a base of polydimethylsiloxane. The amount of RTV used in the service application is also important as it impacts on both the cost of the protection offered and on the electrical performance. This paper reports on a study of the influence of the coating thickness, different substrates, addition of silicone fluid to the coating formulation and different carrier solvents on the leakage current, pulse current count rates and the lifetime of the RTV coatings. It has been found that all these parameters affect the electrical performance under wet and contamination condition in a salt-fog. The optimum coating thickness has been determined for a fixed substrate. Mechanisms by which these four parameters affect the performance are suggested and discussed.