Field experience and laboratory investigation of glass insulators having a factory-applied silicone rubber coating

This paper presents the results of studies carried out on RTV rubber pre-coated toughened glass insulators intended for use in polluted conditions. RTV pre-coated toughened glass insulators have been developed which are coated during manufacture to produce a highly adherent and uniform layer of hydrophobic RTV silicone rubber on the dielectric, vastly improving the lifetime and effectiveness of such a coating when compared to past practice of application of coatings on site or in-situ. Over the last 10 years a test program has been implemented with periodical sampling of RTV precoated insulator strings in service in difficult environmental conditions. The reported returns from the field highlight that the RTV pre-coated insulators are an excellent solution to solve very severe contamination flashovers. This behavior should be predicted by suitable procedures for laboratory testing of such insulators with a hydrophobic coating and the proposed Rapid Flashover test method is presented. Laboratory pollution tests showed a remarkable improvement in the pollution withstand performance of RTV pre-coated glass insulators, compared to their traditional counterparts.