Porcelain Insulators have been mainly used in Korea. Polymer Insulators have been used since 1999, started with pilot, and expanded in 2010. However, 765kV V-string Polymer insulators broke down twice in 2010 and 2012. After two failures, We have limited the use of polymer insulators. In general, the failure modes of polymer insulators are categorized as brittle fracture, flashunder, discharge of rod by discharge activity, mechanical failure due to end fitting pullout or mechanical failure of the rod [1 ]-[2] and flashover due to contamination. The main reason for failure of polymer insulators is exposure of the fiberglass rod to moisture. This may occur either through the rubber weather shed or the end fitting seal. In this work, several tests such as visual inspection, hydrophobicity test, contamination test, UV inspection were conducted to find out the main cause of polymer insulator failures on UHV(765kV) in 2012.
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