A Comprehensive Study of Silicone Rubber Insulators with Different Creepage Distances

Composite insulators with polymeric housing have become an alternative to ceramic insulators during last four decades. Out of different composite insulators, silicone rubber (SIR) insulators have usually exhibited better performance under polluted conditions. In a previous research during 1994-1999, 33 kV SIR insulators with similar creepage distances with ceramic insulators have shown good performance under polluted and clean conditions in Sri Lanka. This paper presents the extension of that study aiming to check whether SIR insulators with shorter creepage distances (Short insulators compared to porcelain insulators) could perform well even under polluted conditions. In 2001 three sets of nine 33 kV SIR insulators with different creepages and two ceramic insulators were installed in two test sites exposed to marine and clean conditions in Sri Lanka. Their performances had been investigated in the field for more than 5 years by visual inspection and hydrophobicity evaluation. After 5 years, they were tested under laboratory conditions by leakage current, time variation of dc resistance and wet flashover measurements. In parallel, a separate set of SIR insulators were aged for 1000 hours under salt fog conditions and the leakage current was continuously monitored. It was found that the housing material influence the insulator performance rather than its creapage distance. Further there is a possibility of stressing the SIR insulators higher than ordinary ceramic insulators.