Water drop corona effects on full-scale 500 kV non-ceramic insulators

It is shown that certain regions of commercially available 500 kV non-ceram ic insulators have surface electric fields that are above the threshold for water drop corona. Observations made in a full scale accelerated aging cha mber, and in service, demonstrate that water drop corona occurs on such ins ulators. A correlation between the magnitude of the surface electric fields and the condition of the silicone rubber non-ceramic insulator surfaces du e to water drop corona is illustrated for two different insulator types in an accelerated aging chamber. Other examples of degradation of non-ceramic insulators due to water drop corona are illustrated.