Flashover mechanism of non-ceramic insulators

The contamination performance of non ceramic (NC) insulators is better than porcelain insulators. The paper describes the pollution collection mechani sm and concludes that silicone rubber insulators collect more pollution tha n porcelain insulators. Long term exposure of silicone rubber insulators pr oduces a thin layer of pollution, which is a mixture of dust, salt and sili cone oil. Fog or morning dew produces droplets on the flat surfaces and for ms conductive regions. Spot discharge starts between the regions, which red uces hydrophobicity. Simultaneously, dry-band arcing starts on the shank of the insulator. The two arcs join together, which leads to flashover. The f lashover voltage of polluted NC insulators is significantly higher than por celain ones. Insulator performance is measured with laboratory tests. Howev er, salt-fog and clean-fog tests can give different flashover values.