Abstract :
Outdoor insulators with a plastic external surface have now been in service for many years. They are generally constructed of three elements: an insulating mechanically strong structural core; metal end fittings bonded in some way to the core which transfer the mechanical stress between the HV conductor and adjacent earthed structural metal work; and finally an exterior weather resistant plastic covering which provides sufficient creepage distance between HV and earth to prevent pollution flashover. All of these elements either singly or together can and do fail. The author discusses the conditions which cause failures and the effects of the failures. The author then discusses the benefits of using PTFE as the weathershed in an outdoor environment. The misconceptions about the use of silicone elastomers is also discussed
