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Abstruct -T h e electrical performance of outdoor insulation degrades severely d u r i n g coinbinations of factors t h a t include surface containination (C), ice (I), fog (F) a n d a n ambient t e m p e r a t u r e t h a t rises tlirougli 0 O C (Too ). 'Failures at operating voltage on llG-kV, 230-kV a n d GOO-BV systcnis occur with increasing probilbili ty u n d c r these conditions. A new CFToo or 'cold-fog' test nictliod has been developed to reproduce t h e flasliovers at a11 three voltage levels. T h r e e options are idrntificd for improving C F T~O performance: use of somi-conductive glazes, substitution of silicone for porcelain a n d use of silicoiie coatings o n existing porcelain insulators.

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