The electrical performance of outdoor insulation degrades severely dur
ing combinations of factors that include surface contamination (C), ic
e (I), fog (F) and an ambient temperature that rises through 0 degrees
C (T-0 degrees). Failures at operating voltage on 115-kV, 230-kV and
500-kV systems occur with increasing probability under these condition
s. A new CFT0 degrees or 'cold-fog' test method has been developed to
reproduce the flashovers at all three voltage levels. Three options ar
e identified for improving CFT0 degrees performance: use of semi-condu
ctive glazes, substitution of silicone for porcelain and use of silico
ne coatings on existing porcelain insulators.