THE COLD-FOG TEST

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.