Leakage resistance of suspension porcelain insulators in coastal fog conditions

The leakage resistance of transmission line insulators suspended along a coast decreases with the accumulation of sea salt due to sea winds, particularly when the relative humidity is higher and the shed surface is slightly wet with fog, rain or wet snow. A test insulator string was installed on the roof of the college building in Otanoshike, on the coast of the Pacific Ocean, in September 1993 to measure real-time leakage resistance characteristics of a string of 3 standard suspension porcelain insulator units, automatically subjected, depending on the coastal weather conditions, to 2000 V DC voltage from a leakage resistance data acquisition system included in a personal computer. Leakage resistance was significantly affected by fog density and the accumulation of sea salt contaminants before fog arrival. The lowest recorded leakage resistance value, 7.5/spl times/10/sup 5/ /spl Omega/ was measured when the shed surface was slightly wet while fog was becoming dense on April 26, 1996, when the fog caused an airplane crash at an airport near the college.