Comparison of leakage current and aging of silicone rubbers and porcelain in both field and salt-fog tests

Silicone rubbers and porcelain intended for outdoor insulation were tested under electric fields at AC 60 V/mm on average for about two years at the field test site at Chubu University. Leakage currents on all materials were characterized and separated into three categories: sinusoidal, local arc, and their transition components. The porcelain allowed a larger leakage current than the silicone rubber samples, for which the cumulative charge of ca. 160 C was recorded in about two years. The cumulative charge of the silicone rubbers was less than 12 C; the cumulative charge of the local arc component, which was likely to be related to surface damage, was less than 3 C. Gas chromatography-mass spectroscopy indicated that the chemical structure change at the silicone rubber surface layer closely resembled that of de-energized surfaces. The dominant aging factor of the silicone rubber in this field test was not electrical stress, but weathering stress such as that resulting from UV radiation. We also performed salt-fog tests of which conditions were adjusted by incorporating non-soluble deposits (kaolin powder) and by changing the salt-fog input duration. The ranking in the salt-fog test was opposite that of the field test. The salt-fog test emphasized the superiority of SIRs to porcelain when compared with the field test. The difference between artificial salt-fog and natural rainfall probably caused such differences