Fundamental and low frequency harmonic components of leakage current as a diagnostic tool to study aging of RTV and HTV silicone rubber in salt-fog

The paper presents the results of using the fundamental and the low frequency harmonic components of leakage current to study aging of silicone rubber in salt-fog. Experiments have been conducted on RTV and HTV coated rods at different fields (0.25-0.6 kV/cm) and conductivities (1000 to 2500 /spl mu/S/cm). The onset of dry-band arcing on samples could be determined by measuring the low frequency harmonic components. A correlation has been found between the fundamental and low harmonic components of leakage current and different forms of aging. Where erosion could be associated with an increase in the level of both the fundamental and low frequency harmonic components of leakage current. For example, surface damage for HTV rods occurred when the fundamental component of leakage current was greater than 2 mA. On the other hand, when the samples approached failure, the fundamental component of leakage current reached relatively high values ( > 6 mA for HTV rods and > 2 mA for RTV rods) and the low frequency harmonic components of the leakage current tended to decrease. The results suggest that both the fundamental and low frequency harmonics of leakage current can be used as a tool to determine both the beginning of aging and end of life of silicone rubber in salt-fog.