Moisture induced local heating of overhead line composite insulators

There has been a growing concern over recent years regarding the phenomenon of local heating of composite insulators. In this paper, the influences of humidity, contamination and local electric field on the temperature and dielectric properties of field-aged insulators were studied experimentally. Aging of the silicone rubber (SIR) material on the weathershed surface, rather than resistive current flow from contamination, was found to be the major cause of local heating observed by thermography. The aged SIR material exhibited strong dielectric loss under high localized AC electric field and high relative humidity. A hypothesis was developed to mitigate the moisture induced local heating on composite insulators.