Leakage current and flashover of field-aged polymeric insulators

In this paper results from leakage current (LC) measurements under steam fo g and voltage withstand tests under rain conditions obtained on various fie ld aged polymeric insulators are reported. Included in this work are severa l silicone rubber (SIR) and ehtylene propylene diene monomer (EPDM) rubber insulators of ac and de design that have been energized at suitably high ac and dc voltages under coastal conditions for a period of more than nine ye ars. Their performances are compared to two sets of identical insulators, n amely one that was outdoors exposed without being energized and one that wa s stored indoors. The LC of each insulator was studied three times, namely as received from the field, after it was gently washed to remove soluble po llution, and finally after a voltage withstand test. In between the measure ments the insulators were left to recover for a period of a week. The resul ts show that the LC of the SIR insulators were generally lower than those o f the EPDM. In both cases, the LC of the insulators that were stored indoor s were significantly lower than those of the outdoor exposed insulators. Th e voltage withstand tests revealed an almost linear relation between the fl ashover voltage (FOV) and the arcing distance of the insulators. In general , for similar SIR and EPDM insulators the FOV of the SIR ones were higher t han those of EPDM insulators.