An experimental approach to the estimation of the long term corona performance of non-ceramic insulator housings

This paper presents the results from a study on the synergistic effects of corona, humidity and mechanical stresses on the degradation of non-ceramic insulator (NCI) housing materials. Three different polymer formulations, namely silicone rubber (SIR), ethylene propylene diene monomer (EPDM) and a mixture of both were evaluated in a test cell and the surface changes resulting from degradation were monitored. Under the experimental conditions adopted in this study, varying degrees of polymer degradation were observed for each material group. A strong influence of humidity on the development of degradation processes was identified. By computing cumulative charge magnitudes up to the time when surface cracking was detected, a simplistic correlation with expected field operating conditions seems to indicate that even under severe circumstances (corona continuously impinging at the same site) degradation similar to that observed in this unlikely to occur for field exposure times amounting to many years.