Estimation of flashover probability of aged nonceramic insulators in service

A procedure for estimating the flashover probability of aged nonceramic ins ulators in-service is presented. The study was carried out using two types of 138 kV EPDM line post insulators received from the Florida Power and Lig ht system. Presented are the laboratory characterization of the naturally c ontaminated insulators, the development of a linear regression model, and t he estimation of the statistical parameters that define the relation betwee n probability of failure and applied voltage for a given contamination leve l. The results obtained in the laboratory were in agreement with the curren t and past held experience. Conservative probabilities of flashover were es timated under the assumption of a cumulative normal distribution. The estim ators of the parameters that define the normal distribution were assessed w ith the original Up and Down method. The results suggest that for one type of EPDM insulator, contamination flashover performance was distinctly infer ior to the other.