Extreme value analysis of leakage current envelope of polluted insulators

Extreme value theory (EVT) deals with extremal behavior at the tails of distributions of random variables (maxima and minima). In this paper the results of applying some basic ideas associated with EVT to the statistical analysis of the leakage current peak magnitude (envelope) are presented. The measurement and analysis of leakage current for condition-based monitoring of polluted insulators is well documented. Research has established that, insulator surface arcing causes significant variations in both the magnitude and shape of the leakage current of polluted insulators and several techniques exist for analysis. A technique is presented here which employs EVT to discriminate and characterize the largest and rarest peaks (which occur with highest severity); namely the characteristic largest value and the extreme value risk function