Analysis of partial discharge phenomena in paper-oil insulation systems as a basis for risk assessment evaluation

Partial discharge (pd)-based risk assessment in electrical insulation systems becomes effective only if the nature of the defect generating pd can be ascertained. In oil/paper insulation systems this is a fundamental item since e.g. harmfulness of pd generated by gas bubbles is much smaller than that of pd occurring between paper layers. For such reasons, partial discharge analysis of oil/paper insulated systems often lacks a clear correlation between cause (i.e., defect type) and effect (partial discharge recording). Results relevant to partial discharge measurements performed on lab-scale objects having different electrode configuration are presented in the paper with the purpose to spotlight characteristic features aimed at identifying the basic nature of partial discharge-generating defects in oil/paper insulated systems.