Partial discharge testing on resin insulated voltage transformers

The lifetime of resin insulated voltage transformers (RIVT) can be considerably shortened due to partial discharge activity taking place inside the insulation close to the active parts of the component. In that region the presence of voids, due to manufacturing processes, and the enhanced electric field stress lead to an intense partial discharge activity which determines accelerated degradation processes and eventually the ultimate failure of the device. Partial discharge measurements together with an estimation of the electric field distribution in RIVT seem to be indispensable in order to fully understand transformer performances. In this paper, a study of the electric field distribution inside the RIVT, together with results of partial discharge tests are presented. The influence of the various test arrangements and methods on the experimental results are investigated.