Partial discharge characteristics and classification in oil-paper insulation under DC voltage

Abstract

DC withstand voltage test is essential for examining the insulation condition of converter transformers. But it's hard to identify the partial discharge under DC voltage since there's no phase information as under AC voltage. The acceptance criteria of the routine test is that discharge number which exceeds 2000pC is less than 30 during last 30 minutes and 10 during last 10 minutes according to standard. This paper aims to study partial discharge characteristics and classify them to establish a fingerprint library of different oil-paper models. The basic parameters of DC partial discharge are discharge quantities q and time interval At between two discharges. The 2-dimensional image is obtained by mathematical processing based on these two parameters. The characteristics of different oil-paper insulation models are distinctive, which makes it possible to recognize the partial discharge caused by themselves or interference. Some statistical operators are discussed and compared in order to select specific ones which can distinguish signals from different models. Furthermore, the fingerprint library of these typical models is established. With this result, we can effectively diagnose DC partial discharge in oil-paper insulation.