Discharge Characteristics with Impulse Voltage Application in Ester Oil/Pressboard Composite

Partial discharge characteristics as well as breakdown phenomena in a power transformer insulation, i.e. oil and paper insulation, has to be clarified for miniaturization of the apparatus. In recent years, environmental-friendly transformers using ester oil, which shows excellent biodegradability, receive much attention due to the worldwide growing environmental awareness. Considering this, researches on fundamental characteristics of discharge phenomena within the ester oil are required. Although various papers on discharge characteristics in the ester oil have been published by many researchers, there are still few reports on these researches using ester oil and pressboard (PB) composite insulation system. In this paper, the discharge inception field and starting point in the ester oil and PB composite insulation configuration are investigated and the results are compared with those in the mineral oil to discuss the detailed discharge mechanisms.