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Influence of Location of Pressboard Barrier on the Development of Electrical Discharges in Synthetic Esters and Mineral Oil at Negative LIV

This article presents the results of an investigation to study the influence of the location of a pressboard barrier on electrical discharge development in synthetic esters and mineral oil under negative lightning impulse voltage (LIV). The measurements were conducted using as a base configuration a point-to-sphere electrode system at a distance of 25 mm oil gap. A 5 mm thick pressboard barrier was considered in the studies and the light emission detection was applied as the main experimental technique. Additionally, the studies were completed by an analysis of electrical field distribution using finite element method (FEM). The results showed that pressboard similarly for synthetic esters and mineral oil prevents against the appearance of breakdown within the considered range of testing voltage changed from 90 to 180 kV. This conclusion concerns all the pressboard locations taken into account in the studies. It is because the differences in the electrical field distributions are small both from the point of view of liquids used and location of the insulating barrier. Concerning the light emission, the studies confirmed previously made observations that in mineral oil the discharges develop with lower intensity of emitted light than in the case of synthetic esters.