Characteristics of partial discharge in the oil gap separated by pressboard barrier in oil/pressboard composite insulation system

This paper deals with the characteristics of partial discharge in oil/pressboard composite insulation system, which is adopted in oil-immersed power transformer. In the insulating structure of the transformer, large oil gaps are often subdivided by pressboard barriers into small ones. Once partial discharge occurs at the point where the electric field is enhanced and progresses, the electric field distribution may change from the static one. As a result, there are possibilities that partial discharge successively occurs at the oil gap across pressboard barrier, which might be the trigger of breakdown of the apparatus. In this study, the authors experimentally observed the partial discharge generation across the pressboard barrier in an element model and examined the mechanism of the above phenomenon.