Barrier effect on breakdown of point-plane oil gaps under alternating current voltage

This study deals with the influence of insulating barriers on AC dielectric strength of transformer oil in point-plane electrode configuration. The influence of the characteristics of barrier such as its position with regard to the point electrode, its thickness and dimension as well as its constituting material is investigated. It is shown that the insertion of barrier near the point electrode generally leads to the increase of breakdown voltage; this later also increases with the dimensions of barrier. The optimal position of barrier is at about 20% of gap starting from the sharp electrode (i.e. the point). The barrier acts as a geometrical obstacle against the direct propagation of discharge. There is an equivalency between distances of systems with barrier and without barrier.