Dielectric withstand of multi barrier arrangements in air subject to a lightning impulse voltage pulse

Summary form only given. Dielectric barriers are frequently used to improve the dielectric insulation in both oil-based and air-based power transformers. The present work focuses on multi barrier concepts where the air in an electrode gap is interrupted by one or more barriers. The electrode setup constitutes an alumina electrode plug with a diameter of 7 mm at live potential and a grounded plate electrode separated by an electrode gap in the range of 80-200 mm. A lightning impulse voltage pulse (1.2 μs / 50 μs) is applied using an up-down method and the voltage level corresponding to a 50% probability of breakdown is derived. Two types of breakdowns are considered; flashover and puncture. Whereas the former is virtually non-destructive, the latter creates a hole in the barrier(s), thus reducing the shortest propagation path between the live electrode and the grounded plate. Both positive and negative polarity of the applied potential are considered. We show how the breakdown voltage increases with an increased number of barriers and an increased length of the propagation path. The role of the polarity is discussed and data of the time to breakdown for the various barrier topologies are presented.