Barrier diameter effect on the behaviour of transformer oil submitted to AC voltage

Dielectric interfaces can have a significant effect on the insulating performances of HV apparatus. The oil/solid interface represents a relatively weak component of an insulation system in power transformer. Therefore, when we are considering the effect of oil breakdown in oil filled transformer, we should consider the interactions which electrical discharges may have with solid surfaces. This work is devoted to the influence of insulating barrier on the behaviour of transformer oil under ac voltage in point-plane electrode configuration. The influence of the characteristics of barrier such as its position between electrodes, and its diameter on the pre-breakdown and breakdown phenomena is investigated. It is shown that the insertion of barrier near the point electrode increases the breakdown voltage and leads to decrease the pre-breakdown charge. The increase of breakdown voltage is due to the channel elongation of the disruptive charge. By determination of the pre-breakdown charge and breakdown voltage, we can estimate the optimal position of the barrier. The barrier diameter influences the breakdown voltage, the pre-breakdown charge and the trajectory of discharge.