Pre-breakdown Current in Long Point-plane Transformer Oil Gaps with Insulating Barrier under AC Voltage

In this paper we present results of carried out investigations on the influence of insulating barriers on AC pre-breakdown current of long point-plane transformer oil gaps up to 12cm. The insertion of an insulating barrier leads to an important pre-breakdown current decrease. The barrier acts as a geometrical and electrostatic obstacle for the disruptive discharge. We present in the paper a comparison between the pre-breakdown current in the system with barrier to that one without barrier. We have considered the parameters of the barrier such as its position between the electrodes, and its nature. We observe that the evolution of the pre-breakdown current versus the applied voltage has a capacitive behavior. The equivalent impedance of the oil gap is deduced from the experimental current-voltage characteristics.