Breakdown phenomena in transformer oil subjected to direct voltages with ripple

This paper reports the results of experimental investigations on the breakdown phenomenon of transformer oil under inhomogeneous field conditions (rod-plate electrode system) and subjected to DC voltage superimposed on AC voltage. The peak breakdown voltage of transformer oil is found to be decrease with the increasing of ripple content in the applied voltage and gap spacing between electrodes. It has been noticed also that the value of breakdown voltage is lower for positive DC voltage than negative voltage for any particular ripple content.