Impulse breakdown of transformer oil under uniform fields

Breakdown voltage versus gap length characteristics were obtained for dehydrated transformer oil and oil containing emulsion droplets of water with fibrous impurities. In general, the breakdown voltage increases with increasing oil gap spacing between electrodes. The breakdown voltage values are higher when aluminum electrodes rather than stainless steel electrodes are used. The breakdown voltage for oil containing emulsion droplets of water by (0.2% by mass) was decreased by about 50% as compared with dehydrated oil. The breakdown voltage decreases with increasing temperature. When an insulating oil was subjected to an impulse electric field between aluminum and stainless steel electrodes, the dielectric loss increased with increasing electric field. The measured increase in the dielectric loss coincides with the visually detected onset of liquid motion