Electrical breakdown voltage of transformer oil with gas bubbles

Electrical breakdown strength of liquid–gas micro bubble mixtures of transformer oil with sulfur hexafluoride and air for the case of quasi homogeneous gas inclusions distribution and $10\%$ volumetric gas content was experimentally investigated. DC voltage up to $140$ kV was applied to a $8$ mm gap between hemispherical electrodes. It is shown that transformer oil bubbled with air leads to threshold breakdown voltage decrease by $34\%$ and $19\%$ when bubbled with sulfur hexafluoride. The stabilization effect of sulfur hexafluoride micro bubbles on the value of threshold breakdown voltage is observed.