Thermal bubble breakdown in liquid nitrogen under nonuniform fields

The electrical forces acting on thermally induced bubbles in nonuniform field gaps with/without fins and the correlation between bubble behavior and dielectric characteristics in liquid nitrogen are studied. The results show that the gradient force and Maxwell stress strongly affect the bubble dynamics and bubble shape in the gap. Especially the pronounced gradient force near the fin tip reduces the growth of bubble there. These electrical forces acting on the bubble result in a lesser effect of thermal bubble on the breakdown voltage if the fins are formed to guide a bubble trapped in the groove from a higher field region to a lower one