We investigate the bubble motion in transformer oil under a typical non-uniform electric field.Based on the principle of virtual work,an analytical equation is derived for the electric force putting on the bubbles.The bubbles visualized motion graphics are then obtained by using the finite-element method,which utilizes Comsol Multiphysics software.The effects of bubble radius and release position on the motion trajectory are studied.It is found that,under the non-uniform electric field,the bubbles have a long residence time between the electrodes.This accordingly can lead to a higher probability of forming a bubble-bridge along the bubble motion trajectory.The bubbles with a particular radius or release position are easier to form bubble-bridge between the electrodes.They can increase the chance of liquid breakdown.