A bubble is a typical insulation defect in transformer oil

which can easily initiate partial discharge. To clarify the bubble dynamics and the effect on the electric field

a gas-liquid two-phase flow model was established based on the finite element method

and the effects of oil flow rate on the trajectory and deformation of bubbles in horizontal and vertical oil ducts were studied by simulation. The results show that the bubble shape periodically pulsates at a frequency of 100 Hz in the power-frequency electric field. In the horizontal oil duct

the deformation of bubbles in the vertical direction increases with the increase of oil flow rate

whereas the electric field distortion decreases. In the vertical oil duct

the deformation of bubbles in the horizontal direction decreases with the increase of oil flow rate

whereas the electric field distortion increases. To verify the simulation model

an oil circulation device with a horizontal oil duct and a bubble motion observation system were set up. The motion and deformation images of bubbles in the horizontal oil duct were captured

showing that the bubble shape also periodically pulsated at a frequency of 100 Hz. The deformation rates of the bubbles at different oil flow rates were extracted

which are in good agreement with the simulation results.