The partial discharge occurring in the weak part of the insulation of a converter transformer results in the formation of a large number of bubbles in the insulating oil. The migration

deformation

and other dynamic behaviors of bubbles in the region of a strong electric field can cause them to easily accumulate into “small bridges” of impurities that can lead to breakdown of the oil gap. The authors of this study experimentally investigate and discuss the mechanisms of migration and deformation of bubbles in oil during partial discharge under composite AC/DC voltage to clarify their dynamic behaviors. The influence of the initial position of the bubbles on their trajectory of migration and velocity as well as the morphological changes occurring in them are analyzed using numerical simulations. The results show that the bubbles move away from the strong electric field due to the action of the dielectrophoretic force. The interface of the bubbles is longitudinally stretched under the action of the electrostrictive force and the vertical component of the drag force and gradually recovers to assume a spherical shape under the influence of surface tension and the horizontal component of the drag force.