Abstract:There is a small number of bubbles in the oil of oil-immersed power transformers with long-term operation. The complex electric field environment inside the equipment can change the motion state of these bubbles, which leads to the electric field distortion and ultimately causing the insulation deterioration. In this paper, an automatic bubble generation device was designed to simulate the formation of bubbles in oil, and their motion trajectories were captured using a high-speed camera. Then a gas-liquid two-phase flow model was established through the finite element simulation software in order to obtain the electric field distribution surrounding the bubbles. Finally, this study discussed the gyration phenomenon that occurs when bubbles rise from a mechanical perspective using simulation models. Furthermore, an image processing software was employed to analyze the effects of the bubble size and the electric field intensity on the motion trajectories of the bubbles in this study. Results revealed that an increase in the bubble size and the electric field intensity can alter the force acting on the bubble itself, which leads to larger deviations in its movement. Based on the simulation calculation and analysis, it can be found that the existence of the extremely inhomogeneous electric field causes variations in the electric field intensity at different regions of the bubble surface. The bubble surface was divided into different regions and simulation results were used to calculate the force acting on the regions. The results showed that the force acting on these regions were not uniform. Based on the final analysis, it can be concluded that the presence of the extremely inhomogeneous electric field led to uneven surface forces. It is the main cause for the displacement and deformation of bubbles, ultimately resulting in the multi bubble gyration. Moreover, the process causes the temporary accumulation of multiple bubbles between the two electrodes, intensifying the distortion of the electric field and resulting in a significant degradation of the insulation performance. The study can be applied to the operational condition assessment of oil-immersed power equipment with long-term operation.