Study on the Dynamic Evolution of Bubbles in Oil/Pressboard Insulation

Abstract

Power transformer may generate bubbles in the transformer oil due to various factors such as internal insulation winding vibration and pressure change. Bubbles distort the spatial electric field, which makes the discharge breakdown along the gas channel, accelerate the discharge breakdown of insulating medium. Therefore, in order to prevent the arc discharge induced by micro bubbles inside the transformer from increasing the risk of transformer combustion damage, it is necessary to conduct in-depth research on the dynamic law of suspended bubbles before insulation breakdown from the source by combining experiments and simulations. In this paper, the bubble dynamic model of needle plate electrode under the multi coupling physical field of transformer is established in terms of the migration and deformation of suspended bubbles in liquid phase. By comparing the migration trajectories of single suspended bubbles obtained from experiments and simulations, the reliability of the model is verified. The variation of velocity component of voltage amplitude and the change of shape stretching of single suspended bubble in power frequency period are simulated, and the fluctuation law of pressure formed by electrostriction force inside and outside the bubble during migration is analyzed. The capacity absorption process of multi bubbles in the strong field region near the needle electrode was simulated. The changes of the surrounding liquid pressure and the spatial electric field distribution during the formation of the gas channel were analyzed, and the internal relationship between the gas channel and the formation of the discharge breakdown was revealed.