Simulation Study on Dynamic Characteristics of Bubbles in Transformer Oil under Extremely Nonuniform Field

Abstract

Bubbles in transformer oil seriously threaten the deterioration of internal insulation performance during its movement, leading to severe transformer failure. A gas-liquid two-phase flow simulation model is established based on the phase field method to study the effect of bubbles on the insulation performance of transformer oil. The dynamic characteristics of bubbles in transformer oil under extremely non-uniform electric fields are studied. The results show that the electric field force has a pushing effect on the bubble. As the voltage increases, the pushing effect is more significant, and the displacement distance of the bubble in the horizontal direction is larger. The velocity curve of a single bubble in the vertical direction shows an oscillating attenuation trend. The pushing effect of electric field force on the bubble causes the bubble velocity near the needle electrode to decrease, but the stretching effect increases the average bubble velocity. When the electric field strength is further improved due to the enhanced push-off impact of the electric field force on the bubbles, the bubbles will gather under the needle electrode to form cluster bubbles, further reducing the insulation performance of the transformer oil. This needs to be paid attention to in the design of the insulation structure to avoid the accumulation of bubbles caused by too high an electric field intensity at a particular place.