Behavior Analysis of Bubble Migration under Coupling of Liquid Nitrogen Velocity and Electric Field

Composite insulation of high temperature superconducting (HTS) cable is prone to flashover caused by bubble aggregation at interface, which affects insulation performance. In order to understand the influence of bubble migration on electric field distortion in liquid nitrogen, the gas-liquid two-phase flow model was established in COMSOL. The change law of bubble shape and trajectory under the coupling effect of liquid nitrogen and electric field was studied under simulation. The change law of bubble shape under different flow rates and migration law of bubbles with different bubble radius were analyzed. The results show that the bubble shape can stretch horizontally and vertically in the process of rising and shifting, and change regularly in a certain range. With the change of flow velocity, deformation rate of bubbles increases and liquid nitrogen region in the vertical direction of bubbles is easier to be broken down. The vibration equilibrium position of bubbles with different sizes is relatively close, which means that bubbles may aggregate and lead to liquid nitrogen breakdown.