Numerical Model of Bubble Evolution in Oil-paper Insulation based on Bubble Dynamics

Bubbles generated from oil-immersed transformer is prone to stimulate partial discharge, causing the failure of liquid insulation. Previous studies about bubbles inception in oil-paper interface mostly used experimental methods qualitatively. But these methods are hard to simulated bubble effect in quantitative. By examining the mechanism of bubble evolution phenomenon in oil-paper interface and bubble dynamics, a numerical model of bubble evolution is established. Firstly, the bubble growth process in oil-paper interface is controlled by Rayleigh-Plesset equation, which governs the dynamics of a spherical bubble in incompressible fluid. Then the kinetic vapor flow rate and bubble internal pressure during the heating environment is controlled by Idea Gas Law and HertzKnudsen equation. Eventually, the bubble growth curve is obtained. The predicted Initial Temperature of Bubble Escape (ITBE) and the detachment radius of bubble are verified by experimental data. The results show that the ITBE decreases with higher moisture content of paper. And the aged paper increases the ITBE by enlarging the capillary pore radius in same conditions. This research could help to study the mechanism of bubbles inception in oil-paper interface.