Bubble Migration and Accumulation in Oil-paper Insulation: Interfacial Forces Modeling

Bubbles in oil-paper insulation migrate and may finally accumulate, posing enormous insulation risks. Accurate simulation of bubble migration and accumulation is of vital importance. The cross-scale nature of micrometer-millimeter bubble movement in meter-scale oil-paper insulation structures makes macroscopic simulation methods often ignore the microscopic details of bubbles, which makes calculation accuracy hard to guarantee. In this study, bubble dynamics in oil-paper insulation were analyzed by the Euler-Lagrange approach, in which the distributed interaction on the bubble interface was simplified to lumped interfacial forces. The lumped bubble-oil drag force and bubble-paper friction were standardized measured, and effectively modeled combining the microscopic behaviors of bubbles. The accuracy of the Euler-Lagrange method with modeled interfacial forces was finally verified by experiment. Results showed that the deformation of a steady-rising bubble in oil intensified as bubble size increased, which had an enhanced effect on the drag force. The bubble-paper contact state and paper friction were affected by bubble-paper contact pressure and bubble motion inertia. The bubble slid in close contact with the paper when contact pressure dominated while slid without contact when bubble inertia dominated. Both the drag force and paper friction were effectively modeled considering these bubble microscopic behaviors. The agreement between simulation results and experimental results of bubble trajectories and accumulation behaviors in a horizontal oil channel was satisfactory, verifying the accuracy of the simulation method with modeled interfacial forces. This method can be further coupled with multi-field simulation realizing the precise bubble distribution analysis in oil-immersed power equipment.