Dynamics of Gas-Phase Bubble Defects in Transformer Oil Ducts Under Electro-Thermo-Hydrodynamic Coupled Fields

Insulation degradation in oil-immersed power transformers is critically influenced by gas-phase bubble impurities within oil ducts. This study establishes a multiphysics-coupled model based on phase-field theory, where the relative dielectric constants of bubbles and insulating oil are defined as 1 and 2.2, respectively. The governing equations integrate the Cahn-Hilliard phase-field equation, Navier-Stokes hydrodynamic equations, and electrostatic Poisson equation. Numerical simulations under representative operating conditions (oil flow velocity: 0.3m*s-1, average electric field intensity: 2.0kV*mm-1) elucidate the dynamic processes of bubble migration, deformation, and coalescence in electro-thermo-hydrodynamic coupled fields. The results demonstrate that fluidic fields primarily govern bubble migration, while electric fields significantly modulate interfacial tension distributions, thereby driving bubble coalescence and fragmentation behaviors. The proposed theoretical framework for bubble dynamics provides critical insights into the insulation design of transformer oil ducts. Furthermore, the developed quantitative model offers a foundation for optimizing duct structures and advancing real-time monitoring systems in industrial applications.