Simulation of Streamer Propagation in Ester-Based Insulating Oils Considering Electron Saturation Velocity

Ester-based insulating oils have emerged as promising alternatives to traditional transformer oils, offering environmentally sustainable benefits. Research on the discharge mechanisms in these oils is crucial for the insulation system design of ultra-high voltage, large-capacity transformers. In this study, a finite element simulation approach was used to develop a branching-streamer model that incorporates the drift-diffusion source term of electron saturation velocity. Simulation results indicate that electron saturation velocity effectively limits streamer branching to maintain second-mode propagation, thereby reflecting the dynamic variations in streamer propagation observed in experiments more accurately than existing models. Specifically, the modified model shows an increased and more uniformly distributed electric field intensity in the needle region and a relatively slower propagation speed of the primary streamer along the z-axis. Additionally, the streamer propagation pattern is significantly influenced by the curvature radius of the needle tip: a smaller curvature radius results in a higher electric field intensity and greater spatial charge generation, which increases the likelihood of field distortion at the streamer head, promoting the formation of additional branched streamers.