Numerical Investigation of Microbubble Effects on Streamer Branching and Propagation

Understanding pre-breakdown phenomena in natural ester insulating oil is crucial for ensuring the safe operation of electrical insulation systems. Meanwhile, Air bubbles may occur as a typical defect in power transformer oil under the effect of thermal stress or the local electrical field. These bubbles are subject to exposure to a high electric field, and this will in turn influence the pre-breakdown phenomena. To evaluate the impact of bubble on streamer propagation, based on electro-hydrodynamic model, a numerical model of natural ester insulating oil with air bubbles is constructed by introducing plasma chemical reaction into the model. The model takes into account the ionization process of gas molecules inside bubbles, laying the foundation for studying bubble-triggered streamer discharges. In addition, Finite element method was used to simulate the streamer discharge in natural ester insulating oil containing bubbles, and the influence of bubble size on the streamer branching behavior was analyzed. Simulating results show that the streamer propagation is dependent on the bubble size, especially the interface contact position between the bubble and the natural ester insulating oil.