The Generation and Migration of Bubbles in Oil-Pressboard Insulation Needle-Plate System

Bubbles in transformer oil can easily lead to partial discharge (PD), which can deteriorate the transformer oil and even breakdown the transformer insulation. To clarify the migration process and the characteristics of bubbles generated in an oil-immersed power transformer exposed to an extremely uneven electric field, we experimentally monitor these phenomena under an extremely nonuniform ac electric field and numerically simulate the migration distance and the migration speed of bubbles with different initial positions and sizes. The results show that the streamer discharge channel formed by a PD in oil is gasified into a bubble channel. After it collides with the surface of the pressboard, its morphology is transformed into approximately spherical bubbles due to the surface tension of the gas–liquid interface. After bubbles are generated in the oil, they move away from areas with a strong electric field due to the electric-field force and gradually approach the oil surface due to the buoyancy force. The experimental results are consistent with the simulation results, which verify the rationality of the simulation model.