Numerical simulation of streamer discharge considering fluctuation of carrier density caused by photoionization in natural ester insulating oil

An improved new multi-branch streamer discharge simulation model in natural ester insulating oil is established based on the theory of fluid mechanics and fractal theory to further consider the influence of the fluctuation of charge carriers caused by photoionization. COMSOL software is used to analyze and study the electric field strength, distribution characteristics of charged particles, and the pattern of the discharge in the fractal discharge process of insulating oil under lightning impulse voltage. The effects of the applied voltage amplitude, the rise time of the applied voltage, and the gap distance on the propagation of the streamer discharge are investigated. The simulation results show that under the influence of photoionization, the discharge begins to branch at the head. The propagation of the main streamer on the needle axis is faster than that of the branch streamer on both sides. With the increase of the applied voltage amplitude, the propagation speed of the streamer increases continuously, and the rate of charge generation by photoionization also increases. The main streamer channel is more likely to be affected by photoionization factors and generate obvious streamer branches on the side. The electric field intensity, positive ion density, and electron density are more concentrated at the head of the streamer, while the density of negative ions is more concentrated at the tail of the streamer. With the increase in the rise time of the applied voltage, the propagation speed of the streamer discharge in the insulating oil gap decreases continuously, and the streamer branches become denser on the side of the main discharge channel. When the oil gap distance increases, the background electric field of the oil gap decreases, the photoionization effect weakens, and the number of streamer branches also decreases relatively.