Numerical Simulation of Long Air Gap Needle-to-Needle Streamer Discharge Characteristics and Cathode Pre-ionization Phenomenon

The study of streamer discharges in long air gaps under needle-to-needle electrode configurations is of significance for partial discharge suppression in power equipment. A numerical analysis model for streamer discharge in long air gaps under a needle-to-needle configuration is established based on the coupled drift-diffusion fluid equations and Poisson's equation. The model incorporates electron collision, recombination/attachment, dissociative quenching reactions, attachment processes, and photoionization. The propagation velocity of streamers, as well as the distributions of electric field and electron density under the needle-to-needle electrodes, are analyzed and compared with those in a needle-to-plane configuration. Furthermore, the cathode-side pre-ionization phenomenon and the charge distribution characteristics of particle clouds in the needle-to-needle structure are investigated. The influence of the pre-ionization region on streamer propagation speed is analyzed. Results indicate that, compared to the needle-to-plane configuration, the needle-to-needle configuration exhibits a cathode-side pre-ionization region caused by local charge accumulation in the particle cloud, which can reduce the streamer propagation speed by up to 4.5%.