Study on the Process and Transition Mechanism of Different Stages in Positive and Negative Corona

Corona discharge, as a partial self-sustaining discharge phenomenon under extremely uneven electric field, has been widely concerned in dc transmission projects. However, the research on the transition mechanism of corona discharge at different stages is not in-depth at present, which leads to the inadequacy of the basic development theory of corona discharge. This article focuses on the research of direct current corona discharge in air and establishes a numerical simulation model of corona discharge fluid plasma in air. The simulation model focuses on the needle-plate discharge model, with an environmental temperature set at 293.15 K and pressure at 101.325 kPa. The curvature radius of the needle electrode is 60 $\mu$ m, and the discharge gap is set to 4.5 mm for positive corona and 5 mm for negative corona. The simulation covers the transition of positive corona discharge from the initial discharge stage, through the initial glow discharge stage, ultimately reaching the glow discharge stage as the needle electrode voltage increases from 2 to 4 kV. Similarly, for negative corona discharge, the simulation captures the evolution from the initial discharge stage to the Trichel pulse discharge stage and finally to the no-pulse discharge stage as the needle electrode voltage changes from $-$ 2 to $-$ 4.2 kV. This article also analyzes the transition mechanism between different stages in positive and negative corona processes. The transition of negative corona at different stages is a process where the nominal electric field and spatial charge electric field mutually constrain each other and reach equilibrium with the participation of secondary electrons. The transition of positive corona discharge at different stages is mainly determined by the nominal electric field and the secondary electrons produced by the collision of positive ion clusters with the needle electrode. Finally, the simulated model was validated by measuring the current and spectral signals during the discharge process in the experiments.