The current pulses characteristics of the negative corona discharge in SF₆/CF₄ mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF₆/CF₄ mixtures for the negative point-plane corona discharge. The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K, respectively. The CF₄ content varies from 20% to 80%. The 2D axisymmetric geometry with point-plane electrodes is investigated, and the three drift-diffusion equations are solved to predict the characteristics of the negative corona discharge. In addition, Poisson's equation is coupled with the above three continuity equations to calculate the electric field. In order to calculate the electron impact coefficients, including the Townsend ionization and attachment coefficients, as well as the mobilities and diffusion coefficients for electrons, the two-term Boltzmann equation is solved. The characteristics of three ionic species at five stages of the first current pulse in 60%SF₆-40%CF₄ and 20%SF₆-80%CF₄ mixtures are selected to discuss the development mechanism of current pulses. Moreover, the reduced electric field strengths at the corresponding time instants are presented to help understand the discharge process. The current waveform and the total number of three species are compared in all the cases to analyze the effects of the CF₄ content on the discharge. The reduced electric field strength is also helpful in understanding the effects of CF₄ content. When the CF₄ content increases to 80%, the discharge is more intensive and the pulse frequency also increases.