Comparison of the first negative corona current pulses in N2 + SF6 and CO2 + SF6 mixtures

The current waveforms of the first negative corona pulses in a small point-to-plane gap have been measured with a nanosecond time resolution in N₂ + SF₆ and CO₂ + SF₆ mixtures at a pressure 50 kPa for various contents of SF₆ as a function of applied gap voltages. The physical mechanism for the pulses in these mixtures with low concentration of SF₆ has been described using the streamer-based theory. The influence of changing admixtures of SF₆ in N₂ and CO₂ has been compared. Differences in the pulse waveforms observed in N₂- and CO₂-based gas mixtures are explained by differences in the first and second Townsend ionization coefficients. This work was supported by the Grant Agency VEGA from the Ministry of Education of Slovak Republic under contracts 1/1011/04 and 1/2017/05.