Numerical simulation of cathode directed streamer discharges in Air and CO₂.

Dielectric breakdown characterization in CO₂ has become as important as that of SF₆ gas in high voltage engineering. This is as a result of the urgent need for replacement of SF₆ gas due to its high GWP. The first stage of breakdown in gases is the streamer discharge which occurs when a gas is suddenly exposed to a high voltage. Modeling streamer discharges numerically is needed to predict intrinsic characteristics of gases such as SF₆ and CO₂, which further allows for an accurate comparison of their dielectric performances.

We used a plasma fluid model implementation in COMSOL^® Multiphysics to study streamer discharges in air gaps of 5 mm with a point to plane geometry. Restriction on gap length was due to long simulation times stemming from limited computational capacity. To overcome this, the plasma fluid model code, Afivo-streamer (https://gitlab.com/MD-CWI-NL/afivo-streamer) was used to study streamers in relatively longer gaps (>10 mm) in air and CO₂. We compared the two implementations and studied the influence of pressure on the discharges. This is of industrial importance especially for equipment manufacturers. We analyzed the relation between the streamer velocity and diameter with increasing pressure and compared the results with in-house experiments and earlier literature.

Index terms: Numerical Modelling, Streamer Discharges, Plasma Fluid Model