Numerical Modeling of the DC Breakdown of a Sphere Gap due to a Weakly Nonuniform Electric Field

Understanding the breakdown (BD) characteristics of air gaps in different electrode systems is essential for insulation coordination. Modeling of the BD mechanism using drift-diffusion equations is proposed as an alternative to expensive and time-consuming experimental procedures to determine the BD strength. The 2D model of sphere gap (SG) with a diameter of 100 mm is modeled in COMSOL Multiphysics, and the plasma hydrodynamic equations are solved for different gap spacings. The formation of electron avalanches and transition of the avalanche to the streamer are analyzed. The variation in electron density from the initial avalanche to the final streamer and the variation in the electric field due to space charges are also discussed. The predicted breakdown voltages (BDV s) are validated using experimental results.