Streamer Criterion for Designing Gas-Insulated Medium Voltage Switchgear

Size optimization of medium voltage (MV) devices, such as switchgear, requires accurate prediction of the impulse and AC power frequency breakdown voltages which is the focus of the paper. Dielectric breakdown was performed on three electrode arrangements that simulate actual switchgear for SF6 and two fluoronitrile/CO2 mixtures and the experimental data were compared with simulation result based on the streamer inception criterion. For weakly non-uniform fields, the experimental values show good agreement with those predicted using an approximation formula for the effective ionization coefficient. For strongly inhomogeneous fields, the breakdown voltage is computed based on the non-uniformity factor. A framework rule for breakdown prediction based on the streamer criterion, when applied to several switchgear electrode designs and gases, show good agreement with experimental results.