Inhomogeneous Field Breakdown in GIS the Prediction of Breakdown Probabilities and Voltages

Extensive investigations into various phases of discharge development in SF6 (corona formation, streamer to leader transition, leader propagation) are summarized in this paper, with the goal of familiarizing the reader with the theoretical and empirical basis of a quantitative model for SF6 breakdown, including breakdown in highly inhomogeneous fields. The quantitative predictive capability of this model is tested for a number of examples, which demonstrate the correct prediction of geometry and pressure dependencies of the breakdown voltage. Combined with the modified volume time “law”, the breakdown model becomes a valuable tool for the power engineer, capable of predicting statistical breakdown characteristics for a wide range of gap geometries and positive voltage waveforms as a function of pressure. At present, the model does not cover negative polarity waveforms and becomes increasingly inaccurate as the waveform risetime increases over about 10 μs. Future research is planned to address both of these limitations. Practical applications are outlined.