Inhomogeneous field breakdown in GIS-the prediction of breakdown probabilities and voltages. III. Discharge development in SF6 and computer model of breakdown

For pt.II see ibid., vol.3, no.3, p.931-8 (1988). Extensive investigations into various phases of discharge development in SF₆ (corona formation, streamer to leader transmission, leader, and propagation) are summarized, with the goal of familiarizing the engineer with the theoretical and empirical basis of a quantitative model 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. The model does not cover negative polarity waveforms and becomes increasingly inaccurate as the waveform risetime increases over about 10 μs. Future research planned to address both of these limitations and practical applications are outline