Breakdown voltage and time-to-breakdown as influenced by the steepness of the applied positive impulse

The volume-time criterion is discussed, and a modification is proposed with the aim of predicting breakdown voltages in SF/sub 6/ under positive impulse stresses without introducing an empiricism in the analysis. The electrons initiating the breakdown are those produced by cosmic rays that penetrate to the gas volume. The results obtained, including the breakdown voltage and the time-to-breakdown, as influenced by the steepness of the applied impulse, are discussed and compared with those measured experimentally.<>