Dielectric Recovery and Predicted AC Performance of Blown SF6 ARCS

The rates of recovery of dielectric strength of gasblasted SF6 arc channels following current interruption have been measured by using the free recovery method. The experiments were performed with upstream arc chamber pressures of 35 psia and 60 psia, with a 1 cm electrode spacing, and 400 μs duration square current pulses whose amplitude was varied between 20 A and 1000 A. These arc chamber pressures were sufficient to ensure that critical pressure and sonic velocity occurred near the nozzle throat. An empirical linearization of the recovery characteristics has enabled these dc results to be translated into terms of ac circuits. This has enabled a prediction of ac interruption capability to be determined, assuming that the arc power input does not approach the energy clogging regime.