Arc instability and current chopping in an air-blast interrupter

The performance of a single gas-blast interrupter, when switching low amplitude inductive currents, has been examined in detail. The effect of local circuit-component variation has been studied, and the factors which dominate the arc-instability condition established. It has been shown that circuit voltage and rate of change of current are of less significance than instantaneous current in determining the point of arc instability, though they can influence arc-restriking performance during the current chopping period. Where the dominant capacitance is separated from the interrupter by some inductance, both instability and chopped-current levels are increased. The nature of the arc-instability oscillation has been studied and related to earlier work. A new technique for predicting instability and hence estimating chopped current level for different circuit arrangements based on a single series of tests is proposed. This, when coupled with a frequency impedance characteristic for the connected circuit, would enable more precise prediction of current chopping levels in a given system application.