Fundamental investigation of arc interruption in gas flows. Final report

Abstract

Work on the problem of early, or thermal, recovery of gas blast interrupters is reported. The objective of this work is to obtain a quantitative understanding of the physical and aerodynamic processes important for the optimization of such apparatus. In investigations of model testing techniques, recovery speed (RRRV) was found to be completely independent of power frequency over a wide range as long as nozzle blocking and metallic electrode vapor contamination effects are avoided. In investigations of nozzle and electrode geometry, a sharply defined optimal position was found for the upstream electrode with respect to the nozzle throat. Correlations were established between RRRV and features of the flow field at various electrode positions. A diffuse arc section, contributing very little to the recovery speed, was found at the downstream end of nozzles in which large divergence angles and/or low nozzle pressure ratios led to separation of the flow from the wall and associated internal shock waves. Gases and gas mixtures which have thermal recovery speeds nearly as fast as that of SF/sub 6/ were identified. Such gas mixtures, particularly those with SF/sub 6/, permit gaining an advantage over pure SF/sub 6/ by operation at higher total pressure. A simple theorymore » which indicates the relative recovery speed of gases based on explicit properties of the gas molecular structure was developed. Collectively, the new information holds promise for significant improvements in the thermal interruption speed of gas blast interrupters. « less

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