Interaction between a high-current arc and the air flow in an air-blast circuit breaker

Results are reported of experiments performed on the arc and air flow in an air-blast circuit breaker having a 19 mm-diameter profiled orifice. The arcs were sustained between fixed electrodes by triangular current pulses (risetime 1.3 ms, total duration 5¿25 ms, peak values 3¿17.5 kA) and subjected to mass-flow rates in the range 0.244¿0.675 kg/s generated by reservoir pressures of 4.46¿14.11 bars absolute (50¿190 lb/in2 g). The parameters measured were the overall arc voltage and current, the axial voltage distributions, the extent of the luminous-arc core and thermal region surrounding the arc, and the radial and axial pressure distributions through the orifice. The experimental results indicate the influence upon local and overall arc properties of the position, polarity and material of the upstream electrode. The detailed nature of these measurements has allowed a critical assessment to be made, for the first time, of integral boundary-layer analysis for high-current arcs under realistic circuit-breaker conditions.