CURRENT-ZERO BEHAVIOR OF AN SF(6) GAS-BLAST ARC .2. TURBULENT-FLOW

The conservation equations of turbulent gas-blast nozzle arcs based on local thermal equilibrium and on boundary layer assumptions have been solved numerically. A Prandtl mixing length model of turbulence has b een adopted because of its simplicity and its success when applied to turbulent rounded jets. The investigation is aimed at an understanding of the arc in a gas-blast circuit-breaker, where the key problem is t he arc behaviour during the current-zero period. Emphasis has been pla ced on quantitative analysis of turbulence-enhanced cooling and its in fluence on arc behaviour during the current-zero period. The dominant energy transport processes and the critical region for thermal interru ption within the nozzle have been identified. The critical rate of ris e of recovery voltage as a function of stagnation pressure has been st udied and the physical mechanism responsible for this functional relat ionship discussed. Good agreement between the prediction and experimen tal measurements has been achieved for the two nozzle geometries inves tigated.