Simulation of gas flow phenomena in high-voltage self-blast circuit breakers at heavy fault current interruption

CFD (computational fluid dynamics) calculations for high- and low-current arcs in an interrupter of the self-blast type have been performed. The high-current simulation provides information about the mixing process of the hot PTFE cloud with the cold SF₆ which is difficult to access for measurement. In addition, it yields the gas state inside the pressure chamber when the fault current approaches its current zero. Depending on the arcing time, fault current and interrupter geometry blow temperatures of up to 2000 K with a PTFE mass fraction of up to 10% have been found. The low-current simulation performed for this blow temperature gives detailed information about the arc behaviour in the time immediately before current zero. Special attention has been paid to the flow phenomena in the expanding nozzle region. Due to the interaction of the supersonic flow with the obtuse arcing contact and the nozzle geometry, a complex flow structure with a shock Is established. This has been simulated for low-current arcs in an extinguishing flow with boundary conditions as obtained from the high-current simulation