Measurements and Simulations of Cold Gas Flows in High Voltage Gas Circuit Breakers Geometries

Measurements and simulations of cold gas flows in Gas Circuit Breakers (GCB) geometries were done. The found flow patterns are related to the dielectric performance during a switching operation. A reference experiment was designed with direct pressure measurements at several positions in the nozzle-diffuser system and on the edge of the plug tip. The results show the development of minimum density regions around the edge of the plug tip. For many contact designs this is also the region of highest electric field stress and thus dielectrically weak. The measurements are compared to CFD simulations and show mostly very good agreement. The flow pattern can be quite complex, including supersonic velocities and shock fronts as well as regions of flow separation and re-attachment. An experimental sensitivity analysis was performed to study the influence of deviations from the idealized reference geometry to real circuit breakers, where deviations from e.g. perfect axis- symmetry are inevitable.