Investigations on the influence of the switching chamber design on the thermal interruption performance of carbon dioxide in high voltage circuit breakers

The search for alternatives for the strong greenhouse gas SF₆ (sulphur hexafluoride) in high voltage gas insulated switchgear (GIS) and circuit breakers lead to the identification of CO₂ (carbon dioxide) as possible substitute for use as quenching gas. Nevertheless the first prototypes of circuit breakers filled with CO₂ up to rated voltages of U_r = 145 kV show that an optimization of the CO₂ technology with regard to the size of the switching chamber and the energy of the operating mechanism is needed. This requires a deep understanding of the interruption process in CO₂ and an identification of the main influencing factors on the interruption performance. For this purpose the thermal interruption performance of two model switching chambers - optimized for the use of CO₂ and SF₆ - is experimentally investigated and compared. From the comparison with CFD (computational fluid dynamics) simulation results, gas temperature and flow velocity are determined as main influencing parameters on the interruption performance.