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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 Ur = 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.