Multiphysics Modeling for Thermal Interruption Capability Evaluation in 72.5 kV GCB Adopting CO₂/O₂ Mixture Gas

The increasing concerns surrounding global warming and its adverse effects have contributed to the rising demand for SF6-free eco-friendly gas circuit breakers (GCBs). In particular, CO2/O2 mixtures possess better arc-quenching capabilities than pure CO2, making them suitable insulation gases for eco-friendly GCBs. This study proposes a multiphysics model combining electric, fluid dynamics, and radiation models to evaluate the thermal interruption capability in a 72.5 kV GCB using a CO2/O2 mixture gas. The pressure rise inside the thermal chamber and arc voltage of a prototype gas interrupter adopting a CO2/O2 mixture gas were calculated using the proposed model. The feasibility of the model was verified through a comparison of the calculated pressure rise and arc voltage with the measurement results. Furthermore, we calculated the temperature, pressure, and polytetrafluoroethylene (PTFE) ablation distribution of the 72.5 kV GCB with the CO2/O2 mixture gas. Based on these results, we estimated the thermal interruption capabilities, specifically, the post-arc current (PAC) and G200 indices. The numerical investigation of the thermal interruption capability can contribute to the design of GCB interrupters using CO2/O2 mixture gas.