Investigation of the Arc Characteristics in a Nozzle with C4F7N/CO2 Mixtures

Abstract

C4F7N is considered the most promising alternative to SF6 due to its higher liquefaction temperature, and it is generally mixed with buffering gases such as CO2 in engineering applications. This paper establishes a two-dimensional axisymmetric nozzle arc model based on magnetohydrodynamics, calculating the nozzle arc for air, SF6, and C4F7N/CO2 mixtures. The simulation model’s accuracy is validated by comparing the calculation results for air with experimental data. This study focuses on comparing and analysing the temperature distribution, arc voltage, and energy balance characteristics of the nozzle arcs for SF6 and C4F7N/CO2 mixtures. By comparing the physical properties of the two gases, the differences in their arc characteristics are explained. Finally, the influence of different C4F7N concentrations on the arc characteristics of the mixed gas is compared. The results show that the arc voltage of the C4F7N/CO2 mixtures is higher than that of the other two gases and increases asymptotically with the decrease in current. Among the three gases, the main form of arc energy dissipation is axial thermal convection, and both radial heat transfer and axial thermal convection are more significant in the C4F7N/CO2 mixtures, resulting in the lowest arc temperature, which is more conducive to arc extinguishing. This study provides an in-depth explanation of the differences in arc morphology and temperature between SF6 and C4F7N mixed gases by comparing their ρCp and ρh. The findings offer theoretical support for the design and optimisation of new environmentally friendly circuit breakers.