Current interruption characteristics of C4F7N/CO2 mixture in a load switch

SF
₆
gas is a good electric medium for its excellent arc extinguishing properties. However, SF
₆
is a strong greenhouse effect gas with a global warming potential (GWP) of 23,900 times that of CO
₂
. It is urgent to find a SF
₆
alternative gas for electrical industry. Nowadays, some kinds of gases are filtered as candidates, and C
₄
F
₇
N is considered the most likely gas to replace SF
₆
in the future. Although C
₄
F
₇
N has a good arc extinguishing property in general, C
₄
F
₇
N cannot be used alone in power equipment and it has to be mixed with some buffer gases like CO
₂
with a determined mixing ratio. Because the arc extinguishing mechanism of C
₄
F
₇
N/CO
₂
in load switch is not clear, in this paper the arc extinguishing performance of gas mixture is studied by numerical simulation. Physical parameters of C
₄
F
₇
N mixture are the data basis for simulation calculations and the accuracy of them has a great impact on the simulation. Because the physical parameters are mostly affected by pressure and temperature, they are all calculated by gas pressure and temperature. The magneto-hydrodynamic (MHD) model is an effective way to describe the process of arc extinguishing. A two-dimensional axisymmetric arc MHD model is established by adding specific source terms based on the flow field control equations. The influence of the ratio of C
₄
F
₇
N/CO
₂
mixture is investigated to explore the C4F7N mixture arc extinguishing performance in load switch. According to MHD analysis, the important parameters such as the rising rate of recovery voltage can be got which is considered as a judging criterion whether the current breaking succeed or not. It can provide sufficient theoretical ways to improve arc extinguishing performance of load switch.