Arc Interruption Performance of C₄F₇N-CO₂Mixture in a 126 kV Disconnector

The C4F7N-CO2 mixture is considered the most promising alternative gas to SF6 in high voltage power apparatuses. This paper demonstrates the feasibility of using C4F7N-CO2 as an SF6 alternative to switch the current in a 126 kV disconnector. Firstly, the insulation performance of the mixture of C4F7N and CO2 was investigated and the appropriate fraction of the C4F7N-CO2 gas mixture was found to be 5% by taking the limitation of minimum operating temperature into account. Secondly, the arc interruption capability of C4F7N-CO2 and SF6 were compared. The arcing process of the bus-Transfer current interruption was evaluated based on the magneto-hydro-dynamics (MHD) arc model. For the small inductive current interruption, the dielectric recovery properties were analyzed. In particular, the dielectric recovery strength of the C4F7N-CO2 during the post-Arc phase was calculated based on the streamer inception criterion. Finally, the interruption experiments and type tests further verified the feasibility of the C4F7N-CO2 in the disconnector. The investigation in this paper demonstrates that the C4F7N-CO2 mixture can be used in the 126 kV disconnector to replace SF6.