Arc Interruption Performance of C4F7N-CO2 Mixture 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.