Arc Interruption Performance of C4F7N-CO2 Mixture in a 126 kV Disconnector

The C 4 F 7 N-CO 2 mixture is considered the most promising alternative gas to SF 6 in high voltage power apparatuses. This paper demonstrates the feasibility of using C 4 F 7 N-CO 2 as an SF 6 alternative to switch the current in a 126 kV disconnector. Firstly, the insulation performance of the mixture of C 4 F 7 N and CO 2 was investigated and the appropriate fraction of the C 4 F 7 N-CO 2 gas mixture was found to be 5% by taking the limitation of minimum operating temperature into account. Secondly, the arc interruption capability of C 4 F 7 N-CO 2 and SF 6 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 C 4 F 7 N-CO 2 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 C 4 F 7 N-CO 2 in the disconnector. The investigation in this paper demonstrates that the C 4 F 7 N-CO 2 mixture can be used in the 126 kV disconnector to replace SF 6 .