Investigation of the performance of CF3I Gas as a Possible Substitute for SF6

Our research has investigated the use of CF₃I, which has lower Global Warming Potential (GWP), as a substitute gas for SF₆. The use of pure CF₃I in gas insulated switchgear (GIS) and gas circuit breakers (GCB) is difficult because liquid CF3I has a high boiling point. We have therefore mixed CF₃I with CO₂ or N₂. By investigating the decomposed gas after a current interruption, we have shown that the iodine density from CF₃I-CO₂(30%-70%) is about 1/3 of that of pure CF₃I. In addition, no fluorine was detected from the gas mixture. Our investigation of the breakdown voltage characteristics has shown that the dielectric strength of CF₃I-CO₂ (30%-70%) is about 0.75 to 0.80 times that of SF₆. In breaker terminal fault (BTF) and short line fault (SLF) interruption, CF₃I-CO₂ is superior to CF₃I-N₂. Because of the high boiling point of CF₃I, the proportion of CF₃I should be small. In BTF interruption, the performance approximates to that of pure CF₃I when the proportion of CF₃I exceeds 30%. Similarly, the SLF interruption performance approximates to that of pure CF₃I when the proportion of CF₃I exceeds 20%.