We investigated the fundamental characteristic of CF3I as a substitute gas for SF6. CF3I has lower global warming potential. The use of pure CF3I in gas-insulated switchgear and gas circuit breakers is difficult because liquid CF3I has a high boiling point. We therefore mixed CF3I with CO2 or N2. In short line fault (SLF, 1 kApeak) and breaker terminal fault (BTF, 3 kApeak) interruption, the performance of CF3I????CO2 approximated that of pure CF3I when the proportion of CF3I exceeded 30. However, for BTF (20 kApeak) interruption, the performance of CF3I????CO2 remarkably decreased. In loop current interruption for disconnecting switches, CF3I????CO2 (30/70) was successfully used 200 times for 4000 A. We also measured CF3I spectra. Investigation of the decomposed gas density after current interruption revealed that fluorine release from CF3I was less than that from SF6. Iodine density released from CF3I-CO2 (30/70) was approximately one-third of that released from pure CF3I. In addition, iodine could be removed using an adsorbent.
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