Evaluation of Interruption Capability on Various Gases

Abstract

SF₆ gas is widely used as interrupting medium for disconnecting switch and circuit breaker in power system whose voltage is above 72kV or medium voltage. Global warming effect of SF₆, however, is well known and emission of this gas is strictly limited by regulation. As for research to find out substitute for SF₆ gas, many works have worked out. Gleitzes [1] compared with SF₆ and N₂ and found out characteristic of dv/dt that SF₆ was about three times larger than that of N₂ Mr. Grant [2] examined dv/dt to the mixture ratio of N₂-SF₆ at the total pressure 5bar, 6bar, and 7bar of di/dt=9 A/ μ s for SLF interruption performance. It was shown that interruptible dv/dt became N₂-SF₆ gas mixture of 65% to 90% had higher than pure SF₆ gas, and this will be explained by synergistic effect. Also for He-SF₆ gas mixture its rate varied from 25%,50% to 75% and interruptible dv/dt characteristic were observed higher for gas mixture compared with pure SF₆. Leel[3] also carried out experiment and showed that the higher the mixture ratio of SF₆ with N₂ and He higher the interruptible current and that of He mixture was always inferior to that of N₂ Mr. Nakagawa [4] measured di/dt, which could interrupt the mixed gas when increasing the pressure of N₂ with a constant SF₆ pressure of 3 bars. As a result, if the pressure of SF₆ was the same, it was shown that increasing of total pressure became higher, interruption performance would be smaller. As mentioned before interruption and insulation abilities with various gas and their mixture have been studied by many researchers, but research especially for interruption was not done sufficiently.