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.