| 摘要 |
Respective contact terminals in respective arc-suppressing spaces of respective breakers are opened at a voltage zero point of any phase of three phases, simultaneously among the three phases. If current breaking is carried out for the three phases at the same time, when the breakers of the three phases are opened, the residual magnetic levels of the respective phases of a transformer can be controlled so that the residual magnetic flux level of the phase opened at the voltage zero point is maximum (for example, -2 K or +2 K) and the residual magnetic flux level of the other two phases are opposite in polarity to the residual magnetic flux level of the phase concerned and equal to substantially the same residual magnetic flux (for example, +K and +K or -K and -K) which is equal to about one half of the residual magnetic flux level of the phase concerned. Accordingly, by throwing the phase broken at the voltage zero point at a first time, the difference in residual magnetic flux between the second throwing phase and the third throwing phase just after the first phase is thrown can be substantially nullified. |
