Patent ID: 8526155

Claim:
A phase-control switchgear provided to a multi-phase AC power transmission line connecting between first and second buses, first and second multi-phase generators being connected to said first and second buses, respectively, said phase-control switchgear comprising: a circuit breaker breaking a current flowing through said power transmission line; a phase difference detection unit detecting a phase difference between a voltage of a specific phase of said first bus and a voltage of one of a plurality of phases of said second bus that is identical to said specific phase, at a plurality of time points; a storage unit storing the phase differences at the plurality of time points detected by said phase difference detection unit; and a control unit, wherein, when said control unit receives a breaking instruction for said circuit breaker, said control unit estimates a breaking time point at which the phase difference between the voltage of said specific phase of said first bus and the voltage of one of the plurality of phases of said second bus that is identical to said specific phase will be a predetermined phase difference, based on the phase differences at the plurality of time points stored in said storage unit, and opens said circuit breaker to break the current at said breaking time point.