PROBLEM TO BE SOLVED: To realize a cogeneration linkage protection relay which optimumly chooses a phase whose reverse power is computed, to use power of a generator to the utmost.;SOLUTION: By providing an instrument current transformer CT for detecting a current of each phase, a potential transformer GPT for detecting a line voltage, operation parts 67PA, 67PB, 67PC for computing reverse power of each three phases on the basis of the current and the line voltage of each phase, and a phase selecting circuit 5 and a switching circuit 6 for selecting a computation result of reverse power of a phase whose reverse power is the smallest, a reverse power protective operation is performed on the basis of this selected reverse power computation result.;COPYRIGHT: (C)2002,JPO
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