| 摘要 |
PROBLEM TO BE SOLVED: To prevent maloperation of an out-of-step relay when an external failure occurs. SOLUTION: In the out-of-step detection relay, which detects a step-out inside the protection zone of a power system composed of a plurality of interconnected terminals with transmission lines, the relay has a signal-sending circuit 25 and a signal-receiving circuit 26, which send and receive data between the own terminal and the opposite terminal; a phase-difference calculation part 27, which calculates phase difference between a voltage quantity received from the opposite terminal and the one inputted into the own terminal, upon compensating with a predetermined impedance value and a current quantity; a decision part 28, which discriminates whether or not an out-of-step locus point is inside the relay-installed zone, depending on whether or not the calculation result of the phase difference passes a predetermined phase-angle point; and a failure discrimination part 30 which discriminates a system failure from a step-out based on voltage and current quantities inputted from the own terminal. When it is decided as the system failure by the failure discrimination part 30, the output of the decision part 28 is locked.
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