RATIO DIFFERENTIAL RELAY AND METHOD OF PREVENTING ERRONEOUS OPERATION OF RATIO DIFFERENTIAL RELAY

摘要

PROBLEM TO BE SOLVED: To provide a ratio differential relay, etc., free from malfunction even if a current transformer circuit for a ratio differential relay under operation is brought into one-to-three-phase short-circuit or disconnection due to a human error.

SOLUTION: The ratio differential relay 10 is provided with: a ratio differential relay circuit 11 for outputting trip signals T1Xto T3X(X=R, S, R) of first-third phases to cause a breaker for transformer protection to break; a current value/variation rate calculating circuit 12 for calculating scholar current values ¾i1X¾ to ¾i3X¾ of secondary currents i1Xto i3Xof first-third phases and their variation rates Δ¾i1X¾ to Δ¾i3X¾; and a locking circuit 13 for generating a locking signal L for locking the ratio differential relay circuit 11 so that the trip signals T1Xto T3Xof the first-third phases is not outputted, on the basis of the scholar current values ¾i1X¾ to ¾i3X¾ from the current value/variation rate calculating circuit 12 and the variation rates Δ¾i1X¾ to Δ¾i3X¾.

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