| 摘要 |
PROBLEM TO BE SOLVED: To provide a ratio differential relay that does not need a constitution for obtaining an cumulative current, and is reduced in erroneous operation caused by a differential current generated by a variety of kinds of errors, in the ratio differential relay constituted for directly obtaining the differential current by using an optical CT (current transformer). SOLUTION: The ratio differential relay is provided with the optical CT that is arranged at each terminal and measures a terminal current; a light source that emits light having a prescribed wave length; an optical fiber cable transmission path that is connected so as to sequentially propagate the light emitted from the light source to each optical CT with the light source set as a starting end; a signal conversion circuit that is arranged at the dead end of the optical fiber cable transmission path, converts light after passing the optical CT to an electric signal, and obtains the differential current that is the sum of currents flowing to protective zones; a means for leading in a current of one arbitrary terminal of the protective zone; and an operation means that operates and obtains a current of the other terminal by using the differential current and the current of the arbitrary terminal, and performs ratio differential operation from the differential current and a constraint amount proportional to the sum of the magnitude of a current of each terminal. COPYRIGHT: (C)2005,JPO&NCIPI
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