| 摘要 |
PROBLEM TO BE SOLVED: To provide an overcurrent relay which is not influenced by the overlapping angle of commutation even for a rectangular wave input and has a small error. SOLUTION: A sanpling (an instantaneous value) data (iR, iS, ir ) is obtained from a three-phase rectangular wave current in a P-wave an N-wave extracting part 11 in place of detection by a conventional fundamental wave extraction. The absolute value of the respective instantaneous values of three-phase components is sought and the three-phase addition of the values is performed in a|IP|and|IN|data preparing part 12, thereby obtaining the quantity of electricity (|If =|iR|+|is|+|ir|) corresponding to a DC current in|If|data preparing part 13. It is detected in a decision part 14 that the value|If|becomes not less than the setting value|Ik|of an overcurrent.
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