| 摘要 |
PURPOSE:To enable a normal load current to be surely discriminated from a fault current even for a large change of the load current with a large operative frequency of a train, by applying a correction replacing a parameter Jn-1 with a current sampling value In in that time when the current decreases. CONSTITUTION:A load current I, detected by a shunt 3, is converted into a digital signal by an A/D converter 11 and sampled by a sampling means 12 in every sampling period DELTAt set in a setting means 13. And a device, which conducts the current as a sampling value In in the n-th time to a comparing means 14, memory 15 and an arithmetic means 16, calculates a variable DELTAIon by using a parameter In-1 stored in the memory 15. And the variable DELTAIon is compared in a comparing means 18 with a preset value DELTAIr set by a setting means 19. Then the device is constituted so as to decide a short-circuit current to flow in a cable when the load current I is allowed to flow in a relation where DELTAIon>DELTAIr. Further the device is constituted so as to realize those after the sampling means 12 to the setting means 19 by a microcomputer.
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