PURPOSE:To make it easy to decide a connection error of wiring from current transformers by forming such a constitution that the phase relation of current guided by current transformers is displayed. CONSTITUTION:The current of a feeder 5 detected by a current transformer 6 and the current of feeder lines 3 and 4 detected by current transformers 7 and 8 is inputted to a power differential type bus bar protective relay 14. The digital conversion of said current is made through a sample-and-hold circuit 15, a multiplexer 16 and an A/D converter 17 to input to a CPU, and an abnormal detection for a bus protection is made. The bus bar protective relay 14 is equipped with a phase display circuit 21 and an Id display circuit 20, the phase relation of the other phase, in case one phase is set as a standard, is displayed on the display circuit 21, and the zero phase current is displayed on the Id display circuit 20. The finding of an error connection is easy because of this display.
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