PROTECTIVE RELAY DEVICE

PROBLEM TO BE SOLVED: To report normal monitor results, etc., to a control system even if abnormality occurs in a system bus, etc. SOLUTION: A processor 10 takes in a signal, which shows the state of a power system, as a digital signal, and judges the state of the above power system, from the setting condition. A man-machine interface 70 is connected to the processor 10 through a system bus 90, whereby the input of setting condition from outside is possible, and also it has a CPU71 within. A relay is operated when it fulfills the setting condition by the judgment of the processor 10. CPU71 built in the man-machine interface 70 is equipped with an operation monitoring means which monitors the operation on the side of system bus, from the signal of the processor 10 transmitted through the system bus 90, and reports the abnormality to an external control system when this operation monitoring means detects the abnormality in the operation on the side of system bus.