| 摘要 |
PROBLEM TO BE SOLVED: To provide a protection relay device in a configuration where a digital input circuit capable of destroying an oxide film covering a contact of a switch is made common between a plurality of power systems at different voltage levels.SOLUTION: A protection relay device 1 includes: a digital input processing part 90 which is connected to an external DC power source E via a switch SW including a mechanical contact, compares a binary voltage inputted in response to opening/closing the switch SW with a threshold voltage Vth that is set in accordance with a voltage of the external DC power source E, and outputs a comparison result as a digital signal; and a CPU 32 which outputs a cutoff command to a circuit breaker by discriminating a state of a power system on the basis of the digital signal. The digital input processing part 90 includes: conversion circuits 53 and 54 which are electrically connected between a positive electrode and a negative electrode of the external DC power source E by closing the switch SW and convert a current that is supplied from the external DC power source E via the switch SW, into a binary voltage; and a constant current circuit 100 which is connected in parallel to the conversion circuits 53 and 54 and makes a constant current flow.SELECTED DRAWING: Figure 2 |
