OVERCURRENT PROTECTION RELAY AND VOLTAGE PROTECTION RELAY

摘要

PROBLEM TO BE SOLVED: To provide an overcurrent protection relay and a voltage protection relay that prevent unwanted operations due to failures in an analog detecting circuit, without preparing double analog detecting circuits.;SOLUTION: Signals based on the currents of each phase from a three-phase main circuit system 1 are converted to those of a given size and afterwards sent out to filter circuits 4a, 4b, 4c, signal amplifiers 5a, 5b, 5c, a multiplexer 6 and an AD converter 7 which constitute an analog detection circuit. Here, the multiplexer 6 transmits signals, based on the currents of each phase from the signal amplifiers 5a, 5b, 5c to a CPU 8 in sequence via the A/D converter 7. If a currents larger than preset by a setting circuit 11 are detected of two or more phases, a CPU 8 begins to accumulate maximum currents for a preset period of time, and when the set time is up, a relay trip action is made.;COPYRIGHT: (C)2000,JPO