| 摘要 |
PROBLEM TO BE SOLVED: To improve the reliability of a bus protective device when a bus interruption occurs by releasing an accident detecting output from a locked state by restoring both an interruption detecting signal and the output of an insufficient voltage relay. SOLUTION: When the AC insufficient voltage relay 21 of an accident detecting unit (AU) 20A operates in all three phases in the event of a bus interruption, the reset input of an RS flip-flop(FF) 29 reaches '0' and, in case the interrupting state continues, the setting input of the FF 29 becomes '1', because the output of an OR circuit 25 becomes '1' due to an interruption detecting signal. Therefore, the accident detecting output of the AU 20A is kept locked. There is no possibility of unlocking the accident detecting output of the AU 20A, because the output of the FF 29 does not become '0' unless the resetting input becomes '1' even when the interruption detecting signal is restored. Eventually, such an accident does not occur that a bus is accidentally cut off by the erroneous output of the AU 20A, because a duplex system composed of a main detection unit 10 and the AU 20A is maintained during the bus interruption. |
