| 摘要 |
PROBLEM TO BE SOLVED: To facilitate multi-stage overcurrent protection coordination by locking protecting operation with an operating lock signal from a lower-level device based on overcurrent detection. SOLUTION: An overcurrent detecting part 12 detects overcurrent based on a current detecting signal from a current transformer 2. When a tripping signal output part 13 outputs a tripping signal s1 to a corresponding switch 6 when an overcurrent signal continues for a prescribed operating period. When an upper-level lock signal output part 14 detects the overcurrent signal, an operating lock signal s2 is outputted to a discriminating circuit 8 in an upper- level overcurrent protective device body 11 through a contact 10. Upon receiving the operating lock signal, a lock possibility discriminating part 15 locks the output of the tripping signal for the tripping signal output part 13. Lock release discrimination is conducted based on the duration of the overcurrent signal, the operating time of a lower-level relay, and lock signal duration from the lower-level relay. If it is fixed, the tripping signal is outputted from the tripping signal output part 13 after lock release. |
