| 摘要 |
PURPOSE:To prevent unneeded operation of a device positively by locking operation output of a zero-phase differential current relay with either operation of a shortage voltage relay, an overcurrent relay, and an overcurrent relay of a destination terminal. CONSTITUTION:The output of each phase-difference current relay 12 is locked by non-operation of a low-sensitivity shortage voltage relay 11 at the time of an accident of secondary side of a transformer of a branch load terminal and the low-sensitivity shortage voltage relay 11 is operated at the time of a grounding accident of external two wires at a power supply edge side, thus locking the output of an AND circuit 13 with a zero-phase differential current relay 13 and a grounding overvoltage relay 14 as input. In the case of the external two-wire grounding accident at the non-power supply edge side, an overcurrent relay 20 is operated, thus locking the output of an AND circuit 31. Also, in the case of the external two-wire grounding accident at the branch load edge side, the AND circuit 31 is locked by output of a destination edge overcurrent relay 21, thus preventing unneeded operation of a device positively and preventing influence due to an external accident from being spread. |
