| 摘要 |
PURPOSE:To stabilize relay unit by determining a ratio between a differential current obtained from vector sum of zero-phase currents at respective terminals and a restraining current obtained from maximum values of zero-phase currents at respective terminals, and locking the output from a ratio operating means upon detection of an eddy current when the restraining current is higher than a predetermined level. CONSTITUTION:A difference derivation means 21 determines a differential current ID from vector sum of zero-phase currents at respective terminals. A restrain derivation means 22 determines a restrain current IR from maximum values or scalar sum of zero-phase currents at respective terminals. A ratio operating means 23 determines the ratio between the currents ID and IR and produces an output if ID>IR. An eddy current detecting means 24 outputs an eddy current signal if the restrain current IR is higher than a value KV0 which is proportional to a zero-phase voltage V0. Upon receiving the eddy current signal, a lock means 25 locks output from the ratio operating means 23. Output is delivered from the ratio operating means 23 on condition that no output is delivered from the eddy current detecting means 24. This constitution enhances safety, accuracy, and coordination in setting of the relay unit. |
