| 摘要 |
PURPOSE:To prevent erroneous function due to saturation of current transformer caused by external fault, by detecting the variations of suppressed terminal voltage due to secondary current of current transformer and suppressed control voltage due to differential current and comparing them to determine suppressed voltage. CONSTITUTION:Gapped transformer is employed as suppressing input transformers 13a, 23a connected to current transformers 12, 22 for the purpose to produces sup pressed terminal voltage ETr proportional with the variation of secondary current of current transformer. Gapped transformer is also employed as suppression controlling input transformer 2d to produce suppressed control voltage EP proportional with the variation of differential current ID. Consequently even when flow-in end current transformer DC error is produced in differential current ID due to external fault, it produces substantially zero voltage because suppression control voltage EP is obtained from the variation of differential current. Consequently suppression voltage is determined without influencing suppressed terminal voltage ET thereby it causes no errorneous function. |
