CURRENT CHANGE-OVER CIRCUIT ON SECONDARY SIDE OF CURRENT TRANSFORMER

摘要

PURPOSE:To prevent the adverse effect due to the open terminal of a current transformer on the secondary side thereof and the erroneous operation of a zero phase relay by connecting a current change-over device between the output side of a protective relay and an ammeter. CONSTITUTION:Protective relays 3a-3c are connected to shunts 7a-7c on the output side thereof and the output sides of the shunts 7a-7c are connected to the output sides of a zero phase relay Q and an ammeter 6. A current change- over device 4 is connected between the relays 3a-3c and the shunts 7a-7c on the input side of the ammeter 6 and constituted of three fixed contacts 8A-8C on the input side and the movable contact 9 on the output side sliding between the fixed contacts. The contact 9 is in contact with the first fixed contact 8A and the current of a main circuit 1a is measured by the ammeter 6 and a current flows to the respective shunts 7a-7c. In this state, even on the way of the change-over of the contact 9 to the second fixed contact 8B, a current transformer 2c can be always prevented from becoming an open terminal on the secondary side thereof by the current flowing to the respective shunts 7a-7c.