Each group is made up of two switches. The first switch for the Phase 1 group is at terminal 7 and 21 and is configured as shown on the right:
Note that terminals 7 and 21 are shorted together regardless of whether the switch is open or closed. The second switch for the Phase 1 group is at terminals 8 and 22. It is configured as shown on the right:
Note that this switch operates as make before break. When this switch is closed terminals 8 and 22 are shorted together. When this switch is open, terminals 8 and 22 open and 22 shorts with 7 and 21. This in turn shorts the Phase 1 CT. It is essential that the CT is connected to the shorted side of the switch as shown on the right. Otherwise, dangerously high voltages would be present at the open circuited current transformer. Also note that currents can be injected into the protection relay from a secondary injection test set.
With the switch between terminals 7 and 21 open and the switch between terminals 8 and 22 closed as shown below, a 515 test plug can be inserted between terminals 7 and 21 to monitor the CT current. See the diagrams below for details. Note that the 515 test plug is made up of two conductors separated by an insulator.
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