A: There is only one CT in the conventional station line; GIS is equipped with CT on both sides of the switch, which is mainly limited by volume.
GIS generally only makes 3 or 4 secondary windings for each CT, so it will be placed on both sides of the switch.
For example, CT of 220kV line has at least 6 secondary windings, and the new standard is 8. Taking six secondary windings as an example, the line protection 1, 2, bus protection 2, 1, measurement and measurement are all arranged in this way, and the protection ranges of bus protection and line protection overlap, so that the occurrence of dead zones can be avoided. In order to save money, China's stations and most conventional stations in the world have set up a set of ct on the line side. Both line protection and bus protection obtain current from the inside, so there is a dead zone. If there is a fault such as grounding between the circuit breaker and ct, the bus differential protection will trip the bus and all switches within the scope of bus differential protection, and the fault current still exists, so the opposite switch will trip.