Not only is the structure of a current transformer similar to that of an ordinary transformer, but it also works on the same principle.
The alternating current in the primary winding induces a magnetic flux in the iron core, which passes to the secondary winding and induces an alternating current there too.
These transformers are basically step-up transformers, i.e. stepping up the voltage from the primary to the secondary. Therefore, the current decreases from the primary to the secondary.
Based on function:
Measuring current transformers:
Current transformers used in metering and indicating circuits are commonly referred to as measuring CTs. Their saturation point is very low. In the event of a fault, the core saturates and the secondary current cannot damage the measuring equipment connected to it.
Protect current transformers:
Current transformers used with protective devices are called protective CTs. The purpose is to detect fault current in the system and pass the signal to the relay. Since it runs at a higher current value than its rating, its core has a high saturation point.
Based on construction:
Bar current transformer:
This type of current transformer uses the actual cable or busbar of the main circuit as the primary winding, which is equivalent to a single turn. They are fully insulated from high operating voltages.
Wire-wound current transformers:
The transformer's primary winding is connected in series with the conductor carrying the measurement current flowing in the circuit.
Toroidal/window current transformers:
These do not contain primary windings. Instead, the lines carrying the current in the network pass through windows or holes in the toroidal transformer. Some current transformers have a "split core" that can be opened, installed, and closed without breaking the circuit they are connected to.