Different types of current transformers:
Wound type Current Transformer:
The primary of the current transformers is directly connected in series with the line conductor that carries the entire current to be measured. The primary and secondary cannot be disconnected. Example: Switchyard High voltage CTs
Toroidal Current Transformer :
These do not contain a primary winding. Instead, the line that carries the current flowing in the network is threaded through a window or hole in the toroidal transformer. The secondary of the current transformer is portable. Example: Digital tongue tester
Bar-type Current Transformer:
The primary of the current transformers is considered as the line or cable or busbar of the load circuit. Typically, the single straight line considers as primary winding. These CTs are connected such as hallow nature. They do not have any physical contact. The secondary of the transformer cannot be removed on live condition. Example: Core Balanced Current transformer CBCT (these current transformers are used to sense the unbalance current flow in the circuit).
Summation Current Transformer:
The output from the multiple current transformer is given to the single transformer, which converts multiple output into single output. It just reduces the metering complexity, installation of multiple equipment cost, wiring cost etc.