A current transformer( CT) is a transformer consisting of a primary circuit and a secondary circuit. The current flowing through the primary is transformed into the secondary windings in proportion to the ratio of the number of turns.
Current transformers are measuring transformers. They operate potential-free and transform high currents into lower currents so that these can be measured by measuring equipment. Due to the absence of potential, the measuring equipment connected to the secondary windings and the protective circuits are isolated from the higher primary circuit.
The secondary current for high primary currents is 1 A or 5 A as standard.