The principle of Electrical Current Transformer is based on the principle of electromagnetic induction. The Electrical Current Transformer is composed of a closed core and windings. Its primary winding has very few turns, which is stringed in the circuit where the current needs to be measured. Therefore, it often has all the current of the line flowing. The secondary winding has a large number of turns. It is serially connected to the measuring instrument and the protection circuit. Electrical Current When Transformer is working, its secondary circuit is always closed, so the impedance of the series coil of the measuring instrument and the protection circuit is very small, and the working state of the Electrical Current Transformer is close to short circuit.