Current transformer is an instrument that converts a large current on the primary side into a small current on the secondary side based on the principle of electromagnetic induction. The current transformer is composed of a closed core and windings. Its primary winding has a small number of turns and is strung in the circuit of the current that needs to be measured. The principle of current transformer is based on the principle of electromagnetic induction. The current transformer is composed of a closed core and windings. Its primary winding has very few turns and is connected in series in the line where the current needs to be measured. Therefore, it often has all the current of the line flowing through it. Its secondary winding has more turns and is connected in series in the measuring instrument and protection circuit. The current mutual inductance When the 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 current transformer is close to the short circuit.