A 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 few turns and is stringed in the line of the current that needs to be measured. Therefore, it often has all the current of the line flowing, and the number of turns of the secondary winding is relatively large. It is connected in series with the measuring instrument and the protection circuit. When the current transformer is working, its secondary circuit is always closed, so the measurement The impedance of the series coil of the instrument and the protection circuit is very small, and the working state of the current transformer is close to a short circuit. The current transformer converts the large current on the primary side into the small current on the secondary side for measurement, and the secondary side cannot be opened. The entry introduces its working principle, parameter description, classification, usage introduction, etc.