Electrical Current Transformer 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 Electrical Current 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 a short circuit. Electrical Current Transformer converts the large current on the primary side into a small current on the secondary side for measurement, and the secondary side cannot be open. The entry introduces its working principle, parameter description, classification, usage introduction, etc.