The actual transformer always works in the AC state, the power loss not only in the coil resistance, but also in the AC current magnetization of the iron core.

The power loss in the iron core is usually called “iron loss” , which is caused by two reasons, one is “hysteresis loss” , the other is “Eddy current loss” . Hysteresis loss is the core loss caused by hysteresis in the course of magnetization, which is proportional to the area surrounded by hysteresis loop. The magnetic hysteresis loop of silicon steel is very narrow, so the magnetic hysteresis loss of the transformer core made of silicon steel is small, and the heating degree can be greatly reduced.