Transformer cores are generally made of silicon steel sheets. Silicon steel is a kind of steel that contains silicon (silicon is also called silicon). Silicon steel is used as the core of the transformer, because silicon steel itself is a magnetic substance with strong magnetic permeability. It can produce a large magnetic induction in the energized coil. .

Therefore, the volume of the transformer can be reduced. Under the AC state of the transformer, the power loss is not only in the resistance of the coil, but also in the iron core under the magnetization of the alternating current. The power loss in the iron core is usually called "iron loss". The iron loss is caused by two reasons: one is "hysteresis loss" and the other is "eddy current loss".

There are many kinds of materials for making iron cores, the common ones are silicon steel sheet, ferrite, etc.

The transformer core is made according to the principle of electromagnetic induction, which mainly plays a role of magnetic permeability. Only after the magnetic permeability, can the magnetoelectric conversion be carried out. The main function of the transformer core is to play the role of magnetic permeability and skeleton. In a transformer as a magnetically conductive part, it is in a constantly changing electromagnetic field, and the magnetization and magnetic induction of the iron core are also constantly changing. Almost all transformer cores require high magnetic permeability. The common iron core is in the shape of "day", and the primary and secondary coils are wound on the middle cross.