The iron core of the transformer constitutes the magnetic circuit of the transformer, and at the same time plays the role of the skeleton of the body. Transformer iron core is generally made of silicon steel sheets with 0.35mm thickness and surface coated insulating paint. The core is coated with insulating paint mainly to reduce core loss:
1. The silicon steel sheet itself is also an electrical conductor. Under the action of AC magnetic flux, an induced current is also generated in the core.
2. If the iron core is not coated with insulating paint, the iron core will become a whole, which is equivalent to a conductor with a large area, and its resistance value is small. Although the induced voltage is not high, the induced current is large. This will cause great eddy current (circulation) loss. In severe cases, it will cause the core to heat up and even melt the rust, which is called "fire" of the core.
3. After the insulating paint is applied between each piece, the core is divided into many small cross-section conductors. In this way, the resistance of the slitting machine becomes larger. The lacquered iron core, although there is also eddy current loss (part of the iron loss), is much smaller.
4. Therefore, silicon steel sheets are relatively thin and must be coated with insulating paint.