Transformers with special purposes are generally called special transformers. In addition to AC voltage conversion, the transformer also has various other purposes, such as changing the frequency of power supply, power supply of rectifier equipment, power supply of welding equipment, power supply of electric furnace, or voltage transformer, current transformer, etc. Because the working conditions and load conditions of these transformers are different from those of general transformers, the calculation method of general transformers cannot be used for calculation.
1. Iron core material
The iron core materials used in the transformer mainly include iron sheet, low silicon sheet and high silicon sheet. Adding silicon to the steel sheet can reduce the conductivity of the steel sheet and increase the resistivity. It can reduce eddy current and reduce its loss. We usually call silicon steel sheet as silicon steel sheet. The quality of silicon steel sheet used in transformer is greatly related to the quality of silicon steel sheet. The quality of silicon steel sheet is usually expressed by magnetic flux density B. generally, the b value of black iron sheet is 6000-8000, low silicon sheet is 9000-11000 and high silicon sheet is 12000-16000,
2. Materials commonly used in wound transformers
Enamelled wire, gauze wire, silk wire, paper wire, the most commonly used enamelled wire. The requirements for the conductor are good conductivity, sufficient heat resistance of the insulating paint layer and certain corrosion resistance. In general, it is best to use high-strength polyester enamelled wire of QZ model.
3. Insulating material
In the winding transformer, insulating materials shall be used for the isolation between coil frame layers and winding resistance. The general transformer frame materials can be made of phenolic paperboard, epoxy board or paperboard. Polyester film, telephone paper and 6520 composite paper can be used as isolation between layers, and yellow tarpaulin or imine film can be used as isolation between winding resistance.
4. Impregnation material
After the transformer is wound, the last process is to impregnate the insulating paint, which can enhance the mechanical strength of the transformer, improve the insulating performance and prolong the service life. Generally, cresol varnish can be used as impregnation material or 1032 insulating paint and resin paint.