Because the loss of silicon steel in the alternating magnetic field is very small, the transformer is mainly made of silicon steel sheet as magnetic material. The silicon steel sheet can be divided into hot rolled and cold rolled two types. The cold rolled silicon steel strip has the advantages of small volume, light weight and high efficiency for making transformers because of its high magnetic conductivity and low loss. The properties of hot rolled silicon steel strip are slightly inferior to those of cold rolled silicon steel strip.
Common EI type transformer is the silicon steel plate is made into 0.35-0.5mm thick E and I wafers, after heat treatment and then inserted into the winding wire package, this kind of iron core to the use of hot rolled silicon steel sheet in the majority (high silicon content of high quality silicon steel sheet model D41, D42, D43, D301). The core of ring type and C type transformer is made of cold rolled silicon steel strip by winding, and the C type transformer is made by heat treatment after soaking paint and then cutting.
The leakage inductance of the transformer is caused by the magnetic flux not passing through the primary and secondary coils, which passes through the air and forms the closed magnetic circuit itself. Enhancing the coupling density between the primary and secondary transformer can reduce the leakage inductance. The leakage induction of a good transformer should not exceed 1/100 of the primary coil inductance, and the leakage induction of a high fidelity Hi-Fi output transformer should not exceed 1/500.
