The one phase EI silicon steel sheet with holes has a small loss in the alternating magnetic field, so silicon steel sheets are currently used as magnetic materials in the transformer. Silicon steel sheets can be divided into hot rolling and cold rolling. Cold rolled silicon steel strips have the advantages of small volume, light weight and high efficiency due to their high magnetic permeability and low loss. The performance of hot rolled silicon steel strips is slightly inferior to that of cold rolled silicon steel strips.
Ordinary EI type transformers are processed with one phase EI silicon steel sheet with holes to form E-type and I-type films with a thickness of 0.35 to 0.5 mm. After heat treatment, they are inserted into the winding wire package. Most of the hot rolled silicon steel sheets are used. The cores of the ring-type and C-type transformers are formed by winding a cold-rolled silicon steel strip, wherein the C-type transformer is formed by heat-treating and varnishing.
When one phase EI silicon steel sheet with holes is used as a core of a transformer, it is often coated with an insulating varnish between each core and divided into a plurality of small-section conductors, so that the electric resistance becomes large. The eddy current is confined within the narrow sheet. When the magnetic flux passes through the narrow section of the sheet, the net electromotive force in these loops is small, the length of the loop is large, the resistance of the loop is large, and the eddy current is greatly weakened. Therefore, the iron core coated with insulating varnish, although there is eddy current loss, is also much smaller. Then apply the insulating varnish for safe and efficient purposes.