In order to reduce eddy current losses;
Commonly used transformer cores are generally made of silicon steel sheets. Silicon steel is a kind of steel containing silicon (silicon is also called silicon), and its silicon content ranges from 0.8 to 4.8%. The iron core of the transformer is made of silicon steel because silicon steel itself is a magnetic material with strong magnetic permeability. In the energized coil, it can produce a large magnetic induction intensity, thereby reducing the size of the transformer.
Actual transformers always work under AC conditions, and power loss occurs not only in the resistance of the coil, but also in the iron core magnetized by alternating current. The power loss in the iron core is usually called "iron loss". Iron loss is caused by two reasons, one is "hysteresis loss" and the other is "eddy current loss".
Hysteresis loss is the iron loss caused by the hysteresis phenomenon during the magnetization process of the iron core. The size of this loss is proportional to the area surrounded by the hysteresis loop of the material. The hysteresis loop of silicon steel is narrow, and the hysteresis loss of the core of a transformer made of silicon steel is small, which can greatly reduce the heat generation.
Since silicon steel has the above advantages, why not use a whole piece of silicon steel to make the motor stator core, but also process it into sheets?
This is because the flake iron core can reduce another type of iron loss - "eddy current loss". When the transformer is working, there is alternating current in the coil, and the magnetic flux it generates is of course alternating. This changing magnetic flux produces an induced current in the iron core. The induced current generated in the iron core circulates in a plane perpendicular to the direction of the magnetic flux, so it is called eddy current. Eddy current losses also heat the core. In order to reduce eddy current losses, the core of the transformer is stacked with silicon steel sheets that are insulated from each other, so that the eddy currents pass through a smaller cross-section in a long and narrow circuit to increase the resistance on the eddy current paths; at the same time, the silicon in the silicon steel makes The increased resistivity of the material also plays a role in reducing eddy currents.
For the iron core of the transformer, 0.35mm thick cold-rolled silicon steel sheet is generally used. According to the required size of the iron core, it is cut into long pieces and then overlapped into a "日" shape or "日" shape. "mouth" glyph.
Theoretically speaking, in order to reduce eddy currents, the thinner the silicon steel sheets and the narrower the spliced ??strips, the better the effect. This not only reduces eddy current losses and temperature rise, but also saves materials for silicon steel sheets. But when actually making silicon steel cores. It is not just based on the above-mentioned favorable factors, because making the iron core in that way will greatly increase the man-hours and also reduce the effective cross-section of the iron core. Therefore, when using silicon steel sheets to make transformer cores, you must start from the specific situation, weigh the pros and cons, and choose the best size.