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Why do transformers use silicon steel sheets?
Apr 28, 2018

Commonly used transformer cores are generally made of silicon steel sheet. Silicon steel is a kind of silicon (silicon, also known as silicon) steel, its silicon content in the 0.8 to 4.8%. The core of transformer made of silicon steel is because silicon steel itself is a magnetic material with strong magnetic permeability. In the energized coil, it can produce large magnetic induction, which can make the transformer smaller in size.

We know that the actual transformer is always operating in the AC state, and the power loss is not only in the resistance of the coil but also in the core under the magnetization of the alternating current. The power loss in the iron core is usually called "iron loss." The iron loss is caused by two factors. One is "hysteresis loss" and the other is "eddy current loss."

The hysteresis loss is the core loss caused by hysteresis in the magnetization process. The magnitude 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 iron core of the transformer is small, which can greatly reduce the degree of heat generation.

Since silicon steel has the above advantages, why not use a whole piece of silicon steel as a core, but also to process it into sheets?

This is because the sheet iron core can reduce another kind of iron loss - "eddy current loss." When the transformer is working, there is an alternating current in the coil, and the magnetic flux it generates is of course alternating. This changing flux creates induced currents in the 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 cause the iron core to heat up. In order to reduce eddy current losses, the core of the transformer is laminated with silicon steel sheets insulated from each other so that the eddy currents in the narrow loops pass through smaller cross-sections to increase the resistance of the eddy current paths; at the same time, the silicon in the silicon steel makes The increased resistivity of the material also acts to reduce eddy currents.

As a transformer core, a 0.35mm thick cold-rolled silicon steel sheet is generally used. According to the required size of the iron core, it is cut into a shape sheet and then overlapped into a “Japanese” shape or an “I” shape. In theory, if the eddy current is reduced, the thinner the silicon steel sheet is, the narrower the spliced strip is, and the better the effect is. This not only reduces the eddy current loss, reduces the temperature rise, but also saves the use of silicon steel sheet. But when actually making silicon steel cores. Not only from the favorable factors mentioned above, because the production of iron cores, it will greatly increase man-hours, but also reduces the effective cross-section of the core. Therefore, when making transformer cores from silicon steel sheets, it is necessary to weigh the pros and cons and select the best size from the specific conditions.

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