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Why do transformers use silicon steel sheets for iron cores?
Sep 06, 2018

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

We know that the actual transformer always works in the AC state, and the power loss is not only in the resistance of the coil but also in the core under the alternating current magnetization. Usually the power loss in the iron core is called "iron loss", and the 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 in the magnetization process of the iron core. The magnitude of this loss is proportional to the area enclosed by the hysteresis loop of the material. The hysteresis loop of silicon steel is narrow, and the core hysteresis loss 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 piece of silicon steel as the iron core, but also process it into a sheet?

This is because the chip core can reduce another type 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 varying magnetic flux produces an induced current 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 core to heat up. In order to reduce the eddy current loss, the iron core of the transformer is laminated with silicon steel sheets insulated from each other, so that the eddy current flows through the narrow cross section to increase the electric resistance on the vortex flow path; at the same time, the silicon in the silicon steel makes The resistivity of the material increases and also acts to reduce eddy currents.

Used as the core of the transformer, a 0.35mm thick cold-rolled silicon steel sheet is generally used. According to the size of the required core, it is cut into long pieces and then overlapped into a "day" shape or a "mouth" shape. In theory, if the eddy current is reduced, the thinner the thickness of the silicon steel sheet, the narrower the spliced strip, and the better the effect. This not only reduces eddy current loss, reduces temperature rise, but also saves silicon steel sheet material. But actually when making silicon steel sheet iron core. It is not only based on the above-mentioned favorable factors, because the iron core is produced in that way, the working time is greatly increased, and the effective cross section of the iron core is also reduced. Therefore, when using a silicon steel sheet to make a transformer core, it is necessary to weigh the pros and cons from the specific situation and choose the best size.

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