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Fabrication of transformer core

Fabrication of transformer core

2022-01-20

Commonly used transformer cores are generally made of silicon steel sheets. Silicon steel is a kind of steel with silicon (silicon is also called silicon), and its silicon content is 0.8 ~ 4.8%. The reason why silicon steel is used as the iron core of transformer is that silicon steel itself is a magnetic material with strong magnetic conductivity. In the energized coil, it can produce large magnetic induction intensity, which can reduce the volume of transformer.

We know that the actual transformer always works in AC state, and the power loss is not only on the resistance of the coil, but also in the iron core magnetized by alternating current. Usually, the power loss in the iron core is called "iron loss". 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 size of this loss is directly 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 transformer core made of silicon steel is small, which can greatly reduce its heating degree. Since silicon steel has the above advantages, why not use the whole silicon steel as the iron core and process it into a sheet?

This is because the sheet iron core can reduce another iron loss - "eddy current loss". When the transformer works, there is alternating current in the coil, and the magnetic flux generated by it is of course alternating. This changing magnetic flux produces an induced current in the iron core. The induced current generated in the iron core flows in a ring in a plane perpendicular to the magnetic flux direction, so it is called eddy current. Eddy current losses also heat the core. In order to reduce the eddy current loss, the iron core of the transformer is stacked with silicon steel sheets insulated from each other, so that the eddy current passes through a small section in the narrow and long circuit, so as to increase the resistance on the eddy current path; At the same time, the silicon in silicon steel increases the resistivity of the material and reduces the eddy current.

As the iron core of the transformer, generally, 0.35mm thick cold} rolled silicon steel sheet is selected. It is cut into long pieces according to the size of the required iron core, and then overlapped into "day" shape or "mouth" shape. In principle, in order to reduce eddy current, the thinner the silicon steel sheet, the narrower the spliced strip, and the better the effect. This not only reduces the eddy current loss and temperature rise, but also saves the material of silicon steel sheet. But in fact, when making silicon steel sheet iron core. Not only from the above favorable factors, because making the iron core in that way will greatly increase the working hours and reduce the effective section of the iron core. Therefore, when making transformer iron core with silicon steel sheet, we should start from the specific situation, weigh the advantages and disadvantages and choose the best size.


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