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The role of the power transformer core

2019-04-01 11:53:28

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 loss of the power 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 sheet core can reduce another type of iron loss - "eddy current loss". When the power transformer core 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 power transformer core 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; meanwhile, in the silicon steel The silicon increases the resistivity of the material and also acts to reduce eddy currents.

Used as a power transformer core, generally use a 0.35mm thick cold-rolled silicon steel sheet, cut it into a long piece according to the size of the required core, and then overlap 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 the eddy current loss, reduces the temperature rise, but also saves the silicon steel sheet.

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.

The transformer is made according to the principle of electromagnetic induction. There are two windings, one primary winding, and one secondary winding on the closed core post. When the original winding is connected with the AC mains voltage.

The original Rao group has an alternating current, and a magnetic potential is established. Under the action of the magnetic potential, an alternating main magnetic flux is generated in the iron core, and the main magnetic flux passes through the iron core at the same time, and the secondary winding is closed due to Electromagnetic induction produces induced electromotive force in the primary and secondary windings respectively. As for why it can boost and step down?

Then it is necessary to explain the magnetic flux generated by the induced current, which always hinders the change of the original magnetic flux. When the original magnetic flux increases, the induced magnetic flux is opposite to the original magnetic flux.

That is to say, the induced magnetic flux generated by the secondary winding is opposite to the main magnetic flux generated by the primary winding, so that the secondary winding has a low-level alternating voltage, so the iron core is the magnetic circuit portion of the transformer, and the winding is the circuit of the transformer. section.