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 iron core magnetized by the alternating current. The power loss in the iron core is usually called "iron loss", which is caused by two reasons, one is "hysteresis loss" and the other is "eddy current loss".
Hysteresis loss is the iron loss due to the hysteresis phenomenon in the magnetization process of the iron core. The size 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 hysteresis loss of the iron core of the transformer is small, which can greatly reduce its heating degree.
Since silicon steel has these advantages, why not use the whole piece of silicon steel to make the iron core, but also process it into sheets?
This is because sheet-like cores reduce another type of iron loss, "eddy current loss". When the transformer works, there is alternating current in the coil, and the magnetic flux it produces is of course alternating. This varying flux produces an induced current in the core. The induced current generated in the core circulates in a plane perpendicular to the direction of the flux, so it is called eddy current. Eddy current loss also heats the core. In order to reduce eddy current loss, the core of the transformer is stacked with silicon steel sheets insulated from each other, so that the eddy current is in the narrow and elongated loop, through a smaller section, to increase the resistance of the eddy current path; At the same time, the silicon in the silicon steel increases the resistivity of the material and also plays a role in reducing the eddy current.
Used as the transformer core, generally choose 0.35mm thick cold rolled silicon steel sheet, according to the size of the required core, it will be cut into long shaped sheet, and then overlap into "day" shape or "mouth" shape. In principle, in order to reduce eddy current, the thinner the thickness of silicon steel sheet, the narrower the splicing strip, the better the effect. This not only reduces the eddy current loss, reduces the temperature rise, but also saves the silicon steel sheet material. But actually when you make a silicon steel sheet iron core. Not only from the above side of the advantageous factors, because the production of iron core, to greatly increase the man-hour, but also reduce the effective section of the core. Therefore, when making transformer core with silicon steel sheet, we should start from the specific situation, weigh the advantages and disadvantages, and choose the best size.
Transformers are made according to the principle of electromagnetic induction. There are two windings, a primary winding and a secondary winding, wound on the closed core column. When the primary winding is added with AC supply voltage. The original Rao group current has alternating current, and the establishment of magnetic potential, under the action of magnetic potential in the iron core will produce alternating main magnetic flux, the main magnetic flux through the core at the same time,] the primary and secondary winding and closed because of electromagnetic induction in the primary and secondary winding respectively generated induced electromotive force, as to why it can boost and step-down? Lenz's law is needed to explain it. Magnetic flux generated by induced current always hinders the change of original magnetic flux. When the original magnetic flux increases, the magnetic flux generated by induced current is opposite to the original magnetic flux, that is to say, the induced magnetic flux generated by secondary winding is opposite to the main magnetic flux generated by primary winding. So the secondary winding has a low level of alternating voltage, so the core is the magnetic circuit part of the transformer, and the winding is the circuit part of the transformer.