The commonly used transformer iron cores are generally made of silicon steel sheets. Silicon steel is a kind of steel containing silicon (silicon is also called silicon). Its silicon content is between 0.8% and 4.8%. Silicon steel is used as the iron core of a transformer because silicon steel itself is a magnetic material with strong magnetic permeability. In a live coil, it can generate a relatively large magnetic induction intensity, thus reducing the volume of the transformer.
We know that an actual transformer always works in an alternating current state. Power loss occurs not only on the resistance of the coil but also in the iron core magnetized by alternating current. Generally, the power loss in the iron core is called "iron loss". Iron loss is caused by two reasons, one is "hysteresis loss" and the other is "eddy current loss".
Hysteresis loss is the iron loss generated in the iron core during the magnetization process due to the existence of hysteresis phenomenon. 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. Using it as the iron core of a transformer has a relatively small hysteresis loss, which can greatly reduce its heating degree.
Since silicon steel has the above advantages, why not use a whole piece of silicon steel as the iron core but process it into sheets? This is because sheet iron cores can reduce another kind of iron loss - "eddy current loss".
When a transformer is working, there is an alternating current in the coil. The magnetic flux it generates is of course alternating. This changing magnetic flux generates an induced current in the iron core. The induced current generated in the iron core circulates in a loop in a plane perpendicular to the magnetic flux direction, so it is called eddy current.
Eddy current loss also heats up the iron core. In order to reduce eddy current loss, the iron core of a transformer is made of insulated silicon steel sheets stacked on top of each other, so that the eddy current passes through a relatively small cross-section in a long and narrow circuit 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 also plays a role in reducing eddy current.
For making the iron core of a transformer, generally cold-rolled silicon steel sheets with a thickness of 0.35mm are selected. According to the required size of the iron core, they are cut into long strips and then stacked into a "日" shape or a "口" shape. In theory, to reduce eddy current, the thinner the silicon steel sheet and the narrower the spliced strips, the better the effect. This not only reduces eddy current loss and lowers the temperature rise but also saves the material of silicon steel sheets.
But in actual production of silicon steel sheet iron cores, it is not only based on the above-mentioned favorable factors. Because making iron cores in that way will greatly increase working hours and also reduce the effective cross-section of the iron core. Therefore, when making transformer iron cores with silicon steel sheets, we should start from specific situations, weigh the pros and cons, and choose the best size.
A transformer is made according to the principle of electromagnetic induction. On the closed iron core column, there are two windings, a primary winding and a secondary winding. When an alternating current power supply voltage is applied to the primary winding. There is an alternating current flowing in the primary winding, and a magnetic potential is established. Under the action of the magnetic potential, an alternating main magnetic flux is generated in the iron core.
Electrical silicon steel sheet is commonly known as silicon steel sheet or silicon steel sheet. As the name suggests, it is electrical silicon steel with a silicon content as high as 0.8% - 4.8%, which is made by hot and cold rolling. Generally, the thickness is less than 1mm, so it is called thin sheet. In a broad sense, silicon steel sheet belongs to the sheet category and forms an independent branch due to its special use. Electrical silicon steel sheet has excellent electromagnetic properties and is an important magnetic material indispensable in the power, telecommunications and instrument industries.