The role of transformer core

Transformer is a kind of equipment widely used in power system. Its main function is to increase or decrease voltage through the principle of electromagnetic induction. In actual operation, transformer is always in AC state. Power loss occurs not only in the resistance of winding, but also in the iron core under the magnetization of alternating current. The power loss in the iron core is usually called "iron loss". Iron loss is mainly caused by two factors: one is "hysteresis loss" and the other is "eddy current loss".

 **Hysteresis loss** refers to the loss caused by hysteresis during the magnetization process of the iron core. The size of this loss is proportional to the area surrounded by the hysteresis loop of the material. The hysteresis loop of silicon steel is relatively small, so the hysteresis loss of the Transformer Core made of silicon steel is low, which effectively reduces the heating of the iron core.

 However, since silicon steel has the above advantages, why not directly use a whole piece of silicon steel as the core, but process it into sheets?

 This is because the sheet iron core can effectively reduce another type of iron loss - "eddy current loss". When the transformer is working, the alternating current flowing in the coil will generate an alternating magnetic flux, and this changing magnetic flux will generate an induced current in the iron core. The induced current circulates in a plane perpendicular to the direction of the magnetic flux, so it is called eddy current. Eddy current loss also causes the iron core to heat up. In order to reduce eddy current loss, the iron core of the transformer is usually made of insulated silicon steel sheets stacked together, so that the eddy current can flow in a narrow loop, thereby increasing the resistance on the eddy current path through a smaller cross-section. At the same time, the silicon element in silicon steel also increases the resistivity of the material, thereby further reducing the generation of eddy currents.

 When making transformer cores, cold-rolled silicon steel sheets with a thickness of 0.35 mm are usually used. According to the required core size, they are cut into long sheets and then overlapped into a "日" shape or a "口" shape. Theoretically, in order to reduce eddy current losses, the thinner the silicon steel sheet should be, the narrower the spliced ​​strips should be, which can more effectively reduce eddy current losses and temperature rise, while saving silicon steel sheet materials. However, when actually making silicon steel sheet cores, it is not simply based on the above favorable factors, because too thin sheets will increase working hours and may reduce the cross-section of the core. Therefore, when choosing silicon steel sheets to make transformer cores, it is necessary to comprehensively consider the specific situation, weigh the pros and cons, and choose the appropriate size.

 The working principle of the transformer is based on electromagnetic induction. Two windings are wound on the closed core column: one is the primary winding and the other is the secondary winding. When the primary winding is connected to the AC power supply voltage, the alternating current flowing in the primary winding will establish a magnetic potential, which will then generate an alternating main magnetic flux in the core. The main magnetic flux passes through the primary and secondary windings at the same time and closes. According to the principle of electromagnetic induction, the change of the main magnetic flux will generate induced electromotive force in the primary and secondary windings respectively. As for why the transformer can achieve voltage step-up and voltage step-down, this needs to be explained with the help of Lenz's law. The magnetic flux generated by the induced current will hinder the change of the primary magnetic flux. When the primary magnetic flux increases, the direction of the magnetic flux generated by the induced current is opposite to that of the primary magnetic flux. Therefore, the induced magnetic flux generated by the secondary winding is opposite to the main magnetic flux of the primary winding, resulting in a lower alternating voltage in the secondary winding. Therefore, the core acts as the magnetic circuit part in the transformer, and the winding constitutes the circuit part.

 In summary, the design and material selection of transformer core are crucial to improving the efficiency of transformer and reducing energy loss. Through reasonable design and material application, the performance of transformer can be effectively improved to ensure its stable operation in the power system.