When we were repairing the transformer. After opening the cover, it was found that the windings immersed in the oil were placed on the iron cores stacked by many silicon steel plates. What is the reason? To answer this question, we must first talk about the basic principles of transformers. The transformer is based on the principle of electromagnetic induction. There is no magnetic connection between the primary and secondary windings of the Han winding or three winding transformer. If the transformer does not have a core, theoretically there is also a transformer effect, but because of the large magnetic reluctance of air. Magnetic leakage is very serious, so it needs a large excitation current to climb the transformer with a core. The magnetic resistance of the dry core is small. When the core is passed through, a strong magnetic field can be obtained, thereby enhancing the power of the primary and secondary windings. Magnetic induction also reduces the excitation current accordingly. If the transformer is not equipped with iron cores, it is not acceptable that the transformer is not loaded with iron cores because the magnetic flux leakage current will inevitably increase. 
This news source China iron core trading network
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