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Why transformers use silicon steel sheets as cores

2019-09-12 10:00:16

The common transformer cores are usually made of silicon steel sheets. Silicon steel is a kind of silicon-containing steel. Its silicon content is 0.8-4.8%. The core of the transformer is made of silicon steel because it is a magnetic material with strong magnetic conductivity. In the electrified coil, it can produce larger magnetic induction intensity, and then reduce the volume of the transformer.

As we know, the actual transformer always operates in the AC state, and the power loss not only occurs in the resistance of the coil, but also in the iron core under the alternating current magnetization. Usually the power loss in iron core is called "iron loss", which is caused by two reasons, one is "hysteresis loss" and the other is "eddy current loss".

Hysteresis loss is a kind of iron loss caused by hysteresis in the process of magnetization of iron core. The magnitude of hysteresis loss is proportional to the magnitude of the area surrounded by the material hysteresis loop. The magnetic hysteresis loop of silicon steel is narrow. The core hysteresis loss of transformer made of silicon steel is small, which can greatly reduce its heating degree.

Since silicon steel has the above advantages, why not use the whole block of silicon steel as the core of the cylinder, but also process it into sheets?

This is because the sheet core can reduce another kind of iron loss - "eddy current loss". When a transformer works, there is alternating current in the coil, and the flux produced by it is of course alternating. This variable flux generates an induced current in the core. The induced current generated in the iron core circulates in a plane perpendicular to the direction of magnetic flux, so it is called eddy current. The same eddy current loss causes the core to heat up. In order to reduce the eddy current loss, the core of transformer is made up of insulated silicon steel sheets, so that the eddy current in the narrow loop can increase the resistance of the eddy current circuit through a smaller cross section. Together, silicon in silicon steel increases the resistivity of the material and also plays a role in reducing the eddy current.