Why silicon steel is used in electrical machines?

Why silicon steel is used in electrical machines?

It has a high silicon content of about 3.2 mass %, which increases the electrical resistivity of iron and, therefore, reduces eddy current losses. Grain-oriented silicon steel that is used for non-rotating applications, i.e. transformers, is characterised by a strong preferred crystallographic orientation. In iron the easiest directions of magnetisation are the <001> crystal directions. In grain-oriented silicon steel the Goss orientation, i.e. the {110}<001> orientation , is technologically realised to minimise magnetic losses in electrical transformers.

Grain-oriented silicon steel (Fe-Si steel; transformer steel; electrical steel) is a soft magnetic polycrystalline metallic alloy that is used as core material in electrical transformer cores and electrical motors.

In the power industry electrical voltage is almost always AC and has a rather low frequency, namely, 50-60 Hz. At these frequencies electrical eddy currents are generated in the transformer core. Alloying the Fe with Si has a large marked effect on the electric resistivity of the material, with an increase of a factor of 4 for 3wt%Si. Silicon also has the effect of reducing the magnetostriction (i.e. length change on magnetisation) and the magnetocrystalline anisotropy. In addition, the material is used in the form of laminations, typically 0.3 to 0.7mm thick. The addition of too much silicon makes the material extremely brittle and difficult to produce, giving a practical limitation of 4wt% to the amount of Si that can be added. Recently, a technique has been developed to produce laminations with >6wt% Si, by a SiCl4 chemical vapour deposition treatment to enrich the laminations with Si after forming the laminations. Typically most commercially available electrical steels will contain between 3 and 4 wt% Si.