Yoke in an electrical machine

The outer frame of an electrical machine either motor or a generator is called yoke.

The yoke provide two functions. First is providing the mechanical support and protection cover to the machine assembly. The second is it provides low reluctance path to carry the magnetic flux. The below figure show the diagram of an electrical machine with the location of Yoke, poles and rotor.

Electrical Machine diagram showing Yoke and the Poles

Yoke is generally made of cast steel or rolled steel for large electrical machines whereas for small machines cast iron may be used.