The material used for the core in a transformer is selected on the basis of its magnetic permeability and its characteristic hysterisis loop. A material with low hysterisis loop area and high permeability need to be selected for higher efficiency of the transformer. Steel, silicon alloys have very narrow hysterisis loop. Silicon steel alloys has high permeability and low hysterisis losses, therefore these material are used for transformer core and armature core which are subjected to rapid reversal of magnetization