Eddy-Current Losses

As the armature rotates inside the field, it cuts the lines of flux at the similar time that the copper coils of wire which are wound on the armature cut the lines of flux.  Because the armature is made of iron, an EMF is induced in the iron that causes a current to flow. These circulating currents inside the iron core are known as eddy-currents.

To decrease eddy-currents, an armature and field cores are constructed from laminated (layered) steel sheets. A laminated sheet is insulated from each other so in which current cannot flow from one sheet to the other.