Laminations in Transformer Core and Motor Stator

Electric machines, especially AC machines such as transformers and alternators are exposed to alternating magnetic fields during operation. 

This alternating magnetic field causes the induction of eddy currents in the core of transformers and the stator of motors.  The eddy current creates a loss of energy in the form of heat loss and hysteresis loss.

In order to avoid this, the core of transformers and the stator of motors and generators are made of a set of laminated steel sheets. Silicon Steel is used.  This steel is cold rolled and has special grain orientation.  Each steel sheet is around .3 mm thick. 

The sheets are insulated on both sides and laid of top of one another.  This arrangement ensures that the eddy current is reduced as it cannot flow over a wide area of cross section.  The laminated surfaces need to be very clean.  Presence of foreign particles can cause laminar faults which lead to core damage.