Hysteresis Losses

Hysteresis losses occur whenever the armature rotates in a magnetic field.  A magnetic domain of the armature is held in alignment along with the field in varying numbers which is dependent upon field strength.  A magnetic domain rotates, within respect to the particles not held in alignment, through one complete turn during every rotation of the armature.  That rotation of magnetic domains in the iron causes heat and friction.  The heat generated through this friction is known as magnetic hysteresis loss.

To decrease hysteresis losses, most DC armatures are constructed of heat-treated silicon steel that has an inherently low hysteresis loss.  Laminations are heated to a dull red and then permitted to cool after the heat-treated silicon steel is established to the desired shape.  This procedure, known as annealing, decreases hysteresis losses to an extremely low value.