Advantages of Stationary Armature-Rotating Field Alternator

Alternators are generally high-current, high-voltage machines, and virtually every commercial design places the armature winding on the STATIONARY stator while the field magnet ROTATES on the rotor -- the opposite arrangement to a simple DC generator or motor -- for four practical advantages. First, the (large) current can be drawn directly from fixed terminals on the stator without needing any brush contact at all for the high-current, high-voltage armature circuit. Second, the insulation of a stationary armature winding is considerably easier to arrange and maintain than insulating a winding that is itself spinning. Third, the number of sliding (brush/slip-ring) contacts needed is reduced, and moreover those contacts are used only for the comparatively small, low-voltage DC excitation source feeding the field winding, not for the large armature current. Fourth, because the armature winding does not r …