3-3
Figure 3-1.—Types of ac generators.
ROTATING-FIELD ALTERNATORS
The rotating-field alternator has a stationary armature winding and a rotating-field winding as shown
in figure 3-1, view B The advantage of having a stationary armature winding is that the generated voltage
can be connected directly to the load.
A rotating armature requires slip rings and brushes to conduct the current from the armature to the
load. The armature, brushes, and slip rings are difficult to insulate, and arc-overs and short circuits can
result at high voltages. For this reason, high-voltage alternators are usually of the rotating-field type.
Since the voltage applied to the rotating field is low voltage dc, the problem of high voltage arc-over at
the slip rings does not exist.
The stationary armature, or stator, of this type of alternator holds the windings that are cut by the
rotating magnetic field. The voltage generated in the armature as a result of this cutting action is the ac
power that will be applied to the load.
