Purpose:

The main purpose of a voltage regulator is to manage the output voltage of a generator at a desired value.  As load on an AC generator modifies, the voltage will also tend to change.  The major reason for this change in voltage is the change within the voltage drop across the armature winding caused through a change in load current.  Within an AC generator, there is an IR drop and an IX_L  drop caused through the AC current flowing by the resistance and inductance of the windings.  An IR drop is dependent on the amount of the load modification only. The IX_L drop is dependent on not just the load change, other than also the power factor of the circuit.  Thus, the output voltage of an AC generator varies along with both changes in load that is current and changes in power factor. Since  of  modifications in voltage because of  changes  in  load  and  changes  in  power  factor and  AC generators need a few auxiliary means of regulating output voltage.