#### When an alternator is loaded the armature terminal voltage will be less than the emf induced in the armature. This is because due to the effect of armature reaction there will be a drop in induced emf. Suppose if the load is disconnected ( open-circuited ) armature current becomes zero, hence no armature flux and armature reaction effect. Therefore the terminal voltage will be equal to induced emf at no-load conditions.

The voltage regulation of an alternator or synchronous generator is defined as the changes in terminal voltage on the application of load at a constant driving speed and field excitation. It is expressed in per-unit or percentage of variation in armature terminal voltage from no-load to full-load divided by the rated terminal voltage.

#### Where,- E
_{o} = No-load induced emf - V = Rated terminal voltage

The variation in terminal voltage also depends upon the magnitude and power factor of the load. If the load connected is inductive or resistive type. For lagging and unity power factor conditions the effect of armature reaction i.e., the effect of armature flux on main flux will be demagnetizing and cross-magnetsing effects respectively. This makes the terminal voltage drop hence regulation will be always positive. In the case of capacitive loads ( leading p.f. ), the effect of armature reaction will be a magnetizing effect i.e., armature flux add up with main flux. This causes to increase in terminal voltage as the load current increases and the regulation becomes negative.

_{o}= No-load induced emf