Voltage Regulation (V.R.):

• The voltage regulation is defined as “the rise in voltage at the terminals, when the load is reduced from full load rated value to zero, speed and field current remaining constant”.
• With the change in load, there is a change in the terminal voltage of an alternator or synchronous generator. 
• The magnitude of this change not only depends on the load but
• also on the load power factor.
• It is also defined as “the rise in voltage when full load is removed divided by the rated terminal voltage when speed and field excitation remains the same.” 

It is given by the formula,

V.R. = ((V_NL  - V_FL ) / (V_FL )) × 100%

Where, 

V_NL : Voltage at no load

V_FL : Voltage at full load