The voltage regulation of a synchronous generator is the rise in voltage at the terminals when the load is reduced from full load to zero, speed and field current remaining constant.

the voltage regulation depends upon the power factor of the load . for unity and lagging power factors, there is always voltage drop with increase of load , but for certain leading power, the full load voltage regulation is zero . in this case, the terminal voltage is the same for both full load and no load conditions. At the leading power factors, the voltage rises with the increase of load , and the regulation is negative.

Determination of Voltage Regulation:
The following methods are used to determine the voltage regulation of smooth cylindrical rotor type alternators.
  • Direct Load test
  • Indirect methods
Direct Load test :
the alternator is run at synchronous speed and its terminal voltage is adjusted to its rated value  V. the load is varied until the ammeter and wattmeter indicate the rated values at the given power factor. then the load is removed and the speed and field excitation are kept constant. the open circuit and no load voltage Ea is recorded. the voltage regulation found from percentage voltage regulation.the method of direct loading is suitable only from small alternators of power rating less than  kVA. 

Indirect methods:
For Large alternators, the three indirect methods which are used to predetermine the voltage regulation smooth cylindrical type alternators are as following.
  1.  Synchronous impedance method or EMF method
  2.  Ampere turn method or EMF method
  3.  Zero power factor method or Potier method


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