Voltage Regulation of an Alternator


Voltage Regulation of an Alternator

the voltage regulation of an alternator is defined as the change in its terminal voltage when full load is removed, keeping field excitation and speed constant, divided by the rated terminal voltage.

  • The value of the regulation not only depends on the load current but also on the power factor of the load.
  • For lagging and unity p.f. conditions there is always drop in the terminal voltage hence regulation values are always positive.
  • While for leading capacitive load conditions, the terminal voltage increases as load current increases. Hence regulation is negative in such cases.
  • The relationship between load current and the terminal voltage is called load characteristics of an alternator.

Determination of Voltage Regulation

  1. In the case of small machines, the regulation may be found by direct loading.
  • The alternator is driven at synchronous speed and the terminal voltage is adjusted to its rated value V.
  • The load is varied until the wattmeter and ammeter (connected for the purpose) indicate the rated values at desired p.f. Then the entire load is thrown off while the speed and field excitation are kept constant.
  • The open-circuit or no-load voltage E0 is read.

             V = Rated terminal voltage
            E0= No load induced e.m.f.

2. In the case of large machines, the cost of finding the regulation by direct loading becomes                                prohibitive.

  • Hence, other indirect methods are used as discussed below.
  • It will be found that all these methods differ chiefly in the way the no-load voltage E0 is found in each case.

Methods OF Determining voltage regulation

  1. Synchronous Impedance or E.M.F. Method.
  2. The Ampere-turn or M.M.F. Method.
  3. Zero Power Factor or Potier Method.
  4. A.S.A. method


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