Voltage regulation of synchronous generator [Alternator] using Direct loading method

The Regulation of a synchronous generator[Alternator] can be determined by various methods.In case of small capacity alternators , direct loading test used to  determine regulation ,while in case of large capacity Alternators Synchronous Impedance method is used.The Synchronous Impedance method has some disadvantages.Another method which is popularly used is ampere-turns method. But this method also have some disadvantages .The disadvantages of above both methods are overcome by another method called Zero Power Factor method.Another important method which gives accurate results is Blondel's two Reaction theory.

Here are some methods below used to determine voltage regulation of an alternator.

1.Direct Loading method

2.Synchronous Impedance method or E.M.F method

3.Ampere-turns method or M.M.F method

4.Zero Power Factor method or Potier triangle method

5.A.S.A modified form of M.M.F method

6.Two Reaction Theory[Blondel's Theory]

1.Voltage Regulation of alternator by Direct Loading method:


The below figure shown is three phase alternator on which Direct Loading test is conducted.A three phase load is connected to star connected armature with the help of TPST [Triple Pole Single Throw] switch.By using a external D.C supply ,the field winding is excited.A rheostat is connected in series with the field winding,to control  the flux i.e. current in the field winding.In the below figure ,the prime mover shown is used to drive the alternator at Synchronous speed.
Voltage Regulation of Alternator
Voltage Regulation of Alternator

Procedure:

 By using prime mover , the alternator is driven at Synchronous speed[Ns].

                           Now Eph  is proportional to phi

After giving the D.C supply to the field winding,the field current is adjusted in order to adjust flux so that rated voltage appears across the terminals.This is 
observed on a voltmeter connected across the terminals.Next load is connected by using the TPST switch.The load is increased in steps so that ammeter reads rated  current.This is the full condition of the alternator.Again adjust the voltage to its rated value by field excitation using the rheostat. Then disconnect the entire load by opening TPST switch,keeping the speed and field excitation constant.As load is disconnected there will be no armature current and associated drops.Now the voltmeter shows a reading which is the actual value of internally induced e.m.f called no load terminal voltage.Next convert both the readings into phase values.The voltage on full load is Vph and voltage when load is thrown off is Eph. So voltage regulation of alternator or synchronous generator can be determined by using the formula
                   
                  %Reg = [Eph - Vph]/Vph  * 100

The value of regulation of alternator or synchronous generator obtained by this method is accurate because a particular load at required power factor is actually connected to note down the readings. 

Also Read:

1.Voltage Regulation Of Synchronous Generator[Alternator] Using Sychronous Impedance Method or EMF Method

2.Principle and Working of Synchronous Generator[Alternator]

3.Difference between Salient pole and Cylindrical pole[Non-Salient pole] rotors used in Synchronous Generator 

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