Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
We have seen that neither of the two methods, M.M.F. method and E.M.F. method is capable of giving the reliable values of the voltage regulation. The error in the results of these methods is mainly due to the two reasons,
Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
This method is also called Potier method.
Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
This method of determining the regulation of an alternator is also called Ampere-turn method or Rothert's M.M.F. method.
Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
A low value of SCR indicates smaller air gap and poor regulation due to large IaXS
Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
Mathematically, SCR (short circuit ratio) = If for rated open circuit voltage / If for rated short circuit current
Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
The method is also called E.M.F. method of determining the regulation. The method requires following data to calculate the regulation.
Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
The synchronous impedance method has some short comings. Another method which is popularly used is ampere-turns method. But this method also has certain disadvantages.
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
Under the load condition, the terminal voltage of alternator is less than the induced e.m.f. Eph.
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
The above voltage equation is to be realised using phasor diagrams for various load power factor conditions.
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
The voltage available to the load is called terminal voltage.
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
As current Ia flows through the armature, there are two voltage drops across Ra and XL as Ia Ra and Ia XL respectively. Hence finally terminal voltage Vt is less than E’ by the amount equal to the drops across Ra and XL
Synchronous Generator or Alternators
Subject and UNIT: Electrical Machines II: UNIT I: b. Armature Reaction and Regulation of Alternators Engineering Electrical Machines - II
The sum of the fictitious armature reaction reactance accounted for considering armature reaction effect and the leakage reactance of the armature is called synchronous reactance of the alternator denoted as XS.