1. VOLTAGE REGULATION OF THREE PHASE ALTERNATOR
The voltage regulation of an alternator is defined as the rise in voltage when full load is removed divided by the rated terminal voltage. % Regulation = (E0 – Vrated) / Vrated × 100 %

2. METHODS
EMF Method
MMF Method
ZPF Method
ASA Method

3. EMF METHOD (OPEN CIRCUIT AND SHORT CIRCUIT TESTS)

4. PROCEDURE OPEN CIRCUIT TEST Initially TPST Switch is kept open.
Supply is given by closing the DPST Switch in the Motor side.
Using the DC three point starter, start the motor.
The field rheostat of motor is adjusted to run the motor at rated speed and note down the corresponding alternator field current.
Increase the field current in steps by varying the resistance of the alternator field and note down the corresponding open circuit voltage.

5. PROCEDURE SHORT CIRCUIT TEST
Supply is given by closing the DPST Switch in the motor side.
Using the DC three point starter, start the motor.
The field rheostat of motor is adjusted to run the motor at rated speed.
The TPST Switch is closed.
The alternator field rheostat is adjusted for the rated short circuit armature current and note down the corresponding field current.

6. OCC and SCC Curves

7. CALCULATION OF REGULATION
Armature resistance, Ra = 1.6 Rdc in Ohms
where,
Rdc = Resistance in DC supply in Ohms
Synchronous Impedance, Zs = E0/ Isc in Ohms
E0= Open circuit voltage in Volts
Isc = Short circuit current in Amps
Synchronous Reactance, Xs = (Zs 2 – Ra 2 )^1/2 in Ohms
Open circuit voltage (For lagging power factor), E0
E0 = [(Vrated cos Φ + Iasc Ra )2 + ( Vrated sin Φ + Iasc Xs )2 ]1/2 in Volts
Iasc = Rated short circuit armature current in Amps

8. CALCULATION OF REGULATION
Open circuit voltage (For leading power factor), E0
E0 = [(Vrated cos Φ + Iasc Ra )2 + ( Vrated sin Φ - Iasc Xs )2 ]1/2
in Volts
Open circuit voltage (Unity power factor), E0
E0 = [(Vrated + Iasc Ra )2 + ( Iasc Xs )2 ]1/2 in Volts
% Regulation = (E0 – Vrated) / Vrated × 100 %

9. % REGULATION Vs POWER FACTOR

10. MMF METHOD (OPEN CIRCUIT AND SHORT CIRCUIT TESTS)

11. PROCEDURE OPEN CIRCUIT TEST Initially TPST Switch is kept open.
Supply is given by closing the DPST Switch in the Motor side.
Using the DC three point starter, start the motor.
The field rheostat of motor is adjusted to run the motor at rated speed and note down the corresponding alternator field current.
Increase the field current in steps by varying the resistance of the alternator field and note down the corresponding open circuit voltage.

12. PROCEDURE SHORT CIRCUIT TEST
Supply is given by closing the DPST Switch in the motor side.
Using the DC three point starter, start the motor.
The field rheostat of motor is adjusted to run the motor at rated speed.
The TPST Switch is closed.
The alternator field rheostat is adjusted for the rated short circuit armature current and note down the corresponding field current.

13. OCC and SCC Curves

14. CALCULATION OF REGULATION
For lagging power factor
Ifr = [(If12+If22 - 2If1If2Cos (90+Φ)] 1/2 in Amps
For leading power factor
Ifr = [(If12+If22 - 2If1If2Cos (90-Φ)] 1/2 in Amps
where,
If1 = Field current required to give open circuit emf, E in Amps
If2 =Field current corresponding to short circuit current in Amps
E = [ Vph + IaRaCos  ] on open circuit in Volts
% Regulation = (E0 – Vrated) / Vrated × 100 %

15. % REGULATION Vs POWER FACTOR