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 %

METHODS EMF Method MMF Method ZPF Method ASA Method

EMF METHOD (OPEN CIRCUIT AND SHORT CIRCUIT TESTS)

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.  

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.

OCC and SCC Curves

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

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 %

% REGULATION Vs POWER FACTOR

MMF METHOD (OPEN CIRCUIT AND SHORT CIRCUIT TESTS)

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.  

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.

OCC and SCC Curves

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 %

% REGULATION Vs POWER FACTOR