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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 %
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METHODSEMF MethodMMF MethodZPF MethodASA Method
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EMF METHOD(OPEN CIRCUIT AND SHORT CIRCUIT TESTS)
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PROCEDUREOPEN 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.
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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.
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OCC and SCC Curves
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CALCULATION OF REGULATIONArmature resistance, Ra = 1.6 Rdc in Ohms
where, Rdc = Resistance in DC supply in Ohms
Synchronous Impedance, Zs = E0/ Isc in Ohms
where, 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
where, Iasc = Rated short circuit armature current in Amps
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CALCULATION OF REGULATIONOpen 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 %
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% REGULATION Vs POWER FACTOR
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MMF METHOD (OPEN CIRCUIT AND SHORT CIRCUIT
TESTS)
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PROCEDUREOPEN 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.
![Page 12: 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](https://reader036.vdocuments.net/reader036/viewer/2022081504/56649e465503460f94b3b4a3/html5/thumbnails/12.jpg)
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.
![Page 13: 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](https://reader036.vdocuments.net/reader036/viewer/2022081504/56649e465503460f94b3b4a3/html5/thumbnails/13.jpg)
OCC and SCC Curves
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CALCULATION OF REGULATIONFor lagging power factor Ifr
= [(If12+If2
2 - 2If1If2Cos (90+Φ)] 1/2 in AmpsFor leading power factor Ifr
= [(If12+If2
2 - 2If1If2Cos (90-Φ)] 1/2 in Amps
where,If1 = Field current required to give open circuit emf, E in
AmpsIf2 =Field current corresponding to short circuit current in
Amps E = [ Vph + IaRaCos ] on open circuit in Volts
% Regulation = (E0 – Vrated) / Vrated × 100 %
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% REGULATION Vs POWER FACTOR