1.EMF and MMF method.docx

8/14/2019 1.EMF and MMF method.docx

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Fuse rating

= 125% of rated current==

Name plate details of induction motor

Rated power =Rated current =

Rated voltage =Rated speed =

Circuit diagram for regulation of an alternator by EMF and MMF methods



EXP. NO:

DATE:

AIM:To determine the voltage regulation of 3-phase alternator by using EMF and MMF method.

APPARATUS REQUIRED:

FORMULAE:

EMF Method:

1. Armature resistance, Rac = 1.6 × Rdc Ω

2. Synchronous impedance, Zs =

(for same If value) Ω

3. Synchronous reactance, Xs = √

Ω

4. Eph = √ (Vph cosФ + Iasc Rac) 2 + (Vph sinФ + Iasc Xs) 2 (Volt)

Where,(+) for lagging power factor

(-) for leading power factor

5. % Regulation =

x 100

SL.NO

NAME OF THE APPARATUS RANGE TYPE QUANTITY

1 Voltmeter (0-600V) MI 1

2 Ammeter (0-5A) MI 1

3 Ammeter (0-2A) MI 1

4 Rheostat 350 Ω / 1.5A Wire wound 2

5 Tachometer (0-3000rpm) Digital 1

6 Connecting wires As required

REGULATION OF AN ALTERNATOR BY EMF AND MMF METHODS



Tabulation:

Open circuit test

Short circuit test

SL. NO Short circuit current, Isc (A) Field current, If (A)

1

SL. NOOpen circuit line voltage,

VL (V)

Field current, If Open circuit phase voltage,

Vph(V)1

2

3

4

5

6



MMF Method:

1. Vph =

(Volts)

2. IL = Iph =

(Volts)

3. Calculating open circuit voltage = Vph + Iph Ra cosФ (Volts)

4. Field current corresponding to short circuit current = F AR (Amps)

5. FR = √ (Fo ± F AR sinФ + Iasc Xs) 2 + (F AR sinФ) 2

Where (+) for lagging power factor

(-) for leading power factor

6. % Regulation = x 100

PROCEDURE:

OPEN CIRCUIT TEST:

1. Give the connections as per the circuit diagram.

2. Keep the alternator side TPST open till the completion of OC test.

3. The motor side DPST switch is closed and the set is started with the help of the 3-point starter.

4. The set is run at various speeds by adjusting the field rheostat of DC motor and the corresponding

voltage generated by the alternator is noted down by the voltmeter.

5. This step is repeated up to the rated voltage generated by the alternator.

6. By varying the alternator field rheostat, the voltage generated for different currents are noted and

tabulated.

SHORT CIRCUIT TEST:

1. Give the connections as per the circuit diagram.

2. The alternator terminals are short circuited by closing the TPST switch.

3. The DC supply is given to the motor by closing DPST switch and the motor starts to rotate.

4. The field rheostat of alternator varied up to rated current and the corresponding field current of

alternator noted down.

5. Now the supply of the set is switched off by opening both DPST switches.



Tabulation:

EMF Method:

cosФ Eph (Volts) % Regulation

Lag Lead Lag Lead

0.2

0.4

0.6

0.8

1

MMF Method:

cosФ Fo F AR Eph (Volts) % Regulation

Lag Lead Lag Lead

0.2

0.4

0.6

0.8

1



GRAPH:

A) OC and SC characteristics curves are drawn as

1. Field current Vs SC current

2. Field current Vs OC voltage

B) The regulation curve is drawn between power factor and regulation.

1. Power factor Vs Regulation



MODEL GRAPH:

OC and SC Characteristics curve

Regulation curve



Model calculation for EMF method



Model calculation for MMF method



RESULT:

Thus the voltage regulation of an 3 phase alternator determined by EMF and MMF method.

1.EMF and MMF method.docx

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