regulation of alternator

8/3/2019 Regulation of Alternator

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10.REGULATION OF ALTERNATOR


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AIM:To find the regulation of a three phase alternator by EMF method .

APPARATUS REQUIRED:

S.No Apparatus Required Range Type Quantity

1. Voltmeter (0-300)V MI 1 No

2. Ammeter (0-10) A MI 1 No

3. Ammeter (0-2)A MI 1 No

4. Rheostat 360 / 1.2 A WW 3 No

5. Tachometer 0-10000rpm Digital 1 No

6. T.P.S.T Switch - - 1 No

7.3-Phase VariableInductive Load

415V,10A Variable 1 No

THEORY (EMF METHOD):

An alternator can be represented by its equivalent circuit as shown in Fig. Terminals a-a are shorted

while the alternator is exited with some field current I f , and is generating a voltage E. The short circuit will

be limited by its synchronous impendence Zs and will be given by Isc = E/Zs amps.

From this equation voltage and Isc is short circuit current (Per phase) is plotted against excitation, the

curve obtained is known as open circuit characteristic (O.C.C). Similarly, when the alternator is running at

synchronous speed and its terminals are shorted, the curve, short circuit current -Vs Excitation can be

obtained. This is known as short circuit characteristic. Two curves are shown in Fig.

Due to saturation, open circuit characteristic is non-linear, when is no saturation in the other case as

total flux in the magnetic circuit is very small when alternator is short-circuited. Hence, S.C.C. is a straight

line. For the rated excitation, if O.C. Voltage is represented by OC and the S.C.

Current is represented by OB, then Za = OC/OB ohms per phase.If armature resistance, per phase is Ra Synchronous reactance is given by

Xs = ./22 phohmsRZaS

After finding the value of armature resistance and synchronous reactance, the pharos diagram can be

draw for different value of load currents and power factor. One such diagram is shown in fig. The p.f. is

taken as login.

Regulation fro this load at p.f. Cos lagging and the terminal voltage V is obtained.

% regulation = %100

V

VE

Similarly regulation for other loads can be predicted.


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TABULAR COLUMN:

Open Circuit Test

Sl.No

Field Current

(If)

Terminal

Voltage/phase

1.

2.

3.

4.

5.

6.

7.

8.

9.

Short Circuit Test

S.No If Isc

1

2

3

4

5

6

78

9

10

PROCEDURE (SYNCHRONOUS IMPEDANCE METHOD):

1. Connect as shown in Fig. (a)2. Set potential dives to Zero output position and field resistance of the motor to a maximum value.3. Switch on the d.c supply and start the d.c motor.4. Adjust motor speed to synchronous speed with the help of field rheostat.5. Note the voltmeter reading. Increase the excitation in steps and note the corresponding voltage

readings. Take reading up to 10% above the rated voltage.6. Switch off d.c supply and connect as shown in fig. (b)


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7. Start the motor with its field rheostat in minimum resistance position and potential divided set to givezero output.

8. Adjust the speed of the motor to synchronous speed.9. Note ammeter reading for different values of excitation (field current). Take reading unto the rated

armature current.10.Measure the value of armature resistance of all three phases by an accurate ohm-meter, or battery,

voltmeter method11.Plot open circuit voltage and short circuit current against field and from this graph, calculate the

value of synchronous impedance for rated value of excitation.

Synchronous speed = 1500 r.p.m.

The experiment can be repeated for other phases to check that all phases have equal resistance. Draw opencircuit and short circuit characteristic as shown in fig. And found the value of short circuit current for ratedvalue of excitation for the same value of excitation, see the value of open circuit voltage. This is the ratedvoltage alternator at no load , from this.

SAMPLE CALCULATIONS:

ZS = VOC /ISC (at same field current)

Ra= 1.2*Rdc

Xs = 2a2s RZ ,

Ef2= ( Vt Cos + IaRa )

2 + ( Vt Sin + IaXa )2

For Power Factor, Cos =__________________________________

Eflead = ( Vt Cos + IaRa )2

+ ( Vt Sin + IaXa )2

Eflag = ( Vt Cos + IaRa )2 + ( Vt Sin + IaXa )

2

% regulation lead = Ef lead -- Vt X 100 =Vt

% regulation lag = Ef lag -- Vt X 100 =Vt

PRECAUTIONS:

1. Connect the circuit as per circuit diagram2. Avoid loose and wrong connections3. Note down the readings without any parallax error.

RESULT:


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VIVA QUESTIONS

1 Define regulation of an alternator?2 Can a DC generator be converted into an alternator/3 How a direct coupled excitation arranged in an alternator?4 Which method gives better regulation in alternation?5 On synchronous impedance method whether the armature reaction drop is considered or not?

regulation of alternator

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