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AC MACHINES LAB 2 (6039)

DEPARTMENT OF ELECTRICAL & ELECTRONICS

ENGINEERING

MA'DIN POLYTECHNIC COLLEGE

TOPICS PAGE NO.

LOAD TEST ON THREE PHASE ALTERNATOR 01

REGULATION OF ALTERNATOR BY EMF METHOD 04

REGULATION OF ALTERNATOR BY MMF METHOD 10

OPEN CIRCUIT CHARACTERISTICS OF ALTERNATOR 14

AN ALTERNATOR AT DIFFERENT SPEED 17

SYNCHRONISATION OF ALTERNATOR 20

V AND INVERTED V CURVE OF SYNCHRONOUS MOTOR 23

SINGLE PHASE INDUCTION MOTOR 26


A C MACHINERY LAB 2 DEPARTMENT OF EEE

MA’DIN Polytechnic college 1

EXPT NO:

DATE:

LOAD TEST ON THREE PHASE ALTERNATOR

AIM:

Conduct load test on three phase alternator and determine the regulation of the alternator.

CIRCUIT DIAGRAM:

APPARATUS REQUIRED:

SI NO APPARATUS REQUIRED TYPE RANGE

QUANTITY




MACHINE DETAILS

THEORY

The most commonly used machine for generation of electrical power for commercial purpose is the synchronous

generator or alternator. An alternator works as a generator when its rotor carrying the field system is rotated by a prime-mover

which in this case is DC shunt motor. The terminal voltage of an alternator changes with load.

Alternators are by far the most important source of electric energy. Alternators generate an AC voltage

whose frequency depends entirely upon the speed of rotation. The generated voltage value depends upon the

speed, the dc field excitation and the power factor of the load

Load test of an alternator provides the information about the regulation. It is performed by driving the

alternator at its rated speed and increase the field excitation till the armature voltage reaches to its rated value.

Increase the load on alternator terminals during this process alternator armature current will increase, terminal

voltage will vary according to the type of the load. By observing the input and output of an alternator at each

load we can calculate the corresponding regulation.

REGULATION=𝐸0−𝑉

𝑉X100%

PROCEDURE

1. Connect the circuit as per the circuit diagram.

2. Maintain the motor field rheostat in in minimum position and generator field rheostat in maximum

position.

3. Switch on the supply and adjust the motor to rated speed by varying motor field rheostat

4. Vary the generator field rheostat to get the rated voltage at alternator terminal.

5. Adjust the load for different load current upto the rated load current of the alternator.

6. Tabulate the readings.

7. Calculate the efficiency and regulation of the alternator.

8. Terminate the work by doing the opposite of the above steps.

TABULATION:

SL NO VOLT METER READING

(VOLT)

AMMETER READING( AMPS) REGULATION %




SAMPLE CALCULATION:

E0= VOLT

V= VOLT

%REGULATION=𝐸0−𝑉

𝑉X100%

RESULT:




EXPT NO:

DATE:

REGULATION OF ALTERNATOR BY EMF METHOD

AIM :

To predetermine the percentage regulation of the given alternator by EMF (Synchronous Impedance Method).

CIRCUIT DIAGRAM:

SHORT CIRCUIT TEST:




OPEN CIRCUIT TEST:

ARMATURE RESISTANCE MEASUREMENT:




APPARATUS REQUIRED:


QUANTITY

NAME PLATE DETAILS :

THEORY:

EMF method, This method is also known as synchronous impedance method.Here the magnetic circuit is

assumed to be unsaturated. In this method the MMFs (fluxes) produced by rotor and stator are replaced by their

equivalent emf, and hence called emf method.To predetermine the regulation by this method the

following information is to be determined.Armature resistance/phase of the alternator, open circuit and short

circuit characteristics of the alternator.Here we discussed Voltage Regulation of Synchronous Generator

[Alternator] by EMF Method or Synchronous Impedance Method.this is better method than direct loading but

not best methods to find out voltage regulation.

To perform voltage regulation by emf method we need to calculate the following data.

1.Armature Resistance per phase [Ra]

2.Open Circuit characteristics which is a graph between open circuit voltage [Vo.c.] and field current.

3.Short circuit characteristics which is a graph between short circuit current [Is.c.] and field current.

FORMULA USED:

EMF Method :

Re = 1.5* Rs

Where,

Rs - DC resistance and

Re - Equivalent AC resistance

E1/I1 Where

E1 = OC voltage




I1 = SC voltage

Zs = E1(open circuit voltage) / I1(short circuit current)

Xs = (Zs2 – Re

2)1/2

Eo = [(Vcos + IRe)

2 + (Vsin (+ or -) IXs)

2]

1/2

Where,

‘+’ sign for lagging Power Factor

‘-‘ sign for leading Power Factor

% Regulation (up) = [(Eo – V)/V] * 100

PROCEDURE:

OC Test:

1.Connections are made as per the circuit diagram is obtained.

2.The supply is obtained from control panel.

3.Observing the precautions, DPST switch on motor side is closed.

4.Using 3-point starter, the DC motor is started.

5.Varying the field rheostat of DC shunt motor, it is set to run at rated speed as per name plate detail.

6.DPST switch in alternator field circuit is closed.

7.Keeping the TPST switch of alternator side open, the field current is varied using the alternator potential

divider. For various values of alternator field current (If), the generated AC line voltage (EOL) is noted down and

the readings are tabulated.(This should be done upto125% of rated voltage).

BLOCKED ROTOR TEST :

1.TPST switch, on alternator side is closed.

2.By slowly increasing potential divider from minimum potential position, the values of If and corresponding Isc

values are noted till rated current flows through the alternator.

3.The readings are tabulated.

4.Potential divider is adjusted to original position. [minimum potential position] and

field rheostat on motor side is s\adjusted to minimum resistance position.




5.DPST and TPST switches are opened.

6.The supply is switched off.

SAMPLE GRAPH:

TABULATION:

OPEN CIRCUIT TEST:

If

(A)

V

(volt)

Vph

(volt)

SHORT CIRCUIT TEST :

If

(A)

V

(volt)




SI.NO Load factor

(X)

Power Factor

(Cos )

Lagging leading

E0 VOLT Regulation % E0 VOLT Regulation %

MODEL CALCULATION

EMF Method :

Re = 1.5 * ______ Ohm

Where,

Rs - DC resistance and

Re - Equivalent AC resistance

Zs = __(open cicuit voltage) / __(short circuit current)

Zs = E1(open circuit voltage) / I1(short circuit current)

Xs = (Zs2 – Re

2)1/2

Eo = [(Vcos + IRe)

2 + (Vsin (+ or -) IXs)

2]

1/2

Xs = (__2 – __

2)1/2

Eo = [(___*_____*____+ ___)2

+ (____*____ (+ or -) ____)2]

1/2

Where,

‘+’

sign for lagging Power Factor

‘-‘ sign for leading Power Factor


% Regulation (up) =[ (__ – __)/]*100




EXPT NO:

DATE:

REGULATION OF ALTERNATOR BY MMF METHOD

AIM :

To predetermine the percentage regulation of the given alternator by MMF (Ampere Turns Method), by conducting OC

and Short circuit test.

CIRCUI DIAGRAM:

SHORT CIRCUIT TEST:




OPEN CIRCUIT TEST:

APPARATUS REQUIRED:


QUANTITY

THEORY:

This method is also known as amp - turns method. In this method the all the emfs produced by rotor and

stator are replaced by their equivalent MMFs (fluxes), and hence called mmf method. In this method also it is

assumed that the magnetic circuit is unsaturated. In this method both the reactance drops are replaced by their




equivalent mmfs. Similar to emf method OC and SC characteristics are used for the determination of regulation

by mmf method. Using the details it is possible determine the regulation at different power factors.

FORMULA USED:


Eo - Voltage corresponding to If.

METHOD TO DRAW CURVE

C

C O

E0

V C

C S

Vo

lta

ge

If

90+

If2

If1

Field current

Steps: 1. By suitable tests plot OCC and SCC

2. From the OCC find the field current If1 to produce rated voltage, V.

3. From SCC find the magnitude of field current If2 to produce the required armature current.

4. Draw If2 at angle (90+Φ) from If1, where Φ is the phase angle of current from voltage. If current is leading, take the angle of If2 as (90-Φ).

5. Find the resultant field current, If and mark its magnitude on the field current axis.

6. From OCC. find the voltage corresponding to If, which will be E0.




TABULATION:

OPEN CIRCUIT TEST:

If

(A)

V

(volt)

Vph

(volt)

SHORT CIRCUIT TEST :

If

(A)

V

(volt)

SI.NO Load factor

(X)

Power Factor

(Cos )

Lagging leading

E0 VOLT Regulation % E0 VOLT Regulation %

RESULT:




EXPT NO:

DATE:

OPEN CIRCUIT CHARACTERISTICS OF ALTERNATER

AIM:

To run an alternator at rated speed and plot open circuit characteristics (OCC).

CIRCUI DIAGRAM:




APPARATUS REQUIRED:


QUANTITY

THEORY:

Open circuit characteristic (OCC) : The open circuit characteristic of an alternator is a curve of the armature

terminal voltage on open circuit as a function of field excitation when the machine is running at synchronous

speed.

The field current is gradually increase in steps, and the terminal voltage Et is measure at each step, The

excitation current may be increased to get 25% more than rated voltage of the alternator. A graph is plotted

between the open circuit test voltage Ep and field excitation current If.

PROCEDURE:

OC Test:








divider. For various values of alternator field current (If), the generated AC line voltage (EOL) is noted down and

the readings are tabulated.(This should be done upto125% of rated voltage).




SAMPLE GRAPH:

TABULATION:

OPEN CIRCUIT TEST:

If

(A)

V

(volt)

Vph

(volt)

RESULT:




EXPT NO:

DATE:

AN ALTERNATOR AT DIFFERENT SPEEDS

AIM:

To run an alternator at differ=rent speed with constant field current and measure the frequency and voltage in

each case.

CIRCUI DIAGRAM:




APPARATUS REQUIRED:


QUANTITY

THEORY:

The most commonly used machine for generation of electrical power for commercial purpose is the

synchronous generator or alternator. An alternator work as a generator when it is rotor carrying the field system

is rotated by a prime mover which in this case is DC shunt motor. The terminal voltage of an alternator changes

with load. Alternators are by far the most important source of electric energy. Alternator generates an AC

voltage whose frequency depends entirely up on the speed of rotation. The generated voltage value depends

upon the speed, the dc field excitation and the power factor of the load.

TABULATION:

SI NO SPEED (N) in RPM FIELD CURRENT

(AMPS)

VOLT METER

READING(VOLT)

FREQUENCY(Hz)

Frequency f = PN/120 unit Hz

Where N = speed in rpm

P= no of poles




PROCEDURE:








divider up to its rated value and keep it is a constant value.

8.Then vary the field rheostat of DC shunt motor, and measure the voltage and frequency of alternator.

RESULT:




EXPT NO:

DATE:

SYNCHRONISATION OF ALTERNATOR

AIM:

To synchronise a three phase alternator to supply main adopting dark lamp method.

CIRCUI DIAGRAM:

APPARATUS REQUIRED:


QUANTITY




THEORY:

The process of matching parameters such as voltage, frequency, phase angle, phase sequence and waveform of

alternator (generator) or other source with a healthy or running power system is called synchronization.

Generator cannot deliver power to electric power system unless its voltage, frequency and other parameters are exactly

matched with the network. Synchronization is accomplished by controlling the exciter current and the engine speed of the

generator.

Synchronization matches various parameters of one alternator (or generator) to another alternator or to the bus bar. The

process of synchronization is also called as paralleling of alternators

Dark lamp method

To synchronize the alternator with bus bar, the prime mover of the alternator is driven at speed close to the synchronous

speed decided by the bus bar frequency and number of poles of the alternator.

Now the field current of the alternater is increased till voltage across the machine terminals is equal to the bus bar voltage

(by observing the readings on voltmeters).

If lamps go ON and OFF concurrently , indicating that the phase sequence of alternator matches with bus bar. On the

other hand, if they ON and OFF one after another, it resembles the incorrect phase sequence.

By changing the connections of any two leads of alternator after shutting down the machine, the phase sequence can be

changed.

Depending on the frequency difference between alternator voltage and bus bar voltage, ON and OFF rate of these lamps

is decided. Hence, the rate of flickering has to be reduced to match the frequency. This is possible by adjusting the speed

of alternator by its prime mover control.

When all these parameters are set, the lamps become dark and then the synchronizing switch can be closed to synchronize

alternator with supply mains.

PROCEDURE:





5.Adjust the field excitation till the synchronize generator line voltage become equal.

6.Adjust the speed of prime mover and synchronizing lamp where bright into long bright and dark period in

proper order and switch is closed.




7.Thus alternator was synchronize with supply mains.

RESULT:


https://www.electronicshub.org/wp-content/uploads/2015/11/What-is-Synchronization-of-Generators.jpg

https://www.electronicshub.org/wp-content/uploads/2015/11/What-is-Synchronization-of-Generators.jpg



EXPT NO:

DATE:

V AND INVERTED V CURVE OF SYNCHRONOUS MOTOR

AIM:

To plot the V curve and inverted V curve of a synchronous motor.

APPARATUS REQUIRED:


QUANTITY

CIRCUI DIAGRAM:




THEORY:

it is clear that if excitation is varied from very low (under excitation) to very high (over excitation) value, then

current Ia decreases, becomes minimum at unity p.f. and then again increases. But initial lagging current

becomes unity and then becomes leading in nature. Excitation can be increased by increasing the field current

passing through the field winding of synchronous motor. If graph of armature current drawn by the motor (Ia)

against field current (If) is plotted, then its shape looks like an English alphabet V. If such graphs are obtained at

various load conditions we get family of curves, all looking like V. Such curves are called V-curves of

synchronous motor.

As against this, if the power factor (cos Φ) is plotted against field current (If), then the shape of the graph looks

like an inverted V. Such curves obtained by plotting p.f. against If, at various load conditions are called Inverted

V-curves of synchronous motor.

PROCEDURE:

1. Close the TPST switch.

2. By adjusting the autotransformer from the minimum position to the maximum position the rated supply is

given to motor. The motor starts as an induction motor.

3. In order to give the excitation to the field for making it to run as the synchronous motor, close the DPST

switch.

4. By varying the field rheostat note down the excitation current, armature current and the power factor for

various values of excitation.

5. The same process has to be repeated for loaded condition.

6. Later the motor is switched off and the graph is drawn.

GRAPH:

The graph is drawn for-

1. Armature current Vs Excitation current.

2. Power factor Vs Excitation current

TABULATION:

SL NO VOLTAGE (Ia) If W1 W2 POWER

W1+W2

POWER

FACTOR




SAMPLE CALCULATION:

SAMPLE GRAPH:

RESULT:




EXPT NO:

DATE:

SINGLE PHASE INDUCTION MOTOR

AIM:

To identify the terminal and run a single phase induction motor in forward and reverse direction.

APARATUS REQUIRED:


QUANTITY

THEORY:

Stator of single phase IM consists of two set of winding, one winding is called main winding(running winding)

while the second winding is called auxillary winding(stationary winding). The phase difference in the current in

the two winding produce starting torque.

A centrifugal switch is provided in series with the capacitor starting winding. The centrifugal switch is

automatically disconnect the starting winding when the motor attain 75% of its normal speed. This type of

motor is known as capacitor start induction motor.

The direction of rotation of all single phase IM can be change either by changing current through the running

winding or starting winding.




CIRCUI DIAGRAM:




PROCEDURE:

1. Connection are made as per the circuit diagram.

2. Switch on the supply and note the volt meter , ammeter readings and direction of rotation.

3. Disconnect the supply.

4. Switch on the supply after reversing the connection of main winding and note the volt meter , ammeter

readings and direction of rotation.

5. Disconnect the supply and disconnect the equipment.

RESULT:


Documents

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