ee2305-lm

LAB MANUAL

EE 2305 ELECTRICAL MACHINES LAB II

EX.NO.1. LOAD TEST ON 3-PHASE CAGE INDUCTION MOTOR

AIM :

To determine the performance characteristics of 3-phase squirrel cage induction motor by direct loading.

APPARATUS REQUIRED:

SI NO APPARATUS REQUIRED TYPE RANGE QUANTITY

NAME PLATE DETAILS :

FUSE RATING CALCULATION :

125% of rated current.No-load test - 25% of rated current.

THEORY :

The load test on 3-phase induction motor is performed to obtain its various characteristics including efficiency. A belt and brake drum arrangement as shown in the circuit diagram can load the motor. If S1 and S2 are the tensions provided at the two sides of the belt, then the load torque is given by

T = (S1 - S2) * 9.81 * R N-m.

Where R is the radius of the brake drum in metre. The mechanical output of the motor is given by Pm = 2 * 3.14 * N * T Watt

60

Where N is the speed of the motor in RPM. The power input to the motor

Pi = VLIL watt

The efficiency of the motor is given by Efficiency = Pm / Pi

FORMULA :

Torque,T = (S1 – S2) * 9.81 * r (Nm)

Input power(Pi) = (W1 + W2) (Watt)

Output power(Po) = 2 NT / 60 (Watt)

Efficiency = Po X 100 Pi

Cos = W/(31/2 VLIL)

Slip = (Ns – N) / Ns *100

PRECAUTION:

1. TPST switch should be at open position.2. 3-phase autotransformer should be at minimum voltage position.3. There should be no-load at the time of starting(Loosen the belt on the brake drum)4. Brake drum should be filled with water.

PROCEDURE:

1. The connections are made as per the circuit diagram.2. Power supply is obtained from the control panel.3. The TPST switch is closed.4. Rated voltage of 3-phase induction motor, is applied by adjusting autotransformer5. The initial readings of ammeter, voltmeter and wattmeter are noted. 6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter7. Step1 to 6 is repeated till the ammeter shows the rated current of 3-phase induction

motor.8. Decrease the load, bring auto-transformer to its minimum voltage position.9. Switch off the supply.

( 0 –600)V,MI

STATOR

TPST

415V,50Hz, 3 SUPPLY

CIRCUIT DIAGRAM

LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR:

M L R

R C V

Y B

Y

M L

C V

N

Fuse

S1

300V , 10 A ,UPF TYPE 3 - ELEMENT WATTMETERNeutral link230 V ACSUPPLYDPST(0-2) A, MCARECTIFIERFuseVARIACSYNCHRONOUS MOTOR STARTER

4

1

5

V

,

5

0

H

z

,

3

S

U

P

P

L

Y

( 0 –600)V,MISTATORV TPST

A(0 – 10) A, MIFuse300V , 10 A ,UPF TYPE WATTMETER( 0 – 2 ) A , MC1000 ,1.5 ANeutral link

D

P

S

T

( 0 – 10) A,MI

D

P

S

T

700 1.5 AAROTORSTATORA

2

2

0

V

D

C

S

U

P

P

L

Y

2

2

0

V

D

C

S

U

P

P

L

Y

M

L

F

A

FuseNeutral linkA

ROT

--

OR

V

S1

S2

BRAKE DRUM

OBSERVATION TABLE :

S.NO

V (volt) I (A) Speed

(rpm)Spring Balance

S1(Kg) S2(Kg)

Torque=((S1 – S2) * 9.81 * R)

N-m

I/P

(V*IL)

watt

O/P2 NT

60 (watt)

Efficiency = Output Power

Input Power 100%

%slip

RESULT :

VIVA QUESTIONS :

1.Explain what is meant by a 3-phase induction motor?2.Write the classification of 3-phase induction motor?3.State the steps to draw the equivalent circuit of 3-phase induction motor?4.State the condition for maximum torque of 3-phase induction motor?5.Give the different methods of speed control of I.M.6.How do you calculate slip speed?7.State the condition when induction motor acts as induction generator?8.Give the other name for induction generator?

EX.NO.2.NO LOAD AND BLOCKED ROTOR TEST ON 3 SQUIRREL CAGE INDUCTION MOTOR

AIMTo conduct no load test and blocked rotor test on given 3 squirrel cage induction

motor and to draw the circle diagram..

APPARATUS REQUIRED

S.No APPARATUS RANGE TYPE QUANTITY

FORMLULAE

Coso=Wo / √3 VoIo

Cosr=Wbr / √3 VbrIbr

Ibm = Ibr (Vo/Vbr)Wbm = Wbr (Vo/Vbr)2

Stator copper loss = 3 Ibr2Rs

PRECAUTION

1. The 3 autotransformer should be kept at initial position.2. Initially the machine should be under no load condition.

PROCEDURE

NO LOAD TEST1. Connections are made as per the circuit diagram.2. 3 AC supply is increased gradually using 3 autotransformer till rated voltage

is applied.3. Readings of voltmeter and wattmeter are noted.

BLOCKED ROTOR TEST1. Connections are made as per the circuit diagram and rotor is blocked from

rotating.2. Applied voltage is increased until rated load current flows.3. Readings of all meters are noted.

MEASUREMENT OF STATOR RESISTANCE1. Connections are made as per the circuit diagram.2. Supply is given by closing the DPST switch.3. Readings of voltmeter and ammeter are noted.4. Stator resistance in ohms is calculated as

Ra/phase = (Vx1.5) /2I

PROCEDURE FOR CONSTRUCTING THE CIRCLE1. Vector OO’ is drawn at an angle of phase with respect to OY represents the

output line.2. O’X’ is drawn parallel to OX.3. Vector OA is Ibr plotted at an angle of phasor with respect to OY. O’A is joined

which represents the output line.4. A perpendicular bisector from output line which cuts O’Y at C. With C as centre

and O’C as radius draw a semi-circle passing through A.5. From A, a perpendicular is drawn meeting O’X’ at E and OD at D.6. AD represents Wbr in CM.

EF represents stator copper loss in CM.AD represents rotor copper loss in CM.

7. Join OF’ which represents the torque line.8. Line AD is extended and points S is marked, where AS is equal to rated output

power.9. Line PS is drawn parallel to output line.10. From P, perpendicular line is drawn meeting OX at y.11. Join OP.

MEASUREMENT OF PARAMETER AT FULL LOAD

Stator current = OP x X%η = (PQ/PV)x 100%Slip = (QR/PR)x 100Torque = (PRxV/(2ΠNT/60))Pf = PV/OP

MAXIMUM OUTPUT

The perpendicular at O’A’ line cuts the circle at P and O’A’ at PQ’. Maximum output = P1Q1x power scale (W)

MAXIMUM TORQUE

( 0 –600)V,MI

ROT--OR

STATOR

TPST

415V,50Hz, 3 SUPPLY

The perpendicular bisector of line cuts the circle at PR and OF’ at Q2. Maximum torque = (PFx power scale)/T Nm

CIRCUIT DIAGRAM

NO LOAD AND BLOCKED ROTOR TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR:

M L R

R C V

Y B

Y

M L

C V

N

FUSE RATING CALCULATION:

125% of full load current rating


Fuse

R

O

T

-

-

O

R

ROT

--

OR

V

S1

S2

BRAKE DRUM

NO LOAD TEST

S.No Vo (V) Io (A) Wo (W) Wo=(W1+W2) WW1 W2

BLOCKED ROTOR TEST

S.No Vo (V) Io (A) Wo (W) Wo=(W1+W2) WW1 W2

MEASUREMENT OF STATOR RESISTANCE

S.No Voltage (V) Current (A) Rs = (Vx1.5) /2I

RESULT:

EX.NO.3 NO LOAD AND BLOCKED ROTOR TEST ON 1-PHASE INDUCTION MOTOR

AIM :

To obtain the equivalent circuit of the given 1-phase induction motor by no-load test and blocked rotor test.

APPARATUS REQUIRED:




Blocked rotor test -> 125% of rater current.No-load test -> 25% of rater current.

CIRCUIT DIAGRAM :

NO-LOAD TEST :

BLOCKED ROTOR TEST :

FORMULA :

NO-LOAD TEST :

Wo = VoIo Cos 0

Where, Cos 0 = Wo / VoIoIw = Io *Cos 0

I = Io *Sin 0


Z01 = Vsc / IscR01 = Wsc / Isc2

X01 = [Z022 - R02

2]1/2

Xm = [Zm2 - Rm2]1/2 ; R2 = R01 – Rm || RsXs = [Zs2 - Rs2]1/2 ; X2 = X01 – [Xm || (Xs-Xc)]

NO-LOAD TEST :

PRECAUTION :DPST switch should be at open position.2. Auto transformer should be at minimum position.

PROCEDURE :The connections are made as per the circuit diagram.Get the power supply from the control panel.Close the DPST switch.Adjust the auto-transformer to the rated voltage of 1-phase induction motor.Note the readings of ammeter, voltmeter and wattmeter. Bring auto-transformer to minimum voltage position. Switch of the supply.


PRECAUTION :Keep the DPST switch in open position.Auto- transformer should be at minimum position.Before switching on the supply, some load is applied in the brake drum, so that rotor does not rotate.

PROCEDURE :Connections are made as per the circuit diagram.Get the power supply from the control panel.

Close the DPST switch.Auto transformer is adjusted to rated current of 1-phase induction motor.Readings of ammeter, voltmeter and wattmeter are noted down.Bring auto-transformer to its minimum voltage position and switch off the supply, after removing the load.

OBSERVATION TABLE

NO-LOAD TEST :

SI NO

Voltage (volt)

Io (Amp)

Wo (Watt)


SI NO

Voltage (volt)

Io (Amp)

Wo (Watt)

RESULT :

VIVA QUESTIONS :

What is a 1-phase induction motor?Write the classification of 1-phase induction motor?Why do we draw the equivalent circuit of 1-phase induction motor?What is double-field revolving theory?Why 1-phase induction, motor is not self starting?

EX.NO.4. REGULATION OF 3 ALTERNATOR BY ZPF METHOD

AIM

To predetermine the regulation of a given 3 alternator at full load condition and

different power by ZPF method.

APPARATUS REQUIRED


PRECAUTIONS

1. Motor field rheostat should be kept at minimum resistance position.

2. Alternator field rheostat should be kept at maximum resistance position.

PROCEDURE

OPEN CIRCUIT TEST

1. Connections are made as per the circuit diagram.

2. Supply is given by closing the DPST switch.

3. DC motor is started and brought to rated speed by adjusting rheostat.

4. Keeping the TPST open, alternator field rheostat is energized.

5. By varying alternator field rheostat, the field (If) current is varied in steps, and E

(internal emf ) is noted.

6. Above procedure is noted till 125% of rated voltage.

SHORT CIRCUIT TEST

1. TPST switch is closed.

2. By varying alternator field rheostat, the field current, (If) is varied in steps and

corresponding short current (Isc) is noted.

3. Above procedure is repeated till rated current is reached.

ZPF TEST

1. DC motor is run at rated speed by adjusting motor field rheostat.

2. 3 ZPF load is connected to alternator by closing TPST switch.

3. By alternatively varying field rheostat, ZPF load, alternator is made to deliver

rated current. Readings are noted.

DRAWING ZPF CURVE

1. OCC is drawn.

2. Point A is located such that OA gives If corresponding to Irated. Under short circuit

test.

3. Point B is located such that it gives If to voltage from ZPF test.

4. Points A and B joined by curve parallel to OC called ZPF curve.

5. From the curve, ZPF curve is extended.

6. From H, HD is drawn parallel to OCC line.

7. From B, BH is drawn parallel and equal to OA.

8. Point D is point to B and BHD is tangent is obtained.

9. From D, perpendicular to BH at E is drawn.

10. DE gives Ia XL. BE gives If necessary to overcome demagnetizing effect of

armature resistance. EH gives If necessary for balancing armature leakage

reactance drop DE.

11. Internal emf, E1 is calculated as

DPST

DPST

1000 ,1.5 A

E1 = √((Vph cosФ + Ia Ra)2 + (Vph sinФ + IaXL)2)

‘+’ – for lagging pf and

‘-‘ – for leading pf.

12. Find If1 corresponding E1 from OCC.

13. If2 is field current, required to overcome armature reaction (BE)

14. If = √(If12+If2

2-2If1If2 cos(90±Ф)) ‘+’ – for lagging pf and


15. From internal emf E1, a horizontal line is drawn cutting the OCC.

16. The regulation is calculated as

% regulation = ((Eo – Vph)/ Vph)x100.

ZPF TEST ON THREE PHASE ALTERNATOR:

A R M L

A1

N F1`

F1 A2

Y B

F2 F1 F2

Fuse

Neutral link

Fuse

Neutral link

220 V DC SUPPLY

STATORR

ROTOR( 0 – 2 ) A ,

MC

( 0 –300)V,MI700

1.5 A

3 point starter (0 – 10) A,

MI

300V,10A,UPF

220 V DC SUPPLY

A

L F A

M

V

A INDUCTIVE

LOAD

DPST

DPST

( 0 – 10) A,MI

700 1.5 A

1000 ,1.5 A

3 point starter


125% of the full load current rating.

SHORT CIRCUIT TEST ON THREE PHASE ALTERNATOR:

R

A1

F1` F1 N A2

B

F2 F1 F2

Y



Fuse

Neutral link

( 0 – 2 ) A , MC

Neutral link

Fuse

L F A

M

220 V DC SUPPLY

220 V DC SUPPLY

A

STATOR

ROTOR

A

RESULT

EX.NO.5. REGULATION OF 3 ALTERNATOR BY ASA METHOD

AIM

To predetermine the regulation of a given 3 alternator at full load condition and

different power by ASA method.

APPARATUS REQUIRED


PRECAUTIONS

3. Motor field rheostat should be kept at minimum resistance position.

4. Alternator field rheostat should be kept at maximum resistance position.

PROCEDURE

OPEN CIRCUIT TEST

7. Connections are made as per the circuit diagram.

8. Supply is given by closing the DPST switch.

9. DC motor is started and brought to rated speed by adjusting rheostat.

10. Keeping the TPST open, alternator field rheostat is energized.

11. By varying alternator field rheostat, the field (If) current is varied in steps, and E

(internal emf) is noted.

12. Above procedure is noted till 125% of rated voltage.

SHORT CIRCUIT TEST

4. TPST switch is closed.

5. By varying alternator field rheostat, the field current, (If) is varied in steps and

corresponding short current (Isc) is noted.

6. Above procedure is repeated till rated current is reached.

ASA TEST

4. DC motor is run at rated speed by adjusting motor field rheostat.

5. 3 ZPF load is connected to alternator by closing TPST switch.

6. By alternatively varying field rheostat, ZPF load, alternator is made to deliver

rated current. Readings are noted.

DRAWING ASA CURVE

12. OCC is drawn.

13. Point A is located such that OA gives If corresponding to Irated. Under short circuit

test.

14. Point B is located such that it gives If to voltage from ZPF test.

15. Points A and B joined by curve parallel to OC called ZPF curve.

16. From the curve, ZPF curve is extended.

17. From H, HD is drawn parallel to OCC line.

18. From B, BH is drawn parallel and equal to OA.

19. Point D is point to B and BHD is tangent is obtained.

20. From D, perpendicular to BH at E is drawn.

21. DE gives Ia XL. BE gives If necessary to overcome demagnetizing effect of

armature resistance. EH gives If necessary for balancing armature leakage

reactance drop DE.

22. Internal emf, E1 is calculated as

E1 = √((Vph cosФ + Ia Ra)2 + (Vph sinФ + IaXL)2)

‘+’ – for lagging pf and


12. Find If1 corresponding E1 from OCC.

13. If2 is field current, required to overcome armature reaction (BE)

DPST

DPST

1000 ,1.5 A

14. If = √(If12+If2

2-2If1If2 cos(90±Ф)) ‘+’ – for lagging pf and


15. From internal emf E1, a horizontal line is drawn cutting the OCC. Distance

between tangent to OCC and tangent to OCC measures If3.

This is added with the field current to get final field current.

Ifr = If+If3

16. Eo corresponding to Ifr is found.

17. The regulation is calculated as

% regulation = ((Eo – Vph)/ Vph)x100.

ASA TEST ON THREE PHASE ALTERNATOR:

A R M L

A1

N F1`

F1 A2

Y B

F2 F1 F2



Fuse

Neutral link

Fuse

Neutral link

220 V DC SUPPLY

STATORR

ROTOR( 0 – 2 ) A ,

MC

( 0 –300)V,MI700

1.5 A

3 point starter (0 – 10) A,

MI

300V,10A,UPF

220 V DC SUPPLY

A

L F A

M

V

A INDUCTIVE

LOAD

DPST

DPST

( 0 – 10) A,MI

700 1.5 A

1000 ,1.5 A

3 point starter

SHORT CIRCUIT TEST ON THREE PHASE ALTERNATOR:

R

A1

F1` F1 N A2

B

F2 F1 F2

Y

TABULAR COLOUMN

OPEN CIRCUIT TEST

S.No Field Current If (A) Induced Voltage Vr (V) Vph =Vr /√3 (V)

Fuse

Neutral link

( 0 – 2 ) A , MC

Neutral link

Fuse

L F A

M

220 V DC SUPPLY

220 V DC SUPPLY

A

STATOR

ROTOR

A

SHORT CIRCUIT TEST

S.No Field Current If (A) Short circuit Current IA (A)

ZPF TEST

RESULT

EX.NO.6 LOAD TEST ON SINGLE PHASE INDUCTION MOTOR

AIM

To conduct load test on single phase induction motor and to draw the performance characteristics.

APPARATUS REQUIRED

S.NO APPARATUS RANGE TYPE QUANTITY

S.No Voltage

(V)

Field Current

If (A)

Armature

Current (A)

FORMULA USED

1. Synchronous speed (Ns)=120f/p (rpm) Where f=frequency in Hz P=no. of poles, calculated by assuming 5% slip

2. % slip =

Where Ns=synchronous speed in rpm Nr=speed of the rotor in rpm3. Torque T = (S1~ S2)*R*9.81 (N-m) Where R=radius of brake drum of motor in meter S1, S2 = spring balance reading in kg

4. Output power Po = (in watts)

5. Input power Pi = W (in watts)6. % efficiency %η = Output power/ Input power*100

PRECAUTIONSThe motor should be at the no load condition while starting.

PROCEDURE1. Connections are given as per the circuit diagram.2. The induction motor is started on no load by using transformer starter.3. Under no load condition, reading of ammeter, voltmeter and wattmeter are noted

down.4. Speed is measured by using tachometer.5. The motor is loaded gradually by increasing tension on the belt over the brake

drum.6. At each load, the readings of ammeter, voltmeter and wattmeter are noted, speed

is measured and spring balance readings are noted down.7. The above procedure is repeated till the rated current is reached.8. The load on motor is gradually reduced to zero and then supply is switched OFF

CIRCUIT DIAGRAM:

RESULT

EX.NO.7 SEPERATION OF LOSSES IN A THREE PHASE INDUCTION MOTOR

AIMTo separate the no load losses in a given three phase induction motor

APPARATUS REQUIREDS.NO APPARATUS RANGE TYPE QUANTITY

FORMULA USEDMagnetic Loss = Wo.-mechanical losses-3Io

2Rs

Where Wo = wattmeter reading Io = current at rated voltage Rs = stator resistanceMechanical losses are obtained from the graph

PRECATIONS1. The motor should be at the no load condition while starting. 2. The 3Φ auto-transformer (variac) should be kept at initial zero position.

PROCEDURESEPERATION OF LOSSES

1. Connections are given as per the circuit diagram.2. The 3Φ A.C supply is given by closing the TPST switch.3. The induction motor is started gradually by applying voltage through the 3Φ auto-

transformer.4. At rated voltage, power input Wo is measured by using wattmeter and no load

current Io and voltage Vo are noted.5. Voltage is gradually reduced till the motor continues to run.6. For each voltage, readings of ammeter, voltmeter and wattmeter are noted.

MEASUREMENT OF STATOR RESISTANCE (Rs)1. Connections are given as per the circuit diagram.2. The D.C supply is given through a DPST switch.3. The loading rheostat is varied, the readings of ammeter and voltmeter are noted.4. Armature resistance in ohms is calculated as Rs/ph = (V*1.5)/2I

CIRCUIT DIAGRAM:

EX.NO. 8 & 9 REGULATION OF ALTERNATOR BY EMF AND MMF METHOD

AIM :

To predetermine the percentage regulation of the given alternator by EMF (Synchronous Impedance Method) and MMF (Ampere Turns Method), by conducting OC and Short circuit test.

APPARATUS REQUIRED:




DC shunt motor =>125 % of rated current .Alternator => 125 % of rated current .

CIRCUIT DIAGRAM :

FORMULA USED:

EMF Method :Re = 1.6 * RsWhere, Rs - DC resistance andRe - Equivalent AC resistanceE1/I1 Where

E1 = OC voltageI1 = SC voltage

Zs = E1(open cicuit voltage) / I1(short circuit current)Xs = (Zs2 – Re2)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

MMF Method :

If = [ If12 + If2

2 -2 If1 If2 Cos ( 90 (+ or -) ) ‘+’ for lagging power factor,

‘-’ for leading power factor.Where,

If1 - Field current corresponding to V1.If2 - Field current corresponding to Isc

V1 = V+I*Re*Cos

% Regulation (up) = [(Eo – V)/V] * 100Eo - Voltage corresponding to If.

PRECAUTION1.DC shunt motor field rheostat should be in minimum resistance position to get minimum speed at the time of starting.2.Alternator field rheostat should be in minimum position.3.DPST and TPST switches should be in open position.

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 :Note: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.

OBSERVATION TABLE

OPEN CIRCUIT TEST:

If

(A) V (volt)

Vph

(volt)

SHORT CIRCUIT TEST :

If

(A) V(volt)

TABULATION :

SI.NO Power Factor (Cos ) No-load Voltage (volt) E0

Terminal Voltage (volt)

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

MODEL CALCULATIONEMF Method :

Re = 1.6 * ______ Ohm

Where, Rs - DC resistance andRe - Equivalent AC resistance

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

MMF Method :

If = [ ___2 + ___2 - 2 *___* ___* Cos ( 90 (+ or -) ___ ) ‘+’ for lagging power factor, ‘-’ for

leading power factor.Where,

If1 - Field current corresponding to V1.If2 - Field current corresponding to Isc

V1 - V+IRecos % Regulation (up) = [(__ – __)/__] *100Eo - Voltage corresponding to If.

RESULT :

EX.NO.10. LOAD TEST ON 3-PHASE SLIP RING INDUCTION MOTOR

AIM :

To determine the performance characteristics of 3-phase squirrel cage induction motor by direct loading.

APPARATUS REQUIRED:




125% of rated current.No-load test - 25% of rated current.

FORMULA :

Torque,T = (S1 – S2) * 9.81 * r (Nm)

Input power(Pi) = (W1 + W2) (Watt)

Output power(Po) = 2 NT / 60 (Watt)

Efficiency = Po X 100 Pi

Cos = W/(31/2 VLIL)

Slip = (Ns – N) / Ns *100

PRECAUTION:

1. TPST switch should be at open position.2. 3-phase autotransformer should be at minimum voltage position.3. There should be no-load at the time of starting(Loosen the belt on the brake drum)4. Brake drum should be filled with water.

PROCEDURE:

1. The connections are made as per the circuit diagram.2. Power supply is obtained from the control panel.3. The TPST switch is closed.4. Rated voltage of 3-phase induction motor, is applied by adjusting autotransformer5. The initial readings of ammeter, voltmeter and wattmeter are noted. 6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter7. Step1 to 6 is repeated till the ammeter shows the rated current of 3-phase induction

motor.8. Decrease the load, bring auto-transformer to its minimum voltage position.9. Switch off the supply.

OBSERVATION TABLE :

S.NO

V (volt) I (A) Speed

(rpm)Spring Balance

S1(Kg) S2(Kg)

Torque=((S1 – S2) * 9.81 * R)

N-m

I/P

(V*IL)

watt

O/P2 NT

60 (watt)

Efficiency = Output Power

Input Power 100%

%slip

RESULT :Thus the load test on three phase Induction Motor is verified experimentally.

VIVA QUESTIONS :

1.Explain what is meant by a 3-phase induction motor?2.Write the classification of 3-phase induction motor?3.State the steps to draw the equivalent circuit of 3-phase induction motor?4.State the condition for maximum torque of 3-phase induction motor?5.Give the different methods of speed control of I.M.

6.How do you calculate slip speed?7.State the condition when induction motor acts as induction generator?8.Give the other name for induction generator?

ee2305-lm

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