EM-2 LAB MANUAL induction motors and alternators

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 autotransformer
5. The initial readings of ammeter, voltmeter and wattmeter are noted.
6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter
7. 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
(0 – 10) A, MI
STATOR
T
P
S
T
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
S
1
3
0
0
V
,
1
0
A
,
U
P
F
T
Y
P
E
3
-
E
L
E
M
E
N
T
W
A
T
T
M
E
T
ROT-
-OR
V
S1 S2
BRAKE
DRUM

OBSERVATION TABLE :
S.N
O
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/P
2  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
AIM
To 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
Coso=Wo / √3 VoIo
Cosr=Wbr / √3 VbrIbr
Ibm = Ibr (Vo/Vbr)
Wbm = Wbr (Vo/Vbr)2
Stator copper loss = 3 Ibr
2
Rs
PRECAUTION
1. The 3 autotransformer should be kept at initial position.
2. Initially the machine should be under no load condition.
PROCEDURE
NO LOAD TEST
1. 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 TEST
1. 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 RESISTANCE
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 CIRCLE
1. 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 100
Torque = (PRxV/(2ΠNT/60))
Pf = PV/OP
MAXIMUM OUTPUT

( 0 –600)V,MI
STATOR
T
P
S
T
415V,50Hz,
3 SUPPLY
The perpendicular at O’A’ line cuts the circle at P and O’A’ at PQ’.
Maximum output = P1Q1x power scale (W)
MAXIMUM TORQUE
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
ROT-
-OR
V
S1 S2
BRAKE
DRUM

FUSE RATING CALCULATION:
125% of full load current rating
NAME PLATE DETAILS:
NO LOAD TEST
S.No Vo (V) Io (A) Wo (W) Wo=(W1+W2)
W
W1 W2
BLOCKED ROTOR TEST
S.No Vo (V) Io (A) Wo (W) Wo=(W1+W2)
W
W1 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 :

FORMULA :
NO-LOAD TEST :
Wo = VoIo Cos 0
Where, Cos 0 = Wo / VoIo
Iw = Io *Cos 0
I = Io *Sin 0
BLOCKED ROTOR TEST :
Z01 = Vsc / Isc
R01 = Wsc / Isc2
X01 = [Z02
2
- R02
2
]1/2
Xm = [Zm2
- Rm2
]1/2
; R2 = R01 – Rm || Rs
Xs = [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

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.

D
P
S
T
D
P
S
T
1000 ,1.5 A
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
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 = √(If1
2
+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
Fus
e
Neutral
link
Fus
e
220 V
DC
SUPP
LY
STATO
RR
ROTO
R
( 0 – 2 ) A ,
MC
( 0 –
300)V,MI
700

1.5 A
3 point
starter (0 – 10) A,
MI
300V,10A,U
PF
220 V
DC
SUPP
A
L F A
M
V
A I
N
D
U
C
T
I
V
E
L
O
A
D

D
P
S
T
D
P
S
T
( 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
Fus
e
L F A
M
220 V
DC
SUPP
LY
220 V
DC
SUPP
LY
A
STATO
R
ROTO
R
A

125% of the full load current rating.
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

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.

D
P
S
T
D
P
1000 ,1.5 A
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)
14. If = √(If1
2
+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
Fus
e
Neutral
link
Fus
e
220 V
DC
SUPP
LY
STATO
RR
ROTO
R
( 0 – 2 ) A ,
MC
( 0 –
300)V,MI
700

1.5 A
3 point
starter (0 – 10) A,
MI
300V,10A,U
PF
A
L F A
M
V
A I
N
D
U
C
T
I
V
E
L
O
A
D

TABULAR COLOUMN
OPEN CIRCUIT TEST
S.No Field Current If (A) Induced Voltage Vr (V) Vph =Vr /√3 (V)
SHORT CIRCUIT TEST
S.No Field Current If (A) Short circuit Current IA (A)
ZPF TEST
S.No Voltage
(V)
Field Current
If (A)
Armature
Current (A)

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
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 =
 
s r
s
N N
*100
N

Where Ns=synchronous speed in rpm
Nr=speed of the rotor in rpm
3. 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 =
2
60
r
N T

(in watts)
5. Input power Pi = W (in watts)
6. % efficiency %η = Output power/ Input power*100
PRECAUTIONS

The motor should be at the no load condition while starting.
PROCEDURE
1. 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:

EX.NO.7 SEPERATION OF LOSSES IN A THREE PHASE INDUCTION
MOTOR
AIM
To separate the no load losses in a given three phase induction motor
APPARATUS REQUIRED
S.NO APPARATUS RANGE TYPE QUANTITY
FORMULA USED
Magnetic Loss = Wo.-mechanical losses-3Io
2
Rs
Where Wo = wattmeter reading
Io = current at rated voltage
Rs = stator resistance
Mechanical losses are obtained from the graph
PRECATIONS
1. The motor should be at the no load condition while starting.
2. The 3Φ auto-transformer (variac) should be kept at initial zero position.
PROCEDURE
SEPERATION OF LOSSES
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)
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

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 * Rs
Where,
Rs - DC resistance and
Re - Equivalent AC resistance
E1/I1 Where
E1 = OC voltage
I1 = 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 = [ If1
2
+ 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] * 100
Eo - Voltage corresponding to If.
PRECAUTION
1.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).
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 sadjusted 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 CALCULATION
EMF Method :
Re = 1.6 * ______ Ohm
Where,
Rs - DC resistance and
Re - 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) = [(__ – __)/__] *100
Eo - 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 autotransformer
5. The initial readings of ammeter, voltmeter and wattmeter are noted.
6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter
7. 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.N
O
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/P
2  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?

EM-2 LAB MANUAL induction motors and alternators

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EM-2 LAB MANUAL induction motors and alternators