EE212 SYNCHRONOUS AND INDUCTION MACHINES

LABORATORY

MACHINE REPORT

Roll No. 107114093

EEE
IV Semester

Aim:

To perform no load and blocked rotor tests on a three phase induction motor to determine
its equivalent circuit parameters.
To generate theoretical performance characteristics from the equivalent parameters.
To perform load test on the three phase induction motor and to obtain the experimental
performance characteristics and to compare it with the theoretical performance
characteristics.
To obtain theoretical performance characteristics for a given different operating voltage,
frequency, rotor resistance and for a constant v/f ratio.

MACHINE NAME PLATE DETAILS

Motor:
Rated Voltage
Rated Current
Rated Power
Rated Speed

: 415 V
: 7.5 A
: 3.7 kW
: 1430 rpm

NO LOAD AND BLOCKED ROTOR TEST

Apparatus Required:
1. Ammeter

0-10 A (MI)
0-5 A (MC)
2. Voltmeter 0-600 V (MI)
0-300 V (MI)
0-50 V (MC)
3. Wattmeter 500 V, 10 A (LPF)
250 V, 10 A (UPF)
4. Rheostat
230 , 5 A

1
1
1
1
1
1
1
1

Precautions:
1. Appropriate fuse wires should be fixed.
2. The TPST switch should be kept in open position.
3. Autotransformer should be kept at minimum voltage position.
4. Initially the motor should be in no load condition.

IL
A

B
V VL
3-Phase
400V
Y
50 Hz
AC
Supply

T
P
S

C
C2

A1

A2
C1

T
S

Y B2

B
B1

Three-phase
Induction
Motor
C

C
L

Double element wattmeter

PANEL BOARD

3
Autotransformer

Fig 1. CIRCUIT DIAGRAM NO-LOAD TEST ON THREE-PHASE INDUCTION MOTOR

IL
A

B
V VL
3-Phase
400V
Y
50 Hz
AC
Supply

T
P
S

S1

C
R

C2

A1

A2
C1

T
S

Y B2

B
B1

Three-phase
Induction
Motor
C

C
L

Double element wattmeter

PANEL BOARD

S2

3
Autotransformer

Fig 2. CIRCUIT DIAGRAM BLOCKED ROTOR TEST ON THREE-PHASE INDUCTION MOTOR

Brake
Drum

FORMULAE TO BE USED
I.

NO LOAD TEST

3 VocIoc COS oc (W)

Woc
3Voc I oc

1. Woc

2. COSoc

3. Iw

I oc

4. Im

I oc

5. Xo

6. Ro

cosoc (A)

sin oc (A)
3
Voc
()
Im
Voc
()
Iw

II. BLOCKED ROTOR TEST

7. Z01

8. R01

9. X01
10. R2'
11. Reff

=
=
=

VSC per phase

I SC per phase

()

WSC

per phase

I SC2

per phase

()

Z 012 R012 ()
(R01 Reff ) ()
Rmean 1.6 ()

III. CALCULATION OF LOSSES AND EFFICIENCY

12. Cos NL

WNL / (3 VNL INL)

13. Cos sc

W sc / (3 V sc I sc)

14. I sc at rated voltage (ISN)

(VNL / V sc) I sc (A)

15. W sc at rated voltage (WSN)

16. Stator copper loss

(VNL / V sc) W sc (W)

=
3 I2NL R1 (W)

17. Rotor copper loss

WSN (3 I2NL R1) (W)

18. Percentage efficiency

(Output power / Input power) * 100

19. Input power (stator input)

(Output power + RotorCopper loss +

Stator Copperloss +Fixed losses)(W)

20. Rotor input

(Stator input Stator Copperloss)(W)

21. Slip

Rotor copper loss / Rotor input

22. Multiplication Factor

3 V I cos
full scale deflection

where,
Woc -

Power consumed under no load (W).

Roc -

No load resistance ()

Ioc

No load current (A)

Xoc -

No load reactance ()

Voc -

Rated voltage (V)

Wsc -

Power consumed when the Rotor is blocked (W)

R01 -

Blocked rotor resistance ()

X01 -

Blocked rotor reactance ()

Z01 -

Blocked rotor impedance ()

WNL -

Power consumed under no load (W)

VNL -

No load supply voltage (V)

INL

No load current (A)

Wsc - Power consumed when rotor is blocked (W)

Vsc -

Blocked rotor voltage (V)

Isc

Blocked rotor current (A)

R1

Stator resistance ()

NL -

No load power factor

sc -

Blocked rotor power factor

TABULATION
Multiplication factor : 4
Terminal
voltage,
Voc (V)

Line current,
Ioc (A)

415

4.3

WOC
Observed (div)

Actual (W)

122

488

Table 1. NO LOAD TEST ON THREE-PHASE INDUCTION MOTOR

Multiplication factor : 2

Terminal voltage
Vsc (V)

Line Current
Isc (A)

82

7.5

Wsc
Observed
(div)

Actual
(W)

265

530

Table 2. BLOCKED ROTOR TEST ON THREE PHASE INDUCTION MOTOR

Sl.No

Voltage, V (V)

Current, I (A)

Resistance, R=V/I ()

1.

0.9

4.45

2.

1.35

4.45

3.

1.75

4.57

4.

10

2.2

4.54

5.

12

2.65

4.53

Table 3. TABLE MEASUREMENT OF STATOR RESISTANCE Reff

Rmean = 4.508
Reff = Rmean*1.6 = 7.213

A1

D
P
S
T

36 V
DC Supply

+
V

_
A2

_
Fig 3. CIRCUIT DIAGRAM MEASUREMENT OF STATOR RESISTANCE ( Reff)

I1

I2 1

>

>

>

X01

Io

>

IW

>

AC
Supply Voltage

R01

I
R'L

R0

X0

N
Fig 4. PER PHASE EQUIVALENT CIRCUIT OF THREE-PHASE INDUCTION
MOTOR

Machine parameters obtained:

Iw = 0.392 A
Im = 2.45 A
Ioc = 4.3 A
Woc = 488 W

Xo = 169.39
Ro = 1058.67
R01 = 9.42
R2 = 2.207

X01 = 16.419
Reff = 7.213

LOAD TEST
Apparatus required:
1. Ammeter 0-10 A (MI)
1
2. Voltmeter 0-600 V (MI)
1
3. Wattmeter 500 V, 10 A (UPF) 1

Formulae to be used:
1.

Torque,

2.

Output power,

P0

3.

Input power,

Pin

4.

% efficiency,

5.

Power Factor,

cos

6.

Synchronous speed,

Ns

7.

Percentage slip,

%s

8.

Multiplication Factor

9.81 (S1~S2) R (N-m)

2NT (W)
60
3 VL I L cos (W)

PO
100
Pin
Pin
3 VL I L

120 f

(rpm)
p
Ns N
100
Ns

3 V I cos
full scale deflection

where S1 and S2 are the readings of spring balance (Kg)

R is the radius of the brake drum (m)
N is the speed of the motor (rpm)
Pin is the input power (W)
P0 is the output power (W)
VL is the line voltage (V)
IL is the line current (A)
f is the frequency of the input supply (Hz)
p is the number of poles

IL
A

B
V VL
3-Phase
400V
Y
50 Hz
AC
Supply

T
P
S

S1

C
C2

A1

A2
C1

T
S

Y B2

C
L

Double element wattmeter

PANEL BOARD

B
B1

Three-phase
Induction
Motor
C

S2

3
Autotransformer

Fig 5. CIRCUIT DIAGRAM LOAD TEST ON THREE-PHASE INDUCTION MOTOR

Brake
Drum

Multiplication factor : 2

Line
Voltage
Sl.No

VL (V)

Line
Current
IL (A)

Spring Balance
Readings (kg)

Speed
N
(rpm)

Torque
factor
T

S1

S2

S1 ~ S2

Cos

(Nm)
(kg) (kg)

Input

Power

(kg)

Output
Power Pin
Power
Obser
ved
(div)

Actual
(W)

Po
(Watts)

%
Slip

%
Efficiency

1.

415

4.5

1497

0.062

100

200

0.2

2.

415

4.6

1491

4.7

3.7

3.147

0.278

460

920

491.36

0.6

53.41

3.

415

4.7

1486

5.103

0.37

625

1250

744.09

0.93

63.53

4.

415

4.75

1484

1.4

6.6

5.613

0.395

675

1350

872.28

1.07

64.61

5.

415

4.8

1483

10

1.5

8.5

7.229

0.435

775

1550

1122.66

1.13

72.43

Table 4. LOAD TEST ON THREE-PHASE INDUCTION MOTOR

Comparison of theoretical & experimental performance curves

Fig 5. Torque slip characteristics

Fig 6. Output power vs Torque

It is seen from Fig 5. that the torque increases steeply with slight increase in slip in the operating
region. The experimental and the theoretical curves almost coincide.
From Fig 6. It is seen that output power and torque follow linear relationship and this holds good
even under practical conditions.

Fig 7. Output power vs Line current

Fig 8. Output power vs Speed

From Fig 7. It is seen that the line current drawn experimentally is less than expected. This is
due to the experimental loading conditions which were far less than the rated load.
From Fig 8. It is seen that the experimental rotor speed is a bit less than the expected values.
This is because of the mechanical losses which are unaccounted in the theoretical curve. It is
also seen that the speed reduces only by a few rpm.

Fig 9. Output power vs % slip

Fig 10. Output power vs efficiency

It is seen in Fig 9. that the experimental slip is a bit more than the expected values. This is
because of the the same reason as of speed, i.e the mechanical losses which are unaccounted in
the theoretical curve.

Fig 11. Output power vs Power Factor

Fig 12. Torque vs slip for varying supply voltage

The power factor increases with loading (Fig 11.) because, the mechanical load on the motor is
seen as an equivalent resistive load. Thus, as the load increases, the motor becomes more and
more resistive, thus the power factor increases.

Fig 13. Torque vs slip for varying rotor resistance

Fig 14. Torque vs slip for varying frequency

Fig 15. Torque vs slip for constant v/f

The efficiency of the motor (Fig 10.) is low initially because under no load and small load
conditions, comparatively more power is dissipated in magnetization and losses than on the
load. This is why efficiency is small initially. On loading, the power used on the load (i.e the
output power) increases, and the output power is larger than the rotor copper losses. Thus the
efficiency increases. But after a limit, the losses start increasing and the curve gets flatter.
In Fig 12. It is seen that torque decreases with decrease in line voltage. This is because torque
is proportional to the square of the line voltage.

So, as voltage is decreased, the shaft torque also decreases

It is seen from Fig 13 that higher rotor resistance provides higher starting torque (at
slip=1). The critical torque for all cases is same because it is proportional to (E22)/(2X2) which
remains constant. The slip increases with increase in rotor resistance because increased rotor
resistance causes an increase in the rotor copper losses. This results in decrease in efficiency of
the machine.
From Fig 14 it is observed that the torque increases with decrease in frequency of the
supply. This is because of the fact that torque is inversely proportional to the synchronous
speed Ns as given by the above expression. As frequency is decreased, Ns also decreases,
causing an increase in torque. But the machine must be designed to withstand high torques.
Since V = 4.44KTf, we can say that, V/f = 4.44KT. (K is constant, T is constant under
running conditions) Flux decreases with decrease in Voltage but flux increases with decrease
in frequency. Thus, when the v/f ratio is kept constant, the flux remains constant, thus the
critical torque is constant. But the speed of the machine decreases because the synchronous
speed decreases with decrease in supply frequency, thus the slip increases with decrease in
frequency.

PERFORMANCE CURVES FOR THE GIVEN CASES:

(i) 75% rated voltage, (ii) 33 Hz, (iii) 33 Hz with constant v/f ratio, (iv) 4 R 2
The given operating conditions are compared with the rated operating conditions.

Fig 16. Power vs Torque

75% Rated Voltage Since torque is proportional to the square of voltage, the torque
decreases with decrease in applied voltage.
33 Hz - Torque increases with decrease in frequency because torque is inversely proportional
to Ns.

33 Hz, constant v/f when v/f is constant, but both V and f are decreased, the torque decreases
because torque is proportional to the square to voltage but inversely proportional to frequency.
But the stalling torque remains the same.
4 R2 Since the rotor resistance is increased four times the actual value, the I 2R losses in the
rotor become so high that the torque reduces drastically.

Fig 17. Power vs slip

75% Rated Voltage Since torque is proportional to the square of voltage, the torque
decreases with decrease in applied voltage. Thus, speed decreases or slip increases with
decrease in voltage.
33 Hz - Torque increases with decrease in frequency because torque is inversely proportional
to Ns. This increase in torque causes the speed to improve, and the slip to decrease, as seen in
the graph.

33 Hz, constant v/f when v/f is constant, but both V and f are decreased, the torque decreases
because torque is proportional to the square to voltage but inversely proportional to frequency.
But the stalling torque remains the same. The decreased torque causes the speed to reduce, or
the slip to increase which is reflected in the above graph.
4 R2 Since the rotor resistance is increased four times the actual value, the I 2R losses in the rotor
become so high that the torque reduces drastically. Due to increased losses, speed also decreases.

Fig 18. Power vs Speed

75% Rated Voltage Since Speed and torque are directly proportional to voltage, speed dips as
voltage is decreased.
33 Hz Here, Ns becomes 990 since frequency is changed. So, the speed is very less compared to
rated operation. But the speed does not dip quickly. It is seen that the slop of the curve depends
on the voltage and not frequency.

33 Hz, constant v/f Here also, Ns becomes 990 since frequency is changed. But, voltage is also
decreased, so the decrease in the speed is more compared to the previous case and it is observed in
the graph.
4 R2 The drastic increase in rotor resistance causes rotor copper losses to increase, and hence the speed
to decrease.

Fig 19. Power vs power factor

75% Rated Voltage When voltage is decreased, the flux produced in the motor decreases,
thus the reactive power supplied to the motor decreases, causing an increase in power factor.
33 Hz With decrease in frequency, the flux produced in the machine increases, i.e the
reactive power required for the machine will increase. This increase in reactive power will
cause a decrease in power factor.
33 Hz, constant v/f a decrease in voltage and decrease in frequency such that v/f ratio
remains constant will result in a constant flux, thus the reactive power does not vary. Thus, the
curve coincides with that of the rated operating conditions
.
4 R2 the increase in rotor resistance causes the motor to be more resistive, thus increasing the power
factor.

Fig 20. Power vs Efficiency

75% Rated Voltage When voltage is decreased, the flux produced in the motor decreases, the
torque also decreases but the losses remain the same. Thus, efficiency decreases when voltage is
decreased.
33 Hz With decrease in frequency, the flux produced in the machine increases, thus
increasing the torque. Also, the decreased frequency also decreases the inductive reactance
losses, hence resulting in an improved efficiency.
33 Hz, constant v/f Since voltage is decreased torque (which is proportional to the square of
voltage) also decreases. Even though frequency is decreased, the effect of decrease in voltage
dominates, resulting in a decreased efficiency.
4 R2 the increase in rotor resistance results in increased rotor copper losses, thus the efficiency
of the machine decreases due to increased losses.

Fig 21. Power vs Line current

75% Rated Voltage When voltage is decreased, to provide a required torque, the motor needs
more current than while operating at rated voltage. Thus, for a particular output power, the line
current drawn increases.
33 Hz Since frequency is decreased, torque increases, and thus, to provide a given output
power, the machine requires less current than that of the rated operating conditions. Moreover,
more flux is produced with less current when frequency is reduced.
33 Hz, constant v/f Since voltage is decreased, it results in increased line current for a given
load condition. But due to the effect of decreased frequency, the machine draws less current
compared to the 75% of rated voltage operating condition.
4 R2 The increase in rotor resistance will result in more losses, thus more current will be
required for a particular load, compared to the rated operating conditions.

INFERENCES:

By analysing the machine performance characteristics at different operating voltages, we can

decide the method of speed control to be used for different necessities.
Since speed is proportional to square of applied voltage, voltage can be varied to control speed
over a large range.
v/f speed control is used because changing frequency alone may cause the cores to saturate
quickly and the no load current of the motor will increase. By keeping flux constant this is
eliminated.
Since increase in rotor resistance increases starting torque, this method is used in starting of
induction motors. An external resistance is included in series with the rotor resistance while
starting to improve the starting torque. Care should be taken so that the starting torque does not
exceed the breakdown torque of the machine. The external resistance is then removed after the
motor has started.
It is seen that increased frequency results in decreased torque and speed. This shows the effect of
harmonics on the motor. Higher frequency harmonics cause decrease in torque and even crawling
in some cases.
Since power factor is poor at low loads, measures must be taken (such as using capacitor banks)
while operating at low loads.

RESULT:
No load and blocked rotor tests were performed on a three phase induction motor to
determine its equivalent circuit parameters. Theoretical performance characteristics were generated
from the equivalent parameters. Load test was performed on the three phase induction motor and the
experimental performance characteristics were obtained and compared with the theoretical
performance characteristics. Theoretical performance characteristics were obtained for a given
different operating voltage, frequency, rotor resistance and for a constant v/f ratio and compared
with the rated performance characteristics.