Scribd
Upload
421 views

Exp.2 - No-Load and Blocked Rotor Test On A Three-Phase Squirrel Cage Induction

The equivalent-circuit of three-phase induction motor has been shown in fig.1. To determine the parameters of equivalent circuit following tests are performed. 1. No Load Test 2. Blocked Rotor Test 3. D.C. test for measurement of resistance

Uploaded by

Masood Rizvi
Copyright
© © All Rights Reserved
Available Formats
Download as PDF, TXT or read online on Scribd
421 views

Exp.2 - No-Load and Blocked Rotor Test On A Three-Phase Squirrel Cage Induction

The equivalent-circuit of three-phase induction motor has been shown in fig.1. To determine the parameters of equivalent circuit following tests are performed. 1. No Load Test 2. Blocked Rotor Test 3. D.C. test for measurement of resistance

Uploaded by

Masood Rizvi
Copyright
© © All Rights Reserved
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 4

Experiment No.

- 2

Object: To perform no-load and blocked rotor test on a three-phase squirrel cage induction
motor and determine its equivalent circuit.

List of equipment:

S. No. Equipment Specification Qty.

1 Autotransformer, Input-415V, Output-( 0 –470)V10Amp. 1 No.

2. Ammeter (0-5)Amp 1No.

3. Voltmeter (0-600)V, (0-150)V 1No.

4. Wattmeter 3, 300 / 600V. 10/ 20Amp. 1No.

5. 3 Phase Induction Motor 1.5 KW/2HP/3.6Amp/ 1410 RPM, 1No.


415V /  Connection

Theory:

The equivalent-circuit of three-phase induction motor has been shown in fig.1. To determine the
parameters of equivalent circuit following tests are performed.
1. No Load Test
2. Blocked Rotor Test
3. D.C. test for measurement of resistance

No Load Test: This test is also called as free-running/light-running test. This test is performed to
determine no-load current I0, no-load power factor cosØ0, no-load resistance R0 and reactance
X0. To perform this test the circuit as shown in figure. The induction motor is started with the
help of a three-phase auto-transformer. The motor is run at the no-load speed by applying rated
voltage. Readings of wattmeter, ammeter and voltmeter are recorded, let these be Wo, Io, Vo
respectively. The equivalent-circuit of the motor under no-load test becomes as shown in figure.
Stator-impedance drop is neglected, since stator-current is very small under no-load condition.
The rotor circuit behaves as open-circuit since under no load condition speed tends to become
synchronous and slip approaches to zero value.
Per-phase no load loss = = V0 I0 cosO
No-load power factor cosO = ;
Energy component of no-load current Ii = I0 cos0
Magnetising component of no-load current Im = I0 sin 0, or Im=

No-load impedance , Z0 = ;

No-load resistance R0= ; No-load reactance X0=


Blocked rotor test : This test is performed to determine the short-circuit current Isc with
normal applied voltage to stator, power factor on short-circuit, total equivalent resistance and
reactance of the motor as referred to stator. To perform this test tightens the belt of the rotor so
that rotor becomes fixed, now apply reduced voltage with the help of auto transformer & slowly
increase the voltage from zero till the ammeter shows the rated current. The readings of
wattmeter, voltmeter & ammeter under this condition be WSC, VSC & ISC respectively. The
equivalent-circuit under this test becomes as shown in figure.

Per phase power = WSC/3


Per phase voltage = (VSC) ph = (If star connection on stator)

Per phase current = (ISC) ph = (If delta connection on stator)

power factor cos = ;

Impedance ZSC = =

; ;

Observations:

WO = (W1 + W2) x m.f. =

if one wattmeter is giving negative reading then reverse the connections of either current-coil or
pressure-coil of that wattmeter and then record the reading

No load test Blocked rotor test


V0 (volts) I0(amp) W0(watts) Vsc (volts) Isc(amp) Wsc(watts)

Stator D.C. Resistance =


Stator A.C. Resistance = 1.2 x Stator D.C. resistance
Circuit Diagram:
3-phase autotransformer
(TPIC Switch)
(0-10 A)
M L
A
R C V
V
(0-600 V)

C V

M L
B

Fig.1 NO LOAD TEST ON A 3 –Φ INDUCTION MOTOR.

3-phase autotransformer
(TPIC Switch)
(Rated current)
M L
A
R C V
V
(0-150 V)
Reduced Volts

C V

M L
B

Fig.2 BLOCKED ROTOR TEST ON A 3 –Φ INDUCTION MOTOR.


Result:-

Precaution:-

1. All connections should be tight and clean.


2. The power supply must be within the limits.
3. The range of the instruments should be selected carefully.
4. Care should be taken for making the connections.

Viva questions:-

1. Why the power factor of a 3 phase induction motor under no-load condition is quite low?
2. What is the power factor of a 3 phase induction motor operating under blocked rotor
condition?
3. How do you obtain a reduced voltage from a 3 phase supply.
4. What approximate fraction of rated current is the me load current ofr a 3 phase induction
motor.
5. Why the no-load current in a 3 phase induction motor is 30-40 % of the rated value as
compared to 3-5% of the rated value in a transformer.

Industrial application:-

1. This experiment is conducted on three-phase induction motor in the industry


manufacturing it, to ascertain the parameters of the machine.
2. Squirrel cage induction motors find a variety of applications in industry and home
appliances.

You might also like