Circuit Diagram:
Tabulation:
M.F=----------VL
Sl.
No
1.
2.
.
6.
IL
Wattmeter
Reading
W1
W2
Input
Power Speed
(W1 +
N
W2)
(rpm)
Sprig
Balance
Reading
F1
( kg )
F2
( kg )
Torque Output
Power
%𝜂
%
Slip
EXPERIMENT NO. 2
LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR
Aim :
To plot the performance characteristics of the given 3-phase squirrel cage induction
motor by direct loading
Apparatus Required :
S.NO
Name of the apparatus
1
Voltmeter
2
Ammeter
3
Wattmeter
4
Tachometer
5
Connecting wires
Type
Range
Quantity
Theory:
A 3 phase squirrel cage induction motor is a type of three phase induction motor which functions
based on the principle of electromagnetism. It is called a ‘squirrel cage’ motor because the rotor
inside of it looks like a squirrel cage. This rotor is a cylinder of steel laminations, with highly
conductive metal (typically aluminum or copper) embedded into its surface. When an alternating
current is run through the stator windings, a rotating magnetic field is produced. This induces a
current in the rotor winding, which produces its own magnetic field. The interaction of the
magnetic fields produced by the stator and rotor windings produces a torque on the squirrel cage
rotor. The load test on induction motor is performed to compute its complete performance i.e.
torque, slip, efficiency, power factor etc. During this test, the motor is operated at rated voltage
and frequency and normally loaded mechanically by brake and pulley arrangement
Range Fixing:
Rated voltage of motor

Range of voltmeter
Rated current of motor

Range of ammeter
= ------------ V
= ------------ V
= ------------ A
= ------------ A
Power factor is normally more than 0.3.

UPF wattmeter
= ------------ V, ------------ A
Sample Calculations
Line Voltage, VL = ___________V
Line Current, IL = ____________A
Radius of Brake Drum, r = ________m
Spring Load, S1 = ________
S2 = _________
Torque applied on the motor, T = (S1 – S2) x r x 9.81 = _____________Nm
Speed of the Motor = _____________rpm
Output Power =
2𝜋𝑁𝑇
60
= ____________Watts
Input Power = W1+W2
% Efficiency, η =
𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
𝑃𝑜𝑤𝑒𝑟 𝐹𝑎𝑐𝑡𝑜𝑟, 𝐶𝑜𝑠 ∅ =
% Slip =
𝑁𝑠 − 𝑁
𝑁𝑠
Model Graphs
= _____________ Watts
× 100 = ________%
𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
3𝑉𝐿 𝐼𝐿
× 100 = __________
× 100 = ________
Precautions:
1. The motor should be started without any load.
2. The supply should not be switched OFF before the motor is unloaded.
3. While running on load, the brake drum is cooled by pouring cold water.
Procedure:
 Connect the circuit as per the circuit diagram.
 Switch on the supply at no load. Take one set of reading at no load.
 Vary the load in suitable step and hence note down all the meter reading up to 100
% of full load.
 Observe one reading slightly above but less than 120% rated current
Result:
Plotted the performance characteristics of the given 3-phase squirrel cage induction
motor by direct loading