Procedure:: Machines Laboratory - 5
Procedure:: Machines Laboratory - 5
Procedure:: Machines Laboratory - 5
INDUCTION MOTORS
In this experiment you would test a three phase induction motor. It has a squirrel cage
rotor. (Conductors placed along the length of the rotor are shorted at either end). The motor runs
a DC generator (Dynamometer) coupled to it by a belt. The induction motor is loaded by loading
the generator (by dissipating the power generated in a resistance located in the dynamometer
module). You would also determine the equivalent circuit of the induction motor.
PROCEDURE:
PART A: LOAD TEST.
Step 1: Set the voltage control to zero. Mechanically couple the dynamometer to the three-phase
induction motor by the belt.
Step 2: Ensure that the low power terminal on the data acquisition interface is connected to the
low power input of the PRIME MOVER / DYNAMOMETER module. The Torque Output,
Speed Output and Ground terminals of the module are respectively connected to T, N and
Ground terminals of the data acquisition interface (use the three thin connectors)
Step 3: Set the MODE switch (located between the PRIME MOVER INPUT BOX and the
DYNAMOMETER LOAD CONTROL BOX to Dynamometer. Set the MODE switch in the
dynamometer load control box to Man(ual). Set the potentiometer marked MANUAL (located
on the left in the dynamometer load control panel ) to the minimum. It controls the load power of
the dynamometer. In the following text, it is referred to as POWER CONTROL KNOB.
Step 6: Turn the voltage control clockwise. The motor starts to rotate. Set the control at 100. The
display panel in the Prime Mover / Dynamometer module displays either the speed or the torque
based on the position of the toggle switch located on the left of the display. If the speed indicated
is negative, reverse the direction of rotation of the motor. You can do it by interchanging the
inputs 4 and 5 (Do so after setting the voltage control to zero). The torque displayed is the torque
on the dc machine (uncompensated torque). The torque measured by the meter is the torque on
the motor (compensated torque). The compensated torque is the sum of uncompensated torque
and the torque on the motor when the power control knob is set at the minimum i.e., the
uncompensated torque is zero.
Step 7: Enter the data in the table by clicking on Record Data. Turn the power control knob
clockwise to increase the load. Record the data. The current I1 should not be more than 1.2 A.
Record at least six data sets in the range 0 to 1.2 A of I1. Set the power control knob to the
minimum and voltage control knob to zero.
Step 8: Obtain the plot Speed Vs Torque.
PART B: VOLTAGE-SPEED CHARACTRISTIC FOR A GIVEN LOAD.
Step 1: Set the Voltage Control at 100. Turn the power control knob till I1 is about 1A. Record
the data.
Step 2: Set the voltage control at 90. Record data.
Step 3: Repeat step 2 for voltage control settings at 80, 70 and 60. Set the power and the voltage
controls at the minimum values.
Step 4: Plot Speed Vs Voltage.
PART C: EQUIVALENT CIRCUIT.
The approximate equivalent circuit of an induction motor is shown below:
DATA: PART A
E1
I1
P1
P2
Pm
A-1
A-2
A-3
I1
P1
P2
Pm
A-1
A-2
A-3
PART B
E1
PART C
E1
I1
P1+P2
Power Factor
PART D
E1
I1
P1
P2
Pm
A-1
A-2
A-3