LAB: 2 ELEC3310
THE UNIVERSITY OF QUEENSLAND
School of Electrical Engineering and Computer Science
Induction Machine Experiment
1. Aim.
To determine the equivalent circuit parameters and analyze the characteristics of an
induction motor.
2. Introduction
In this experiment, you will be examining the characteristics of an induction machines.
As such, this “lab” or experiment will concentrate on your analysis of the results that
provided for you. You will be required to write individual reports on your analysis of
the results you obtain. Write the report based on the experimental data provided.
Because you are not confined to the laboratory during these experiments, this practical
sheet will not give you any background theory regarding AC machine behavior.
Instead, when analyzing the data to submit your report, you can access your usual study
materials for the course (i.e. lecture notes and textbook) to examine and explain the
data.
The AC machine which you will be testing can be seen in Figure 1 below. Physical
step of these Machines is available in 50- S104 and you are encouraged to talk to
Tutors to organize a visit to the lab to look at the Machines. What you are looking
at in Figure 1 is two induction machines. The shafts of both machines are mechanically
coupled together. The purpose of having two induction machines in this experiment is
for one to be the machine under test, and the other to provide opposing torque. More
details regarding the specific role of the induction motor in the tests will be discussed
at each experimental stage.
Both induction motors are rated at 5.5kW, the three phase windings are connected in
star configuration. When the motor delivers rated power output, if it connected to a
660V (VLL) voltage, it will draw 6.2A at 0.886 lagging power factor. If the supplied
frequency is 50 Hz, its full load mechanical speed is 1460 r.p.m. These data referes to
the machine name plate data. However, you should follow the measurement data for
finding out applied voltages and currents drawn.
LAB: 2 ELEC3310
Figure 1 – Two induction machines.
3. Experiments and Results
3.1 Locked rotor test
The locked rotor test is used to calculate the equivalent rotor and stator impedances of
an induction motor. When the rotor is stationary, the slip is equal to 1, therefore the
equivalent rotor resistance is low. Because the equivalent rotor resistance is low, the
relatively high impedance magnetizing branch in the equivalent circuit can be
neglected. Therefore, the information received from the locked rotor test gives
information on solely the rotor and stator impedances of the induction motor under test.
The data retrieved from this test will be the line-to-line voltage, line current, motor
speed (in rpm) and power factor of the machine under test.
In this experiment, there is no fixed mechanical locking mechanism to hold the rotor
in place. Rather, the shafts of both the variable speed drive (VSD) controlled induction
motor and the direct on-line machine under test (MUT) are mechanically coupled
together. The VSD induction motor is speed controlled to 0 rpm. Therefore, when the
MUT is connected to the AC supply, the VSD induction machine will supply
counteracting torque to ensure that the coupled shaft speed remains at 0 rpm, which is
equivalent to a locked rotor. The machine under test induction motor is connected to
the mains 415V (line to line) three phase supply via three single phase 240/28.9V
toroidal transformers. This step-down voltage ensures that close to rated current flows
during the locked rotor test.
Locked rotor test results are given in Table 1.
LAB: 2 ELEC3310
TABLE 1: Locked Rotor Results
---Experiment Information---
Timestamp Mon 29 Aug 2022 10:04:55 AM
Experiment Id 49629
Unit Id 4
---Experiment Specification---
Setup Name Locked Rotor
---Experiment Results---
Ph-Ph Voltage (Volts) 425.4
Phase Current (Amps) 0.77
Power Factor 0.518
Motor Speed (RPM) 0
Important to note: The current and voltages measured in this test are taken from the
primary side of the step-down transformer. These values must be converted to the
secondary side of the transformer to use as data for the locked rotor test.
The test is performed at rated frequency.
Use these results to answer the following questions:
3.1.1. The line-to-line voltage on the secondary side of the step down transformer is
50V. In what configuration are the three phase torodial transformers connected
(i.e. star-star, delta-delta, star-delta or delta-star)?
3.1.2. What is the real power consumed in the locked rotor test?
3.1.3. What parameters of the induction machine equivalent circuit are being assessed
in this test?
3.2.3. Use the test results to determine the equivalent impedance, resistance and
reactance of the locked rotor test.
3.2 No load test
The no load test is used to gather information about the magnetizing branch in the
induction machine equivalent circuit. When an induction motor is unloaded, the shaft
will be running at practically synchronous speed (not quite however, as if it were
running at synchronous speed no currents would be induced in the rotor windings) and
therefore a very small, practically zero slip. This causes the equivalent rotor impedance
to be very large. Therefore, the rotor can be considered to be an open circuit in this test,
and the data obtained from this test will give information on the stator and magnetizing
impedance. The data retrieved from this test will be the line-to-line voltage, line current
(equal to phase current as star connected), motor speed (in rpm) and power factor of the
machine under test.
No load test Results are given in Table 2.
LAB: 2 ELEC3310
TABLE 2: No Load Test Results
---Experiment Information---
Timestamp Mon 29 Aug 2022 9:57:30 AM
Experiment Id 49625
Unit Id 3
---Experiment Specification---
Setup Name No Load
---Experiment Results---
Ph-Ph Voltage (Volts) 423.6
Phase Current (Amps) 6.62
Power Factor 0.121
Motor Speed (RPM) -1499
The three phase transformer bank mentioned in the locked rotor test has been switched
out in this experiment, therefore measured voltages and currents do not need to be
converted or adjusted.
3.2.1. What is the real power consumed in the no load test?
3.2.2. What parameters of the induction machine equivalent circuit are being assessed
in this test?
3.2.3. Use test results to determine the equivalent impedance, resistance and reactance
of the no load test.
3.2.4. How many poles does this induction machine have? Explain how you find it?
3.2.5. Determine the slip?
3.2.6. By what method could the stator resistance be determined?
3.2.7. Assume the stator resistance (R1) of the machine under test is 0.988 Ω/phase.
Using the results from sections 3.2 and 3.3, determine the full equivalent circuit
of the induction machine under test. Consider that stator and rotor reactance are
equal.
3.2.8. Determine rotational losses?
LAB: 2 ELEC3310
3.3 Full load test
This experiment will give information regarding the behavior of the MUT induction
machine under full load conditions. In this experiment, rather than having a separate
mechanical load for the MUT induction machine, the VSD controlled induction
machine will act as a mechanical load. The VSD induction machine will act in torque
control mode to ensure that a counteracting full load torque is applied to the MUT
induction motor. The data retrieved from this test will be the line-to-line voltage, line
current (equal to phase current as star connected), motor speed (in rpm) and power
factor of the machine under test.
Full load and synchronous speed results are given in Tables 3 and 4 Respectively.
TABLE 3: Full Load Test Results
---Experiment Information---
Timestamp Mon 29 Aug 2022 10:01:26 AM
Experiment Id 49627
Unit Id 2
---Experiment Specification---
Setup Name Full Load
---Experiment Results---
Ph-Ph Voltage (Volts) 422
Phase Current (Amps) 12.87
Power Factor 0.833
Motor Speed (RPM) -1475
TABLE 4: Synchronous Speed Results
---Experiment Information---
Timestamp Mon 29 Aug 2022 10:06:40 AM
Experiment Id 49630
Unit Id 2
---Experiment Specification---
Setup Name Synchronous Speed
---Experiment Results---
Ph-Ph Voltage (Volts) 424.3
Phase Current (Amps) 0.82
Power Factor 0.676
Motor Speed (RPM) 1499
The three phase transformer bank mentioned in the locked rotor test has been switched
out in this experiment, therefore measured voltages and currents do not need to be
converted or adjusted.
3.3.1. What is the real power being delivered to the machine in this test?
3.3.2. What is the reactive power being delivered to the machine in this test?
LAB: 2 ELEC3310
3.3.3. Using the cantilever (approximate) equivalent circuit, determine the output
power delivered by the MUT induction machine.
3.3.4. What is the machine efficiency?
3.3.5. Determine the electrical and mechanical torque.
Your report should include a cover page, including your details, i.e., name and ID, and
answer to those questions with discussion.
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