Electrical Machine (EET 306/4)
Laboratory Module
EXPERIMENT 5
SQUIRREL CAGE INDUCTION MOTOR
Objective:
Understand the structure and principle of squirrel cage induction motor and control the
rotary direction.
Equipment:
Starting resistor module (NO-5302) ……………………………………….………. 1 set
Machine field frame module (NO-5310) …………… ………………………….…. 2 set
Power supply module (NO-5306) ……………………………………………….…. 1 set
AC Voltage/Ammeter module (NO-5307) ……………………………………….… 1 set
DC Voltage/Ammeter module (NO-5308) …………………………………….…… 1 set
3 phase machine graphic board (NO-5314) ………………………………….…… 1 set
Rotary converter graphic board (NO-5315) ………………………………….……. 1 set
Disc slot B Type rotor (A02) ………………………………………………….……… 1 set
3 pole rotor (A04) ……………………………………………………………….…….. 1 set
Cage rotor (A06) ……………………………………………………………….……… 1 set
Wide pole piece for field winding (A10) ……………………………………………. 5 set
Field winding/300 turns (A13) ………………………………………………………. 3 set
Field winding/700 turns (A14) ………………………………………………………. 2 set
C Type brush holder set (A18) ……………………………………………………… 1 set
Rotor fixture (A20) ……………………………………………………………………. 2 set
Magnetic pole fixture (A21) ………………………………………………………….. 5 set
8 mm spanner (A24) …………………………………………………………………. 1 set
Fixing bolt (A22) ………………………………………………………………………. 6 set
Introduction:
The induction motor is an AC motor commonly used at homes in fans, compressor
and in some certain office appliances such as photocopy machine. An induction motor has the
same physical stator as synchronous machine, with a different rotor construction. There are
two different types of induction motor rotors which can be placed inside the stator. One is
called a squirrel cage rotor, while the other is called a wound rotor.
A squirrel cage induction motor rotor consists of a series of conducting bars laid into
slots carved in the face of the rotor and shorted at either end by large shorting rings. This
design is referred to as a cage rotor because the conductors, if examined by them, would look
like one of the exercise wheels that squirrels run on.
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Electrical Machine (EET 306/4)
Laboratory Module
Procedure:
1. Install the 8 modules which are power supply (NO-5306), Starting resistor module (NO5302), AC Voltage/Am meter module (NO-5307), DC Voltage/Am meter module (NO5308), 2 Machine field frame (NO-5310), Rotary converter graphic board (No-5315)
and 3 phase machine graphic board (NO-5314) on the experimental board rack.
2. Fill the field winding/300 turns (A13) in the magnetic pole and assemble it in machine
field frame (NO-5310). See Figure 5.1 for details.
Figure 5.1 Assembling drawing for induction motor principle
3. Fill 3-phase machine graphic board (NO-5314) in the terminal slot of stator winding
(A13) as in Figure 5.1.
4. Fill also the field winding/700 turns (A14) in the magnetic pole and assemble it in
machine field frame (NO-5310). See Figure 5.2 for details.
Wide pole piece for field winding
(A10)
C type brush holder set (A18)
3-pole rotor (A04)
Field winding/700 turns (A14)
Figure 5.2 Assembling drawing for the rotary converter
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Electrical Machine (EET 306/4)
Laboratory Module
5. Fill rotary converter graphic board (NO-5315) in the terminal slot of stator winding
(A14) as in Figure 5.2.
6. Connect the rotary converter and induction motor referring to Figure 5.3 and Figure
5.4. Install the disc slot B Type rotor where straight angle short line is mounted with
rotor of induction motor; initiate the experiment about starting resistor at the position of
maximum resistance value.
Figure 5.3 Connection of the Cage Directed Motor
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Electrical Machine (EET 306/4)
Laboratory Module
Figure 5.4 Principle experiment circuit of induction motor
7. Turn ON the power supply (NO-5306), compare and observe the rotary speed of rotary
converter and the speed of disc slot B type. Adjust the starting resistor (NO-5302)
gradually. Explain in the discussion.
8. Turn OFF the power supply and replace the disc B Type rotor with cage rotor (A06).
9. Then, turn ON the power supply and adjust the starting resistor (NO-5302) (at the
minimum location) until the cage induction motor spine at appropriate speed. Record
the value of normal current and voltage as indicated at the ammeter, A2 and voltmeter,
V2 at that time. (Fill in both values in results section).
10. Turn OFF the power supply. Wait for the cage induction motor stops completely, next
turn ON the power supply again. Record the maximum value of starting current and
voltage at that time. (Fill in both values in results section).
11. Turn OFF the power supply, change and connect two lines out of 3-phase power (U, V,
W) supply to the cage induction motor. Operate the motor and observe how the rotary
direction changed. Explain in the discussion.
12. When the experiment is completed, turn all the switches ‘OFF’ and disconnect the
connecting code. Disassemble the equipment, parts and store in the designated
places.
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Electrical Machine (EET 306/4)
Laboratory Module
Name:______________________________ Matrix no.:_____________ Date:_________
RESULT
Normal current, I = ____________________ A
V = ____________________ V
Starting current, Is = ___________________ A
V = ___________________ V
Instructor Approval: …………………………….
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Date: ………………
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Electrical Machine (EET 306/4)
Laboratory Module
Name:______________________________ Matrix no.:_____________ Date:_________
DISCUSSION:
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CONCLUSION:
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Instructor Approval: …………………………….
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Date: ………………
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Electrical Machine (EET 306/4)
Laboratory Module
Name:______________________________ Matrix no.:_____________ Date:_________
PROBLEM:
1. The starting current of cage induction motor is much bigger than the one under normal
operation. Explain the method used to limit this starting current.
Instructor Approval: …………………………….
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Date: ………………
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