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Job 1
NAME ________________________________ DATE_______________
DISASSEMBLE AND REASSEMBLE AN ALTERNATING CURRENT MOTOR
PRE-JOB QUESTIONS:
1.
What is the formula for finding the synchronous speed of an AC induction motor?
2.
What is the synchronous speed of the following motors operating on 60 cycle AC?
2 pole ____________________
4 pole ____________________
6 pole ____________________
8 pole ____________________
3.
Does the motor assigned to you run at synchronous speed? Why or why not? (See the motor
nameplate)
4.
Why should the motor end bells and the frame be marked before disassembly?
5.
Why should the growler switch be turned off when there is no rotor on the growler face?
6.
Why should the rotor be turned as you tighten the end bell bolts?
7.
What must you do with the motor before returning it to the shelf?
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8.
Record your motor’s nameplate data in the table below
HP
RPM
Volts
Amps
Cycles
Type
Frame
SF
Temp. Rise
Model #
Serial #
Phase
# of poles
Code
#of slots
Duty Rating
References:
Lab Manual Information Sheet #1, “The Basic Use of Growlers”
Lab Manual Information Sheet #5, “Types and Characteristics of Fractional HP
Motors”
Electric Motors and Motor Controls - Keljik
Delmars Standard Textbook of Electricity - Herman
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Objectives:



Identify the general construction of a small single-phase motor.
Identify parts nomenclature of an AC motor.
To test an AC motor with growlers.
General Instructions:




Disassemble the assigned motor.
Examine the parts and determine how they are connected and operate.
Test the motor for grounds, shorts and opens.
Reassemble the motor.
Equipment, Tools and Materials:
Assigned motor
Screwdrivers
Crescent Wrench
Permanent marker
Internal Growler
External Growler
Megger
Multimeter
Wrenches
Plastic Hammer
Precautions:




Use the proper tools - do not use pliers for wrenches.
During reassembly, tighten the end bells evenly and alternately to prevent warping.
Replace all spacer washers on the proper shaft end.
Take care not to pinch wires between the end bells and the motor frame.
Operating Steps:
1. Examine the motor to determine if it is properly marked. If it is not, correctly mark the end bells
using a
permanent marker.
STATOR
PUNCH MARKS
END BELLS
2.
Use the Megger to test the windings. Record the results on the Motor Test Form. (See the instructor
if you have any questions)
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Operating Steps (Continued):
3. Measure and record the combined resistance of the motor windings.
4.
Disassemble the motor using proper tools.
5.
Examine the rotor and the stator construction, count the number of slots in each one. Study the
centrifugal mechanism and the switch. Note when it is open and when it closes.
6.
Study the windings and trace their circuits. Draw these circuits at the end of this section.
7.
Measure and record the resistance of the start and run windings.
8.
Test the stator and the rotor for shorts, grounds and opens using both the internal and external
growlers. Record the results on the Motor Test Form.
9.
Reassemble the motor.
a.
b.
c.
d.
e.
Mount the front end bell (Starting switch side).
Arrange the wires from the open end of the motor so they will clear the rotor when installed.
Insert the rotor.
Mount the other end bell.
Tighten the bolts alternately and evenly. Turn the rotor occasionally as you tighten to insure
that the rotor does not bind.
10. Present the motor to the instructor for inspection prior to returning it to the shelf.
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Motor Test Form
Resistance
Number of
Noisy/Quiet
Good/Poor
Megger Test
Rotor slots
Stator slots
Start windings
Run windings
Combined windings
Internal Growler test
External Growler test
Motor Circuit Diagram : Connect and label the circuit and the windings of the split-phase motor
below.
L1
run
rotor
L2
start
cent. switch
Instructor’s OK ___________________________
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FINAL QUESTIONS: (Answer on a separate sheet)
1. Describe the operation of the starting switch during start, while running at full speed, and during
deceleration.
2. Describe the construction of the rotor of this motor? What is another term for the rotor of a squirrelcage induction motor?
3. How is current caused to flow in this rotor?
4. How is the direction of rotation reversed on a split-phase motor?
5. What does a single code letter on a motor nameplate indicate?
6. Describe, in detail; the operation of a split-phase motor?
7. The speed of a split-phase motor is
A. constant.
B. varies over a small range.
C. adjustable.
8. The starting torque of a split-phase motor is what percentage of its running torque?
9.
List 5 applications for a split-phase induction motor.
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10. Define synchronous speed.
11. Describe the construction of the run windings.
12. Describe the construction of the start windings.
13. Explain why a squirrel-cage induction motor cannot run at synchronous speed.
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