rida batool naqvi modified
TRANSCRIPT
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Rida Batool Naqvi
B.Sc Metallurgy and Material EngineeringInstitute Of Advanced MaterialsBahauddin Zakariya University
Multan.
failure analysis center investigating the cause of failure of an air conditioner’s motor
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Introduction:
An Acson ALC18C / AWM20J 1.5 Ton Split Air Conditioner motor was received at FAC. Air conditioner was installed in IST 6 Block. It was required to examine the root cause of the fire that either it was the motor that started the fire after getting short circuit or an external fire affected the motor.
Air conditioner motor and its parts:
An AC motor is an electric motor driven by an alternating current (AC). The AC
motor commonly consists of two basic parts, an outside stationary stator having
coils supplied with alternating current to produce a rotating magnetic field, and an
inside rotor attached to the output shaft producing a second rotating magnetic field.
The rotor magnetic field may be produced by permanent magnets, reluctance
saliency, or DC or AC electrical windings.
Different components of an A.C motor are shown in the Figure 1.
Fig. 1
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Comparison between an intact and a damaged motor:
Fig. 2-Intact Motor
Fig. 3-Burnt Motor
As Received Burnt Motor
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Visual Observations:
The motor received was Blackish in color and one side of the motor that
should consist of a blower was melted over the surface of motor.
Comparison of intact and received motor:
Fig. 4-Intact motor assembly
The actual intact motor should consist of a blower on its one side but the motor
that was received consist of just a melted part that was further examined after
dismantling.
Blower
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The motor was completely burnt from outside. Figure 5 shows the still images of
the as received motor.
Fig. 5-As received part
Stereomicroscopy:
The stereomicroscopy was performed on the part to examine the macroscopic
features of damage and signs of mechanical failure associated with the motor but
there were no signs of any dominant external forces acting on the motor that
caused fire.
There were only the signs of burning and melting on the outer surface of the motor
as shown in Figure 6.
Melted Blower
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Fig. 6-Stereomicroscopic images of burnt motor
Dismantling:
The motor was dismantled to examine it from inside and to find out the condition
of the internal windings. Following findings were drawn from dismantling:
1. The screws were not completely melted.
2. The internal copper wires were just blackish in color due to external heat.
3. The winding was not melted at all.
4. All of the internal parts of the motor were at their respective positions.
5. The blower was melted and stuck to the outer surface of motor.
Melted outer region
Melted wire attached to burnt surface
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Fig. 7 Intact screws
Fig. 4 External wire
Melted portion of wire
Undamaged screws
External portion of wire
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Fig. 8-Inner side of melted blower
Fig. 9-outer surface of blower
This outer area of the blower was hidden below melted plastic debris
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Fig. 10-Images after dismantling
Fig. 11-Image of full dismantled motor
Black but intact copper winding
Rotor
Outer shell
Rotor
Stator
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Conclusion:
It was concluded from the tests and visual observations that the motor was not
damaged internally and all of the internal windings were intact thus indicating that
the fire was not due to internal problem.
The fire probably came from external side that melted the blower and all the plastic
material outside the motor as the external casing was more damaged than interior
portion.