Page 222 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Maintenance, service and troubleshooting in AC 3

phase squirrel cage induction motor and starters

Objectives: At the end of this lesson you shall be able to
• list and state about the maintenance schedule of AC 3 phase motor
• list out the possible faults, causes and remedies in 3 phase motors
• explain the mechanical problems in motor, bearings and their remedies
• state the lubrication techniques on learning
• explain the troubleshooting of AC motor starters and maintenance of starters.

Generally due to the rugged construction of the AC squirrel cage induction motor, it requires less maintenance.
However to get trouble-free service and maximum efficiency, this motor needs a scheduled routine maintenance.
As found in most of the industries the AC squirrel cage motor is subjected to full load for 24 hours a day and 365
days a year. Therefore the maintenance should be scheduled to have periodic maintenance for a selected area
on daily, weekly, monthly, half yearly and yearly periods for increasing the working life of the motor and to reduce
the break down time.
Maintenance schedule: Suggested maintenance schedule for the AC squirrel cage induction motor is given below
as a guide.

Daily maintenance
• Examine earth connections and motor leads.
• Check motor windings for overheating. (Note that the permissible maximum temperature is above that which
can be comfortably felt by hand.)
• Examine the control equipment.
In the case of oil ring lubricated machines
i examine bearings to see that oil rings are working
ii note the temperature of the bearings

iii add oil if necessary
iv check end play.
Weekly maintenance
• Check belt tension. In a case where this is excessive it should immediately be reduced and in the case of
sleeve bearing machines, the air gap between the rotor and stator should be checked.
• Blow out the dust from the windings of protected type motors, situated in dusty locations.
• Examine the starting equipment for burnt contacts where motor is started and stopped frequently.
• Examine oil in the case of oil-ring lubricated bearings for contamination by dust, dirt etc. (This can be roughly
ascertained on inspection by the colour of the oil).
Monthly maintenance
• Overhaul the controllers.

• Inspect and clean the oil circuit breakers.
• Renew oil in high speed bearings in damp and dusty locations.
• Wipe brush holders and check the bedding of brushes of slip-ring motors.
• Check the condition of the grease.

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CITS : Power - Electrician & Wireman - Lesson 93-100 CITS : Power - Electrician & Wireman - Lesson 93-100