Page 223 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Half-yearly maintenance
• Clean the winding of the motors which are subjected to corrosive or other such elements. Also bake and
varnish if necessary.
• In the case of slip ring motors check slip rings for grooving or unusual wear.
• Renew grease in ball and roller bearings.
• Drain all oil bearings, wash with kerosene, flush with lubricating oil and refill with clean oil.

Annual maintenance
• Check all high speed bearings and renew if necessary.
• Blow out clean dry air over the windings of the motor thoroughly. Make sure that the pressure is not so high
as to damage the insulation.
• Clean and varnish dirty and oily windings.
• Overhaul motors that are subject to severe operating conditions.
• In the case of slip ring motors, check the slip ring for pittings and the brush for wear. Badly pitted slip rings and
worn out brushes should be replaced.
• Renew switch and fuse contacts if badly pitted.
• Renew oil in starters that are subjected to damp or corrosive elements.
• Check insulation resistance to earth and between phases of motor windings, control gear and wiring.

• Check resistance of earth connections.
• Check air gaps.
Records : Maintain independent cards or a register (as per specimen shown in trade practical) giving a few pages
for each machine and record therein all important inspections and maintenance works carried out from time to
time. These records shall show past performance, normal insulation level, gap measurements, nature of repairs
and time between previous repairs, and other important information which would be of help for good performance
and maintenance.
Faults which occur in AC 3-phase squirrel cage motor can be broadly divided into two groups
They are

1 Electrical faults
2 Mechanical faults.
In most of the cases both the faults may be individually present or both may be present, as one type of fault
creates the other fault. The following charts give the cause, the test to be carried out and possible remedy.

210

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