Specifications

166
 Check voltage of alternator at terminals and panel boards. If the generator is operating
satisfactory, load the alternator gradually for 2 to 4 hours to evaporate remaining moisture.
While testing it should be within 5% of rated voltage and 3 phases load should be well
balanced.
 Always open bus bar switches and then stop the alternator. Be sure that all the switches
are in
‘
off’ condition before working on the equipment.
 Reversed coil connections of pole windings can be detected by passing Direct current
through winding and testing poles by soft iron strip or bar. If polarity is correct soft iron
piece will be held tightly. If not the bar will not be held in its place. Great care is to be
taken if D.C. exciter is to be removed for check up of main alternator itself.
 Sliprings on rotor are made of Bronze or non ferrous metal which are polished by fine
sand paper or polishing stone. If the rings are worn-out excessively, the rotor should be
removed and the rings be reduced down in diameter on the lathe machine. Insulation
resistance is then measured by Megger, ring to ring and ring to shaft. Accumulation of
carbon or metal dust in the vicinity of rings should be cleaned thoroughly.
 Before starting the motor or alternator – clean the motor/alternator surrounding area to
make sure that there is sufficient open space for air movement, also be sure of dry
windings.
 Make sure from name plate data that type, design of the motor for that work and load.
 Check that operating speed reaches in minimum time, if not there may be overload or
centrifugal switch or starting coil is defective. If motor is running in improper direction
check for the proper connections as per manufacturing data.
 Check for unusual noises. Poor alignment of end plates, which causes the rotor core
to strike against the stator core. Bearing may be defective. If motor becomes overloaded
and begins smoking, there may be over loading or defective starting winding or switch.
Clean the commutator or reset brushes or adjust spring tension of brushes, if there is
sparking at brushes.
15.9 General procedure for overhaul of motors :
1) Disconnect the supply cables at the terminal box of the motor, uncouple the motor from
the driven machine, unfasten the foundation bolts or nuts and remove the motor to the
maintenance shop.
2) Remove the external fan covers, canopies, heat exchanger or other fitments.
3) Dismantle the motor without using the excessive force, and without the hammer blows.
Care should be taken to see that the rotor does not touch the stator winding overhangs.
If possible do not open cartridge bearing housings.
4) Clean dust, dirt, oil and grit from every part of the machine with the help of blower,
compressed air hose, bellows or brushes and then wash with petrol to which a few
drops of lubricating oil have been added. The windings may be cleaned by means of
carbon tetra-chloride. Care being taken to avoid its application to slip rings and brushes.
5) Carry out visual inspection of all parts for wear or damage, replace worn out or damaged
parts.