Manual for Induction Motors and Generators
Maintenance -
79
3BFP 000 050 R0101 REV E
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Spray-varnish equipment, the frame of the machine, and the windings should be earthed
during spray varnishing
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Take necessary precautions when working in pits and cramped places
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Only people trained to do high-voltage work can carry out a voltage test
•
Do not smoke, eat, or drink at the work site.
For a test record for winding maintenance, see
.
7.6.2 The timing of the maintenance
There are three main principles for timing the winding maintenance:
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Maintenance of the windings should be arranged according to other machine maintenance
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Maintenance should be performed only when necessary
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Important machines should be serviced more often than the less important ones. This also
applies to windings that become contaminated rapidly and to heavy drives.
NOTE: As a thumb rule, an insulation resistance test should be made once a year. This should
suffice for most machines in most operating conditions. Other tests should only be
conducted if problems arise.
A maintenance program for the complete machine, including windings, is presented in
. This maintenance program however, should be adapted to the
customer's particular circumstances, i.e. servicing of other machines and operating conditions as
long as recommended servicing intervals are not exceeded.
7.6.3 The correct operating temperature
The correct temperature of the windings is ensured by keeping the exterior surfaces of the
machine clean, by seeing to the correct operation of the cooling system and by monitoring the
temperature of the coolant. If the coolant is too cold, water may condense inside the machine.
This can wet the winding and deteriorate the insulation resistance.
***Following paragraph for cooling type: Open air
For air-cooled machines, it is important to monitor the cleanliness of the air filters. The cleaning
and change interval of the air filters should be planned according to the local operating
environment.
The stator operating temperatures must be monitored with resistance temperature detectors.
Significant temperature differences among the detectors could be a sign of damage in the
windings. Make sure that the changes are not caused by the drifting of the measuring channel.
7.6.4 Insulation resistance test
During general maintenance work and before the machine is started up for the first time or after
a long period of standstill, the insulation resistance of stator and rotor windings must be
measured.
The insulation resistance measurement provides information about the humidity and dirtiness of
the insulation. Based upon this information, correct cleaning and drying actions can be
determined.
