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GE Pegasus MHV GEEP-427-I Instuctions page 24

Horizontal induction motor totally enclosed water-to-air cooled sleeve bearing
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abrasive environmental contaminates can wear away
wedges. However, such an affect may not be visible on
the wedges except at inspection in which the rotor is
removed.
The insulation resistance should be measured and
recorded during each inspection of the winding. Refer to
the information on page 15 - Insulation Resistance. If the
measured value of insulation resistance in megohms is
less than (KV + 1), when corrected to 40C, the machine
should not be put back into service until steps have been
successfully taken on the winding to restore its insulation
resistance to that value, or more. At this point, a
polarization index measurement may also be helpful as
additional data on the condition of the winding. See the
information on page 16 - Polarization Index.
Moisture and dirt are the two primary causes of
low insulation resistance of a winding. Accordingly, the
first two steps in correcting such a condition are to dry
the winding and to remove all possible dirt and
contamination. Space heaters should always be turned on
when the machine is shut down. If this is not done, the
insulation resistance will usually decrease because of
condensation on the windings. Space heaters may be
used to dry out a winding, but adequate time must be
allowed to accomplish it. Also, low voltage may be
applied across the winding terminals (ac or dc) to
circulate a fraction of must be monitored in order to keep
the temperature below rated during the drying out
process. Six to eight hours, depending upon the size of
the unit, are required for drying a winding with
circulating current. The winding should be thoroughly
24
GE Energy Motors GEEP-427-I
GEEP-427-I Pegasus, Horizontal Induction Motor
cleaned, in order to remove dirt and contamination, as an
important part of the program to increase the insulation
resistance value.
A thorough cleaning and drying program will
usually restore the winding insulation resistance to (KV
+ 1) megohms, or more, corrected to 40C. If it does not,
it is probable that some additional factor, beyond
moisture and dirt, exists. If the incoming cable was not
disconnected from the motor leads in the conduit box, the
additional cable could significantly affect the insulation
resistance. Surge capacitors which are directly connect to
the stator winding could procedure a similar affect. In
both cases, the connection with the stator winding should
be opened and the insulation resistance test repeated.
If all the above corrective actions fail to restore
the insulation resistance value, it is highly probable that
expert Assistance will be required. It is recommended
that a General Electric Service Shop be contacted for
assistance.
There are additional tests which are available for
use on stator windings, particularly on older windings, to
determine their present condition and serviceability.
Among these are high potential dc and ac testing. It is
important that such testing be done only by people
trained in conducting the tests, to avoid unnecessarily
damaging the winding, to correctly interpret the results
and to observe all the safety precautions necessary to
protect personnel. If it is desired to do such testing at
some point in the history of the unit, it is recommended
that a General Electric Service Shop be contacted.
Copyright 2009, The General Electric Company, USA
TEWAC, Sleeve Bearing

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