Regular monitoring of the following six parameters is required:
Temperature of stator windings
Core temperature
Temperature of slip rings
Vibration levels at the bearings
Brush gear inspection (monthly or bimonthly)
Remove the brush holder. Clean the carbon brushes by compressed air. Inspect the brushes for uneven wear (do not touch the brushes with bare hands). Replace worn brushes. Use a stroboscope to inspect the slip rings. Vary the frequency of the stroboscope to check for uneven wear of the slip rings. The temperature of the slip rings should be measured using an infrared detector. If the slip ring temperature is high, the brushes would overheat and wear quickly. Generator derating is required if the slip ring temperature is high.
On-line partial discharge activity
The electrical and mechanical tests that are required are described in Appendixes A and B, respectively. In summary, the work includes the following:
Perform insulation resistance and polarization index tests.
Investigate causes of partial discharge.
Check the tightness of the stator wedges by tapping them with a hammer. The wedges must be tight to minimize the movement of the stator conductor bars during operation. Rewedging and adding packing may be required.
Perform EL-CID test to determine if there is any loosening in the core laminations or deterioration in the core insulation. Apply penetrating epoxy if insulation is degrading.
Perform casing pressure, and stator pressure and vacuum decay tests.
Refurbish rotor, including inspection of radial...
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