Cooling coils and generator air coolers
The bearing cooling coils and generator air coolers should be thoroughly inspected
for leaks, corrosion, and mineral buildup. The end of the air coolers should be
removed to allow the inspection of the tube sheet and the connection of the tubes.
Leaking tubes should be replaced. If a significant number of tubes are leaking or if
their general condition is questionable, the entire cooler should be retubed. After
retubing, the cooler should be hydrostatically tested at a pressure of at least 110
percent of the working pressure to check for leaks.
The bearing cooling coils should be thoroughly inspected and hydrostatically tested.
Due to corrosion and weakening of joints due to years of vibration, it is sometimes
more economical to replace the coolers rather than trying to repair them. If it is
determined that it is feasible to repair the coils, a hydrostatic test should be
performed after the repair to insure the repair was successful and that no new leaks
The piping to the air coolers and cooling coils should be checked for corrosion and
mineral buildup and replaced if necessary.
The condition of collector ring and commutator of the exciter rotor should be
checked for roundness and evidence of wear or arcing. The groove on the
commutator should be thoroughly cleaned of carbon dust or other contaminants. If
necessary, the collector rings should be machined in a lathe to restore their surface
finish and roundness.
With the unit disassembled, it is possible to perform a thorough inspection of
components not normally accessible. The upper and lower bridges should be
checked for cracked welds or other signs of damage. The torque on the stator frame
bolts should be checked and the dowels checked to make sure they haven't backed
out. The rotor spider should be checked for cracks with special attention given to
where the arms connect to the hub and the rotor ring. The brake ring should be
checked for uneven wearing, cracks, and evidence of excessive heating.
4.10 Generator brakes
The generator brakes should be disassembled for inspection. If there is corrosion or
scoring in the cylinder, it should be rebored or honed, depending on the extent of
damage, and if necessary, a new piston fabricated and installed. Leather packing
should be replaced with a fluorocarbon or similar material.