On site we have a GE Gas turbine 9FA DLN2.0+ coupled with a GE Hydrogen Cooled Generator 324H. It was noticed recently that we have smoke leak or mist oil leak from the generator shaft at collector end. Measures with the portable analyzers have not indicated presence of hydrogen. The operational values of the generator and seal/lube oil system are ok. The bucket test is within limits, the smoke/mist oil leak is shown mainly with the unit in turning gear (8 rpm) but also with the unit in operation. In the past we had the following problems in that area:
1) arching in the end shields upper/lower, it was repaired with epoxy application,
2) hydrogen leakage due to crack in the white metal of hydrogen seals, the seals have been replaced 4 times in 121 years,
3) remaining problem is the fact that the generator fixators are stiff and can not take the proper loading but this is a more generic and complex problem.
We made also operational tests, by operating both mist eliminators. The suction filter is new, less than one year before replaced. Can you please suggest any possible cause? The fact of smoke./oil mist leak from that area (between generator shaft surface) can indicate that there is leak from the bearing outer deflector.