Need your expertise feedback,
I'm having gas turbine generator which specification as below :
Turbine : GE Frame 5, 5105rpm (2 bearing)
Load gear : GE S-624 (4 bearing)
Generator : 28kVA, 2pole, 3600rpm (1 bearing)
Recently gone for major overhoule ( replace turbine rotor, replace bearing gearbox and generator cleaning, ) previously this unit was detected having high vibration in all axial point vibration in gearbox up to 0.829 inc/sec. the field analyses was recommended to inspect gear and bearing.
The project was given to well known service , as per request by user the above mention repaired was delivered, during service they found bearing gear on #3 dan #6 were having some burnt part on the housing bearing.
Commisioning was carried out, and somehow similar vibration signal were happening high axial vibration on bearing #3 and #6 and now up to 1.5 in/sec. ( other point vibration all in normal level vibration ) generator 1st order signal was clearly seen on vibration data, balancing were decided to be executed
After 2 x correction, we were managed to lower the vibration level to 0.9 in/sec on those axial gearbox bearing, the problem is during first 2 hour operation with 15 MW load the vibration were on acceptable level some where around 0.5 - 0.52 in/sec and suddenly rise up to 0.9 - 1.0 in/sec , oil temperature were also detected rise up .
What could possibly make those high vibration appeared after 2 hours on steady and normal vibration level.