Intermittent Vibration on 4.16KV Generators.
Intermittent Vibration on 4.16KV Generators.
(OP)
Units: 4160 V, 4750 KW, 60Hz, 1800RPM; 0.8pf
We have a few of the above unit that start vibrating once they are put back in service after a recondition in a manufacturer certified shop. The vibration is intermittent; it can happen as often as 3 times in a day or once in 3 weeks. The vibration amplitude is also inconsistent; it can range from 1mil to 5 mils, and last anywhere from 2 minutes to 10minutes. The generators are set to alarm at 4 mils and trip at 5 mils. We've had a couple of trips. The vibration only occurs at 1x, but we can't find a reason for it. It doesn't appear to be instrumental, since on one unit all the Bentley Nevada probes were cleaned &/or replaced, but the vibration returned. We are trying to figure out if it is electrically induced or due to a mechanical (or physical) fault in the rotor.
Does anyone have an idea of what might be going on? So far the repair shop and manufacturer are just as clueless as we are.
We have a few of the above unit that start vibrating once they are put back in service after a recondition in a manufacturer certified shop. The vibration is intermittent; it can happen as often as 3 times in a day or once in 3 weeks. The vibration amplitude is also inconsistent; it can range from 1mil to 5 mils, and last anywhere from 2 minutes to 10minutes. The generators are set to alarm at 4 mils and trip at 5 mils. We've had a couple of trips. The vibration only occurs at 1x, but we can't find a reason for it. It doesn't appear to be instrumental, since on one unit all the Bentley Nevada probes were cleaned &/or replaced, but the vibration returned. We are trying to figure out if it is electrically induced or due to a mechanical (or physical) fault in the rotor.
Does anyone have an idea of what might be going on? So far the repair shop and manufacturer are just as clueless as we are.






RE: Intermittent Vibration on 4.16KV Generators.
If actual, you will need to get phase to help identify the problem. Do you have access to a"TurboBalancer" for logging magnitude and phase. It can accept B-N along with siesmic like IRD.
If it were bearing instablity (oil whipping)due to change in bearing geometry or alignment changing bearing loading, it should be 0.6 to 0.8X
A change in the mounting of the B-N could allow the probes to go into resonance giving errounous readings. If the probes are long (over a couple inches) the mounting should have bushings near the shaft to damping out probe resonace.
Shaft voltages my generate errounous readings(and be causing damage). I would expect the driven end bearing has a grounding brush and the bearing insulated.
Is the excursion related to changes in excitation current? If the field bar's expansions are restricted
can cause problems.
RE: Intermittent Vibration on 4.16KV Generators.
RE: Intermittent Vibration on 4.16KV Generators.
----------------------------------
If we learn from our mistakes,
I'm getting a great education!
RE: Intermittent Vibration on 4.16KV Generators.
Hopefully I am not way out in left field with this reply.