Sudden high vibration in GTG unit
Sudden high vibration in GTG unit
(OP)
We have a 5100/3000 RPM, 20 MW Gas Turbine-Gear-Generator unit. Velocity probes are mounted on the generator bearings (two) and turbine bearings (two). The gear does not have any probes.
The unit runs normally with vibration velocities at above points not exceeding 6 mm/sec. But, without any appreciable change in noise or vibration, the probe in the generator front bearing trips on high vibration (over 25 mm/sec)when the load exceeds 18 MW. But this does not happen every time. Only occasionally enough to cause concern.
The vibration probes/cards/cables have been interchanged/replaced/calibrated but no use. The generator is certified healthy.
What could be the reason for this sudden high vibration? The low speed gear (3000 RPM) is found to have free vertical play of over 10 mm in decoupled state. Could this free play of gear create sudden high vibration especially at high loads? If so, how ?
The unit runs normally with vibration velocities at above points not exceeding 6 mm/sec. But, without any appreciable change in noise or vibration, the probe in the generator front bearing trips on high vibration (over 25 mm/sec)when the load exceeds 18 MW. But this does not happen every time. Only occasionally enough to cause concern.
The vibration probes/cards/cables have been interchanged/replaced/calibrated but no use. The generator is certified healthy.
What could be the reason for this sudden high vibration? The low speed gear (3000 RPM) is found to have free vertical play of over 10 mm in decoupled state. Could this free play of gear create sudden high vibration especially at high loads? If so, how ?





RE: Sudden high vibration in GTG unit
RE: Sudden high vibration in GTG unit
Is the bearing gone?
Load dependent vibration is likely from the gear - transmitting vibration to the generator - gear torque causes radial loads due to gear tooth angles. If this speed decreaser is an upmesh gear, the pinion would be forcing the bull gear up in its bearings. The coupling could be resisting - getting more and more misaligned. If it is an out-dated gear-type coupling you could have torque-lock. Inspections should be done of coupling and bearings and then the gear (for backlash, damage etc.)
RE: Sudden high vibration in GTG unit
It is also possible that you are getting a feedback from the electrical circuitry. If you have a way to capture the data leading up to the trip, it should have the information you are looking for.
RE: Sudden high vibration in GTG unit
We also think the gear vertical play is way beyond limits. The gear is more than 30 years old and has never been opened and checked all these years. Thanks for your comments. We will take up the gear inspection asap.
bluemax & Mcvibe,
As I said, the vibration is too sudden to take any signature. It all happens in a trice. Though we have online monitoring (metrix), there is no provision to capture any data. Any suggestions, how we can capture data (like what on line vibration monitoring and data acquisition system we should use) ?
RE: Sudden high vibration in GTG unit
But again, what is the frequency? Is it true vibration or just spike caused by instrument grounding? Frequency will let you know.
RE: Sudden high vibration in GTG unit
http://www.teac-recorders.com/drindex.html
Another transient data recorder should be available from: http://www.maars.com/
RE: Sudden high vibration in GTG unit
http://www.maars.com
phone +1-865-212-0006
Knoxville, TN
Good luck,
Skip Hartman
http://www.machinerywatch.com
RE: Sudden high vibration in GTG unit
RE: Sudden high vibration in GTG unit
RE: Sudden high vibration in GTG unit
IRD velocity probes aren't made anymore to my knowledge.
Can also be a problem with accelerometers:
http://www.wilcoxon.com/technotes/tn14.html
http://www.skfcm.com/products/sensor/vib/cm2005.pdf
RE: Sudden high vibration in GTG unit
RE: Sudden high vibration in GTG unit
It could be that currents are at the front bearing affecting the probe. Perhaps the bearing insulation capability is intermittent. We had rare cases of currents when monitoring the motors driving our PAP industrial air compressors We made a home-made version of a shield, then used one from IRD. Aluminum can extended around entire probe and connector for output cable. We now use an accelerometer and integrate to get velocity / displacement for motor vibration (shaft displacement probes for compressor).