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Can anyone explain why during start up of GE 5001 gas turbine there a high vibration level which can shut down the machine? To enable complete start we short cut the regulation (control) during start up.

I need documentation in this matter.

Hello,

During start-up you experience high vibration.
What kind of maintenance was done on the turbine? Was it a major inspection done? Vibration are caused due to many reasons.

After maintenance unit may have not turned on ratchet minimum 42 hrs, check lube oil temperatures, blockage of lube oil supply to bearings, check for good sealing air to the bearings, check alignment of turbine, loose fitted bearings, cooling water to turbine support legs, last but not the least... check cables to vibration sensors and the their layout up to control panel - they must not pass through high voltage cables.

What kind of control do you have? GE-Speedtronics-MK2, 5, 6? Is the application for a power plant or compressor?

Best Regards,

Mambo

Most every GE-design heavy duty gas turbine and generator passes through two critical vibration speed ranges (GE never publishes the exact speed ranges) during acceleration from zero speed to FSNL. Usually, the machines are all balanced to minimize the vibrations and so any unit should not be experiencing such high vibration spikes as to even cause a high vibration alarm to be annunciated during starting and acceleration.

You haven't told us what the maximum vibration experienced is, at what speed (range) it occurs, if the vibration is being experienced on the turbine (bearing No.1 or No. 2), the reduction gear, or the generator (turbine- or collector end). You also haven't told us when this problem started, such as after a maintenance outage, or a trip from load. Does it occur on every start, or just when the unit is cold, or just when it's hot? What is the L.O. Header temperature when the vibration is occurring? Are there redundant vibration sensors (velocity ("seismic"), proximity, or ???) on the bearing which is exhibiting the high vibration, and if so, do both sensors indicate approximately the same vibration or is it just a single pick-up of the two that's causing the problem?

What have you done to try to troubleshoot the problem?

Have you verified the problem is not a sensor/instrumentation problem? Have you used hand-held or other vibration measuring equipment to confirm the vibration levels being indicated by the turbine control system?

It would seem that if indeed you are experiencing some high vibrations during start-up (not a sensor problem) that something is amiss with the unit.

I would suggest you obtain the services of a vibration consultation firm to measure and analyze the vibration which is causing the problem, and to make recommendations for reducing the vibration to more acceptable levels. It's likely this hasn't existed since the unit was first started-up, or if it did that it wasn't properly balanced to begin with.

And, stop "short cutting" the control during start-up. Fix the real cause of the problem instead of using the control system to avoid fixing it.

It is quite common in Frame 5 machines during startup you can see high amplitude in load gear box & generator bearings, but after machine warmup, and with load it will come down. For better conclusion take the reading after 24 hours.

I experienced this myself with 0.7in/s axial reading in generator bearings which became 0.2 after 24 hours. Please give more details about your machine condition.