intermittent high 1x vibration on steam turbine
intermittent high 1x vibration on steam turbine
(OP)
I have a steam turbine/generator that undergoes huge escalations in 1x radial vibration at the front turbine bearing. The odd part is that the vibration increases greatly and then reduces to normal running conditions over about a 10-20 minute period. Has anyone seen this before?





RE: intermittent high 1x vibration on steam turbine
The symptoms seem like Spiral Vibration. If you have a 1xSS tach pulse (Key Phasor), then measure filtered vibration level and phase. A polar plot of the 1xSS vector would take a spiral path, or circular path if vibratoin amplitude does not keep growing. The cause is related to a shaft/rotor rub in combination with a critical speed (balance resonance) near operating speed.
Walt
RE: intermittent high 1x vibration on steam turbine
If this is a steady operating speed phenomenon, how far away from the T-G lateral critical speed do you operate.
Possibly is it a thermally-bowed rotor due to thermal gradients throughout the rotor that "blend out" after some period of running? Is it possibly a bearing oil film issue? Changes in bearing oil film flow (during startup) could change the bearing spring rate and thus the critical speed. Are the oil pumps started first (before the turbine)?
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
Skip Hartman
http://www.machinerywatch.com
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
On the steam side, there is normally a rise in steam flow when the vibration event occurs. This happens after vibration begins... seemingly a result not a cause.
I have posted more info in Thread666-82790. Your input has been muchly appreciated.
RE: intermittent high 1x vibration on steam turbine
This is a two stage compressor running at 11,100 to 12,600 RPM with overhung steam turbine and hot gas expander at opposite ends. Rotor components are connected through highly tensioned curvic couplings.
Problem was corrected on two rotors by opening up axial clearance on 2nd stage, converting to honeycomb shaft seals, and mininmizing mechanical runout in shaft segments.
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
Skip Hartman
http://www.machinerywatch.com
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
The problem has not occured for some time as the machine is running on load limit at less than full load.
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
I agree with DAVELEO that this is due to thermal gradients that "blend out" after some period of running, but not necesary throughout the rotor, but throughout the turbine casing.
After the turbine is shut-down the rotor barring system is rotating the rotor at about 200-250rpm and therefore it is not very likely that the rotor will be thermally-bowed. But on the other hand the turbine casing could egxert thermal-distorsion and that could cause large bearing loads or tip-clearance exitation. After same time (10-20 min), the thermal gradinets reduce to normal running conditions together with the vibration level.
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
You are describing load changes on your machine.
RE: intermittent high 1x vibration on steam turbine
RE: intermittent high 1x vibration on steam turbine
ultimately you have to open the machine for a detailed inspection.
RE: intermittent high 1x vibration on steam turbine
Cheers
Greg Locock
RE: intermittent high 1x vibration on steam turbine
the thermally bowed rotor i suggested would be due to the rotor stationary with the machine not operating, but still partially hot from running. if the rotor is not on a turning gear, it will heat on the top side due to radiation from the hot steam that migrates to the top side. the rotor will then bow for a time before the temperature soaks out. if you try to restart the machine, the unbalanced rotor will shake until the thermal gradients wash out and the vibration stops.
however this would not occur during continuous running, so it's not your problem.
possibly its a slight rub....the casing heats up due to rubbing and grows away from the rotor, the rub stops, the casing cools and shrinks back and rub restarts and the cycle repeats.
i could go on guessing, but would start asking a lot more questions.
that's my ten cents.
daveleo