High Vibration in Steam Turbine

It could be #2 here.

Thanks Mukesh for your logical answer. There is no bypassing of high pressure steam. There are five nozzles opening sequentially while increasing load. There may be chances that the fifth nozzle is in damaged condition and inlet trajectory getting affected after 45 MW load. From fifth nozzle steam impinges on first row of blades which is like pelton wheel.

Have you checked the linkage to the Load for misalignment, wear or damage? and what about the bearings of the load (generator?)?

Yes, these aspects were examined & analysed.

i believe it is not misalignment. some further information is needed however.

1- what is the oil temperature? 2-what is the orientation of the sensor for the vibration instrument? [axial? x? or y?] 3- what type of vibration test was performed? acceleration, velocity, enveloped ? peak, or averaged ?4- when was this bearing installed? [how many hours /months of operation?] 5 has there been any changes in oil viscosity or type recently?

this 0.38 x rpm is sub synchronous vibration and does coincide with oil whirl.[oil whirl .38 to .49 rpm ]

some turbine vibration problems have been solved [not by me] by altering the oil temperature by as little as a 10 deg F increase. this had affected the oil viscosity [oil whirl] and vibration was eliminated. good luck. let us know.

What type of journal bearings are there?, What is the phase difference of vibrations at two pedastals, Were the bearing clearances on higher side at the time of last overhaul. Is there any change observed in bearing temperatures at higher load? By the data we have seen so far only valid reason seems to be defect of inlet nozzle at highre load.

Here are a some thoughts:

I assume the bearings are roller races - is the preload within the bearing manufacturer's specifications (bearing design limits)? and the equipment manufacturer's specifications(equipment design limits)?

Are the replacement bearings different in any way to the originals? - eg different number of rollers .....etc

Is there a possibility of some strange resonance if the number of rollers in one of the races and the number of vanes on the turbine are related by an integral multiple.

In how many different positions can the turbine output shaft and the load be coupled - has it been coupled in exactly the same alignment as original?

I read an engineering report years ago about a steamer (reciprocating engine) which had operated without a problem for many years, then after a refit blades kept breaking off its propeller ..... after much investigation it was found that the propeller had been replaced one or two bolt holes different relative to the engine crankshaft after the refit and this resulted in one blade being now vertical at the bottom of the stroke and this set up a resonance in that propeller blade which over time fatigued and broke away from the hub. They fitted another new(the third or fourth) propeller in the original orientation relative to the engine crankshaft and the problem disappeared.

WAWAUS, your whole comment is circling around rollers of rolling bearings which is totally irrelevant, because such big turbines have journal bearings. Some one has adjudged it as GA also, may be for narrating your good experience with recip engine steamer.

"some strange resonance" may be possible but not with "the number of rollers in one of the races" I'm quite confident.