steam turbine

if this is back pressure type then it is possible that extraction pr. increases beyond certain value so because of that vibration increases. or there may be some fault in mechanical parts which creat vibrations.

It may actually be a combination of the two, if extraction pressure naturally causes an increase in vibration and the bearing stationary ring has some kind of damage (fatigue or otherwise) then this could trigger excitation at certain rotation speeds after which it appears to disappear. If it was a one of occurrence of this sudden increase of vibration than it could also have been contamination that entered the bearing (and got dispersed again).

Have you checked the turbine blades - are there any missing? any shrouding missing?

When was the last time you had your shaft balanced????

Rgds

Doug Michael (Engr) Mech T.M.I.E.T. C&G. M Navy Engr ( Mech)

Bearing Vibration ? or Rotor Vibration it was indicate on Bearing. A lot of reasson about vibration. Alignment ? Is it your turbine rotor was balance before ? in Low or High speed balance in example ? How about the bearing clearance ? Axial movements ? Steam Pressure (flow) stability & Temperature ? Lube oil pressure & temperature ? etc. . .