What you said is too vague. There are many reasons why bearings vibrate. Let me list a few: (1)
There is a significant mass imbalance in the rotor, or there is a significant imbalance. rotor heat during bending start.
(2)
The static clearance of the turbine disappears and friction occurs.
(3)
The expansion of the steam turbine is blocked or uneven, causing the cylinder to deflect or deform.
(4)
The turbine blades are broken or internal parts are falling off.
(5)
The turbine rotor is bent.
(6)
The steam turbine enters cold steam and cold water.
(7)
The steam turbine bearing does not work properly, the oil film is unstable, and the oil film oscillates.
(8)
Steam excitation.
(9)
Electrical reasons such as unequal air gap inthe generator.
(10)
Abnormal friction occurs in the sealing tile.
(11)
The temperature of the hydrogen gas in the generator changes significantly.
(12)
The temperature or pressure of the lubricating oil changes significantly.