Some sub-critical 300 MW and 600 MW turbogenerator units

which were put into operation in recent years by North United Electric Power Corporation

Ltd.

have undergone vibration problems.These vibration problems include over-vibration of low-pressure rotor bearing chock

sudden low-frequency vibration of No.1 and No.2 bearings due to the vibration of high-or medium-pressure rotor excited by steam under heavy load

and vibration measuring error because of defective insulation of generator bearing chocks.This paper describes the features of the vibrations in the units

analyzes the causes of vibration

and summarizes the field treatments for reducing these vibrations.