Rotor Instability Due to Coupled Effect of Lateral and Torsional Modes and Improper Bearing Design

Abstract

Abstract This paper deals with a special subsynchronous vibration problem, namely rotor instability caused by partly coupled effect of torsional and bending modes and partly improper bearing design. A theoretical model is presented to investigate such complicated vibration problem. The analysis shows that a single bending or torsional vibration analysis is not enough to predict the stability of a geared rotor system, which includes a turbine, a gear, a generator, several bearings, a squeeze film damper and stators. Either a bearing design, which gives stability in single lateral vibration analysis, cannot guarantee the stability if a torsional vibration mode is involved. This indicates that the bearing design plays much more significant role in a geared rotor system. The theoretical model has been successfully applied to a steam turbine set, which experienced such kind of subsynchronous vibration, by modifying the original bearing design.