Modal Analysis of Coupled Steam Turbine and Generator Rotors

Abstract

Torsional vibrations occur due additional oscillatory motions superposed on the mean rotation. Rotating systems at running speed near the natural frequencies are prone to excessive angular deflections and hence large stresses can occur which can cause rotating components failure or premature fatigue failures. The objective of the present work is to study the torsional vibration characteristics of multi-rotors of a coupled steam turbine generator using finite element analysis technique in Ansys Workbench. Holzer method and Matrix method used on principle to find precise solutions to torsional natural frequency of a coupled steam turbine and generator rotors. The information about the natural frequencies for rotating systems like coupled steam turbine generator rotor system can help to avoid system failure by giving the safe operating speed range. In the present work, finite element method of analysis technique has been used to find the natural frequencies of a coupled steam turbine generator rotor systems using software Ansys Workbench. The results obtained have been compared with Holzer's method or Matrix method to establish the variance between two techniques.