Unbalance Response Analysis of a Heavy Duty Gas Turbine-Generator with Rigid Coupling Offset

Abstract

Heavy duty gas turbine and generator are connected through rigid coupling. The bearing levels of gas turbine-generator rotor are changed relatively due to thermal expansion of casings and supports during operation, therefore bending moment is concentrated on the coupling. So the rigid coupling needs to be offset in order to be minimized the bending moment when the gas turbine and generator are assembled. In this paper an analysis method is presented to obtain the steady state dynamic response from the finite element based equations of a rotor-bearing system with initial deflection. The method is applied to analyze the dynamic response of the two-shaft rotor-bearing system with rigid coupling offset in a heavy duty gas turbine-generator. Bumps in the dynamic response of each rotor system are observed at each critical speed due to the effect of initial deflection for rigid coupling offset. Also the dynamic responses are shown to reduce for operating condition changes from cold to hot. Especially it is confirmed that the dynamic responses are sensitively affected by phase of residual mass unbalance.