Model-Based Identification of a Shaft Bow Caused by Rubs in the Generator of a Power Unit

The dynamic behavior of rotating machines due to faults can be simulated with model-based methods in which the faults are modelled with suitable sets of equivalent excitations. When rotor-to-stator rubs occur the friction forces can cause time-varying thermal bows of the shafts. The equivalent bending moments that cause the shaft bows can be estimated with model-based identification methods developed in the frequency domain: these techniques minimize the error between the machine experimental vibrations induced by the rubs and the system response provided by the simulating model. In this paper the results of the analysis of the experimental vibrations of a large turbine-generator unit that was subjected to partial-arc rubs are shown and discussed along with the diagnostic strategy used to identify the fault severity and the location of the shaft cross-sections where the heaviest rubs occurred. Comparisons between experimental data and simulated vibrations caused by the identified fault are shown.