Identification of a Shaft Thermal Bow by Means of Model-based Diagnostic Techniques

The most important faults of rotating machines can be modelled by means of proper sets of equivalent excitations having a suitable harmonic content. Therefore, mathematical models of rotating machines can be used by fault identification techniques that compare the experimental vibration data to the corresponding theoretical response of the rotor-system caused by a specific set of excitations. Unfortunately, several different faults can cause similar symptoms in the vibration of large rotating machines and, in the common case of flexible rotors, only a well-tuned model is able to provide reliable fault identifications. This paper shows the results of a study in which the cause of the abnormal vibration of the generator of a power unit has been investigated considering different types of fault. A thermal bow of the generator rotor has shown to be able to fit the simulation of the experimental transient vibrations. The diagnostic strategy used to investigate this case study can be applied to identify many other types of faults in rotating machines.