The Vibration Signature of Chordal Cracks in Asymmetric Rotors

The study of asymmetric rotors is important because virtually all electrical machines have rotors which fall into this category and their have been a number of cracks in such rotors which have been reported in the literature. In a symmetric rotor, the diagnosis of a transverse crack from an examination of the free-free modes is relatively straightforward, but the presence of inherent asymmetry leads to a considerable complication of the situation. In this paper, a simple model is presented to represent this situation. The changes in natural frequencies, modes shapes and cross coupling of the original principal planes is examined.