Effects of the simultaneous presence of static eccentricity and broken rotor bars on the stator current of induction machine

Many papers are available in the literature about detection of faults in induction machines. However, they generally deal only with a single fault. Instead, in practice, the case of mixed faults is quite common: the simultaneous presence of broken rotor bars and an intrinsic eccentricity or a coupling misalignment occurs often in an induction machine. The aim of this paper is to analyze theoretically and experimentally the stator current of an induction machine operating with mixed faults: broken rotor bars and static eccentricity (SE). First, an analytical expression for the mutual inductances under SE is derived using a mixture of modified winding function and Fourier series approach. Then, both theoretical and simulation studies are presented to show how the stator current is influenced by the simultaneous presence of (SE) and broken rotor bars with the consideration of the speed ripple effect. It is demonstrated that, in addition to the well-known characteristic frequencies of broken bars, and the rotor slot harmonic (RSH) used for the detection of (SE), this kind of mixed fault introduces in the stator current a series of additional harmonics, in the form of sidebands centered around the fundamental and RSH. More important, it is shown that some of these harmonics are similar to the frequencies introduced by the mixed eccentricity. Finally, experimental results have been presented to validate the analytical and simulation results.