Comparison of the Unbalanced Magnetic Pull Mitigation by the Parallel Paths in the Stator and Rotor Windings
ABSTRACT An eccentric rotor creates an electromagnetic force between the rotor and stator of an electrical machine. This force tends to further increase the rotor eccentricity and may severely degrade the performance of the machine, causing acoustic noise, vibration, excessive wear of bearing, rotor and stator rubbing, and so forth. Parallel connections are known to be a simple yet effective remedy for the problems associated with rotor eccentricity. We have investigated two common types of electrical machines running with eccentric rotors. We examined operation over a wide whirling frequency range. We numerically evaluated and compared the effects of parallel connections in the stator and rotor windings on the eccentricity force. We found that the parallel stator windings can be more effective in mitigating the unbalanced magnetic pull than the rotor cage (or damper winding), which normally has many more parallel circuits.
Conference Paper: Vibration Transient Detection of Broken Rotor Bars by PSH Sidebands[Show abstract] [Hide abstract]
ABSTRACT: In recent years, the study of transients of induction motors for diagnosis purposes has gained strength in order to overcome some inherent problems of the classical diagnosis of such machines, which uses Fourier analysis of steady-state quantities. Novel time-frequency techniques have been applied to these transient quantities, in order to detect the characteristic evolutions of fault-related harmonic components. The detection of these patterns, which are usually specific for each type of fault, enables reliable diagnostic of the corresponding failures. In this context, most of the works hitherto developed have been based on analysis of currents. However, in some applications vibration measurements are also available. The goal of this work is to validate the applicability of this transient-based diagnosis framework to vibration measurements. A specific time-frequency decomposition tool, the Wigner-Ville Distribution, is proposed. Experimental results prove the ability of the approach to complement the information obtained from the current analysis.Electrical Machines (ICEM), 2012 XXth International Conference on; 01/2012
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ABSTRACT: We prove that combinations of small eccentricity, ovality and/or triangularity in the rotor and stator can produce complex whirling motions of an unbalanced rotor in large synchronous generators. It is concluded which structures of shape deviations that are more harmful, in the sense of producing complex whirling motions, than others. For each such structure, we derive simplified equations of motions from which we conclude analytically the relation between shape deviations and mass unbalance that yield non-smooth whirling motions. Finally we discuss validity of our results in the sense of modeling of the unbalanced magnetic pull force.The European Physical Journal Applied Physics 05/2014; Volume 66(Issue 02). DOI:10.1051/epjap/2014130447 · 0.71 Impact Factor
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ABSTRACT: A detailed study of a Principal Slot Harmonic (PSH) energy of an induction motor directly connected to the grid and operating under variable load under different faulty conditions is carried out. Broken rotor bars, mixed eccentricity and interturn short circuit faults are considered in the paper. A combined time-frequency distribution and particle filtering post processing approach is used in the work for PSH tracking even for the case of severe pulsating load operation. The proposed fault indicator provides values that are comparable with the traditional one for stationary operation. The results show that the energy in the PSH reflects the overall state of the machine under this kind of operation. Furthermore, its changing pattern is studied as a mean to discriminate between different faults.2014 International Conference on Electrical Machines (ICEM), Berlin (GERMANY); 09/2014