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Analysis and determination of mechanical bearing load caused by unbalanced magnetic pull

Andreas Ruf (Institute of Electrical Machines, RWTH Aachen University, Aachen, Germany)
Michael Schröder (Institute of Electrical Machines, RWTH Aachen University, Aachen, Germany)
Aryanti Kusuma Putri (Institute of Electrical Machines, RWTH Aachen University, Aachen, Germany)
Roman Konrad (Institute of Electrical Machines, RWTH Aachen University, Aachen, Germany)
David Franck (Institute of Electrical Machines, RWTH Aachen University, Aachen, Germany)
Kay Hameyer (Institute of Electrical Machines, RWTH Aachen University, Aachen, Germany)

Abstract

Purpose

The purpose of this paper is to focus on the mechanical bearing load caused by the unbalanced magnetic pull (UMP), which is studied in detail. The applied approach is based on an analysis of static and dynamic eccentricities at different positions and different amplitudes. The influence of the operating points is calculated to show the effective bearing load for machines operating at different speeds. The decreasing lifetime of the applied bearings is examined and evaluated in detail.

Design/methodology/approach

To evaluate the proposed methodology a permanent magnet synchronous machine (PMSM) with buried magnets is used. To consider effects of slotting and saturation, a finite element (FE) model is employed. The Monte Carlo method is used to determine the most likely amplitudes of the eccentricities. Calculating the UMP for all possible operating points using a control strategy for the machine and coupling this results with a drive cycle, determines the effective force acting on the bearing.

Findings

It has been shown that the position of the eccentricity has a not significant influence on the behavior of the UMP and may therefore be neglected. The amplitude of the eccentricity vector influences the amplitude of the UMP including all harmonic force components. For technical relevant eccentricities, the influence is approximately linear for the average and the dominant harmonics of the UMP. In most cases, it is sufficient to displace the rotor at an arbitrary position and amplitude. It is sufficient to simulate one type of eccentricity (static or dynamic) with an arbitrary value of displacement (rotor or stator) to evaluate all possible airgap unbalances. Using stochastic simulations of the eccentricity amplitudes enables an a priori design and lifetime estimation of bearings.

Originality/value

This paper gives a close insight on the effect of mechanical bearing load caused by rotor eccentricities. The effect of the position of the eccentricity vector, the operational range and a drive cycle are considered. A stochastic simulation and an empirical lifetime model of one bearing gives an example of using this methodological approach.

Keywords

Acknowledgements

The results presented in this paper have been developed in a research project granted by the Federal Ministry for Economic Affairs and Energy with the reference number 01MY12006A.

Citation

Ruf, A., Schröder, M., Putri, A.K., Konrad, R., Franck, D. and Hameyer, K. (2016), "Analysis and determination of mechanical bearing load caused by unbalanced magnetic pull", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 35 No. 2, pp. 728-743. https://doi.org/10.1108/COMPEL-03-2015-0111

Publisher

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Emerald Group Publishing Limited

Copyright © 2016, Emerald Group Publishing Limited

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