Numerical and experimental assessment of a large industrial thrust bearing

Nowadays, Active Magnetic Bearings (AMB) are widely utilized in different industrial applications. Several applications have been successfully implemented in the field of Turbomachinery especially for large centrifugal compressors. These machines are subjected to high axial transient loads due to process operations. Considered simpler than radial bearings, the thrust bearing optimization has been largely neglected. Consequently, the thrust bearing suffers from sizing difficulties that lead to bad overall system optimization. Thrust behavior exhibits several peculiarities mainly due to the specific arrangement of thrust actuator made with a solid disk instead of laminated sheets for radial bearings. The work presented here aims to improve the prediction of thrust dynamic in order to better size this component and ensure smooth operation of machinery. The paper describes the complete analysis of a 25kN thrust bearing. The study is divided in two sections, first the actuator analysis and then the dynamic behavior of the complete system. The thrust bearing electromagnetic design was developed with the aid of Finite Element Analysis (FEA). The thrust bearing performance calculations are disclosed in this paper and compared with those of an actuator characterization test bench. Later, the thrust actuator is mounted on a complete AMB experimental set-up, equipped with a 200 kg rotor on two radial magnetic bearings. The test rig is equipped with a contactless axial actuator that enables the excitation of the rotor with different axial force amplitudes and ramps. The first FEA and experimental results are used to feed a simplified model of the complete thrust bearing. The experimental results are compared with numerical ones. The different phenomena observed are discussed and the system limitations are highlighted. This study enables better understanding of the behavior of large thrust bearings. In addition, the work realized help to predict and optimize thrust bearing response for each machine.