The measurement and characterization of power losses in high speed magnetic bearings

A test apparatus for the measurement of rotating power losses in high speed magnetic bearings was successfully designed and built to study the effect of various parameters on the power loss mechanisms associated with magnetic bearings. The major results of this work present loss measurements for four industrial quality rotor-bearing configurations at multiple levels of flux and rotor speed from a dedicated high speed test rig as well as an extensive analysis of the results.; The test apparatus consists of a shaft supported in two radial magnetic bearings. The shaft is accelerated up to peak speed by end-mounted electric motors, whose stators can be withdrawn from the shaft after run-up to eliminate virtually all residual magnetic coupling. The rotor is then allowed to coast down in speed. The coast down times, due only to magnetic drag from the bearings and rotor windage, are measured. Losses have been measured in several different industrial bearing configurations including 8-pole and 16-pole heteropolar bearings, and an eight pole per plane homopolar bearing. Tests involving variations in tip clearance ratio (ratio between pole-to-pole chord length and radial gap) and in gap thickness were studied. All configurations were tested at multiple average static flux levels ranging from {dollar}sim{dollar}0.3 T to 0.6 T as measured by a Hall sensor.; The rotating losses in a magnetic bearing are due to eddy currents (which can include skin effects), alternating hysteresis, rotating hysteresis, and windage which create drag on a rotating shaft. Analytical/empirical predictions of electromagnetic losses for comparison to measured data have been made based on the classical equations for power losses in transformers and electric motors modified by the author. Models based on turbulent flow theory are used for the calculation of windage losses on the rotor.; A regression analysis is performed including the fitting of a model to the data to determine the composition of the bulk loss data in terms of the individual loss components. The individual loss components derived from the rundown data in this manner are compared to the corresponding analytical/empirical models.; The high speed magnetic bearing power loss test rig performs well with smooth rundown operation resulting in useful information about how power losses in magnetic bearings are affected by certain parameters. The application of the regression analysis allows for the separation of the bulk measured power loss into individual loss components. The results from this study demonstrate basic power loss behavior of magnetic bearings for the variation of certain key parameters including number of stator poles, tip clearance ratio, gap length and flux path. Closed form analytical/empirical formulas are provided for the initial estimation of power losses in magnetic bearings. The results of this study represent the foundation for the verification of detailed numerical analyses for the evaluation of electromagnetic loss mechanisms in magnetic bearings such as the finite element (FEM) codes currently under development at the University of Virginia.