Calculation of rotational power losses in eight pole radial magnetic bearings

Abstract

The need for low-loss high speed bearings in rotating machinery invites the use of active control magnetic bearings. The present study investigates the theoretical power losses of these bearings associated with shaft rotation at a constant angular velocity. Electromagnetic field modeling of bearing and rotor assemblies incorporate eddy current ten-terms generated as a result of conductive materials in relative motion. Mechanically, these eddy currents manifest themselves into a drag producing torque on the rotor shaft. This study seeks to quantify the power losses associated with this drag torque. A finite element code for two and three-dimensional applications is developed for computation of the electromagnetic field. In two-dimensional applications, this code is verified by comparison with a known theoretical solution. A preprocessor is developed to transform the finite element mesh created by commercially available software into a mesh suitable for solution by banded algorithms. A postprocessor computes the magnitude of the eddy current vectors and electrical power loss.