Analytical Calculation of Fields, Forces and Losses of a Radial Magnetic Bearing with Rotating Rotor Considering Eddy Currents

This paper presents an analytical model of a radial magnetic bearing with which magnetic fields, forces and losses are calculated. When an unlaminated rotor rotates in a radial magnetic bearing, eddy currents are caused to flow inside the conducting material of the rotor. These eddy currents change the magnetic field of the radial bearing and, therefore, the forces on the rotor depend on the eddy currents. Additionally to the levitation force, a tangetial force acts on the rotor. This tangential force causes a retardation torque which has been measured for many magnetic bearing systems. When the rotor is excited, the tangential force additionally leads to a cross coupling between the x and y axis which may destabilize the system. It will be shown that the forces and losses of a radial bearing depend on the pole configuration. It can be seen that the configuration NSNS has smaller losses than NNSS. The analytical results presented in this paper correspond with measurements [8].