The Specific Load Capacity of Radial-Flux Radial Magnetic Bearings

This paper addresses the specific load capacity of radial-flux radial magnetic bearings and provides some insight into what values are achievable and how these values depend on various parameters such as air-gap thickness, allowable temperature rise in the coils, certain heat-transfer coefficients, and certain de-rating factors associated with the distribution of the bearing load in time and space. We define the specific load capacity of a radial magnetic bearing as the ratio of the largest sustainable root-mean-square radial force to the total self-weight of all parts necessary for the electromagnetic function of the bearing. We show that it is possible to push the limit of the specific load capacity of naturally cooled bearings up to around 35:1 with present-day materials, for a wide range of practical bearing sizes. This figure is still very small compared with the capacity of mechanical bearings.