Experimental Setup and Efficiency Evaluation of Zero-Field-Cooled (ZFC) YBCO Magnetic Bearings

Abstract

Abstract-This paper presents the conception, simulation and experimental evaluation of magnetic bearings based on NdFeB magnets and zero-field-cooled (ZFC) YBCO bulk superconductors to replace the bearings of a standard electric machine. Advanced research on HTS magnetic levitation has been carried out for the construction of large scale flywheels or for industry applications. However, those approaches used fieldcooled (FC) superconductors, whereas the approach shown in this paper uses ZFC superconductors. Actually, as previously shown by the authors, ZFC implementation presents much less AC losses. The approach in our horizontal flywheel research follows the ZFC-maglev structure, where the linear track was closed into a circular one with the same diameter of the superconductor magnetic bearing. The conception and geometric placement of magnets and superconductors was designed to keep symmetry along the rotating axis and minimizing air gaps. A 3D finite element model was built for simulation and validation of the effectiveness of the solution. Experimental validation was then achieved measuring the balanced and unbalanced rotor lifting and guiding forces.

Prototype of a Zero-Field-Cooled YBCO Bearing With Continuous Ring Permanent Magnets

“…stator and ring PMs in the rotor. A 3D Finite Element Method (FEM) model was obtained assuming a relative magnetic permeability of µ r = 0.2, as explained in [3]. This approach cannot be used for computation of Joule losses and the associated temperature increase in the superconductors.…”

“…This approach cannot be used for computation of Joule losses and the associated temperature increase in the superconductors. However, this simple model allows the proposed SMB design to be tested without excessive computational effort due to its 3D representation and is sufficient to produce reliable quantitative results [3]. In both figures, a zoom of the region close to PMs and HTS Bulks is presented to show the magnetic flux in this region.…”

“…Fig. 5 shows lifting forces vs. rotor vertical offset obtained from the 3D FEM model [3], for the three different rotors. Results were obtained for decentering the rotors over a range of ±7 mm, which represents the possible axial displacement of the rotor into the stator.…”

“…I N PREVIOUS work, our research team achieved reliable results using superconductor technology to create and study levitation systems, namely a new Maglev design using ZFC YBCO superconductors [1], [2], among others. Following similar concepts and strategies, a ZFC YBCO magnetic bearing has been developed [3]- [5], using PMs and type II superconductor bulks. Lately, most of the existing levitation systems use these two components; and regarding levitating bearings and flywheels, their application is expected to increase.…”

“…Each PM (B r = 1.25 T) has a rectangular form with dimensions of 25 × 25 × 12 mm. The three inner discontinuous rings of PMs are magnetized in an alternating North-South-North configuration, such that the two outer rings of magnets have concordant polarizations and the middle ring of magnets opposite polarization [3]- [5].…”