Anaclara Ferreira

Magnetic Bearing Sets for a Flywheel System

This paper presents a magnetic bearing set developed to work in a flywheel energy storage system. The bearing set is composed of a permanent magnetic bearing (PMB) and a superconducting magnetic bearing (SMB). A new configuration of a PMB having Nd-Fe-B magnet rings and a back yoke is proposed and compared with an existing one. Finite element method (FEM) simulations were used to design two different PMB configurations. Measurement results of axial and radial forces were carried out in zero field cooling (ZFC) and field cooling (FC) processes in two SMB topologies. These measured force results are presented and discussed in order to discover which configuration is more promising for the proposed application.

Flywheel Energy Storage System Description and Tests

This paper presents test results of a flywheel energy storage system (FESS) prototype. The bearing system is composed of a superconducting magnetic thrust bearing (SMB) and a permanent magnet bearing (PMB). The SMB was built with Nd-Fe-B magnet and YBCO superconducting blocks. The PMB has the function of positioning radially the switched reluctance machine (SRM) used as motor/generator and reduce the load over the SMB. The SRM drive is responsible to convert electrical into mechanical energy, and vice versa. The prototype still operates at low speeds, but the dynamical simulations of the SRM drive showed that the system can work at high speed, supplying the required energy during disturbances. In the tests performed with the FESS prototype, the system took or delivered energy from/to the grid when requested.

Halbach array superconducting magnetic bearing for a flywheel energy storage system

In order to develop a new magnetic bearing set for a flywheel energy storage prototype, it was designed and simulated some configurations of Permanent Magnetic Bearings (PMB) and Superconducting Magnetic Bearings (SMB). The bearings were assembled with Nd-Fe-B permanent magnets and the simulations were carried out with the Finite Element Method (FEM). The PMB was designed to reduce the load on SMB and provide radial positioning of the whole set. SMB were designed with YBCO superconductors and an assembly of permanent magnets. Several configurations of permanent magnets were simulated, trying to maximize the magnetic flux gradient in direction orthogonal to the movement and flux density in the surface of the superconductors. Early experiments have shown an increasing stiffness and levitation force with increasing field gradient and intensity. It was also a goal to reduce the stray field outside the bearing. The levitation force of the SMB using a flux shapers configuration was measured and compared with FEM simulation, showing very good agreement. The simulation of a SMB using Halbach array configuration shows that it increases the levitation force and reduces the stray field.

Voltage sags compensation using a superconducting flywheel energy storage system

This paper presents a voltage sag compensator, which uses a flywheel energy storage system with superconducting magnetic axial thrust bearing (SMB) and a permanent magnet radial bearing (PMB). The SMB was built with Nd-Fe-B magnet and YBCO superconducting blocks, refrigerated with liquid Nitrogen. The magnets are assembled with magnetic flux shapers in order to increase the levitation force and the stiffness. The radial PMB is used to positioning the vertically arranged switched reluctance machine (SRM) used as motor/generator. Simulations of the power electronics and SRM show that the system can work up to 30,000 rpm supplying the required energy during disturbances.

Tests With One Module of the Brazilian Maglev-Cobra Vehicle

Approximately a decade ago, superconducting maglev train prototypes started to be developed. Researchers from China, Germany, and Brazil have built prototypes carrying people based on superconducting levitation technology. The Brazilian MagLev project, named MagLev-Cobra, started in 2000 with a small-scale prototype that was concluded in 2006. After that, efforts toward a full-scale test vehicle for 30 passengers began. This vehicle will be composed of 4 modules, each one 1.5 m long, with six levitation cryostats and a linear induction motor. The first module and 12 m of test track are already constructed and this paper will describe the following tests: air gap as a function of load, temporal air gap stability, linear motor traction force, and vehicle acceleration. The paper will also describe the construction details of module, linear motor, and the rail.

Test and Simulation of Superconducting Magnetic Bearings

This work presents the study of superconducting magnetic bearings (SMB). Two SMB prototypes were constructed using Nd-Fe-B magnets rotors (each one having approximately 80 mm of external diameter) and a 75 mm diameter YBCO disc. The magnetic rotors of the SMB prototypes were manufactured in two different topologies: flux shaper and axially magnetized rings. Beans critical state model is applied to simulate those SMBs. The model was implemented using magnetostatic solutions calculated by finite element method (to solve the problem in space) and finite difference method (to solve the problem in time). Simulated and measured results were very similar, showing the applied simulation model is efficient for this purpose.

MagLev Cobra: Test Facilities and Operational Experiments

The superconducting MagLev technology for transportation systems is becoming mature due to the research and developing effort of recent years. The Brazilian project, named MagLev-Cobra, started in 1998. It has the goal of developing a superconducting levitation vehicle for urban areas. The adopted levitation technology is based on the diamagnetic and the flux pinning properties of YBa2Cu3O7−δ (YBCO) bulk blocks in the interaction with Nd-Fe-B permanent magnets. A laboratory test facility with permanent magnet guideway, linear induction motor and one vehicle module is been built to investigate its operation. The MagLev-Cobra project state of the art is presented in the present paper, describing some construction details of the new test line with 200 m.

Simulation of Dynamic Levitation Force Taking Flux Creep Into Account

This work compares dynamic levitation force measurements, at different approaching speeds, with levitation force simulations that take flux creep into account. This was done using a power-law electric field current-voltage relationship that can be derived from the Anderson-Kim model. The algorithm for the simulation starts from the analytical expressions of the classical electromagnetic theory to write the integral equation of the time derivative of the current density inside the superconductor, depending on the geometry of the system and the configurations of the applied field. Then, using the Method of Moments, the analytical integral equation was written in its matrix formulation. The current density in each time step is obtained by a simple integral rule (method of Euler). From the current density profile in the superconductor, the levitation force between a permanent magnet and a superconductor, with finite cylindrical geometry, is calculated. The current density profile depends on the approaching speed. The results of the simulations were compared favorably with the experimental measurements.

The flux creep effect in superconducting magnetic bearings levitation force

The main characteristic of superconducting magnetic bearings (SMBs) is the levitation force between the permanent magnet rotor and the superconducting stator. This force can relax with time due to the flux creep effect in the superconductor. In order to investigate the effect of the flux creep in the levitation force, several dynamic levitation force measurements were made in simple axis-symmetric SMBs. These measurements were conducted with different magnet approaching speeds and with the magnet stopped after the movement at a fixed position. The SMBs were composed of superconducting YBCO seeded melt textured cylinders and Nd-Fe-B cylindrical permanent magnets, with different YBCO diameters, heights and pinning characteristics. The measurements were compared with simulations that have taken the flux creep into account. The simulation algorithm finds the current density profile inside the superconductor at each magnet approaching time step. The current density profile was found by solving an integral inside the superconductor and using a power-law for calculating the electric field. This power-law relationship can be derived from the Anderson-Kim model. The time evolution was obtained using time dependent finite difference method and the levitation force was calculated from the Lorentz force. The simulation results show a good agreement with measurements.

A superconducting levitated small scale vehicle with linear synchronous motor

This paper presents a small scale MAGLEV vehicle prototype that is under development at UFRJ. The levitation is done by Y-Ba-Cu-O superconducting blocks refrigerated by liquid nitrogen in the presence of Nd-Fe-B magnets. A long primary linear synchronous motor gives the traction. Design considerations and experimental results show the characteristics and performance of this system.