R. Nicolsky

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.

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.

Levitation force and stability of superconducting linear bearings using NdFeB and ferrite magnets

Abstract In the frame of a project on the development of a reduced-scale-levitating rail-vehicle prototype, the performance of two different permanent magnets have been tested in linear bearings using YBa2Cu3O7−y bulk superconductors. The levitation forces, the stiffness and the vibration damping have been measured using two different rail assemblies: one mounted with NdFeB magnets and another with ferrite ones. The levitation force of the NdFeB rail is more than one order of magnitude larger than that of the ferrite one. The stiffness of those linear bearing and the vibration damping were measured for several cooling heights from the rail. The stiffness increases with the decrease of the cooling height and is larger in the NdFeB rail. The vibration damping is rather low in both systems. Finally, we conclude that the NdFeB magnets are the most suitable for applications on linear levitating bearings.

The characterization of levitation force and attractive force of single-domain YBCO bulk under different field cooling process

Abstract The interaction forces were measured at 77 K by changing the field cooling distance Z fc between a YBCO bulk and a permanent magnet. It is found that the maximum levitation force ( F mlf ), maximum attractive force ( F maf ) and the gap distance ( Z maf ) corresponding to F maf can be well described by exponential laws as a function of Z fc , which allow us to predict these values according to Z fc . It is also found that the distance between the Z 0fa (gap distance corresponding to the zero force) and Z maf in the ascending process is a constant value, which can be well interpreted by the constant reduction rate of the axial component magnetic flux density along the axis line of the magnet within the constant distance. These results are very interesting to physical research and helpful for the practical designing and applications.

Performance of Nd-Fe-B and ferrite magnets in superconducting linear bearings with bulk YBCO

The performance of two different magnets has been tested in linear bearings with YBCO bulk superconductors, prepared by seeded melt texturing technique. Two different rails have been assembled with opposite magnetic polarization and intercalation of ferromagnetic flux concentrators. One rail has been mounted with Nd-Fe-B magnets and the other one, with Ferrite magnets. The levitation force of the Nd-Fe-B permanent magnets rail is more than one order of magnitude larger than that one of Ferrite. The stiffness of the linear bearing and the vibration damping were measured in the field cooling procedure for several cooling heights from the rail. The different cooling heights result in different gaps between the YBCO blocks and the magnets, for the same load. The stiffness increases with the decrease of gap, for the same load, in both cases, but is higher in the Nd-Fe-B rail. The vibration damping is rather low in both systems (/spl sim/0.01). We conclude that the Nd-Fe-B magnets are the most suitable for applications on linear levitating bearings.

The effect of different field cooling processes on the levitation force and attractive force of single-domain YBa2Cu3O7-x bulk

The effects of different field cooling processes on the levitation force and attractive force of single-domain YBa2Cu3O7−x (YBCO) bulk have been investigated. The forces were measured at 77 K by changing the field cooling distance Zfc between the YBCO bulk and a permanent magnet. We found that the stiffness between the YBCO and magnet increases with the decrease of Zfc; the maximum levitation force (Fmlf) of the sample decreases from 74 N to 48 N with a decrease of the Zfc from 7 cm to 0.7 cm; but the maximum attractive force (Fmaf) increases from 2.96 N to 30.6 N with a decrease of Zfc from 7 cm to 0.1 mm. Both of them obey the first decreasing exponential law. It is also found that the distance Zmaf, corresponding to Fmaf, decreases in an exponential law with the decrease of Zfc. The Fmlf, Fmaf and Zmaf are all saturated in the range of Zfc from 3 to 4 cm. All the relations between Fmlf, Fmaf and Zfc are closely related with the axial magnetic field distribution of the magnet, which allow us to easily predict the values between the Fmlf, Fmaf and Zfc, which is very helpful for practical designing and for applications.

Superconducting axial bearing for induction machines with active radial magnetic bearings

A superconducting passive axial bearing has been developed for an induction machine with vertical rotor and two active radial magnetic bearings, resulting in a fully levitating system. This prototype has been designed on the basis of a previous one reported by Salazar-Stephan as a 4-pole 2-phase induction machine using windings of a standard motor. Each active radial bearing measures four shaft-positions using eddy-current sensors, each displaced by 90 degrees. The levitation has been performed using two NdFeB permanent magnets and bulk pieces of seeded-melt-textured YBCO. The YBCO pieces have been characterized by measuring the levitation forces and mapping the remanent magnetic field with Hall probes. The radial stability of the system is modeled and discussed.

Radiofrequency generation using a SNS microbridge

The feasibility of a sinusoidal oscillator is demonstrated using a SNS microbridge linked with a series RLC tank circuit, supplied by a constant DC current, and operated at the negative differential resistance range of its I-V characteristic curve. The frequency of this sinusoidal generator is equal to the resonant frequency of the tank RLC circuit. This type of generator can be operated for a wide range of frequencies, from audio frequencies up to the limit of microwaves. Other possible electronic applications based on the appropriate use of the negative resistance region of the I-V characteristic curve of the SNS microbridge are suggested.

Simplified model for current-voltage characteristics of a superconductor-normal metal-superconductor junctions

Abstract We calculate an analytical approximate density of Andreev states which is used to simplify substantially the microscopic current-voltage expression of the Kummel-Nicolsky theory for superconductor-normal metal-superconductor junctions. The current expression obtained is easy to be numerically integrated and the resulting CVC exhibits all essential features of the original one and the same shape. That simplified expression for the current may fit experimental curves using only junction parameters with relevant physical meaning. In this way it may substitute the known RSJ model, which is just an equivalent circuit without a physical content.

Microwave Generation using a SNS Junction

It has been shown recently that the current-voltage characteristic of a metallic (non-tunneling) Josephson junction could exhibit a negative differential resistance at low voltages, as a predictable and reproducible effect. This letter shows an alternative procedure to generate non-Josephson microwaves (in the cm and mm range) taking advantage of this effect. It is shown that, instead of obtaining harmonic oscillations with the AC Josephson effect, it is possible to generate microwaves using the averaged IVC (current-voltage characteristics) of a SNS junction (a Josephson junction which exhibits no tunneling and has no hysteresis in the IVC).