This paper describes the present status of high temperature superconductors (HTS) and of bulk superconducting magnet devices, their use in bearings, in flywheel energy storage systems (FESS) and linear transport magnetic levitation (Maglev) systems. We report and review the concepts of multi-seeded REBCO bulk superconductor fabrication. The multi-grain bulks increase the averaged trapped magnetic flux density up to 40% compared to single-grain assembly in large-scale applications. HTS magnetic bearings with permanent magnet (PM) excitation were studied and scaled up to maximum forces of 10 kN axially and 4.5 kN radially. We examine the technology of the high-gradient magnetic bearing concept and verify it experimentally. A large HTS bearing is tested for stabilizing a 600 kg rotor of a 5 kWh/250 kW flywheel system. The flywheel rotor tests show the requirement for additional damping. Our compact flywheel system is compared with similar HTS–FESS projects. A small-scale compact YBCO bearing with in situ Stirling cryocooler is constructed and investigated for mobile applications. Next we show a successfully developed modular linear Maglev system for magnetic train operation. Each module levitates 0.25t at 10 mm distance during one-day operation without refilling LN2. More than 30 vacuum cryostats containing multi-seeded YBCO blocks are fabricated and are tested now in Germany, China and Brazil.

http://iopscience.iop.org/article/10.1088/0953-2048/25/1/014007/pdf

Superconductor bearings, flywheels and transportation

A 45-m-long high-temperature superconducting (HTS) Maglev ring test line, named “Super-Maglev,” has been successfully developed in Chengdu, China, in February 2013, 12 years after the birth of the first man-loading HTS Maglev test vehicle. The Maglev vehicle (2.2 m in length, 1.1 m in width) is designed for one passenger with a levitation height of 10–20 mm; the permanent-magnet guideway (PMG) (45 m in length, 0.77 m of track gauge) is a racetrack shape with a curve radius of 6 m; the driving is accomplished by a linear induction motor with a maximum running speed of 50 km/h. The linear motor is composed of four submotors installed at one straight section in the middle of the double PMGs, and the total length is 3 m. This second-generation HTS Maglev vehicle system is highlighted by the cost-performance and the wireless multiparameter onboard monitoring function. The current same-level load capability has been achieved over a small-section low-cost PMG whose cross-sectional area is only 3000 mm
 2
. On the vehicle, parameters of levitation weight, levitation height, running speed, acceleration, lateral offset, online position, and total running distance of the vehicle are real-time monitored and displayed on the onboard tablet computer. The system component and test data are reported in detail in this paper.

A High-Temperature Superconducting Maglev Ring Test Line Developed in Chengdu, China

As a bellwether transportation mode, albeit with hot controversy, evacuated tube transport (ETT) can dramatically reduce air friction, and incorporating Maglev technology could also thoroughly eliminate wheel-rail friction. It is not difficult to imagine that incorporation of these two technologies could establish an innovative transportation system, with particular advantages in terms of high speed, safety, energy saving, and environmental protection. The integration of these two technologies has been a great challenge, however, due to the composite technology. To realize this revolutionary idea, we have successfully developed the first proof-of-principle prototype of a 45-m-long high-temperature superconducting Maglev evacuated tube transport (HTS Maglev-ETT) test system, called the “Super-Maglev,” based on the passive self-stable HTS Maglev conceived in our group in 2000. The system mainly consists of three parts: an HTS Maglev-vehicle-guideway coupling system with 1-t load capability at a levitation gap of 10 mm, a 45-m-long racetrack-type evacuated tube with a 2-m-diameter circular cross section pumped by a hybrid air extraction system, and a 3-m linear induction motor to provide sectional propulsion. The system can achieve a pressure as low as 2.9 kPa in the tube. Experiments show that air drag on the vehicle is greatly reduced at that low air pressure, and a maximum speed of 50 km/h was recorded on the 6-m-diameter test guideway. Theoretically, the reduction of the aerodynamic consumed power could reach as high as to 90% under 10 kPa. This “Super-Maglev” strongly demonstrates the feasibility and potential merits of the HTS Maglev-ETT transportation concept.

A High-Temperature Superconducting Maglev-Evacuated Tube Transport (HTS Maglev-ETT) Test System

An overview summary of recent Boeing work on high-temperature superconducting (HTS) bearings is presented. A design is presented for a small flywheel energy storage system that is deployable in a field installation. The flywheel is suspended by a HTS bearing whose stator is conduction cooled by connection to a cryocooler. At full speed, the flywheel has 5 kW h of kinetic energy, and it can deliver 3 kW of three-phase 208 V power to an electrical load. The entire system, which includes a containment structure, is compatible with transportation by forklift or crane. Laboratory measurements of the bearing loss are combined with the parasitic loads to estimate the efficiency of the system. Improvements in structural composites are expected to enable the operation of flywheels with very high rim velocities. Small versions of such flywheels will be capable of very high rotational rates and will likely require the low loss inherent in HTS bearings to achieve these speeds. We present results of experiments with small-diameter rotors that use HTS bearings for levitation and rotate in vacuum at kHz rates. Bearing losses are presented as a function of rotor speed.

https://iopscience.iop.org/article/10.1088/0953-2048/23/3/034021/pdf

An overview of Boeing flywheel energy storage systems with high-temperature superconducting bearings

This paper describes the construction and main components of a full-scale superconducting magnetic levitation vehicle. The prototype, comprising four 1.5-m-long wagons, will travel a short test line of 200 meters, connecting two buildings inside the campus of the Federal University of Rio de Janeiro. The efforts to implement this technology started thirteen years ago with a small-scale prototype in an attempt to prove the concept. The second step was the construction of a functional prototype that could levitate more than one Ton. The actual stage of this project is the construction of an operational prototype mentioned above, designed to transport up to 24 passengers. This work has been reported in several previous editions of the ASC conference. New details about the elevated test line, the permanent magnetic (Nd-Fe-B) guideways, the cryostats with YBCO high critical temperature superconductors, the energy conditioning, the linear induction motor and its regenerative braking, as well as the automatic supply system of liquid nitrogen will be presented in the proposed paper. Tests with this operational prototype demonstrate the technology feasibility.

A Full Scale Superconducting Magnetic Levitation (MagLev) Vehicle Operational Line

SupraTrans is an innovative transportation concept based on the principle of superconductive magnetic levitation. The aim of the project is to create a fully working prototype, which proves its ability for passenger transport by explicit consideration of the compatibility between systems for propulsion, safety, positioning, power supply, transport logistics and the levitation system itself. The SupraTrans technology uses the flux pinning in high temperature superconductors (HTS) to stabilize the lateral and vertical position of the vehicle on the magnetic track. This self-stabilizing system is the main advantage of the superconductive levitation in comparison to all other levitation systems, which need electronic control and power to keep a constant distance between the train and the track.

Superconductively levitated transport system - the SupraTrans project

The technical progress in the manufacture of high temperature superconducting bulk material (HTS) provides various possible applications. These include non-contact linear transport systems and frictionless rotating bearings using the pinning effect in Type-II superconductors. During the last five years, a group of industrial and research partners have developed an innovative magnetic levitation system (SupraTrans) with a permanent magnetic rail and YBCO superconducting bulks in the vehicle. To optimize the levitation and guidance system, further investigations in the static and dynamic behavior have been accomplished and are reported. Comparisons between the statics and the dynamics show a very good agreement in all comparable parameters.

Static and Dynamic Behavior of a Superconducting Magnetic Bearing Using YBCO Bulk Material

The complex microstructure of melt grown YBCO bulk material and the non-linear electromagnetic behavior makes it difficult to determine their thermal, electrical and magnetic properties. The knowledge of these parameters is essential to design superconducting magnetic bearings (SMB) for various applications. The main characteristic of a SMB is the levitation force that arises between the superconductor and the magnetic source. The availability of simulation tools can greatly simplify the design of new prototypes. An algorithm based on the critical state model and the Finite Element Method (FEM) was developed. This method is based on the determination of the current density profile within the superconductor due to the penetration of the flux lines. This algorithm showed satisfactory to simulate the levitation force for a rotational magnetic bearing used in a flywheel prototype. In the present paper, this method is used to simulate a linear bearing and to design the optimal geometries for a magnetic rail that is being developed for a MAGLEV vehicle prototype. The linear bearing consists of two parts: a rail assembled with Nd-Fe-B magnets and YBCO bulks mounted inside a cryostat. Some simulated bearings were mounted and tested. The simulation results agree with the measurements.

Simulations and Tests of Superconducting Linear Bearings for a MAGLEV Prototype

Within the SupraTrans project, a joint venture between research institutes, universities and industrial companies, a full working prototype of a superconductively levitated transport system has been constructed and developed. The levitation and guidance system is based on flux pinning in melt-textured bulk YBa2Cu3O7-delta (YBCO) that stabilizes the vertical and lateral position of the vehicle above the magnetic track. In contrast to conventional electromagnetic Maglev systems, track and vehicle do not mechanically envelop each other in the superconducting Maglev. It is therefore possible, to construct a non-mechanical turnout switch using electromagnets. Such fast working turnout switches are essential to establish a highly branched transportation network. An experimental set-up for an electromagnetic turnout switch has been created for a toy sized model train. Investigations regarding levitation force and stiffness of the vehicle during several crossings have been performed. Thereby the ideal line across the switch has been used to measure vertical and lateral forces in every step of the movement. The evaluation shows a small delay but appropriate levitation and guidance behavior.

A Turnout Switch for a Superconductively Levitated Linear Transport System

This paper will deliver insight into technology and physics of the levitation system for the SupraTrans project, a prototype of a superconducting transportation system. The technology used herein bases on the flux pinning in melt-textured bulk YBa2Cu3O7-X (YBCO) that stabilizes the lateral and the vertical position of the vehicle above the magnetic track. A track made from permanent magnets and soft magnetic steel-yokes acting as flux collectors has been designed and its capability is presented. The concept also includes a fast electromagnetic turnout switch to establish a highly branched transportation network.

/pdf/guideway-and-turnout-switch-for-the-supratrans-project-2jpc9hisaq.pdf

O. de Haas

Papers

Superconductively levitated transport system - the SupraTrans project

Static and Dynamic Behavior of a Superconducting Magnetic Bearing Using YBCO Bulk Material

Simulations and Tests of Superconducting Linear Bearings for a MAGLEV Prototype

A Turnout Switch for a Superconductively Levitated Linear Transport System

Guideway and turnout switch for the SupraTrans project