R. Rothfeld

Bio: R. Rothfeld is an academic researcher. The author has contributed to research in topics: Magnetic bearing & Bearing (mechanical). The author has an hindex of 13, co-authored 38 publications receiving 852 citations.

Superconductor bearings, flywheels and transportation

Abstract: 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.

A Compact HTS 5 kWh/250 kW Flywheel Energy Storage System

Abstract: Flywheel energy storage systems (FESS) are expected to contribute to uninterruptible power supplies (UPS) and power quality tasks significantly. We present design and the component results of a compact 5 kWh/250 kW HTS flywheel whereby the rotor will be totally magnetically stabilized. The design is optimized for highly integrated functionality of rotor body, generator/motor and bearings. The heart of the FESS is an ironless high power PM generator/motor delivering 250 kW. An advanced flywheel body manufactured from graphite fiber is stabilized by two magnetic bearings. A prototype 200 mm HTS bearing has been constructed and tested up to a load of 1 ton axially and 0.47 ton radially capable to carry the rotor weight of about 0.5 t. With a coefficient of friction (COF) of about 10-6 the rotational drag was low. A passive PM bearing giving 80 N/mm radial stiffness/per pole was studied. HTS-PM damping response dependent on the temperature shows Lehr factors of 5-10% damping between 50 and 80 K. Eddy current dampers could support rotor dynamic stability.

Large-scale HTS bulks for magnetic application

Abstract: ATZ Company has constructed about 130 HTS magnet systems using high-Tc bulk magnets. A key feature in scaling-up is the fabrication of YBCO melts textured multi-seeded large bulks with three to eight seeds. Except of levitation, magnetization, trapped field and hysteresis, we review system engineering parameters of HTS magnetic linear and rotational bearings like compactness, cryogenics, power density, efficiency and robust construction. We examine mobile compact YBCO bulk magnet platforms cooled with LN 2 and Stirling cryo-cooler for demonstrator use. Compact cryostats for Maglev train operation contain 24 pieces of 3-seed bulks and can levitate 2500–3000 N at 10 mm above a permanent magnet (PM) track. The effective magnetic distance of the thermally insulated bulks is 2 mm only; the stored 2.5 l LN 2 allows more than 24 h operation without refilling. 34 HTS Maglev vacuum cryostats are manufactured tested and operate in Germany, China and Brazil. The magnetic levitation load to weight ratio is more than 15, and by group assembling the HTS cryostats under vehicles up to 5 t total loads levitated above a magnetic track is achieved.

HTS Magnetic Bearings in Prototype Application

Abstract: ATZ Company has successfully developed high temperature superconducting (HTS) magnetic bearings for power energy application and high-speed machinery. Journal-type design and improved HTS magnetic properties increasingly fulfill industrial prototype requirements. Maximum load up to 1.1 ton, stiffnesses in 3-4 kN/mm level, simultaneous self-stabilization in axial and radial directions, largegap operation of 5-6 mm and reliable machine cooling in the 50-60 K region characterize the present progress of HTS magnetic bearings. A 200 mm HTS bearing of 10 kN load capacity is fabricated and integrated in a 5 kWh/250 kW flywheel energy storage system. We report about a new large-gap HTS magnetic coupling system ensuring 300 mm wafer treatment inside a closed processing chamber in semiconductor industry. A linear MAGLEV transport system consisting of four modular cryostat units have been recently fabricated in a prototyping process. The four HTS cryostats can carry almost 1 ton at 10 mm magnetic gap above a magnetic guideway with a force density of about 5 N/cm2. Due to perfect thermal insulation each cryostat operates more than 24 hours without refilling LN2.

Fabrication of HTS Bearings With Ton Load Performance

Abstract: The considerable development effort of HTS magnetic bearings with respect to heavy loads is demonstrated. Radial type 200 mm bearing in an optimized design was developed for implementation in a new 5 kWh superconducting flywheel energy storage system. A prototype bearing, consisting of a modular assembled melt textured YBCO bulk 200 mm hollow cylinder with permanent magnet rotor is presented. Axial rotor displacement causes pinning forces of 8 and 10 kN axially at a temperature of 78 K and 71 K, respectively. Maximum radial forces are 4.7 kN at sub- cooled LN2. Fabrication technology incorporates the construction and engineering of a low-weight, nonmagnetic G-10 bearing cryostat. Ultra-low heat transfer structural elements were designed and constructed to reduce the thermal loss through the support to less than 2 Watt under 1 ton load.

Superconductor bearings, flywheels and transportation

Abstract: 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.

Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T

Abstract: Cuprate superconductors have found limited application for high-field magnets because of difficulties related to grain boundaries. Now, this issue is partially overcome and round wires suitable for magnetic coils are fabricated from Bi2Sr2CaCu2O8−x.

A comprehensive review of Flywheel Energy Storage System technology

Abstract: Energy storage systems (ESSs) play a very important role in recent years. Flywheel is one of the oldest storage energy devices and it has several benefits. Flywheel Energy Storage System (FESS) can be applied from very small micro-satellites to huge power networks. A comprehensive review of FESS for hybrid vehicle, railway, wind power system, hybrid power generation system, power network, marine, space and other applications are presented in this paper. There are three main devices in FESS, including machine, bearing, and Power Electronic Interface (PEI). Furthermore, advantages and disadvantages all of them have been presented. In addition a brief review of new and conventional power electronic converters used in FESS, have been discussed. Finally, practical ways to develop this technology in the future are presented.

Review of Flywheel Energy Storage Systems structures and applications in power systems and microgrids

Abstract: Flywheel Energy Storage System (FESS) is an electromechanical energy storage system which can exchange electrical power with the electric network. It consists of an electrical machine, back-to-back converter, DC link capacitor and a massive disk. Unlike other storage systems such as the Battery Energy Storage System (BESS), FESS is an environmentally-friendly short- or medium-term energy storage system, which has the capability of numerous charge and discharge cycles. These characteristics make the FESS a suitable choice for different applications in the power system such as power quality improvement, power smoothing, renewable energies integration support, stability improvement, etc. This paper presents an overview on the structures and applications of FESS in power system and Microgrid (MG) and also challenges, problems and future works discussed. It can be a driver for development of FESS applications and also recommends suggestions to use its advantages in other areas. Investigation of different studies shows that FESS, as a developing technology, can play an effective role in the operation of the present and future power system and MG.