Dietmar Berger

Superconductively levitated transport system - the SupraTrans project

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.

Superconducting Magnetic Bearing as Twist Element in Textile Machines

Superconducting magnetic bearings (SMBs) enable the levitation of a magnet in a stable position over a cooled superconductor without the need for an additional positioning system. These passive bearings are being investigated for applications wherever a stationary levitation or a contact-free rotary or linear motion is desired and cannot be realized by simpler means. Ring spinning is the most widely used technique for the production of short staple yarn in the textile industry. The productivity of the ring-spinning process depends on the rotational speed of the spindle. It is limited by friction in the so-called ring-traveler twist element. During the spinning process, the traveler is dragged along the ring by the yarn with up to 30000 r/min. The resulting friction causes wear of the twist element and melting of synthetic yarn at high spindle speeds due to strong heat generation. Recently, an SMB was implemented as a contact-free twist element in a ring-spinning machine up to 11000 r/min. This prototype SMB consists of a rotating permanent-magnetic (PM) NdFeB ring acting as a yarn-driven traveler and a stationary bulk YBCO ring at 77 K in an open LN2 bath. In this paper, we investigate the bearing properties of this SMB with regard to the special requirements of the ring-spinning process. Dynamics of the spatially vibrating and rotating PM ring are analyzed including the forced vibration due to interaction with the yarn. For the expected yarn forces, the displacement amplitude at the resonance frequency remains below the field-cooling height. In addition, the possibility of realizing higher rotational speeds by mechanically reinforcing the NdFeB ring with a shrunk-on steel shell is discussed.

Innovative twisting mechanism based on superconducting technology in a ring-spinning system:

Twist plays an important role to impart tensile strength in yarn during the spinning process. In the most widely used ring-spinning machine for short staple yarn production, a combination of ring and traveler is used for inserting twist and winding the yarn on cops. The main limitation of this twisting mechanism is the friction between the ring and traveler, which generates heat at higher speed and limits the productivity. This limitation can be overcome by the implementation of a magnetic bearing system based on superconducting technology, which replaces completely the existing ring/traveler system of the ring-spinning machine. This superconducting magnet bearing consists of a circular superconductor and permanent magnet ring. After cooling the superconductor below its transition temperature, the permanent magnet ring levitates and is free to rotate above the superconductor ring according to the principles of superconducting levitation and pinning. Thus the superconducting magnetic bearing (SMB) ensures a friction-free operation during spinning and allows one to increase spindle speed and productivity drastically. The yarn properties using the SMB system have also been investigated and they remain nearly identical to those of conventional ring yarns.

Dynamics of rotating Superconducting Magnetic Bearings in Ring Spinning

A superconducting magnetic bearing (SMB) consisting of a stationary superconductor in a ring-shaped flowthrough cryostat and a rotating permanent-magnetic (PM) ring is investigated as a potential twist element in the textile technological process of ring spinning. Since the dynamic behavior of the rotating PM influences the yarn and the stability of the spinning process, these factors are studied in this paper considering the acting forces of the yarn on the PM-ring, its vibration modes, and the resulting oscillation amplitudes. For the assessment of a safe field-cooling distance during the operation of the rotating SMB in a ring-spinning machine, a correct calculation of the resonance magnification is particularly important. Therefore, the decay constant δ of the damped oscillation was measured as a function of the field-cooling distance (FCD) and the displacement. The observed increase of the decay constant δ with the initial lateral displacement and decreasing FCD is discussed in correlation to the number of depinned flux lines.

Cryogenic System for the Integration of a Ring-Shaped SMB in a Ring-Spinning Tester

A liquid nitrogen cryostat has been developed for experiments with a Superconducting Magnetic Bearing (SMB) in a ring spinning machine. The use of an SMB without friction instead of the common friction afflicted twist element is a promising approach leading to increased productivity and material variety. Here, an SMB designed as an axial ring system consisting of a liquid nitrogen (LN2)-cooled high-temperature superconductor ring YBa2Cu3O7-x and a permanent-magnet ring at room temperature is investigated. To assure the high quality of the yarn, the process has strong edge conditions concerning the air moisture and the ambient temperature. To protect the yarn from LN2 temperature, a continuous-flow cryostat was designed, tested, and integrated in the ring spinning tester. The geometric requirements of the spinning process lead to a ring-shaped vessel with a hole in the middle for the rotating spindle. First spinning experiments running at rotations in the range of 20 000 rpm show a reliable operation of the continuous flow cryostat in the SMB-based spinning process. In addition, easy process handling and low LN2 consumption are demonstrated.

Finite element analysis of the forces developed on linear induction motors

Superconducting magnetic levitation (SML) vehicles use a levitation technology based on the diamagnetic property of Y-Ba-Cu-O blocks and the magnetic field of Nd-Fe-B magnets. Brazilian SML project, MagLev-Cobra uses for the propulsion a short primary linear induction motor (LIM) with a squirrel cage secondary type. SupraTrans 2, the Germany MagLev vehicle, uses a short primary motor with secondary with copper plate and back-iron. Both motors assembly contribute to increase the levitation force. Brazilian tests with one levitating module on a 12 m track have shown a variation of the levitation height with the motor loading. In this paper, 2D - 3D finite element analysis will be used to study lateral, levitation and traction forces. Simulation and experimental results will be compared.