Polycrystalline HTS material for bearings and electric power devices

Abstract

The choice of the material strategies to fabricate bulk high temperature superconductors larger than 10 cm has a significant influence on the performance and reliability of HTS components. The paper considers the various techniques in which magnetic bearings and local current transport devices (current leads and fault current limiters) may be provided: improvement in materials and design. Among bulk growth technique polycrystalline melt textured YBCO rings, rods and plates are a promising concept for the modular up-scaling of current transport and magnetic components if the weak-link behaviour of grain boundaries can be reduced. The fabrication is based on ceramo-crystal growth Bridgman-like directional solidification with an applied spatial and time-dependent thermal gradient on Y 1+ x Ba 2Cu 3O 7− δ ( x=0.30–0.60). Novel superconducting magnetic U-shaped bearings are designed, assembled and tested in a magnetically rotating Si wafer carrier. Rotor dynamics is studied in terms of unbalance and critical rpm's. Fabricating and assembling of current lead components and resistive fault current limiter devices with a transport J c of 5–10 kA/cm 2 at 10 μV/cm and at 77 K are discussed, including a galvanic metal surface deposition technology to contact, protect and stabilize the HTS.