Cryogenics in high-current busbars and multistage cooled current leads

Abstract

The use of high-temperature superconductors (HTS) has big advantages especially in high direct current applications. Relevant industrial applications can be found in chlorine, zinc or copper electrolysis and aluminum plants. We developed a superconducting busbar for 20 kA based on YBCO tapes including two novel multistage cooled current leads at the ends. The special characteristic of the system is the closed-loop operation evaporating no cryogens after initial cool down. This feature is advantageous particularly with regard to industrial application. A 25 m long demonstrator will be installed in a chlorine plant at BASF in Ludwigshafen under real industrial conditions within the scope of government-granted 3S project. In high current busbars the major cooling demand is generated in the current leads. To minimize these current lead losses we increased the efficiency by installing common cooling machines for three different temperature stages. To reduce the required quantity of high temperature superconductors, the superconductors inside the busbar are cooled by sub-cooled liquid nitrogen at a temperature between 65 and 70 K. The need of superconductor is further minimized by increasing the distance between the single HTS tapes. Both technical measures create high demands on the supporting structure plus the pipe cryostat elements and their cooling system. Test results of the current lead and busbar sections will be ...