Cryogenics in high-current busbars – Solutions and requirements.

In superconducting high-current busbars the major cooling demand is generated in the current leads. To minimize these current lead losses we developed a novel multistage cooled current lead. Depending on the amperage from 20 kA in chlorine electrolysis up to 500 kA in aluminium plants one can choose from a limited variety of cooling machines. Most effective are refrigeration plants based on the Claude-cycle providing cooling power on different temperature levels. But these systems are only available for higher cooling demands i. e. amperages around and above 200 kA. To reduce the required quantity of high-temperature superconductor, the superconductor inside the busbar should be cooled by sub-cooled liquid nitrogen at a temperature between 65 and 70 K. For long-distance transmission lines it is recommended to reduce the busbar temperature down to 20 K and to use helium gas as coolant.