New cryogenic technology for cooling superconducting cables

Industrial gases specialist Messer Group GmbH (Bad Soden, Germany; www.messergroup.com) has developed a new cryogenic technology that makes it possible to use liquid nitrogen (LN2) to cool high-temperature superconducting (HTS) cables down to –209°C, which is significantly lower than that normally achieved by LN2 (–196°C). The new process was developed for the AmpaCity project of RWE Deutschland GmbH (Essen, Germany; www.rwe.com), in which a 1-km long, 10-kV superconductor cable replaced the conventional 110-kV lines between two substations in the city center of Essen, Germany. The HTS cable was developed by project partner, Nexans Deutschland GmbH (Hannover, Germany; www.nexans.com), and was commissioned in April 2014. In Messer’s process (diagram), N2 is vaporized at about 150 mbar, which lowers the boiling point to –209°C, thus achieving the specification for the cables (N2 freezes at –210°C, so lower temperatures are not possible). The LN2 is pumped through the HTS cable in order to conduct away any heat that penetrates through the thermal insulation, explains Friedhelm Herzog, senior manager for industrial application at Messer. The N2 heats up from –206°C when it enters the cable, to –201°C at the exit.…