Cable Architecture and Materials
The architecture of Nexans superconducting cables is similar to conventional cables but copper or aluminum wires are replaced by superconducting tapes for the current transport. The conductors are sheathed with low temperature proof high voltage insulation and surrounded by a superconducting screen which provides electromagnetic shielding. Liquid nitrogen cools the cable core to its operating temperature of approximately -200 °C. A flexible, double-walled corrugated cryostat thermally separates both the cable core and the coolant from the environment. The cables are typically delivered with an outer jacket of polyethylene.
The superconducting tapes used in Nexans cables consist of a metallic substrate and an oxide ceramic material which displays virtually perfect electricity conducting properties if cooled to temperatures below -180 °C. A superconducting tape of this kind can transmit current densities that more than a hundred times exceed the current carrying capacity of a copper conductor of the same cross section. The ampacity of a superconductor cable is determined by the number of parallel connected superconducting tapes deployed.
Compact Size and Routing
Nexans superconducting cables stand out for high ampacity, compact size, and the absence of electromagnetic or thermal impacts on the environment. In metropolitan areas, where space is limited and rights-of-way frequently cannot be extended, these features enable laying superconducting cables in existing routings. If the space requirement of new overhead transmission lines proves an obstacle to grid expansion, superconducting cables can be laid in narrow routings with a minimal environmental footprint. In the medium and long term, this technology will also enable eco-friendly “electricity highways” with ultra-high transmission capacities.
High Capacities at Low Voltages
Nexans superconducting cables enable an efficient transmission of high current densities at lower voltage levels in comparison to copper or aluminum cables. While superconducting DC cables cause no voltage drops at all, losses in superconducting AC cables are very limited. With this technology, transmission distances that used to require conventional high voltage equipment can be bridged on medium voltage level. In metropolitan areas, this offers attractive opportunities for power grid operators: Valuable space for urban development can be regained if medium voltage superconducting cables are installed to replace large high voltage installations which are due for refurbishment. In environments with power-intensive industrial processes, Nexans high current cables take up 90% less space than conventional high current leads and, at the same time, avoid electrical losses. Similar advantages can be obtained with superconducting power supplies for high-performance electric ship propulsions.
No Electromagnetic and Thermal Impact on the Environment
The design of Nexans superconducting cables prevents external electromagnetic fields and enables operation in the immediate vicinity of data cables without interference effects. These characteristics greatly facilitate modernization and construction of metropolitan electricity supply networks as
superconducting cables gain better acceptance from residents than conventional overhead transmission lines.
Unlike copper or aluminum cables, Nexans superconducting cables do not produce thermal output. The cable core, cooled to operating temperatures around -200 °C by liquid nitrogen, is encased in a vacuum-insulated cryostat which thermally decouples its content from the environment. Despite the cables’ ultra-high current carrying capacities, this solution prevents soil desiccation and avoids overheating in crowded routings. More than three decades of development and manufacturing have earned Nexans unique expertise in cable cryostat technology.