Industrial Products and Applicationsyear , issue 2, april-may 2021

Nexans has successfully commissioned the world's first resistive superconducting fault current limiter

Nexans, a worldwide leading expert in the cable industry, has successfully commissioned the world's first resistive superconducting fault current limiter (SFCL) based on second-generation superconductor tapes. The SFCL, equipped with superconducting elements developed in cooperation with the Karlsruhe Institute of Technology, has been installed on behalf of Vattenfall Europe Generation AG to provide short-circuit protection for the internal medium voltage power supply that feeds coal mills and crushers in the Boxberg lignite power plant in Saxony, Germany. A first generation SFCL, based on solid superconducting materials, was installed by Nexans at Boxberg in 2009 as part of a long-term test programme. Following the successful completion of this project, Nexans has returned to the plant for live testing of a new SFCL device featuring superconducting tapes. These tapes reduce the already low losses in the conductor material by around 90 percent, thereby lowering operating costs. They also provide an even faster response to a short circuit than the first generation materials. "We now have a second superconductor material option for manufacturing power systems, and this will provide us with an even wider range of applications for our fault current limiters to help customers improve the safety of personnel and equipment while also reducing infrastructure costs. The upgrading and expansion of power networks to meet the fast-changing needs of our customers requires intelligent solutions and new functions," explains Jean-Maxime Saugrain, Corporate Vice President Technical at Nexans. "The power plant's house load is just one of many potential applications for SFCL technology. For example, in the renewable energy sector the capability to supply more power from renewable sources is frequently restricted by the level of the short circuit currents." The current limiter works in a similar way to the low voltage safety cut-out in domestic homes, but operates on the medium/high voltage network. In addition, after operating, it does not interrupt the electricity flow completely. Under normal circumstances, its superconducting elements allow the electricity to flow unhindered and with practically no resistance. If a critical current level is exceeded, such as during a short circuit, the conductor drops out from its superconducting state within milliseconds to act as a strong electrical resistor. Only a precisely defined residual current will then flow. This enables the device to protect all the downstream components, such as switchgear, from the damaging overloading of a short circuit.