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Type Testing of Superconductor Cable for the “AmpaCity” Project Successfully Completed

Over one hundred years after the discovery of the superconductor effect, people are now realising what generations of scientists were enthusing about – the almost loss-free transportation of electricity.

With the handover of the test certificate for a high-temperature superconductor (HTS) cable system, Nexans and RWE Deutschland AG will mark the completion of the 18-month development phase in the “AmpaCity” project on 11 March 2013. Following the successful test series of the prototype in the Nexans’ Hanover plant’s high-voltage laboratory, production of the 10 kV HTS system, which is 1 kilometre in length, will now start. It is set to replace a 110 kV copper cable in the RWE-operated distribution network in the city of Essen at the end of the year, and transport the same power of up to 40 MW.

Its suitability was proven by the prototype of the HTS cable in a lightning impulse voltage test at roughly seven times the nominal voltage as well as during continuous loading at three times the operating voltage. During the tests, the connection joint belonging to the system and the specially developed, particularly compact cable terminators were also tested. The terminators are used to create the transition from the cryogenic superconductor system to the conventional copper network.

Twofold world premiere in Essen’s city centre
The three-phase, concentric 10 kV cable from the AmpaCity project will now be the longest installation of a superconductor cable in the world. The combination of a superconductor cable with a superconducting fault current limiter also constitutes a premiere. This device is produced at Nexans SuperConductors GmbH in Hürth and protects the grid and the cable from overloading caused by short circuit currents, preventing them from spreading to other network parts.

Superconductor cables are a solution for avoiding further expansion of city networks with high-voltage cables; their use would mean that resource- and land-intensive transformer stations could be demolished. Although copper or aluminium medium-voltage cables could also be used in inner-city areas to transmit high power, the cost efficiency of this solution would be cancelled out by the much higher losses during electricity transportation.

“The superconductor cable being laid in Essen city centre runs between two transformer stations and is the first to have a length of one kilometre. It will facilitate a discernible increase in the power density and efficiency of the city centre power supply,” says Dr Andreas Breuer, Head of the New Technologies / Projects division at RWE Deutschland AG. Christof Barklage, CEO of Nexans Deutschland stated that “this project could revolutionise the power networks. We are happy to be among the pioneers in this fascinating, trend-setting technology.”

Technical superiority of ice-cold conductors
The technical superiority of the superconductor cable system can be attributed to the material properties of the conductor material. At temperatures of around -200°C, it is transformed into an almost perfect electrical conductor that can transport at least 100 times more electricity than copper. The required operating temperature can be created without considerable effort using liquid nitrogen, which is also used as a coolant for many other industrial purposes. Despite the essential heat insulation of the superconductor cable, it succeeds in transporting five times the electricity as a copper cable with the same outer diameter – and with much fewer losses compared to copper.

Efficiency technology to soon compete with conventional solutions
High-temperature superconductors as used here in AmpaCity in the cable system and the fault current limiter have been ready for deployment in energy-related applications for some years now. Experts anticipate that these innovative cable systems will soon be in a position to compete with copper solutions in energy-intensive applications, from a cost-effective perspective as well. They are of interest wherever a high level of electrical power must be transported where space is restricted. Thanks to these special properties and minimised electricity losses, superconducting power equipment is regarded as a major element in the energy supply of the future by the German Federal Ministry of Economics and Technology (BMWi) and in the consortium led by RWE Deutschland AG, and is therefore promoted as part of the AmpaCity project.

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