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Underground 525kV HVDC cables qualified to German TSO standards

4th December 2018

Nexans

Alex Lynn

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Germany’s ‘Energiewende’, the transition in energy policy to focus on renewable sources of energy, is presenting significant challenges for the country’s transmission grid. In particular, Germany’s TSOs must transmit huge amounts of renewable energy over long distances from the north to demand centres in the the south and they are now building some of the world’s longest ever underground cable projects.

Nexans has responded to this challenge by qualifying its HVDC cable systems for the German TSOs for operation at 525kV, a major voltage increase that enables them to carry much more power than the previous industry-standard cables.

HVDC technology offers significant advantages for transmitting large amounts of power over long distances thanks to its improved power carrying capacity, lower losses and reduced cable footprint compared with conventional alternating current (AC) cable systems. However, Germany’s four TSOs - 50Hertz, Amprion, TenneT and TransnetBW – were reportedly looking for a significant increase in power capacity over the industry-standard 320 kV HVDC underground land cables.

Nexans developed an HVDC cable system, based on a triple extruded cross-linked polyethylene (XLPE) insulation design, to operate at a ground breaking voltage of 525 kV, with a power rating of 2 GW. In a one-year test programme under real outdoor installation conditions at the third party test facility STRI in Sweden with ambient temperatures from -20°C during winter time and up to +31°C during summer time, the Nexans HVDC cable system has successfully demonstrated its reliability and performance.

Deploying the 525kV cable will enable the TSOs, which attended the prequalification, to transmit much more power with a cable of the same cross-section. In some projects this could eliminate the need to construct an additional circuit, resulting in savings on cable infrastructure and civil works as well as reducing the installation footprint.

“Qualification of our 525 kV HVDC cable systems with Germany’s TSOs is an important breakthrough for Nexans at both the technology and commercial levels,” said Johannes Rothfeld, Nexans Strategic Account Manager for German TSOs. “It also illustrates the advantages of Nexans as a complete system supplier for HVDC cable systems as our capability to offer full turnkey solutions with local support for engineering, project management and installation was a vital factor in obtaining this qualification.”