Superconducting cables for the extra-high voltage range


The total length of the German transmission system is currently about 35,000km. In the course of the energy transition, the four German transmission system operators (TSOs) are faced with the demanding task of expanding the grid by around 5,300km, so that electricity from renewable sources reliably reaches the consumption centres in the south and west of the country. Especially near cities and villages, the TSOs are required to employ underground cables instead of overhead lines to increase public acceptance of the grid extension.

The Dutch-German TSCNET shareholder TenneT is convinced that in the officially specified pilot sections superconducting cable systems should be used, as they offer significant advantages over traditional cable systems. This is the result of a feasibility study conducted by the renowned Karlsruhe Institute of Technology (KIT) in close cooperation with TenneT in the framework of the government-funded “Kopernikus”-project “Ensure”. With this research project, TenneT once again shows its great interest in the further development of underground cable technologies.

The main challenge of the project is that superconducting technology has never been used at the extra-high voltage level. The cable test system is designed for a continuous output of 2300MW and, at high current load, has significantly lower losses than conventional cables with a copper conductor. Superconductor technology could also be beneficial for the width of the cable trench, since a superconducting cable system only requires six cables, while a conventional one comprises twelve three-phase cables, explains Hanno Stagge, project manager at TenneT.

The newly designed superconducting cables for the transmission network are based on high-temperature superconductors made of ceramic. They need less cooling and can therefore be operated relatively cost-effectively. The study should be completed by the end of the year and will also include ecological and economic considerations. However, there is still a long way to go before the superconductor is ready for use: “Subsequent to the study, the cable in combination with the necessary connecting sleeves and closures have to be manufactured and then intensively tested together with a cooling system”, comments Mr Stagge.

TSCNET shareholder TenneT conducts a feasibility study on underground superconducting cables together with KIT (collage of images by ITEP/KIT and TenneT).

> See TenneT press release, in German (html)

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High costs prevent superconductor in Enschede


A transmission system operator (TSO) is responsible for a secure and sufficient supply of electricity within its control area. But besides issues of system security and reliability, TSOs have to operate cost-efficiently to provide customers with an appropriate electricity rate. Such economic requirements apply to the Dutch-German TSCNET shareholder TenneT as well as to any other TSO, and also in consideration of the given official regulations, TenneT is expected to be economical in its publicly-funded investments in the high-voltage grid.

In the city of Enschede in the eastern Dutch province of Overijssel, TenneT investigated wether the installation of a 3.4km-long section of superconducting cable is feasible and reasonable. As it turned out, a superconductor would cost about four times more than a conventional cable under the specific conditions in Enschede. This excessive difference in investment costs led TenneT to refrain from the ambitious cable project.

A High-Temperature Superconductivity (HTS) cable can transmit up to five times more electricity than a conventional cable. Apart from that, it emits neither an electromagnetic field nor heat, resulting in significantly lower spatial requirements. Although this actually makes a superconductor highly suitable for inner-city applications, it would currently be too expensive to install a superconducting cable of only a few kilometres in length. But as HTS-technology is developing rapidly, a superconductor could become more affordable in the future. Given these conditions, TenneT will reconsider the deployment of HTS even for short intra-urban cable sections.

> See TenneT press release (html)

Picture: “Kleurrijk Enschede” by Fred Veenkamp (Creative Commons BY-SA 2.

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