TenneT to trial first ‘super cable’

TenneT is planning to install a trial run consisting of 3.4 km of underground superconducting high-voltage cable in the Dutch electricity grid. The project, subbed Supernet NL, will be a first – a section of superconducting cable at this length has not yet been installed anywhere else in the world. The project is scheduled for completion in June 2019. “With this project, we are meeting society’s demand to install more high-voltage lines underground,” commented TenneT CEO Mel Kroon. “With these superconducting cables, it should become easier in future to integrate high-voltage lines in urban areas.”

The superconducting state in HTSC (high temperature superconducting) cables is achieved by means of refrigeration to minus 200°C using liquid nitrogen. The 150 kV cables currently in use require a right of way at least 12 metres wide to dissipate the heat generated. HTSC cables can be laid much closer together because they generate no heat, and no magnetic field, so that a 3 metre wide RoW strip ought to be sufficient.

Progress

TenneT has completed the process of finding a suitable demonstration site where the cable can be taken into operation for the first time, and has selected the town of Enschede where the test cable, estimated length about 3.4 km, will connect the substations Van Heekstraat and Vechtstraat. It is currently engaged in exploring the route.

No specific technology has been selected as yet, and no manufacturer, although it is expected that the cable will be a liquid nitrogen cooled system operating at 110 kV.

The test programme will follow the procedures of IEC 63075, currently being finalised for the project, with some added requirements.

It is now possible to enter the tender stages, and the project has received the green light to do so. Manufacturers and their consortiums on a list of qualified tender organisations have been requested to prepare for quoting based on the specifications issued.

Next steps

TenneT is working with several leading institutes on the project. Researchers at Delft University of Technology, University of Twente, the Institute for Science and Sustainable Development, HAN University of Applied Sciences, and Imtech Marine will investigate topics including the control engineering aspects and the requirements that the cable must meet.

TenneT does not anticipate that superconducting cables can be applied in current projects. Further research must be conducted and additional experience gained before such a step can be taken, and initially, it will only be possible to use superconducting cables in sections of up to four km – longer sections cannot yet be realised because of the liquid nitrogen supply required to cool the cable.

Superconducting cables are also expensive, costing approximately three times as much as a standard 110 kV or 150 kV cable.

However, the technology is developing quickly. It is expected that it will be possible to use superconducting cables more widely and/or across greater distances in future, thanks to improved cooling methods and mass production.