Nexans in modernisation of high-voltage section in London – first phase of project successfully completed

State-of-the-art grid modernisation method minimises civil engineering work and reduces the risk of system disturbances

Hanover, 18 November 2010 – On behalf of distribution network operator UK Power Networks, Nexans Deutschland GmbH (Hanover) is assisting with a project to upgrade 11.5 km of 132 kV power cables between Twickenham and Laleham in London.

Replacing the two existing paper-insulated external gas pressure cables with new, plastic-insulated cables is designed to prevent failures of the redundant connection and ensure the city's security of supply. Nexans completed the first of the two sub-projects in August after just four months of installation work. This was thanks not only to the experienced Nexans installation team but also to the installation technology used. The job involved the use of more than 23 km of “pipe type cables” made of three high-quality, stranded high-voltage XLPE cables with a copper wire screen and aluminium laminated sheath protected by flat steel wire armouring.

High-quality XLPE mixtures ensured a highly compact design, which enabled these pipe type cables to be drawn into the existing pipes. With a value of several million Euro, this was the biggest pipe type cable project ever undertaken by the Hanover plant. The dimensions involved were also record-breaking for Nexans: the cables, which had a cross-section diameter of 3 x 630 mm² making them the biggest pipe type cables ever manufactured by Nexans, were drawn into pipes with diameters of less than 160 mm.

Civil engineering costs cut and permission procedures reduced

Pipe type cables are designed for the modernisation of inner-city sections where paper-insulated external gas pressure cables are to be replaced. The pipe type cables are drawn into the steel pipe that contained the old cable, which minimises road digging and excavation work. Traffic disruptions are largely avoided and therefore local residents are only minimally affected. This is achieved thanks to the highly compact design of the Nexans pipe type cables: a high-quality XLPE (cross-linked polyethylene) mixture ensures the required insulation with relatively thin walls. The pipes do need neither to be gas-pressurised again nor monitored following installation, which cuts operating costs.

Half of the project’s high-voltage cables have been replaced so far

In the modernisation process, the pipe type cable is pulled in section by section. The 11.5 km section in London comprises more than 20 sub-sections with cable lengths of between 400 m and 500 m. The first of the two systems was replaced this year and has been successfully commissioned. The second, parallel system is due to be replaced in the summer of 2011.

Contingency plan for highly stressed cable section

Nexans had devised a contingency plan to ensure power supplies remained flowing during the upgrade. Had the existing parallel section failed during the installation of the first, new cable, the defective sub-section could have been replaced by a pipe type cable. Transition joints specially manufactured for this project can connect the ends of the XLPE cable to the ends of the external gas pressure cable, allowing the existing system to be restored.
Jörg Niehoff, Nexans project manager in Hanover said: “The ability to prevent power outages is particularly important on this connection because while one cable is being installed, the other remains under load. Any weak points in the existing cables mean that there can be a risk of failure”. 

In summer of this year, Nexans Deutschland upgraded the first cable section between Twickenham and Laleham in London. The use of “pipe type cables” largely avoids the need for civil engineering work on the 11.5 km section and helps minimise traffic disruption.

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Nexans Germany is one of the leading cable manufacturers in Europe. The company is offering an extensive range of high performance cables, systems, and components for the telecommunications and energy sectors, rounded off by superconducting materials and components, Cryoflex transfer systems and special machinery for the cable industry. Producing at manufacturing plants with 7.260 employees in Germany and abroad, the sales in 2010 amounts to approx. 810 Mio Euro. The full integration into the Nexans Group Nexans Germany also benefits from excellent opportunities to use the available synergies in all corporate fields, which not only applies to worldwide projects but also to research and development, the exchange of know how, and to other areas. More information on