National Grid’s cable replacement programme


National Grid’s cable replacement programme


The current distribution system for the high-voltage cable network around London needs to be urgently replaced due to an ever-increasing demand.


London currently accounts for 20 per cent of the UK’s electricity usage, which is increasing by between three and five per cent every year. In order to satisfy the city’s energy demand, National Grid is building more than 30km of underground tunnels, of 3m to 4m internal diameters, that will accommodate the 400,000V transmission line cables needed. One of the tunnels will also carry additional 132,000V cables to supply the distribution networks and so will be a metre wide.


The tunnels will connect substations in Wimbledon in the south, Hackney in the east and Willesden in the west with St John’s Wood, just north of central London. They will run underneath the Thames, Regent’s Park and some of the most densely populated residential areas and most expensive real estate in the UK.


National Grid project manager, David Luetchford, said: “We’re replacing old assets and increasing capacity, making sure we’re looking at what the energy network is going to be doing in five, 10, 20 years’ time. We’ll be getting more from the east coast [for example]. The energy flows will change across the whole country over the


The electricity utility company’s £1billion has been awarded with the Environmental Initiative of the Year for its sustainable practices, which are dramatically reducing CO2 emissions. With the assistance of its contract partners (Costain, Skanska, Halcrow, VVB, Mott McDonald and Arup) the project team is achieving a 40 per cent cut in CO2 emissions by:


  • Reusing 100 per cent of the earth excavated during tunnel. It's projected that a third of the London clay dug up during tunnelling will be used for the remediation of former gasworks sites in the capital. This saves landfill space, reduces lorry movements and means former industrial sites can be freed up for redevelopment


  • Using low carbon tunnel lining segments and low carbon spray concrete



It is expected that the first tunnel will be energised before 2016, and the entire project will be finished by 2018. “The transmission network will always continue to develop,” commented Luetchford, “but these particular assets will be in place at least for at least the next 50 years.”

Photo: Halcrow