London Power Tunnels is a project by National Grid plc to reinforce the electricity transmission network in London, UK, by constructing more than 60km of new deep-level tunnels carrying high-voltage cables. The new network of tunnels replaces a series of ageing power transmission cables, most of which were buried just beneath the road surface. These existing cables were becoming unreliable, difficult to maintain without disrupting traffic, and were unable to meet future demand for electricity in London. The new tunnels allow the power cables to be upgraded and maintained without disruption to traffic and residents on the surface. The project is divided into two phases: the first phase involved constructing tunnels connecting substations at Wimbledon, Hackney, and Willesden, and was completed in 2018. The second phase involves linking Wimbledon substation with Crayford, and is expected to be completed in 2026.
Phase 1
The first phase of the London Power Tunnels project, costing £1bn, involved the construction of 32km of tunnels spanning between the National Grid substations at Wimbledon in south west London and Hackney in north east London. The 3-4m diameter tunnels were dug by tunnel boring machines and run 20-60m below street level. The tunnels were constructed by a joint venture between Costain Group and Skanska. This phase linked Wimbledon and Hackney with existing substations at Willesden, St John's Wood, St Pancras, and Islington. It also involved the construction of two new substations: one at Seven Sisters Road in Highbury, and another at Kensal Green to feed traction power to the Crossrail project. As well as the main 400 kV power transmission circuits for the National Grid, the tunnels also carry 132 kV circuits from Islington substation to St Pancras and Seven Sisters Road, which form part of the London power distribution networkoperated byUK Power Networks. The project was started in February 2011 and the first section was energised six years later in February 2016. The project was officially opened by Prince Charles in February 2018.
The second phase is due to start in spring 2020 at a cost of £750m, and will span 32.5km from Wimbledon substation to Crayford in south-east London. The tunnels will be between 3m and 3.5m in diameter, and will be constructed 10-63m below street level, with the majority of the tunnel being around 30m deep. The contract for digging the tunnels for this phase was awarded to a joint venture between Murphy Group and Hochtief in December 2019. This phase aims to link Wimbledon substation to existing substations at New Cross, Kidbrooke, and Hurst, with intermediate shafts being built at Eltham and King's Avenue in Brixton. Phase 2 is expected to be completed by October 2026.
