Posted: 23 March 2015
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Rewiring London

The London Power Tunnels project has been described as the most significant addition to the capital’s electricity system since the 1960s. The scheme will see almost £1 billion invested in ‘rewiring London’ to create an energy superhighway of 10 new transmission circuits deep underground. Gareth Burden, National Grid Senior Project Manager, explains the scale of the challenge and the long-term benefits.

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Rewiring London

Rewiring London

The team on the London Power Tunnels project celebrate after completing the 32km tunnel network.

"Watching the completion of tunnelling was a great moment for all of us."

Gareth Burden, Senior Project Manager, National Grid.


At their deepest point, the tunnels are 197 feet below the surface. That's 30 feet deeper than the height of Nelson's Column.

Source: National Grid

One news image which has stayed with me since childhood is a moment in December 1990. This was when the British and French teams constructing the Channel Tunnel broke through and shook hands as tunnelling work was completed and a brand new connection was created to the continent. Their obvious pride in the efforts was clear from the news broadcast and photos that followed in the newspapers.

I was reminded of that moment the other week when at 10.46am on Thursday 12 March, the London Power Tunnels project reached its own equivalent milestone. It was the final tunnelling breakthrough in a programme that is essential to making sure that London’s electricity infrastructure is fit for the 21st century.

Peering down the shaft some 40 metres underground at our Kensal Green substation site and watching the tunnel boring machine complete the final metre of a 32km tunnel network was a really significant moment for all of us on the project team and for me personally, having been involved in the scheme from its inception in 2010. But the wider significance, of course, is what this means for London and the objective of meeting the city’s electricity needs in the decades ahead.

London’s insatiable demand for power

Electricity consumption in London rises by 4-5 per cent each year, compared to the national average of 1-2 per cent. In fact, the city accounts for about 20 per cent of the UK’s electricity usage. We all rely on the instant availability of electricity: to switch on lights, access our mobile phone network, or to travel efficiently on the Tube. Our job at National Grid is to make sure that there is a safe and reliable transmission network in place to meet these needs now and in the future.

The London Power Tunnels project has three main objectives. Firstly, it replaces existing assets, removing 1960s era technology and replacing it with modern infrastructure. Secondly, we are reinforcing parts of the network. We are building two new substations at Kensal Green and Seven Sisters Road in Islington, as well as modifications to four existing National Grid substations.

Finally, we are providing new grid supply points for Crossrail and UK Power Networks. The Crossrail project will deliver a new, high frequency rail service for London and the South East. The substation at Kensal Green is specifically required to provide a traction supply point for Crossrail.

What we’re delivering

The work that we are doing will increase London’s electricity capacity by 2018, the planned completion date for the project. To make that happen we have constructed a 32km tunnel network that stretches from Willesden in north west London to Hackney in the east and from Wimbledon south of the Thames, teeing into our Kensal Green substation. These tunnels will each carry six high voltage (400kV) cables, effectively the arteries of the new system that will feed London’s power requirements.

Our tunnels are three or four metres in diameter and they lie between 20m and 60m below London. Two tunnel boring machines have been deployed on the project and both have been named by local schoolchildren. Cleopatra and Evelyn have become very familiar names over the past three years or so!

The cabling itself is a massive undertaking because we’re installing 196km of 400kV cable in the tunnels and to and from substations, along with a further stretch of 132kV cable. We have been installing cable for over a year now in the completed tunnel sections, this final breakthrough will see this continue seamlessly until 2017.

Approvals and public acceptance

The creation of such a major network of underground infrastructure presents many challenges, not least of which is the need to gain the necessary planning permissions and technical approvals, and to work with a very large number of stakeholders to make sure they understand what we’re doing and why. To put this into context we have completed a total of 281 easements, which is essentially the permission you need to tunnel under private land, such as someone’s home.

Some of the key stakeholders include Transport for London, for the obvious reason that needing to tunnel in close proximity to the London Underground network requires careful planning! We are also working very closely with other parties such as Network Rail, Thames Water and UKPN. Alongside these stakeholders, we have also sent letters to householders, businesses and the local communities along the route, and have set up a dedicated 24/7 helpline to answer any questions they might have.

It’s a strange sensation standing in our tunnels underground and hearing the trains in the running tunnels of the Tube network thundering along just a few metres above your head or below your feet, taking thousands of passengers on their way.

Looking to the future

The London Power Tunnels project has come a long way in the past four years. There is a true sense of pride within the team at what has been achieved so far on time and within budget. Watching the completion of tunnelling was a great moment for all of us.

The project team is now very much focused on our remaining challenges and programme of works; completing the tunnel assets, installing a further 100km of cable and completing and commissioning substations across London, but we recognise that a secure and robust electricity network for London will be very much worth the wait.

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