Cable Tunnels - National Grid London Cable Tunnels (400kV)

Ellis Patents Centaur Cable Saddle Cleats For High Voltage Cable Support

National Grid Cable Tunnels

London accounts for 20% of the UK's electricity demand and this is continuing to grow by 3-5% a year - thisEllis Patents Cable Saddles - Centaur Saddles for 132kV 275kV 400kV Cable compares to the UK average of 1-2% a year. It is National Grids responsibility to ensure there is sufficient transmission infrastructure available to support future energy demand in London and as part of National Grid investment programme there are plans to build four deep cable tunnels which will house new 400,000 volt (400kV) extra high voltage cables. These high voltage cable tunnels will connect existing substations at :

*St Johns Wood

In London most electricity is transmitted through underground cables. They are traditionally located just beneath the road surface and work to maintain these cables is carried out in the road. By housing new electricity cables in tunnels deep below the road surface a number of advantages are achieved compared to traditional methods:

*Major disruption to the road network throughout Lononis avoided as we do not need to dig up the streets to lay the cable.

*Overall distruption to Londoners and road users during construction is significantly reduced as the majority of the works take place under the ground.

*Future repair and maintenance work can be carried out without disrupting traffic, businesses and residents.

*Additional cables can be installed in the tunnels to meet future deand.

A shaft, approximately 15m in diameter, is sunk at a large construction site known as a drive site. A tunnel boring machine (TBM) is then lowered down the shaft and starts tunnelling along a pre-determined route at approximately 120m per week. The TBM carries out two main activities. It moves forward cutting through the earth and it also inserts a tunnel lining of concrete segments. The TBM ends its journey at a reception site where another shaft is sunk and the TBM is removed.

Once the tunnel is complete the high voltage cables are pulled through the tunnel from large drums at the drive site. These lengths are then joined together using specialist techniques. The cables connect to National Grid's substations at either end of the route via the shafts. Once the cables are installed, any shafts which are not required for access or ventilation are backfilled.

Intermediate shafts and headhouses are required at key points along the route of the tunnel. The tunnel boring machine will link these points as it progresses along the routes. The Shafts and headhouses are needed for the following reasons:

*Health & Safety - It is essential to have access points to ensure the safety of the workforce during construction. The shafts are also used to access the tunnel for maintenance work once the tunnel is commissioned.

* Ventilation - Ventilation equipment, in the form of fans, is required to cool the cables and regulate the temperature inside the tunnel.
The headhouses will be designed in order to minimise their visual impact on the local area. For example, the building materials will be chosen to complement the surrounding enviroment in agreement with the local council.

National Grid is an international electricity and gas company and one of the largest investor-owned energy companies in the world. National Grid play a vital role in delivering gas and electricity to millions of people across Great Britain and northeastern US in an efficient, reliable and safe manner. National Grid believe the power of action can play a major role in safeguarding the global enviroment for future generations and tackling the effects of climate change, providing all customers with the highest standards of service through network investment and through a talented, diverse workforce. National Grid owns the high-voltage electricity transmission network in England and Wales and operates the system across Great Britain. It also owns and operates the high pressure gas transmission system in Britain and its distribution business delivers gas to 11 million homes and businesses.

*The total length of the four tunnels is approximately 40km.
*Average depth of the tunnels is between 12m and 60m
*The tunnel and shafts are below ground and do not require planning approval.
*Headhouses built on private land require planning approval.
*Planning applications will be submitted from early 2009.
*Total investment will be in the region of £600, 000,000

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Cable Tunnels - National Grid London Cable Tunnels (400kV)