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Transport and construction


We think it will take four to five years to build and test the connection, with additional time to reinstate the land and restore it to its previous use. At any one time, there are likely to be a number of working sections along the route, so we won't be working on the whole connection all of the time.  

Our work typically happens in phases. Each element of the project will be built following four main steps. 

We will:

  • set up construction sites by levelling the land and installing works compounds and access roads from public roads 
  • build the connection
  • test all the equipment ensuring it’s constructed correctly before making it live at high voltage 
  • look to carry out additional planting to screen equipment where required

Construction

Overhead line construction

Overhead line connections are made up of wires (known as conductors) supported by pylons. The line carries two electrical circuits one on each side of the pylons.

(Click image to enlarge)

We will typically:

Set up the sites
 
  • install temporary access roads to pylon locations along the route which could be made from stone or track-mats. We might need to make modifications to the existing roads, such as widening existing field entrances
  • install the works compounds, which will include facilities for workers, site offices, storage for materials and parking for workers and construction vehicles
  • clear or trim trees that could interfere with the pylons when they’re transmitting electricity
  • make our sites secure and control traffic on the access roads

Construction
 
  • create a level surface for pylon construction sites
  • dig and build the foundations
  • deliver pylon components and build the pylons using cranes 
  • deliver the electrical equipment including the wires
  • string the wires on the pylons – wires are usually installed in sections of about 10 pylons. The wire is then set up at its finished tension and height above ground

Testing
 
  • make sure equipment is installed correctly and safely

Reinstatement
 
  • reinstate the land used for our temporary works so it can return to its previous use
  • carry out any tree planting to help screen the pylons or to replace trees we have needed to remove

You can see how the proposals might look in your area by exploring our interactive map.

Tunnel construction under the Menai Strait

Inside the tunnel we will install the cables that will carry the power from Wylfa Newydd underneath the Menai Strait.

Because of the geology and challenging ground conditions, construction of the tunnel under the Menai Strait will be a hugely complex process and we will be working on this part of the project throughout the construction stage. 

At both ends of the tunnel we will need a tunnel head house.

 

(Click image to enlarge)

You can see how the proposals might look in your area by exploring our interactive map

We will typically:
 
Set up the sites
  • carry out any modifications to public roads where required
  • construction of new access roads, drainage and vegetation clearance
  • where necessary put diversions in place for any public rights of way our work may effect 
  • prepare compound area, including any necessary drainage
  • install the temporary works compounds, which would include facilities for workers, site offices, storage for materials and parking for workers and construction vehicles 
  • secure the site by installing a security fence and control the traffic on the access road
 
Construction
  • at each end of the tunnel we will build a permanent vertical shaft and lower a specialist piece of equipment called a tunnel boring machine down the shaft
  • the boring machine will then drill the tunnel
  • as it drills the tunnel, the tunnel interior is lined with concrete and a track is installed along the tunnel which will be used by a vehicle to get people and equipment from the tunnel entrance to the tunnel boring machine
  • inside the tunnel we will install the cables that are needed to carry the power. We'll need to install at least six cables in the tunnel to carry all the power that Wylfa Newydd will generate
  • the tunnel needs to be large enough so the cables can be spaced apart so they don’t overheat
Testing
  • make sure all equipment has been installed correctly and then carry out detailed inspections and tests before making the substation live at high voltage ready for operation
 
Reinstatement
  • after construction, the only visible part of the tunnel will be the tunnel head houses, which will be built on top of each vertical shaft
  • the tunnel head houses will be around 12 metres tall and will provide access for maintenance. They will also contain important equipment such as ventilation fans, which will help keep air circulating inside the tunnel and help with cooling
  • to help reduce visual impact, we will look at ways we can help the tunnel head house fit into the surrounding environment, by using a design in keeping with the local area

Sealing end compound construction

A sealing end compound contains the equipment required to connect overhead lines and underground cables together.

 We need one on Anglesey and one in Gwynedd. They will contain equipment up to 14m high and be securely enclosed by a fence. 

The sealing end compound will be located with the tunnel head house in an area approximately two acres in size. This includes the area within the security fence and spaces for parking.

(Click image to enlarge)

We will typically:

 
Set up the sites
  • prepare and build permanent access roads to the sites and install a security fence and control traffic on access roads 
  • install the works compounds, which will include facilities for workers, site offices, storage for materials and parking for workers and construction vehicles
 
Construction
  • level the ground to provide a flat and stable surface for foundations install temporary covered scaffolding about 25m tall. This will provide a dry and clean environment so we can safely connect the underground cables to the sealing ends 
  • connect the cable sealing ends to the overhead line 
 
Testing 
  • make sure equipment is installed correctly and safely
 
Reinstatement
  • reinstate the land used for our temporary works so it can return to its previous use
  • carry out any tree planting to help screen the site or to replace trees we have needed to remove

 

Substation construction

The function of Wylfa substation is to ‘collect’ power from the Wylfa Newydd Power station for onward transmission and to supply Anglesey.

 The substation at Pentir collects and provides power to the local network in North Wales, as well as transmitting it to the wider UK network. 

Both substations need extending to connect with the proposed second line.

This will involve installing a range of equipment such as electrical switchgear and sealing ends, which allow us to maintain and operate the new line. 

Suitable mitigation measures such as timing restrictions would be agreed and enforced in order to reduce impacts on the existing road network.

You can see how the proposals might look in your area by exploring our interactive map.

To extend the substation, we will typically:

 
Set up the site
  • construct any temporary construction access routes to the site 
  • install the temporary works compounds, which would include facilities for workers, site offices,  storage for materials and parking for workers and construction vehicles 
  • secure the site by installing a security fence and control the traffic on the access road
 
Construction
  • start by creating a surface for the site extensions
  • extend underground ‘earthing’, drainage systems and build the foundations
  • build all the structures that support the electrical equipment, and associated buildings
  • install all the electrical equipment and receive any transformers on large specialist vehicles before installing them
 
Testing
  • make sure all equipment has been installed correctly and then carry out detailed inspections and tests before making the substation extensions live at high voltage ready for operation
 
Reinstatement
  • re-instate the surrounding land, carry out any screening work required to reduce visual effects and replace habitat that may have been lost during construction

Transport

Main construction traffic

We’re proposing to use the A55, A5, and A5025 as these are the main roads which are closest to our work. We'll also need to use smaller rural roads off the main road network so we can get to the sites where we will build our equipment.

 Most of the equipment we will need, including the components for the connection, cranes to build theconnection, and all the materials for temporary work (such as works compounds and access roads), will be transported on lorries (HGVs). 

We'll also need vans and cars to take workers to and from site and anticipate needing some larger vehicles such as mobile cranes and low loaders to carry equipment like large drums of cables. In addition to our work, Horizon Nuclear Power will also have its own requirements for the construction of Wylfa Newydd. All of this work will result in an increased volume of traffic on the road network. 

To identify transport routes, we’ve considered how we can best reduce effects on road users, including local people and tourists. 

We have consulted with the local county councils, North and Mid Wales Trunk Road Agency, Welsh Government and other relevant bodies to request their feedback on which routes will offer the best opportunity to reduce effects on the area.

Additional transport works - tunnel construction

The construction of the tunnel under the Menai Strait requires a range of specialist equipment such as a tunnel boring machine, cranes to lower equipment down the tunnel shafts, and equipment needed for the excavation of rock and soil. 

This equipment is large and heavy and may require specialist vehicles to deliver it to the tunnel construction sites in Anglesey and Gwynedd. 

The specialist vehicles would be larger and move more slowly when compared to normal HGVs. There would only be a small number of these and they may require escort vehicles and traffic management. 

To construct the tunnel we will need to remove many thousands of tonnes of rock and soil and deliver lots of materials to site, such as aggregates and concrete linings. This will require a large number of conventional HGV journeys. However, the tunnel construction will take place over a number of years and the number of HGV journeys will be spread out.

Additional transport works - substation construction

As the works at Wylfa and Pentir substations are extensions to existingsites, the transport routes are already well established for maintenance and operation. We will look to use these routes during the construction phase. Keeping the works close to the existing sites, where there is good access and space for construction will help reduce the number of deliveries. Most of the deliveries to these locations will be on conventional HGVs. 

Some of the equipment needed to construct the substation extensions is large and heavy and this may require specialist vehicles, such as low loaders. These would be larger and move more slowly compared to normal HGVs and may require escort vehicles or traffic management. We would only need a small number of these.

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