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Our work in West Gwynedd

We need to make some important upgrades to the electricity network near Porthmadog and Bryncir to provide secure and reliable power supplies to North Wales and beyond. 

This work is needed because of the new low carbon power that will be generated by Wylfa Newydd nuclear power station on Anglesey and wind farms in Ireland. This new energy generation will increase the amount of power in the electricity network. That means we need to upgrade the network so we can get the power to the millions of homes and businesses in Wales and the rest of the UK that need it. 

Our work involves:

  • work on the existing overhead line between Pentir and Trawsfynydd,and minor work at our existing substation at Trawsfynydd 
  • a new substation near Bryncir
  • replacing the existing cables at the Glaslyn Estuary with 12 new cables and carrying out work to our existing equipment at Wern and Y Garth

(Click map to enlarge)

We’ll be able to say more about our plans for how we will carry out this work in 2017. In the meantime, we thought it would be helpful to provide you with an update on our work so far.

Our work in West Gwynedd

Pentir to Trawsfynydd

The existing line between Pentir and Trawsfynydd is owned by National Grid but currently we share it with SP Energy Networks, which is responsible for the local electricity network. The pylons on the line carry two setsof wires. SP Energy Networks uses the wires on one side to supply power to the local area; we use the wires on the other side as part of the overall national electricity network.  

With the amount of new power that’s being proposed in North Wales, we now need to use the wires on both sides of the pylons. 

SP Energy Networks will therefore need a new connection to continue to provide power to local homes and businesses. A new substation is needed for this new connection and a site has been identified near Bryncir. We are working closely with SP Energy Networks to identify the most appropriate way of connecting the substation to the local network. 

We will also need to undertake some work on the existing line between Pentir and Trawsfynydd but we don’t think we’d need any additional pylons.  

And we need to carry out some work to our existing substation at Trawsfynydd to help strengthen the network. This work will be within the existing site and we won’t need to install any equipment that’s higher than what’s there already.

A new substation south of Bryncir

We need a new substation to make sure that electricity supplies are maintained to the local area. We’ve chosen a new substation site south of Bryncir. 

In 2012, we presented three possible sites for the new substation. These were called north, central and south. We asked for your feedback and you told us that communities, landscape and views were important to you. We have chosen the south site. It is away from the immediate area of Bryncir and Garndolbenmaen and avoids important ecology sites. It also gives us good opportunities to plant trees to screen the substation. 

You can find out more about how we construct a substation here.


What does a substation look like?

Our image library has lots of pictures of what existing substations look like.


(Click image to enlarge)

How long would it take to build?

We think it would take around a year to build the substation near Bryncir and connect it to our network.

Upgrading the underground cables at the Glaslyn Estuary

We need to upgrade the existing underground cables at the Glaslyn Estuary with 12 new cables and update equipment at existing sealing end compounds (where the underground cables connect to overhead lines) at Wern and Y Garth. We’ve chosen a route for the new underground cables which we think will reduce effects on the area and mean that after our work is finished, the estuary area will look much the same as it does today. 

In 2012 we proposed route options for the new cables. You told us to consider local railways, roads and wildlife at the estuary. Our proposed route is the most direct and takes into account important ecology sites in the area. 

The route gives us flexibility on when and where we cross the railways and bypass. We are investigating construction techniques to replace the cables to choose an option that has the least effect on the area. Our work to date suggests horizontal direct drilling (HDD) – a process using a steerable drill to create a series of underground cable ducts – could be the preferred option compared to open trench construction. 

Would your work affect the landscape or views?

There’d be some temporary effects during construction – we’d need to work in an area about 65 metres wide to install the cables. Keeping the cables underground would mean that when our work has finished, the estuary would look much the same as it does now. 

How long would construction take?

We expect construction would take up to three years.  

What about traffic and transport in the area?

We’d use local roads to move our equipment and materials to site. This might cause some disruption but we’d try to keep this to a minimum. We’d expect to develop a plan for managing traffic with the local highways authority before we start our work. 

How have you considered ecology?

We’ve considered ecology sites and carried out surveys looking at the landscape and local wildlife. As far as possible, our route keeps away from Glaslyn Site of Special Scientific Interest (SSSI) and Meirionnydd Oakwoods and Bat Sites Special Area of Conservation (SAC). We’ll continue to work with Natural Resources Wales and other stakeholders to understand any concerns they have.

What happens next?


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