The existing network runs south on overhead lines from the substation at Pentir, before going underground at Wern, passing between Porthmadog and Tremadog and emerging above ground again at Y Garth near Minffordd.

The line continues overhead on pylons to Trawsfynydd, although part of it is being put underground with our Eryri Visual Impact Provision (EVIP) project. Learn more about the EVIP project on the project website.

Our reinforcement and refurbishment work includes:

• Installing new and replacement underground cables and other equipment within the existing substation sites at Pentir and Trawsfynydd
• Constructing a new substation south of Bryncir
• Replacing one side of the overhead line between Bryncir and Trawsfynydd
• Replacing the underground cables that run beneath the Glaslyn Estuary at Porthmadog from Wern to Minfordd
• Connecting the new Glaslyn cables to the EVIP cables at Minffordd with new equipment, and removing the existing equipment nearby.

We will not need to build any additional pylons as part of this project

Replacing and upgrading the existing underground cables

The existing underground cables run from Wern to Garth between Porthmadog and Tremadog, and beneath the Glaslyn Estuary. They were installed in the late 1970s and have been in use ever since.

They are now nearing the end of their operational life and need replacing to maintain the security of electricity supplies for the local area and beyond.

To accommodate the increase in energy being generated in North Wales we need to replace them, and also upgrade the overall capacity of this part of the network with additional cables. Because the existing cables need to stay connected while the new ones are put in, we need to find different routes for our new cables.

As with the existing connection, the new cables will need to pass beneath part of the Glaslyn Estuary and the Traeth Glaslyn Nature Reserve.

We know this is a challenging and environmentally sensitive area that floods regularly and we are accommodating these sensitivities in our project designs.

The cables will also need to cross the field to the west of the A487 roundabout joining Porthmadog High Street, the top of the playing field at Ysgol Eifionydd, Porthmadog’s two heritage railway lines, and the main railway line.

We have already been discussing these technically complex proposals with the relevant organisations, so we can carry out the work safely and sensitively. We will also work closely with local communities and businesses to minimise any disruption.

In some of these locations, we will use a safe and proven method known as Horizontal Directional Drilling (HDD). This involves drilling a bore hole under an obstacle, installing a duct and pulling the new cable through. This is a precise technique that we have used successfully on many other projects across the UK.