EGL1 is a 196km long high voltage direct current (HVDC) link. A HVDC link functions like a superhighway for electricity, allowing large amounts of power to be transmitted over long distances before being fed into the electrical grid.
The link will be constructed in three main sections:
1.Scottish point of connection
In the Torness area in East Lothian, we will build a new onshore converter station adjacent to existing industrial facilities and connect into a new substation near Branxton to tie into the existing transmission network. Underground electricity cables will be installed to connect the substation to the converter station and from the converter station to the landfall point south of Thorntonloch beach.
2. Marine cable route
176km of subsea cables will be installed from south of Thorntonloch beach, through Scottish and English waters to a landfall point just north of Seaham, in County Durham.
3.English point of connection
Underground onshore cables will be installed from the landfall point just north of Seaham, to a new converter station and substation at Hawthorn Pit, County Durham, between the villages of Murton and South Hetton. Several existing overhead line connections into the substation at Hawthorn Pit will also be reconfigured, resulting in fewer pylons than there are today.
Converter stations and substations
A converter station converts electricity between alternating current (AC) and direct current (DC). AC is used in the UK transmission network system as this is easily converted to different voltages for industrial, commercial and domestic use, while DC is used for transmitting large amounts of electricity efficiently over long distances. In the UK this is normally through subsea cables. Our converter stations will house the technology that will enable clean electricity to be transmitted through the 196km cable link.
Substations are crucial for the day-to-day operation of the network and for controlling the voltage of electricity between the country-wide transmission network and people’s homes and businesses. They house switchgear and other critical operational plant alongside transformers which ‘step down’ the high-voltage electricity running in the transmission network to lower voltage electricity which is suitable for everyday use.
Our cables and their installation
The HVDC link will consist of two electrical cables and a fibre optic cable, running 176km under the sea: most of its 196km length.
Onshore, these will be either direct buried, installed in ducts or carried in cable bridges depending on the site condition and will be fully reinstated on completion.
Offshore, we use two methods to lay the cables under the seabed: simultaneous lay and burial (fig.1) and post lay and burial (fig 2).
The seabed surface conditions determine which method we use. During simultaneous lay and burial, one vessel both lays and buries the cables, and during post lay and burial, one vessel will lay the cables and a second follows behind and uses a range of specialist equipment to bury it.
To make landfall, the cables will be installed using Horizontal Directional Drilling (HDD).
This method drills conduits to carry the cables under the intertidal zone and the near-shore seabed at the landfall points and then installs ducts which the cables can later be pulled through.
This approach minimises work in the intertidal zone and also reduces related environmental impacts including those on protected species and sensitive habitats, and on people using the foreshore.
For more information on converter stations and cables, including diagrams, maps and images, please view the public consultation materials in the Document library.