The National Grid is the high-voltage electric power transmission network supporting the UK's electricity market, connecting power stations and major substations, and ensuring that electricity generated anywhere on the grid can be used to satisfy demand elsewhere. The network serves the majority of Great Britain and some of the surrounding islands. It does not cover Northern Ireland, which is part of the Irish single electricity market.
The National Grid is a wide area synchronous grid operating at 50 hertz and consisting of 400 kV and 275 kV lines, as well as 132 kV lines in Scotland. It has several undersea interconnectors: an AC connector to the Isle of Man, and HVDC connections to Northern Ireland, the Shetland Islands, the Republic of Ireland, France, Belgium, the Netherlands, Norway, and Denmark.