The term ‘the national grid’ is commonly used to describe the entire electrical network in Great Britain, at every voltage from 230V in people’s homes up to 400,000V pylon lines crossing the countryside. However, from a network perspective, ‘National Grid’ is a much more specific term relating to the operator of the transmission network in England and Wales – the higher-voltage backbone of the electrical network, equivalent to the motorways of the road network – rather than the whole thing.
Who owns the transmission networks?
In GB, there are three separately owned transmission networks. In the north of Scotland, SSEN (Scottish and Southern Electricity Networks) is the transmission operator, whilst in the south of Scotland it is SP Energy Networks. In England and Wales, the transmission operator is the company National Grid.
You can see the ENA network operator map for the area these three companies cover (scroll down to the map and click on the ‘Electricity transmission operators’ button above the map).
Who is the System Operator?
National Grid is also the System Operator for the whole of GB, balancing demand and generation second by second, to keep the system frequency at 50Hz.
Customers can connect directly to the transmission system at 275kV or 400kV in England and Wales, and at 132kV as well in Scotland – and to some tertiary windings at a typical 13kV. Typically, new transmission connections are for large power stations, such as new off-shore wind farms.
The Distribution Network Operators (DNOs) take a supply from the transmission network and then distribute electrical power at lower voltages on a more local level, into homes and businesses, as well as connecting smaller-scale generators.