Transmission system operators
A system operator is responsible for an area to be electrically stable, and for the security of supply in his area. A system operator has to be a non-commercial organization, neutral and independent with regard to the market members.
In the Nordic countries, the system operators have the responsibility for both the security of supply and the high-voltage grid (the transmission grid).
The Nordic transmission system operators are Statnett SF (Norway), Svenska Kraftnät (Sweden), Fingrid (Finland) and Energinet (Denmark). The Estonian TSO is Elering and the Lithuanian TSO is Litgrid. In Latvia it is the independent transmission system operator AST.
In the UK National Grid is the transmission system operator.