Synchronous grid of Northern Europe

The Nordic System or Interconnected network of Northern Europe of ENTSO-E is a synchronous electrical grid composed of the electricity grids of Norway, Sweden, Finland and the eastern part of Denmark (Zealand with islands and Bornholm) since 2009. The grid was managed by Nordel from 1963 until 2009 as it was integrated into ENTSO-E. The grid is not synchronized with the Continental Europe Synchronous Area, but has several non-synchronous DC connections with that as well as other synchronous grids.

Source: Wikipedia — Synchronous grid of Northern Europe (CC BY-SA 4.0)