sentences:  Norway and Sweden's grids have long been connected.Beginning in 1977 the Norwegian and Danish grids were connected with the Skagerrak power transmission system with a transmission capacity of 500 MW, growing to 1,700 MW in 2015.Since 6 May 2008, the Norwegian and Dutch electricity grids are interconnected by NorNed submarine HVDC (450 kilovolts) cable with a capacity of 700 megawatts.