A developer of electric power transmission plans to break ground in 2020 for a $100-million converter station in Plymouth, Mass. Green Line Devco LLC is developing the Green Line Maine project, a 220-mile-long, high-voltage direct-current submarine cable from Orrington, Maine, to eastern Massachusetts, delivering up to 1,200 MW of wind-generated electricity. The Plymouth station would convert the power to alternating current before connecting with the New England grid. The line is scheduled to go into service by 2021 or 2022. The total estimated project cost will be approximately $1.5 billion.