Converter Sites And Cable Routing
Green Line will include two new HVDC converter stations, one in Maine at the northern end of the DC line, and one in Massachusetts at the southern end of the DC line. HVDC converter stations convert between AC and DC power, thus enabling direct current power to flow through the new DC transmission line and alternating current power to synchronize with the existing AC grid.
Converter stations have a footprint of 5 to 20 acres. The building structure is similar in appearance to a medium scale industrial building with an adjacent electric switchyard and can be designed to be compatible with the character of the surrounding built or natural environment.
TERRESTRIAL AND SUBMARINE ROUTING
The terrestrial segment of the Green Line within the state of Maine will be installed primarily within an existing railroad right of way in which NEITC has acquired the exclusive right to transmit electricity. Use of the existing railroad corridor minimizes the amount of new greenfield right of way and will reduce the overall environmental impact by using already disturbed land. Further, DC transmission lines require less right of way width than comparable AC lines that would transmit equivalent amounts of energy. Electro-magnetic fields associated with DC transmission lines are far less expansive than those associated with AC transmission lines.
In the marine environment, the transmission line will be in the form of a cable beneath the Gulf of Maine between Maine and Massachusetts. Water depths in the Gulf range from zero feet in shoreline areas to 900 feet in an area known as Murray Basin, which is 36 nautical miles east of Rockport, Massachusetts. Water depths are generally 480 feet or less within 12 nautical miles of the shoreline. The cable length and water depths are well within the design and construction parameters of existing submarine cables installed and operating around the world.