ISO New England has selected the Eversource Energy (formerly Northeast Utilities) and National Grid alternating current (AC) transmission proposal as the preferred transmission solution to bolster the region’s power grid in the Greater Boston area.

The all-AC proposal was chosen over another proposal supported by New Hampshire Transmission (NHT), which included the use of both AC and underwater, high-voltage direct current (HVDC) components. The AC plan was ultimately selected because it is significantly less expensive and also because it is superior when other performance criteria are considered, the ISO said

The components unique to the all-AC project include two new 345 kV transmission lines as well as the reconductoring of several 115 kV transmission lines, and other substation and transmission equipment upgrades. The project also requires voltage support equipment to be located in Maine. The estimated costs of unique elements to the AC project is $394.3 million.

Notable projects include:

• The Merrimack Valley Reliability Project: a new overhead 345-kV line in existing rights-of-way in Londonderry, Windham, Hudson, and Pelham, NH, and Dracut, Andover, and Tewksbury, MA (in service 2017)

• The Woburn to Wakefield Line: a new underground 345-kV line through Woburn, Winchester, Stoneham, and Wakefield, MA (in service 2018)

• The Mystic (Everett) to Woburn Line: a new underground 115-kV line through Everett, Boston (Charlestown), Somerville, Medford, Winchester, and Woburn, MA (in service 2018)

The NU-National Grid proposal was selected over an alternative solution, known as SeaLink and proposed by a unit of NextEra Energy

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