Massachusetts siting board approves, subject to conditions, Eversource’s 115-kV underground line

The Massachusetts Energy Facilities Siting Board, in a March 13 final decision, approved, subject to certain conditions, NSTAR Electric’s d/b/a Eversource Energy’s (NYSE:ES) petition to build a new, approximately 7.7-mile, 115-kV underground transmission line in Woburn, Winchester, Medford, Somerville, Boston and Everett in Massachusetts.

The board said that it approves, subject to certain conditions, Eversource’s petition for a determination that the proposed line is necessary, serves the public interest, and is consistent with the public interest; as well as the company’s petition for individual zoning exemptions from the Woburn Zoning Ordinance in connection with necessary improvements to the Woburn substation in Woburn associated with the proposed transmission facilities.

As noted in the decision, Eversource has proposed to build the new line between its Woburn substation and its Mystic substation in Everett. The new line would operate in parallel with, and supplement the capacity of, the company’s existing 211-514 line (referred to as the existing line), which is a 115-kV underground transmission line that runs between the Woburn and Mystic substations. Eversource said that the two parallel lines would operate as a single circuit and would effectively be a single, larger-capacity transmission line.

The board also noted that the company proposed to install a new air-core series reactor at the Woburn substation to balance power flows between the existing line and the new line, as well as to modify the connection arrangement of the existing line and the 115-kV 488-518 transmission line within the Mystic substation to accommodate connection of the new line.

Eversource’s most recent cost estimate for the project is $81.5m, and the project is expected to be in service by December 2018.

The company’s primary route for the new line exits the Woburn substation at the Winchester town line and travels primarily under streets for about 7.2 miles, parallel to the existing line, through Winchester, Medford, Somerville, and the Charlestown section of Boston, and then an additional 0.5 miles within an existing pipe under the Mystic River to the Mystic substation fence line in Everett.

The board further noted that in addition to traveling within an existing pipe under the Mystic River, the primary route crosses the Aberjona River in Winchester and the Mystic River in Medford.

The primary route is shorter than the approximately $101.9m “noticed alternative route” by nearly two miles, passes fewer residential and commercial/industrial land uses, and would result in lower impacts during construction activities, the board said, adding that the primary route is preferable with respect to land use impacts.

In order to address the City of Somerville’s concerns regarding the primary route, the company identified a proposed variation that would avoid crossing a Home Depot parking lot and potential adverse effects on the continuing redevelopment of the Assembly Row area. The board also said that Eversource is continuing to develop the Massachusetts Bay Transportation Authority crossing design for the primary route – with and without the proposed variation – and is advancing negotiations with the City of Boston to obtain permanent easement rights needed for the proposed variation.

The company is to first take all actions necessary to pursue the construction of the proposed variation, and should the construction of the proposed variation prove infeasible, then the company may instead follow the primary route without the use of the proposed variation, the board said. If the use of the proposed variation is infeasible, then the company is to notify the board in writing as soon as possible, but in no event fewer than 60 days prior to the start of construction.

Discussing the company’s demonstration of need, the board noted that ISO New England (ISO-NE) conducts periodic needs assessments on a system-wide or specific-area basis, and develops an annual regional transmission plan using a 10-year planning horizon. ISO-NE recently issued one such assessment, the “Greater Boston Area Updated Transmission Needs Assessment,” and Eversource’s assertion of need for the project is based extensively on that assessment, the decision said.

The existing line is located within the broader transmission area referred to as the Greater Boston Area, which generally includes communities north and east of Interstate 495 up to the New Hampshire border, Boston itself, and some of the suburbs south of Boston. The board added that ISO-NE in 2008 established a working group to identify and address performance issues affecting the transmission system serving the Greater Boston Area.

According to Eversource, the working group in July 2009 completed its initial assessment of the area’s reliability needs, and that a number of subsequent updates to that assessment were required in order to reflect significant changes on the transmission system. Eversource said that the most recent needs assessment that was issued in January 2015, the “2015 Needs Assessment,” identified numerous reliability concerns throughout the Greater Boston Area, including numerous thermal and voltage violations following certain N-1 and N-1-1 contingencies.

The board added that according to Eversource, by 2023, post-contingency overloads were observed across the 69-kV, 115-kV, and 345-kV transmission facilities within the Greater Boston Area, and that the system was susceptible to those overloads at peak load levels prior to 2013.

The working group identified as one of the areas of concern “Sub-Area B,” which contains five 345-kV transmission lines and eight 115-kV transmission lines that connect a number of company-owned substations.

Eversource, the board added, identified two key substations: the Woburn substation, which receives 345-kV power from the north and distributes it across the 345-kV and 115-kV transmission systems towards Burlington and Lexington to the west, and Waltham, North Cambridge, and the Mystic substations to the south; and the Mystic substation, which also connects the 345-kV and 115-kV transmission systems, and is the connection point for Sub-Area B’s three large electric generating units, Mystic 7, 8 and 9.

ISO-NE indicated its support of the need for the project, and no other parties provided comments on the identified need.

The working group’s assessment of Sub-Area B demonstrated that the existing transmission system would be insufficient to reliably supply customers in the Greater Boston Area under pre-existing and forecast summer peak load conditions following certain N-1-1 contingencies, the board added.

Among other things, the board said that the conditions include that Eversource is to – in consultation with Woburn, Winchester, Medford, Somerville, Everett, and Boston – develop a comprehensive outreach plan for the project that describes the procedures to be used to notify the public about the scheduled start, duration and hours of construction in particular areas.

Also, the company is to limit construction of the line to Monday through Friday, from 7 a.m., to 5 p.m., and subject to municipal authorization, Saturday from 9 a.m., to 5 p.m., (from the Woburn substation property line to the intersection of South Street and Main Street in Medford).

The board also said that the company is to submit an updated and certified cost estimate for the project before construction begins.

About Corina Rivera-Linares 3286 Articles
Corina Rivera-Linares was TransmissionHub’s chief editor until August 2021, as well as part of the team that established TransmissionHub in 2011. Before joining TransmissionHub, Corina covered renewable energy and environmental issues, as well as transmission, generation, regulation, legislation and ISO/RTO matters at SNL Financial from 2005 to 2011. She has also covered such topics as health, politics, and education for weekly newspapers and national magazines.