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345kV Line Feasibility Study

345kV Line Feasibility Study – ROW, Construction & Environmental Impacts

345kV Lower SEMA (Southeast Massachusetts) Carver to Barnestable Right-of-Way Corridor

Project Scope:
This project consisted of evaluating the feasibility of building a new 345kV transmission line approximately (20) miles in length.  Starting from the Carver Substation to just outside the Bourne Switching Station, where the new line tied into an existing 345kV line and continued to Barnestable Substation.  Northern and southern line route alternatives were evaluated for optimum structure configuration, constructability in proximity to energized power lines, available and required right-of-way (ROW) needs, and environmental impact.

Engineering Activities:
The Northern Route alternative had (2) existing 345kV transmission lines. One line was located on the inside set of arms of a double-circuit lattice tower, and the second line located on wooden H-frame structures.  Engineering was performed to locate a third, independent 345kV transmission line between the (2) lines.  The H-frame line had to be moved or modified while energized.

The Southern Route alternative was on an existing double circuit 115kV transmission line ROW from Carver Station through the towns of Carver, Middleborough, Rochester, Wareham, and Plymouth, where the route joined the Northern Route into Bourne Substation.  From Carver to Wareham, there were (2) existing 115kV transmission lines located on double-circuit steel poles, the line then split onto (2) parallel H-frame lines.  To make room, options were (1) H-frame line would have to be rebuilt double circuit with the new 345kV line, or both H-frame lines rebuilt double circuit to make room for the new 345kV line.

The (2) route alternatives became common north of the Cape Cod Aggregate Power Plant and continued east, crossing a (1) mile wide canal. Two (2) existing 345kV transmission lines crossed on a double-circuit lattice tower. For reliability, part of the project scope was to separate the (2) 345kV transmission lines crossing the canal onto separate structures; in total there would be (3) independent 345kV transmission line crossings of the canal when the new line was built.

Project Highlights:
Cost comparisons of multiple and alternative options were completed.  One of the design alternatives required the need for energized reconstruction of an existing 345kV line on the Northern route, which originally was not the preferred route, but eventually became the primary alternative due to the impacts of population density, constructability in cranberry bog areas, and several miles of additional line length, making the Northern alternative the most viable.