As currently proposed, The Northern Pass project will construct 140 miles of direct-current transmission line in New Hampshire from the Canadian border to a converter terminal in Franklin. There it will be converted to alternating current and sent to a substation in Deerfield, where it will connect to the New England power grid, which serves all customers in the region—including those in New Hampshire.
DC Transmission Line
- +/-300 kV line, approximately 140 miles long, extending from the Québec/New Hampshire border to the Franklin, NH converter terminal
- 1,200 megawatt transfer rating
AC Transmission Line
- 345 kV line, approximately 40 miles long, extending from the Franklin converter terminal to the Deerfield Substation in Deerfield, NH
- Certain existing AC lines will be relocated to support the construction of the new lines
The anticipated height of most Northern Pass transmission structures is as follows:
- For the new right of way in the North Country, from the Canadian border to Groveton, NH, the most common structure height will be 85 to 90 feet.
- In the existing right of way between Groveton and Franklin, which currently contains an existing transmission line, the most common structure height will be 80 to 95 feet.
- In the existing right of way between Franklin and Deerfield, which currently contains an existing transmission line, the most common structure height will be somewhat taller, between 90 and 110 feet, because the right of way here is slightly narrower than in other sections of the route.
Taller structures are used along the route when necessary:
- To span larger rivers and roadways;
- To cross over other lines and structures;
- To account for changes in terrain being spanned by the line, and to maintain the clearances required by the National Electrical Safety Code between the transmission wires and the ground or other nearby objects; and
- In select areas in the existing rights of way where the right of way is constrained and cannot be expanded to a width necessary to allow for the use of shorter structures.
The National Electrical Safety Code requires a minimum height based upon the line's operating voltage. As a general rule, the wider a right of way the shorter a structure needed - to a point. Today, the majority of the structures in the existing rights of way that will be shared by The Northern Pass are 45 to 75 feet tall. The majority of these existing lines operate at a voltage of 115 kV AC. The Northern Pass will construct lines that operate at voltages of +/-300 kV DC and 345 kV AC. These higher voltages require greater height and separation for safety.
- Simulations of what the line will look like from actual locations along the preliminary preferred route (based on preliminary engineering)
Visual Simulations - 8½ x 11 | 11 x 17
Note: The 8½ x 11 version of the Visual Simulations booklet, though easier to print, has been reduced by 40%, which may impact the perceived scale (i.e. objects may be larger or smaller than they appear). Exact sizes can be found in the 11 x 17 version, which is the full size document.
- A comparison of common structure heights
- To be constructed in Franklin, NH
- An electrical facility that houses the equipment necessary to convert power from direct current to alternating current
- Includes buildings with conversion equipment and controls, and an outdoor area with filter banks and other equipment similar to a conventional substation