Route Hydro-Québec's electricity transmission system

450kv high-voltage direct current (hvdc) line (at right), on south side of autoroute 20 east of nicolet station.

after 6 735 kv wires split 2 groups of 3 power lines each, hvdc line follows eastern group, , western set diverges away. line remains overhead until reaches north shore of saint lawrence river near grondines, 450 kv hvdc line descends underwater tunnel traversing river. power line surfaces on south shore near lotbinière substation. after river crossing, line enters nicolet terminal near sainte-eulalie, northeast of drummondville. south of terminal, line heads south , after relatively short distance, enters des cantons close sherbrooke.

leaving des cantons station, power line crosses canada–us border , passes through hilly appalachian mountains in u.s. state of vermont, reaching elevation of 650 metres (2,130 ft). line continues heading south-southeast , enters state of new hampshire, reaches comerford terminal near monroe. continuing southward massachusetts, line reaches sandy pond terminal outside of boston in ayer. terminal southernmost extent of hvdc line.

in december 2008, hydro-québec, along american utilities northeast utilities , nstar, created joint venture build new hvdc line windsor, quebec deerfield, new hampshire. hydro-québec own segment within quebec, while segment within owned northern pass transmission llc, partnership between northeast utilities (75%) , nstar (25%). estimated cost us$1.1 billion build, projected line either run in existing right-of-way adjacent hvdc line runs through new hampshire, or connect right-of-way in northern new hampshire run through white mountains. 180-to-190-mile (290 310 km) line, projected carry 1,200 megawatts, bring electricity approximately 1 million homes.