Petition of NSTAR Electric Company and New England Power Company D/b/a National Grid for Approval to Upgrade An Existing 115 kV Underground Transmission Line Pursuant to G.L. C. 164, [Section] 72 in the Cities of Boston and EverettPetition of NSTAR Electric Company and New England Power Company D/b/a National Grid for Approval to Upgrade An Existing 115 kV Underground Transmission Line Pursuant to G.L. C. 164, [Section] 72 in the Cities of Boston and Everett