AES Granite Ridge, LLC
The Granite Ridge transmission line for AES Granite Ridge, LLC was necessary to interconnect approximately 700 MW of new combined cycle gas generation into the electrical grid to safely and reliably deliver electric energy to the end users. Commonwealth assisted with the design of the transmission line interconnection of the 700 MW Granite Ridge Plant to the transmission line system of National Grid at 230 kV and Public Service of New Hampshire at 115 kV. The design project was the continuation of the routing, land acquisition, and systems study work done earlier by Commonwealth for the interconnection.
The 2.9-mile 230 kV interconnection used double-circuit steel structures in both vertical single-pole and H-frame configurations. The H-frame construction was used to minimize visibility. The structures for the 1.3-mile 115 kV interconnection were a single-circuit H-frame configuration using both guyed wood and self-supporting steel. The line contained numerous angle structures. Single 1272 54/19 ACSR was used for the 230 kV conductor, and twin-bundled 1272 54/19 ACSR was used for the 115 kV conductor.
All shield wires were fiber optic for communication between substations. Concrete caisson foundations were installed in both soil and rock. PLS-CADD was used in the routing and design phases of the project.
Commonwealth supervised the survey and soil boring operations and coordinated the interface with the substation design engineering. Separate construction contracts were made for clearing, road building, and restoration, foundation construction, and overhead construction.