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| Maine-New Hampshire tie-line | |
|---|---|
| Name | Maine–New Hampshire tie-line |
| Country | United States |
| States | Maine; New Hampshire |
| Owner | Multiple utilities |
| Operator | Regional transmission organizations; Independent System Operators |
| Length | ~90 miles |
| Capacity | Varies by segment |
| AC DC | AC |
Maine-New Hampshire tie-line
The Maine–New Hampshire tie-line is a high-voltage alternating-current interconnection between Maine (U.S. state), New Hampshire (U.S. state), and the wider New England grid linking utilities, grid operators, and wholesale markets. It facilitates transfers among companies such as Central Maine Power, Eversource Energy, and municipal systems while interfacing with regional entities like the New England Power Pool and ISO New England, and federal agencies including the Federal Energy Regulatory Commission and the Department of Energy.
The tie-line forms part of the transmission backbone connecting substations near Augusta, Maine, Portland, Maine, Concord, New Hampshire, and Manchester, New Hampshire, enabling flows between generation hubs such as plants at Maine Yankee-adjacent sites, Seabrook Station Nuclear Power Plant interties, and balancing areas represented by New England Governors and Eastern Canadian Premiers (NEG-ECP) dialogues. It serves market participants in the New England Independent System Operator footprint and supports reliability standards set by the North American Electric Reliability Corporation.
Initial construction phases traced to utility expansions managed by companies like Central Maine Power and Public Service Company of New Hampshire during mid-20th-century electrification initiatives influenced by federal statutes including the Public Utility Regulatory Policies Act of 1978 and regional planning by the New England Electric System. Subsequent upgrades were driven by transmission planning from ISO New England and federal orders from the Federal Energy Regulatory Commission following congestion events involving cross-border flows with New Brunswick and Quebec interties. Notable project milestones involved environmental reviews with stakeholders such as the Maine Department of Environmental Protection and the New Hampshire Department of Environmental Services and coordination with tribal interests including Penobscot Nation.
The corridor traverses mixed terrain across counties including Cumberland County, Maine, Androscoggin County, Maine, Hillsborough County, New Hampshire, and Rockingham County, New Hampshire. Typical construction uses lattice steel towers and monopoles rated for voltage classes comparable to other Northeast corridors such as lines feeding Seabrook Station Nuclear Power Plant and connections to Vermont Yankee-related infrastructure. Conductor types, right-of-way widths, and thermal ratings conform to standards set by the Institute of Electrical and Electronics Engineers and design guides from the American Society of Civil Engineers. Protection schemes incorporate relays interoperable with North American Electric Reliability Corporation reliability standards and integrate Supervisory Control and Data Acquisition systems interoperating with ISO New England control centers.
Operational control is coordinated among transmission owners, ISO New England, and regional entities including the New England Power Pool Participants Committee. Day-ahead scheduling, real-time dispatch, and congestion management use markets administered under ISO New England tariffs filed at the Federal Energy Regulatory Commission. Maintenance planning follows industry best practices from organizations such as the Electric Power Research Institute and involves coordination with transmission service providers like New England Power Company and municipal utilities represented by the American Public Power Association.
Environmental review processes have engaged agencies including the National Environmental Policy Act-mandated assessments overseen by the Environmental Protection Agency, state agencies such as the Maine Department of Environmental Protection and the New Hampshire Department of Environmental Services, and conservation groups like The Nature Conservancy and Sierra Club affiliates. Permitting involved consultations under statutes including the Endangered Species Act when routes intersected habitats for species listed by the U.S. Fish and Wildlife Service. Regulatory challenges have referenced precedent from FERC orders and litigation involving stakeholders such as Conservation Law Foundation and municipal intervenors.
The tie-line affects wholesale prices in the New England wholesale electricity market administered by ISO New England, influences capacity market outcomes in the Forward Capacity Market, and alters dispatch for generators including fossil plants, hydroelectric facilities in Maine and imports from Quebec transmission interfaces. Economic analyses by regional planners and entities such as the New England States Committee on Electricity assess benefits including congestion reduction, resource adequacy contributions, and operational savings for utilities like Central Maine Power and Eversource Energy.
Historic outages and reliability events prompted investigations and corrective actions involving the North American Electric Reliability Corporation and filings with the Federal Energy Regulatory Commission. Incidents range from storm-related line damages tied to Nor'easter events and ice storms recorded by the National Weather Service to vegetation-contact outages addressed via coordination with county emergency management offices such as those in Cumberland County, Maine and Hillsborough County, New Hampshire. Restoration efforts have involved mutual assistance under frameworks promoted by the American Public Power Association.
Category:Energy infrastructure in Maine Category:Energy infrastructure in New Hampshire