A truck carries ground-up tree tops along the NECEC corridor in Johnson Mountain Township in November 2021. Gregory Rec/Staff Photographer

The developer of a 145-mile transmission line through western Maine has prevailed in federal court in a dispute over a New Hampshire circuit breaker, clearing away another challenge to the contentious power project.

The legal dispute between Avangrid Inc. and NextEra Energy Inc. in U.S. Court of Appeals for the District of Columbia Circuit is part of a years-long battle between the two energy giants. Avangrid, the Connecticut-based parent company of Central Maine Power and subsidiary of Spanish energy giant Iberdrola, is building the $1.5 billion New England Clean Energy Connect power line to bring 1,200 megawatts of hydropower from Canada to the New England electrical grid.

In 2021, it accused NextEra, the owner of the Seabrook nuclear plant in Seabrook, New Hampshire, of failing to perform a necessary safety upgrade of equipment at the plant, blocking the project.

ISO-New England, the region’s grid operator, said Seabrook Station could not safely remain connected to the grid unless it upgraded its circuit breaker, according to the court’s decision.

Seabrook and Avangrid disputed whether or how the circuit breaker should be upgraded, the court said. NextEra and Avangrid entered into an agreement governing the terms of Seabrook’s connection to the regional transmission grid that requires Seabrook to install and maintain circuit breakers, the court said.

Seabrook asked the Federal Energy Regulatory Commission to declare it was not required to upgrade the circuit breaker or, alternatively, that it was entitled to a full recovery of costs. Avangrid sought to prevent Seabrook from blocking the interconnection, the court said.

FERC ruled in February primarily in favor of Avangrid. Regulators said the agreement between the two utilities required Seabrook to upgrade the breaker and that Avangrid was not required to reimburse Seabrook for indirect costs of the upgrade such as lost profits or legal expenses. The Appeals Court voted 2-1 Oct. 4 to uphold FERC’s decision.

It said FERC did not exceed its jurisdiction and correctly interpreted the agreement between the utilities. And it said FERC “permissibly denied” Seabrook compensation for indirect costs.

A spokesman said Avangrid will not comment and representatives of NextEra did not respond to an email seeking comment about the dispute and the appeals court decision.

Avangrid several years ago accused NextEra of seeking to interfere with the transmission project to benefit its fossil and nuclear generation in Maine and New Hampshire.

NextEra, which owns the W.F. Wyman oil-fired power station in Yarmouth, said Avangrid’s complaints were baseless. The Maine Ethics Commission said last November that NextEra Energy concealed its identity as a large donor to Democrats in the days before the 2018 election and funded a group that should have registered as a political action committee in 2019 when it worked to oppose the construction of the transmission line.

Avangrid reported to the Maine Public Utilities Commission in July that access to the transmission route is about 81% complete. In a regulatory filing, it reported expenses as of June 30 of about $1 billion for interest payments, construction and other costs.

ISO-New England, the region’s grid operator, told FERC in a draft capital budget that it will run a test power delivery in late 2025; it will first update applications and complete software and operating adjustments, it said.

The state Department of Environmental Protection halted work on the corridor in November 2021 after Maine voters killed the project in a referendum. In court battles that followed, NECEC’s backers said the project had established “vested rights” to continue construction. A Cumberland County jury decided in April 2023 that the project may resume.

Advocates said the project would help reduce greenhouse gas emissions. Opponents are skeptical of the environmental benefits and said the transmission line would cut through some of Maine’s most pristine forested areas.