THE COMPANY seeking to build a Massachusetts-financed transmission line carrying hydro-electricity from Quebec to Maine cleared another hurdle on its comeback trail when federal regulators dismissed objections raised by the nuclear power plant Seabrook Station.

In a 52-page ruling, the Federal Energy Regulatory Commission ruled on Wednesday that Seabrook must upgrade a circuit breaker at the nuclear power plant to accommodate hydro-electricity expected to come into the region from Canada.

FERC also ruled that Seabook’s owner, NextEra, can only charge Avangrid, the company building the power line, for the cost of replacing the circuit breaker and not for “opportunity costs” of $560,000 a day or legal fees.

Avangrid and NextEra are big competitors in the New England energy market and have been battling each other for years on a variety of fronts.

NextEra, which operates a number of power plants in New England, helped finance a ballot question campaign in Maine to block Avangrid’s hydro-electric transmission line. The ballot question passed, but then was deemed unconstitutional by the Maine Supreme Judicial Court. Avangrid is now hoping to get the transmission line back on track.

Avangrid claims the fight over the circuit breaker at Seabrook is an extension of the fight in Maine. In its appeal to FERC to intervene, Avangrid said Seabrook could lose significant revenues if the transmission line is completed, possibly putting it out of business. Avangrid alleged that NextEra executives offered to reduce their opposition to the transmission project if Avangrid would agree to buy a large portion of the power produced by Seabrook at above-market prices.

In its ruling, the FERC dismissed a number of Avangrid’s arguments, but ultimately concluded Seabrook is required to upgrade the circuit breaker to maintain the safety of the nuclear power plant and to keep the power grid working properly.

“Seabrook would not be exercising reasonable judgment to operate the breaker from the moment Avangrid is energized because it would risk the breaker being overdutied,” the FERC ruling said. “We share [the power grid operator’s] concern that operating the breaker in an overdutied condition could lead to an uninterrupted short circuit current that could lead to catastrophic equipment failure at the nuclear facility.”

According to FERC, the circuit breaker replacement will occur in fall 2024, with the transmission line from Quebec into Maine expected to come online in December 2024.