Massachusetts electric ratepayers will receive a $115 million refund as the result of a ruling last week in an administrative court case brought by the attorney general and supported by AIM.

A federal administrative law judge, ruling in a case first brought in 2011, reduced to 9.59 percent the guaranteed return granted to the companies that develop and operate transmission lines that bring electricity long distances. It marked the second time that regulators have lessened the rate of return, bringing New England ratepayers total refunds of $310 million.

“Massachusetts employers and homeowners pay some of the highest electricity rates in the country, and that’s why AIM participates in actions like this one that put money back into the hands of growing companies,” said John Regan, Executive Vice President of Government Affairs at AIM.

AIM supported the attorney general in litigation filed in 2011 at the Federal Energy Regulatory Commission (FERC) to challenge the return on equity that New England transmission companies (utilities) are guaranteed on transmission-related projects.

Unlike local distribution rates, which are regulated by the state Department of Public Utilities (DPU), the profits on large transmission projects, which form the backbone of the electric grid, are regulated at the federal level by FERC.

The return on equity for electric transmission companies was set in 2006 at 11.14 percent. AIM was the only general trade association in Massachusetts to sign on to the complaint arguing that the costs were too high in light of economic conditions.

In October 2014, based on the attorney general’s complaint, FERC lowered the transmission owners’ allowed profits to 10.57 for rates in effect in 2011 and 2012 – not as low as the attorney general and AIM wanted, but still enough to generate $78 million in refunds. Those refunds were given back to ratepayers in the form of credits throughout 2015.

The administrative law judge on March 22 further reduced the guaranteed return to 9.59 percent for rates in effect from January 2013 to April 2014. If FERC approves the decision, New England ratepayers will receive another $234 million refund, about half of which will be distributed in Massachusetts. A decision is expected by the end of the year.

And the attorney general isn’t done. She is now arguing that the rates after April 2014 should also be lower than the transmission companies are currently receiving.

“AIM thanks attorney General Maura Healey and her Office of Ratepayer Advocacy for allowing us to be part of this ongoing litigation to bring electric costs down,” Regan said.