Electric ratepayers throughout New England could get more than $1 billion in refunds in addition to reduced transmission bills moving forward, following a recent decision by federal energy regulators.

The Federal Energy Regulatory Commission found that electrical utilities in the region, including in Maine, charged higher-than-reasonable transmission rates, raking in inflated profits, according to the Maine Office of the Public Advocate.

The decision came in response to four different complaints, the first of which dates to 2011, when it was filed by the OPA and consumer advocates from other New England states.

In a written statement, Public Advocate Heather Sanborn commended regulators for “recognizing that the profits granted to New England transmission owners over the last 15 years have been far too high.”

“We will press for the refunds due to Mainers to be returned swiftly to provide real rate relief for folks who are struggling to pay high utility bills,” Sanborn continued.

Federal regulators found that the transmission companies’ rates of return on equity were “unjust and unreasonable,” the office said. Return on equity represents the amount of profit an electrical utility is allowed to collect from consumer bills based on how much the utility has invested in capital projects.

Some analysts have pointed to heightened returns on equity as one driver of rising electricity rates across the country.

Regulators ruled that an 11.1% return on equity rate in 2011 and a 10.6% interim rate from 2014 were both higher than justified. The rate should have been about 9.6%, regulators said.

Regulators ordered transmission owners to provide refunds on the overpayment, including interest, for the period spanning October 2011 to the end of 2012 and from Oct. 16, 2014, to the present.

That decision will reduce transmission rates paid by New England customers by roughly $140 million each year, and it could trigger refunds worth more than $1.5 billion to the region, according to the public advocate.

But it’s not clear when Mainers should expect relief, or exactly how much they should anticipate, Sanborn said in a email Tuesday. She noted that Mainers pay about a tenth of the region’s transmission costs, so they can likely expect to see about 10% of the future rate reductions and 10% of the total refunds. Those refunds would likely reach customers in the form of further rate reductions, she said.

“This could represent several dollars in reductions on the average residential customer’s bill, but it’s too soon to say exactly,” Sanborn wrote.

The federal order demands that refunds be issued within 30 days, setting a deadline of mid-April, but the companies involved are likely to file appeals or further motions before then, Sanborn added. That makes it difficult to predict a timeline for the next steps, she said.

Judy Long, a spokesperson for Versant Power Company, said it is “analyzing the full impact of this order and determining how we can meet the terms.”

A spokesperson for Avangrid, Central Maine Power Co.’s parent company, declined to comment on the decision.