Dominion Resources Inc. plans to sell three power plants, two in Illinois and one in Massachusetts, capable of generating a combined 4,118 megawatts.

Dominion will use proceeds from the sale to reduce debt and boost its regulated businesses, according to a statement from the Virginia-based company today. The plants generate enough power for 3.29 million average US homes, according to the Energy Department.

Selling the plants will mark Dominion’s exit from the PJM- West wholesale power market, chairman and chief executive Thomas Farrell said at a Barclays Plc conference today. The sale is necessary because of narrowing profit margin, he said.

“The sale of these assets and the redeployment of capital to our regulated businesses is the best path forward for shareholders,” Farrell said in the statement. The transaction is expected to close in the first half of 2013.

The Brayton Point power station in Massachusetts has three coal-fired units and one fueled by oil or natural gas. The Kincaid plant has two coal-fired units. Dominion is also selling its 50 percent stake in the Elwood plant outside Chicago, which has nine gas-fired turbines.