SIOUX FALLS, S.D. — Several Midwest utilities, including Sioux Falls-based NorthWestern Energy, are studying the economics of building high-voltage transmission lines to carry wind energy to eastern markets. Pewaukee, Wis.-based American Transmission Co. joined with utilities in Ohio, Illinois, Iowa and South Dakota on a study that will address the need for new transmission lines to carry electricity from renewable power sources. ATC chose Quanta Technology of Raleigh, N.C., to come up with recommendations for transmission development in the Dakotas, Illinois, Indiana, Iowa, Minnesota, Wisconsin and Michigan’s upper peninsula. Some of the same utilities backing the Strategic Midwest Area Renewable Transmission Study also have endorsed a plan by Novi, Mich.-based ITC Holdings Corp. to develop a high-voltage power line to move wind energy from the Midwest to homes in Chicago and other cities. The study will be combined with other studies under way by the Midwest Independent Transmission System Operators to help plan for future transmission needs. That group oversees operations of the electrical grid in the region.