Wind turbines across the Great Plains states produced, for the first time, more than half the region’s electricity last Sunday. The power grid that supplies a corridor stretching from Montana to the Texas Panhandle was getting 52.1 percent of its power from wind at 4:30 a.m. last Sunday, Little Rock, Arkansas-based Southwest Power Pool Inc. said in a statement last Monday. As more and more turbines are installed across the country, Southwest Power has become the first North American grid operator to get a majority of its supply from wind.