Duke Energy has notified 3,700 landowners in five North and South Carolina counties that their property may be within 500 feet of a planned high-voltage transmission line to be constructed in a project to convert Duke’s coal-burning Asheville, N.C., power plant to natural gas. Duke’s letter said the company will spend $320 million to construct a 45-mile, 230-kilovolt transmission line from the Asheville plant to South Carolina and a substation in Campobello. The letters were mailed to landowners in Spartanburg and Greenville counties, as well as landowners in Polk, Henderson and Buncombe counties in North Carolina. Duke Energy spokeswoman Meghan Musgrave said the company does not have a preferred route for the transmission line, but several options will be unveiled at three community meetings.