Tennessee Valley Authority spokeswoman Gail Rymer says automatic shutdown procedures began at the Watts Bar plant when the electrical fault was detected on Friday afternoon.
Rymer says a homeowner cut down the tree that fell onto a 500 kilovolt transmission line close to the plant located near Spring City, about 55 miles southwest of Knoxville. All six reactors were back online by Sunday afternoon.
TVA is the nation's largest public utility. It provides power to about 9 million people in Alabama, Georgia, Kentucky, Mississippi, North Carolina, Tennessee and Virginia.