Unit 2 of the twin-unit generating station was taken down Oct. 29 and restored to 100 percent power Thursday.
South Texas Project President and CEO Ed Halpin said Friday more than 10,000 maintenance, testing and inspection tasks were made by some 1,100 contractors. Unit 1 at the plant, which began commercial operation in 1988, underwent the same maintenance earlier this year.
The next scheduled downtime for Unit 2 is in 18 months. That unit started commercial operation in 1989.
The plant -- co-owned by Austin Energy, CPS Energy and NRG Energy -- provides power to 2 million Texas homes.
Bay City is 80 miles southwest of Houston.