The executive who has been in charge of constructing the Vogtle nuclear power plant’s expansion has been named to head Southern Co.’s wholesale energy arm.

Southern Co. said Tuesday Joseph "Buzz" Miller will become president and chief executive of Southern Power on March 7. He replaces 32-year veteran Oscar C. Harper IV, who is retiring.

Since 2006, Miller has been the point man for the Atlanta utility’s nuclear expansion project, as both Georgia Power’s vice president of nuclear development and Southern Nuclear’s president of nuclear development. Both are subsidiaries of Southern Co.

Southern Power, the wholesale power subsidiary Miller will now head, buys, sells and generates electricity for Southern Co.’s other utility units from both conventional power plants and alternative sources such as wind and solar power.

“Since the beginning of the Vogtle project, Buzz has provided exceptional guidance and direction for one of the most important construction projects in the country,” said Georgia Power CEO W. Paul Bowers.

However, during Miller’s tenure, the $16 billion-plus nuclear expansion near Augusta has fallen more than 3 years behind schedule and more than $3 billion over budget.

With Tuesday’s announcement, Miller will no longer be in charge of construction of the Vogtle 3 and 4 units, which are now expected to be completed in 2019 and 2020.

Southern said Miller’s replacement is Mark D. Rauckhorst, who was named executive vice president of construction for the Vogtle project. He has been vice president of construction since 2011.

In a statement, Southern said the moves “are further aligning the Vogtle 3 & 4 organization to best achieve upcoming project milestones while creating a streamlined approach for interacting and communicating with key stakeholders.”

Bobby Baker, a former commissioner on the Georgia Public Service Commission board and sometimes critic of the Vogtle project, said Southern’s move seems to be a typical promotion of an executive on the rise within the utility.

Miller is “taking over a national division,” said Baker. “If you do well, they keep moving you up.”