Several emergency calls reported a loud noise at the plant, which is located about 40 miles (65 km) north of New York City, a New York State police spokesman said.
Unit 3 at the plant was shut down following the transformer failure, Entergy Corp, the company that operates the facility, said in a message on Twitter.
"No threat to public safety at any time," the company said on Twitter.
The police spokesman said no injuries were reported at the site and officers at the scene could not immediately confirm reports of a transformer fire or explosion.Local television station WABC reported that at one point smoke could be seen rising from the plant.