The Zaporizhzhia station, Europe's largest with six reactors, was seized by Russian forces in the early days of Russia's February 2022 invasion of Ukraine. Each side regularly accuses the other of attacking or plotting to attack the plant.
The plant's management, writing on Telegram, said an artillery strike had hit the transformer at the "Raduga" substation in the town of Enerhodar in southeastern Ukraine.
It described the incident as "yet another terrorist act aimed at destabilising the situation in the Zaporizhzhia nuclear plant's satellite city".
Also posted was a photograph showing smoke billowing from the top of a building. It said power supplies to Enerhodar had not been interrupted.