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.
President Volodymyr Zelenskiy says Russia had dropped 900 bombs on Ukraine in the past week. (AP PHOTO)
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.
The plant's management accused the Ukrainian military on September 20 of attacking a second substation in Enerhodar.
The following day, Ukrainian Foreign Minister Andriy Sybiha accused Russia of planning strikes on Ukrainian nuclear facilities before the winter.
He provided no detailed explanation.
Power lines to the Zaporizhzia plant have been cut on several occasions, increasing the chance of a blackout that could cause a nuclear accident.
The United Nations nuclear watchdog, the International Atomic Energy Agency, has stationed monitors permanently at the plant and urged both sides to refrain from all attacks on it.
Meanwhile, heavy artillery duels and Russian air strikes have shaken the front lines in eastern Ukraine, according to the Ukrainian General Staff's evening situation report on Sunday.
Russian artillery shelled 20 settlements near Sumy and Kharkiv, it said.
Russian attacks against Ukrainian defence lines were reported from conflict areas surrounding Donbas, with the Ukrainian forces successfully repelling 13 attacks near Pokrovsk and halting 17 advances by Russian troops near Kurakhove.
The information could not be independently verified.
Heavy fighting was reported in the area around Vuhledar, raising concerns among Ukrainian military experts that the small town in the southern section of Donbas, which has endured two years of war, could fall to Russian troops.
Ukrainian President Volodymyr Zelenskiy said Russia had dropped 900 bombs on Ukraine in the past week alone.
In addition, there had been 300 drone and 40 missile attacks, he wrote on Telegram.
In Moscow, the Russian defence ministry reported that its air defences had shot down 125 Ukrainian drones.
In addition to Voronezh, the border regions of Belgorod and Rostov were targeted in particular, it said.
Authorities in the southwestern city of Voronezh reported damage caused by falling debris.
Fires also reportedly broke out.
Several cars, two apartments and a children's playground were damaged, Governor Alexander Gusev said but added that no one was injured.
The regions of Bryansk, Kursk and Krasnodar were also attacked in isolated cases, according to the ministry.
The Ukrainian army also reported a successful attack against a Russian ammunition depot in the Volgograd region.
An arsenal of missiles, ammunition and explosives was hit in the village of Kotluban.
According to the Ukrinform agency, a large fire broke out there after the attack.
with DPA
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