The Russian military attacked Ukraine overnight with 20 Iranian-made combat drones, many of them targeting energy infrastructure.
All of them were shot down, air force chief Mykola Oleshchuk said on Telegram on Tuesday.
The drones were intercepted over southern and central areas, as well as western Ukraine.
Maksym Kozytskyi, the governor of the western Lviv region, said drone debris fell on "critical infrastructure" site. The Energy Ministry in Kiev said later that a substation had been impacted and the damage was still being assessed.
The ministry said another substation was damaged in the central Ukrainian region of Poltava. The ensuing fire was extinguished.
Two high-voltage power lines in the Dnipropetrovsk region in the south-east also failed, leaving an industrial building without power, the ministry said.
Russia frequently attacks Ukraine's energy infrastructure as part of the full-scale invasion Moscow launched more than two years ago.
In the eastern Ukrainian region of Kharkiv, electricity is only available a few hours a day following a string of devastating attacks in March.