The Nordic electricity power system was disrupted early on Wednesday, and two Swedish nuclear power reactors were disconnected, Finnish grid operator Fingrid and its Swedish counterpart said.
Those two reactors were expected to resume full operations by late on Wednesday, according to operator Vattenfall.
"Due to the disruption, replacement production from the Nordic balancing power market was activated and the situation was stabilised," Fingrid said, adding that Sweden, Finland, Norway and eastern Denmark were affected.
Separately, Swedish grid operator Svenska Kraftnaet told Reuters maintenance work at an electricity substation north of Stockholm led to two transformers being disconnected inadvertently, leading to a short circuit.
That caused Swedish nuclear reactors Forsmark 1 and 2 to trip, and replacement power had to be brought in to stabilise the grid.
"The situation is stable now", said a Svenska Kraftnaet spokesperson.
Forsmark 1 and 2, which have a combined installed capacity of 2.1 gigawatts (GW), will remain offline until midnight on Thursday (2200 GMT on Wednesday), operator Vattenfall said in a market message posted via Nordic power exchange Nord Pool.
