I've tried to find something about the accident at the Sayano-Shushinskaya power station (Siberia), and I found only this small bit:
"Russia: Seven people died after an accident at the Sayano-Shushinskaya power station, Russia’s largest hydroelectric plant, yesterday, officials said. The plant, which supplies several large aluminum plants in Siberia, has been shut".
Russian media gives more details:
Accident at the Sayano-Shushinskaya hydroelectric plant happened on August 17 at 8 a.m. local time, but the causes are still unknown.
As the result of some strong impact, which could be either a hydraulic impact or something, resulted from explosion of oil transformer the 2nd unit, the wall and ceiling of the machine room were destroyed and the water instantly rushed inside machine room. The other 9 units of the hydroelectric plant, including heavily damaged 7th unit were stopped immediately. The dam have not been damaged, that is why they managed to stop water flow inside plant very quickly. This helped to stop panic among the local livers – brake of the dam would result in flooding of the nearest settlements. According to the newest information the emergency has taken 12 lives, 11 employees of the power plant are injured and 62 people lost.
Sayano-Shushinskaya hydro station is one of the biggest ones not only in Russia, but in the world. The installed power is about 6 800 MW, annual average production - 24 500 mln. kWh. In the first 6 months of this year the station had produced more than 12 500 mln. kWh. It is clear that shutting of the station has instantly impacted power supply of the entire region.
Luckily, they managed to restore power supply taking power from other regions.
From the article "Hydraulic impact on the electric-power industry" published in Izvestia on 19.08.09 it is clear, that they were repairing something in unit 2 at the moment of the accident. According to one of the plant workers (unnamed) they were caring out the scheduled repair works, which had to be finished at night, the night shift had to launch the plant. This launching is to be done slowly to avoid impact, but someone wanted to show efficient management trying to do this quickly.