On August 17, 2009, turbine 2 of the Sayano–Shushenskaya hydroelectric power station near Sayanogorsk in Khakassia, Russia, broke apart violently. The turbine hall and engine room were flooded, the ceiling of the turbine hall collapsed, 9 of 10 turbines were damaged or destroyed, and 75 people were killed. The entire plant output, totaling 6,400 MW and a significant portion of the supply to the local grid, was lost, leading to widespread power failure in the local area, and forcing major users such as aluminum smelters to switch to diesel generators. An official report on the accident was issued on 4 October 2009.
Sayano–Shushenskaya hydroelectric power station is located on the Yenisei River, near Sayanogorsk in Khakassia. Before the accident, it was the largest hydroelectric power station in Russia and the sixth-largest hydroelectric power station in the world, by average power generation. The plant is operated by RusHydro. On 2 July 2009, RusHydro announced the station’s all-time highest electricity output per 24 hours.
Turbine 2 had experienced problems for a long time prior to the 2009 accident. After its installation in 1979, the first problems appeared. During 1980-1983, many more problems with seals, turbine shaft vibrations, and bearings surfaced. From the end of March to the end of November 2000, a complete reconditioning of turbine 2 was performed. Cavities up to 12 mm deep and cracks up to 130 mm long were found on the turbine wheel and repaired. Many other defects were found in the turbine bearings and subsequently repaired. In 2005 further repairs were made to turbine 2. Problems found were similar in several aspects to the defects observed during the previous repair.
From January to March 2009, turbine 2 was undergoing scheduled repairs and modernization. It was the first and only turbine in the station which was equipped with a new electro-hydraulic regulator of its rotational speed supplied by the Promavtomatika company. During the course of the repair, the turbine blades were welded, because, after a long period of operation, cracks and cavities had appeared. However, the turbine wheel was not properly rebalanced after these repairs had been completed. After the repairs, turbine 2 had increased vibration, ca 0.15 mm for the main bearing at the full load of the turbine. However it did not exceed specifications, but the increased vibration was unacceptable for long term use. The elevated vibration compared to other turbines was apparent for turbine 2 before the repair as well. The vibration exceeded the allowed specification in the beginning of July and continued to increase with accelerated speed.
On the night of 16–17 August, the level of vibration increased substantially. There were several attempts to stop the turbine. During 16 August up to 20:30, the load of turbine 2 was 600 MW, then it was reduced to 100–200 MW. On 17 August 2009 at 3:00, the load was increased again to 600 MW; at 3:30, the load was decreased to 200 MW; and at 3:45, it was increased again to 600 MW. During this time, the level of vibration was very high, and was also registered by seismic instruments in the plant. During attempts to shut it down, the rotor inside the turbine was pushed up, which in turn created pressure pushing up on the turbine cover. The cover was kept in place by 80 bolts of 8-centimetre (3.1 in) diameter.
During the morning of 17 August 2009, 50 people were around turbine 2. As the plant general director, Nikolai Nevolko, was celebrating his 17th anniversary, early in the morning he went to Abakan to greet the arriving guests, and none of the workers present wanted to make or had no authority to make decisions about further actions regarding the turbine. It seems they were used to those high levels of vibration.
Turbine 2 was started on 16 August 2009 at 23:14 local time. At 23:44 it was running at full load of 600 MW. During the night its load varied between 10 and 610 MW. At the moment of the accident, which was 8:13 local time (00:13 GMT), its load was 475 MW and water consumption was 256 m3/s (9,000 cu ft/s). Vibration of the bearing was 0.84 mm which exceeded the values of other turbines by more than fourfold. The work life defined by the manufacturer for the turbines was specified for 30 years. At the moment of accident the age of the turbine was 29 years and 10 months.
The turbines of this type have a very narrow working band at high efficiency regimes. If this band is exceeded the turbines begin to vibrate, caused by the pulsation of water flow and waters strokes. These vibrations and shocks on the turbines will degrade them over time. These problems were observed many times in the plant.
On the day of accident the turbines worked at working level 212 metres (696 ft). At this pressure the recommended power band for the turbines is 570–640 MW (band III) and the allowed band is 0-265 MW also (band I). Band 265–570 MW (band II) at this pressure is not recommended and output over 640 MW (band IV) is forbidden. On the day of accident turbine 2 worked as the plants power output regulator and due to this, its output power changed constantly. The turbine often operated in band II regime which is accompanied with pulsation and strokes of water flow.
The accident occurred on 17 August 2009 at 08:13 local time (00:13 GMT). There was a loud bang from turbine 2. The turbine cover shot up and the 920-tonne (910-long-ton; 1,010-short-ton) rotor then shot out of its seat. After this, water spouted from the cavity of the turbine into the machinery hall. As a result, the machinery hall and rooms below its level were flooded. At the same time, an alarm was received at the power station’s main control panel, and the power output fell to zero, resulting in a local blackout. The steel gates to the water intake pipes of the turbines, weighing 150 tonnes (150 long tons; 170 short tons) each, were closed manually by opening the valves of hydraulic jacks keeping them up between 8:35 and 9:20 hours (9.30 by official report). The operation took 25 minutes, which is near the minimum time (highest speed) allowed for this operation. The emergency diesel generator was started at 11:32. At 11:50, the opening of 11 spillway gates of the dam was started and was finished at 13:07. 75 people were later found dead.
Nine out of the ten turbines were operating at the time, with a total output 4,400 MW. Turbine ? 6 was undergoing scheduled maintenance, but was ready for a restart.
Oleg Myakishev, a survivor of the accident, described it as follows:
…I was standing upstairs when I heard some sort of growing noise, then I saw the corrugated turbine cover rise and stand on end. Then I saw the rotor rising from underneath it. It was spinning. I could not believe my eyes. It rose about three meters. Rocks and pieces of metal went flying, we started to dodge them… At that point the corrugated cover was nearly at roof level, and the roof itself had been destroyed… I made a mental calculation: the water is rising, 380 cubic meters per second, so I took to my heels and ran for the ? 10 turbine. I thought that I wouldn’t make it, I climbed higher, stopped, looked down, and saw everything getting destroyed, water coming in, people trying to swim… I thought: someone must urgently shut the gates to stop the water, manually… Manually, because there was no power, none of the protection systems had worked…
On 9 September 2009 at 17:40 local time (09:40 GMT), a fire started in the turbine hall during repair works. Around 200 people were evacuated. There were no fatalities or injuries. According to RusHydro the fire was extinguished “within a few minutes”.
On 4 October 2009 the official report about Sayano-Shushenskaya hydro accident was published by the Federal Environmental, Technological and Atomic Supervisory Service (Rostekhnadzor) on its website. However, later the report and the press release on the report were removed from the website.
Names of people killed and those who bear responsibility for the accident, and other data including a historical and technical review about the plant and plans for its future, are given in the report. The report states that the accident was primarily caused by the turbine vibrations which led to the fatigue damage of the mountings of the turbine 2, including the cover of the turbine. It was also found that at the moment of accident at least six nuts were missing from the bolts securing the turbine cover. After the accident 49 recovered bolts were investigated from which 41 had fatigue cracks. On 8 bolts, the fatigue damaged area exceeded 90% of the total cross-sectional area.
According to this report, on 17 August 2009 at 1:20AM (local time) there was a fire at the hydroelectric power station of Bratsk which broke both communications and the automatic driving systems of other power plants in the region, including Sayano-Shushenskaya. The situation was recovered on 17 August 2009 at 15:03. At 8:12AM local time, turbine 2’s output power was reduced by the turbine regulator and it entered into the non-recommended powerband II. Shortly after this, the bolts keeping the turbine cover in place were broken, and under water pressure of about 20 bars (2,000 kPa), the spinning turbine with its cover, rotor, and upper parts started to move up, destroying machinery hall installations. At the same time, pressurized water flooded the rooms and continued damaging plant constructions.
According to Rostekhnadzor, the automatic shutdown system of the water intake pipes’ gates failed after failure of the turbine 2. This accusation was dismissed by Rakurs, the company which designed the automated safety system for the plant.
According to the newspaper Izvestia, the increased vibration of turbine 2 was going on for some 10 years and was well-known to the plant personnel. According to the former director of Irkutskenergo, Viktor Bobrovski, the accident could have been caused by an incorrect start-up process of the turbine which resulted in an hydraulic pressure surge, or the excess load of the turbine caused by the peak consumption of electricity. According to Bobrovski, it is common practice in the region to compensate for peak load by overloading hydroelectric power plants, and the energy system of the region is near collapse, as the main goal of its owners is to take out as much profit as possible cutting down on maintenance, investment, safety, and educational costs. Since the load for other turbines ceased after the collapse of the turbine 2, they probably started to spin without load at increasing speed until they smashed. He said that former director of Sayano–Shushenskaya hydroelectric power station, Valentin Bryzgalov, had alerted that it is dangerous to operate the plant at its maximum loads when the turbines are starting to vibrate in the axial direction. He said that the accident probably would not have had such catastrophic results if the safety systems had worked and the safety rules had been followed.
The former general director of the plant, Alexander Toloshinov, has said that the accident was most likely due to a “manufacturing defect” in a turbine. According to Toloshinov, the construction of the turbine blades of this type of turbine is not very reliable and cracks are known to develop in them under some working conditions.
On 11 September 2009, RusHydro refuted allegations that the dam overwhelmed the machinery hall leading to the destruction of turbine 2. According to RusHydro, displacements of the dam are seasonal and have been reduced in recent years. The maximum displacement (141.5 millimetres / 5.57 inches) was recorded in 2006, which was below the allowed maximum of 145.5 mm (5.73 in). According to RusHydro, the scope of displacement between the anchor legs and the machinery hall does not exceed 2.3 mm (0.091 in), which is less than the width between them (50 mm/2.0 in), and therefore the dam cannot overwhelm the machinery hall.
- Technical investigation into the accident at the Sayano-August 17, 2009 by the Federal Service for Ecological, Technological and Nuclear Supervision (Russian | Word doc)
- Sayano-Shushenskaya Hydroelectric Station Accident Report (Machine-translated from Russian | PDF)