On August 17th, 2009, the Sayana-Shushenskaya powerplant suffered a massive accident that resulted in the flooding of the engine and turbine rooms and two electric generators to explode underwater due to short circuit. Due to fatigue caused by extensive vibrations, the pins holding turbine number 2 breaks apart. Water rushing down the penstocks forces the 1500 ton turbine through the powerhouse floor launching it 50 feet into the air. A fountain of water flowing at 67,600 gallons per second destroys the roof and floods the turbine hall causing power failures and short circuit to turbines 7 and 9[6].

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4. 1 Design & Process Factors Shortly after its installation, turbine number 2 had been experiencing problems due to defects in seals and shaft vibrations. In March 2000, a complete overhaul on turbine 2 was performed where cavities of 12 mm in depth and cracks up to 130mm in length found and repaired. Despite these efforts, turbine number 2 continued to have problems resulting in further repairs in 2005 and 2009[7][5]. Prior to the accident, the turbine was undergoing scheduled maintenance from January through March 2009.

During the maintenance period, the turbine blades were welded due to appearance of cracks and cavities caused by long period of operation. The turbine was also equipped with a new electro hydraulic speed regulator supplied by Promavtomatika company [7]. It was resynchronized to the grid on March 16 although the vibrations remained high but did not exceed specifications. The vibrations increased between April and July exceeding the specifications causing the unit to be taken offline until August 16th when the Bratsk fire forced managers to push the turbine into service again.

LMZ, the St. Petersburg metalworks that manufactured the turbines gave it a 30 year service lifespan. Turbine 2’s age on August 17th was 29 years 10 months [6]. Turbine 2 was started and switched to regulating mode due to the Bratsk fire. Data on turbine 2’s start-up and operation period through to the failure time is recorded in Figure 5[3]. Figure : Operating condition of Turbine 2[3] The turbine models are RO-230/833-V-677. As shown in Figure 5, they have very narrow recommended zone of power control.

Excessive vibrations occur when it is being operated with a power setting out of the recommended zone or when it is in transitioning through the “not recommended” zone. Furthermore, when turbine 2 was hastily pushed back into service, the vibrations were unusually high and continued to rise. Figure 6 bellow shows data of the vibration from the plant logs. [3] Figure : Increasing Vibration level of turbine 2[3] The log data shows that the bearing vibration level of turbine 2 increased exponentially and exceeded the values of other turbines by more than fourfold.

At the period of the accident vibrations were at 840µm when its maximum acceptable value is 160 µm. Figure 6 also shows that turbine 2 was operating with vibration levels above 600 µm for a long period while the rest of the turbines were at around 200 µm. [3] This led to the equipment fatigue, primarily in the turbine anchor bolts as a result of the extensive vibration causing it to finally reach the point of failure. 4. 2 Human Factors Human factor also played its part in causing the accident at the powerplant.

If small details that were overlooked and ignored were fixed instead, the accident could have been averted. For instance, when turbine 2 was under maintenance from January to March 2009, after the repairs on the turbine were completed, the turbine wheel was not properly rebalanced before commencing operation [7]. This might have contributed to why the turbine continued to vibrate extensively during April and July leading it to be halted until August 16. However, turbine 2 was hastily pushed back into operation due to the Bratsk plant fire.

The Siberian Unified Dispatching Control Centre (UDCC) made the decision to start turbine 2 at the Sayano-Shushenskaya plant and switch it to regulating mode immediately as cover for the Bratsk plant even though it was halted due to the extensive vibrations. This means that it was subjected to even more intense cycling service due to the flow of water, forcing it through several passes through the “not recommended” zones of power output as seen in Figure 5. Furthermore, these turbine models have a very fine working band at high efficiency conditions.

When this band is exceeded the turbines will begin to vibrate due to the force of water flow. This in turn leads to degrading of the turbine eventually due to vibrations and shocks. The problem was observed many times and yet the load on turbine 2 was not reduced. During the morning of the accident on August 17th, 2009, the plant general director, Nikolai Nevolko, was celebrating his 17th anniversary. While he was away early in the morning to greet the arriving guests, the levels of vibrations were very high because turbine 2 was operating in the “not recommended” zone to meet grid demands [3].

None of the 50 staff present around turbine 2 had authority to make any decisions about taking further actions to cope with the increasing vibrations. They were used to those high levels of vibration and choose to ignore them. The report of the accident listed former state controlled utility chief Anatoly Chubais as one of the people it says were “conductive” to the accident [8]. Chubais is said to have approved an order to allow the powerplant to continue operating despite known problems and what the report described as “lack of an adequate evaluation of its current safety conditions”.

It was even more puzzling why the order came years after the plant had actually been operating. [8] 5. 0 Consequences & Effects of Accident 5. 1 Health In the aftermath of the accident, rescue operations were started to search for survivors with 400 employees assembled to clear the flood in the turbine hall and clear the wreckage. The operation spanned two weeks with 177,000 cubic feet of debris removed and 14 survivors were rescued from the wreckage. However that was not the case for everyone as 75 personnel were pronounced dead when trapped in the turbine hall.

Due to the catastrophic results of the accident, the director of the plant Nikolai Nevolko resigned and was replaced by Valerii Kjari. [6][9] 5. 2 Environment & Ecology Due to accident the penstocks had to be shut down due to repairs, hence all the river water was forced to pass through the spillway. The spillway was not designed to sustain large amounts of water during winter partly due to formation of huge amounts of ice blocking its path. The problem was later resolved by running some of the restored units and construction of in-rock bypass channels [3].

In addition to this, transformer oil spillage that was used as the coolant spilled into the river when the transformers exploded. Approximately at least 40 tons of transformer oil was spread over 80 kilometers downstream of the Yenisei River [11]. This spill led to the killing of tons of trout fish in two fisheries downstream and also affected other wildlife by the river [5]. 5. 3 Damage Costs The total cost of restoring the powerplant is at 40,981 million rubles. The restoration process was finances by the RusHydro’s equity capital and also by raising 4,832.

1 million from the federal budget in 2009 [10]. Payments were also made to the families of the deceased amounting to 38,170 rubles for funeral costs, two average monthly salaries of the deceased employee and also one year’s salary of the deceased for each member of the family that are unable to work amounting to about 1,000,00 rubles per family. Furthermore all employees that were injured will be provided with material assistance and their treatment and rehabilitation cost will be covered in full [12].

6. 0 Improvement & Prevention 6. 1 Design & Process During the accident, the plant’s automatic safety system did not shut down the turbines and close the entry gates to the penstock at the top of the dam due to short circuits. The system now has been improved to close the gates in case of a power loss. In addition to that, the gates can now also be controlled manually from the main control room. Emergency backup power has been installed for further security incase the main power supply fails [3][6].

The powerplant should also install a vibration monitoring system on each of the turbines. They should be programmed to follow specific rules that do not depend on manual interaction to shut down a faulty unit. This device could act as an emergency shutdown in case of excessive vibrations. The turbines should not be allowed to operate in the “not recommended” zone for two long. Its operation should be monitored constantly to avoid formation of cracks and cavities. 6. 2 Human Resources

The installation and maintenance of all turbines and equipment should be monitored and accepted by the primary equipment manufacturers and not by the powerplant chiefs as before. This is because the manufacturers would have more knowledge of how to deal with defects in the systems. The directors and management board should make sure to never neglect and ignore even a small problem with the operation. They should ensure the turbines be put offline at the first indication of abnormalities. 6. 3 Safety & Health

The main improvement that can be made is for the directors of the plant to place more value on human and equipment safety than on the economics of power production. Staff should be given sufficient training and guidelines to handle emergency situation. They should be given sufficient authority to make crucial decisions in the absence of a superior. Finally, a fully funded extensive inspection, repair and maintenance program should be put into action more often. Furthermore, random inspections by an independent organization that is familiar to safety hazards should be encouraged.

7. 0 Conclusion To summarize this report, the accident at the Sayano-Shushenskaya hydroplant was caused mainly by poor management and technical flaws. It could have been avoided if a more tight maintenance had been implemented. Also staff working at the powerplant should have been more aware about problems with turbine number 2 especially since it has been giving problems since the dam was built. Tighter safety rules and safety inspections should be made in the future to avoid this catastrophic event from repeating itself again.

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