By Russell W. Ray
associate editor of HRW-Hydro Review Worldwide
As regulators work to understand what caused a fatal accident at Russia's largest hydropower plant, repairs to the plant are underway and partial production has resumed. The long-term plan to restore the plant calls for the installation of ten new hydro units by 2014. JSC Power Machines won a RUR 11.7 billion (US$392 million) contract to supply the equipment.
Rebuilding Russia's largest power plant, the 6,400-MW Sayano-Shushenskaya hydroelectric plant in southern Siberia, may take longer than expected as engineers deal with challenging logistics, a rare design, and uncertainty surrounding the accident that killed 75 people in August 2009.
Russian equipment supplier JSC Power Machines is supplying the damaged plant with ten new turbines, nine new generators, and six new excitation systems for 11.7 billion rubles (US$392 million). Power Machines General Director Igor Kustin said the manufacturer will be "taking into account corrections" deemed necessary in a report by Rostechnadzor, the government watchdog that investigated the disaster.
RusHydro, the plant's owner and operator, was the second-largest hydropower producer in the world, with 25,400 MW of capacity. Sayano-Shushenskaya accounted for a quarter of that output. Before the accident, Sayano-Shushenskaya was the largest hydropower plant in Russia and the sixth largest in the world.
On the morning of Aug. 17, 2009, Unit 2 was operating under load, with the rotor spinning at nominal frequency, according to RusHydro. From 8:12 a.m., output from unit 2 was reduced by an automatic power regulator, the company said.
According to RusHydro, six of the ten hydro units were destroyed. In materials provided to HRW-Hydro Review Worldwide, RusHydro said: "As the turbine's output power entered into a power band not recommended for long-term operation, the bolts keeping the turbine's cover were broken. Under water pressure in the hydropower unit, its rotor with the turbine cover and the upper bracket shot up. After this, water sprouted from the cavity of the turbine and flooded the machinery hall in less than a minute."1
RusHydro: Restoration work on schedule
In the short-term, RusHydro said it plans to restore four units in 2010.
Yuri Gorbenko, a member of RusHydro's Management Board, said the restoration work is on schedule and involves 2,508 workers and 91 pieces of equipment.
On February 24, 2010, the company restarted unit 6, which can generate up to 640 MW. From the plant's central control board, Russian Federation Prime Minister Vladimir Putin launched unit 6 into production. Unit 5 was scheduled to be placed back into service in March 2010.
The operation of units 5 and 6 means the introduction of 1,280 MW of capacity, minimizing flooding risks and guaranteeing water supply to residents and industrial operations, RusHydro said.
The launch of unit 6 was carried out ahead of schedule. Units 3 and 4 will be put back into production by the end of 2010. Following these launches, the Sayano-Shushenskaya plant's installed capacity will stand at 2,560 MW.
|Before the Aug. 17, 2009, accident, the Sayano-Shushenskaya plant produced 20 percent of Siberia's power and was the sixth largest hydropower plant in the world.|
Putin said the Russian government plans to allocate more than 10 billion rubles to the restoration project in 2010 and 3.5 billion rubles for construction of the first stage of a shore spillway.
The long-term plan calls for the installation of ten new units by 2014. Power Machines will supply the equipment.
Under its contract, Power Machines will complete six hydro units in 2011. The rest will be completed in 2012. Each unit will have a life span of 40 years and will operate at 96.6 percent efficiency.
"This large transaction is vitally important for the restoration of the company's Sayano-Shushenskaya hydropower plant," said Evgeny Dod, chairman of RusHydro's Management Board, "and it is also extremely critical, particularly in terms of delivery guarantees and technical tracking, for the equipment operating process."
Power Machines also is supplying nine turbines and nine generators for RusHydro's Boguchanskaya hydroelectric project. Construction of the 3,000-MW project began in 1980.
It is now "the most acceptable and effective option to promptly substitute the capacities of the Sayano-Shushenskaya plant that were temporarily lost as a result of the accident," RusHydro said. "The stage-by-stage launch of the Boguchanskaya project will reduce considerably the resulting shortage of electric power in the Siberian United Power System and provide for further safe and uninterrupted power supply to consumers in the region."
The Boguchanskaya project includes a 259-foot-high and 2,545-foot-wide gravitational concrete dam and nine hydro units. Three units will begin commercial production in 2010. Three more units will be placed online in 2011, and the rest will be put into service in 2012, RusHydro said.
Meanwhile, the reconstruction of the Sayano-Shushenskaya plant with ten new units is expected to take about four years and cost about 37 billion rubles (US$1.23 billion).
Donald Erpenbeck is vice president of MWH Americas Inc., which provides engineering design and remediation solutions for hydropower projects throughout the world. Erpenbeck said the reconstruction of Sayano-Shushenskaya may take more than four years because of a number of engineering challenges.
"The primary challenge they're going to have is logistics and timing," Erpenbeck said. "They're going to have space limitations that will drag this out."
Erpenbeck said RusHydro may be forced to "re-engineer" the plant. "If you don't understand the root cause of the failure, then you won't know what design changes to make," he said.
Specialists of Narynhydrostroi Co. (Kyrgyzstan) will take part in reconstruction of Sayano-Shushenskaya.
Kyrgyz and Russian hydro specialists will carry out joint works on the construction of a bypass surface spillway to improve the dam's reliability before the spring floods. About 100 Kyrgyz experts — engineers, welders, concrete workers, carpenters and mounters — will work on the project.
"Our specialists have significant experience in hydro construction and we are ready to render professional support to our Russian counterparts," said Albert Abazbekov, chairman of Narynhydrostroi.
Meanwhile, construction of the additional shore spillway continues.
RusHydro said it decided to build an additional spillway to handle spring floods and enhance reliability and safety. The existing spillways can handle spring floods of up to 12,870 cubic meters per second. The new spillway will have a capacity of 4,000 cubic meters per second. The first stage of that project is expected to be operational by June 2010. About 3,000 people are working on the project, which will cost an estimated 13.2 billion rubles (US$441 million).
Why did Unit 2 fail?
According to the official accident report released by Rosthekhnadzor on Oct. 3, 2009, strong vibrations in unit 2 led to metal fatigue in the mounting bolts of the turbine cover. According to the report, nuts on at least six bolts keeping the turbine cover in place were missing. What's more, 41 of the 49 bolts recovered from unit 2 had fatigue cracks, the report showed.
Bolt failure from fatigue is one of several possible causes of the accident, Erpenbeck said. Bolt failure would explain why there was no sequence of events, he said.
"We don't think that water hammer from a governor closure could have caused this problem," he said. "There are other things in the system that should not have allowed the wicket gates to close that fast."
In its official report, Rostechanadzor concluded that the bolt failure was caused "by the low quality of March 2009 intermediate maintenance of the second hydroelectric unit conducted by an organization affiliated to the Sayano-Shushenskaya HPP leadership during which the condition of the bolts of the turbine's cover was not determined."
Erpenbeck and other experts say more information is needed to determine the exact cause of the accident. The official accident report concludes that unit 2 was running too hard and too long.
"The vibration itself was a cry for help from the machine that something was going on," Erpenbeck said. "That machine, with that vibration level, should probably have been the last unit on and the first unit off. In the 12 to 14 hours preceding the failure, they ran that machine in zones that most places don't let their units even run."
Erpenbeck said the stator and the copper surrounding the rotor poles on three units (2, 7, and 9) were destroyed in the accident. "On a machine of this size, that's incredible," he said.
"Is that a result of the water coming up? Maybe. But we also think that there's a possibility of a generator short circuit," Erpenbeck said. "There could have been an extreme short circuit event on unit 2 and that the short circuit was large enough to rip the stator right off its mounts. We believe that could have caused the head cover failure."
According to the accident report, a complete reconditioning of unit 2 was performed in 2000. Several defects were found and repaired, including cavities up to 12 millimeters (mm) deep and cracks up to 130 mm long on the turbine wheel. Further repairs to unit 2 were performed in 2005, when similar defects were found and repaired.
|Six out of ten turbines were destroyed in an Aug. 17, 2009, accident at the Sayano-Shushenskaya plant in southern Siberia. RusHydro estimates it will take US$1.23 billion (37 billion rubles) and four years to rebuild the facility.|
A modernization of unit 2 was performed from January to March 2009, when it was equipped with a new electro hydraulic regulator. Increased vibration in unit 2 was reported following the repairs, according to Rostechnadzor's investigation.
|Hydro-Unit 9 was one of six units that were destroyed in an Aug. 17, 2009, accident at the Sayano-Shushenskaya plant in southern Siberia.|
Structure under constant monitoring
The arch-gravity concrete dam is 804 feet high and 3,497 feet wide. It was designed by Lengidroproyekt institute. Construction began in 1968. The plant's first hydro unit was put into operation in 1978. The other nine generating units were launched into operation between 1979 and 1985. In 1988, the plant's construction was largely completed, and in 1990, its reservoir rose to its designed level of 1,772 feet for the first time.
According to RusHydro, the condition of the plant's hydropower facilities is normal and adequate to the existing water load and temperature impacts. The company said the dam suffered no structural damage and that control and measuring equipment did not register any shift in foundation blocks.
"The safety and reliability of the facilities' operation have no cause for specialists' concern," RusHydro said.
The company said its assessment was based on ten cycles of readings after the Aug. 17, 2009, accident. According to RusHydro, the readings involved several thousand instruments in the rock foundation and the measuring of the most important reference parameters of the structure.
"The reliability of the dam of the Sayano-Shushenskaya hydropower plant is confirmed daily by the automatic monitoring system, readings of control and measuring equipment, additional measurements, and inspections," the company said.
During a recent meeting on the restoration work at Sayano-Shushenskaya, Igor Sechin, deputy prime minister of the Russian Federation, said the plant's hydro-engineering structures are in full working order.
"Their operating reliability and safety are ensured," Sechin said. "The arched gravity dam was in operating order before the accident and it still is."
All of the technological systems for the Sayano-Shushenskaya plant were flooded and damaged to different degrees. Cable tunnels and galleries of the tailrace in the area of generators 2, 7, and 9 collapsed.
The surge of water caused electric and mechanical damage of different extents to all ten units:
— Unit 1: Serious electric and mechanical damage and varying degrees of damage to the construction elements;
— Unit 2: Complete destruction of the construction elements, the generator and the turbine;
— Units 3 and 4: Electric and mechanical damage and varying degrees of damage to the construction elements;
— Unit 5: Electric damage to the generator;
— Unit 6: Damage to the generator caused by flooding;
— Unit 7: Serious damage to the construction elements and complete destruction of the generators;
— Unit 8: Serious electric and mechanical damage and varying degrees of damage to the construction elements;
— Unit 9: Serious damage to the construction elements and complete destruction of the generators;
— Unit 10: Serious electric and mechanical damage and varying degrees of damage to the construction elements.
|The arch-gravity concrete dam is 804 feet high and 3,497 feet wide. It was designed by the St. Petersburg branch of the hydro project institute, Lengidroproyekt. Construction began in 1968. The plant's first hydro unit was placed into commercial production in 1978.|
Before the accident, the Sayano Shushenskaya plant supplied 20 percent of the power consumed in Siberia. Work to repair Russia's largest power plant continues amid lingering questions about the cause of the disaster and the safety of Russia's aging infrastructure.
"A lot of the repair will be dealing with the consequences of the failure and the damage that was done," Erpenbeck said.
1RusHydro, "Reference material on the Sayano-Shushenskaya HPP named after P.S. Neporozhny."