Major loss in hydroelectric power plant
Sayano-Shushenskaya is one of the world’s biggest hydro power plants. Years of overloading the turbines and inadequate maintenance were probably behind the major accident in 2009. Could greater care have prevented the catastrophe?
On 17 August 2009, a turbine unit was torn out of its anchorage by fluctuating water pressure and catapulted into the air in the Sayano-Shushenskaya hydroelectric power plant in Russia. Weighing in at around 2,000 tonnes, the turbine destroyed the 27-m-high roof of the turbine hall, as well as several nearby structures and plant parts. Propelled by the pressure of a 200-m water column, an incredible 360 cubic metres of water per second shot through the entire turbine hall, including the lower floors, causing numerous short circuits and immediate failure of the power plant. Those units which were still in operation sustained various degrees of mechanical and electrical damage. All in all, 75 people were killed and many others injured.
Clear warning signs had been ignored
The damaged turbine unit was extensively overhauled in 2000 and 2005, followed by another minor overhaul in the spring of 2009. At the same time, a new control system was installed so that the hydro power plant could be controlled externally in line with grid requirements. This system was not adapted exactly to the installed turbines.
After the turbine was recommissioned, the vibrations measured in the turbine rotor were only just below the maximum permitted by the manufacturer. However, in the following weeks and months, these vibrations did not stabilise, but instead increased steadily, presumably exceeding the permitted maximum by June 2009. Nevertheless, the turbine remained in operation. Fatigue cracks appeared in the retaining bolts. The bolts sheared as soon as the water pressure was sufficiently high to cause residual forced rupture. The turbine cover with turbine rotor and generator weighing around 2,000 tonnes lost its anchorage in the foundation and led to the accident.
Catastrophe court case
Even today, it is unclear why neither the plant management nor the operators halted the turbine which had been vibrating strongly for many months. Many documents are still in the hands of the judiciary. Others were reputedly washed away by the water. After the water had been pumped out of the turbine hall, 49 of the 80 retaining bolts holding the turbine cover in place were subjected to metallographic analysis. Six of them did not even have a nut. They may have been forgotten when the turbine was last serviced. Investigations by the public prosecutor are still ongoing. One year after the accident, charges were filed against the people responsible in the plant operating company and in the maintenance companies. The plant’s operator plans to completely replace all ten turbines between 2011 and 2014.
Improper plant operation
The catastrophe could have been prevented if the machines had been operated in base load mode as specified. Also, basic principles ensuring trouble-free operation, such as investigation of the causes leading to the increase in vibrations, were disregarded here. Even when the vibrations had increased to five times the permitted level, the unit was not switched off. Moreover, necessary maintenance work was evidently performed inadequately or not at all.
"Professional risk management can help prevent such catastrophes. But regular maintenance and proper use of machinery are indispensable, the more so towards the end of a machine's originally planned life span", Bernd Richter, an engineer and Claims Manager in Munich Re's Europe and Latin America unit, and Klaus Wenselowski, head of the Property Claims Management unit at Munich Re's Global Clients/North America division explain. "To prevent such major losses from occurring, we assist our clients in setting up risk management programmes and attach great importance to compliance with agreed measures and guidelines."