August 17, 2009 at 8:13 a.m.
The failure start at turbine unit 2 when output power was reduced by the turbine regulator and it entered into the non-recommended powerband zone. First, the 1,860-ton turbine cover was blown off, leaving the unit 2 turbine in its pit with no turbine mountings. In an instant, the water head pressure from the dam immediately ejected the turbine rotor from the pit. The rotor is continuing to spin as it flew across the turbine gallery, destroyed everything and everyone in its path As the turbine gallery filled with water, Unit 7 and 9 turbines continued to operate when their safety shutdown systems failed to trip. Eventually, the turbines were submerged, causing extensive damage to equipment and structures.