Cougar Dam - Replacement of Turbines

Replacement of Turbines

The runners from the two turbines in the Cougar powerhouse experienced significant cavitation damage during operation and by the 1980s they were in need of repair and had to be taken out of service four times a year for inspections and repair. In 1987, the U.S. Army Corps of Engineers installed replacement runners that were designed by Voith Siemens Hydro Power Generation. By 2000, the replacement runners were again experiencing cavitation problems and in need of repair. Repair of the runners would prove to be difficult because the runner blades are thin, making them difficult to weld, and the spacing between the blades is small which gives limited access to the damaged area. The U.S. Army Corps of Engineers realized that a state-of-the-art runner design was required and devised a turbine-generator rehabilitation program. Due to the technical challenges associated with the program, the Corps chose a best value procurement method for this project. In 2003, the contract was awarded to General Electric Hydro of Montreal, Quebec, Canada and the project was completed in March 2005. The project included physical model testing, new turbine runners, a major turbine overhaul, a generator rewind, and disassembly and reassembly of the units. The problems with the runners for the turbines at Cougar powerhouse are associated with the cycle of large head changes of the Cougar Reservoir. Since Cougar Reservoir is built for flood control, the levels of the reservoir very greatly, causing the units to operate at heads between 400 and 438 feet (120 and 134 m) one third of the time and at heads between 270 and 310 feet (82 and 94 m) one fifth of the time. In 2002, the Corps began lowering the level of the reservoir for the construction of a temperature control facility. The reservoir level was lowered to an elevation below the turbine intakes, which put the powerhouse out of service and provided an opportunity to overhaul the turbine-generator units.