The overhaul of hydroelectric power generating units 22, 23 and 24 inside the Nathaniel “Nat” Washington Power Plant at the 6809MW Grand Coulee Dam – the largest power generating complex in the US – have been successfully completed, the US Bureau of Reclamation and the Bonneville Power Administration have announced.

Planning for the major project began back in 2008, and in 2012, the contractor arrived onsite to begin preparatory work on the project. By March 2013, disassembly was underway on G24, taking the first of the three massive units offline to begin the overhaul. G24 and G23 were back online by 2016 and 2019, respectively, with the final unit, G22, returning to service on 30 September 2021.

Each 805MW hydroelectric unit was completely disassembled as part of the project, with all of the mechanical and electrical surfaces restored and returned to like-new condition. Approximately 6.5 million pounds of steel were removed from each unit once every component down to the turbine runner was fully taken apart. While the units were disassembled, each component was sand blasted, welded, ground, polished, and then repainted before reassembly. Restoring the mechanical and electrical components results in less friction. As a result, the generating units operate with less wear and tear, making them more reliable and efficient.

“Overhauling something of this magnitude does not happen overnight; it takes years of planning and strong partnerships to complete such a milestone,” said Columbia-Pacific Northwest Regional Director Lorri Gray. “The overhaul of these units is key to accomplishing Reclamation’s mission and represents one of the most significant infrastructure investments in the region’s recent history. This overhaul enables us to optimize Coulee’s performance as one of the most coveted clean energy assets in the world.”

Known as the crown jewel of the Pacific Northwest, Grand Coulee Dam provides about one-quarter of the total generation of hydroelectric power for the Federal Columbia River Power System. The Nathaniel “Nat” Washington Power Plant was built between 1967 and 1975, and is the largest of the four powerhouses at the complex. The plant contains six generating units capable of producing more than 4200MW, and it contributes to about 2/3 of the total power generated by the dam. 

“As the region’s reliance on clean energy continues to grow, so does the need to maximize hydropower generated by the dam,” added Gray. “The successful completion of the overhaul helps ensure we continue to provide clean, renewable, economical and reliable power for another 30 years or more.”

Completed in 1941, Grand Coulee Dam serves as a multipurpose facility, providing water for irrigation, hydroelectric power production, flood control, fish and wildlife conservation, and recreation. The Grand Coulee Power facility is comprised of 33 generators in three power plants, the John W. Keys III Pump-Generating Plant, and three switchyards.