History

Construction of the original project started in 1933 and was completed in 1941. The first power was generated in 1941 and the last of the original 18 units (Right and Left Powerhouses) began production in 1950. Pumping for irrigation commenced in 1951. Six pumps (P-1 through P-6) were installed from 1951 to 1953. In addition, six pump-generators were installed from the mid-1970`s (P/G-7 and P/G-8) to the early 1980s (P/G-9 through P/G-12). Construction of the Third Power Plant and Forebay Dam commenced in 1967 with the first unit (G-19) commissioned in 1975 and the last (G-24) in 1980. The 18 original generators in the Right and Left Powerhouses have had the stator windings replaced increasing the rating from the original 108,000 kW to 125,000 kW. The last three generators in the Third Power Plant (G-22, G-23, and G-24) had their stators and cores replaced increasing their rating from 700 MW to 805 MW at 825.6 MVA and power factor of 0.975. All banks of the original transformers in the Left Powerhouse have been replaced with the ratings increased to between129,000 and 150,000 kilovolt amperes. Turbine runners for units G-1 through G-18 were replaced between 2000 to 2010.

Project Authorization

The Columbia Basin Project began with fund allocation for Grand Coulee Dam pursuant to the National Industrial Recovery Act of June 16, 1933. The project was specifically authorized for construction by the Rivers and Harbors Act approved August 30, 1935. The Columbia Basin Project Act of March 10, 1943 (57 Stat. 14), reauthorized the project, bringing it under the provisions of the Reclamation Project Act of 1939.

Construction of the Third Power Plant was authorized by Public Law 89-448 (80 Stat.200) dated June 14, 1966, as amended by Public Law 89-561 (80 Stat. 714) dated September 7, 1966.

Plan

Grand Coulee Dam is a key feature of Reclamation`s Columbia Basin Project in central Washington. A multi-purpose project, it provides flood control, irrigation, hydropower production, recreation, stream flows, and fish and wildlife benefits. Facilities at the dam include three powerplants, a pump-generating plant, and three switchyards. Franklin D. Roosevelt Lake behind the dam is 151 miles long with over 5,000,000 acre feet of active storage. Water is pumped for irrigation in the Columbia Basin to irrigate approximately 670,000 acres with an ultimate potential of 1.1 million acres.

Grand Coulee Dam is the largest concrete structure built in North America. Raising the water surface 380 feet above the old riverbed, the dam is 5,233 feet long, 550 feet high, and contains 11,975,500 cubic yards of concrete. The original dam was modified for the Third Power Plant by a 1,170-foot-long, 201-foot-high forebay dam along the right abutment approximately parallel to the river and at an angle of 64 degrees to the axis of Grand Coulee Dam.

The power facilities at Grand Coulee Dam consist of a powerplant on both the left and right sides of the spillway on the downstream face of the dam, the Third Power Plant, on the downstream face of the forebay dam, the pumping generation plant on the left abutment of the dam, and a 11.95/115-kilovolt switchyard, a 230-kilovolt consolidated switchyard, and a 525-kilovolt Third Power Plant switchyard located high on the hills west of Grand Coulee Dam.

Construction of the original project started in 1933 and was completed in 1941. The first power was generated in 1941 and the last of the original 18 units (Right and Left Powerhouses) began production in 1950. Pumping for irrigation commenced in 1951. Six pumps (P-1 through P-6) were installed from 1951 to 1953. In addition, six pump-generators were installed from the mid-1970`s (P/G-7 and P/G-8) to the early 1980s (P/G-9 through P/G-12). Construction of the Third Power Plant and Forebay Dam commenced in 1967 with the first unit (G-19) commissioned in 1975 and the last (G-24) in 1980. The 18 original generators in the Right and Left Powerhouses have had the stator windings replaced increasing the rating from the original 108,000 kW to 125,000 kW. The last three generators in the Third Power Plant (G-22, G-23, and G-24) had their stators and cores replaced increasing their rating from 700 MW to 805 MW at 825.6 MVA and power factor of 0.975. All banks of the original transformers in the Left Powerhouse have been replaced with the ratings increased to between129,000 and 150,000 kilovolt amperes. Turbine runners for units G-1 through G-18 were replaced between 2000 to 2010.

The Left Powerhouse contains three station service generators rated at 10,000 kW and nine generators rated at 125,000 kW. The Right Powerhouse contains nine generators rated at 125,000 kW. The Third Power Plant contains three generators nameplate rated at 600,000 kW but able to operate up to 690,000 kW, and three generators rated at 805,000 kW. The Pump-Generating Plant contains six pumps rated at 65,000 horsepower, two pump-generators rated at 67,500 horsepower, and four pump-generators rated at 70,000 horsepower. Each of the generators is fed by an individual penstock with the largest (Third Power Plant) approximately 40 feet in diameter and carrying up to 34,000 cubic feet per second of water. One switchyard has 11.95 kilovolt distribution and four 115 kilovolt transmission lines; one switchyard has 230 kilovolt generation (from eighteen 125,000 kW units) and eleven transmission lines; the third switchyard has 525 kilovolt generation (from six Third Power Plant Units) and six transmission lines. There are electrical connections through transformers between the 115 and 230 kilovolt switchyards and the 230 and 525 kilovolt switchyards. The main dam contains 11 drum gates, each 135 feet long and 40 outlet tubes with 102-inch ring seal gates for spilling water. The average water released from Grand Coulee Dam is 110,000 cubic feet per second. The average power generation is 21 billion kilowatt hours per year.

Recently Completed Activities

Replacing 500 kV Cables with Overhead Lines: The degraded condition of high voltage cables that transmitted power from the Third Power Plant to the switchyard constituted an unacceptable risk for loss of generation. The nine oil-filled cables for G-19, G-20, and G-21 had been operated near or above their continuous current rating for 30 years. It had become apparent that the condition of the high voltage cables transmitting power from the Third Power Plant to the 525KW switchyard had degraded. At the same time it had been determined that units G-19, G-20, and G-21 could each be uprated from 600MW to 770MW if the cables transferring power to the grid were also replaced with a means of transmission having higher capacity. Replacing these cables with overhead transmission lines solved several problems: Overhead transmission lines can be inspected and maintained more safely than oil filled cables. The new lines are of adequate size to allow up-rating Third Power Plant generators. Replacing these cables with overhead transmission lines removed the potential of one cable failure causing the loss of 2,100MVA or more of generation. The new overhead lines were installed by December 2012. The removal of the existing oil filled cables was completed by December 2013.

Present Activities

Installation of a new Supervisory Control and Data Acquisition (SCADA) System is underway.

Failure of a single phase transformer on Unit G10 resulted in re-evaluation of the need for replacement transformers. Installation of replacement transformers is underway.

The Third Power Plant generating units are in need of complete mechanical overhauls. Each unit will be taken apart and worn parts will be refurbished or replaced. The first unit, G-24, has been overhauled and was returned to service in April 2016. G-23 is currently undergoing overhaul. G-22 will be overhauled once G-23 is finished. A second contract will be awarded in the future for Units G-19 through G-21.

Special Issues

Since Grand Coulee has such a large amount of generation; it is used as a peaking facility by BPA. Fluctuations in the downstream tailbay/river have required extensive downstream stabilization measures, including elaborate monitoring and pump systems to maintain riverbank stability.

Water releases from Grand Coulee play a significant role in providing water for the fish that have been listed under the Endangered Species Act. In addition, to the extent possible, spill is minimized to keep the Total Dissolved Gas (TDG) below the state standards. As part of the power peaking operation the pumps and pump-generators in the John W. Keys, III Pump Generating Plant are load factored (used for pumping during light load hours) to allow BPA to sell more power during peak hours and also to provide a load during light load hours (to reduce spill). The pump-generating plant provides an approximate load swing - from consuming 600 MW with all 12 units pumping to generating 300 MW with 6 pump-generators generating. Western Electricity Coordinating Council, Northwest Power Pool Area Bonneville Power Administration

General