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THE THIRD POWERPLANT OF GRAND COULEE DAM
Electric power requirements are rapidly increasing along with the demand of finding sources of energy that are renewable and non-polluting; thus increasing the power production at Grand Coulee Dam was timely and justifiable with the construction of the Third Powerplant. With the existing capacity of 2,195,000 kilowatts, the first stage of the Third Powerplant construction makes available an added 3,900,000 kilowatts, and two new pump-generators at the other end of the dam can contribute another 100,000 kilowatts, for a total increase of 4 million kilowatts to the Grand Coulee Dam power complex. That is more power than is required for Seattle and Portland combined, and brings total capacity to 6,195,000 kilowatts.
Part of the power from the big Dam is used for irrigation pumping, and the balance is distributed over the lines of the Bonneville Power Administration into a Pacific Northwest power grid for commercial, industrial and residential use. During the summer months, when demand in the Northwest decreases, the energy surplus to the needs of our area is transmitted over the Pacific Northwest - Pacific Southwest Intertie to help meet the need of the residents of the southwest, where the demand for energy increases as temperatures go up.
Prior to the Third Powerplant construction, a treaty was negotiated with Canada which provides for the cooperative development of the Columbia River with benefits to both countries. Under this treaty, Canada has built three dams in British Columbia for water storage purposes. This treaty also permitted the construction of Libby Dam in Montana and its huge storage. These increases in storage capacity above Grand Coulee Dam made building the Third Powerplant feasible. Over forty-five percent of the average yearly stream flow can be stored behind the various dams as the snow melts, thus the flood damage can be avoided and stored water can be drawn as needed to power generators at Grand Coulee, and at five other government owned dams and five public utility dams on the Columbia River below Grand Coulee Dam. In return for building the three storage projects, Canada is to receive one-half of the additional power produced at the United States dams in the base system. The owners of the project here retain the other half. Canada elected to sell the first thirty years of its share of the entitlement to United States purchasers for approximately $254,000,000. This was paid in September, 1964. Canada used the funds to build its treaty dams. In addition, the United States paid Canada $64,400,000 representing one-half of the present value of the flood control benefits to be provided in the United States over the treaty period.
The Third Powerplant has been a study in superlatives. Sizes have taxed the imagination, skills, and creativeness of engineers, manufacturers, and contractors alike. Studies for installation of a Third Powerplant were started by the Bureau of Reclamation in 1962. On the basis of these reports the first three turbines and generators were purchased. But
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before these were installed increased confidence in the practicality of larger units than the 600 megawatts of the first ones resulted in the award of another contract for three 700 megawatt units. This is almost six times the capacity of the 125 megawatt units in the existing powerplants. The amount of water required, the size of penstocks, and the turbines needed to power these units are all in the same proportions. Because of their size, the turbines and many other parts of the equipment for the Third Powerplant had to be shipped in small parts and fabricated or assembled on the site. The generators were also shipped in many pieces to be assembled and put together in the generator bay of the Third Powerplant. Each unit requires about 100 railroad cars for shipment of components. A 1,900 ton capacity gantry crane has been installed to handle the generator rotors. This hydraulic-lift crane will place the generators with pinpoint accuracy. In addition there are two 275 ton and two 50 ton capacity bridge cranes inside the Powerplant which are used to handle the turbines and other loads.
Before construction could start on the Third Powerplant, it was necessary to modify the existing plants and route all generation to a new 230,000 volt consolidated switchyard. Originally there was a switchyard on each side of the river, one for each of the existing powerplants. The right switchyard was in the area now occupied by parts of the forebay dam and the Third Powerplant. A new high voltage cable system running through oil filled pipes conveys the power from the original powerplants through existing galleries in Grand Coulee Dam and an underground tunnel up to the new low-profile, consolidated switchyard. Construction of this new switchyard without power interruption was technically one of the more difficult and hazardous parts of the project.
To carry the power generated by the first three mammoth units at the Third Powerplant, nine cables, each almost five inches thick, run from the powerplant transformers through a gallery in the dam and through a tunnel to a cable spreading yard located high on the hills west of the dam. A man could safely place his hand on the cables an inch and a half from the copper core which carries enough electrical energy to supply the needs of 1.8 million people. Almost 11 miles of this 525,000 volt cable is installed through galleries and tunnels to connect the Third Powerplant to the cable spreading yard.
Former Third Powerplant Construction Engineer Roscoe Granger stated, quoting from a paper by Harold Arthur, Director of Design and Construction for the Bureau of Reclamation:
"To get maximum power, the amount of water to operate one of these new turbines in the Third Powerplant is 30,000 cubic feet per second -- this is the average mean flow of the Colorado river through the Grand Canyon!"With such a huge undertaking, numerous contracts have been issued for Third Powerplant construction. The first major commitment was to Jelco, Gibbons and Reed Company, a joint venture of a firm from Salt Lake City,
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Utah, involving some $10,500,000 for modification to the right and left switchyards. Completed in 1969 was another important contract, that of Green Construction Company of Des Moines, Iowa, for their bid of $12,524,517 which was for the forebay channel and forebay excavations. Gordon H. Ball, Inc., of Danville, California, was the contractor for removing existing structures from the right 230 KV switchyard and for excavating material for the construction of the penstocks. The principal contract was awarded March, 1970 to a joint venture of Vinnell Corporation-Dravo Corporation-Lockheed Ship Building and Construction Company-Mannix Construction Company of Alhambra, California, for the construction of Grand Coulee Dam's Third Powerplant and Forebay Dam with a bid of $112,525,612. Contractwise this has been completed. Installation of the power units on the first three has begun with Bingham-Willamette of Portland, Oregon, doing the turbines, and Westinghouse Electric placing the generators. A contract has been awarded to Canadian General Electric for the turbines and generators for the three 700 megawatt units yet to be installed.
Organizational head for the Third Powerplant Construction activity was Roscoe Granger who was Third Powerplant Construction Engineer for the Bureau of Reclamation from 1967 to 1972, when he retired. His assistant, Howard L. Fink took over from 1972 to 1974. After Mr. Fink's retirement, Darrel Hansen became Third Powerplant Construction Engineer, a position he still holds.
The economic impact of the Third Powerplant construction has been a tremendous boost to our Grand Coulee Dam Area. Though major contracts have been finished or are now nearing completion, the Third Powerplant construction payroll monthly is listed at $850,000 according to the August 22, 1976 issue of the Wenatchee Daily World. After Congress authorizes the doubling of the Third Powerplant to accommodate additional turbine-generators, the number of which will be decided in a feasibility report which the Bureau of Reclamation is scheduled to complete next October, another drastic increase in construction is in prospect. With such an addition, the total complex is scheduled to have a capacity of about 10,000,000 kilowatts, which would again make Grand Coulee Dam the largest power producing plant in the world.
Taken from Bureau of Reclamation
Publications and Interviews
Helen Rinker
Wayne Monteith
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