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Hydropower

Introduction:

Hartwell Dam and Lake was the U.S. Army Corps of Engineers second multipurpose “project” in the Savannah River Basin. Authorized by Congress under the Flood Control Act of 1950, the Hartwell Project was built between 1955 and 1962 for the purposes of hydropower, flood control, and downstream navigation. Additional purposes of the project now include water supply, water quality, recreation, and fish and wildlife management. Filling of the lake began in February 1961, and was completed in March 1962. The powerplant first went on-line in April 1962.

The powerplant originally consisted of four generators, with provisions made for a 5th generator based on the foresight that additional power demands would be likely. The 5th generator was installed in 1983. The Hartwell Project powerplant has the distinction of being the only hydroelectric plant to be totally designed and constructed by the Corps, with the generators located outdoors.

Hartwell Dam is a concrete-gravity structure flanked on both sides by embankments of compacted earth. The concrete section is 1,900 feet long and rises 204 feet above the riverbed at its highest point. The earthen embankments on each side of the dam lengthen it to over 3 miles. The dam creates a 55,900-acre lake that stretches 49 miles up the Tugaloo River, and 45 miles up the Seneca River. These two rivers – the Tugaloo and Seneca – come together to create the Savannah River, 7.1 miles above the Hartwell Dam.

The dam is located approximately 300 river miles above the mouth of the Savannah River, where it empties into the Atlantic Ocean (in Savannah, Georgia) and 90 miles above Augusta, Georgia. Two other Corps projects – J. Strom Thurmond (formerly Clarks Hill) located near Augusta (completed in 1954), and Richard B. Russell, located between Hartwell and Thurmond Projects near Elberton, Georgia (completed in 1985) – join Hartwell to form a chain of lakes 120 miles long.

The Corps of Engineers is the nation’s leading producer of hydroelectric energy, and Hartwell Dam and Powerplant is part of the Corps’ national commitment to this energy. Hydroelectric power generation continues to be the only pollution-free means of producing commercial energy.

Hydropower Generation:

Hartwell Powerplant is referred to as a “peaking” plant – which means the powerplant is designed to supply dependable power during hours of “peak” daily demand. In addition to being a very clean energy source, another major advantage of hydropower is the availability to come “on-line” (begin producing power) within a few minutes. Other types of powerplants such as nuclear and fossil fuels often take several hours, at which point the peak demand has often passed. This ability to virtually produce power on demand during peak periods helps to reduce energy shortages (especially during the summer months) and makes hydropower, and the Hartwell Powerplant, an exceptional resource.

The original four generators were designed with a nameplate rating of 66,000 kW. In other words, under controlled conditions, each unit could produce up to 66,000 kW of electricity per hour (the latter installed 5th unit has a nameplate rating of 80,000 kW). However, the nameplate rating of the first four generators recently increased due to a “rehabilitation” or overhaul. The rehab increased the overall plant capacity from 344,000 kW to 422,000 kW, a 22.7% increase; this is equivalent to adding a 6th generator.

On average, the Hartwell Powerplant produces over 468 million-kilowatt hours per year. Revenues during 2001 totaled over $14 million, and have exceeded $330 million since 1962.

How Hydropower Works:

Hydroelectric power is produced when water from Hartwell Lake flows through the intake section of the dam by large pipes called “penstocks”. The penstocks are located approximately 100 ft. below the surface of the reservoir. Water flows through these 24 ft. in diameter penstocks at a rate of 2 – 3 million gallons per minute when generating. The force of the water rotates the “turbines” which resemble large water wheels or fan blades.

The rotating turbine causes the 41-inch diameter generator shaft to spin, which then causes the rotor to turn (the rotor is a series of magnets where the magnetic field is created). The rotor turns inside the “stator” – a stationary part of the generator made of copper coils of wire called “windings”. Electricity is produced as the rotor spins past (inside of) these windings.

The generators create electricity in the form of volts. By means of transformers, the electric current produced is “stepped up” or increased in voltage from 13,800 volts to 230,000 volts for transmission to power companies or decreased in voltage for use in powerplant operations. Water used in generating the power is discharged into the river below the dam, where it can be “reused” for additional purposes such as water supply and water quality needs of the Savannah River Basin.

Where Does the Power Go?

Power produced at Hartwell and all other Corps operated powerplants in the southeast, is marketed by the Department of Energy’s Southeastern Power Administration (SEPA). Power is sold through SEPA to private power companies and public cooperatives in the Southeastern U.S. and from there to customers of those companies. Although electricity is not sold directly to the consumer, the underlying goal of all Corps hydroelectric projects is to provide power to consumers at the lowest possible rates. Rates are set by the marketing agency and approved by the Federal Energy Regulatory Commission. Revenue from Corps powerplants is returned to the U.S. Treasury.