Hiwassee Dam Unit 2 Reversible Pump-Turbine (1956)
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TVA Tennessee Valley Authority HIWASSEE DAM UNIT 2 REVERSIBLE PUMP-TURBINE (1956) A National Historic Mechanical Engineering Landmark July 14, 1981 Murphy, North Carolina ACKNOWLEDGEMENTS The East Tennessee Section of the American Society of Mechanical Engineers gratefully acknowledges the efforts of those who helped organize the landmark dedication of the Hiwassee unit 2. The American Society of Mechanical Engineers Dr. Robert Gaither, President Robert Vogler, Vice President, Region IV J. Karl Johnson, immediate past Vice President, Region IV Sylvan J. Cromer, History & Heritage, Region IV Earl Madison, Field Service Director ASME National History & Heritage Committee ASME East Tennessee Section Prof. J. J. Ermenc, Chairman Charles Chandley, Chairman R. Carson Dalzell, Secretary Mancil Milligan, Vice Chairman R. S. Hartenberg Larry Boyd, Treasurer J. Paul Hartman Steve Doak, Secretary R. Vogel, Smithsonian Institution Guy Arnold Allis-Chalmers Corporation Siemens-Allis, Inc. James M. Patterson, Manager, Marketing Services Paul Rieland, Large Rotating Apparatus Division Hydro-Turbine Division Lloyd Zellner, Public Relations NATIONAL HISTORIC MECHANICAL ENGINEERING LANDMARK Hiwassee Unit 2 Reversible Pump-Turbine 1956 This integration of pump and turbine was the first of many to be installed in power plant systems in the United States; it was the largest and most powerful in the world. As a "pump storage" unit in the Tennessee Valley Authority's system it offered significant economies in the generation of electrical energy. The unit was designed by engineers of the Tennessee Valley Authority and the Allis-Chalmers Company. It was built by Allis-Chalmers Company. The Hiwassee unit 2 is the 61st landmark designated by the American Society of Mechanical Engineers. For a complete listing of landmarks, please contact the Public Information Department, ASME, 345 E. 47th St., New York, NY 10017. HIWASSEE POWER PLANT BACKGROUND The Hiwassee dam and power plant on the Hiwassee River near Murphy, North Carolina, was built by TVA between 1936 to 1940 as a flood control and electrical generat- ing facility. The initial power installation consisted of a single conventional Francis turbine driving a generator with a rating of 57,600 kW, placed in service in May 1940. Space was provided in the powerhouse for later installation of a second unit. When studies were begun for the installation of a second generating unit in the late 1940’s, a reversible pump-turbine was considered. Installation of a pump-turbine was selected to provide additional generating capacity during periods of system daily peak loads, especially during the months of January through March which at that time corre- sponded to TVA’s seasonal peak period. Apalachia Reservoir, immediately downstream from Hiwassee, provided sufficient storage for approximately 27 hours of pumping with the pump-turbine. The pump-turbine selected has a generator rating of 59,500 kW and a pump capacity of 3900 cfs at 205-foot total head (102,000 hp). The pump-turbine unit was installed and placed in operation in May 1956 after ex- tensive commissioning tests. Performance tests for both pumping and generating operation were made in April 1957, using the Allen salt-velocity method for measuring discharge, and again in March 1958, utilizing Apalachia reservoir for volumetric flow measurement. These tests showed that both the turbine guaranteed efficiency of 88.4 percent and pump guaran- teed efficiency of 90.0 percent were met or exceeded. HISTORICAL SIGNIFICANCE Hiwassee unit 2 was the first reversible pump-turbine installed in this country solely for the purpose of storing electrical energy in a pumped storage plant. An earlier pump- turbine, installed in 1954 at the Flatiron Power and Pumping Plant in Colorado, was used primarily for irrigation rather than electrical energy storage. It was much smaller than the Hiwassee pump-turbine and had a somewhat specialized design, providing no control of turbine power output. Pumped storage plants had been in use for electrical energy storage in Europe for some years prior to operation of Hiwassee unit 2. But these plants employed either completely separate motor-driven pumps and turbine-generators or a pump, a turbine, and a generator/motor all on a single shaft. They did not use reversible pump-turbines which are now standard for pumped storage plants. Finally, there were a few instances of pumps being retrofitted for reverse operation as turbines prior to the introduction of reversible pump-turbines. These machines were designed as pumps and had less-than-optimum performance when operated as turbines. UNIQUE FEATURES The Hiwassee pump-turbine was the first reversible pump-turbine built and installed in this country using wicket gates for control of turbine output power and improved pump efficiency. The unit also was much larger and more powerful than any reversible pump- turbine in service in the world at the time it went into operation. The rated turbine power output of 80,000 hp was over four times greater than the next largest pump-turbine, installed at the Pederia power plant in Brazil in 1953. With a diameter of 266 inches, the impeller/runner was the largest water wheel in the world for either a pump-turbine or conventional Francis turbine at the time it was built. The impeller was so large that it had to be shipped in three sections and assembled at the power plant site. Operating as a pump, it had more than three times the capacity of each pump serving the Grand Coulee irrigation project, which then had the world’s largest pumps. CONTRIBUTION TOWARD DEVELOPMENT OF THE NATION The Hiwassee pump-turbine demonstrated to electric power companies world- wide that reversible pump-turbines could be used in a pumped storage plant to effi- ciently and economically store electrical energy during periods of low demand to meet peak load demands. Prior to the installation of Hiwassee unit 2, pumped storage plants used separate pumps and conventional turbines for storage and generation. But the size and reversible nature of the Hiwassee unit served as a prototype for design and construction of subsequent pumped storage plants. The 59.5-MW capacity far exceeded the 25-MW ceiling predicted when reversible units were first studied. Larger units meant that pumped storage could better fulfill its promising role in meeting peak demand. The compact physical arrangement also improved opportunities to build pumped storage. Today, reversible pump-turbines have almost completely supplanted the use of separate pumps and turbines in these facilities. Cross Section of Hiwassee Unit 2 Pump-Turbine Allis-Chalmers Awarded Contract to Build World’s Largest Electric Motor and Reversible Pump-Turbine Unit Will Serve as Heart the time the upper reservoir is pump-turbine. In June, 1950, the filled, the head will increase to company conducted a conference Of Pump Storage Project 254.5 feet. The rated pumping ca- on pump-turbines at its West At TVA’s Hiwassee Dam pacity will be 3900 cubic feet Allis Works which was widely per second against a 205-ft head. attended by hydraulic and power Contracts for the largest elec- At the beginning of operation company engineers. Models of tric motor and reversible pump- as a turbine, the unit will gen- pump-turbines were demonstrated erate 120,000 horsepower and turbine ever built have been at this conference. Following it, drop to 36,000 horsepower as the awarded to the Allis-Chalmers the company obtained contracts Manufacturing Company, accord- reservoir approaches the low point. Guaranteed efficiencies are for three 19,000-hp reversible ing to an announcement by R. M. pump-turbines for the Sao Paulo Casper, manager of the firm’s 90 percent as a pump and 89.5 Light & Power Company Ltd. in Power department. percent as a turbine. Brazil. These units are now under The equipment will be the heart The application of this type of a pump-storage project at Hi- of unit is economically feasible construction at the Canadian wassee Dam in southwestern and profitable because off-peak Allis-Chalmers plant in Mon- North Carolina on the Tennessee power for pumping will cost less treal. Valley Authority’s power network and improve the load factor on Allis-Chalmers is also build- and is scheduled for completion the system, while the power gen- ing a 12,000-hp reversible pump- late in 1955. erated for peak loads will bring turbine for the Flatiron power in more revenue. and pumping plant in Colorado Serves Two Purposes Model tests, standard practice for the Bureau of Reclamation. In this installation a single hy- with all new turbine designs, will This unit is under construction be made within the next few draulic machine will operate in at the West Allis Works and is one direction as a turbine and in months at the company’s hydrau- lic laboratory where they will be a new development in that it the reverse direction as a pump. will be run at two speeds. It A direct-connected electrical ma- witnessed and approved by TVA chine will serve as a motor for engineers. will have a synchronous genera- pump operation and as a gen- tor-motor which will run at 257 A-C is Pioneer of Unit erator for turbine operation. rpm as a generator when driven When in service, water from Allis-Chalmers has pioneered by the turbine and at 300 rpm the Hiwassee reservoir, driving the development of the reversible as a motor when pumping. the unit as a turbine-generator, will add needed energy to the TVA system in peak demand periods. During off-peak periods, when surplus power is available from other plants, the unit will operate as a motor-driven pump to lift water back into the reser- voir. It will act, in other words, as a huge storage battery for storing energy.