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| HISTORY A Bold Effort in Vermont
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Carl Sulzberger | ||
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Soon after building his summer house on Cape Cod, Massachusetts, in 1934, Palmer Cosslett Putnam found that both the prevailing winds and his electric utility bills were surprisingly high. He reasoned that a wind turbine producing ac electricity could reduce his electric bills if the local electric utility remained available to maintain service when there was no wind and would also accept into its system excess electrical energy generated by the wind turbine. Putnam's calculations showed that the small wind-driven electric generators then available would be unable to supply the peak load requirements of his house. With his interest in wind power thus aroused, Putnam embarked on a pioneering project that would result in the design, construction, testing, and operation of the first megawatt-size wind turbine and one of the earliest to be integrated into an electric utility system. In advancing wind-produced electrical energy knowledge and technology, the Smith-Putnam wind turbine became an important forerunner of today's large wind turbine designs for the production of electrical energy. Concept and DesignPutnam, an accomplished consulting engineer, approached his wind turbine project by enlisting the aid of leading scientists and engineers in each of the needed disciplines. He also carefully studied the designs of wind-powered electric generators that had been proposed by others in North America and Europe in the years following World War I. Putnam's early work led to the conclusion that the most economically attractive course would be the production of ac electrical energy using a large, high-speed, two-bladed wind turbine operating downwind (facing away from the wind). Moreover, the output from the unit should feed directly into the electric utility system that would then be able to reduce output from its other hydro or steam-generating units when the wind turbine was operating. Since the power in the wind increases as the cube of the wind velocity, and as wind velocity increases with altitude, the ideal site would be a mountain top or ridge with a rounded, aerodynamic profile that would further increase the speed of the wind over its summit.In 1937, Vannevar Bush, then dean of engineering at MIT, referred Putnam to Thomas Knight, the Boston-based commercial vice president of the General Electric Company. Knight was interested in the possibility of the large-scale production of electric energy using the power of the wind. He assisted Putnam in developing his plans to the point where more complete cost studies could be made. Next, Walter Wyman, president of the New England Public Service Corporation, based in Augusta, Maine, was approached by Alan Goodwin, the hydroelectric specialist in Knight's Boston office. Wyman saw the potential benefit of wind power to his utility company, and the Central Vermont Public Service Corporation (CVPS), one of his company's subsidiaries, was designated to participate in the project by providing the site and connection facilities and by accepting the electrical energy produced by the test unit into its utility system. CVPS President Albert Cree and Chief Engineer Harold Durgin supported the project because the hydro capacity of CVPS was not adequate to supply peak load. A successful wind-turbine test unit could lead to a block of wind-produced electrical capacity and a consequent reduction in CVPS's purchase of electric power from the Bellows Falls Hydro Electric Corporation to meet peak load and excess demand. Remaining important tasks were to find and enlist a source to finance the engineering and construction of the test wind-turbine unit and a manufacturer to engineer and fabricate the unit according to Putnam's design. Again, Knight was able to provide invaluable insight and assistance. In the early fall of 1939, he introduced Putnam to Beauchamp Smith, then vice president of the family-owned S. Morgan Smith Company of York, Pennsylvania. The Smith Company was a small but highly successful long-time manufacturer of pump turbines and controllable-pitch hydraulic turbines. Recognizing that the market for such products in New England was dwindling because most of the commercially feasible hydroelectric sites had been exploited, the company was interested in developing new products, including those related to wind power. The Smith Company agreed to finance, engineer, and build the Smith-Putnam wind turbine. In the words of Beauchamp Smith, the company was eager “…to test the feasibility of large-scale utilization of the natural energy available in wind for the production of electricity in commercial quantities and to learn something of the economics involved.” Palmer Putnam served as project manager at the request of Smith, and John Wilbur, head of the MIT Department of Civil Engineering, was retained as structural consultant. Wilbur later served as chief engineer of the project, reporting to George Jessop, chief engineer of the Smith Company. Jessop had overall supervision of the project, and Stanton Dornbirer, also of the Smith Company, was put in charge of the field erection of the wind turbine and its supporting structure. General Electric agreed to develop and provide the necessary electrical generator and other equipment at cost. With these participants and other leading authorities in their fields in place, the final overall design and functional specification of the Smith-Putnam wind turbine test unit were finalized (see Figure 1). The design included a 175-ft (53.3-m) diameter rotor consisting of two stainless steel blades, each about 66 ft (20 m) long by 11 ft (3.4 m) wide. The blades each weighed 8 tons (7.3 metric tons) and were connected to a hub mechanism attached to the turbine unit about 120 ft (36.6 m) above grade. The General Electric generator was a synchronous machine rated at 1,250 kVA at 2,400 V. It operated at 600 r/min. The steel lattice tower on top of which the unit was mounted rose 110 ft (33.5 m) above grade. The turbine mechanism and associated equipment were supported on a box-type pintle girder about 40 ft (12.2 m) long and 8 ft (2.4 m) wide. The pintle girder was rigidly fixed to a vertical shaft supported by upper and lower antifriction pintle shaft bearings. This pintle mechanism allowed the downwind turbine to rotate in yaw in response to changes in wind direction. Regulation of electric power output was achieved by hydraulically controlling the pitch of the two blades using a speed governor that operated in response to variations in the rotational speed of the main turbine shaft. After much investigation, it was decided to install the test unit on a then-unnamed mountain on the border of Castleton and West Rutland, Vermont, in the western foothills of the Green Mountains. The summit of this smoothly glaciated peak was at 2,000 ft (610 m), high enough to take advantage of increased wind velocity but low enough to avoid destructive winter icing conditions. When the mountain was purchased for the project from a farmer whose family had long referred to the site as “Grandpa's,” the project team named the peak Grandpa's Knob because of this local reference and the smoothly rounded shape of the summit. ConstructionThe outbreak of World War II in Europe in September 1939 and the growing threat of war in the Pacific had a significant impact on the project. Many correctly believed that the United Stated would be drawn into the war and that resources for other than military needs would quickly become scarce. As a result, some design decisions concerning the wind turbine were made without completing the full complement of studies and tests that would have likely revealed hidden design flaws. This design expediency was implemented so that forgings and other critical items could be ordered and the fabrication process finished while materials and manufacturing capacity were still available. Taking this calculated risk contributed to some of the mechanical and structural problems encountered with the test unit, including the failure of one of the rotor blades that ended the test program in 1945. Second, the Smith Company experienced rapid growth in orders for its regular hydraulic turbine products because its customers shared the view that materials for civilian use were soon likely to be in short supply. In addition, the Smith Company was called upon to begin producing some items for the federal government during a military buildup that began at that same time. This backlog at the Smith Company made it necessary to outsource much of the engineering and fabrication of the components of the Smith-Putnam wind turbine test unit.The Wellman Engineering Company of Cleveland, Ohio, designers and manufacturers of mining and material handling equipment, was enlisted to complete the mechanical design of the blade roots, hub, and tower cap. The fabrication and erection of the supporting tower was undertaken by the American Bridge Company of Pittsburgh, Pennsylvania, as was the design and manufacture of the steel spars used in the turbine blades. The completed spars were shipped to the Philadelphia plant of the Budd Company, famous for its design and construction of stainless steel railroad cars. Budd designed and fabricated the stainless steel skin of the blades and the stainless steel ribs that supported the skin (see Figure 2). The completed blades were then shipped to the Wellman Engineering Company for the construction and fitting of the hub and the remainder of the rotating mechanism (see Figure 3). After the shop assembly and static balancing of the rotor in early 1941, it was shipped to West Rutland, Vermont. Field erection of the test unit at the site began in August 1940 following the construction in six weeks of a 2.2 mi (3.5 km) access road connecting the Vermont road system with the summit of Grandpa's Knob. The maximum grade on this steep road-way approached 15%, and nowhere was the grade less than 12%. Early in the project, it was realized that little was known about the behavior of wind in mountainous terrain. Between 1940 and 1945, the project conducted a comprehensive study of the interaction of wind and mountain height and the effect of the geometry and profile of a given site upon wind velocity and airflow. Recording anemometers and other meteorological instruments were installed and monitored at 20 sites, with 16 in the Green Mountains of Vermont, one in New Hampshire, and three in Massachusetts. A guyed 185-ft (56.4-m) meteorological tower, referred to as the “Christmas tree,” was installed at the summit of Grandpa's Knob with instrumentation to comprehensively monitor and record wind and weather conditions at that site. The wind research program was under the direction of Sverre Petterssen, head of the MIT Department of Meteorology and former director of the weather bureau in Bergen, Norway. The mass of data collected and analyzed by Pet-terssen and his expert staff contributed greatly to the body of knowledge concerning wind and its behavior in mountainous terrain. The wind turbine's four concrete tower footings were installed in the fall of 1940 to a depth of about 23 ft (7 m) into the mountain at the summit. The footings were completed in early December, and the lattice tower structure was erected by the American Bridge Company during the following two months. Work continued through the winter of 1940–1941 with temperatures as low as –18 °F (–27.8 °C) and with wind velocities as high as 60 mi/h (97 km/h). By taking advantage of the winter to move as much heavy material as possible, the spring thaw and its adverse effect on the roads was avoided. Hauling the major components of the unit to the summit of the mountain was done using a truck to pull the trailer with a half track in front of the truck and one or two large bulldozers either pushing or pulling as needed. One incident that delayed the project occurred on a bitterly cold and windy day at a hairpin turn in the access road about 1,000 ft (305 m) below the summit of Grandpa's Knob. The pintle girder with the pintle shaft and the upper and lower main bearings attached was being moved through the hairpin turn when the lashings securing the assembly to the trailer broke. The 43-ton (39-metric ton) pintle girder assembly rolled off the trailer and into a ditch next to the access road. Inspection showed that no serious damage had occurred, and after three weeks of rigging and blocking, the pintle girder assembly was again on its way to the top of the mountain. The turbine assembly arrived at the West Rutland rail yard of the Vermont Marble Company in March 1941. The blades and the hub mechanism were moved to the foot of the mountain between 15 March and 1 May. The pintle girder assembly was hoisted into place on 15 May 1941. The first blade made the trip to the top of the mountain in early August (see Figure 4). After being lifted into place and attached to the hub, the blade and rotor assembly had to be rotated through 180 of arc so that the first blade was now pointing up. This made it possible to install the second blade. By mid-August, the Smith-Putnam wind turbine test unit stood complete at the summit of Grandpa's Knob (see Figure 5). Testing and OperationA field office under the direction of Wilbur, chief engineer, was set up in Rutland in July 1941. A small staff was assigned to this office to conduct the test program. After checking the mechanics of the unit and the controls, it was decided that operational testing should begin. The blades of the unit turned in the wind for the first time on 29 August 1941. The engineers conducted many test runs at no load, starting at very low speed and gradually changing the pitch of the blades to increase rotor speed. After several weeks, the wind turbine was operated at its full speed of 28.7 r/min, but at no load.The first time that electrical energy produced by the wind was synchronously delivered into the CVPS electric utility system occurred on the evening of 19 October 1941, in the presence of executives of CVPS and with the owners of the S. Morgan Smith Company participating by long-distance telephone. After bringing the turbine up to speed at no load over a period of 20 min in a gusty 25-mi/h (40-km/h) northeast wind, William Bagley of General Electric phased the unit into the CVPS system. The time was 6:56 p.m. This first operational test lasted until 8:35 p.m. with the wind turbine carrying loads which varied from zero to 700 kW. The news release reported, “There was no difficulty. Operation was smooth. Regulation was good.” In the following weeks and months, many adjustments were made to improve the operation of the unit and to correct design flaws and other problems that were uncovered. Over the next 16 months, the unit operated about 1,000 h, produced electrical energy in wind velocities up to 70 mi/h (113 km/h), and withstood gales up to 115 mi/h (185 km/h) while not operating. A main turbine shaft bearing failed on 21 February 1943, and operations were halted until a replacement could be manufactured and installed. Because of the wartime shortage of both materials and available manufacturing capacity, a replacement bearing could not be secured until early 1945. The wind turbine returned to service on 3 March 1945 as a CVPS generating station with three shifts of CVPS operators and three shifts of inspectors supplied by the Smith Company. The unit ran, without incident, for a total of 143 h and 25 min over the next three weeks, carrying an average load of 431 kW. On 26 March 1945, the wind velocity was only 5 mi/h (8 km/h) at midnight, insufficient to operate the wind turbine. The wind velocity increased to a steady 25-mi/h (40-km/h) southwest wind over the next several hours, and the unit was phased in to the CVPS system at 2:55 a.m., carrying a load of up to 475 kW. At 3:10 a.m., Harold Perry was on duty in the powerhouse at the top of the tower. He was separated from the control panel by the rotating 24-in (61-cm) diameter main turbine shaft. He was suddenly thrown against the wall by a strong concussion. After being knocked down two more times in rapid succession, Perry managed to dive over the rotating shaft, reach the control panel, and override the automatic controls, thus feathering the turbine and bringing the unit to a full stop. One of the two turbine blades had separated from the hub at the blade root, had flown some 1,000 ft (305 m) through the air, and landed about 750 ft (229 m) down the mountain slope. Perry's prompt action had prevented further serious damage to the wind turbine. It was later calculated that the blade had separated while at approximately the 7 o'clock position and that the hub, with its remaining blade, made three revolutions at full speed and another four revolutions as it slowed to a stop. The catastrophic blade failure had occurred at a known weak point in the rotor structure. Cracks in the blade skin at the blade roots were discovered as early as May 1942 after only 360 h of operation. Inspection showed that the blade spars had failed due to a number of cracks across 90% of their cross-sectional area. As a result, the centrifugal force in tension of the operating rotor was being withstood by only a small portion of the steel spar. Perhaps this weakness would have been discovered if, as discussed earlier, sufficient time had been available in the design and engineering stages to allow for complete study and testing. Field repairs were made to the blade roots in 1942, but Wilbur remained apprehensive that the stresses in the root sections were significantly greater than had been earlier calculated. In early 1945, when the restart of the unit after the 1943 main bearing failure was approaching, he recommended that the unit be taken out of service after the test program was completed and that completion of the test program be expedited. After the blade failure, it was initially believed that repairs could be made fairly quickly (an improved blade root section had already been included in the design of a potential future production unit) and the test unit put back into service. However, wartime shortages of materials and manufacturing capacity remained a serious problem. Also, the cost to produce electricity by conventional means was significantly lower than the cost to produce power from the wind at that time. A 1945 study led by Carl Wilcox and Stanton Dornbirer indicated that a block of six modified test units comprising a total of 9 MW and located on the 4,000-ft (1,219-m) high Lincoln Ridge in Vermont could be installed at that time for about US$190 per kW. However, the value of such capacity to CVPS was determined to be only about US$125 per kW. The S. Morgan Smith Company had spent more than US$1,250,000 on the test unit and program, and the directors concluded that it would not be prudent for that small company to invest further in the project, especially since there was no clear prospect of economic gain. In November 1945, the company reluctantly decided to abandon the Smith-Putnam wind turbine project and to place all of the patents and patent applications in the public domain. EpilogueThe Smith-Putnam wind turbine unit was dismantled and removed from Grandpa's Knob in mid-1946. All that remains at the site today are the four concrete footings for the tower legs and a steel plaque on which the names of those who had worked at the site are engraved. While the unit operated only some 1,100 h during its short, 3 1/2-year life, it was an engineering success that had a significant impact on today's large-scale development of wind-produced electrical energy. In his 1946 introduction to Palmer C. Putnam's detailed book on the project and the prospect for the development of wind power, Power from the Wind, Dr. Vannevar Bush, the distinguished scientist and former dean of engineering at MIT, best summed up what the project achieved: “The great wind-turbine on a Vermont mountain proved that men could build a practical machine which would synchronously generate electricity in large quantities by means of wind-power. It proved also that the cost of electricity so produced is close to that of the more economical conventional methods. And hence it proved that at some future time homes may be illuminated and factories may be powered by this new means.” For Further ReadingP. C. Putnam, Power from the Wind. New York: Van Nostrand Reinhold Company, 1948. P. Gipe, Wind Energy Comes of Age. New York: Wiley, 1995. P. Gipe. (2009) Comprehensive Web site on wind energy [Online]. Available: http://www.wind-works.org P. Gipe. (2009) Smith-Putnam industrial photos [Online]. Available: http://www.wind-works.org/photos/Smith-PutnamPhotos.html | |
