Steam turbines power an industry
A condensed history of steam turbines
By John C. Zink, Ph.D., P.gif.,Managing Editor
In 1896 a young New Yorker named Charles G. Curtis presented E. W. Rice Jr., vice president of the new General Electric Co., with an idea for a radically new way to drive dynamos: a high-speed turbine device to be driven by steam. Also in 1896, J. Frank Duryea in Springfield, Mass., built the first of what he hoped to be a large number of factory-produced horseless carriages. That same year Charles Dow formulated a method to track the performance of the New York stock exchange and included Thomas Edison`s fledgling General Electric Co. (GE) in his first list of Dow Jones industrial stocks. And in Philadelphia, a new magazine, The Practical Engineer, was established to meet the needs of those who were attempting to deal with all the new mechanical technology that was blossoming throughout America.
As the next century passed, many people recognized the potential of the steam turbine and devoted significant effort and resources to refining and improving it. These engineers applied advances in the knowledge of thermodynamics and aerodynamics, developments in metallurgy and new manufacturing techniques, and improved the new machine until it reached its current status as the dominant technology for producing electricity world wide.
Steam power rises
The steam turbine shares its conceptual basis with both the gas turbine and the steam boiler. All of these trace to 62 AD when Hero of Alexandria demonstrated the basic principle of action and reaction with his boiler and rotating sphere device called the Aeolipile. The steam turbine next showed up in 1629, when Giovanni Brance experimented with blowing a jet of steam against a modified water wheel. The wheel turned, but the device did not have enough power to do any useful work.
The earliest useful work obtained from a steam-powered machine was not from a turbine, however. It was from a reciprocating device, the steam engine. Thomas Savery invented the first known machine of this type in 1698. Its function was to pump water using the vacuum created by condensing steam. Just a few years later, in 1705, Thomas Newcomen produced an “atmospheric engine” which had a piston connected to a large crossbeam. Newcomen introduced steam into a cylinder and the steam pressure raised the piston. Next, he reversed the process by spraying cold water into the cylinder, condensing the steam and allowing the piston to move back down in the cylinder. This up and down movement of one end of the crossbeam caused the other end to move in the opposite direction, operating a pump.
James Watt, who is often credited with being the father of the steam engine, first got involved by repairing one of Newcomen`s machines. In 1765, Watt created an improved version of the engine. But it took a totally unrelated event, Thomas Edison`s invention of the electric light bulb in 1879, to create the impetus for serious refinement of the steam engine and, eventually, for development of the steam turbine.
Engines vs. turbines
The first central station for generating electricity was Edison`s Pearl Street Station in New York. It had six dynamos, each connected to a 750 hp steam engine. This landmark power plant began furnishing electricity to nearby customers at precisely 3:00 p.m. Sept. 4, 1882, when one of Edison`s men closed the breaker at Pearl Street. Edison, himself, with a flair for the dramatic, turned on the first light–in financier J. P. Morgan`s office on Wall Street a half mile away. Pearl Street Station initially served 59 customers with a 72 kW load, made up of about 1,300 16-candlepower dc lamps. That load grew tenfold in the ensuing three years.
Once Pearl Street Station had demonstrated the feasibility of central station electricity, the demand grew rapidly. Initially, Edison`s system needed a large number of scattered power plants because it utilized direct current, and dc transmission was uneconomical over large distances. In 1885, George Westinghouse`s Union Switch & Signal Co. acquired rights to manufacture and sell a European-design transformer, and the company then developed ac distribution capability to utilize its transformers. This made longer-distance transmission of electricity practical, and Westinghouse Electric Co. was formed to exploit this device. By 1900 there were numerous dc, and a few ac, generating stations in the United States, all with reciprocating steam engines or hydraulic turbines as prime movers.
Although they were reliable, the early steam engines were huge, heavy devices that were not very efficient. Thus, nearly all companies in the electric equipment business seized the opportunity to develop the steam turbine as an alternative. In 1897, GE entered into an agreement with Charles Curtis, who directed turbine development work at GE until 1900, to exploit his patent (No. 566,969) for the Curtis steam turbine. In 1895, Westinghouse acquired rights to manufacture reaction turbines invented and patented in 1884 by the English inventor, Thomas Parsons. Allis-Chalmers also acquired rights to manufacture under Parsons` patents, so early machines of these two manufacturers were quite similar.
The Curtis and the Parsons turbine designs were based on different fundamental principles of fluid flow. The Curtis turbine was an impulse design, where the steam expands through nozzles so it reaches a high velocity. The high-velocity, low-pressure steam jet then impacts the blades of a spinning wheel. In a reaction turbine such as the Parsons design, the steam expands as it passes through both the fixed nozzles and the rotating blades. While the difference appears subtle, it affects the shape and size of the nozzles and blades. In most modern steam turbines the high-pressure stages are impulse blades. The steam pressure drops quickly through these stages, thus reducing the stress on the high pressure turbine casing. The many subsequent stages may be either impulse or reaction designs.
Turbines win a round
GE assigned one of its engineers, William LeRoy Emmett, to redesign and improve the Curtis machine. He made major changes in the shape and arrangement of the buckets and nozzles so the turbine`s efficiency would exceed that of reciprocating engines. To prove the success of his design, Emmett engaged Prof. J.gif. Denton of Stevens Institute of Technology to witness the GE turbine tests. Professor Denton observed tests on Aug. 24, 1900, and confirmed that at a 150-psi boiler pressure, with 27.7-inch vacuum, and running at 4,500 rpm, the test turbine developed 272.3 hp with a dry steam consumption of 15.12 lb. per hp-hr. At that time the average economy of condensing reciprocating engines with similar hp was about 19.7 lb per hp-hr. The steam turbine had shown it could compete with the reciprocating engines of the day. Efficiency comparisons between steam turbines and steam engines continued to be a topic of general interest for several years. The Feb. 15, 1902, issue of The Engineer reported on the favorable efficiency and economics of the new steam turbines.
GE placed its first turbine into operation in Schenectady, N.Y., in November 1901. This 500 kW turbine operated at 1,200 rpm and had a horizontal shaft and two multiple-row blade wheels in separate casings. A crossover pipe below floor level contained a baffle and a separator for moisture removal. GE built a second machine, a 500 kW, 1,800-rpm unit with a vertical shaft, and subsequently shipped it to Newport, R.I., for use in a new generating station.
Encouraged by the success of the Newport installation, in 1902 GE offered vertical-axis turbines with ratings of 500, 1,500 and 5,000 kW. Emmett said, “a vertical shaft arrangement would accomplish many simplifications and would save space and cost.” Besides, GE already had facilities in place to test the vertical-shaft Niagara Falls hydro generators and could use the same test facilities to test vertical-shaft steam turbines.
Samuel Insull, who had been Thomas Edison`s private secretary, was GE`s first turbine customer. Insull had started his own company, Chicago Edison (predecessor of today`s Commonwealth Edison), to exploit Edison`s inventions. Chicago Edison ordered two 500 kW turbines for its new Fisk Street power station, and Insull witnessed the successful first test of the first turbine on March 7, 1903. One of these original Fisk Street turbines is on display in front of the former GE steam-turbine laboratory in Schenectady.
After building and shipping more than 20,000 kW in vertical axis machines by 1913, GE abandoned that design and went to horizontal axis machines only.
From 1903 to 1907, GE obtained 49 steam-turbine related patents, of which 14 proved important to future steam-turbine performance. In 1903, the automatic governor appeared. In 1905 and 1906, patents were issued for reheating steam during expansion. A mechanism to adjust for longitudinal expansion of the rotor was patented in 1905. In 1907, GE patented an impulse machine with full peripheral admission and increasing bucket lengths from stage to stage.
Turbines by George
George Westinghouse`s company actually built and shipped its first steam turbine before Edison`s company did. In 1897, Westinghouse built a 120 kW turbine for Nichols Chemical Co. In 1899, Westinghouse installed three of its turbines to provide power at its own Westinghouse Air Brake Co. The pioneer U.S. central station turbine was Westinghouse serial number 8, a 1,500 kW, 1,200-rpm unit installed in 1900 by the Hartford Electric Light Co. By 1907, Westinghouse was producing turbines of an improved design, with impulse blading instead of reaction blades. This redesign improved part-load efficiency, enabled the use of more control valves for finer control and decreased turbine length.
Allis in turbineland
As early as 1901, Allis-Chalmers had experimented with building the Parsons reaction turbine. For example, it had constructed a single-wheel radial steam turbine designed for 300 hp, but it could not produce more than 12 hp. Development continued, and by 1907 Allis-Chalmers` Parsons steam turbines were serving industrial customers, with the central station business going largely to Allis-Chalmers` two biggest competitors. In 1908, Allis-Chalmers sold a 3,250 kW unit, the largest 1,800 rpm unit in the United States, to the Virginia Passenger and Railway Co. In 1910, Allis-Chalmers sold three similar units, with capacity of 4,500 kW each, for a new central station at West Reading, Penn.
After more than a half century of producing steam-turbines, Allis-Chalmers ceased steam turbine production in 1962. Allis-Chalmers then combined with Siemens to begin production again in the late 1960s.
C. E. L. Brown, cofounder of Brown-Boveri Corp. (BBC), invented an ac generator with a high-speed, smooth rotor that had the conductors placed in longitudinally milled slots. To exploit this device, BBC established the Brown-Boveri-Parsons Company for Steam Turbines in Baden, Germany, on April 19, 1900. This company had the exclusive rights to the Parsons patent in Switzerland, Germany, France and Russia. BBC delivered its first steam turbine, a 250 kW machine operating at 3,000 rpm, in 1901. By the middle of 1902, BBC had produced 17 steam turbines and generators with output totaling more than 15,000 kW. Only four years after it started manufacturing steam turbines, these devices comprised nearly half of BBC sales.
James Moore founded the Moore turbine company in 1916 in Wellsville, N.Y., after he left his job at the Kerr Steam Turbine Co. across town. In the 1920s, the Moore product line grew to include turbines up to 4,500 kW. After numerous purchases and mergers, including merger with the Terry Turbine Co., founded in 1906, the company became what is now known as Dresser-Rand.
Many early steam turbine generators served 25 H¥traction power systems and operated at 750 or 1,500 rpm. After about 1925, utilities stopped adding 25 H¥power and adopted 60 H¥power. Thus, the wide variety of turbine speeds–720, 750, 1,200, 1,500 and 1,800 rpm–gave way to standardization on either 1,800 or 3,600 rpm. Materials advances led to ever-improving efficiency as forged steel parts replaced cast iron. Development of improved steel alloys in the 1920s, and of chrome-moly steels a little later, allowed designers to increase inlet steam temperatures from 500 F to beyond 900 F, with pressures increasing at the same time. Designers also pursued enhanced efficiency through more complex cycles, with regenerative feedwater heating added by the early 1920s and reheat added shortly thereafter.
Early turbines had bearings cooled by water pipes embedded in the bearing material. A 1921 patent issued to J.L. Roberts provided an arrangement of grooves, reversing the direction of flow, that allowed the lubricating oil to also provide the necessary cooling. No more water-cooled bearings were built.
Many of the early units were single-case designs, but with the increase in unit size, manufacturers adopted multiple-flow exhausts with separate shells for the high-pressure (HP) and low-pressure (LP) sections. For example, the State Line power station at Hammond, Ind., designed in the 1930s, had a 208,000 kW unit with one HP turbine and two double-flow LP turbines. Some of the larger reheat units even had two parallel flows in the HP section.
The 1930s also saw much experimentation with single- and multiple-shaft designs. Some cross-compound machines had HP elements operating at 1,600 rpm and LP elements operating at 1,800 rpm. The smaller, high-speed elements were conducive to efficient nozzle and bucket designs. There were a number of vertical compounds that had the HP turbine mounted directly over the LP turbine. In this case an HP turbine, running at 3,600 rpm, was small enough that it could be mounted, along with its generator, on top of the 1,800-rpm LP turbine.
Some customers wanted a single generator, and in 1930 GE built the first triple-tandem compound turbine generator. This unit operated at 1,800 rpm, with steam pressure and temperature of 600 psi and 750 F, respectively, and was built for a generating station at Powerton, Ill. Total output was 315,000 kW.
From the beginning, turbine designers have wanted to increase steam temperatures and pressures in order to increase efficiency. Standard pressures in the 1920s were 350 to 400 psi, but studies at that time showed significant performance improvements if pressures could be advanced to 600 to 1,200 psi. Increased pressures, however, lead to excessive moisture content in the last stages of the LP turbine. Metallurgical advancements in the 1930s permitted increases in initial steam temperatures and pressures by providing alloy steels that could withstand this increased moisture at the exhaust. These advances made reheat unnecessary. Designers continued to increase steam temperature and pressure so, by the early 1940s, steam temperatures from 900 F to 1,050 F and pressures of 1,400 to 2,300 psig were common. With these conditions, manufacturers were again pushing the metallurgical limits in the latter LP stages and reheat again became necessary.
The first commercial steam turbines in the United States were rated at 1.5 MW. From 1910 to about 1920, 30 to 70 MW units were common. By 1945, the median size unit sold in the United States was still only 100 MW, but by 1967 the median size unit had increased to 700 MW. Today, the average size is somewhat smaller, but the decrease is the result of non-technical factors, mostly the prevalence of cogeneration and independent power units in the present-generation mix. Efficiencies have continued to improve and supercritical steam conditions on the order of 3,500 psi and 1,000 F are common. Steam turbines now comprise 586 million kW of capacity, or approximately 78 percent of all the generation capability in this country.
Both the steam turbine and the automobile have become major forces in American society over the past century. The Dow Jones Industrial Average still includes GE and is still the most widely watched index of stock market performance. And The Practical Engineer, after a number of iterations, is today`s Power Engineering, still serving the needs of those dealing with power generation technology. It has been quite a century. z
Ronald L. Bannister and Silvestri Jr., G.J., “Evolution of the Central Station Steam Turbine in the United States,” presented at the American Society of Mechanical Engineers Winter Meeting, Chicago, Ill., November 1988.
F. Landis, “Steam Turbines,” America Online.
Ernest L. Robinson, “The Steam Turbine in the United States. III–Developments by the General Electric Co.,” Mechanical Engineering, April 1937.
A. Schwarzenbach, Hard, F., Mez, F. and Blum, W., “The Steam Turbine,” An article on the historical development on the occasion of the 75th anniversary of the Brown Boveri steam turbine, 1976.
The Engineer, Feb. 15, 1902, p.117.
“The Magnificent West Allis Works, 1902-1910,” Siemens Power Corp.
“Reheat,” Allis Chalmers Electrical Review, First Quarter, 1949.
“Pearl St. Station, Opened 50 Years Ago, Beginning of a Mighty Industry,” The GE Monogram, October 1932.
“A Legacy of Leadership,” General Electric Co.
“Brief History of the Dresser-Rand Steam Turbine Operation,” Dresser-Rand Co.
“Power Generation,” Hall of History Foundation, Schenectady, N.Y.
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First turbine-driven generator providing power from a central station–Hartford, Conn., 1901 (Westinghouse Electric Co.)
Dresser-Rand steam turbine factory, Wellsville, N.Y., 1940s (Dresser-Rand Steam Turbine, Motor and Generator Division)
Thomas A. Edison with C.P. Steinmentz, E.W. Rice Jr., and others in front of the GE 5,000 kW turbine-generator monument in Schenectady, N.Y., 1922
(Hall of History Foundation, Schenectady, N.Y.)
George Westinghouse, 1846-1914
In 1920 a GE engineer named Oscar Junggren, who had been responsible for most of the early GE turbine patents, was looking for estimates of the thermodynamic benefits of operating turbines at steam pressures up to 1,000 psi. Unfortunately, the Marks and Davis steam tables that were available at that time only went up to 600 psi, and even those numbers were an extrapolation from data taken at only 200 psi. Junggren convinced his professional colleagues of the need for better data, and ASME formed a committee to obtain and publish reliable steam properties at higher pressures. After eight years` work at Harvard, MIT and the Bureau of Standards, in 1930 ASME officially published the results as the well-known Keenan steam tables.