51204283-turbine

(1)

steam turbine

Dictionary: steam turbine Sponsored Links

MAN TURBO Steam Turbines

Compressors and turbines for industrial processes. www.manturbo.com

Steam Turbine

Sulzer Turbo Services: Repair, maintenance and refurbishment. www.sulzerts.com/steam_turbines

Home > Library > Literature & Language > Dictionary n.

A turbine operated by highly pressurized steam directed against vanes on a rotor.

• Answers.com ▼ ○ Home Page ○ Browse ○ Personalize ○ Print page ○ Email page ○ Translate page • WikiAnswers.com ▼ ○ Home Page ○ Browse ○ Recently Answered ○ Recently Asked ○ Unanswered questions • Search • Help • •

(2)

Top of Form

new ansGo

s te a m tu r b in e

• Browse: Unanswered questions | Most-recent questions | Reference library Bottom of Form

Enter a word or phrase...

Top of Form All

0

Community Q&A Reference topics s te a m tu r b in e

History

The first device that may be classified as a reaction steam turbine was little more than a toy, the classic Aeolipile, described in the 1st century by Hero of Alexandria in Roman Egypt.[1][2][3]_A

thousand years later, the first impact steam turbine with practical applications was invented in 1551 by Taqi al-Din in Ottoman Egypt, who described it as a prime mover for rotating a spit. Similar smoke jacks were later described by John Wilkins in 1648 and Samuel Pepys in 1660. Another steam turbine device was created by Italian Giovanni Branca in 1629.[4]

The modern steam turbine was invented in 1884 by the Englishman Charles A. Parsons, whose first model was connected to a dynamo that generated 7.5 kW of electricity. His patent was licensed and the turbine scaled-up shortly after by an American, George Westinghouse. A number of other variations of turbines have been developed that work effectively with steam. The de Laval turbine (invented by Gustaf de Laval) accelerated the steam to full speed before running it against a turbine blade. This was good, because the turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam. It is also, however, considerably less efficient. The Parson's turbine also turned out to be relatively easy to scale-up. Within Parson's lifetime the generating capacity of a unit was scaled-up by about 10,000 times. [5]

(6)

Parsons turbine from the Polish destroyer ORP Wicher II

Types

Steam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines.

Steam Supply and Exhaust Conditions

These types include condensing, noncondensing, reheat, extraction and induction.

Noncondensing or backpressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are available. Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.

Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.

Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled.

Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

Casing or Shaft Arrangements

These arrangements include single casing, tandem compound and cross compound turbines. Single casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross

(7)

Principle of Operation and Design

An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly “isentropic”, however, with typical isentropic efficiencies ranging from 20%-90% based on the application of the turbine. The interior of a turbine

comprises several sets of blades, or “buckets” as they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage.

Turbine Efficiency

Schematic diagram outlining the difference between an impulse and a reaction turbine

To maximize turbine efficiency, the steam is expanded, generating work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as impulse or reaction turbines. Most modern steam turbines are a combination of the reaction and impulse design. Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.

Impulse Turbines

An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage.

As the steam flows through the nozzle its pressure falls from steam chest pressure to condenser pressure (or atmosphere pressure). Due to this relatively higher ratio of expansion of steam in the nozzle the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades is a large portion of the maximum velocity of the steam when leaving the nozzle. The loss

(8)

of energy due to this higher exit velocity is commonly called the "carry over velocity" or "leaving loss".

Reaction Turbines

In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.

Operation and Maintenance

When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also a turning gear is engaged when there is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven

expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10 to 15 RPM to slowly warm the turbine.

Problems with turbines are now rare and maintenance requirements are relatively small. Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. It is, however, essential that the turbine be turned with dry steam. If water gets into the steam and is blasted onto the blades (moisture carryover) rapid impingement and erosion of the blades can occur, possibly leading to imbalance and catastrophic failure. Also, water entering the blades will likely result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine.

Speed regulation

The control of a turbine with a governor is essential, as turbines need to be run up slowly, to prevent damage while some applications (such as the generation of alternating current electricity) require precise speed control. Uncontrolled acceleration of the turbine rotor can lead to an

overspeed trip, which causes the nozzle valves that control the flow of steam to the turbine to close. If this fails then the turbine may continue accelerating until it breaks apart, often spectacularly. Turbines are expensive to make, requiring precision manufacture and special quality materials.

Direct drive

Electrical power stations use large steam turbines driving electric generators to produce most (about 80%) of the world's electricity. Most of these centralised stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their generators. As the generators must rotate at constant

synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. In installations with

(9)

high steam output, as may be found in nuclear power stations, the generator sets may be arranged to operate at half these speeds, but with four-pole generators.[6]

Speed reduction

The Turbinia - the first steam turbine-powered ship

Another use of steam turbines is in ships; their small size, low maintenance, light weight, and low vibration are compelling advantages. (Steam turbine locomotives were also tested, but with limited success.) A steam turbine is only efficient when operating in the thousands of RPM range while application of the power in propulsion applications may be only in the hundreds of RPM and so requiring that expensive and precise reduction gears must be used, although several ships, such as Turbinia, had direct drive from the steam turbine to the propeller shafts. This purchase cost is offset by much lower fuel and maintenance requirements and the small size of a turbine when compared to a reciprocating engine having an equivalent power, except for diesel engines which are capable of higher efficiencies. Steam turbine efficiencies have yet to break 50% yet diesel engines routinely exceed 50%, especially in marine applications.[7][8][9][10]

References

1. ^ turbine. Encyclopedia Britannica Online

2. ^ A new look at Heron's 'steam engine'" (1992-06-25). Archive for History of Exact Sciences 44 (2): 107-124.

3. ^ O'Connor, J. J.; E. E. Roberston (1999). Heron of Alexandria. MacTutor

4. ^ Ahmad Y Hassan (1976). Taqi al-Din and Arabic Mechanical Engineering, p. 34-35. Institute for the History of Arabic Science, University of Aleppo.

5. ^ Parsons, Sir Charles A.. "The Steam Turbine".

http://www.history.rochester.edu/steam/parsons/part1.html.

6. ^ Leyzerovich, Alexander (2005). Wet-steam Turbines for Nuclear Power Plants. Tulsa OK: PennWell Books. pp. p111. ISBN 1593700326.

7. ^ www.ansys.com/assets/testimonials/siemens.pdf 8. ^ http://pepei.pennnet.com/display_article/152601/6/ARTCL/none/none/1/New-Benchmarks-for-Steam-Turbine-Efficiency/ 9. ^ http://en.wikipedia.org/wiki/Wärtsilä-Sulzer_RTA96-C 10.^ https://www.mhi.co.jp/technology/review/pdf/e451/e451021.pdf

External link

• Steam Turbines: A Book of Instruction for the Adjustment and Operation of the Principal Types of this Class of Prime Movers by Hubert E. Collins.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Donate to Wikimedia

http://www.answers.com/topic/steam-turbine

wind turbine

Dictionary: wind turbine (wĭnd) Sponsored Links

Used Steam Turbines

Europe's largest provider of used Steam Turbines & Power Plants www.lohrmann.com

Siemens answers:

Efficient energy supply with Offshore Windparks. www.Siemens.com/Answers

A turbine that is powered by the wind.

• Answers.com ▼ ○ Home Page

(11)

○ Browse ○ Personalize ○ Print page ○ Email page ○ Translate page • WikiAnswers.com ▼ ○ Home Page ○ Browse ○ Recently Answered ○ Recently Asked ○ Unanswered questions • Search • Help • •

Search unanswered questions...

Top of Form

new ansGo

w in d tu r b in e

Top of Form

All 0

Community Q&A Reference topics w in d tu r b in e

Background

A wind turbine is a machine that converts the wind's kinetic energy into rotary mechanical energy, which is then used to do work. In more advanced models, the rotational energy is converted into electricity, the most versatile form of energy, by using a generator.

For thousands of years people have used windmills to pump water or grind grain. Even into the twentieth century tall, slender, multi-vaned wind turbines made entirely of metal were used in American homes and ranches to pump water into the house's plumbing system or into the cattle's watering trough. After World War I, work was begun to develop wind turbines that could

produce electricity. Marcellus Jacobs invented a prototype in 1927 that could provide power for a radio and a few lamps but little else. When demand for electricity increased later, Jacobs's small, inadequate wind turbines fell out of use.

The first large-scale wind turbine built in the United States was conceived by Palmer Cosslett Putnam in 1934; he completed it in 1941. The machine was huge. The tower was 36.6 yards (33.5 meters) high, and its two stainless steel blades had diameters of 58 yards (53 meters). Putnam's wind turbine could produce 1,250 kilowatts of electricity, or enough to meet the needs of a small town. It was, however, abandoned in 1945 because of mechanical failure.

With the 1970s oil embargo, the United States began once more to consider the feasibility of producing cheap electricity from wind turbines. In 1975 the prototype Mod-O was in operation. This was a 100 kilowatt turbine with two 21-yard (19-meter) blades. More prototypes followed (Mod-OA, Mod-1, Mod-2, etc.), each larger and more powerful than the one before. Currently, the United States Department of Energy is aiming to go beyond 3,200 kilowatts per machine. Many different models of wind turbines exist, the most striking being the vertical-axis Darrieus, which is shaped like an egg beater. The model most supported by commercial manufacturers, however, is a horizontal-axis turbine, with a capacity of around 100 kilowatts and three blades not more than 33 yards (30 meters) in length. Wind turbines with three blades spin more

smoothly and are easier to balance than those with two blades. Also, while larger wind turbines produce more energy, the smaller models are less likely to undergo major mechanical failure, and thus are more economical to maintain.

Wind farms have sprung up all over the United States, most notably in California. Wind farms are huge arrays of wind turbines set in areas of favorable wind production. The great number of interconnected wind turbines is necessary in order to produce enough electricity to meet the needs of a sizable population. Currently, 17,000 wind turbines on wind farms owned by several wind energy companies produce 3.7 billion kilowatt-hours of electricity annually, enough to meet the energy needs of 500,000 homes.

Raw Materials

A wind turbine consists of three basic parts: the tower, the nacelle, and the rotor blades. The tower is either a steel lattice tower similar to electrical towers or a steel tubular tower with an inside ladder to the nacelle. Most towers do not have guys, which are cables used for support, and most are made of steel that has been coated with a zinc alloy for protection, though some are painted instead. The tower of a typical American-made turbine is approximately 80 feet tall and weighs about 19,000 pounds.

(13)

The nacelle is a strong, hollow shell that contains the inner workings of the wind turbine. Usually made of fiberglass, the nacelle contains the main drive shaft and the gearbox. It also contains the blade pitch control, a hydraulic system that controls the angle of the blades, and the yaw drive, which controls the position of the turbine relative to the wind. The generator and electronic controls are standard equipment whose main components are steel and copper. A typical nacelle for a current turbine weighs approximately 22,000 pounds.

The most diverse use of materials and the most experimentation with new materials occur with the blades. Although the most dominant material used for the blades in commercial wind turbines is fiberglass with a hollow core, other materials in use include lightweight woods and aluminum. Wooden blades are solid, but most blades consist of a skin surrounding a core that is either hollow or filled with a lightweight substance such as plastic foam or honeycomb, or balsa wood. A typical fiberglass blade is about 15 meters in length and weighs approximately 2,500 pounds.

Wind turbines also include a utility box, which converts the wind energy into electricity and which is located at the base of the tower. Various cables connect the utility box to the nacelle, while others connect the whole turbine to nearby turbines and to a transformer.

The Manufacturing

Process

Before consideration can be given to the construction of individual wind turbines, manufacturers must determine a proper area for the siting of wind farms. Winds must be consistent, and their speed must be regularly over 15.5 miles per hour (25 kilometers per hour). If the winds are stronger during certain seasons, it is preferred that they be greatest during periods of maximum electricity use. In California's Altamont Pass, for instance, site of the world's largest wind farm, wind speed peaks in the summer when demand is high. In some areas of New England where wind farms are being considered, winds are strongest in the winter, when the need for heating increases the consumption of electrical power. Wind farms work best in open areas of slightly rolling land surrounded by mountains. These areas are preferred because the wind turbines can be placed on ridges and remain unobstructed by trees and buildings, and the mountains

concentrate the air flow, creating a natural wind tunnel of stronger, faster winds. Wind farms must also be placed near utility lines to facilitate the transfer of the electricity to the local power plant.

Preparing the site

• Wherever a wind farm is to be built, the roads are cut to make way for transporting parts. At each wind turbine location, the land is graded and the pad area is leveled. A concrete foundation is then laid into the ground, followed by the installation of the underground cables. These cables connect the wind turbines to each other in series, and also connect all of them to the remote control center, where the wind farm is monitored and the electricity is sent to the power company.

Erecting the tower

• Although the tower's steel parts are manufactured off site in a factory, they are usually assembled on site. The parts are bolted together before erection, and the tower is kept horizontal until placement. A crane lifts the tower into position, all bolts are tightened, and stability is tested upon completion.

(14)

Nacelle

• The fiberglass nacelle, like the tower, is manufactured off site in a factory. Unlike the tower, however, it is also put together in the factory. Its inner workings—main drive shaft, gearbox, and blade pitch and yaw controls—are assembled and then mounted onto a base frame. The nacelle is then bolted around the equipment. At the site, the nacelle is lifted onto the completed tower and bolted into place.

Rotary blades

• Aluminum blades are created by bolting sheets of aluminum together, while wooden blades are carved to form an aerodynamic propeller similar in cross-section to an airplane wing.

• By far the greatest number of blades, however, are formed from fiberglass. The

manufacture of fiberglass is a painstaking operation. First, a mold that is in two halves like a clam shell, yet shaped like a blade, is prepared. Next, a fiberglass-resin composite mixture is applied to the inner surfaces of the mold, which is then closed. The fiberglass mixture must then dry for several hours; while it does, an air-filled bladder within the mold helps the blade keep its shape. After the fiberglass is dry, the mold is then opened and the bladder is removed. Final preparation of the blade involves cleaning, sanding, sealing the two halves, and painting.

• The blades are usually bolted onto the nacelle after it has been placed onto the tower. Because assembly is easier to accomplish on the ground, occasionally a three-pronged blade has two blades bolted onto the nacelle before it is lifted, and the third blade is bolted on after the nacelle is in place.

Installation of control systems

• The utility box for each wind turbine and the electrical communication system for the wind farm is installed simultaneously with the placement of the nacelle and blades. Cables run from the nacelle to the utility box and from the utility box to the remote control center.

Quality Control

Unlike most manufacturing processes, production of wind turbines involves very little concern with quality control. Because mass production of wind turbines is fairly new, no standards have been set. Efforts are now being made in this area on the part of both the government and

manufacturers.

While wind turbines on duty are counted on to work 90 percent of the time, many structural flaws are still encountered, particularly with the blades. Cracks sometimes appear soon after manufacture. Mechanical failure because of alignment and assembly errors is common. Electrical sensors frequently fail because of power surges. Non-hydraulic brakes tend to be reliable, but hydraulic braking systems often cause problems. Plans are being developed to use existing technology to solve these difficulties.

Wind turbines do have regular maintenance schedules in order to minimize failure. Every three months they undergo inspection, and every six months a major maintenance checkup is

scheduled. This usually involves lubricating the moving parts and checking the oil level in the gearbox. It is also possible for a worker to test the electrical system on site and note any problems with the generator or hookups.

(15)

Environmental Benefits

and Drawbacks

A wind turbine that produces electricity from inexhaustible winds creates no pollution. By comparison, coal, oil, and natural gas produce one to two pounds of carbon dioxide (an emission that contributes to the greenhouse effect and global warming) per kilowatt-hour produced. When wind energy is used for electrical needs, dependence on fossil fuels for this purpose is reduced. The current annual production of electricity by wind turbines (3.7 billion kilowatt-hours) is equivalent to four million barrels of oil or one million tons of coal.

Wind turbines are not completely free of environmental drawbacks. Many people consider them to be unaesthetic, especially when huge wind farms are built near pristine wilderness areas. Bird kills have been documented, and the whirring blades do produce quite a bit of noise. Efforts to reduce these effects include selecting sites that do not coincide with wilderness areas or bird migration routes and researching ways to reduce noise.

The Future

The future can only get better for wind turbines. The potential for wind energy is largely untapped. The United States Department of Energy estimates that ten times the amount of electricity currently being produced can be achieved by 1995. By 2005, seventy times current production is possible. If this is accomplished, wind turbines would account for 10 percent of the United States' electricity production.

Research is now being done to increase the knowledge of wind resources. This involves the testing of more and more areas for the possibility of placing wind farms where the wind is reliable and strong. Plans are in effect to increase the life span of the machine from five years to 20 to 30 years, improve the efficiency of the blades, provide better controls, develop drive trains that last longer, and allow for better surge protection and grounding. The United States

Department of Energy has recently set up a schedule to implement the latest research in order to build wind turbines with a higher efficiency rating than is now possible. (The efficiency of an ideal wind turbine is 59.3 percent. That is, 59.3 percent of the wind's energy can be captured. Turbines in actual use are about 30 percent efficient.) The United States Department of Energy has also contracted with three corporations to research ways to reduce mechanical failure. This project began in the spring of 1992 and will extend to the end of the century.

Wind turbines will become more prevalent in upcoming years. The largest manufacturer of wind turbines in the world, U.S. Windpower, plans to expand from 420 megawatt capacity (4,200 machines) to 800 megawatts (8,000 machines) by 1995. They plan to have 2,000 megawatts (20,000 machines) by the year 2000. Other wind turbine manufacturers also plan to increase the numbers produced. International committees composed of several industrialized nations have formed to discuss the potential of wind turbines. Efforts are also being made to provide developing countries with small wind turbines similar to those Marcellus Jacobs built in the 1920s. Denmark, which already produces 70 percent to 80 percent of Europe's wind power, is developing plans to expand manufacture of wind turbines. The turn of the century should see wind turbines that are properly placed, efficient, durable, and numerous.

Where To Learn More

(16)

Assessment of Research Needs for Wind Turbine Rotor Materials Technology. National Academy Press, 1991.

Eggleston, David M. Wind Turbine Engineering Design. Van Nostrand Reinhold, 1987.

Hunt, Daniel V. Windpower: A Handbook on Wind Energy Conversion Systems. Van Nostrand Reinhold, 1981.

Kovarik, Tom, Charles Pupher, and John Hurst. Wind Energy. Domus Books, 1979. Park, Jack. The Wind Power Book. Cheshire Books, 1981.

Putnam, Palmer Cosslett. Power from the Wind. Van Nostrand Company, 1948.

Periodicals

Frank, Deborah. "Blowing in the Wind," Popular Mechanics, August, 1991, pp. 40-43+. Mohs, Mayo. "Blowin' in the Wind," Discover. June, 1986, pp. 68-74.

Moretti, Peter M. and Louis V. Divone. "Modern Windmills," Scientific American. June, 1986, pp. 110-118.

Price, Marshall. "Basement-Built Wind Generator," Mother Earth News. July-August, 1986, p. 103.

Stefanides, E. J. "Hydraulic Yaw Control Upgrades Wind Turbine," Design News. March 3, 1986, p. 240.

Vogel, Shawna. "Wind Power," Discover. May, 1989, pp. 46-49. [Article by: Rose Secrest]

History

Main article: History of wind power

The world's first automatically operated wind turbine was built in Cleveland in 1888 by Charles F. Brush. It was 60 feet tall, weighed four tons and had 12kW turbine.[1]

(19)

Wind machines were used in Persia as early as 200 B.C.[2]_{This type of machine was introduced}

into the Roman Empire by 250 A.D. However, the first practical windmills were built in Sistan, Iran, from the 7th century. These were vertical axle windmills, which had long vertical

driveshafts with rectangle shaped blades.[3]_{Made of six to twelve sails covered in reed matting or}

cloth material, these windmills were used to grind corn and draw up water, and were used in the gristmilling and sugarcane industries.[4]

By the 14th century, Dutch windmills were in use to drain areas of the Rhine River delta. In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The first known electricity generating windmill operated was a battery charging machine installed in 1887 by James Blyth in Scotland, UK[citation needed]_{. The first windmill for electricity production in the United States was} built in Cleveland, Ohio by Charles F Brush in 1888, and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, most for water-pumping.[5]_{By the}

1930s windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.

A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines.[6]

The first utility grid-connected wind turbine operated in the UK was built by the John Brown Company in 1954 in the Orkney Islands. It had an 18 meter diameter, three-bladed rotor and a rated output of 100 kW.

Resources

Main article: Wind power

Wind turbines require locations with constantly high wind speeds. With a wind resource assessment it is possible to estimate the amount of energy the wind turbine will produce. A yardstick frequently used to determine good locations is referred to as Wind Power Density (WPD.) It is a calculation relating to the effective force of the wind at a particular location, frequently expressed in terms of the elevation above ground level over a period of time. It takes into account wind velocity and mass. Color coded maps are prepared for a particular area

described, for example, as "Mean Annual Power Density at 50 Meters." The results of the above calculation are included in an index developed by the National Renewable Energy Lab and referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class.[7]

Types of wind turbines

Wind turbines can be separated into two types based by the axis in which the turbine rotates. Turbines that rotate around a horizontal axis are more common. Vertical-axis turbines are less frequently used.

(20)

Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position

Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.[8]

Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount.

Downwind machines have been built, despite the problem of turbulence, because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds, the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since turbulence leads to fatigue failures, and reliability is so important, most HAWTs are upwind machines.

HAWT Subtypes

Doesburger windmill, Ede, The Netherlands. 12th-century windmills

These squat structures, typically (at least) four bladed, usually with wooden shutters or fabric sails, were developed in Europe. These windmills were pointed into the wind manually or via a tail-fan and were typically used to grind grain. In the Netherlands they were also used to pump water from low-lying land, and were instrumental in keeping its polders dry.

(21)

In Schiedam, the Netherlands, a traditional style windmill (the Noletmolen) was built in 2005 to generate electricity.[9]_{The mill is one of the tallest Tower mills in the world, being some}

42.5 metres (139 ft) tall. 19th-century windmills

The Eclipse windmill factory was set up around 1866 in Beloit, Wisconsin and soon became successful building mills for pumping water on farms and for filling railroad tanks. Other firms like Star, Dempster, and Aeromotor also entered the market. Hundreds of thousands of these mills were produced before rural electrification and small numbers continue to be made.[5]_They

typically had many blades, operated at tip speed ratios (defined below) not better than one, and had good starting torque. Some had small direct-current generators used to charge storage batteries, to provide power to lights, or to operate a radio receiver. The American rural electrification connected many farms to centrally-generated power and replaced individual windmills as a primary source of farm power by the 1950s. They were also produced in other countries like South Africa and Australia (where an American design was copied in 1876[10]_).

Such devices are still used in locations where it is too costly to bring in commercial power. Modern wind turbines

Three bladed wind turbine

Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of up to six times the wind speed, high efficiency, and low torque ripple, which contribute to good reliability. The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 metres (65 to 130 ft) or more. The tubular steel towers range from 200 to 300 feet (60 to 90 metres) tall. The blades rotate at 10-22 revolutions per minute.[11][12]_{A gear}

box is commonly used to step up the speed of the generator, although designs may also use direct drive of an annular generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with shut-down features to avoid damage at high wind speeds.

HAWT advantages

• Variable blade pitch, which gives the turbine blades the optimum angle of attack.

Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.

• The tall tower base allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%.

(22)

• High efficiency, since the blades always move perpendicularly to the wind, receiving power through the whole rotation. In contrast, all vertical axis wind turbines, and most proposed airborne wind turbine designs, involve various types of reciprocating actions, requiring airfoil surfaces to backtrack against the wind for part of the cycle. Backtracking against the wind leads to inherently lower efficiency.

HAWT disadvantages

Turbine blade convoy passing through Edenfield in the UK

• The tall towers and blades up to 90 meters long are difficult to transport. Transportation can now cost 20% of equipment costs.

• Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators.

• Massive tower construction is required to support the heavy blades, gearbox, and generator.

• Reflections from tall HAWTs may affect side lobes of radar installations creating signal clutter, although filtering can suppress it.

• Their height makes them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition.

• Downwind variants suffer from fatigue and structural failure caused by turbulence when a blade passes through the tower's wind shadow (for this reason, the majority of HAWTs use an upwind design, with the rotor facing the wind in front of the tower).

• HAWTs require an additional yaw control mechanism to turn the blades toward the wind.

Cyclic stresses and vibration

Cyclic stresses fatigue the blade, axle and bearing; material failures were a major cause of turbine failure for many years. Because wind velocity often increases at higher altitudes, the backward force and torque on a horizontal-axis wind turbine (HAWT) blade peaks as it turns through the highest point in its circle. The tower hinders the airflow at the lowest point in the circle, which produces a local dip in force and torque. These effects produce a cyclic twist on the main bearings of a HAWT. The combined twist is worst in machines with an even number of blades, where one is straight up when another is straight down. To improve reliability, teetering hubs have been used which allow the main shaft to rock through a few degrees, so that the main bearings do not have to resist the torque peaks.

When the turbine turns to face the wind, the rotating blades act like a gyroscope. As it pivots, gyroscopic precession tries to twist the turbine into a forward or backward somersault. For each blade on a wind generator's turbine, precessive force is at a minimum when the blade is

(23)

horizontal and at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue and crack the blade roots, hub and axle of the turbines.

Vertical axis

Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Key

advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. VAWTs can utilize winds from varying directions.

With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque. Drag may be created when the blade rotates into the wind. It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life. However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.

VAWT subtypes

30 m Darrieus wind turbine in the Magdalen Islands Darrieus wind turbine

"Eggbeater" turbines. They have good efficiency, but produce large torque ripple and cyclic stress on the tower, which contributes to poor reliability. Also, they generally require some external power source, or an additional Savonius rotor, to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in a higher solidity for the rotor. Solidity is measured by blade area over the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing.

(24)

A helical twisted VAWT. Giromill

A subtype of Darrieus turbine with straight, as opposed to curved, blades. The

cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting.

[13]_{The advantages of variable pitch are: high starting torque; a wide, relatively flat torque}

curve; a lower blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used.

12 m Windmill with rotational sails in Osijek, Croatia Savonius wind turbine

These are drag-type devices with two (or more) scoops that are used in anemometers, Flettner vents (commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They are always self-starting if there are at least three scoops. They sometimes have long helical scoops to give a smooth torque.

VAWT advantages

• A massive tower structure is less frequently used, as VAWTs are more frequently mounted with the lower bearing mounted near the ground.

(25)

• A VAWT can be located nearer the ground, making it easier to maintain the moving parts.

• VAWTs have lower wind startup speeds than HAWTs. Typically, they start creating electricity at 6 m.p.h. (10 km/h).

• VAWTs may be built at locations where taller structures are prohibited.

• VAWTs situated close to the ground can take advantage of locations where mesas, hilltops, ridgelines, and passes funnel the wind and increase wind velocity.

• VAWTs may have a lower noise signature.

VAWT disadvantages

• Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. Versions that reduce drag produce more energy, especially those that funnel wind into the collector area[citation needed]_.

• A VAWT that uses guy-wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guy wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guy wired models.

• While VAWTs' parts are located on the ground, they are also located under the weight of the structure above it, which can make changing out parts nearly impossible without dismantling the structure if not designed properly.

• Having rotors located close to the ground where wind speeds are lower due to wind shear, VAWTs may not produce as much energy at a given site as a HAWT with the same footprint or height.

• Because VAWTs are not commonly deployed due mainly to the serious disadvantages mentioned above, they appear novel to those not familiar with the wind industry. This has often made them the subject of wild claims and investment scams over the last 50 years.

[14][15]

Turbine design and construction

(26)

Main article: Wind turbine design

Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades, and blade shape.

Wind turbines convert wind energy to electricity for distribution. The turbine can be divided into three components. The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low speed rotational energy. The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gearbox component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity. The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor pointing mechanism.[16]

Low temperature

Utility-scale wind turbine generators have minimum temperature operating limits which apply in areas that experience temperatures below –20 °C. Wind turbines must be protected from ice accumulation, which can make anemometer readings inaccurate and which can cause high structure loads and damage. Some turbine manufacturers offer low-temperature packages at a few percent extra cost, which include internal heaters, different lubricants, and different alloys for structural elements. If the low-temperature interval is combined with a low-wind condition, the wind turbine will require an external supply of power, equivalent to a few percent of its rated power, for internal heating. For example, the St. Leon, Manitoba project has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to –30 °C. This factor affects the economics of wind turbine operation in cold climates.

Unconventional wind turbines

Main article: Unconventional wind turbines

One E-66 wind turbine at Windpark Holtriem, Germany, carries an observation deck, open for visitors. Another turbine of the same type, with an observation deck, is located in Swaffham, England.

A series of lighter-than-air wind turbines are in development in Canada by Magenn Power. They deliver power to the ground by a tether system.[17]

Wind turbines may also be used in conjunction with a large vertical solar updraft tower to extract the energy due to air heated by the sun. Or as part of wave powered generators where air

displaced by waves drives turbines.[18]

(27)

A small wind turbine being used at the Riverina Environmental Education Centre near Wagga Wagga, New South Wales, Australia

Main article: Small wind turbine

Small wind turbines may be as small as a fifty-watt generator for boat or caravan use. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Larger, more costly turbines generally have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.

Record-holding turbines

The world's largest turbines are manufactured by the Northern German companies Enercon and REpower. The Enercon E-126 delivers up to 6 MW, has an overall height of 198 m (650 ft) and a diameter of 126 meters (413 ft). The Repower 5M delivers up to 5 MW, has an overall height of 183 m (600 ft) and has a diameter of 126 m (413 ft).

The turbine closest to the North Pole is a Nordex N-80 in Havøygavlen near Hammerfest, Norway. The turbines currently operating closest to the South Pole are two Enercon E-30 in Antarctica, used to power the Australian Research Division's Mawson Station,[19]_{although a}

modified HR3 turbine from Northern Power Systems operated at the Amundsen-Scott South Pole Station in 1997 and 1998.[20]

Matilda was a wind turbine located on Gotland, Sweden. It produced a total of 61.4 GW·h in the 15 years it was active. That is more renewable energy than any other single wind power turbine had ever produced to that date. It was demolished on June 6, 2008.

The world's highest wind turbine of company DeWind is located in the Andes/Argentina to 4,100 metres (13,000 ft) above sea level. Turbine type D8.2 - 2000 kW / 50 Hz was used for that site. This turbine has a new drive train concept with a special torque converter (WinDrive) of the company Voith and a synchronous generator. The WKA was put into operation in December 2007 and has supplied the local gold mine with electricity since then.[21][22]

Criticisms

Main article: Environmental effects of wind power

While wind turbines in operation can generate electricity without the emission of greenhouse gases or the consumption of fuel, they have significant disadvantages over conventional generation.

(28)

One disadvantage is that wind power is an intermittent power source. The production from a wind turbine may increase or decrease dramatically over a short period of time with little or no warning. In the absence of large scale energy storage, the balance of the grid must be able to quickly compensate for this change.

The economics of wind turbines can be challenging as well. With high quality wind resources often located in areas inhospitable to people, logistics and transmission capacity can introduce significant obstacles to new installations.

The impact of wind turbines on wildlife has often been cited as a disadvantage of wind installations. Wind turbines can pose a danger to birds and bats, though the magnitude and gravity of this danger is much less than more ubiquitous threats such as house cats or plate glass. In fact, less than one bird is killed per 10,000 wind turbines annually.[23]

Wind turbines are certainly not without critics, but may have much more favorable life cycle impacts than conventional generation technologies.

References

1. ^ A Wind Energy Pioneer: Charles F. Brush, Danish Wind Industry Association, http://www.windpower.org/en/pictures/brush.htm, retrieved on 2008-12-28

2. ^ "Part 1 — Early History Through 1875". http://www.telosnet.com/wind/early.html. Retrieved on 2008-07-31.

3. ^ Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history, p. 54. Cambridge University Press. ISBN 0-521-42239-6.

4. ^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)

5. ^ ab_{Quirky old-style contraptions make water from wind on the mesas of West Texas}

6. ^ Alan Wyatt: Electric Power: Challenges and Choices. Book Press Ltd., Toronto 1986, ISBN 0-920650-00-7

(29)

7. ^ Kansas Wind Energy Project, Affiliated Atlantic & Western Group Inc, 5250 W 94th Terrace, Prairie Village, Kansas 66207

8. ^ http://www.windpower.org/en/tour/wtrb/comp/index.htm Wind turbine components retrieved November 8, 2008

9. ^ Molendatabase Dutch text

10.^ Extract from Triumph of the Griffiths Family,

http://au.geocities.com/ozwindmills/SouthernCross.htm, Bruce Millett, 1984, accessed January 26, 2008

11.^ 1.5 MW Wind Turbine Technical Specifications 12.^ Size specifications of common industrial wind turbines 13.^ http://www.awea.org/faq/vawt.html

14.^ http://www.rebelwolf.com/essn/ESSN-Aug2005.pdf

15.^ http://www.motherearthnews.com/Renewable-Energy/2008-02-01/Wind-Power-Horizontal-and-Vertical-Axis-Wind-Turbines.aspx

16.^ "Wind Turbine Design Cost and Scaling Model," Technical Report NREL/TP-500-40566, December, 2006, page 35,36. http://www.nrel.gov/docs/fy07osti/40566.pdf 17.^ Magenn Power Inc. - Technology

18.^ see http://www.bwea.com/marine/devices.html and scroll down to SPERBOY™, 19.^ Mawson Station Electrical Energy - Australian Antarctic Division

20.^ Bill Spindler, The first Pole wind turbine.

21.^ http://www.youtube.com/watch?v=VxYm2bWUdjo

22.^ http://www.voithturbo.com/vt_en_pua_windrive_project-report_2008.htm 23.^ www.awea.org/pubs/factsheets/MythsvsFacts-FactSheet.pdf

External links

(30)

• Photo journal and tutorial for 1.5kw residential wind turbine

• Domestic Wind Turbine installation and videos

• Wind Projects

• Guided tour on wind energy

• Wind Energy Technology World Wind Energy Association

• Wind turbine simulation, National Geographic

• Domestic and Commercial wind turbine directory and information wiki, SustainableX.com

v • d • e

Wind power Wind

power Wind powereffects · Wind turbine · Windmill · History · Environmental Wind

turbines Airborneaxis · Darrieus · Design · Savonius · Unconventional · Vertical Wind

power

industry Manufacturers · Consultants · Wind farm management · Software Wind

farms List of offshore wind farmsowned · List of onshore wind farms · Community-Concept

s

Betz' law · Capacity factor · EROEI · Grid energy storage · HVDC ·

Intermittency · Net energy gain · Storage · Subsidies · Wind power forecasting · Wind profile power law · Wind resource assessment

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Donate to Wikimedia

(31)

gas turbine

Dictionary: gas turbine Sponsored Links

Gas Turbine

Sulzer Turbo Services: Repair, maintenance and refurbishment. www.sulzerts.com/gas_turbines

Siemens answers:

Efficient energy supply The world's largest gas turbine. www.Siemens.com/Answers

An internal-combustion engine consisting essentially of an air compressor, combustion chamber, and turbine wheel that is turned by the expanding products of combustion.

• Answers.com ▼ ○ Home Page ○ Browse ○ Personalize ○ Print page ○ Email page ○ Translate page • WikiAnswers.com ▼ ○ Home Page ○ Browse ○ Recently Answered (C lic k to enl ar ge ) ga s tur bi ne turboj et engin e (Prec ision Grap hics)

(32)

○ Recently Asked ○ Unanswered questions • Search • Help • •

Search unanswered questions...

Top of Form

new ansGo

g a s tu r b in e

Top of Form All

0

Community Q&A Reference topics g a s tu r b in e

51204283-turbine

steam turbine

Contents

History

Types

Steam Supply and Exhaust Conditions

Casing or Shaft Arrangements

Principle of Operation and Design

Turbine Efficiency

Operation and Maintenance

Speed regulation

Direct drive

Speed reduction

References

Further Reading

External link

wind turbine

Background

Raw Materials

The Manufacturing

Process

Preparing the site

Erecting the tower

Nacelle

Rotary blades

Installation of control systems

Quality Control

Environmental Benefits

and Drawbacks

The Future

Where To Learn More

Periodicals

Contents

History

Resources

Types of wind turbines

Vertical axis

Turbine design and construction

Low temperature

Unconventional wind turbines

Record-holding turbines

Criticisms

See also

References

Further reading

External links

gas turbine