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| [[File:Modern Steam Turbine Generator.jpg|thumb|right|400px|U.S. [[Nuclear Regulatory Commission|NRC]] image of a modern steam turbine generator]]
| | Golda is what's written on my beginning certificate even though it is not the name on my birth certification. The preferred hobby for him and his kids is fashion and he'll be starting some thing else along with it. For a while I've been in Mississippi but now I'm considering other choices. Invoicing is my occupation.<br><br>Here is my web site - tarot card readings ([http://ece.modares.ac.ir/mnl/?q=node/1304748 ece.modares.ac.ir]) |
| [[File:Generator-20071117.jpg|thumb|right|Early [[Ganz]] Generator in [[Zwevegem]], [[West Flanders]], [[Belgium]]]]
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| [[File:Gorskii 04414u.jpg|thumb|right|Early 20th century [[alternator]] made in [[Budapest]], [[Hungary]], in the power generating hall of a [[hydroelectric]] station]]
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| In [[electricity generation]], an '''electric generator''' is a device that converts [[mechanical energy]] to [[electrical energy]]. A generator forces electric current to flow through an external [[electrical circuit|circuit]]. The source of mechanical energy may be a reciprocating or [[turbine]] [[steam engine]], water falling through a [[hydropower|turbine or waterwheel]], an [[internal combustion engine]], a [[wind turbine]],<ref>{{citation
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| | journal = International Journal of Dynamics and Control
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| | title = A Review on the Development of the Wind Turbine Generators across the World
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| | author = Navid Goudarzi
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| | publisher = Springer
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| | date = June 2013
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| | volume = 1
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| | issue = 2
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| | pages = 192–202
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| |doi=10.1007/s40435-013-0016-y
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| | url = http://link.springer.com/article/10.1007/s40435-013-0016-y
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| }}</ref> a hand [[crank (mechanism)|crank]], [[compressed air]], or any other source of mechanical energy. Generators provide nearly all of the power for [[electric power grid]]s.
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| The reverse conversion of electrical energy into mechanical energy is done by an [[electric motor]], and motors and generators have many similarities. Many motors can be mechanically driven to generate electricity and frequently make acceptable generators.
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| ==History==
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| Before the connection between [[magnetism]] and [[electricity]] was discovered, [[electrostatic generator]]s were used. They operated on [[electrostatic]] principles. Such generators generated very high [[voltage]] and low [[Electric current|current]]. They operated by using moving [[Electric charge|electrically charged]] belts, plates, and disks that carried charge to a high potential electrode. The charge was generated using either of two mechanisms:
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| *[[Electrostatic induction]]
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| *The [[triboelectric effect]], where the contact between two insulators leaves them charged.
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| Because of their inefficiency and the difficulty of [[Electrical insulation|insulating]] machines that produced very high voltages, electrostatic generators had low power ratings, and were never used for generation of commercially significant quantities of electric power. The [[Wimshurst machine]] and [[Van de Graaff generator]] are examples of these machines that have survived.
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| In 1827, Hungarian [[Anyos Jedlik]] started experimenting with the electromagnetic rotating devices which he called electromagnetic self-rotors, now called the [[Jedlik's dynamo]]. In the prototype of the single-pole electric starter (finished between 1852 and 1854) both the stationary and the revolving parts were electromagnetic. He formulated the concept of the dynamo at least 6 years before [[Ernst Werner von Siemens|Siemens]] and [[Charles Wheatstone|Wheatstone]] but didn't patent it as he thought he wasn't the first to realize this. In essence the concept is that instead of permanent magnets, two electromagnets opposite to each other induce the magnetic field around the rotor. It was also the discovery of the principle of [[self-excitation]].<ref>{{citation
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| | journal = Nature
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| | title = Anianus Jedlik
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| | author = Augustus Heller
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| | publisher = Norman Lockyer
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| | date = 2 April 1896
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| | volume = 53
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| | issue = 1379
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| | page = 516
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| | url = http://books.google.com/books?id=nWojdmTmch0C&pg=PA516&dq=jedlik+dynamo+1827&lr=&as_brr=3&ei
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| |bibcode = 1896Natur..53..516H |doi = 10.1038/053516a0 }}</ref>
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| [[File:Faraday disk generator.jpg|thumb|left|Faraday disk, the first electric generator. The horseshoe-shaped magnet ''(A)'' created a magnetic field through the disk ''(D)''. When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact ''m'', through the external circuit, and back into the center of the disk through the axle.]]
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| In the years of 1831–1832, [[Michael Faraday]] discovered the operating principle of electromagnetic generators. The principle, later called [[Faraday's law of induction|Faraday's law]], is that an [[electromotive force]] is generated in an electrical conductor which encircles a varying [[magnetic flux]]. He also built the first electromagnetic generator, called the [[Faraday disk]], a type of [[homopolar generator]], using a [[copper]] disc rotating between the poles of a horseshoe [[magnet]]. It produced a small DC voltage.
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| This design was inefficient, due to self-cancelling counterflows of current in regions that were not under the influence of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards in regions that were outside the influence of the magnetic field. This counterflow limited the power output to the pickup wires, and induced waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction.
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| Another disadvantage was that the output voltage was very low, due to the single current path through the magnetic flux. Experimenters found that using multiple turns of wire in a coil could produce higher, more useful voltages. Since the output voltage is proportional to the number of turns, generators could be easily designed to produce any desired voltage by varying the number of turns. Wire windings became a basic feature of all subsequent generator designs.
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| [[File:High-Current Copper-Brush Commutated Dynamo.jpg|thumb|300px|Dynamos are no longer used for power generation due to the size and complexity of the commutator needed for high power applications. This large belt-driven high-current dynamo produced 310 amperes at 7 volts, or 2,170 watts, when spinning at 1400 RPM.]]
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| The '''dynamo''' was the first electrical generator capable of delivering power for industry. The dynamo uses [[electromagnetic induction]] to convert mechanical rotation into [[direct current]] through the use of a [[commutator (electric)|commutator]]. The first dynamo was built by [[Hippolyte Pixii]] in 1832. | |
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| A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of rotating windings which turn within that field. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils.
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| Through a series of accidental discoveries, the dynamo became the source of many later inventions, including the DC [[electric motor]], the AC [[alternator]], the AC [[synchronous motor]], and the [[rotary converter]].
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| Alternating current generating systems were known in simple forms from the discovery of the [[Electromagnetic induction|magnetic induction of electric current]]. The early machines were developed by pioneers such as [[Michael Faraday]] and [[Hippolyte Pixii]].
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| Faraday developed the "rotating rectangle", whose operation was ''heteropolar'' - each active conductor passed successively through regions where the magnetic field was in opposite directions.<ref>Thompson, Sylvanus P., ''Dynamo-Electric Machinery''. pp. 7</ref> The first public demonstration of a more robust "alternator system" took place in 1886.<ref>Blalock, Thomas J., "''[http://www.ieee.org/organizations/history_center/stanley.html Alternating Current Electrification, 1886]''". IEEE History Center, IEEE Milestone. (''ed''. first practical demonstration of a dc generator - ac transformer system.)</ref> Large two-phase alternating current generators were built by a British electrician, [[James Edward Henry Gordon|J.E.H. Gordon]], in 1882. [[Lord Kelvin]] and [[Sebastian Ziani de Ferranti|Sebastian Ferranti]] also developed early alternators, producing frequencies between 100 and 300 [[hertz|Hz]]. In 1891, [[Nikola Tesla]] patented a practical "high-frequency" alternator (which operated around 15 kHz).<ref>{{Cite patent|US|447921}}, Tesla, Nikola, "Alternating Electric Current Generator".</ref> After 1891, [[Polyphase system|polyphase]] alternators were introduced to supply currents of multiple differing phases.<ref>Thompson, Sylvanus P., ''Dynamo-Electric Machinery''. pp. 17</ref> Later alternators were designed for varying alternating-current frequencies between sixteen and about one hundred hertz, for use with arc lighting, incandescent lighting and electric motors.<ref>Thompson, Sylvanus P., ''Dynamo-Electric Machinery''. pp. 16</ref>
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| Large power generation dynamos are now rarely seen due to the now nearly universal use of [[alternating current]] for power distribution. Before the adoption of AC, very large direct-current dynamos were the only means of power generation and distribution. AC has come to dominate due to the ability of AC to be easily [[transformer|transformed]] to and from very high voltages to permit low losses over large distances.
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| ==Electromagnetic generators==
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| ===Dynamo===
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| {{main|Dynamo}}
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| [[File:DynamoElectricMachinesEndViewPartlySection USP284110.png|thumb|"Dynamo Electric Machine" (end view, partly section, {{US patent|284110}}), 1883]]
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| A dynamo is an electrical generator that produces [[direct current]] with the use of a [[commutator (electric)|commutator]]. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the [[electric motor]], the alternating-current [[alternator]], and the [[rotary converter]]. Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices (vacuum tube or more recently [[Solid state (electronics)|solid state]]) is effective and usually economic.
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| ===Alternator===
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| {{main|Alternator}}
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| Without a [[commutator (electric)|commutator]], a dynamo becomes an [[alternator]], which is a [[singly fed electric machine|synchronous singly fed generator]]. Alternators produce [[alternating current]] with a frequency that is based on the rotational speed of the rotor and the number of magnetic poles.
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| Automotive alternators produce a varying frequency that changes with engine speed, which is then converted by a rectifier to DC. By comparison, alternators used to feed an [[Grid (electricity)|electric power grid]] are generally operated at a speed very close to a specific frequency, for the benefit of AC devices that regulate their speed and performance based on grid frequency. Some devices such as [[incandescent lamp]]s and ballast-operated [[fluorescent lamp]]s do not require a constant frequency, but synchronous motors such as in electric wall clocks do require a constant grid frequency.
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| When attached to a larger electric grid with other alternators, an alternator will dynamically interact with the frequency already present on the grid, and operate at a speed that matches the grid frequency. If no driving power is applied, the alternator will continue to spin at a constant speed anyway, driven as a synchronous motor by the grid frequency. It is usually necessary for an alternator to be accelerated up to the correct speed and phase alignment before connecting to the grid, as any mismatch in frequency will cause the alternator to act as a synchronous motor, and suddenly leap to the correct phase alignment as it absorbs a large inrush current from the grid, which may damage the rotor and other equipment.
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| Typical alternators use a rotating field winding excited with direct current, and a stationary (stator) winding that produces alternating current. Since the rotor field only requires a tiny fraction of the power generated by the machine, the brushes for the field contact can be relatively small. In the case of a brushless exciter, no brushes are used at all and the rotor shaft carries rectifiers to excite the main field winding.
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| ===Induction generator===
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| {{main|induction generator}}
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| An induction generator or asynchronous generator is a type of AC [[electrical generator]] that uses the principles of [[induction motor]]s to produce power. Induction generators operate by mechanically turning their rotor faster than the synchronous speed, giving negative slip. A regular AC asynchronous motor usually can be used as a generator, without any internal modifications. Induction generators are useful in applications such as minihydro power plants, wind turbines, or in reducing high-pressure gas streams to lower pressure, because they can recover energy with relatively simple controls.
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| To operate an induction generator must be excited with a leading voltage; this is usually done by connection to an electrical grid, or sometimes they are self-excited by using phase correcting capacitors.
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| ===MHD generator===
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| {{main|MHD generator}}
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| A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. MHD generators were originally developed because the output of a plasma MHD generator is a flame, well able to heat the boilers of a [[Rankine cycle|steam]] [[power plant]]. The first practical design was the AVCO Mk. 25, developed in 1965. The U.S. government funded substantial development, culminating in a 25 MW demonstration plant in 1987. In the [[Soviet Union]] from 1972 until the late 1980s, the MHD plant U 25 was in regular commercial operation on the Moscow power system with a rating of 25 MW, the largest MHD plant rating in the world at that time.<ref>Langdon Crane, ''Magnetohydrodynamic (MHD) Power Generator: More Energy from Less Fuel, Issue Brief Number IB74057'', Library of Congress Congressional Research Service, 1981, retrieved from [http://digital.library.unt.edu/govdocs/crs/permalink/meta-crs-8402:1 Digital.library.unt.edu] 18 July 2008</ref> MHD generators operated as a [[topping cycle]] are currently (2007) less efficient than [[combined cycle]] [[gas turbines]].
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| ===Other rotating electromagnetic generators===
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| Other types of generators, such as the [[singly fed electric machine|asynchronous or induction singly fed generator]], the [[doubly fed electric machine|doubly fed generator]], or the [[brushless wound-rotor doubly fed electric machine|brushless wound-rotor doubly fed generator]], do not incorporate permanent magnets or field windings that establish a constant magnetic field, and as a result, are seeing success in variable speed constant frequency applications, such as [[wind turbine]]s or other [[renewable energy|renewable energy technologies]].
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| The full output performance of any generator can be optimized with electronic control but only the [[doubly fed electric machine|doubly fed generator]]s or the [[brushless wound-rotor doubly fed electric machine|brushless wound-rotor doubly fed generator]] incorporate electronic control with power ratings that are substantially less than the power output of the generator under control, a feature which, by itself, offers cost, reliability and efficiency benefits.
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| ===Homopolar generator===
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| {{main|Homopolar generator}}
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| [[Image:Faraday disk generator.jpg|thumb|Faraday disk, the first homopolar generator]]
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| A homopolar generator is a [[Direct current|DC]] [[electrical generator]] comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder), the [[electrical polarity]] depending on the direction of rotation and the orientation of the field. It is also known as a '''unipolar generator''', '''acyclic generator''', '''disk dynamo''', or '''Faraday disc'''. The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large research generators can produce hundreds of volts, and some systems have multiple generators in series to produce an even larger voltage.<ref>Losty, H.H.W & Lewis, D.L. (1973) Homopolar Machines. Philosophical Transactions for the Royal Society of London. Series A, Mathematical and Physical Sciences. 275 (1248), 69-75</ref> They are unusual in that they can produce tremendous electric current, some more than a million [[amperes]], because the homopolar generator can be made to have very low internal resistance.
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| ===Excitation===
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| [[File:Murray Alternator with Belt-Driven Exciter.jpg|thumb|400px|A small early 1900s 75 [[kilovolt-ampere|kVA]] direct-driven power station AC alternator, with a separate belt-driven exciter generator.]]
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| {{main|Excitation (magnetic)}}
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| An electric generator or electric motor that uses field coils rather than permanent magnets requires a current to be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at all.
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| Smaller generators are sometimes ''[[Self-excitation|self-excited]]'', which means the field coils are powered by the current produced by the generator itself. The field coils are connected in series or parallel with the armature winding. When the generator first starts to turn, the small amount of [[remanent magnetism]] present in the iron core provides a magnetic field to get it started, generating a small current in the armature. This flows through the field coils, creating a larger magnetic field which generates a larger armature current. This "bootstrap" process continues until the magnetic field in the core levels off due to [[saturation (magnetic)|saturation]] and the generator reaches a steady state power output.
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| Very large power station generators often utilize a separate smaller generator to excite the field coils of the larger. In the event of a severe widespread [[power outage]] where [[islanding]] of power stations has occurred, the stations may need to perform a [[black start]] to excite the fields of their largest generators, in order to restore customer power service.<ref>[http://www.youtube.com/watch?v=zduGlpGZrkk&feature=related SpecSizer: Generator Set Sizing]</ref>
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| ==Electrostatic generator==
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| {{main|electrostatic generator}}
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| [[File:Van de graaff generator sm.jpg|thumb|right|alt= Large metal sphere supported on a clear plastic column, inside of which a rubber belt can be seen. A smaller sphere is supported on a metal rod. Both are mounted to a baseplate, on which there is a small driving electric motor.|A [[Van de Graaff generator]], for class room demonstrations]]
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| [[File:WimshurstElectricMachine.jpg|thumb|left|Suppose that the conditions are as in the figure, with the segment A1 positive and the segment B1 negative. Now, as A1 moves to the left and B1 to the right, their potentials will rise on account of the work done in separating them against attraction. When A1 and neighboring sectors comes opposite the segment B2 of the B plate, which is now in contact with the brush Y, they will cause a displacement of electricity along the conductor between Y and Y1 bringing a negative charge, larger than the positive charge in A1 alone, on Y and sending a positive charge to the segment touching Y1. As A1 moves on, it passes near the brush Z and is partially discharged into the external circuit. It then passes on until, on touching the brush X, has a new charge, this time negative, driven into it by induction from B2 and neighboring sectors. As the machine turns, the process causes exponential increases in the voltages on all positions, until sparking occurs limiting the increase.]]
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| An '''electrostatic generator''', or '''electrostatic machine''', is a mechanical device that produces ''[[static electricity]]'', or electricity at [[high voltage]] and low [[continuous current]]. The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying [[phenomenon]], without a theory to explain its behavior and often confused with magnetism. By the end of the 17th Century, researchers had developed practical means of generating electricity by friction, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies about the new science of [[electricity]]. Electrostatic generators operate by using manual (or other) power to transform [[mechanical work]] into [[electric energy]]. Electrostatic generators develop [[electrostatic]] [[electrical charge|charge]]s of opposite signs rendered to two conductors, using only electric forces, and work by using moving plates, drums, or belts to carry electric charge to a high [[Electric potential|potential]] [[electrode]]. The charge is generated by one of two methods: either the [[triboelectric effect]] (friction) or [[electrostatic induction]].
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| <br />
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| ===Wimshurst machine===
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| {{main|Wimshurst machine}}
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| The '''Wimshurst influence machine''' is an [[electrostatic generator]], a machine for generating high [[voltage]]s developed between 1880 and 1883 by British [[inventor]] [[James Wimshurst]] (1832–1903).
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| It has a distinctive appearance with two large contra-rotating discs mounted in a vertical plane, two crossed bars with metallic brushes, and a [[spark gap]] formed by two metal spheres.
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| [[File:Wimshurst.jpg|thumb|centre|Wimshurst machine with two [[Leyden jar]]s.]]
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| ===Van de Graaff generator===
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| {{main|Van de Graaff generator}}
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| A '''Van de Graaff generator''' is an [[electrostatic generator]] which uses a moving belt to accumulate very high [[voltage]]s on a hollow metal globe on the top of the stand. It was invented by American physicist [[Robert J. Van de Graaff]] in 1929. The [[potential difference]] achieved in modern Van de Graaff generators can reach 5 megavolts. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a [[capacitor]] and a very large electrical resistance, so it can produce a visible electrical discharge to a nearby grounding surface which can potentially cause a "spark" depending on the voltage.
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| ==Terminology==
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| The two main parts of a generator or motor can be described in either mechanical or electrical terms.
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| Mechanical:
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| * [[rotor (electric)|Rotor]]: The rotating part of an [[electrical machine]]
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| * [[Stator]]: The stationary part of an electrical machine
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| Electrical:
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| * [[Armature (electrical engineering)|Armature]]: The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current. The armature can be on either the rotor or the stator.
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| * [[Field coil|Field]]: The magnetic field component of an electrical machine. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator.
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| Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field current must be transferred to the moving rotor, using [[slip ring]]s. Direct current machines (dynamos) require a [[commutator (electric)|commutator]] on the rotating shaft to convert the [[alternating current]] produced by the armature to [[direct current]], so the armature winding is on the rotor of the machine.
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| ==Equivalent circuit==
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| [[File:Generator-model.svg|thumb|right|Equivalent circuit of generator and load.<br>G = generator<br>V<sub>G</sub>=generator open-circuit voltage<br>R<sub>G</sub>=generator internal resistance<br>V<sub>L</sub>=generator on-load voltage<br>R<sub>L</sub>=load resistance]]
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| The equivalent circuit of a generator and load is shown in the diagram to the right. The generator's <math>V_G</math> and <math>R_G</math> parameters can be determined by measuring the winding resistance (corrected to [[operating temperatur]]e), and measuring the open-circuit and loaded voltage for a defined current load.
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| ==Vehicle-mounted generators==
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| Early motor vehicles until about the 1960s tended to use DC generators with electromechanical regulators. These have now been replaced by [[alternator (automotive)|alternator]]s with built-in [[rectifier]] circuits, which are less costly and lighter for equivalent output. Moreover, the power output of a DC generator is proportional to rotational speed, whereas the power output of an alternator is independent of rotational speed. As a result, the charging output of an alternator at engine idle speed can be much greater than that of a DC generator. Automotive alternators power the electrical systems on the vehicle and recharge the [[car battery|battery]] after starting. Rated output will typically be in the range 50-100 A at 12 V, depending on the designed electrical load within the vehicle. Some cars now have electrically powered [[Power steering|steering assistance]] and [[air conditioning]], which places a high load on the electrical system. Large commercial vehicles are more likely to use 24 V to give sufficient power at the [[starter motor]] to turn over a large [[diesel engine]]. Vehicle alternators do not use permanent magnets and are typically only 50-60% efficient over a wide speed range.<ref>''Horst Bauer Bosch Automotive Handbook'' 4th Edition Robert Bosch GmbH, Stuttgart 1996 ISBN 0-8376-0333-1, page 813</ref> Motorcycle alternators often use permanent magnet [[stator]]s made with [[Rare earth element|rare earth]] magnets, since they can be made smaller and lighter than other types. See also [[hybrid vehicle]].
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| A [[magneto]], like a dynamo, uses permanent magnets but generates alternating current like an alternator. Because of the limited field strength of permanent magnets, [[magneto (generator)|magneto generator]]s are not used for high-power production applications, but have had specialist uses, particularly in [[lighthouse]]s as they are simple and reliable. This reliability is part of why they are still used as [[ignition magneto]]s in aviation piston engines.
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| Some of the smallest generators commonly found power [[Bicycle lighting|bicycle lights]]. Called a [[bottle dynamo]] these tend to be 0.5 ampere, permanent-magnet alternators supplying 3-6 W at 6 V or 12 V. Being powered by the rider, efficiency is at a premium, so these may incorporate [[rare-earth magnet]]s and are designed and manufactured with great precision. The maximum efficiency is around 80% for the best of these generators—60% is more typical—due in part to the rolling friction at the tire–generator interface, imperfect alignment, the small size of the generator, and bearing losses. Cheaper designs tend to be less efficient. Due to the use of permanent magnets, efficiency falls at high speeds because the magnetic field strength cannot be controlled in any way. [[Hub dynamo]]s remedy many of these flaws since they are internal to the bicycle hub and do not require an interface between the generator and tire. The increasing use of [[Light-emitting diode|LED]] lights, more [[Energy conversion efficiency|efficient]] than incandescent bulbs, reduces the power needed for cycle lighting.
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| Sailing boats may use a water- or wind-powered generator to trickle-charge the batteries. A small [[propeller]], [[wind turbine]] or [[impeller]] is connected to a low-power alternator and rectifier to supply currents of up to {{nowrap|12 A}} at typical cruising speeds.
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| Still smaller generators are used in [[micropower]] applications.
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| ==Engine-generator==
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| {{main|Engine-generator}}
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| [[File:Caterpillar 3512C Generator Set.JPG|thumb|The Caterpillar 3512C Genset is an example of the engine-generator package. This unit produces 1225 kilowatts of electric power.]]An ''engine-generator'' is the combination of an electrical generator and an [[engine]] ([[wikt:prime mover|prime mover]]) mounted together to form a single piece of self-contained equipment. The engines used are usually piston engines, but gas turbines can also be used. And there are even hybrid diesel-gas units, called dual-fuel units. Many different versions of engine-generators are available - ranging from very small portable [[petrol]] powered sets to large turbine installations. The primary advantage of engine-generators is the ability to independently supply electricity, allowing the units to serve as backup power solutions.<ref>{{cite web|url=http://www.wpowerproducts.com/blog/2011/05/hurricane-preparedness-protection-provided-by-power-generators/ |title=Hurricane Preparedness: Protection Provided by Power Generators | Power On with Mark Lum |publisher=Wpowerproducts.com |date=10 May 2011 |accessdate=2012-08-24}}</ref>
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| ==Human powered electrical generators==
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| {{main|Self-powered equipment}}
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| [[File:Day 47 Occupy Wall Street November 2 2011 Shankbone 15.JPG|thumb|Protesters at [[Occupy Wall Street]] using bicycles connected to a motor and one-way diode to charge batteries for their electronics<ref>[http://cityroom.blogs.nytimes.com/2011/10/30/with-generators-gone-wall-street-protesters-try-bicycle-power/ With Generators Gone, Wall Street Protesters Try Bicycle Power], Colin Moynihan, ''New York Times'', 30 October 2011; accessed 2 November 2011</ref>]]A generator can also be driven by human muscle power (for instance, in field radio station equipment).
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| Human powered direct current generators are commercially available, and have been the project of some [[DIY]] enthusiasts. Typically operated by means of pedal power, a converted bicycle trainer, or a foot pump, such generators can be practically used to charge batteries, and in some cases are designed with an integral inverter. The average adult could generate about 125-200 watts on a pedal powered generator, but at a power of 200 W, a typical healthy human will reach complete exhaustion and fail to produce any more power after approximately 1.3 hours.<ref>{{cite web|url=http://www.ohio.edu/mechanical/programming/hpv/hpv.html |title=Program: hpv (updated 6/22/11) |publisher=Ohio.edu |date= |accessdate=2012-08-24}}</ref> Portable radio receivers with a crank are made to reduce battery purchase requirements, see [[clockwork radio]]. During the mid 20th century, pedal powered radios were used throughout the [[Australian outback]], to provide schooling ([[School of the Air]]), medical and other needs in remote stations and towns.
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| ==Linear electric generator==
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| {{main|Linear alternator}}
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| In the simplest form of linear electric generator, a sliding [[magnet]] moves back and forth through a [[solenoid]] - a spool of copper wire. An [[alternating current]] is induced in the loops of wire by [[Faraday's law of induction]] each time the magnet slides through. This type of generator is used in the [[Faraday flashlight]]. Larger linear electricity generators are used in [[wave power]] schemes {{Linear electric generator }}
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| ==Tachogenerator==
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| A tachogenerator is an electromechanical device which produce an output voltage proportional to its shaft speed. It can be employed as an analogue speed indicator, velocity feedback device or a signal integrator. Two commonly used tachogenerators are DC and AC tachogenerators.
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| Tachogenerators are frequently used to power [[tachometer]]s to measure the speeds of electric motors, engines, and the equipment they power. Generators generate voltage roughly proportional to shaft speed. With precise construction and design, generators can be built to produce very precise voltages for certain ranges of shaft speeds.
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| ==See also==
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| {{Portal|Energy}}
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| {{Div col|3}}
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| * [[Diesel generator]]
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| * [[Electric motor]]
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| * [[Faraday's law of induction]]
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| * [[Goodness factor]]
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| * [[Hybrid vehicle]]
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| * [[Induction motor]]
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| * [[Mechanical generator]]
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| * [[Radioisotope thermoelectric generator]]
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| * [[Solar cell]]
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| * [[Superconducting electric machine]]
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| * [[Thermogenerator]]
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| * [[Tidal generator]]
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| * [[Tidal power]]
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| * [[Turbine hall]]
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| * [[Wave power]]
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| * [[Wind turbine]]
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| {{Div col end}}
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| ==References==
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| {{reflist|2}}
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| ==External links==
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| {{commons category|Electrical generators}}
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| * [http://amasci.com/amateur/coilgen.html Simple generator]
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| * [http://www.vega.org.uk/video/programme/224 Demonstration of an electrical generator]
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| * [http://www.vega.org.uk/video/programme/309 Short video of a simple generator]
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| {{Electric motor}}
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| [[Category:Electrical generators|*]]
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| [[Category:English inventions]]
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