Editing Alternator

{{Short description|Device converting mechanical into electrical energy}}
{{Use dmy dates|date=June 2024}}

[[File:Gorskii 04414u.jpg|thumb|right|200px|Alternators made in 1909 by [[Ganz Works]] in the power generating hall of a Russian [[hydroelectric]] station (photograph by [[Prokudin-Gorsky]], 1911).<ref>{{cite web| title=Abraham Ganz at the Hindukush| url=http://riowang.com/2015/09/abraham-ganz-at-hindukush.html| website=Poemas del río Wang|publisher=Studiolum| access-date=30 September 2015| archive-url=https://web.archive.org/web/20160211052141/http://riowang.com/2015/09/abraham-ganz-at-hindukush.html|archive-date=11 February 2016| url-status=dead| df=dmy-all}}</ref>]]

An '''alternator''' (or '''synchronous generator''') is an [[Generator (device)|electrical generator]] that converts [[mechanical energy]] to [[electrical energy]] in the form of [[alternating current]].<ref>{{cite book|last=Aylmer-Small|first=Sidney|title=Electrical railroading; or, Electricity as applied to railroad transportation|publisher=Frederick J. Drake & Co.|location=Chicago|date=1908|pages=456–463|chapter=Lesson 28: Alternators|chapter-url=https://books.google.com/books?id=jdk7AAAAMAAJ}}</ref> For reasons of cost and simplicity, most alternators use a rotating [[magnetic field]] with a stationary [[Armature (electrical engineering)|armature]].<ref name=Slemon>Gordon R. Selmon, ''Magnetoelectric Devices'', John Wiley and Sons, 1966 no ISBN pp. 391-393</ref> Occasionally, a [[linear alternator]] or a rotating armature with a stationary magnetic field is used. In principle, any [[alternating current|AC]] [[electrical generator]] can be called an alternator, but usually, the term refers to small rotating machines driven by [[Car|automotive]] and other internal combustion engines.

An alternator that uses a [[magnet|permanent magnet]] for its [[magnetic field]] is called a [[magneto]]. Alternators in [[power station]]s driven by [[steam turbine]]s are called turbo-alternators.  Large 50 or 60&nbsp;Hz [[three-phase]] alternators in [[power plants]] generate most of the world's electric power, which is distributed by [[electric power grid]]s.<ref>{{cite web|title=List of Plug/Sockets and Voltage of Different Countries|url=http://www.worldstandards.eu/electricity/plug-voltage-by-country/|website=World Standards|ref=List of Plug/Sockets and Voltage of Different Countries}}</ref>

==History==
[[File:Ames Colorado generator alternating current power plant 1891 Gold King Mine.png|thumb|right|In what is considered the first industrial use of alternating current in 1891, workers pose with a Westinghouse alternator at the [[Ames Hydroelectric Generating Plant]]. This machine was used as a generator producing 3,000-volt, 133-hertz, single-phase AC, and an identical machine {{convert|3|miles|km}} away was used as an AC motor.<ref name="books.google.com">[https://books.google.com/books?id=31O4upzTHQwC&dq=In+1891+Telluride+westinghouse+induction+motor&pg=PA39 D. M. Mattox, The Foundations of Vacuum Coating Technology, page 39]</ref><ref>{{Cite magazine |url= http://www.historycolorado.org/sites/default/files/files/Researchers/ColoradoMagazine_v49n3_Summer1972.pdf |title=Charles C. Britton, An Early Electric Power Facility in Colorado |magazine=Colorado Magazine |volume=49 |issue=3 |date=Summer 1972 |page=185 |access-date=15 August 2016 |archive-url= https://web.archive.org/web/20160728160650/http://www.historycolorado.org/sites/default/files/files/Researchers/ColoradoMagazine_v49n3_Summer1972.pdf |archive-date=28 July 2016 |url-status=dead }}</ref><ref>{{cite web |url=http://www.ieeeghn.org/wiki/index.php/Milestones:Ames_Hydroelectric_Generating_Plant,_1891 |title=Milestones:Ames Hydroelectric Generating Plant, 1891 |work=IEEE Global History Network |publisher=IEEE |access-date=29 July 2011}}</ref>]]

Alternating current generating systems were known in simple forms from the discovery of the [[electromagnetic induction|magnetic induction of electric current]] in the 1830s. Rotating generators naturally produced alternating current, but since there was little use for it, it was normally converted into [[direct current]] via the addition of a [[commutator (electric)|commutator]] in the generator.<ref name="Christopher Cooper 2015, page 93">Christopher Cooper, The Truth about Tesla: The Myth of the Lone Genius in the History of Innovation, Quarto Publishing Group USA – 2015, page 93</ref> The early machines were developed by pioneers such as [[Michael Faraday]] and [[Hippolyte Pixii]]. 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''. p. 7.</ref> [[Lord Kelvin]] and [[Sebastian Ziani de Ferranti|Sebastian Ferranti]] also developed early alternators, producing frequencies between 100 and 300 [[hertz|Hz]].

The late 1870s saw the introduction of the first large-scale electrical systems with central generation stations to power [[Arc lamp]]s, used to light whole streets, factory yards, or the interior of large warehouses. Some, such as [[Yablochkov candle|Yablochkov arc lamps]] introduced in 1878, ran better on alternating current, and the development of these early AC generating systems was accompanied by the first use of the word "alternator".<ref>Jill Jonnes, Empires of Light: Edison, Tesla, Westinghouse, And The Race To Electrify The World, Random House – 2004, page 47</ref><ref name="Christopher Cooper 2015, page 93"/> Supplying the proper amount of voltage from generating stations in these early systems was left up to the engineer's skill in "riding the load".<ref>Donald Scott McPartland, Almost Edison: How William Sawyer and Others Lost the Race to Electrification, ProQuest – 2006, page 135</ref> In 1883 the [[Ganz Works]] invented the constant voltage generator<ref>{{cite book|author=American Society for Engineering Education|title=Proceedings, Part 2|year=1995|page=1848|url= https://books.google.com/books?id=EZVRAAAAMAAJ&q=ganz+%22constant+voltage+generator%22|author-link=American Society for Engineering Education}}</ref> that could produce a stated output voltage, regardless of the value of the actual load.<ref>{{cite book|author=Robert L. Libbey|title=A Handbook of Circuit Math for Technical Engineers|publisher=[[CRC Press]]|year=1991|page=22|isbn=9780849374005|url= https://books.google.com/books?id=b6dD_bqZNyoC&q=%22constant+voltage+generator%22&pg=PA22}}</ref> The introduction of [[transformer]]s in the mid-1880s led to the widespread use of alternating current and the use of alternators needed to produce it.<ref>{{cite web|url= http://www.ieeeghn.org/wiki/index.php/Milestones:Alternating_Current_Electrification,_1886 |last=Thompson |first=Sylvanus P. |title=Milestones:Alternating Current Electrification, 1886 |publisher=IEEE Global History Network  |access-date=22 September 2013 }}</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 various 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> Specialized radio frequency alternators like the [[Alexanderson alternator]] were developed as [[longwave]] [[radio transmitter]]s around World War 1 and used in a few high power [[wireless telegraphy]] stations before vacuum tube transmitters replaced them.{{citation needed|date=August 2022}}

==Principle of operation==
[[File:Alternator 1.svg|thumb|Diagram of a simple alternator with a rotating magnetic core (rotor) and stationary wire (stator) also showing the current induced in the stator by the rotating magnetic field of the rotor.]]

A conductor moving relative to a magnetic field develops an [[electromotive force]] (EMF) in it ([[Faraday's law of induction|Faraday's Law]]). This EMF reverses its polarity when it moves under magnetic poles of opposite polarity. Typically, a rotating magnet, called the [[Rotor (electric)|rotor]], turns within a stationary set of conductors, called the [[stator]], wound in coils on an iron core. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn.{{citation needed|date=August 2022}}

The [[rotating magnetic field]] induces an [[alternating current|AC voltage]] in the stator windings.  Since the currents in the stator windings vary in step with the position of the rotor, an alternator is a synchronous generator.<ref name=Slemon/>

The rotor's magnetic field may be produced by permanent magnets or by a field coil electromagnet. Automotive alternators use a rotor winding, which allows control of the alternator's generated voltage by varying the current in the rotor field winding.  Permanent magnet machines avoid the loss due to magnetizing current in the rotor, but are restricted in size due to the cost of the magnet material.  Since the permanent magnet field is constant, the terminal voltage varies directly with the speed of the generator.  Brushless AC generators are usually larger than those used in automotive applications.{{citation needed|date=August 2022}}

An automatic voltage control device controls the [[field current]] to keep the output voltage constant. If the output voltage from the stationary armature coils drops due to an increase in demand, more current is fed into the rotating field coils through the [[voltage regulator]] (VR). This increases the magnetic field around the field coils, which induces a greater voltage in the armature coils. Thus, the output voltage is brought back up to its original value.{{citation needed|date=August 2022}}

Alternators used in central [[power station]]s also control the field current to regulate [[reactive power]] and to help stabilize the power system against the effects of momentary [[fault (power engineering)|faults]]. Often, there are three sets of stator windings, physically offset so that the rotating magnetic field produces a [[three phase]] current, displaced by one-third of a period with respect to each other.<ref>B. M. Weedy. ''Electric Power Systems Second Edition'', John Wiley and Sons, 1972, {{ISBN|0 471 92445 8}},  p. 141</ref>

==Synchronous speeds==
One cycle of alternating current is produced each time a pair of field poles passes over a point on the stationary winding. The relation between speed and frequency is <math>N = 120f/P</math>, where <math>f</math> is the frequency in Hz (cycles per second). <math>P</math> is the number of poles (2, 4, 6, …), and <math>N</math> is the rotational speed in [[revolutions per minute]] (r/min).<ref name="GraingerStevenson1994">{{cite book|first1=John J. |last1=Grainger|first2=William D.|last2= Stevenson|title=Power system analysis|url={{google books |plainurl=y |id=NBIoAQAAMAAJ}}|date=1994|publisher=McGraw-Hill|isbn=978-0-07-061293-8|page=91}}</ref> Old descriptions of [[alternating current]] systems sometimes give the frequency in terms of alternations per minute, counting each half-cycle as one ''alternation''; so 12,000 alternations per minute corresponds to 100&nbsp;Hz.{{citation needed|date=August 2022}}

An alternator's output [[frequency]] depends on the number of poles and the rotational speed. The speed corresponding to a particular frequency is called the ''synchronous speed''. This table<ref>The Electrical Year Book 1937, published by Emmott & Co. Ltd., Manchester, England, page 72</ref> gives some examples:

{| class="wikitable" style="text-align:right;"
|-
! rowspan=2 | Poles
! colspan=3 | Rotation speed (r/min), giving…
|-
! 50&nbsp;Hz
! 60&nbsp;Hz
! 400&nbsp;Hz
|-
| 2
| 3,000
| 3,600
| 24,000
|-
| 4
| 1,500
| 1,800
| 12,000
|-
| 6
| 1,000
| 1,200
| 8,000
|-
| 8
| 750
| 900
| 6,000
|-
| 10
| 600
| 720
| 4,800
|-
| 12
| 500
| 600
| 4,000
|-
| 14
| 428.6
| 514.3
| 3,429
|-
| 16
| 375
| 450
| 3,000
|-
| 18
| 333.3
| 400
| 2,667
|-
| 20
| 300
| 360
| 2,400
|-
| 40
| 150
| 180
| 1,200
|}

== Classifications ==
Alternators may be classified by the method of excitation, number of phases, the type of rotation, cooling method, and their application.<ref name="faa">{{cite book|title=Aviation Maintenance Technician Handbook—General (FAA-H-8083-30) |date=2008|url= http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_handbook/media/FAA-8083-30_Ch10.pdf |publisher=Federal Aviation Administration |pages=10_160–10_161|access-date=6 September 2013|archive-url= https://web.archive.org/web/20130906013000/http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_handbook/media/FAA-8083-30_Ch10.pdf |archive-date=6 September 2013 |url-status=dead}}</ref>

=== By excitation ===
There are two main ways to produce the magnetic field used in the alternators: by using [[permanent magnet]]s, which create their persistent magnetic field, or by using [[field coil]]s. The alternators that use permanent magnets are specifically called [[Magneto (generator)|magnetos]].{{citation needed|date=August 2022}}
 
In other alternators, wound field coils form an [[electromagnet]] to produce the rotating magnetic field.{{citation needed|date=August 2022}}

A device that uses permanent magnets to produce alternating current is called a permanent magnet alternator (PMA). A permanent magnet generator (PMG) may produce either alternating current or direct current if it has a [[Commutator (electric)|commutator]].{{citation needed|date=August 2022}}

==== Direct-connected direct-current (DC) generator ====
This method of excitation consists of a smaller [[direct current|direct-current]] (DC) generator fixed on the same shaft as the alternator. The DC generator generates a small amount of electricity, just enough to ''excite'' the field coils of the connected alternator to generate electricity. A variation of this system is a type of alternator that uses direct current from a battery for initial excitation upon start-up, after which the alternator becomes self-excited.<ref name="faa"/>

==== Direct-connected alternating-current (AC) generator ====

This method of excitation consists of a smaller [[alternating current|alternating-current]] (AC) generator fixed on the same shaft as the alternator. The AC stator generates a small amount of field coil excitation current, which is induced in the rotor and rectified to DC by a bridge rectifier built in to the windings where it excites the field coils of the larger connected alternator to generate electricity. This system has the advantage of not requiring brushes, which increases service life, although with a slightly lower overall efficiency. A variation of this system is a type of alternator that uses direct current from a battery for initial excitation upon start-up, after which the alternator becomes self-excited.<ref name="faa"/>

==== Transformation and rectification ====
This method depends on residual magnetism retained in the iron core to generate a weak magnetic field, which would allow a weak voltage to be generated. This voltage is used to excite the field coils so the alternator can generate stronger voltage as part of its ''build up'' process. After the initial AC voltage buildup, the field is supplied with [[rectifier|rectified voltage]] from the alternator.<ref name="faa"/>

==== Brushless alternators ====
A brushless alternator is composed of two alternators built end-to-end on one shaft. Until 1966, alternators used brushes with rotating field.<ref>{{cite web|url= https://www.stamford-avk.com/heritage/cummins-generator-technologies |title=Cummins Generator Technologies |website=stamford-avk.com|publisher=Cummins Generator Technologies |access-date=18 August 2022}}</ref> With the advancement in semiconductor technology, brushless alternators are possible. Smaller brushless alternators may look like one unit, but the two parts are readily identifiable in the large versions. The main alternator is the larger of the two sections, and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature. A [[bridge rectifier]], called the rotating rectifier assembly, is mounted on the rotor. Neither brushes nor slip rings are used, which reduces the number of wearing parts. The main alternator has a rotating field and a stationary armature (power generation windings).

Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result is that a small DC exciter current indirectly controls the output of the main alternator.<ref>G. K. Dubey, ''Fundamentals of Electrical Drives'', CRC Press, 2002, {{ISBN|084932422X}}, page 350</ref>

=== By number of phases ===
{{Main|Single-phase generator|Polyphase coil}}
Another way to classify alternators is by the number of phases of their output voltage. The output can be single phase or polyphase. Three-phase alternators are the most common, but polyphase alternators can be two-phase, six-phase, or more.<ref name="faa"/>

=== By rotating part ===
The revolving part of alternators can be the [[Armature (electrical engineering)|armature]] or the magnetic field. The revolving armature type has the armature wound on the rotor, where the winding moves through a stationary magnetic field. The revolving armature type is not often used.<ref name="faa"/> The revolving field type has a magnetic field on the rotor to rotate through a stationary armature winding. The advantage is that then the rotor circuit carries much less power than the armature circuit, making the [[slip ring]] connections smaller and less costly; only two contacts are needed for the direct-current rotor, whereas often a rotor winding has three phases, and multiple sections which would each require a slip-ring connection. The stationary armature can be wound for any convenient medium voltage level, up to tens of thousands of volts; manufacture of slip ring connections for more than a few thousand volts is costly and inconvenient.{{citation needed|date=August 2022}}

===Cooling methods===
Many alternators are cooled by ambient air, forced through the enclosure by an attached fan on the shaft that drives the alternator.  In vehicles such as transit buses, a heavy demand on the electrical system may require a large alternator to be oil-cooled.<ref>Gus Wright, ''Fundamentals of Medium/Heavy Duty Diesel Engines'', Jones & Bartlett Publishers, 2015,  {{ISBN|128406705X}} page 1233</ref> In marine applications water-cooling is also used. Expensive automobiles may use water-cooled alternators to meet high electrical system demands.{{citation needed|date=August 2022}}

==Specific applications==
===Synchronous generators===
Most power generation stations use synchronous machines as their generators. The connection of these generators to the utility grid requires synchronization conditions to be met.<ref>[https://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6175812 Soft synchronization of dispersed generators to micro grids for smart grid applications]</ref>

===Automotive alternators===
{{further|Alternator (automotive)}}
[[File:Jeep 2.5 liter 4-cylinder engine chromed e.jpg|thumb|Alternator mounted on an automobile engine with a [[serpentine belt]] pulley (belt not present.)]]
Alternators are used in modern [[internal combustion engine]] [[automobile]]s to charge the [[Automotive battery|battery]] and to power the electrical system when its engine is running.<ref>{{cite web |title=How It Works: The Charging System |url=https://www.hotrod.com/features/how-it-works-december-1993-982-1510-38-1/ |website=Hot Rod |date=2023-01-01 |access-date=2025-04-16}}</ref>

Until the 1960s, automobiles used DC [[dynamo]] generators with [[commutator (electric)|commutator]]s. With the availability of affordable [[diode|silicon-diode]] rectifiers, alternators were used instead.<ref>{{cite web |title=A History of Alternators |url=https://www.elreg.com/blog/a-history-of-alternators/ |publisher=Elreg |access-date=2025-04-16}}</ref>

=== Diesel-electric locomotive alternators ===
In later [[diesel-electric locomotive]]s and [[diesel electric multiple unit]]s, the [[prime mover (locomotive)|prime mover]] turns an alternator which provides electricity for the [[traction motor]]s (AC or DC).<ref>{{cite journal |last1=Kapetanović |first1=Marko |last2=Vajihi |first2=Mohammad |last3=Goverde |first3=Rob M. P. |title=Analysis of Hybrid and Plug-In Hybrid Alternative Propulsion Systems for Regional Diesel-Electric Multiple Unit Trains |journal=Energies |volume=14 |issue=18 |pages=5920 |year=2021 |doi=10.3390/en14185920 |doi-access=free |hdl=11573/1587483 |hdl-access=free }}</ref><ref>{{cite journal |last1=Saadat |first1=M. |last2=Esfahanian |first2=M. |last3=Saket |first3=M.H. |title=Reducing fuel consumption of diesel-electric locomotives using hybrid powertrain and fuzzy look-ahead control |journal=[[Sage Publishing]] |volume=231 |issue=4 |pages=406–418 |year=2017 |doi=10.1177/0954409716631010 |url=https://journals.sagepub.com/doi/10.1177/0954409716631010|access-date=2025-04-16|url-access=subscription }}</ref>

The traction alternator usually incorporates integral silicon diode rectifiers to provide the traction motors with up to 1,200 volts DC.<ref>{{cite web |title=Global Traction Alternators Market |url=https://www.precisionreports.co/global-traction-alternators-market-27225755 |website=Precision Reports |date=2024-04-17 |access-date=2025-04-16}}</ref>

The first diesel electric locomotives, and many of those still in service, use DC generators as, before silicon power electronics, it was easier to control the speed of DC traction motors. Most of these had two generators: one to generate the excitation current for a larger main generator.<ref>{{cite web |last=Guss |first=Chris |title=What Locomotive Generators Do |url=https://www.trains.com/trn/railroads/locomotives/what-locomotive-generators-do/ |website=[[Trains Magazine]] |date=2022-08-03 |access-date=2025-04-16}}</ref>

Optionally, the generator also supplies [[head-end power]] (HEP) or power for [[electric train heating]]. The HEP option requires a constant engine speed, typically 900&nbsp;r/min for a 480&nbsp;V 60&nbsp;Hz HEP application, even when the locomotive is not moving.{{citation needed|date=August 2022}}

=== Marine alternators ===
Marine alternators used in yachts are similar to automotive alternators, with appropriate adaptations to the salt-water environment. Marine alternators are designed to be [[explosion proof]] (ignition protected) so that brush sparking will not ignite explosive gas mixtures in an engine room environment. Depending on the type of system installed, they may be 12 or 24 volts. Larger marine diesels may have two or more alternators to cope with the heavy electrical demand of a modern yacht. On single alternator circuits, the power may be split between the engine starting battery and the domestic or house battery (or batteries) by use of a [[split-charge diode]] ([[battery isolator]]) or a voltage-sensitive relay. Due to the high cost of large house battery banks, Marine alternators generally use external regulators. Multistep regulators control the field current to maximize the charging effectiveness (time to charge) and battery life. Multistep regulators can be programmed for different battery types. Two temperature sensors can be added: one for the battery to adjust the charging voltage and an over-temperature sensor on the actual alternator to protect it from overheating.{{citation needed|date=August 2022}}

=== Aviation ===
{{further|Auxiliary power unit|l1=APU|Ram air turbine|l2=RAT|Hydraulic motor}}

=== Radio alternators ===
High-frequency alternators of the variable-reluctance type were applied commercially to radio transmission in low-frequency radio bands. These were used for transmitting [[Morse code]] and, experimentally, for transmitting voice and music. In the [[Alexanderson alternator]], both the field winding and armature winding are stationary, and current is induced in the armature by the changing magnetic reluctance of the rotor (which has no windings or current-carrying parts). Such machines were made to produce radio frequency current for radio transmissions, although the efficiency was low.<ref>{{cite web |last=Wilson |first=Keith |title=Have you ever heard of the Alexanderson alternator? |url=https://www.megger.com/en-us/et-online/march-2020/have-you-ever-heard-of-the-alexanderson-alternator |website=Megger |date=2020-03-17 |access-date=2025-04-15}}</ref>

== See also ==
{{Div col|colwidth=30em}}
* [[Bottle dynamo]]
* [[Dynamo]]
* [[Electric generator]]
* [[Engine-generator]]
* [[Flux switching alternator]]
* [[Folsom Powerhouse State Historic Park]]
* [[Hub dynamo]]
* [[Induction generator]]
* [[Jedlik's dynamo]]
* [[Linear alternator]]
* [[Magneto]]
* [[Polyphase coil]]
* [[Revolving armature alternator]]
* [[Single-phase generator]]
* [[Synchronverter]]

{{div col end}}

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Alternators}}
* White, Thomas H.,"''[https://earlyradiohistory.us/sec008.htm Alternator-Transmitter Development] (1891–1920)''". EarlyRadioHistory.us.
* [http://www.tpub.com/content/construction/14273/css/14273_47.htm Alternators] at Integrated Publishing (TPub.com)
* [http://www.otherpower.com/pmg2.html Wooden Low-RPM Alternator], ForceField, Fort Collins, Colorado, USA
* [https://web.archive.org/web/20040405172313/http://www.windstuffnow.com/main/3_phase_basics.htm Understanding 3 phase alternators] at WindStuffNow
* [http://home.freeuk.net/dunckx/wireless/sparksnarcs/sparksnarcs.html Alternator, Arc and Spark. The first Wireless Transmitters] (G0UTY homepage)

{{Electric motor}}
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[[Category:Electrical generators]]
[[Category:Energy conversion]]
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