Transformer and Félix Guattari: Difference between pages

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:''This article is about transformers as used in electrical and [[electronics]] applications. For other meanings, see [[Transformers]]''.

{{Infobox_Philosopher |

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[[Image:PoleMountTransformer02.jpg|thumb|300px|right|Three-phase pole-mounted step-down transformer.]]

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A '''transformer''' is an electrical device that transfers energy from one [[electrical network|circuit]] to another by [[Inductive coupling|magnetic coupling]] with no moving parts. A transformer comprises two or more coupled [[coil#Electromagnetic|windings]], or a single [[tap (transformer)|tapped]] winding and, in most cases, a [[magnetic core]] to concentrate [[magnetic flux]]. An alternating [[electric current|current]] in one winding creates a time-varying magnetic flux in the core, which induces a [[voltage]] in the other windings. Transformers are used to convert between high and low voltages, to change [[impedance]], and to provide electrical isolation between circuits. <br />

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== Overview ==

name = Pierre-Félix Guattari|

birth = [[April 30]], [[1930]] ([[Villeneuve-les-Sablons]], [[Oise]], [[France]])|

death = [[August 29]], [[1992]] ([[La Borde clinic]], [[Cour-Cheverny]], [[France]])|

school_tradition = [[Psychoanalysis]], [[Autonomism]] |

main_interests = [[Psychoanalysis]], [[Politics]], [[Ecology]], [[Semiotics]]|

influences = [[Freud]], [[Lacan]], [[Gregory Bateson|Bateson]], [[Sartre]], [[Hjelmslev]]|

influenced = [[Eric Alliez]], [[Michael Hardt]], [[Brian Massumi]], [[Antonio Negri]] |

notable_ideas = [[assemblage]], [[desiring machine]], [[deterritorialization]], [[ecosophy]], [[schizoanalysis]]|

}}

'''Pierre-Félix Guattari''' ([[April 30]], [[1930]] – [[August 29]], [[1992]]) was a [[France|French]] [[militant]], institutional [[psychotherapist]] and [[philosopher]], a founder of both [[schizoanalysis]] and [[ecosophy]]. Guattari is best known for his intellectual collaborations with [[Gilles Deleuze]], most notably ''[[Anti-Oedipus]]'' (1972) and ''[[A Thousand Plateaus]]'' (1980).

==Biography==

The transformer is one of the simplest of electrical devices. Its basic principles have not changed over the last one hundred years, yet transformer designs and materials continue to be improved. Transformers are essential for high voltage [[power transmission]], which makes long distance transmission economically practical. This advantage was the principal factor in the selection of [[alternating current/AC]] power transmission in the "[[War of Currents]]" in the late 1880s.

=== Clinic of La Borde ===

Born in Villeneuve-les-Sablons, [[Oise]], [[France]].{{Fact|date=February 2007}} Guattari was encouraged by psychiatrist [[Jean Oury]] towards the practice of [[psychiatry]], becoming impassioned from 1950 towards that field.{{Fact|date=February 2007}} Due to his frustrations with the theories and methods of French [[psychoanalyst]] [[Jacques Lacan]] — who both taught and analysed Guattari in the 1950s – Guattari became convinced that he needed to continue exploring as vast an array of domains as possible ([[philosophy]], [[ethnology]], [[linguistics]], [[architecture]], etc.,) in order to better define the orientation, delimitation and psychiatric efficacy of the practice. Guattari would later proclaim that psychoanalysis is "the best [[capitalist]] drug" because in it desire is confined to a couch: desire, in Lacanian psychoanalysis, is an energy that is contained rather than one that, if freed, could militantly engage itself in something different. He continued this research, collaborating in Jean Oury's private clinic of [[La Borde clinic|La Borde]] at Court-Cheverny, one of the main centers of institutional psychotherapy at the time. La Borde was a venue for conversation amongst innumerable students of philosophy, psychology, ethnology, and [[social work]]. La Borde was Félix Guattari's principal anchoring until he died of a heart attack in [[1992]].

=== 1960s to 1970s ===

[[Audio frequency]] transformers called [[repeating coil]]s were used by the earliest experimenters in the development of the [[telephone]]. While some electronics applications of the transformer have been made obsolete by new technologies, transformers are still found in many electronic devices.

From 1955 to 1965, Félix Guattari animated the [[trotskyist]] group ''Voie Communiste'' ("Communist Way"). He would then support [[anticolonialist]] struggles as well as the Italian ''[[Autonomists]]''. Guattari also took part in the movement of the psychological G.T., which gathered many psychiatrists at the beginning of the sixties and created the Association of Institutional Psychotherapy in November [[1965]]. It was at the same time that he founded, along with other militants, the F.G.E.R.I. (Federation of Groups for Institutional Study & Research) and its review research, working on philosophy, mathematics, psychoanalysis, education, architecture, ethnology, etc. The F.G.E.R.I. came to represent aspects of the multiple political and cultural engagements of Félix Guattari: the Group for Young Hispanics, the Franco-Chinese Friendships (in the times of the popular communes), the opposition activities with the wars in [[Algerian War of Independence|Algeria]] and Vietnam, the participation in the M.N.E.F., with the U.N.E.F., the policy of the offices of psychological academic aid (B.A.P.U.), the organisation of the University Working Groups (G.T.U.), but also the reorganizations of the training courses with the Centers of Training to the Methods of Education Activities (C.E.M.E.A.) for psychiatric male nurses, as well as the formation of Friendly Male Nurses (Amicales d'infirmiers) (in [[1958]]), the studies on architecture and the projects of construction of a day hospital of for "students and young workers".

Transformers come in a range of sizes from a thumbnail-sized [[coupling (electronics)|coupling]] transformer hidden inside a stage [[microphone]] to huge [[gigawatt]] units used to interconnect large portions of national [[electric power transmission|power grids]]. All operate with the same basic principles and with many similarities in their parts.

[[Image:Polemount-singlephase-closeup.jpg|thumb|left|180px|Single phase pole-mounted step-down transformer]]

Transformers alone cannot do the following:

*Convert [[Direct current|DC]] to [[Alternating current|AC]] or vice versa

*Change the voltage or current of DC

*Change the AC supply [[frequency]].

However, transformers are components of the systems that perform all these functions.

Guattari was involved in the [[events of May 1968]], starting from the [[Movement of March 22]]. It was in the aftermath of 1968 that Guattari met [[Gilles Deleuze]] at the [[University of Vincennes]] and began to lay the ground-work for the soon to be infamous ''[[Anti-Oedipus]]'' (1972), which [[Michel Foucault]] described as "an introduction to the non-fascist life" in his preface to the book. Throughout his career it may be said that his writings were at all times correspondent in one fashion or another with sociopolitical and cultural engagements. In 1967, he appeared as one of the founders of OSARLA (Organization of solidarity and Aid to the Latin-American Revolution). It was with the head office of the F.G.E.R.I. that he met, in [[1968]], [[Daniel Cohn-Bendit]], [[Jean-Jacques Lebel]], and [[Julian Beck]]. In [[1970]], he created C.E.R.F.I. (Center for the Study and Research of Institutional Formation), which takes the direction of the Recherches review. In 1977, he created the CINEL for "new spaces of freedom" before joining in the 1980s the [[ecological]] movement with his "[[ecosophy]]".

===Mutual induction===

The expanding and collapsing magnetic field around a conductor carrying a changing current can induce a voltage into a neighbouring conductor. This effect, called mutual induction, is an example of electromagnetic induction.

===An analogy1980s to 1990s ===

The transformer may be considered as a simple two-wheel '[[gearbox]]' for electrical voltage and current. The primary winding is analogous to the input shaft and the secondary winding to the output shaft. In this analogy, current is equivalent to shaft speed, voltage to shaft [[torque]]. In a gearbox, mechanical power (torque multiplied by speed) is constant (neglecting losses) and is equivalent to electrical power (voltage multiplied by current) which is also constant.

In his last book, ''Chaosmose'' ([[1992]]), the topic of which is already partially developed in ''What is Philosophy?'' (1991, with Deleuze), Félix Guattari takes again his essential topic: the question of subjectivity. "How to produce it, collect it, enrich it, reinvent it permanently in order to make it compatible with mutant Universes of value?" This idea returns like a leitmotiv, from ''Psychanalyse and transversality'' (a regrouping of articles from [[1957]] to [[1972]]) through ''Années d'hiver'' ([[1980]] - [[1986]]) and ''Cartographies Schizoanalytique'' ([[1989]]). He insists on the function of "a-signification", which plays the role of support for a subjectivity in act, starting from four parameters: "significative and [[semiotic]] flows, Phylum of Machinic Propositions, Existential Territories and Incorporeal Universes of Reference."

The [[gear ratio]] is equivalent to the transformer step-up or step-down ratio. A step-up transformer acts analogously to a reduction gear (in which mechanical power is transferred from a small, rapidly rotating gear to a large, slowly rotating gear): it trades current (speed) for voltage (torque), by transferring power from a primary coil to a secondary coil having more turns. A step-down transformer acts analogously to a multiplier gear (in which mechanical power is transferred from a large gear to a small gear): it trades voltage (torque) for current (speed), by transferring power from a primary coil to a secondary coil having fewer turns.

In 1995, the posthumous release ''Chaosophy'' featured Guattari's first collection of essays and interviews focuses on the French anti-psychiatrist and theorist's work as director of the experimental La Borde clinic and collaborator of philosopher Gilles Deleuze. ''Chaosophy'' is a groundbreaking introduction to Guattari's theories on "schizo-analysis", a process meant to replace [[Sigmund Freud]]'s interpretation with a more pragmatic, experimental, and collective approach rooted in reality. Unlike Freud, Guattari believes that [[schizophrenia]] is an extreme mental state co-existent with the capitalist system itself. But capitalism keeps enforcing [[neurosis]] as a way of maintaining normality. Guattari's post-Marxist vision of capitalism provides a new definition not only of mental illness, but also of micropolitical means of subversion. It includes key essays such as "Balance-Sheet Program for Desiring Machines," cosigned by Deleuze (with whom he coauthored Anti-Oedipus and A Thousand Plateaus), and the provocative "Everybody Wants To Be a Fascist."

==Basic principles==

=== Coupling by mutual induction ===

A simple transformer consists of two electrical [[Electrical conduction|conductor]]s called the '''primary winding''' and the '''secondary winding'''. Energy is coupled between the windings by the time-varying [[magnetic flux]] that passes through (links) both primary and secondary windings.When the current in a coil is switched on or off or changed, a voltage is induced in a neighbouring coil. The effect, called mutual induction, is an example of electromagnetic induction.

''Soft Subversions'' is another collection of Félix Guattari's essays, lectures, and interviews traces the militant anti-psychiatrist and theorist's thought and activity throughout the 1980s ("the winter years"). Concepts such as "micropolitics," "schizoanalysis," and "becoming-woman" open up new horizons for political and creative resistance in the "postmedia era." Guattari's energetic analyses of art, cinema, youth culture, economics, and power formations introduce a radically inventive thought process engaged in liberating subjectivity from the standardizing and homogenizing processes of global capitalism.

=== Elementary analysis ===

[[Image:Transformer3d col3.svg|right|thumb|350px|Practical transformer showing magnetising flux in the core]]

If a time-varying voltage <math>{v_P}\, </math> is applied to the primary winding of <math>N_P\, </math> turns, a current will flow in it producing a [[magnetomotive force]] (MMF). Just as an [[electromotive force]] (EMF) drives current around an electric circuit, so MMF tries to drive magnetic flux through a [[magnetic circuit]]. The primary MMF produces a varying [[magnetic flux]] <math>\Phi_P\, </math> in the core, and, with an open circuit secondary winding, induces a back [[electromotive force]] (EMF) in opposition to <math>{v_P}\, </math>. In accordance with [[Faraday's law of induction]], the voltage induced across the primary winding is proportional to the rate of change of flux:

== Bibliography ==

:<math>{v_P} = {N_P} \frac {d \Phi_P}{dt}</math>&nbsp;&nbsp;&nbsp;&nbsp; and &nbsp;&nbsp;&nbsp;&nbsp;<math>{v_S} = {N_S} \frac {d \Phi_S}{dt}</math>

=== Works published in English ===

*''Molecular Revolution: Psychiatry and Politics'' (1984). Trans. Rosemary Sheed. Selected essays from ''Psychanalyse et transversalité'' (1972) and ''La révolution moléculaire'' (1977).

where

*''Les Trois écologies'' (1989). Trans. ''The Three Ecologies.'' Partial translation by Chris Turner (Paris: Galilee, 1989), full translation by Ian Pindar and Paul Sutton (London: The Athlone Press, 2000).

*<math>v_P</math> and <math>v_S</math> are the voltages across the primary winding and secondary winding,

*''Chaosmose'' (1992). Trans. ''Chaosmosis: an ethico-aesthetic paradigm'' (1995).

*<math>N_P</math> and <math>N_S</math> are the numbers of turns in the primary winding and secondary winding,

*''Chaosophy'' (1995), ed. Sylvere Lotringer. Collected essays and interviews.

*<math>d \Phi_P / dt</math> and <math>d \Phi_S / dt</math> are the derivatives of the flux with respect to time of the primary and secondary windings.

*''Soft Subversions'' (1996), ed. Sylvere Lotringer. Collected essays and interviews.

*''The Guattari Reader'' (1996), ed. Gary Genosko. Collected essays and interviews.

*''Ecrits pour L'Anti-Œdipe'' (2004), ed. Stéphane Nadaud. Trans. ''The Anti-Œdipus Papers'' (2006). Collection of texts written between 1969 and 1972.

*''Chaos and Complexity'' (Forthcoming 2008, MIT Press). Collected essays and interviews.

In collaboration with [[Gilles Deleuze]]:

Saying that the primary and secondary windings are perfectly coupled is equivalent to saying that <math>\Phi_P = \Phi_S\, </math>. Substituting and solving for the voltages shows that:

*''Capitalisme et Schizophrénie 1. L'Anti-Œdipe'' (1972). Trans. ''[[Anti-Oedipus]]'' (1977).

:<math>\frac{v_P}{v_S}=\frac{N_P}{N_S}</math>&nbsp;&nbsp;&nbsp;&nbsp;

*''Kafka: Pour une Littérature Mineure'' (1975). Trans. ''Kafka: Toward a Theory of Minor Literature'' (1986).

*''Rhizome: introduction'' (Paris: Minuit, 1976). Trans. "Rhizome," in ''Ideology and Consciousness'' 8 (Spring, 1981): 49-71. This is an early version of what became the introductory chapter in ''Mille Plateaux.''

*''Capitalisme et Schizophrénie 2. Mille Plateaux'' (1980). Trans. ''[[A Thousand Plateaus]]'' (1987).

*''On the Line'' (1983). Contains translations of "Rhizome," and "Politics" ("Many Politics") by Deleuze and Parnet.

*''Nomadology: The War Machine.'' (1986). Translation of "Plateau 12," ''Mille Plateaux.''

*''Qu'est-ce que la philosophie?'' (1991). Trans. ''What Is Philosophy?'' (1996).

Other collaborations:

where

*<math>v_p </math> and <math>v_s</math> are voltages across primary and secondary,

*''Les nouveaux espaces de liberté'' (1985). Trans. ''Communists Like Us'' (1990). With [[Antonio Negri]].

*<math>N_p </math> and <math>N_s</math> are the numbers of turns in the primary and secondary , respectively.

*''Micropolitica: Cartografias do Desejo'' (1986). Trans. ''Molecular Revolution in Brazil'' (Forthcoming October 2007, MIT Press). With Suely Rolnik.

*''The party without bosses'' (2003), by Gary Genosko. Features a 1982 conversation between Guattari and [[Luiz Inácio Lula da Silva]], the current [[President of Brazil]].

=== Works untranslated into English ===

Hence in an ideal transformer, the [[ratio]] of the primary and secondary voltages is equal to the ratio of the [[coil|number of turns]] in their windings, or alternatively, the voltage per turn is the same for both windings. The ratio of the currents in the primary and secondary circuits is inversely proportional to the turns ratio. This leads to the most common use of the transformer: to convert electrical energy at one voltage to energy at a different voltage by means of windings with different numbers of turns. In a practical transformer, the higher-voltage winding will have more turns, of smaller conductor cross-section, than the lower-voltage windings.

Note: Many of the essays found in these works have been individually translated and can be found in the English collections.

*''Psychanalyse et transversalité. Essais d'analyse institutionnelle'' (1972).

*''La révolution moléculaire'' (1977, 1980). The 1980 version (éditions 10/18) contains substantially different essays from the 1977 version.

*''L'inconscient machinique. Essais de Schizoanalyse'' (1979).

*''Les années d'hiver, 1980-1985'' (1986).

*''Cartographies schizoanalytiques'' (1989).

Other collaborations:

The EMF in the secondary winding, if connected to an electrical circuit, will cause current to flow in the secondary circuit. The MMF produced by current in the secondary opposes the MMF of the primary and so tends to cancel the flux in the core. Since the reduced flux reduces the EMF induced in the primary winding, increased current flows in the primary circuit. The resulting increase in MMF due to the primary current offsets the effect of the opposing secondary MMF. In this way, the [[Electric power|electrical energy]] fed into the primary winding is delivered to the secondary winding.

*''L’intervention institutionnelle'' (Paris: Petite Bibliothèque Payot, n. 382 - 1980). On [[institutional pedagogy]]. With Jacques Ardoino, G. Lapassade, Gerard Mendel, Rene Lourau.

For example, suppose a power of 50 watts is supplied to a resistive load from a transformer with a turns ratio of 25:2.

*''Pratique de l'institutionnel et politique'' (1985). With [[Jean Oury]] and Francois Tosquelles.

* ''P'' = ''EI'' (power = electromotive force &times; current)

*(it) ''Desiderio e rivoluzione. Intervista a cura di Paolo Bertetto'' (Milan: Squilibri, 1977). Conversation with Franco Berardi (Bifo) and Paolo Bertetto.

:: 50 W = 2 V &times; 25 A in the primary circuit

* Now with transformer change:

:: 50 W = 25 V &times; 2 A in the secondary circuit.

=== AlternativeSelect transformersecondary analysissources ===

This treats the [[winding]]s as a pair of mutually coupled coils with both [[primary]] and secondary windings passing [[current]]s. In an ''ideal'' transformer the primary MMF must equal the secondary MMF, and since these are in opposite directions, they cancel so that there is no overall resultant flux in the core. That this is so can be seen by realising that any unopposed primary [[emf]] would create a large primary current and therefore a large [[flux]] in the core due to the primary winding. However, this large flux would necessarily cause a large current to flow in the secondary circuit and this current must create an opposing flux that effectively cancels the initiating primary flux.

In a non-ideal transformer, the [[resultant]] flux in the core is that needed to magnetise the core. This is called the [[magnetising flux]].

*[[Éric Alliez]], ''La Signature du monde, ou Qu'est-ce que la philosophie de Deleuze et Guattari'' (1993). Trans. ''The Signature of the World: Or, What is Deleuze and Guattari's Philosophy?'' (2005).

=== Direct current ===

*Gary Genosko, ''Félix Guattari: An Aberrant Introduction'' (2002).

*Gary Genosko (ed.), ''Deleuze and Guattari: Critical Assessments of Leading Philosophers, Volume 2: Guattari'' (2001).

==External links==

Transformers should not be driven with DC nor, generally, have any DC component present at the input. Relatively small amounts of direct current can cause core [[Saturation (magnetic)|saturation]] and thus prevent proper operation. Also, since a DC voltage source would not give a time-varying flux in the core, no induced counter-EMF would be generated and so current flow into the transformer would be limited only by the series resistance of the windings. In this situation, the transformer would heat until the transformer either reaches thermal equilibrium or is destroyed. This principle is actually exploited when large power transformers must be dried (have condensation and other water removed from their windings) — they are simply heated using DC.

*[http://www.revue-chimeres.org/guattari/guattari.html Chimeres site on Guattari (in French)]

*[http://multitudes.samizdat.net/_Guattari-Felix_.html Multitudes page on Guattari (in French)]

{{DEFAULTSORT:Guattari, Felix}}

For the same reason, transformers should generally not have DC components present in their output windings. A notable violation of this rule occurs with [[Rectifier#Half-wave rectification|half-wave rectifier]]s, where the transformer winding must also carry the DC load current; these circuits are usually used in low-power applications because of this. [[Rectifier#Full-wave rectification|Full-wave rectifier]]s, by comparison, do not require direct current to flow through the transformer and so are capable of much higher power levels.

[[Category:1930 births]]

[[Category:1992 deaths]]

[[Category:French anarchists]]

[[Category:Postmodern theory]]

[[Category:Psychoanalytic theory]]

[[Category:Psychoanalysts]]

[[Category:Anti-psychiatry]]

[[Category:Psychotherapists]]

[[Category:French non-fiction writers]]

[[Category:French philosophers]]

[[Category:Political philosophers]]

[[Category:Deleuze-Guattari]]

[[de:Félix Guattari]]

=== The Universal '''emf''' equation ===

[[es:Félix Guattari]]

If the flux in the core is [[sinusoidal]], the relationship for either winding between its number of turns, voltage, [[magnetic flux density]] and core cross-sectional area is given by the universal emf equation (from Faraday's law):

[[fr:Félix Guattari]]

[[gl:Félix Guattari]]

:<math> E={\frac {2 \pi f N a B} {\sqrt{2}}} \!=4.44 f N a B</math>

[[it:Félix Guattari]]

where

[[nl:Félix Guattari]]

*<math>E</math> is the sinusoidal [[root mean square]] voltage of the winding,

[[ja:フェリックス・ガタリ]]

*<math>f</math> is the [[frequency]] in [[hertz]],

[[pt:Félix Guattari]]

*<math>N</math> is the number of turns of wire,

[[fi:Félix Guattari]]

*<math>a</math> is the cross-sectional area of the core in square meters and

*<math>B</math> is the peak magnetic flux density in [[Tesla (unit)|teslas]] (and therefore <math>B / {\sqrt{2}}</math> is the root mean square flux density).

==Invention==

Those credited with the invention of the transformer include:

* [[Michael Faraday]], who invented an 'induction ring' on [[August 29]] [[1831]]. This was the first transformer, although Faraday used it only to demonstrate the principle of [[electromagnetic induction]] and did not foresee the use to which it would eventually be put.

* [[Lucien Gaulard]] and [[John Dixon Gibbs]], who first exhibited a device called a 'secondary generator' in London in 1881 and then sold the idea to American company [[Westinghouse Electric Corporation|Westinghouse]]. This may have been the first practical power transformer, but was not the first transformer of any kind. They also exhibited the invention in [[Turin]] in 1884, where it was adopted for an electric lighting system. Their early devices used an open iron core, which was later abandoned in favour of a more efficient circular core with a closed magnetic path.

[[Image:StanleyTransformer.png|none|right]]

* [[William Stanley (physicist)|William Stanley]], an engineer for Westinghouse, who built the first practical device in 1885 after George Westinghouse bought Gaulard and Gibbs' patents. The core was made from interlocking E-shaped iron plates. This design was first used commercially in 1886.

* [[Hungary|Hungarian]] [[engineer]]s [[Károly Zipernowsky]], [[Ottó Bláthy]] and [[Miksa Déri]] at the [[Ganz company]] in [[Budapest]] in 1885, who created the efficient "ZBD" model based on the design by Gaulard and Gibbs.

* [[Nikola Tesla]] in 1891 invented the [[Tesla coil]], which is a high-voltage, air-core, dual-tuned resonant transformer for generating very high voltages at high frequency.

Many others have [[List of transformer patents|patents on transformers]].

==Practical considerations==

===Classifications===

Transformers are adapted to numerous engineering applications and may be classified in many ways:

* By power level (from fraction of a volt-ampere(VA) to over a thousand MVA),

* By application (power supply, impedance matching, circuit isolation),

* By frequency range (power, audio, radio frequency(RF))

* By voltage class (a few volts to about 750 kilovolts)

* By cooling type (air cooled, oil filled, fan cooled, water cooled, etc.)

* By purpose (distribution, rectifier, arc furnace, amplifier output, etc.).

* By ratio of the number of turns in the coils

:*'''Step-up'''

:: The secondary has more turns than the primary.

:*'''Step-down'''

:: The secondary has fewer turns than the primary.

:*'''Isolating'''

:: Intended to transform from one voltage to the same voltage. The two coils have approximately equal numbers of turns, although often there is a slight difference in the number of turns, in order to compensate for losses (otherwise the output voltage would be a little less than, rather than the same as, the input voltage).

:*'''Variable'''

:: The primary and secondary have an adjustable number of turns which can be selected without reconnecting the transformer.

===Circuit symbols===

''Standard symbols''

<table align="center" border="1" cellpadding="2" cellspacing="0">

<tr>

<td>[[Image:Transformer-iso.png|circuit symbol]]</td>

<td>Transformer with two windings and iron core.</td>

</tr>

<tr>

<td>[[Image:Transformer-2s.png|circuit symbol]]</td>

<td>Transformer with three windings.<br>

The dots show the relative winding configuration of the windings.</td>

</tr>

<tr>

<td>[[Image:Transformer-sd.png|circuit symbol]]</td>

<td>Step-down or step-up transformer.<br>

The symbol shows which winding has more turns,<br>

but does not usually show the exact ratio.</td>

</tr>

<tr>

<td>[[Image:Transformer-es.png|circuit symbol]]</td>

<td>Transformer with electrostatic screen,<br>

which prevents [[capacitive coupling]] between the windings.</td>

</tr>

</table>

===Losses===

An ideal transformer would have no losses, and would therefore be 100% efficient. In practice, energy is dissipated due both to the [[electrical resistance|resistance]] of the windings (known as ''[[copper loss]]''), and to magnetic effects primarily attributable to the core (known as ''[[iron loss]]''). Transformers are, in general, highly efficient. Large power transformers (over 50 MVA) may attain an efficiency as high as 99.75%. Small transformers, such as a plug-in "power brick" used to power small consumer electronics, may be less than 85% efficient.

Transformer losses arise from:

* '''Winding resistance'''

Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, [[skin effect]] and [[proximity effect]] create additional winding resistance and losses.

* '''Eddy currents'''

Induced [[eddy currents]] circulate within the core, causing resistive heating.

*'''Hysteresis losses'''

Each time the magnetic field is reversed, a small amount of energy is lost to [[hysteresis]] within the magnetic core. The amount of hysteresis is a function of the particular core material.

* '''Magnetostriction'''

Magnetic flux in the core causes it to physically expand and contract slightly with the alternating magnetic field, an effect known as [[magnetostriction]]. This in turn causes losses due to frictional heating in susceptible [[ferromagnetic]] cores.

* '''Mechanical losses'''

In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, creating a familiar humming or buzzing noise, and consuming a small amount of power.

* '''Stray losses'''

Not all the magnetic field produced by the primary is intercepted by the secondary. A portion of the [[leakage flux]] may induce eddy currents within nearby conductive objects, such as the transformer's support structure, and be converted to heat.

* '''Cooling system'''

Large power transformers may be equipped with cooling fans, oil pumps or water-cooled heat exchangers designed to remove the heat caused by copper and iron losses. The power used to operate the cooling system is typically considered part of the losses of the transformer.

===Operation at different frequencies===

The equation shows that the EMF of a transformer at a given flux density increases with frequency. By operating at higher frequencies, transformers can be physically more compact without reaching [[saturation (magnetic)|saturation]], and a given core is able to transfer more power. However, other properties of the transformer such as losses due to the core and skin-effect also increase with frequency. Generally, operation of a transformer at it's designed voltage but at a higher frequency than will lead to reduced magnetising (no load primary) current. At a frequency lower than the design value,with the rated voltage applied, the magnetising current may increase to an excessive level.

Steel cores develop a larger hysteresis loss as the operating frequency is increased. Ferrite cores are typically used for frequencies above 1kHz. Aircraft traditionally use 400 Hz power systems since the slight increase in thermal losses is more than offset by reduced weight. Military gear includes 400 Hz (and other frequencies) to supply power for [[radar]] or [[servomechanism]]s.

[[Flyback transformer]]s are built using ferrite cores. They supply high voltage to the [[cathode ray tube|CRT]]s at the frequency of the horizontal oscillator. In the case of television sets, this is about 15.7kHz. It may be as high as 75 - 120kHz for high-resolution computer monitors.

[[Switched-mode power supply|Switching power supply]] transformers usually operate between 50-1000 kHz. The tiny cores found in wristwatch [[backlight]] power supplies produce audible sound (about 1 kHz).

Operation of a power transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. For example, transformers at [[hydroelectric]] generating stations may be equipped with over-excitation protection, so-called "volts per hertz" protection [[relay]]s, to protect the transformer from overvoltage at higher-than-rated frequency which may occur if a generator loses its connected load.

== Construction ==

===Cores===

==== Steel cores ====

[[Image:Transformer.filament.agr.jpg|thumb|300px|Laminated core transformer showing edge of laminations at top of unit.]]

Transformers for use at power or audio frequencies have cores made of many thin laminations of [[silicon steel]]. By concentrating the magnetic flux, more of it is usefully linked by both primary and secondary windings. Since the steel core is conductive, it, too, has currents induced in it by the changing magnetic flux. Each layer is insulated from the adjacent layer to reduce the energy lost to [[eddy current]] heating of the core. A typical laminated core is made from E-shaped and I-shaped pieces, leading to the name "EI transformer".

A steel core's [[magnetic hysteresis]] means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high [[inrush current]] until the effect of the remanent magnetism is reduced, usually after a few cycles of the applied alternating current. Overcurrent protection devices such as [[fuse (electrical)|fuses]] must be selected to allow this harmless inrush to pass. On transformers connected to long overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core, and false operation of transformer [[relay|protection devices]].

Distribution transformers can achieve low off-load losses by using cores made with amorphous (non-crystalline) steel, so-called "[[Amorphous#Metallic glass|metal glasses]]" — the high cost of the core material is offset by the lower losses incurred at light load, over the life of the transformer. In order to maintain good voltage regulation, distribution transformers are designed to have very low [[leakage inductance]].

Certain special purpose transformers use long magnetic paths, insert air gaps, or add magnetic shunts (which bypass a portion of magnetic flux that would otherwise link the primary and secondary windings) in order to intentionally add leakage inductance. The additional leakage inductance limits the secondary winding's short circuit current to a safe, or a controlled, level. This technique is used to stabilize the output current for loads that exhibit [[negative resistance]] such as [[electric arc]]s, [[mercury vapor lamp]]s, and [[neon sign]]s, or safely handle loads that may become periodically short-circuited such as electric arc welders.

==== Solid cores ====

[[Image:Transformer Iron Core.svg|none|45px|left]]

Powdered [[iron]] cores are used in circuits (such as switch-mode power supplies) that operate above mains frequencies and up to a few tens of kilo[[hertz]]. These materials combine high magnetic [[permeability]] with high bulk electrical [[resistivity]].

At even higher, [[radio]]-frequencies (RF), other types of cores made from non-conductive magnetic [[ceramic]] materials, called ''[[ferrite (magnet)|ferrites]]'', are common. Some RF transformers also have moveable cores (sometimes called slugs) which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits.

==== Air cores ====

[[Image:Transformer Air Core.svg|none|45px|left]]

High-frequency transformers may also use air cores. These eliminate the loss due to [[hysteresis]] in the core material. Such transformers maintain high coupling efficiency (low stray field loss) by overlapping the primary and secondary windings.

==== Toroidal cores ====

[[Image:Transformers.jpg|thumb|left|Various transformers. The top right is toroidal. The bottom right is from a 12 VAC [[w:wall wart|wall wart]] supply.]]

Toroidal transformers are built around a ring-shaped core, which is made from a long strip of silicon [[steel]] or [[permalloy]] wound into a coil, from powdered iron, or [[ferrite (magnet)|ferrite]], depending on operating frequency. The strip construction ensures that the [[grain boundary|grain boundaries]] are optimally aligned, improving the transformer's efficiency by reducing the core's [[reluctance]]. The closed ring shape eliminates air gaps inherent in the construction of an EI core. The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimises the length of wire needed, and also provides screening to minimize the core's magnetic field from generating [[electromagnetic interference]].

Ferrite toroid cores are used at higher frequencies, typically between a few tens of kilohertz to a megahertz, to reduce losses, physical size, and weight of [[Switched-mode power supply|switch-mode power supplies]].

Toroidal transformers are more efficient (around 95%) than the cheaper laminated EI types. Other advantages, compared to EI types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and more choice of shapes. This last point means that, for a given power output, either a wide, flat [[toroid]] or a tall, narrow one with the same electrical properties can be chosen, depending on the space available. The main disadvantage is higher cost.

A drawback of toroidal transformer construction is the higher cost of windings. As a consequence, toroidal transformers are uncommon above ratings of a few kVA. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings.

When fitting a toroidal transformer, it is important to avoid making an unintentional [[short-circuit]] through the core. This can happen if the steel mounting bolt in the middle of the core is allowed to touch metalwork at both ends, making a loop of conductive material which passes through the hole in the toroid. Such a loop could result in a dangerously large current flowing in the bolt.

=== Windings ===

In most practical transformers, the primary and secondary conductors are multi-turn coils of conducting [[wire]] because each turn of the coil contributes to the [[magnetic field]], creating a higher [[magnetic flux density]] than would a single turn. The wire of adjacent turns and different windings must be electrically insulated from each other.

The conducting material used for the winding depends upon the application. Small power and signal transformers are wound with solid copper wire, insulated usually with [[Enameled wire|enamel]] and sometimes additional insulation. Larger power transformers may be wound with wire, copper or aluminum rectangular conductors, or strip conductors for very heavy currents. High frequency transformers operating in the tens to hundreds of kilohertz will have windings made of [[Skin effect#Mitigation|Litz wire]], to minimize the skin effect losses in the conductors. Large power transformers use multiply-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings. Each strand is insulated from the others, and the strands are arranged so that either at certain points in the winding or throughout the winding, each portion occupies different relative positions in the complete conductor. This "transposition" equalises the current flowing in each strand of the conductor, and reduces [[eddy current]] losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size. (see reference (1) below)

For signal transformers the windings may be arranged in a way to minimise leakage inductance and stray capacitance, to improve high-frequency response.

[[Image:Transformer Centre-tap Iron Core.svg|none|45px|right]]

Windings on both primary and secondary of power transformers may have external connections (called taps) to intermediate points on the winding to allow adjustment of the voltage ratio; taps may be connected to automatic on-load [[tap changer]] [[switchgear]] for [[Voltage regulator|voltage regulation]] of [[Power distribution|distribution]] circuits. Audio-frequency transformers used for distribution of audio to public address loudspeakers have taps to allow adjustment of power supplied to each speaker. A center-tapped transformer is often used in the output stage of an audio power [[amplifier]] in a [[push-pull]] circuit. Tapped transformers are also used as components of amplifiers, oscillators, and for [[feedback]] linearization of amplifier circuits.

=== Insulation ===

The turns of the windings must be insulated from each other to ensure that the current travels through the entire winding. The potential difference between adjacent turns is usually small, so that enamel insulation is usually sufficient for small power transformers. In larger transformers additional layers of insulation are used.

The transformer may also be immersed in [[transformer oil]] that provides further insulation. To ensure that the insulating capability of the transformer oil does not deteriorate, the transformer casing is completely sealed against moisture ingress. The oil serves as both cooling medium to remove heat from the core and coil and as part of the insulation system.

=== Shielding ===

The proximity of the primary and secondary windings can create a mutual [[capacitance]] between the windings. Where transformers are intended for high electrical isolation between primary and secondary circuits, an electrostatic shield can be placed between windings to minimize this effect.

Transformers may also be enclosed by magnetic shields, electrostatic shields, or both to prevent outside interference from affecting the operation of the transformer, or to prevent the transformer from affecting the operation of other devices (such as [[Cathode ray tube|CRTs]] near the transformer).

=== Coolant ===

[[Image:Transformer_01.jpg|thumb|180px|right|Three phase dry-type transformer with cover removed; rated about 200 KVA, 480 V.]]

Small signal transformers do not generate significant amounts of heat. Power transformers rated up to a few kilowatts rely on natural convective air cooling. Transformers handling higher power can be fan-cooled.

Specific provision must be made for cooling of high-power transformers. Some dry transformers are enclosed in pressurized tanks and are cooled by [[nitrogen]] or [[sulfur hexafluoride]] gas.

The windings of high-power or high-voltage transformers are immersed in [[transformer oil]] — a highly-refined [[mineral oil]] that is stable at high temperatures. Large transformers to be used indoors must use a non-flammable liquid. Formerly, [[polychlorinated biphenyl]] (PCB) was used as it was not a fire hazard in indoor power transformers and it is highly stable. Due to the stability of PCB and its environmental accumulation, it is no longer permitted in new equipment. Today, nontoxic, stable [[silicone]]-based oils or [[fluorocarbon|fluorinated hydrocarbon]]s may be used, where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault. Other less-flammable fluids such as [[canola oil]] may be used but all fire resistant fluids have some drawbacks in performance, cost, or toxicity compared with mineral oil.

The oil cools the transformer, and provides part of the electrical insulation between internal live parts. It has to be stable at high temperatures so that a small short or arc will not cause a breakdown or fire. The oil-filled tank may have radiators through which the oil circulates by natural convection. Very large or high-power transformers (with capacities of millions of [[watt]]s) may have cooling fans, oil pumps and even oil to water [[heat exchangers]]. Oil-filled transformers undergo prolonged drying processes, using vapor-phase heat transfer, electrical self-heating, the application of a [[vacuum]], or combinations of these, to ensure that the transformer is completely free of [[water vapor]] before the cooling oil is introduced. This helps prevent electrical breakdown under load.

Oil-filled power transformers may be equipped with [[Buchholz relay]]s — safety devices sensing gas build-up inside the transformer (a side effect of an [[electric arc]] inside the windings) and switching off the transformer.

Experimental power transformers in the 2 MVA range have been built with [[superconductivity|superconducting]] windings which eliminates the copper losses, but not the core steel loss. These are cooled by liquid [[nitrogen]] or [[helium]].

===Terminals===

Very small transformers will have wire leads connected directly to the ends of the coils, and brought out to the base of the unit for circuit connections. Larger transformers may have heavy bolted terminals, bus bars or high-voltage insulated [[Bushing (electrical)|bushings]] made of polymers or porcelain. A large bushing can be a complex structure since it must provide electrical insulation without letting the transformer leak oil.

===Enclosure===

Small transformers often have no enclosure. Transformers may have a shield enclosure, as described above. Larger units may be enclosed to prevent contact with live parts, and to contain the cooling medium (oil or pressurized gas).

== Transformer designs ==

=== Autotransformers ===

{{main|Autotransformer}}

[[Image:Autotransformer.svg|none|35px|left|]]

An [[autotransformer]] has only a single winding, which is tapped at some point along the winding. AC or pulsed voltage is applied across a portion of the winding, and a higher (or lower) voltage is produced across another portion of the same winding. While theoretically separate parts of the winding can be used for input and output, in practice the higher voltage will be connected to the ends of the winding, and the lower voltage from one end to a tap. For example, a transformer with a tap at the center of the winding can be used with 230 volts across the entire winding, and 115 volts between one end and the tap. It can be connected to a 230 volt supply to drive 115 volt equipment, or reversed to drive 230 volt equipment from 115 volts. As the same winding is used for input and output, the flux in the core is partially cancelled, and a smaller core can be used. For voltage ratios not exceeding about 3:1, an autotransformer is cheaper, lighter, smaller and more efficient than a true (two-winding) transformer of the same rating.

In practice, transformer losses mean that autotransformers are not perfectly reversible; one designed for stepping down a voltage will deliver slightly less voltage than required if used to step up. The difference is usually slight enough to allow reversal where the actual voltage level is not critical.

By exposing part of the winding coils and making the secondary connection through a sliding [[brush (electric)|brush]], an autotransformer with a near-continuously variable turns ratio can be obtained, allowing for very small increments of voltage.

=== Polyphase transformers ===

For [[Three-phase electric power|three-phase power]], three separate single-phase transformers can be used, or all three phases can be connected to a single polyphase transformer. The three primary windings are connected together and the three secondary windings are connected together. The most common connections are Y-Δ, Δ-Y, Δ-Δ and Y-Y. A [[vector group]] indicates the configuration of the windings and the [[phase angle]] difference between them. If a winding is connected to earth ([[Ground (electricity)|grounded]]), the earth connection point is usually the center point of a Y winding. There are many possible configurations that may involve more or fewer than six windings and various tap connections.

[[Image:Wye_Delta_01.png|300px|thumb|left|The [[Y-Δ transform]] is a mathematical technique to simplify analysis of an electrical network.]]

=== Resonant transformers ===

A [[resonance|resonant]] transformer is one that operates at the [[resonant frequency]] of one or more of its coils and, usually, an external [[capacitor]]. The resonant coil, usually the secondary, acts as an [[inductor]], and is connected in series with a [[capacitor]]. If the primary coil is driven by a periodic source of [[alternating current]], such as a [[Square wave|square]] or [[Sawtooth wave]] , each pulse of current helps to build up an oscillation in the secondary coil. Due to resonance, a very high voltage can develop across the secondary, until it is limited by some process such as [[electrical breakdown]]. These devices are therefore used to generate high alternating voltages. The current available from this type of coil can be much larger than that from electrostatic machines such as the [[Van de Graaff generator]] and [[Wimshurst machine]]. They also run at a higher operating temperature than standard units.

Examples:

*[[Tesla coil]]

*[[Oudin coil]] (or Oudin resonator; named after its inventor [[Paul Oudin]])

*[[Jacques Arsene d'Arsonval|D'Arsonval]] apparatus

*[[Ignition coil]] or [[induction coil]] used in the [[ignition system]] of a [[petrol engine]]

*[[Flyback transformer]] of a [[Cathode ray tube|CRT]] [[television]] set or video monitor.

*[[Electrical breakdown]] and insulation testing of high voltage equipment and cables

Other applications of resonant transformers are as coupling between stages of a [[superheterodyne receiver]], where the selectivity of the receiver is provided by the tuned transformers of the intermediate-frequency amplifiers.

A voltage regulating transformer uses a resonant winding and allows part of the core to go into saturation on each cycle of the alternating current. This effect stabilizes the output of the regulating transformer, which can be used for equipment that is sensitive to variations of the supply voltage. Saturating transformers provide a simple rugged method to stabilize an ac power supply. However, due to the hysteresis losses accompanying this type of operation, efficiency is low.

===Instrument transformers===

====Current transformers====

[[Image:CurrentTransformers.jpg|right|thumb|300px|Current transformers used in [[electricity meter|metering equipment]] for [[three-phase]] 400 ampere electricity supply]]A '''current transformer''' is a type of "''instrument transformer''" that is designed to provide a current in its secondary which is '''accurately''' proportional to the current flowing in its primary.

Current transformers are commonly used in metering and protective relaying to facilitate the measurement of large currents and isolation of high voltage systems which would be difficult to measure more directly.

Current transformers are often constructed by passing a single primary turn (either an insulated cable or an uninsulated conductor (copper or aluminum are typical in electric utility applications) through a well-insulated toroidal core wrapped with many turns of wire. Current transformers (CTs) are used extensively in the electrical power industry for monitoring of the [[power grid]]. The CT is described by its current ratio from primary to secondary. Common secondaries are 1 or 5 amperes. The secondary winding can be single ratio or multi ratio, with five taps being common for multi ratio CTs. Typically, the secondary connection points are labeled as X1, X2 and so on. The multi ratio CTs are typically used for current matching in current differential protective relaying applications. Often, multiple CTs will be installed as a "stack" for various uses (for example, protection devices and revenue metering may use separate CTs). For a three-stacked CT application, the secondary winding connection points are typically labeled Xn, Yn, Zn.

Specially constructed "''[[wideband]] current transformers''" are also used (usually with an [[oscilloscope]]) to measure [[waveform]]s of [[high frequency]] or pulsed currents. One type of specially constructed wideband transformer provides a voltage output that is proportional to the measured current. Another type (called a [[Rogowski coil]]) requires an external [[integrator]] in order to provide a voltage output that is proportional to the measured current.

Care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary, as this will produce a dangerously high voltage across the open secondary.

====Voltage transformers====

Voltage transformers (also called potential transformers) are another type of instrument transformer. They are used by the electricity supply industry to accurately measure high voltages for metering and protective relay purposes. They are designed to present negligible load to the voltage being measured and to have a precise turns ratio to accurately step down dangerously high voltages so that metering and protective relay equipment can be operated at a lower, and safer, potential.

This safer voltage is typically 66 to 69 volts phase to ground. 69 volts phase to ground is equivalent to 120 volts phase to phase (69&radic;3) which is required by some protective relays.

The transformer winding connection points are typically labled as H1, H2 (sometimes H0 if it is internally grounded) and X1, X2, and sometimes an X3 may be present. X3 allows the tapping of 120 volts and 69 volts from the same winding. In other applications a Y winding (Y1, Y2, Y3) may also be available on the same voltage transformer, and is identical to the X winding but electrically isolated. The H windings (sometimes called high side or primary) are connected to the high voltage and the X and Y windings (sometimes called low side or secondary) to the metering or protective relay. The high side (primary) may be connected phase to ground or phase to phase. The low side (secondary) is usually phase to ground.

The nomenclature (H1, X1, Y1, etc.) are often referred to as polarity. This applies to current transformers as well. This should not to be confused with polarity as found on DC sources, but as a reference for proper phase relationship between other AC sources, voltage and current. This is important for proper operation of protective relays and revenue metering.

=== Pulse transformers ===

A '''pulse transformer''' is a transformer that is optimised for transmitting rectangular electrical pulses (that is, pulses with fast rise and fall times and a constant [[amplitude]]). Small versions called ''signal'' types are used in [[digital logic]] and [[telecommunications]] circuits, often for matching logic drivers to [[transmission line]]s. Medium-sized ''power'' versions are used in power-control circuits such as [[camera flash]] controllers. Larger ''power'' versions are used in the [[electrical power distribution]] industry to interface low-voltage control circuitry to the high-voltage gates of [[Power semiconductor device|power semiconductor]]s such as [[TRIAC]]s, [[IGBT]]s, [[thyristor]]s and [[MOSFET]]s. Special [[high voltage]] pulse transformers are also used to generate high power pulses for [[radar]], [[particle accelerators]], or other [[pulsed power]] applications.

To minimise distortion of the pulse shape, a pulse transformer needs to have low values of leakage inductance and distributed capacitance, and a high open-circuit inductance. In power-type pulse transformers, a low coupling capacitance (between the primary and secondary) is important to protect the circuitry on the primary side from high-powered transients created by the load. For the same reason, high insulation resistance and high breakdown voltage are required. A good transient response is necessary to maintain the rectangular pulse shape at the secondary, because a pulse with slow edges would create switching losses in the power semiconductors.

The product of the peak pulse voltage and the duration of the pulse (or more accurately, the voltage-time integral) is often used to characterise pulse transformers. Generally speaking, the larger this product, the larger and more expensive the transformer.

===RF transformers (transmission line transformers) ===

[[Image:Transformer with Tickler.svg|frame|right|50px|Coils with tickler.]]

For [[radio frequency]] use, transformers are sometimes made from configurations of transmission line, sometimes [[bifilar]] or [[coaxial]] cable, wound around [[ferrite]] or other types of core. This style of transformer gives an extremely wide [[bandwidth]] but only a limited number of ratios (such as 1:9, 1:4 or 1:2) can be achieved with this technique.

The core material increases the inductance dramatically, thereby raising its [[Q factor]]. The cores of such transformers help improve performance at the lower frequency end of the band.

Older style RF transformers sometimes used a third coil (called a tickler winding) to inject [[feedback]] into an earlier ([[Detector (radio)|detector]]) stage in antique [[Regenerative circuit|regenerative]] radio receivers.

==== Baluns ====

Baluns are transformers designed specifially to connect between [[balanced]] and [[unbalanced]] circuits. These are sometimes made from configurations of transmission line and sometimes [[bifilar]] or [[coaxial]] cable and are similar to transmission line transformers in constructuion and operation. This style of transformer is frequently used as an [[impedance matching]] [[balun]] to convert from 300 ohm balanced to 75 ohm unbalanced in [[FM]] [[receiver]]s.

== Audio transformers ==

[[Image:Audion-sterling-transformers.jpg|left|thumb|Transformers in a tube amplifier. Output transformers are on the left. The power supply toroidal transformer is on right.]]

Transformers are used in [[vacuum tube|valve (vacuum tube)]] audio circuits to match the high impedance of the valve to the lower impedance of the load. This is no longer necessary with [[transistor]] circuits, which can always be made with a lower output impedance than that of the load, and so these circuits use [[impedance bridging]] instead. <ref>[http://www.shure.com/ProAudio/Products/us_pro_ea_imepdance "Impedance Matching for Microphones: Is It Necessary?", Shure Audio, visited 2006-07-25</ref>

Audio transformers are usually the factor which limit sound quality; electronic circuits with wide [[frequency response]] and low [[distortion]] are relatively simple to design.

Transformers are also used in [[DI box]]es to convert impedance from high-impedance instruments (for example, [[bass guitar]]s) to enable them to be connected to a microphone input on the [[mixing console]].

=== Output transformers ===

A particularly critical component is the output transformer of an [[sound|audio]] [[power amplifier]]. Valve circuits for quality reproduction have long been produced with no other (inter-stage) audio transformers, but an output transformer is needed to [[Coupling (electronics)|couple]] the relatively high impedance (up to a few hundred ohms depending upon configutation) of the output valve(s) to the low impedance of a [[loudspeaker]]. (The valves can deliver a low current at a high voltage; the speakers require high current at low voltage.)

For good low-frequency response a relatively large iron [[Magnetic core|core]] is required; high power handling increases the required core size. Low distortion requires [[iron]] of adequate properties; special cores with oriented [[magnetic ___domain]]s are used for best results. Good high-frequency response requires carefully designed and implemented [[Wikt:winding|windings]] without excessive [[leakage inductance]] or [[stray capacitance]]. All this makes for an expensive component.

Output transformerless audio power valve amplifiers are possible (e.g., a design by [[Julius Futterman]]), but were rarely used due to other disadvantages.

Early [[transistor]] audio power amplifiers often had output transformers, but they were eliminated as designers discovered how to design amplifiers without them.

=== Speaker transformers ===

In the same way that transformers are used to create high voltage power transmission circuits that minimize transmission losses, speaker transformers allow many individual [[loudspeaker]]s to be powered from a single audio circuit operated at higher-than normal speaker voltages. This application is common in [[public address]] (e.g., [[Tannoy]]) applications. Such circuits are commonly referred to as ''constant voltage'' or ''70 volt'' speaker circuits although the audio waveform is obviously a constantly changing voltage.

At the audio amplifier, a large audio transformer may be used to step-up the low impedance, low-voltage output of the amplifier to the designed line voltage of the speaker circuit. (For high-powered amps, the amplifier transformer may not be needed.) Then, a smaller transformer at each speaker returns the voltage and impedance to ordinary speaker levels. The speaker transformers commonly have multiple primary taps, allowing the volume at each speaker to be adjusted in a number of discrete steps.

Use of a constant-voltage speaker circuit means that there is no need to worry about the impedance presented to the amplifier output (which would clearly be too low if all of the speakers were arranged in [[Series and parallel circuits|parallel]] and would be too complex a design problem if the speakers were arranged in series-parallel). The use of higher transmission voltage and impedance means that power lost in the connecting wire is minimized, even with the use of [[wire gauge|small-gauge]] conductors (and leads to the term ''constant voltage'' as the line voltage doesn't change much as additional speakers are added to the system). Also, the ability to adjust, locally, the volume of each speaker (without the complexity and power loss of an [[L pad]]) is a useful feature.

== Uses of transformers ==

*For supplying power from an alternating current power grid to equipment which uses a different voltage. May be followed by a [[rectifier|rectification]] circuit, if direct rather than alternating power is needed.

** Adaptation of electrical equipment to supply voltages for which it was not made. For example, to use U.S. equipment, designed for 117&nbsp;V AC, in European countries with 230&nbsp;V AC. A transformer or autotransformer may be used, or electronic voltage changers which do not use transformers.

** Use inside solid-state equipment which requires low voltages to reduce the main electricity voltage to the required value.

** Use as an external adapter to power low-voltage solid-state equipment from higher-voltage main electricity.

* [[Electric power transmission]] over long distances.

* High-voltage direct-current [[HVDC]] power transmission systems

* Large, specially constructed power transformers are used for [[electric arc furnace]]s used in [[steelmaking]].

* Rotating transformers are designed so that one winding turns while the other remains stationary. A common use was the video head system as used in VHS and Beta video tape players. These can pass power or radio signals from a stationary mounting to a rotating mechanism, or [[radar]] [[antenna (electronics)|antenna]].

* Sliding transformers can pass power or signals from a stationary mounting to a moving part such as a machine tool head. See [[linear variable differential transformer]].

* Some rotary transformers are precisely constructed in order to measure distances or angles. Usually they have a single primary and two or more secondaries, and electronic circuits measure the different amplitudes of the currents in the secondaries. See [[synchro]] and [[Resolver (electrical)|resolver]].

* Small transformers are often used internally to isolate and link different parts of [[radio receiver]]s and [[audio amplifier]]s, converting high current low voltage circuits to low current high voltage, or vice versa.They are usually tuneable, and labelled [[electronic filter|filter]]/[[bandpass]], though technically being transformers/operating on the same electromagnetic principes. See [[electronics]] and [[impedance matching]]. See also [[isolation transformer]] and [[repeating coil]].

*Transformers may be used as external accessories for impedance matching; for example to match a microphone to an amplifier. These were frequently required with valve equipment, but solid-state electronics are more capable of matching a wide range of impedances without the need for a transformer.

* Balanced-to-unbalanced conversion. A special type of transformer called a [[balun]] is used in radio and audio circuits to convert between balanced circuits and unbalanced [[transmission line]]s such as antenna downleads. A [[balanced line]] is one in which the two conductors (signal and return) have the same [[impedance]] to ground: twisted pair and "balanced twin" are examples. [[Unbalanced line]]s include [[coaxial cable]]s and strip-line traces on [[printed circuit board]]s. A similar use is for connecting the "single ended" input stages of an amplifier to the high-powered "push-pull" output stage.

* Safety. Transformers are used in home electronics, such as computers, to decouple them from the power grid that they are connected to. This is called [[Galvanic isolation]].

==See also==

{{wikibookspar||School science/How to make a transformer}}

* ''Main'' : [[Distributed generation]], [[Electronic power supply]], [[Electronics]], [[Inductor]], [[Pickup]], [[Electrical network]], [[Electricity distribution]], [[Wet transformer]], [[List of electronics topics]], [[Electronic transformer]], [[Load profile]], [[Transformer effect]]

* ''Circuits'': [[Clamp meter]], [[Repeating coil]], [[Inverter (electrical)]], [[Ignition system]], [[Electricity generation]], [[Linear variable differential transformer]], [[Neon signage]], [[Regulator]], [[Electrical substation]], [[Switched-mode power supply]], [[Technological applications of superconductivity]], [[Tesla coil]], [[Transducer]]

* ''Electromagnetism'': [[Alternating current]], [[Electric power]], [[Electric power transmission]], [[Electromagnetic induction]], [[Equivalent series resistance]], [[High-voltage direct current]], [[Impedance matching]], [[Inductive coupling]], [[Potential difference]], [[Skin effect]], [[Leakage inductance]], [[Superconductivity]]

* ''People'': [[Ottó Bláthy]], [[Miksa Déri]], [[John Ambrose Fleming]], [[Otto A. Knopp]], [[William Stanley (physicist)|William Stanley]], [[Nikola Tesla]], [[Milan Vidmar]], [[George Westinghouse]], [[Károly Zipernowsky]]

* ''Other'': [[DI unit]], [[Polychlorinated biphenyl]], [[Stafford]], [[Timeline of invention]], [[War of Currents]], [[World's Columbian Exposition]]

== External links ==

*[http://www.btbplaza.com/web2/content/view/13/14/lang,en/ ''Transformer Learning Centre'' Learn more about Transformers and how they work]

*[http://www.du.edu/~jcalvert/tech/transfor.htm ''Inside Transformers'' from Denver University]

*[http://www.conformity.com/0509/0509understanding.html ''Understanding Transformers: Characteristics and Limitations'' from Conformity Magazine]

*[http://www.3phasepower.org/3phasetransformers.htm 3 Phase Transformer Information and Construction — The 3 Phase Power Resource Site]

* [[DMOZ]]: Business: Electronics and Electrical: [http://dmoz.org/Business/Electronics_and_Electrical/Substation_and_Transmission/ Substation and Transmission] Transformers for the Utility sector

*[http://www.butlerwinding.com/elelectronic-transformer/index.html Electronic Transformers types and structures]

*[http://www.itee.uq.edu.au/~aupec/aupec00/edwards00.pdf J.Edwards and T.K Saha, ''Power flow in transformers via the Poynting vector'' (PDF)]

*[http://www.youtube.com/watch?v=BH5UudSEMQw A transformer explodes]

== References ==

* (1) {{cite book | author=Central Electricity Generating Board | title=Modern Power Station Practice |publisher=Pergamon | year=1982 | id=ISBN 0-08-016436-6}}

* {{cite book | author=Daniels, A.R. | title=Introduction to Electrical Machines|publisher=Macmillan | year=1985 | id=ISBN 0-333-19627-9}}

* {{cite book | first=A. E. | last=Fitzgerald | authorlink= | coauthors=Kingsley, Charles Jr. and Umans, Stephen D. | year=1983 | title=Electric Machinery | edition=4th ed. | publisher=Mc-Graw-Hill, Inc. | ___location= | id=ISBN 0-07-021145-0 }}

* {{cite book | author=Heathcote, MJ | title=J&P Transformer Book, 12th ed. | publisher=Newnes| year=1998 | id=ISBN 0-7506-1158-8}}

* {{cite book | author=Hindmarsh, J. | title=Electrical Machines and their Applications, 4th ed. | publisher=Pergamon | year=1984 | id=ISBN 0-08-030572-5}}

* {{cite book | author=Shepherd,J; Moreton, A.H; Spence, L.F. | title=Higher Electrical Engineering | publisher=Pitman Publishing| year=1970 | id=ISBN 0-273-40025-8}}

*[http://www.gass-transformatoren.de/en/frame_wissenswert.htm Kinds of Transformers]

*Electrical Engineering Fundamentals by J P Neal dept of Elec Eng, University of illinois. publ McGraw Hill 1960 Library of Congress No 59-13210. Sect 7-9 on mutual inductance , p301,

[[Category:Electronics]]

[[Category:Transformers (electrical)|*]]

[[ar:المحوّل]]

[[ca:Transformador]]

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[[da:Transformator]]

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[[es:Transformador]]

[[eo:Transformatoro]]

[[fr:Transformateur électrique]]

[[gl:Transformador]]

[[id:Transformator]]

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[[ru:Трансформатор]]

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[[sl:Transformator]]

[[sr:Трансформатор]]

[[sh:Transformator]]

[[fi:Muuntaja]]

[[sv:Transformator]]

[[ta:மின்மாற்றி]]

[[th:หม้อแปลงไฟฟ้า]]

[[tr:Transformatör]]

[[zh:变压器]]

[[zh-yue:火牛]]