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INDUKTOR DAN TRANSFORMATOR

5.1. INDUKTOR

5.1.1. Pendahuluan

Induktor adalah lilitan kawat berisolasi yang dibentuk sedemikian rupa sehingga akan menghasilkan induktansi apabila lilitan dialiri oleh arus bolak-balik. Cara membuat inductor relative lebih mudah. Dengan membuat gulungan kawat email baik diberi inti atau tidak bisa terbentuk sebuah inductor.Fungsi inti dalam inductor adalah untuk memperbesar nilai induksi diri yang dinyatakan dalam satuan Henry.Ada tiga jenis inti yang biasa digunakan untuk membuat inductor yaitu :

1. Inti Besi untuk inductor yang bekerja di frekuensi rendah2. Inti Ferrit (Serbuk besi yang dipadatkan dengan perekat) untuk inductor yang

bekerja di frekuensi tinggi.3. Inti Udara untuk inductor yang bekerja di frekuensi sangat tinggi.

Menghitung induksi diri dengan inti

[ Henry ]

r = Permeabilitas Relatif intio =

( permeabilitas absolute)N = banyaknya lilitanA = luas lilitan pada inti (m2)p = panjang lilitan (m)

Memperkirakan induktansi kumparan tanpa inti

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Kumparan satu lapis ( singgle layer)

Lr N

r p

0 39

9 10

2 2, . .

N

r p L

r

9 10

0 39 2,

L = induktansi diri (mH)r = jari - jari kumparan (cm)p = panjang kumparan (cm)N = banyaknya lilitan

Kumparan berlapis

Lr N

r p d

0 3 1 5

6 9 1 0

2 2, . .

Nr p d L

r

( )

,

6 9 10

0 315 2

d = tebal lilitan

Contoh Iduktor ( Kumparan ) :

Kumparan redam atau filter (choke coil) inti besi untuk frekuensi 50 Hz

Toroidal Coil

Induktor dengan inti ferrite

Adjustment of the Inductance Value

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Induktor dengan inti udara inti ferrite

Induktor dengan inti ferrite

5.1.2. Karakteristik Induktor

Induktansi

Sebuah lilitan (coil) mempunyai induktansi satu Henry, bila arus yang mengalir dalam coil tersebut berubah dengan laju 1 A/det dan menghasilkan tegangan balik sebesar 1 volt.

atau

Reaktansi Induktif

Bila inductor bekerja pada rangkaian arus bolak-balik akan muncul nilai Reaktansi induktif pada lilitannya yang besarnya :

XL = L = 2πfL ( Ω )

Artinya inductor akan mempunyai tahanan sebanding dengan besarnya frekuensi kerja dari arus AC-nya. Tetapi bila inductor bekerja pada arus searah, maka nilai XL = 0, yang muncul hanya nilai tahanan dari lilitan kawatb yang nilianya relative kecil. Sebagai aplikasi dari fungsi inductor bisa dilihat pada rangkaian di bawah ini dimana inductor berfungsi meredam riak gelombang AC dan meloloskan tegangan DC-nya.

Rankaian ekivalen inductor pada rangkaian AC :

Diagram Phasornya :

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Kerugian

Konstruksi sebuah inductor memunculkan masalah pada saat inductor tersebut digunakan pada suatu rangkaian. Ada dua jenis kerugian yang muncul pada konstruksi sebuah inductor yaitu :i. Kerugian dalam lilitan yang besarnya tergantung pada besarnya resistansi kawat

dan besarnya arus yang mengalir (Loss besar jika I bertambah besar)ii. Kerugian dalam inti yang besarnya terghantung pada bahan inti dan frekuensi

kerjanya akibat dari kerugian hysteresis inti ( kerugian Hysterisis artinnya energi untuk memagnetisasi dan demagnetisasi) .

Faktor kualitas (Q)

Faktor kualitas adalah perbandingan antara reaktansi induksi (XL) dengan kerugian- kerugian yang ada pada kumparan (R). Dari gambar rangkaian ekivalen inductor di samping dapat diturunkan persamaan untuk factor kualitas atau Q adalah :

Qtg

L

R

X

RL

1

Faktor Q sangat penting dalam rangkaian penala dan filter, karena faktor Q menentukan lebar pita frekuensi (Band Width) dan faktor Q bergantung pula pada frekuensi.

Untuk rangkain yang perlu melewatkan suatu jalur frekuensi yang sempit seperti rangkaian penala (Tuning) radio sehingga tuningnya lebih selektif dalam memilih frekuensi radio maka diperlukan Q yang besar, tetapi bila diinginkan respon frekuensi dengan jalur frekuensi yang lebar diperlukan

Rankaian ekivalen inductor :

Diagram Phasornya :

Q besar, BW sempit

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faktor Q yang kecil seperti pada penerima frekuensi baseband saluran TV ( BW PAL 7MHz). Untuk membuat Q yang rendah lebih mudah, pada lilitan bisa ditambah lagi sebuah tahanan yang dipasang seri.

Qkecil, BW lebar

5.1.3. Rangkaian Resonansi

Ketika sebuah inductor dan kapasitor dikombinasikan dapat menghasilkan rangkaian yang mempunyai karakteristik khusus. Impedansi dari rangkaian berubah terhadap perubahan frekuensi dari sumber tegangannya. Arus akan lewat dengan mudah untuk frekuensi yang sesuai dengan frekuensi resonansi rangkaian LC dan akan sulit un tuk sinyal dengan frekuensi yang lain. Rangakain Penala (Tuning Circuit) adalah salahsatu rangkaian yang memanfaatkan karakteristik ini.

5.2. TRANFORMATOR

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5.2.1. PendahuluanTransformator adalah komponen elektronika yang berfungsi mengubah tegangan

bolak-balik menjadi lebih besar ataupun lebih kecil dari tegangan sumbernya. Konstruksi transformator terdiri dari dua buah induktor yang dililit dalam satu inti sehingga terjadi proses mutual inductance ( induksi bersama).

Bila di salahsatu lilitan (bagiaan primer) dialiri arus bolak-balik, maka perubahan arus tersebut akan menimbulkan fluks magnet pada inti. Karena satu inti, maka fluks magnet tersebut akan mengimbas ke bagian lilitan yang ada disisi lain (bagian sekunder). Pada liltan sekunder fluk magnet tersebut diubah menjadi tegangan induksi yang muncul pada kedua terminal lilitan di sekunder transformator.

Besarnya tegangan induksi yang dihasilkan akan sebanding dengan banyaknya jumlah lilitannya. Np:Ns disebut dengan perbandingan lilitan (turns ratio). Besarnya tegangan induksi pada lilitan sekunder tergantung dari perbandingan banyaknya lilitan antara primer dan sekunder dengan hubungan :

V

V

N

NP

S

P

S

....................................... ( 1 )

Bila Np>Ns, maka tegangan sekunder akan lebih kecil dari tegangan primer. Transformator tersebut disebut sebagai Step Down Transformator.

Bila Np<Ns, maka tegangan sekunder akan lebih besar dari tegangan primer. Transformator tersebut disebut sebagai Step Up Transformator.

Konstruksi dasar dan Rangkaian Transformator5.2.2. Karakteristik Transformator

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5.2.2.1. Hubungan dasar

Untuk trafo ideal (asumsi tidak ada kerugian daya yang hilang ) besarnya daya yang diberikan pada primer akan sama dengan daya yang dipakai pada sekunder,dengan hubungan :

Vp . Ip = Vs . Is ........................................... ( 2 )

atau : V

V

I

IP

S

S

P

.................................................. ( 3 )

dari persamaan ( 1 ) : V

V

I

I

N

NP

S

S

P

P

S

……................... ( 4 )

Sehingga besarnya arus lilitan berbanding terbalik dengan banyaknya lilitan.Dengan mengganti bagian primer trafo dengan ekuivalen impedansinya Z1 dan beban sekunder dengan Z2, maka besarnya arus primer dan sekunder menjadi :

IV

ZPP

P

................................................ ( 5 )

IV

ZSS

S

................................................ ( 6 )

5.2.2.2. Polaritas

Gambar di samping memperlihatkan polaritas dari sebuah transformator. Titik bulat menunjukkan suatu terminal dengan polaritas yang sama. Tanda ( + ) dan tanda ( ) menunjukkan polaritas sesaat, yaitu saat Vp dan Vs mencapai ayunan positif maksimum yang sama.

5.2.2.3. Regulasi Perbandingan perbedaan tegangan sekunder antara saat tanpa beban dan saat berbeban penuh.

Persen regulasi = V V

VNL FL

FL

100%

5.2.2.4. Faktor daya

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Perbandingan dari daya input transformator dengan input volt-ampere-nya.

Faktor daya = DayaInput

VoltxAmperInput

5.2.2.5. Effisiensi

Untuk transformator ideal effisiensi 100%, daya pada input akan sama dengan daya pada outputnya (Vp . Ip = Vs . Is). Pada prakteknya, transformator akan kehilangan energi dalam bentuk dissipasi panas.

Kerugian ini diakibatkan oleh 2 hal, yaitu :

a) Kerugian dalam kawat tembagaLoss ini terjadi oleh adanya resistansi lilitan. Semakin besar arusnya semakin banyak pula loss dayanya.

b) Kerugian dalam intiKerugian dalam inti menunjukkan energi yang dibutuhkan untuk memagnetisasikan dan mende- magnetisasikan inti besi.Kerugian ini disebut kerugian hysterisis yang besarnya tergantung dari bahan inti dan besarnya frekuensi.

Effisiensi didefinisikan sebagai perbandingan daya output dan daya input.

Effisiensi = = Pout

Pin100%

5.2.3. Konstruksi Elemen Inti Transformator

Transformator terdiri dari lilitan (kumparan) dari kawat tembaga berisolasi (dilapisi email) digulung pada sebuah gelondongan yang terbuat dari plastic dengan bagian tengahnya berongga sebagai tempat memasukan inti trafo. Pada Transformator daya dengan frekuensi rendah (umumnya frekuensi jala-jala 50-60 Hz) menggunakan inti yang terbuat dari lempengan besi yang dilapisi pernis yang bersifat isolator dan tahan panas. Bentuk Laminasinya ada yang berbentuk E - I, F, V - I, L. Dari keempat bentuk tersebut model E-I yang banyak dipakai.

Bentuk-bentuk inti Besi trafo yang dilaminasiUntuk tranformator daya dengan frekuensi kerja yang tinggi ( Orde Puluhan

KHz), inti yang digunakan bukan besi karena inti besi akan saturasi bila digunakan frekuensi dalam orde KHz. Inti yang cocok untuk frekuensi tinggi adalah bahan Ferrit

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(serbuk besi yang dipadatkan dengan perekat). Bentuk inti ferrit yang umum adalah inti berbentuk C, E, dan Ring atau cincin untuk tranformator jenis toroidal.

Bentuk-bentuk inti Ferrite

Fungsi inti pada transformator yaitu untuk :

1. Memperkuat induksi diri ( umumnya pada trafo daya)

2. Mengatur induksi diri pada konstruksi trafo IF pada penerima radio.

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Transformer

From Wikipedia, the free encyclopedia• Learn more about using Wikipedia for research •

Jump to: navigation, searchFor other uses, see Transformer (disambiguation).

Figure 1:Three-phase pole-mounted step-down transformer.

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled wires. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary). By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other.

The secondary induced voltage VS is scaled from the primary VP by a factor ideally equal to the ratio of the number of turns of wire in their respective windings:

By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.

A key application of transformers is to reduce the current before transmitting electrical energy over long distances through wires. Most wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage, and therefore low-current form for transmission and back again afterwards, transformers enable the economic transmission of power over long distances. Consequently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand.[1] All but a fraction of the world's

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electrical power has passed through a series of transformers by the time it reaches the consumer.[2]

Transformers are some of the most efficient electrical 'machines',[3] with some large units able to transfer 99.75% of their input power to their output.[4] Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge gigavolt-ampere-rated units used to interconnect portions of national power grids. All operate with the same basic principles, though a variety of designs exist to perform specialized roles throughout home and industry.

Basic principles

The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism) and, second, that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). By changing the current in the primary coil, one changes the strength of its magnetic field; since the secondary coil is wrapped around the same magnetic field, a voltage is induced across the secondary.

Figure 2: An ideal step-down transformer showing magnetic flux in the core

A simplified transformer design is shown in Figure 2. A current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron; this ensures that most of the magnetic field lines produced by the primary current are within the iron and pass through the secondary coil as well as the primary coil.

[edit] Induction law

The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that

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where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals the total magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic field strength B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary.

Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,[5] the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for VS and VP gives the basic equation[6] for stepping up or stepping down the voltage

[edit] Ideal power equation

Figure 4: The ideal transformer as a circuit element

If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient; all the incoming energy is transformed from the primary circuit to the magnetic field and thence to the secondary circuit. If this condition is met, the incoming electric power must equal the outgoing power

Pincoming = IPVP = Poutgoing = ISVS

giving the ideal transformer equation

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Thus, if the voltage is stepped up (VS > VP), then the current is stepped down (IS < IP) by the same factor. In practice, most transformers are very efficient (see below), so that this formula is a good approximation.

The impedance in one circuit is transformed by the square of the turns ratio.[5] For example, if an impedance ZS is attached across the terminals of the secondary

coil, it appears to the primary circuit to have an impedance of . This relationship is reciprocal, so that the impedance ZP of the primary circuit appears to

the secondary to be .

[edit] Technical discussion

The simplified description above avoids several complicating factors, in particular the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit.

Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance.[7] When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core.[7]. The current required to create the flux is termed the magnetising current; since the ideal core has been assumed to have near-zero reluctance, the magnetising current is negligible, although a presence is still required to create the magnetic field.

The changing magnetic field induces an electromotive force (EMF) across each winding.[8] Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VS measured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the "back EMF".[9] This is due to the lenz's law which states that the induction of EMF would always be such that it will oppose development of any such change in magnetic field.

[edit] Practical considerations

Flux leakage in a two-winding transformer

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[edit] Flux leakageMain article: Leakage inductance

The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings.[10] Such flux is termed leakage flux, and manifests itself as self-inductance in series with the mutually coupled transformer windings.[9] Leakage results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not itself directly a source of power loss, but results in poorer voltage regulation, causing the secondary voltage to fail to be directly proportional to the primary, particularly under heavy load.[10] Distribution transformers are therefore normally designed to have very low leakage inductance.

However, in some applications, leakage can be a desirable property, and long magnetic paths, air gaps, or magnetic bypass shunts may be deliberately introduced to a transformer's design to limit the short-circuit current it will supply.[9] Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs; or for safely handling loads that become periodically short-circuited such as electric arc welders.[11] Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers that have a DC component added.

[edit] Effect of frequency

The time-derivative term in Faraday's Law shows that the flux in the core is the integral of the applied voltage.[12] An ideal transformer would, at least hypothetically, work under direct-current excitation, with the core flux increasing linearly with time.[13] In practice, the flux would rise very rapidly to the point where magnetic saturation of the core occurred, causing a huge increase in the magnetising current and overheating the transformer. All practical transformers must therefore operate under alternating (or pulsed) current conditions.[13]

Transformer universal EMF equation

If the flux in the core is sinusoidal, the relationship for either winding between its rms EMF E, and the supply frequency f, number of turns N, core cross-sectional area a and peak magnetic flux density B is given by the universal EMF equation:[7]

The EMF of a transformer at a given flux density increases with frequency, an effect predicted by the universal transformer EMF equation.[7] By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation, and fewer turns are needed to achieve the same impedance. However properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment

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traditionally employ 400 Hz power supplies which are less efficient but this is more than offset by the reduction in core and winding weight.[14]

In general, operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetising current. At a frequency lower than the design value, with the rated voltage applied, the magnetising current may increase to an excessive level. Operation of a 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 may need to be equipped with "volts per hertz" over-excitation relays to protect the transformer from overvoltage at higher than rated frequency.

Knowledge of natural frequencies of transformer windings is of importance for the determination of the transient response of the windings to impulse and switching surge voltages.

[edit] Energy losses

An ideal transformer would have no energy losses, and would therefore be 100% efficient. Despite the transformer being amongst the most efficient of electrical machines, with experimental models using superconducting windings achieving efficiencies of 99.85%,[15] energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 95%.[16] A small transformer, such as a plug-in "power brick" used for low-power consumer electronics, may be no more than 85% efficient; although individual power loss is small, the aggregate losses from the very large number of such devices is coming under increased scrutiny.[17]

Transformer losses are attributable to several causes and may be differentiated between those originating in the windings, sometimes termed copper loss, and those arising from the magnetic circuit, sometimes termed iron loss. The losses vary with load current, and may furthermore be expressed as "no-load" or "full-load" loss, or at an intermediate loading. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, meaning that even an idle transformer constitutes a drain on an electrical supply, and lending impetus to development of low-loss transformers (also see energy efficient transformer).[18]

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Transformers are amongst the most efficient of machines, but all exhibit losses

Losses in the transformer arise from:

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

Hysteresis lossesEach time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected.[18]

Eddy currentsFerromagnetic materials are also good conductors, and a solid core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.[18]

MagnetostrictionMagnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers,[6] and in turn causes losses due to frictional heating in susceptible cores.

Mechanical lossesIn addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power.[19]

Stray lossesLeakage inductance is by itself lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat.[2]

[edit] Equivalent circuit

The physical limitations of the practical transformer may be brought together as an equivalent circuit model built around an ideal lossless transformer.[20] Power loss in the windings is current-dependent and is easily represented as in-series resistances RP and RS. Flux leakage results in a fraction of the applied voltage

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dropped without contributing to the mutual coupling, and thus can be modeled as self-inductances XP and XS in series with the perfectly-coupled region. Iron losses are caused mostly by hysteresis and eddy current effects in the core, and tend to be proportional to the square of the core flux for operation at a given frequency.[21] Since the core flux is proportional to the applied voltage, the iron loss can be represented by a resistance RC in parallel with the ideal transformer.

A core with finite permeability requires a magnetizing current IM to maintain the mutual flux in the core. The magnetizing current is in phase with the flux; saturation effects cause the relationship between the two to be non-linear, but for simplicity this effect tends to be ignored in most circuit equivalents.[21] With a sinusoidal supply, the core flux lags the induced EMF by 90° and this effect can be modeled as a magnetising reactance XM in parallel with the core loss component. RC and XM are sometimes together termed the magnetising branch of the model. If the secondary winding is made open-circuit, the current I0 taken by the magnetising branch represents the transformer's no-load current.[20]

The secondary impedance RS and XS is frequently moved (or "referred") to the primary side after multiplying the components by the impedance scaling factor

.

Transformer equivalent circuit, with secondary impedances referred to the primary side

The resulting model is sometimes termed the "exact equivalent circuit", though it retains a number of approximations, such as an assumption of linearity.[20] Analysis may be simplified by moving the magnetising branch to the left of the primary impedance, an implicit assumption that the magnetising current is low, and then summing primary and referred secondary impedances.

[edit] TypesFor more details on this topic, see Transformer types.

A variety of specialised transformer designs has been created to fulfil certain engineering applications, though they share several commonalities. Several of the more important transformer types include:

[edit] Autotransformer

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Main article: Autotransformer

An autotransformer with a sliding brush contact

An autotransformer has only a single winding with two end terminals, plus a third at an intermediate tap point. The primary voltage is applied across two of the terminals, and the secondary voltage taken from one of these and the third terminal. The primary and secondary circuits therefore have a number of windings turns in common.[22] Since the volts-per-turn is the same in both windings, each develops a voltage in proportion to its number of turns. By exposing part of the winding coils and making the secondary connection through a sliding brush, an autotransformer with a near-continuously variable turns ratio is obtained, allowing for very fine control of voltage.[23]

[edit] Polyphase transformersMain article: Three-phase electric power

For three-phase supplies, a bank of three individual single-phase transformers can be used, or all three phases can be incorporated as a single three-phase transformer. In this case, the magnetic circuits are connected together, the core thus containing a three-phase flow of flux.[24] A number of winding configurations are possible, giving rise to different attributes and phase shifts.[25] One particular polyphase configuration is the zigzag transformer, used for grounding and in the suppression of harmonic currents.[26]

[edit] Resonant transformers

A resonant transformer uses the inductance of its primary winding in series with a capacitor to form a tuned resonant circuit. When the primary winding is driven at its resonant frequency, each pulse of current develops an oscillation in the secondary coil. Due to resonance, a very high voltage develops across the secondary, until it is limited by some process such as electrical breakdown. Resonant transformers such as the Tesla coil can generate very high voltages, able to provide much higher current than electrostatic machines such as the Van de Graaff generator.[27] Another application of the resonant transformer is to couple between stages of a superheterodyne receiver, where the selectivity of the receiver is provided by tuned transformers in the intermediate-frequency amplifiers.[28]

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Current transformers, designed to be looped around conductors

[edit] Instrument transformers

A current transformer is a measurement device designed to provide a current in its secondary coil proportional to the current flowing in its primary. Current transformers are commonly used in metering and protective relaying, where they facilitate the safe measurement of large currents. The current transformer isolates measurement and control circuitry from the high voltages typically present on the circuit being measured.[29]

Voltage transformers (VTs) are used for metering and protection in high-voltage circuits. They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential.[30]

[edit] Classification

The many uses to which transformers are put leads them to be classified in a number of different ways:

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

By frequency range: power-, audio-, or radio frequency;

By voltage class: from a few volts to hundreds of kilovolts;

By cooling type: air cooled, oil filled, fan cooled, or water cooled;

By application function: such as power supply, impedance matching, output voltage and current stabilizer, or circuit isolation;

By end purpose: distribution, rectifier, arc furnace, amplifier output;

By winding turns ratio: step-up, step-down, isolating (near equal ratio), variable.

[edit] Construction

[edit] Cores

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Laminated core transformer showing edge of laminations at top of unit.

[edit] Laminated steel cores

Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel.[31] The steel has a permeability many times that of free space, and the core thus serves to greatly reduce the magnetising current, and confine the flux to a path which closely couples the windings.[32] Early transformer developers soon realised that cores constructed from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.[33] Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.[24] The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.

The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude. Thinner laminations reduce losses,[31] but are more laborious and expensive to construct.[34] Thin laminations are generally used on high frequency transformers, with some types of very thin steel laminations able to operate up to 10 kHz.

Laminating the core greatly reduces eddy-current losses

One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces, leading to its name of "E-I transformer".[34] Such a design tends to exhibit more losses, but is very economical to manufacture. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. It is then cut in

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two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap.[34] They have the advantage that the flux is always oriented parallel to the metal grains, reducing reluctance.

A steel core's remanence 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.[35] Overcurrent protection devices such as 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 operation of transformer protection devices.[36]

Distribution transformers can achieve low no-load losses by using cores made with low loss high permeability silicon steel or amorphous (non-crystalline) metal alloy. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load.[37]

[edit] Solid cores

Powdered iron cores are used in circuits (such as switch-mode power supplies) that operate above main frequencies and up to a few tens of kilohertz. These materials combine high magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond the VHF band, cores made from non-conductive magnetic ceramic materials called ferrites are common.[34] Some radio-frequency transformers also have moveable cores (sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits.

[edit] Toroidal cores

Small transformer with toroidal core

Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or permalloy wound into a coil, powdered iron, or ferrite.[38] A strip construction ensures that the 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 E-I core.[39] The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also

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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.

Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I 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 greater choice of shapes. The main disadvantages are higher cost and limited rating.

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

[edit] Air cores

A physical core is not an absolute requisite and a functioning transformer can be produced simply by placing the windings in close proximity to each other, an arrangement termed an "air-core" transformer. The air which comprises the magnetic circuit is essentially lossless, and so an air-core transformer eliminates loss due to hysteresis in the core material.[9] The leakage inductance is inevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in power distribution.[9] They have however very high bandwidth, and are frequently employed in radio-frequency applications,[40] for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary windings.

[edit] Windings

The conducting material used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn.[12] For small power and signal transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard.[41]

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Windings are usually arranged concentrically to minimise flux leakage

High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided litz wire to minimize the skin-effect and proximity effect losses.[12] Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings.[41] Each strand is individually insulated, and the strands are arranged so that at certain points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. The transposition equalizes 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, aiding manufacture.[41]

For signal transformers, the windings may be arranged in a way to minimise leakage inductance and stray capacitance to improve high-frequency response. This can be done by splitting up each coil into sections, and those sections placed in layers between the sections of the other winding. This is known as a stacked type or interleaved winding.

Both the primary and secondary windings on power transformers may have external connections, called taps, to intermediate points on the winding to allow selection of the voltage ratio. The taps may be connected to an automatic on-load tap changer for voltage regulation of distribution circuits. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. Modulation transformers in AM transmitters are very similar.

Certain transformers have the windings protected by epoxy resin. By impregnating the transformer with epoxy under a vacuum, air spaces within the windings are replaced with epoxy, thus sealing the windings and helping to prevent the possible formation of corona and absorption of dirt or water. This produces transformers more suited to damp or dirty environments, but at increased manufacturing cost.[42]

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Three-phase oil-cooled transformer with cover cut away. The oil reservoir is visible at the top. Radiative fins aid the dissipation of heat.

[edit] Coolant

Extended operation at high temperatures is particularly damaging to transformer insulation.[43] Small signal transformers do not generate significant heat and need little consideration given to their thermal management. Power transformers rated up to a few kVA can be adequately cooled by natural convective air-cooling, sometimes assisted by fans.[44] Specific provision must be made for cooling high-power transformers, the larger physical size requiring careful design to transport heat from the interior. Some power transformers are immersed in specialized transformer oil that acts both as a cooling medium, thereby extending the lifetime of the insulation, and helps to reduce corona discharge.[45] The oil is a highly refined mineral oil that remains stable at high temperatures so that internal arcing will not cause breakdown or fire; transformers to be used indoors must use a non-flammable liquid.[4]

The oil-filled tank often has radiators through which the oil circulates by natural convection; large transformers employ forced circulation of the oil by electric pumps, aided by external fans or water-cooled heat exchangers.[45] Oil-filled transformers undergo prolonged drying processes 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 transformers may be equipped with Buchholz relays, which detect gas evolved during internal arcing and rapidly de-energize the transformer to avert catastrophic failure.[35]

Polychlorinated biphenyl has properties that once favored its use as a coolant, though concerns over its toxicity and environmental persistence led to a widespread ban on its use.[46] Today, non-toxic, stable silicone-based oils, or

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fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault.[43][4]

Some "dry" transformers are enclosed in pressurized tanks and cooled by nitrogen or sulphur hexafluoride gas.[43] To ensure that the gas does not leak and its insulating capability deteriorate, the transformer casing is completely sealed. Experimental power transformers in the 2 MVA range have been built with superconducting windings which eliminates the copper losses, but not the core steel loss. These are cooled by liquid nitrogen or helium.[47]

[edit] 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 bushings made of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil.[48]

[edit] History

The transformer principle was demonstrated in 1831 by Michael Faraday, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee its practical uses. Viable designs would not appear until the 1880s.[49] Within less than a decade, the transformer was instrumental during the "War of Currents" in seeing alternating current systems triumph over their direct current counterparts, a position in which they have remained dominant.

[49] Russian engineer Pavel Yablochkov in 1876 invented a lighting system based on a set of induction coils, where primary windings were connected to a source of alternating current and secondary windings could be connected to several "electric candles". The patent claimed the system could "provide separate supply to several lighting fixtures with different luminous intensities from a single source of electric power". Evidently, the induction coil in this system operated as a transformer.

Lucien Gaulard and John Dixon Gibbs, who first exhibited a device with an open iron core called a 'secondary generator' in London in 1882 and then sold the idea to American company Westinghouse.[33] They also exhibited the invention in Turin in 1884, where it was adopted for an electric lighting system.

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A historical Stanley transformer.

William Stanley, an engineer for Westinghouse, built the first commercial device in 1885 after George Westinghouse had bought Gaulard and Gibbs' patents. The core was made from interlocking E-shaped iron plates. This design was first used commercially in 1886.[49] Hungarian engineers Zipernowsky, Bláthy and Déri from the Ganz company in Budapest created the efficient "ZBD" closed-core model in 1885 based on the design by Gaulard and Gibbs.[50] Their patent application made the first use of the word "transformer".[33] Russian engineer Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer in 1889. In 1891 Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for generating very high voltages at high frequency. Audio frequency transformers (at the time called repeating coils) were used by the earliest experimenters in the development of the telephone. Many others have patents on transformers.

While new technologies have made transformers in some electronics applications obsolete, transformers are still found in many electronic devices. Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical.

[edit] See also

Electromagnetism

Inductor

Polyphase system

Balun

http://en.wikipedia.org/wiki/Transformer

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Physics

[edit] Overview

Inductance (measured in henries, H) is an effect which results from the magnetic field that forms around a current-carrying conductor. Electrical current through the conductor creates a magnetic flux proportional to the current. A change in this current creates a change in magnetic flux that, in turn, generates an electromotive force (emf) that acts to oppose this change in current. Inductance is a measure of the generated emf for a unit change in current. For example, an inductor with an inductance of 1 henry produces an emf of 1 V when the current through the inductor changes at the rate of 1 ampere per second. The number of turns, the area of each loop/turn, and what it is wrapped around affect the inductance. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability.

[edit] Stored energy

The energy (measured in joules, in SI) stored by an inductor is equal to the amount of work required to establish the current through the inductor, and therefore the magnetic field. This is given by:

where L is inductance and I is the current flowing through the inductor.

[edit] Hydraulic model

Electrical current can be modeled by the hydraulic analogy. The inductor can be modeled by the flywheel effect of a turbine rotated by the flow. As can be demonstrated intuitively and mathematically, this mimics the behavior of an electrical inductor; voltage is proportional to the derivative of current with respect to time. Thus a rapid change in current will cause a big voltage spike. Likewise, in cases of a sudden interruption of water flow the turbine will generate a high pressure across the blockage, etc. Magnetic interactions such as in transformers are not usefully modeled hydraulically.

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[edit] Inductor construction

Inductors. Major scale in centimetres.

An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic material. Core materials with a higher permeability than air confine the magnetic field closely to the inductor, thereby increasing the inductance. Inductors come in many shapes. Most are constructed as enamel coated wire wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are called "shielded". Some inductors have an adjustable core, which enables changing of the inductance. Inductors used to block very high frequencies are sometimes made with a wire passing through a ferrite cylinder or bead.

Small inductors can be etched directly onto a printed circuit board by laying out the trace in a spiral pattern. Small value inductors can also be built on integrated circuits using the same processes that are used to make transistors. In these cases, aluminium interconnect is typically used as the conducting material. However, practical constraints make it far more common to use a circuit called a "gyrator" which uses a capacitor and active components to behave similarly to an inductor.

[edit] In electric circuits

While a capacitor opposes changes in voltage, an inductor opposes changes in current. An ideal inductor would offer no resistance to a constant direct current; however, only superconducting inductors have truly zero electrical resistance.

In general, the relationship between the time-varying voltage v(t) across an inductor with inductance L and the time-varying current i(t) passing through it is described by the differential equation:

When there is a sinusoidal alternating current (AC) through an inductor, a sinusoidal voltage is induced. The amplitude of the voltage is proportional to the product of the amplitude (IP) of the current and the frequency ( f ) of the current.

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In this situation, the phase of the current lags that of the voltage by 90 degrees.

[edit] Laplace circuit analysis (s-domain)

When using the Laplace transform in circuit analysis, the transfer impedance of an ideal inductor with no initial current is represented in the s domain by:

where L is the inductance, ands is the complex frequency

If the inductor does have initial current, it can be represented by:

adding a voltage source in series with the inductor, having the value:

(Note that the source should have a polarity that opposes the initial current)

or by adding a current source in parallel with the inductor, having the value:

where L is the inductance, andI0 is the initial current in the inductor.

[edit] Inductor networksMain article: Series and parallel circuits

Inductors in a parallel configuration each have the same potential difference (voltage). To find their total equivalent inductance (Leq):

The current through inductors in series stays the same, but the voltage across each inductor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total inductance:

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These simple relationships hold true only when there is no mutual coupling of magnetic fields between individual inductors.

[edit] Q factor

An ideal inductor will be lossless irrespective of the amount of current flowing through the winding. However, typically inductors have winding resistance from the metal wire forming the coils. Since the winding resistance appears as a resistance in series with the inductor, it is often called the series resistance. The inductor's series resistance converts electrical current flowing through the coils into heat, thus causing a loss of inductive quality. The quality factor (or Q) of an inductor is the ratio of its inductive reactance to its resistance at a given frequency, and is a measure of its efficiency. The higher the Q factor of the inductor, the closer it approaches the behavior of an ideal, lossless, inductor.

The Q factor of an inductor can be found through the following formula, where R is its internal electrical resistance:

By using a ferromagnetic core the inductance is increased for the same amount of copper, raising the Q. Cores however also introduce losses that increase with frequency. A grade of core material is chosen for best results for the frequency band. At VHF or highter frequencies an air core is likely to be used. Inductors wound around a ferromagnetic core may saturate at high currents, causing a dramatic decrease in inductance (and Q). This phenomenon can be avoided by using a (physically larger) air core inductor. A well designed air core inductor may have a Q of several hundred.

An almost ideal inductor (Q approaching infinity) can be created by immersing a coil made from a superconducting alloy in liquid helium or liquid nitrogen. This supercools the wire, causing its winding resistance to disappear. Because a superconducting inductor is virtually lossless, it can store a large amount of electrical energy within the surrounding magnetic field (see superconducting magnetic energy storage).

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[edit] Formulae

1. Basic inductance formula for a cylindrical coil:

L = Inductance in henries (H)μ0 = permeability of free space = 4π × 10-7 H/mμr = relative permeability of core materialN = number of turnsA = area of cross-section of the coil in square metres (m2)l = length of coil in metres (m)

2. Inductance of a straight wire conductor:

L = inductance in Hl = length of conductor in metresd = diameter of conductor in metres

Hence a 10 mm-long conductor having 1 mm diameter will have an inductance of about 5.38 nH but 100 mm of the same will get about 100 nH. The same formula in English units:

L = inductance in nanohenriesl = length of conductor in inchesd = diameter of conductor in inches

3. Inductance of a short air core cylindrical coil in terms of geometric parameters:

L = inductance in µHr = outer radius of coil in inchesl = length of coil in inchesN = number of turns

4. For a multilayer air core coil:

L = inductance in µHr = mean radius of coil in inchesl = physical length of coil winding in inchesN = number of turnsd = depth of coil in inches (i.e., outer radius minus inner radius)

5. Inductance of a flat spiral air core coil:

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L = inductance in Hr = mean radius of coil in metresN = number of turnsd = depth of coil in metres (i.e., outer radius minus inner radius)

Hence a spiral coil with 8 turns at a mean radius of 25 mm and a depth of 10 mm would have an inductance of 5.13 µH.

The same formula in imperial units:

L = inductance in µHr = mean radius of coil in inchesN = number of turnsd = depth of coil in inches (i.e., outer radius minus inner radius)

6. Inductance of a winding around a toroidal ring of core material with relative permeability of μr with circular cross-section:

L = inductance in Hμ0 = permeability of free space = 4π × 10-7 H/mμr = relative permeability of core materialN = number of turnsr = radius of coil winding in metersD = overall diameter of toroid in meters

Classical transformer

A autotransformer 4:1 wideband balun using two windings on a ferrite rod.

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Isolated transformer

In an isolated transformer unbalanced connections are made to one winding, and then balanced to another. Isolated transformers have a real impedance at a resonance frequency where self-inductance and self-capacitance for each individual winding cancel themselves out.

In an autotransformer, two coils on a ferrite rod can be used as a balun by winding the individual strands of enameled wire comprising the coil very tightly together. This winding can take one of two forms: either the two windings must be wound such that the two form a single layer where each turn is touching each of the adjacent turns of the other winding; or the two wires are twisted together before being wound into the coil.

[edit] Transmission line transformer

Simple homemade 1:1 balun using a toroidal core and coaxial cable. This is a simple RF choke which works as a balun by preventing signals passing along the outside of the braid. Such a device can be used to cure television interference by acting as a braid-breaker.

Baluns can be considered as simple forms of transmission line transformers.

A more complex (and subtle) type results when the transformer type (magnetic coupling) is combined with the transmission line type (electro-magnetic coupling). This is where whole transmission lines are used as windings, resulting in devices capable of very wideband operation. This whole class known generally as "Transmission Line Transformers" spawn their own huge variety. Very commonly,

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they use small ferrite cores in toroidal or "binocular" shapes. Something as simple as 10 turns of coaxial cable coiled up on a diameter about the size of a dinner plate makes an extremely effective choke balun to beyond 30 MHz. The magnetic material may be "air", but it is a transmission line transformer.

An RF choke can be used in place of a balun. If a coil is made using coaxial cable near to the feed point of a balanced antenna then the RF current that flows on the outer surface of the coaxial cable can be attenuated. One way of doing this would be to wrap a lossy material, such as ferrite around the coaxial cable;

The Guanella transmission line transformer is often combined with a balun to change impedance. Putting balancing aside a 1:4 transformer of this type consists of a 75 Ohm transmission line divided in parallel into two 150 Ohm cables, which are then combined in series for 300 Ohm. It is implemented as a specific wiring around the ferrite core of the balun.

[edit] Delay line

A large class of baluns uses connected transmission lines of specific lengths, with no obvious "transformer" part. These are usually built for (narrow) frequency ranges where the lengths involved are some multiple of a quarter wavelength of the intended frequency in the transmission line medium. A common application is in making a coaxial connection to a balanced antenna, and designs include many types involving coaxial loops and variously connected "stubs".

One easy way to make a balun is a one-half wavelength (λ/2) length of coaxial cable. The inner core of the cable is linked at each end to one of the balanced connections for a feeder or dipole. One of these terminals should be connected to the inner core of the coaxial feeder. All three braids should be connected together. This then forms a 4:1 balun which works at only one frequency.

Another narrow band design is to use a λ/4 length of metal pipe. The coaxial cable is placed inside the pipe; at one end the braid is wired to the pipe while at the other end no connection is made to the pipe. The balanced end of this balun is at the end where the pipe is wired to the braid. The λ/4 conductor acts as a transformer converting the infinite impedance at the unconnected end into a zero impedance at the end connected to the braid. Hence any current entering the balun through the connection, which goes to the braid at the end with the connection to the pipe, will flow into the pipe. This balun design is not good for low frequencies because of the long length of pipe that will be needed. An easy way to make such a balun is to paint the outside of the coax with conductive paint, then to connect this paint to the braid.

[edit] Applications

A balun's function is generally to achieve compatibility between systems, and as such, finds extensive application in modern communications, particularly in

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realising frequency conversion mixers to make cellular phone and data transmission networks possible..

[edit] Radio frequency applications

A 75-to-300 ohm balun.

In television, amateur radio, and other antenna installations and connections, baluns convert between 300 ohm ribbon cable (balanced) and 75 Ω coaxial cable (unbalanced) or to directly connect a balanced antenna to (unbalanced) coax. To avoid EMC problems it is a good idea to connect a centre fed dipole antenna to coaxial cable via a balun. Match 300 Ω twin-lead cable to 75 Ω coaxial cable

In electronic communications, baluns convert Twinax cables to Category 5 cables, and back, or they convert between coaxial cable and ladder line. Baluns can be used to convert video coming from an S-video, RCA or VGA connector to run over Cat5 cables.

Baluns are present in radars, transmitters, satellites, in every telephone network, and probably in most wireless network modem/routers used in homes. It can be combined with transimpedance amplifiers to compose high voltage amplifiers out of low voltage components.

[edit] Audio frequency applications

Three audio transformers.

In audio applications, baluns convert between high impedance (see Nominal impedance) unbalanced and low impedance balanced lines.

Except for the connections, the three devices in the image are electrically identical, but only the leftmost two can be used as baluns. The device on the left would normally be used to connect a high impedance source, such as a guitar, into a balanced microphone input, serving as a passive DI unit. The one in the centre is for connecting a low impedance balanced source, such as a microphone, into a

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KOMPONEN ELEKTRONIKA TC 1412

BAB : INDUKTOR DAN TRANSFORMATOR

guitar amplifier. The one at the right is not technically a balun, as it provides only impedance matching.

In power line communications, baluns are used in coupling signals onto a power line.

[edit] See also

choke (electronics)

Electromagnetic interference

Ferrite (magnet)

[edit] Applications

A choke with two 47mH windings, such as might be found in a power supply.

Inductors are used extensively in analog circuits and signal processing. Inductors in conjunction with capacitors and other components form tuned circuits which can emphasize or filter out specific signal frequencies. This can range from the use of large inductors as chokes in power supplies, which in conjunction with filter capacitors remove residual hum or other fluctuations from the direct current output, to such small inductances as generated by a ferrite bead or torus around a cable to prevent radio frequency interference from being transmitted down the wire. Smaller inductor/capacitor combinations provide tuned circuits used in radio reception and broadcasting, for instance.

Two (or more) inductors which have coupled magnetic flux form a transformer, which is a fundamental component of every electric utility power grid. The efficiency of a transformer decreases as the frequency increases but size can be decreased as well; for this reason, aircraft used 400 hertz alternating current rather than the usual 50 or 60 hertz, allowing a great savings in weight from the use of smaller transformers.

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KOMPONEN ELEKTRONIKA TC 1412

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An inductor is used as the energy storage device in some switchmode power supplies. The inductor is energized for a specific fraction of the regulator's switching frequency, and de-energized for the remainder of the cycle. This energy transfer ratio determines the input-voltage to output-voltage ratio. This XL is used in complement with an active semiconductor device to maintain very accurate voltage control.

Inductors are also employed in electrical transmission systems, where they are used to intentionally depress system voltages or limit fault current. In this field, they are more commonly referred to as reactors.

As inductors tend to be larger and heavier than other components, their use has been reduced in modern equipment; solid state switching power supplies eliminate large transformers, for instance, and circuits are designed to use only small inductors, if any; larger values are simulated by use of gyrator circuits.

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