sound energy to electrical energy

8/9/2019 sound energy to electrical energy

1/55

ELECTRICAL ENERGY

GENRATION

THROUGH SOUND

PROJECT REPORT SUBMITTED

BY:INDRESH KUNWARGAURAV SHAKYASHIVJE


2/55


3/55


4/55

2 Polarity

3 Safety

4 Electrical behavior of electrolytics

5 Capacitance

6 Variants

7 See also

8 External links

References

INTRODUCTION

This project is to construct a Sound Battery (generation ofelectrical energy by sound energy) and to study the current variation
http://en.wikipedia.org/wiki/Electrolytic_capacitor#Polarity%23Polarityhttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Safety%23Safetyhttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Electrical_behavior_of_electrolytics%23Electrical_behavior_of_electrolyticshttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Capacitance%23Capacitancehttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Variants%23Variantshttp://en.wikipedia.org/wiki/Electrolytic_capacitor#See_also%23See_alsohttp://en.wikipedia.org/wiki/Electrolytic_capacitor#External_links%23External_linkshttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Polarity%23Polarityhttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Safety%23Safetyhttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Electrical_behavior_of_electrolytics%23Electrical_behavior_of_electrolyticshttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Capacitance%23Capacitancehttp://en.wikipedia.org/wiki/Electrolytic_capacitor#Variants%23Variantshttp://en.wikipedia.org/wiki/Electrolytic_capacitor#See_also%23See_alsohttp://en.wikipedia.org/wiki/Electrolytic_capacitor#External_links%23External_links


5/55


6/55

The project is basically used to generation of electrical energy bysound energy, this consists of some components which are :-

1. Speaker

2. Transformer (step up)

3. Diode (bridge rectifier)

4. Electrolytic capacitor

5. Micro Volt Meter or LED

SPEAKER


7/55

A loudspeaker, or speaker, is an electromechanicaltransducerwhichconverts an electricalsignal into sound. The term loudspeaker is used

to refer to both the device itself, and a complete system consisting ofone or more loudspeaker drivers (as the individual units are oftencalled) in an enclosure.

Sound Basics

To understand what and how speakers work, you first need tounderstand how sound works.

Inside your ear is a very thin piece of skin called the eardrum. Whenyour eardrum vibrates, yourbrain interprets the vibrations as sound --that's how you hear. Rapid changes in air pressure are the mostcommon thing to vibrate your eardrum.

An object produces sound when it vibrates in air (sound can also

travel through liquids and solids, but air is the transmission mediumwhen we listen to speakers). When something vibrates, it moves theair particles around it. Those air particles in turn move the air particlesaround them, carrying the pulse of the vibration through the air as atraveling disturbance.

To see how this works, let's look at a simple vibrating object -- a bell.When you ring a bell, the metal vibrates -- flexes in and out -- rapidly.When it flexes out on one side, it pushes out on the surrounding airparticles on that side. These air particles then collide with the

particles in front of them, which collide with the particles in front ofthem and so on. When the bell flexes away, it pulls in on thesesurrounding air particles, creating a drop in pressure that pulls in onmore surrounding air particles, which creates another drop inpressure that pulls in particles that are even farther out and so on.This decreasing of pressure is called rarefaction.

.
http://en.wikipedia.org/wiki/Electromechanicalhttp://en.wikipedia.org/wiki/Transducerhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Loudspeaker_enclosurehttp://electronics.howstuffworks.com/brain.htmhttp://electronics.howstuffworks.com/hearing.htmhttp://en.wikipedia.org/wiki/Electromechanicalhttp://en.wikipedia.org/wiki/Transducerhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Loudspeaker_enclosurehttp://electronics.howstuffworks.com/brain.htmhttp://electronics.howstuffworks.com/hearing.htm


8/55

In this way, a vibrating object sends a wave of pressure fluctuationthrough the atmosphere. When the fluctuation wave reaches your ear,

it vibrates the eardrum back and forth. Our brain interprets thismotion as sound.

Differentiating Sound

We hear different sounds from different vibrating objects because ofvariations in:

Sound-wave frequency - A higher wave frequency

simply means that the air pressure fluctuates faster. Wehear this as a higher pitch. When there are fewerfluctuations in a period of time, the pitch is lower.

Air-pressure level - This is the wave's amplitude,which determines how loud the sound is. Sound waves withgreater amplitudes move our ear drums more, and weregister this sensation as a higher volume.

A microphone works something like our ears. It has a diaphragm thatis vibrated by sound waves in an area. The signal from a microphonegets encoded on a tape orCD as an electrical signal. When you playthis signal back on your stereo, the amplifier sends it to the speaker,which re-interprets it into physical vibrations. Good speakers areoptimized to produce extremely accurate fluctuations in air pressure,

just like the ones originally picked up by the microphone. In the nextsection, we'll see how the speaker accomplishes this.

Making Sound
http://electronics.howstuffworks.com/question309.htmhttp://electronics.howstuffworks.com/cassette.htmhttp://electronics.howstuffworks.com/cd.htmhttp://electronics.howstuffworks.com/question309.htmhttp://electronics.howstuffworks.com/cassette.htmhttp://electronics.howstuffworks.com/cd.htm


9/55


10/55

This, in turn, determines the frequency and amplitude of the soundwaves produced by the diaphragm.

Different driver sizes are better suited for certain frequency ranges.For this reason, loudspeaker units typically divide a wide frequencyrange among multiple drivers. In the next section, we'll find out how

speakers divide up the frequency range, and we'll look at the maindriver types used in loudspeakers.

Making Sound: Voice Coil

The voice coil is a basic electromagnet.

you know that an electromagnet is a coil of wire, usually wrappedaround a piece of magnetic metal, such as iron. Running electricalcurrent through the wire creates a magnetic field around the coil,magnetizing the metal it is wrapped around. The field acts just like themagnetic field around a permanent magnet: It has a polar orientation-- a "north" end and and a "south" end -- and it is attracted to ironobjects. But unlike a permanent magnet, in an electromagnet you canalter the orientation of the poles. If you reverse the flow of the current,the north and south ends of the electromagnet switch.

This is exactly what a stereo signal does -- it constantly reverses theflow of electricity. If you've ever hooked up a stereo system, then youknow that there are two output wires for each speaker -- typically ablack one and a red one.

Essentially, the amplifieris constantly switching the electrical signal,

fluctuating between a positive charge and a negative charge on thered wire and black wire. Since electrons always flow in the samedirection between positively charged particles and negatively chargedparticles, the current going through the speaker moves one way andthen reverses and flows the other way. This alternating currentcauses the polar orientation of the electromagnet to reverse itselfmany times a second.
http://electronics.howstuffworks.com/electromagnet.htmhttp://electronics.howstuffworks.com/iron.htmhttp://electronics.howstuffworks.com/amplifier.htmhttp://electronics.howstuffworks.com/electromagnet.htmhttp://electronics.howstuffworks.com/iron.htmhttp://electronics.howstuffworks.com/amplifier.htm


11/55

Types Of Speakers:

A wooferis a driver capable of reproducing low (bass) frequencies.

The usable frequency range varies widely according to design. Whilstsome woofers can cover the audio band from bass to 3 kHz, othersonly work up to 1 kHz or less. Some woofers are capable of verydeep bass performance in the proper enclosure, while others becomeunusable below 50 or 60 Hz.

A tweeteris a driver capable of reproducing the higher end of theaudio spectrum, usually from about somewhere around 3-5 kHz up to20 kHz and beyond.

A mid-range speaker, also called a squawker, is designed to coverthe middle of the audio spectrum, typically from 200 Hz to about 4-5 kHz. Midranges are used when the other drivers are incapable ofadequately covering the mid audio range.
http://en.wikipedia.org/wiki/Wooferhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Tweeterhttp://en.wikipedia.org/wiki/Mid-range_speakerhttp://en.wikipedia.org/wiki/Wooferhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Tweeterhttp://en.wikipedia.org/wiki/Mid-range_speaker


12/55

Transformer

A transformer is an electrical device that transfers energy from onecircuit to another by magnetic coupling, without requiring relativemotion between its parts. A transformer comprises two or morecoupled windings, and, in most cases, a magnetic core to concentratemagnetic flux. A changing voltage applied to one winding creates atime-varying magnetic flux in the core, which induces a voltage in theother windings.

The transformer is one of the simplest of electrical devices, yettransformer designs and materials continue to be improved.

Transformers come in a range of sizes from a thumbnail-sizedcoupling transformer hidden inside a stage microphone to hugegigawatt units used to interconnect large portions of national powergrids. All operate with the same basic principles and with manysimilarities in their parts.

Coupling by mutual induction

The principles of the transformer are illustrated by consideration of ahypothetical ideal transformer. In this case, the core requiresnegligible magnemotive force to sustain flux, and all flux linking theprimary winding also links the secondary winding. The hypotheticalideal transformer has no resistance in its coils. A simple transformerconsists of two electrical conductors called the primary winding andthe secondary winding. Energy is coupled between the windings bythe time varying magnetic flux that passes through (links) both
http://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Inductive_couplinghttp://en.wikipedia.org/wiki/Coil#Electromagnetichttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Coupling_(electronics)http://en.wikipedia.org/wiki/Microphonehttp://en.wikipedia.org/wiki/Gigawatthttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/w/index.php?title=Magnemotive_force&action=edithttp://en.wikipedia.org/wiki/Electrical_conductionhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Inductive_couplinghttp://en.wikipedia.org/wiki/Coil#Electromagnetichttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Coupling_(electronics)http://en.wikipedia.org/wiki/Microphonehttp://en.wikipedia.org/wiki/Gigawatthttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/w/index.php?title=Magnemotive_force&action=edithttp://en.wikipedia.org/wiki/Electrical_conductionhttp://en.wikipedia.org/wiki/Magnetic_flux


13/55

primary and secondary windings. Whenever the amount of current ina coil changes, a voltage is induced in the neighboring coil. Theeffect, called mutual inductance, is an example of electromagneticinduction.

If a time-varying voltage is applied to the primary winding ofturns, a current will flow in it producing a magnetomotive force (MMF).Just as an electromotive force (EMF) drives current around an electriccircuit, so MMF tries to drive magnetic flux through a magnetic circuit.

The primary MMF produces a varying magnetic flux in the core,

and, with an open circuit secondary winding, induces a backelectromotive force (EMF) in opposition to . In accordance withFaraday's law of induction, the voltage induced across the primarywinding is proportional to the rate of change of flux:

and

where

vP and vS are the voltages across the primary winding andsecondary winding,
http://en.wikipedia.org/wiki/Inductance#Mutual_inductancehttp://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_circuithttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Faraday's_law_of_inductionhttp://en.wikipedia.org/wiki/Image:Transformer3d_col3.svghttp://en.wikipedia.org/wiki/Inductance#Mutual_inductancehttp://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_circuithttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Faraday's_law_of_induction


14/55

NP and NS are the numbers of turns in the primary winding andsecondary winding,

dP / dt and dS / dt are the derivatives of the flux with respect totime of the primary and secondary windings.

In the hypothetical ideal transformer, the primary and secondary

windings are perfectly coupled, or equivalently, .Substituting and solving for the voltages shows that:

where

vp and vs are voltages across primary and secondary,

Np and Ns are the numbers of turns in the primary and secondary,respectively.

Hence in an ideal transformer, the ratio of the primary and secondaryvoltages is equal to the ratio of the 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 isinversely proportional to the turns ratio.

The EMF in the secondary winding will cause current to flow in asecondary circuit. The MMF produced by current in the secondarywinding opposes the MMF of the primary winding and so tends tocancel the flux in the core. Since the reduced flux reduces the EMFinduced in the primary winding, increased current flows in the primarycircuit. The resulting increase in MMF due to the primary currentoffsets the effect of the opposing secondary MMF. In this way, theelectrical energy fed into the primary winding is delivered to thesecondary winding. In addition, the flux density will always stay thesame as long as the primary voltage is steady.

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

P = EI (power = electromotive force current)

50 W = 2 V 25 A in the primary circuit if the load is a resistive load.(See note 1)

Now with transformer change:
http://en.wikipedia.org/wiki/Ratiohttp://en.wikipedia.org/wiki/Coilhttp://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/AC_powerhttp://en.wikipedia.org/wiki/Ratiohttp://en.wikipedia.org/wiki/Coilhttp://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/AC_power


15/55

50 W = 25 V 2 A in the secondary circuit.

Since a direct current by definition does not change, it produces asteady MMF and so steady flux in the core; this quantity does notchange and so cannot induce a voltage in the secondary winding. In a

practical transformer, direct current applied to the winding will createonly heat.

The universal electromotive force (EMF) equation

If the flux in the core is sinusoidal, the relationship for either windingbetween its number of turns, voltage, magnetic flux density and core

cross-sectional area is given by the universal emf equation (fromFaraday's law):

where

E is the sinusoidal rms orroot mean square voltage of the winding,

f is the frequency in hertz,

N is the number of turns of wire on the winding,

a is the cross-sectional area of the core in square metres

B is the peak magnetic flux density in teslas,

Other consistent systems of units can be used with the appropriateconversions in the equation.

Operation at different frequencies
http://en.wikipedia.org/wiki/Sinusoidalhttp://en.wikipedia.org/wiki/Magnetic_flux_densityhttp://en.wikipedia.org/wiki/Root_mean_squarehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Tesla_(unit)http://en.wikipedia.org/wiki/Sinusoidalhttp://en.wikipedia.org/wiki/Magnetic_flux_densityhttp://en.wikipedia.org/wiki/Root_mean_squarehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Tesla_(unit)


16/55

The equation shows that the EMF of a transformer at a given fluxdensity increases with frequency. By operating at higher frequencies,transformers can be physically more compact without reachingsaturation, and a given core is able to transfer more power. However,other properties of the transformer, such as losses within the core andskin-effect, also increase with frequency. Generally, operation of a

transformer at its designed voltage but at a higher frequency thanintended will lead to reduced magnetising (no load primary) current.At a frequency lower than the design value, with the rated voltageapplied, the magnetising current may increase to an excessive level.

Operation of a power transformer at other than its design frequencymay require assessment of voltages, losses, and cooling to establishif safe operation is practical. For example, transformers athydroelectric generating stations may be equipped with over-excitation protection, so-called "volts per hertz" protection relays, to

protect the transformer from overvoltage at higher-than-ratedfrequency which may occur if a generator loses its connected load.

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 thousandMVA),

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

Circuit symbols
http://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Hydroelectrichttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Hydroelectrichttp://en.wikipedia.org/wiki/Relay


17/55

Standard symbols

Transformer with two windings and iron core.

Transformer with three windings.

The dots show the relative winding configuration

of the windings.

Step-down or step-up transformer.

The symbol shows which winding has more turns,

but does not usually show the exact ratio.

Transformer with electrostatic screen,

which prevents capacitive coupling between the.

WINDINGS

Energy Losses

An ideal transformer would have no losses, and would therefore be100% efficient. In practice, energy is dissipated due both to theresistance of the windings known as copper loss or I2R loss, and tomagnetic effects primarily attributable to the core (known as ironloss). Transformers are, in general, highly efficient: large powertransformers (over 50 MVA) may attain an efficiency as high as99.75%. Small transformers, such as a plug-in "power brick" used topower small consumer electronics, may be less than 85% efficient.
http://en.wikipedia.org/wiki/Capacitive_couplinghttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Copper_losshttp://en.wikipedia.org/wiki/Iron_losshttp://en.wikipedia.org/wiki/Iron_losshttp://en.wikipedia.org/wiki/Image:Transformer-es.pnghttp://en.wikipedia.org/wiki/Image:Transformer-sd.pnghttp://en.wikipedia.org/wiki/Image:Transformer-2s.pnghttp://en.wikipedia.org/wiki/Image:Transformer-iso.pnghttp://en.wikipedia.org/wiki/Capacitive_couplinghttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Copper_losshttp://en.wikipedia.org/wiki/Iron_losshttp://en.wikipedia.org/wiki/Iron_loss


18/55

Transformer losses

Winding resistance

Current flowing through the windings causes resistive heating of theconductors (I2 R loss). At higher frequencies, skin effect andproximity effect create additional winding resistance and losses.

Eddy currents

Induced eddy currents circulate within the core, causing resistiveheating. Silicon is added to the steel to help in controlling eddycurrents. Adding silicon also has the advantage of stopping ageing ofthe electrical steel that was a problem years ago.

Hysteresis losses

Each time the magnetic field is reversed, a small amount of energy islost to hysteresis within the magnetic core. The amount of hysteresisis 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 (producing a buzzingsound), an effect known as magnetostriction. This in turn causeslosses due to frictional heating in susceptible ferromagnetic cores.

Mechanical losses
http://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Proximity_effecthttp://en.wikipedia.org/wiki/Eddy_currentshttp://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Magnetostrictionhttp://en.wikipedia.org/wiki/Ferromagnetichttp://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Proximity_effecthttp://en.wikipedia.org/wiki/Eddy_currentshttp://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Magnetostrictionhttp://en.wikipedia.org/wiki/Ferromagnetic


19/55

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

Stray losses

Not all the magnetic field produced by the primary is intercepted bythe secondary. A portion of the leakage flux may induce eddy currentswithin nearby conductive objects, such as the transformer's supportstructure, and be converted to heat.

Cooling system

Large power transformers may be equipped with cooling fans, oilpumps orwater-cooled heat exchangers designed to remove the heatcaused by copper and iron losses. The power used to operate thecooling system is typically considered part of the losses of thetransformer.

Losses may be either load-dependent('load-losses') or independent ofit ('no-load loss'). Winding resistance dominates load-losses, whereashysteresis and eddy currents losses contribute to over 99% of the no-load loss.

Construction

A) Cores

i) Steel cores

Transformers for use at power or audio frequencies have cores madeof many thin laminations ofsilicon steel. By concentrating themagnetic flux, more of it is usefully linked by both primary andsecondary windings. Since the steel core is conductive, it, too, has
http://en.wikipedia.org/wiki/Leakage_fluxhttp://en.wikipedia.org/wiki/Cooling_fanhttp://en.wikipedia.org/wiki/Oil_pumphttp://en.wikipedia.org/wiki/Oil_pumphttp://en.wikipedia.org/w/index.php?title=Water-cooled_heat_exchanger&action=edithttp://en.wikipedia.org/wiki/Silicon_steelhttp://en.wikipedia.org/wiki/Leakage_fluxhttp://en.wikipedia.org/wiki/Cooling_fanhttp://en.wikipedia.org/wiki/Oil_pumphttp://en.wikipedia.org/wiki/Oil_pumphttp://en.wikipedia.org/w/index.php?title=Water-cooled_heat_exchanger&action=edithttp://en.wikipedia.org/wiki/Silicon_steel


20/55

currents induced in it by the changing magnetic flux. Each layer isinsulated from the adjacent layer to reduce the energy lost to eddycurrent heating of the core. The thin laminations are used to reducethe eddy currents, and the insulation is used to keep the laminationsfrom acting as a solid piece of steel. The thinner the laminations, thelower the eddy currents, and the lower the losses. Very thin

laminations are generally used on high frequency transformers. Thecost goes up when using thinner laminations mainly over the labor instacking them.

A typical laminated core is made from E-shaped and I-shaped pieces,leading to the name "EI transformer". In the EI transformer, thelaminations are stacked in what is known as an interleaved fashion.Due to this interleaving a second gap in parallel (in an analogy toelectronic circuits) to the gap between E and I is formed between theE-pieces. The E-pieces are pressed together to reduce the gap width

to that of the insulation. The gap area is very large, so that theeffective gap width is very small (in analogy to a capacitor). For this towork the flux has to gradually flow from one E to the other. Thatmeans that on one end all flux is only on every second E. That meanssaturation occurs at half the flux density. Using a longer E andwedging it with two small Is will increase the overlap and additionallymake the grains more parallel to the flux (think of a wooden frame fora window). If an air gap is needed (which is unlikely considering thelow remanence available for steel), all the E's are stacked on one

side, and all the I's on the other creating a gap.The cut core or C-core is made by winding a silicon steel strip arounda rectangular form. After the required thickness is achieved, it isremoved from the form and the laminations are bonded together. It isthen cut in two forming two C shapes. The faces of the cuts are thenground smooth so they fit very tight with a very small gap to reducelosses. The core is then assembled by placing the two C halvestogether, and holding them closed by a steel strap. Usually two C-cores are used to shorten the return path for the magnetic flux

resulting in a form similar to the EI. More cores would necessitate atriangular cross-section. Like toroidal cores, they have the advantage,that the flux is always in the oriented parallel the grains. Due to thebending of the core, some area is lost for a rectangular winging.

A steel core's remanence means that it retains a static magnetic fieldwhen power is removed. When power is then reapplied, the residualfield will cause a high inrush current until the effect of the remanentmagnetism is reduced, usually after a few cycles of the applied
http://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/E-shapedhttp://en.wikipedia.org/wiki/I-shapedhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Remanencehttp://en.wikipedia.org/wiki/Inrush_currenthttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/E-shapedhttp://en.wikipedia.org/wiki/I-shapedhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Remanencehttp://en.wikipedia.org/wiki/Inrush_current


21/55

alternating current. Overcurrent protection devices such as fusesmust be selected to allow this harmless inrush to pass. Ontransformers connected to long overhead power transmission lines,induced currents due to geomagnetic disturbances during solarstorms can cause saturation of the core, and false operation oftransformerprotection devices.

Steel cores develop a larger hysteresis loss due to eddy currents asthe operating frequency is increased. Ferrite, or thinner steellaminations for the core are typically used for frequencies above1kHz. The thinner steel laminations serve to reduce the eddycurrents. Some types of very thin steel laminations can operate at upto 10 kHz or higher. Ferrite is used in higher frequency applications,extending to the VHF band and beyond. Aircraft traditionally use 400Hz power systems since the slight increase in thermal losses is morethan offset by the reduction in core and winding weight. Military gear

includes 400 Hz (and other frequencies) to supply power forradarorservomechanisms.

Distribution transformers can achieve low off-load losses by usingcores made with low loss high permeability silicon steel andamorphous (non-crystalline) steel, so-called "metal glasses" thehigh cost of the core material is offset by the lower losses incurred atlight load, over the life of the transformer. In order to maintain goodvoltage regulation, distribution transformers are designed to havevery low leakage inductance.

Certain special purpose transformers use long magnetic paths, insertair gaps, or add magnetic shunts (which bypass a portion of magneticflux that would otherwise link the primary and secondary windings) inorder to intentionally add leakage inductance. The additional leakageinductance limits the secondary winding's short circuit current to asafe, or a controlled, level. This technique is used to stabilize theoutput current for loads that exhibit negative resistance such aselectric arcs, mercury vapor lamps, and neon signs, or safely handleloads that may become periodically short-circuited such as electricarc welders. Gaps are also used to keep a transformer fromsaturating, especially audio transformers that have a DC componentadded.

ii) Solid cores
http://en.wikipedia.org/wiki/Fuse_(electrical)http://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Servomechanismhttp://en.wikipedia.org/wiki/Silicon_steelhttp://en.wikipedia.org/wiki/Amorphous#Metallic_glasshttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Negative_resistancehttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Mercury_vapor_lamphttp://en.wikipedia.org/wiki/Neon_signhttp://en.wikipedia.org/wiki/Fuse_(electrical)http://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Servomechanismhttp://en.wikipedia.org/wiki/Silicon_steelhttp://en.wikipedia.org/wiki/Amorphous#Metallic_glasshttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Negative_resistancehttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Mercury_vapor_lamphttp://en.wikipedia.org/wiki/Neon_sign


22/55

Powdered iron cores are used in circuits (such as switch-mode powersupplies) that operate above mains frequencies and up to a few tensof kilohertz. These materials combine high magnetic permeability withhigh bulk electrical resistivity.

At even higher, radio-frequencies (RF), other types of cores made

from non-conductive magnetic ceramic materials, called ferrites, arecommon. Some RF transformers also have moveable cores(sometimes called slugs) which allow adjustment of the couplingcoefficient (and bandwidth) of tuned radio-frequency circuits.

Cores are available in a wide variety of shapes, including toroids.Other shapes include so-called E-cores and C-cores.

iii) Air cores

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

iv) Toroidal cores

Various transformers. The top right is toroidal. The bottom right isfrom a 12 VAC wall wart supply.

Toroidal transformers are built around a ring-shaped core, which ismade from a long strip of silicon steel orpermalloy wound into a coil,from powdered iron, orferrite, depending on operating frequency. Thestrip construction ensures that the grain boundaries are optimallyaligned, improving the transformer's efficiency by reducing the core's

reluctance. The closed ring shape eliminates air gaps inherent in theconstruction of an EI core. The cross-section of the ring is usuallysquare or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils areoften wound concentrically to cover the entire surface of the core.This minimises the length of wire needed, and also providesscreening to minimize the core's magnetic field from generatingelectromagnetic interference.
http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Permeabilityhttp://en.wikipedia.org/wiki/Resistivityhttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Ferrite_(magnet)http://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Wall_warthttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Permalloyhttp://en.wikipedia.org/wiki/Ferrite_(magnet)http://en.wikipedia.org/wiki/Grain_boundaryhttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Electromagnetic_interferencehttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Permeabilityhttp://en.wikipedia.org/wiki/Resistivityhttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Ceramichttp://en.wikipedia.org/wiki/Ferrite_(magnet)http://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Wall_warthttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Permalloyhttp://en.wikipedia.org/wiki/Ferrite_(magnet)http://en.wikipedia.org/wiki/Grain_boundaryhttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Electromagnetic_interference


23/55

Ferrite toroid cores are used at higher frequencies, typically betweena few tens of kilohertz to a megahertz, to reduce losses, physicalsize, and weight ofswitch-mode power supplies.

Toroidal transformers are more efficient than the cheaper laminatedEI types of similar power level. Other advantages, compared to EI

types, include smaller size (about half), lower weight (about half), lessmechanical hum (making them superior in audio amplifiers), lowerexterior magnetic field (about one tenth), low off-load losses (makingthem more efficient in standby circuits), single-bolt mounting, andmore choice of shapes. This last point means that, for a given poweroutput, either a wide, flat toroid or a tall, narrow one with the sameelectrical properties can be chosen, depending on the spaceavailable. The main disadvantages are higher cost and limited size.

A drawback of toroidal transformer construction is the higher cost of

windings. As a consequence, toroidal transformers are uncommonabove ratings of a few kVA. Small distribution transformers mayachieve some of the benefits of a toroidal core by splitting it andforcing it open, then inserting a bobbin containing primary andsecondary windings.

When fitting a toroidal transformer, it is important to avoid making anunintentional short-circuit through the core. This can happen if thesteel mounting bolt in the middle of the core is allowed to touchmetalwork at both ends, making a loop of conductive material that

passes through the hole in the toroid. Such a loop could result in adangerously large current flowing in the bolt.

B) Windings

The wire of the adjacent turns in a coil, and in the different windings,must be electrically insulated from each other. The wire used is

generally magnet wire. Magnet wire is a copper wire with a coating ofvarnish or some other synthetic coating. Transformers for years haveused Formvarwire, which is a varnished type of magnet wire.

The conducting material used for the winding depends upon theapplication. Small power and signal transformers are wound with solidcopper wire, insulated usually with enamel, and sometimes additionalinsulation. Larger power transformers may be wound with wire,copper, or aluminium rectangular conductors. Strip conductors are
http://en.wikipedia.org/wiki/Switched-mode_power_supplyhttp://en.wikipedia.org/wiki/Toroidhttp://en.wikipedia.org/wiki/Short-circuithttp://en.wikipedia.org/wiki/Enameled_wirehttp://en.wikipedia.org/w/index.php?title=Formvar&action=edithttp://en.wikipedia.org/wiki/Enameled_wirehttp://en.wikipedia.org/wiki/Switched-mode_power_supplyhttp://en.wikipedia.org/wiki/Toroidhttp://en.wikipedia.org/wiki/Short-circuithttp://en.wikipedia.org/wiki/Enameled_wirehttp://en.wikipedia.org/w/index.php?title=Formvar&action=edithttp://en.wikipedia.org/wiki/Enameled_wire


24/55

used for very heavy currents. High frequency transformers operatingin the tens to hundreds of kilohertz will have windings made ofLitzwire to minimize the skin effect losses in the conductors. Large powertransformers use multiple-stranded conductors as well, since even atlow power frequencies non-uniform distribution of current wouldotherwise exist in high-current windings. Each strand is insulated from

the other, and the strands are arranged so that at certain points in thewinding, or throughout the whole winding, each portion occupiesdifferent relative positions in the complete conductor. This"transposition" equalizes the current flowing in each strand of theconductor, and reduces eddy current losses in the winding itself. Thestranded conductor is also more flexible than a solid conductor ofsimilar size is. (see reference (1) below)

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

frequency response. This can be done by splitting up each coil intosections, and those sections placed in layers between the sections ofthe other winding. This is known as a stacked type or interleavedwinding.

Windings on both the primary and secondary of power transformersmay have external connections (called taps) to intermediate points onthe winding to allow adjustment of the voltage ratio. Taps may beconnected to an automatic, on-load tap changertype ofswitchgearforvoltage regulation ofdistribution circuits. Audio-frequency

transformers, used for the distribution of audio to public addressloudspeakers, have taps to allow adjustment of impedance to eachspeaker. A center-tapped transformer is often used in the output stageof an audio poweramplifierin a push-pull type circuit. Modulationtransformers in AM transmitters are very similar. Tapped transformersare also used as components of amplifiers, oscillators, and forfeedback linearization of amplifier circuits.

C) Insulation of windings

The turns of the windings must be insulated from each other toensure that the current travels through the entire winding. Thepotential difference between adjacent turns is usually small, so thatenamel insulation is usually sufficient for small power transformers.
http://en.wikipedia.org/wiki/Skin_effect#Mitigationhttp://en.wikipedia.org/wiki/Skin_effect#Mitigationhttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Tap_changerhttp://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Voltage_regulatorhttp://en.wikipedia.org/wiki/Power_distributionhttp://en.wikipedia.org/wiki/Amplifierhttp://en.wikipedia.org/wiki/Push-pullhttp://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Skin_effect#Mitigationhttp://en.wikipedia.org/wiki/Skin_effect#Mitigationhttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Tap_changerhttp://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Voltage_regulatorhttp://en.wikipedia.org/wiki/Power_distributionhttp://en.wikipedia.org/wiki/Amplifierhttp://en.wikipedia.org/wiki/Push-pullhttp://en.wikipedia.org/wiki/Feedback


25/55

Supplemental sheet or tape insulation is usually employed betweenwinding layers in larger transformers.

The transformer may also be immersed in transformer oil thatprovides further insulation. Although the oil is primarily used to coolthe transformer, it also helps to reduce the formation ofcorona

discharge within high voltage transformers. By cooling the windings,the insulation will not break down as easily due to heat. To ensurethat the insulating capability of the transformer oil does notdeteriorate, the transformer casing is completely sealed againstmoisture ingress. Thus the oil serves as both a cooling medium toremove heat from the core and coil, and as part of the insulationsystem.

Certain power transformers have the windings protected by epoxyresin. By impregnating the transformer with epoxy under a vacuum,

air spaces within the windings are replaced with epoxy, therebysealing the windings and helping to prevent the possible formation ofcorona and absorption of dirt or water. This produces transformerssuitable for damp or dirty environments, but at increasedmanufacturing cost.

D) Shielding

Where transformers are intended for minimum electrostatic couplingbetween primary and secondary circuits, an electrostatic shield canbe placed between windings to reduce the capacitance betweenprimary and secondary windings. The shield may be a single layer ofmetal foil, insulated where it overlaps to prevent it acting as a shortedturn, or a single layer winding between primary and secondary. Theshield is connected to earth ground.

Transformers may also be enclosed by magnetic shields, electrostatic

shields, or both to prevent outside interference from affecting theoperation of the transformer, or to prevent the transformer fromaffecting the operation of nearby devices that may be sensitive tostray fields such as CRTs.

Small signal transformers do not generate significant amounts ofheat. Power transformers rated up to a few kilowatts rely on naturalconvective air-cooling. Specific provision must be made for cooling of
http://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Coronahttp://en.wikipedia.org/wiki/Coronahttp://en.wikipedia.org/wiki/Resin_castinghttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Coronahttp://en.wikipedia.org/wiki/Coronahttp://en.wikipedia.org/wiki/Resin_castinghttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Cathode_ray_tube


26/55

high-power transformers. Transformers handling higher power, orhaving a high duty cycle can be fan-cooled.

Some dry transformers are enclosed in pressurized tanks and arecooled by nitrogen orsulphur hexafluoride gas.

The windings of high-power or high-voltage transformers are

immersed in transformer oil a highly refined mineral oil, that isstable at high temperatures. Large transformers to be used indoorsmust use a non-flammable liquid. Formerly, polychlorinated biphenyl(PCB) was used as it was not a fire hazard in indoor powertransformers and it is highly stable. Due to the stability and toxiceffects of PCB by-products, and its accumulation in the environment,it is no longer permitted in new equipment. Old transformers that stillcontain PCB should be examined on a weekly basis for leakage. Iffound to be leaking, it should be changed out, and professionally

decontaminated or scrapped in an environmentally safe manner.Today, non-toxic, stable silicone-based oils, orfluorinatedhydrocarbons may be used where the expense of a fire-resistantliquid offsets additional building cost for a transformer vault. Otherless-flammable fluids such as canola oil may be used but all fireresistant fluids have some drawbacks in performance, cost, or toxicitycompared with mineral oil.

The oil cools the transformer, and provides part of the electricalinsulation between internal live parts. It has to be stable at high

temperatures so that a small short or arc will not cause a breakdownor fire. The oil-filled tank may have radiators through which the oilcirculates by natural convection. Very large or high-powertransformers (with capacities of millions ofwatts) may have coolingfans, oil pumps and even oil to waterheat exchangers. Oil-filledtransformers undergo prolonged drying processes, using vapor-phaseheat transfer, electrical self-heating, the application of a vacuum, orcombinations of these, to ensure that the transformer is completelyfree ofwater vaporbefore the cooling oil is introduced. This helpsprevent electrical breakdown under load.

Oil-filled power transformers may be equipped with Buchholz relayswhich are safety devices that sense gas build-up inside thetransformer (a side effect of an electric arc inside the windings), andthus switches off the transformer.

Experimental power transformers in the 2 MVA range have been builtwith superconducting windings which eliminates the copper losses,
http://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Sulphur_hexafluoridehttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Mineral_oilhttp://en.wikipedia.org/wiki/Polychlorinated_biphenylhttp://en.wikipedia.org/wiki/Fire_hazardhttp://en.wikipedia.org/wiki/Siliconehttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Canola_oilhttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Heat_exchangershttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Buchholz_relayhttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Superconductivityhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Sulphur_hexafluoridehttp://en.wikipedia.org/wiki/Transformer_oilhttp://en.wikipedia.org/wiki/Mineral_oilhttp://en.wikipedia.org/wiki/Polychlorinated_biphenylhttp://en.wikipedia.org/wiki/Fire_hazardhttp://en.wikipedia.org/wiki/Siliconehttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Canola_oilhttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Heat_exchangershttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Buchholz_relayhttp://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Superconductivity


27/55

but not the core steel loss. These are cooled by liquid nitrogen orhelium.

E) Terminals

Very small transformers will have wire leads connected directly to theends of the coils, and brought out to the base of the unit for circuitconnections. Larger transformers may have heavy bolted terminals,bus bars or high-voltage insulated bushings made of polymers orporcelain. A large bushing can be a complex structure since it mustprovide electrical insulation without letting the transformer leak oil.

F) Enclosure

Small transformers often have no enclosure. Transformers may havea shield enclosure, as described above. Larger units may beenclosed to prevent contact with live parts, and to contain the coolingmedium (oil or pressurized gas).

Transformer types and uses

A) Autotransformers

An autotransformerhas only a single winding, which is tapped at

some point along the winding. AC or pulsed voltage is applied acrossa portion of the winding, and a higher (or lower) voltage is producedacross another portion of the same winding. While theoreticallyseparate parts of the winding can be used for input and output, inpractice the higher voltage will be connected to the ends of thewinding, and the lower voltage from one end to a tap. For example, atransformer with a tap at the center of the winding can be used with230 volts across the entire winding, and 115 volts between one end
http://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Heliumhttp://en.wikipedia.org/wiki/Bushing_(electrical)http://en.wikipedia.org/wiki/Autotransformerhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Heliumhttp://en.wikipedia.org/wiki/Bushing_(electrical)http://en.wikipedia.org/wiki/Autotransformer


28/55

and the tap. It can be connected to a 230-volt supply to drive 115-voltequipment, or reversed to drive 230-volt equipment from 115 volts. Asthe same winding is used for input and output, the flux in the core ispartially cancelled, and a smaller core can be used. For voltage ratiosnot 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 notperfectly reversible; one designed for stepping down a voltage willdeliver slightly less voltage than required if used to step up. Thedifference is usually slight enough to allow reversal where the actualvoltage level is not critical.

By exposing part of the winding coils and making the secondaryconnection through a sliding brush, an autotransformer with a near-

continuously variable turns ratio can be obtained, allowing for verysmall increments of voltage.

B) Constant voltage transformer (ferro-resonance)

By arranging particular magnetic properties of a transformer core,and installing a resonant tank circuit (a capacitor and an additionalwinding), a transformer can be arranged to automatically keep thesecondary winding voltage constant regardless (within some limits) ofany variance in the primary supply without additional circuitry ormanual adjustment. CVA transformers run hotter than standard powertransformers, for the regulating action is dependent on core

saturation, which reduces efficiency somewhat.

The output voltage of a transformer varies some with varyingload resistances, even with a constant voltage input. The degree ofvariance is affected by the primary and secondary windinginductances, among other factors, not the least of which includeswinding resistance and the degree of mutual inductance (magneticcoupling) between the primary and secondary windings. For powertransformer applications, where the transformer is seen by the load
http://en.wikipedia.org/wiki/Brush_(electric)http://en.wikipedia.org/wiki/Brush_(electric)


29/55

(ideally) as a constant source of voltage, it is good to have thesecondary voltage vary as little as possible for wide variances inload current.

The measure of how well a power transformer maintains constantsecondary voltage over a range of load currents is called the

transformer's voltage regulation. It can be calculated from thefollowing formula:

Characteristic of CVT Physical view

Circuit diagram

C) Polyphase transformers


30/55

Forthree-phase power, three separate single-phase transformers canbe used, or all three phases can be connected to a single polyphasetransformer. The three primary windings are connected together andthe three secondary windings are connected together. The most

common connections are Y-, -Y, - and Y-Y. A vector groupindicates the configuration of the windings and the phase angledifference between them. If a winding is connected to earth(grounded), the earth connection point is usually the center point of aY winding. If the secondary is a winding, the ground may beconnected to a center tap on one winding (high leg delta) or onephase may be grounded (corner grounded delta). A special purposepolyphase transformer is the zigzag transformer. There are manypossible configurations that may involve more or fewer than sixwindings and various tap connections.

D) Resonant transformers

A resonant transformer operates at the resonant frequency of one ormore of its coils and (usually) an external capacitor. The resonantcoil, usually the secondary, acts as an inductor, and is connected inseries with a capacitor. When the primary coil is driven by a periodicsource ofalternating current, such as a square orSawtooth wave atthe resonant frequency, each pulse of current helps to build up anoscillation in the secondary coil. Due to resonance, a very highvoltage can develop across the secondary, until it is limited by someprocess such as electrical breakdown. These devices are used togenerate high alternating voltages, and the current available can bemuch larger than that from electrostatic machines such as the Van deGraaff generatororWimshurst machine.

Examples:

Tesla coil

Oudin coil (or Oudin resonator; named after its inventorPaul Oudin)

D'Arsonval apparatus

Ignition coil orinduction coil used in the ignition system of a petrolengine
http://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Vector_grouphttp://en.wikipedia.org/wiki/Phase_anglehttp://en.wikipedia.org/wiki/Ground_(electricity)http://en.wikipedia.org/wiki/High_leg_deltahttp://en.wikipedia.org/wiki/Zigzag_transformerhttp://en.wikipedia.org/wiki/Resonancehttp://en.wikipedia.org/wiki/Resonant_frequencyhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Square_wavehttp://en.wikipedia.org/wiki/Sawtooth_wavehttp://en.wikipedia.org/wiki/Electrical_breakdownhttp://en.wikipedia.org/wiki/Van_de_Graaff_generatorhttp://en.wikipedia.org/wiki/Van_de_Graaff_generatorhttp://en.wikipedia.org/wiki/Wimshurst_machinehttp://en.wikipedia.org/wiki/Tesla_coilhttp://en.wikipedia.org/wiki/Oudin_coilhttp://en.wikipedia.org/wiki/Paul_Oudinhttp://en.wikipedia.org/wiki/Jacques_Arsene_d'Arsonvalhttp://en.wikipedia.org/wiki/Ignition_coilhttp://en.wikipedia.org/wiki/Induction_coilhttp://en.wikipedia.org/wiki/Ignition_systemhttp://en.wikipedia.org/wiki/Petrol_enginehttp://en.wikipedia.org/wiki/Petrol_enginehttp://en.wikipedia.org/wiki/Three-phase_electric_powerhttp://en.wikipedia.org/wiki/Vector_grouphttp://en.wikipedia.org/wiki/Phase_anglehttp://en.wikipedia.org/wiki/Ground_(electricity)http://en.wikipedia.org/wiki/High_leg_deltahttp://en.wikipedia.org/wiki/Zigzag_transformerhttp://en.wikipedia.org/wiki/Resonancehttp://en.wikipedia.org/wiki/Resonant_frequencyhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Square_wavehttp://en.wikipedia.org/wiki/Sawtooth_wavehttp://en.wikipedia.org/wiki/Electrical_breakdownhttp://en.wikipedia.org/wiki/Van_de_Graaff_generatorhttp://en.wikipedia.org/wiki/Van_de_Graaff_generatorhttp://en.wikipedia.org/wiki/Wimshurst_machinehttp://en.wikipedia.org/wiki/Tesla_coilhttp://en.wikipedia.org/wiki/Oudin_coilhttp://en.wikipedia.org/wiki/Paul_Oudinhttp://en.wikipedia.org/wiki/Jacques_Arsene_d'Arsonvalhttp://en.wikipedia.org/wiki/Ignition_coilhttp://en.wikipedia.org/wiki/Induction_coilhttp://en.wikipedia.org/wiki/Ignition_systemhttp://en.wikipedia.org/wiki/Petrol_enginehttp://en.wikipedia.org/wiki/Petrol_engine


31/55

Flyback transformerof a CRTtelevision set or video monitor.

Electrical breakdown and insulation testing of high voltage equipmentand cables. In the latter case, the transformer's secondary isresonated with the cable's capacitance.

Other applications of resonant transformers are as coupling between

stages of a superheterodyne receiver, where the selectivity of thereceiver is provided by the tuned transformers of the intermediate-frequency amplifiers.

A voltage-regulating transformer uses a resonant winding and allowspart of the core to go into saturation on each half-cycle of thealternating current. This effect stabilizes the output of the regulatingtransformer, which can be used for equipment that is sensitive tovariations of the supply voltage. Saturating transformers provide asimple rugged method to stabilize an AC power supply. However, dueto the hysteresis losses accompanying this type of operation,efficiency is low.

E) Instrument transformers

i) current transformer

A current transformer is a type of "instrument transformer" that isdesigned to provide a current in its secondary which is accuratelyproportional to the current flowing in its primary. This accuracy isdirectly related to a number of factors including the following:

burden,

rating factor,

load,

external electromagnetic fields,

temperature and

physical CT configuration.

The burden in a CT metering circuit is essentially the amount ofimpedance (largely resistive) present. Typical burden ratings for CTsare B-0.1, B-0.2, B-0.5, B-1.0, B-2.0 and B-4.0. This means a CT with
http://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Televisionhttp://en.wikipedia.org/wiki/Electrical_breakdownhttp://en.wikipedia.org/wiki/Superheterodyne_receiverhttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Televisionhttp://en.wikipedia.org/wiki/Electrical_breakdownhttp://en.wikipedia.org/wiki/Superheterodyne_receiver


32/55

a burden rating of B-0.2 can tolerate up to 0.2 of impedance in themetering circuit before its output current is no longer a fixed ratio tothe primary current. Items that contribute to the burden of a currentmeasurement circuit are switch blocks meters and intermediateconductors. The most common source of excess burden in a currentmeasurement circuit is the conductor between the meter and the CT.

Often times, substation meters are located significant distances fromthe meter cabinets and the excessive length of small gaugeconductor creates a large resistance.

Rating factor is a factor by which the nominal full load current of a CTcan be multiplied to determine its absolute maximum measurableprimary current. Conversely, the minimum primary current a CT canaccurately measure is "light load," or 10% of the nominal current. Therating factor of a CT is largely dependent upon ambient temperature.Most CTs have rating factors for 35 degrees Celsius and 55 degrees

Celsius. A CT usually demonstrates reduced capacity to maintainaccuracy with rising ambient temperature. It is important to be mindfulof ambient temperatures and resultant rating factors when CTs areinstalled inside pad-mounted transformers or poorly ventilatedmechanical rooms. Recently, manufacturers have been movingtowards lower nominal primary currents with greater rating factors.This is made possible by the development of more efficient ferritesand their corresponding hysteresis curves. This is a distinctadvantage over previous CTs because it increases their range of

accuracy. For example, a 200:5 CT with a rating factor of 4.0 is mostaccurate between 20A (light load)and 800A (4.0 times the nominalrating, or "full load," of the CT) of primary current. While previousrevisions of CTs were on the order of 500:5 with a rating factor of 1.5yielding an effective range of 50A to 750A. This is an 11% increase ineffective range for two CTs that would be used at similar services. Notto mention, the relative cost of a 500:5 CT is significantly greater thanthat of a 200:5.

Physical CT configuration is another important factor in reliable CT

accuracy. While all electrical engineers are quite comfortable withGauss' Law, there are some issues when attempting to apply theoryto the real world. When conductors passing through a CT are notcentered in the circular (or oval) void, slight inaccuracies may occur. Itis important to center primary conductors as they pass through CTs topromote the greatest level of CT accuracy. Afterall, in an electricmetering circuit, the most inaccurate component is the CT.


33/55

Current transformers (CTs) are commonly used in metering andprotective relaying in the electrical power industry where theyfacilitate the safe measurement of large currents, often in thepresence of high voltages. The current transformer safely isolatesmeasurement and control circuitry from the high voltages typicallypresent on the circuit being measured.

Current transformers are often constructed by passing a singleprimary turn (either an insulated cable or an uninsulated bus bar)through a well-insulated toroidal core wrapped with many turns ofwire. Current transformers are used extensively for measuring currentand monitoring the operation of the power grid. The CT is typicallydescribed by its current ratio from primary to secondary. Commonsecondaries are 1 or 5 amperes. For example, a 4000:5 CT wouldprovide an output current of 5 amperes when the primary waspassing 4000 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 labelled as 1s1, 1s2, 2s1, 2s2and so on. The multi ratio CTs are typically used for current matchingin current differential protective relaying applications. Often, multipleCTs will be installed as a "stack" for various uses (for example,protection devices and revenue metering may use separate CTs). Fora three-stacked CT application, the secondary winding connectionpoints are typically labelled Xn, Yn, Zn. Care must be taken that thesecondary of a current transformer is not disconnected from its load

while current is flowing in the primary, as this will produce adangerously high voltage across the open secondary and maypermanently affect the accuracy of the transformer.

Specially constructed wideband current transformers are also used(usually with an oscilloscope) to measure waveforms of highfrequency or pulsed currents within pulsed powersystems. One typeof specially constructed wideband transformer provides a voltageoutput 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.Unlike CTs used for power circuitry, wideband CTs are rated in outputvolts per ampere of primary current.

ii) Voltage transformers
http://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Widebandhttp://en.wikipedia.org/wiki/Oscilloscopehttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/High_frequencyhttp://en.wikipedia.org/wiki/High_frequencyhttp://en.wikipedia.org/wiki/Pulsed_powerhttp://en.wikipedia.org/wiki/Rogowski_coilhttp://en.wikipedia.org/wiki/Integratorhttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Widebandhttp://en.wikipedia.org/wiki/Oscilloscopehttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/High_frequencyhttp://en.wikipedia.org/wiki/High_frequencyhttp://en.wikipedia.org/wiki/Pulsed_powerhttp://en.wikipedia.org/wiki/Rogowski_coilhttp://en.wikipedia.org/wiki/Integrator


34/55

Voltage transformers (VTs) or potential transformers (PTs) areanother type of instrument transformer, used for metering andprotection in high-voltage circuits. They are designed to presentnegligible load to the supply being measured and to have a precisevoltage ratio to accurately step down high voltages so that meteringand protective relay equipment can be operated at a lower potential.

Typically the secondary of a voltage transformer is rated for 69 or 120Volts at rated primary voltage, to match the input ratings of protectionrelays.

The transformer winding high-voltage connection points are typicallylabelled as H1, H2 (sometimes H0 if it is internally grounded) and X1,X2, and sometimes an X3 tap may be present. Sometimes a secondisolated winding (Y1, Y2, Y3) may also be available on the samevoltage transformer. The high side (primary) may be connected phaseto ground or phase to phase. The low side (secondary) is usually

phase to ground.

The terminal identifications (H1, X1, Y1, etc.) are often referred to aspolarity. This applies to current transformers as well. At any instantterminals with the same suffix numeral have the same polarity andphase. Correct identification of terminals and wiring is essential forproper operation of metering and protection relays.

While VTs were formerly used for all voltages greater than 240Vprimary, modern meters eliminate the need VTs for most secondary

service voltages. For new, or rework, meter packages, VTs aretypically only installed in primary voltage (typically 12.5kV) orgeneration voltage (13.2kV) meter packages.

iii) Pulse transformers

A pulse transformer is a transformer that is optimised for transmitting

rectangular electrical pulses (that is, pulses with fast rise and falltimes and a constant amplitude). Small versions called signal typesare used in digital logic and telecommunications circuits, often formatching logic drivers to transmission lines. Medium-sized powerversions are used in power-control circuits such as camera flashcontrollers. Larger power versions are used in the electrical powerdistribution industry to interface low-voltage control circuitry to thehigh-voltage gates ofpower semiconductors. Special high voltagepulse transformers are also used to generate high power pulses for
http://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Digital_logichttp://en.wikipedia.org/wiki/Telecommunicationshttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Camera_flashhttp://en.wikipedia.org/wiki/Electrical_power_distributionhttp://en.wikipedia.org/wiki/Electrical_power_distributionhttp://en.wikipedia.org/wiki/Power_semiconductor_devicehttp://en.wikipedia.org/wiki/High_voltagehttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Digital_logichttp://en.wikipedia.org/wiki/Telecommunicationshttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Camera_flashhttp://en.wikipedia.org/wiki/Electrical_power_distributionhttp://en.wikipedia.org/wiki/Electrical_power_distributionhttp://en.wikipedia.org/wiki/Power_semiconductor_devicehttp://en.wikipedia.org/wiki/High_voltage


35/55

radar, particle accelerators, or other high energy pulsed powerapplications.

To minimise distortion of the pulse shape, a pulse transformer needsto have low values of leakage inductance and distributedcapacitance, and a high open-circuit inductance. In power-type pulse

transformers, a low coupling capacitance (between the primary andsecondary) is important to protect the circuitry on the primary sidefrom high-powered transients created by the load. For the samereason, high insulation resistance and high breakdown voltage arerequired. A good transient response is necessary to maintain therectangular pulse shape at the secondary, because a pulse with slowedges 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 thisproduct, the larger and more expensive the transformer.

iv) RF transformers (transmission line transformers)

Forradio frequency use, transformers are sometimes made fromconfigurations of transmission line, sometimes bifilarorcoaxial cable,

wound around ferrite or other types of core. This style of transformergives 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, therebyraising its Q factor. The cores of such transformers help improveperformance at the lower frequency end of the band. RF transformerssometimes used a third coil (called a tickler winding) to injectfeedback into an earlier (detector) stage in antique regenerative radioreceivers.

v) Baluns

Baluns are transformers designed specifically to connect betweenbalanced and unbalanced circuits. These are sometimes made fromconfigurations of transmission line and sometimes bifilarorcoaxial
http://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Particle_acceleratorshttp://en.wikipedia.org/wiki/Pulsed_powerhttp://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Bifilarhttp://en.wikipedia.org/wiki/Coaxialhttp://en.wikipedia.org/wiki/Ferritehttp://en.wikipedia.org/wiki/Bandwidthhttp://en.wikipedia.org/wiki/Q_factorhttp://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Detector_(radio)http://en.wikipedia.org/wiki/Regenerative_circuithttp://en.wikipedia.org/wiki/Balancedhttp://en.wikipedia.org/wiki/Unbalancedhttp://en.wikipedia.org/wiki/Bifilarhttp://en.wikipedia.org/wiki/Coaxialhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Particle_acceleratorshttp://en.wikipedia.org/wiki/Pulsed_powerhttp://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Bifilarhttp://en.wikipedia.org/wiki/Coaxialhttp://en.wikipedia.org/wiki/Ferritehttp://en.wikipedia.org/wiki/Bandwidthhttp://en.wikipedia.org/wiki/Q_factorhttp://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Detector_(radio)http://en.wikipedia.org/wiki/Regenerative_circuithttp://en.wikipedia.org/wiki/Balancedhttp://en.wikipedia.org/wiki/Unbalancedhttp://en.wikipedia.org/wiki/Bifilarhttp://en.wikipedia.org/wiki/Coaxial


36/55

cable and are similar to transmission line transformers in constructionand operation.

vi) Audio transformers

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

Transformers are also used in DI boxes to convert impedance fromhigh-impedance instruments (for example, bass guitars) to enablethem to be connected to a microphone input on the mixing console.

A particularly critical component is the output transformer of an audio

power amplifier. Valve circuits for quality reproduction have long beenproduced with no other (inter-stage) audio transformers, but an outputtransformer is needed to couple the relatively high impedance (up toa few hundred ohms depending upon configuration) of the outputvalve(s) to the low impedance of a loudspeaker. (The valves candeliver a low current at a high voltage; the speakers require highcurrent at low voltage.) Solid-state power amplifiers may need nooutput transformer at all.

For good low-frequency response a relatively large iron core isrequired; high power handling increases the required core size. Goodhigh-frequency response requires carefully designed andimplemented windings without excessive leakage inductance orstraycapacitance. All this makes for an expensive component.

Early transistoraudio power amplifiers often had output transformers,but they were eliminated as designers discovered how to designamplifiers without them.

vii) Speaker transformers
http://en.wikipedia.org/wiki/Frequency_responsehttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/DI_boxhttp://en.wikipedia.org/wiki/Bass_guitarhttp://en.wikipedia.org/wiki/Mixing_consolehttp://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Power_amplifierhttp://en.wikipedia.org/wiki/Coupling_(electronics)http://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wiktionary.org/wiki/windinghttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Stray_capacitancehttp://en.wikipedia.org/wiki/Stray_capacitancehttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Frequency_responsehttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/DI_boxhttp://en.wikipedia.org/wiki/Bass_guitarhttp://en.wikipedia.org/wiki/Mixing_consolehttp://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Power_amplifierhttp://en.wikipedia.org/wiki/Coupling_(electronics)http://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wiktionary.org/wiki/windinghttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Stray_capacitancehttp://en.wikipedia.org/wiki/Stray_capacitancehttp://en.wikipedia.org/wiki/Transistor


37/55

In the same way that transformers are used to create high voltagepower transmission circuits that minimize transmission losses,speaker transformers allow many individual loudspeakers to bepowered from a single audio circuit operated at higher-than normalspeaker 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 audiowaveform 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 thedesigned line voltage of the speaker circuit. Then, a smallertransformer at each speaker returns the voltage and impedance toordinary speaker levels. The speaker transformers commonly havemultiple primary taps, allowing the volume at each speaker to beadjusted in a number of discrete steps.

Use of a constant-voltage speaker circuit means that there is no needto worry about the impedance presented to the amplifier output(which would clearly be too low if all of the speakers were arranged inparallel and would be too complex a design problem if the speakerswere arranged in series-parallel). The use of higher transmissionvoltage and impedance means that power lost in the connecting wireis minimized, even with the use ofsmall-gauge conductors (and leadsto the term constant voltage as the line voltage doesn't change muchas additional speakers are added to the system). In addition, the

ability to adjust, locally, the volume of each speaker (without thecomplexity and power loss of an L pad) is a useful feature.

viii) Small Signal transformers

Moving coil phonograph cartridges produce a very small voltage. Inorder for this to be amplified with a reasonable signal-noise ratio, atransformer is usually used to convert the voltage to the range of the

more common moving-magnet cartridges.

ix) 'Interstage' and coupling transformers
http://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Public_addresshttp://en.wikipedia.org/wiki/Tannoyhttp://en.wikipedia.org/wiki/Series_and_parallel_circuitshttp://en.wikipedia.org/wiki/Wire_gaugehttp://en.wikipedia.org/wiki/L_padhttp://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Public_addresshttp://en.wikipedia.org/wiki/Tannoyhttp://en.wikipedia.org/wiki/Series_and_parallel_circuitshttp://en.wikipedia.org/wiki/Wire_gaugehttp://en.wikipedia.org/wiki/L_pad


38/55

A use for interstage transformers is in the case of push-pull amplifierswhere an inverted signal is required. Here two secondary windingswired in opposite polarities may be used to drive the output devices.

Uses of transformers

For supplying power from an alternating current power grid toequipment which uses a different voltage.

For regulating the secondary output of a constant voltage (orferro-resonant), in which a combination of core saturation andthe resonance of a tank circuit prevents changes in the primaryvoltage from appearing on the secondary.

Electric power transmission over long distances.

Large, specially constructed power transformers are used forelectric arc furnaces used in steelmaking.

Rotating transformers are designed so that one winding turnswhile the other remains stationary. A common use was thevideo head system as used in VHS and Beta video tapeplayers. These can pass power or radio signals from a

stationary mounting to a rotating mechanism, orradarantenna. Other rotary transformers are precisely constructed in order to

measure distances or angles. Usually they have a singleprimary and two or more secondaries, and electronic circuitsmeasure the different amplitudes of the currents in thesecondaries. See synchro and resolver.

Sliding transformers can pass power or signals from astationary mounting to a moving part such as a machine toolhead.

A transformer-like device is used for position measurement. Seelinear variable differential transformer.

Some rotary transformers are used to couple signals betweentwo parts which rotate in relation to each other.

Small transformers are often used internally to couple differentstages ofradio receivers and audio amplifiers.
http://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_arc_furnacehttp://en.wikipedia.org/wiki/Steelmakinghttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Antenna_(electronics)http://en.wikipedia.org/wiki/Synchrohttp://en.wikipedia.org/wiki/Resolver_(electrical)http://en.wikipedia.org/wiki/Linear_variable_differential_transformerhttp://en.wikipedia.org/wiki/Rotary_transformerhttp://en.wikipedia.org/wiki/Radio_receiverhttp://en.wikipedia.org/wiki/Audio_amplifierhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_arc_furnacehttp://en.wikipedia.org/wiki/Steelmakinghttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Antenna_(electronics)http://en.wikipedia.org/wiki/Synchrohttp://en.wikipedia.org/wiki/Resolver_(electrical)http://en.wikipedia.org/wiki/Linear_variable_differential_transformerhttp://en.wikipedia.org/wiki/Rotary_transformerhttp://en.wikipedia.org/wiki/Radio_receiverhttp://en.wikipedia.org/wiki/Audio_amplifier


39/55

Transformers may be used as external accessories forimpedance matching; for example to match a microphone to anamplifier.

Balanced-to-unbalanced conversion. A special type oftransformer called a balun is used in radio and audio circuits to

convert between balanced linecircuits and unbalancedtransmission lines such as antenna downleads.

Flyback transformers are built using ferrite cores. They supplyhigh voltage to the CRTs at the frequency of the horizontaloscillator. In the case of television sets, this is about 15.7kHz. Itmay be as high as 75 - 120kHz for high-resolution computermonitors.

Switching power supply transformers usually operate between

30-1000 kHz. The tiny cores found in wristwatch backlightpower supplies produce audible sound (about 1 kHz).
http://en.wikipedia.org/wiki/Balunhttp://en.wikipedia.org/wiki/Balanced_linehttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Switched-mode_power_supplyhttp://en.wikipedia.org/wiki/Backlighthttp://en.wikipedia.org/wiki/Balunhttp://en.wikipedia.org/wiki/Balanced_linehttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Switched-mode_power_supplyhttp://en.wikipedia.org/wiki/Backlight


40/55

Types of transformers

In general, transformers are used for two purposes: signal matchingand power supplies.

Power Transformers

Power transformers are used to convert from one voltage toanother, at significant power levels.

Step-up transformers

A "step-up transformer" allows a device that requires a high voltagepower supply to operate from a lower voltage source. The transformertakes in the low voltage at a high current and puts out the highvoltage at a low current.

Examples:

You are a Swiss visiting the U.S.A., and want to operate your220VAC shaver off of the available 110 VAC.

The CRT display tube of your computer monitor requiresthousands of volts, but must run off of 110 VAC from the wall.

Limitations

Transformers alone cannot do the following:

Convert DC to AC or vice versa

Change the voltage or current of DC

Change the AC supply frequency.
http://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Frequency


41/55

Diode

A diode is a tube or semiconductor device, intended to passcurrent in only one direction. Diode can be used for a widevariety of different purposes. The semiconductor diode is farmore common than the tube diode in modern electronic circuits.A diode consists of N-type semiconductor material, usuallygermanium or silicon, and P-type material. Electrons flow intothe N-type material and out of the Pterminal.

The schematic symbol for a semiconductor diode is shown at B.Positive current flows in the direction of the arrow. Electronmovement is contrary to the arrow. The positive terminal of a

diode is called Anode, and the negative terminal is calledCathode, under conditions of forward bias (conduction).Semiconductor diode can be very small, and still handlehundreds or even thousands of volta at several amperes. Theolder tube type diodes are much bulkier and less efficient than


42/55

the semiconductor diodes. Some of the tube type diodes requirea separate power supply for the purpose of heatihg a filament.Semiconductor diodes are used for many different purposes inelectronics. They can be used as amplifiers, frequencycontrollers, oscillators, voltage regulators, switches, mixers, andin many other types of circuits.

Diode Bridge

A diode bridge or bridge rectifier (occasionally called a Graetzbridge) is an arrangement of fourdiodes connected in a bridgecircuit as shown below, that provides the same polarity of outputvoltage for any polarity of the input voltage. When used in its mostcommon application, for conversion ofalternating current (AC)

input into direct current (DC) output, it is known as a bridgerectifier. The bridge recitifier provides full wave rectification from atwo wire AC input (saving the cost of a center tapped transformer)but has two diode drops rather than one reducing efficiency over acenter tap based design for the same output voltage.

Schematic of a diode bridge

The essential feature of this arrangement is that for bothpolarities of the voltage at the bridge input, the polarity of theoutput is constant.
http://en.wikipedia.org/wiki/Graetz_AGhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Bridge_circuithttp://en.wikipedia.org/wiki/Bridge_circuithttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Image:Diode_bridge.svghttp://en.wikipedia.org/wiki/Image:Diode_bridge.svghttp://en.wikipedia.org/wiki/Graetz_AGhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Bridge_circuithttp://en.wikipedia.org/wiki/Bridge_circuithttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Voltage


43/55

Basic operation

When the input connected at the left corner of the diamond ispositive with respect to the one connected at the right handcorner, current flows to the right along the upper colored path tothe output, and returns to the input supply via the lower one.

When the right hand corner is positive relative to the left handcorner, current flows along the upper colored path and returnsto the supply via the lower colored path.

In each case, the upper right output remains positive withrespect to the lower right one. Since this is true whether theinput is AC or DC, this circuit not only produces DC power whensupplied with AC power: it also can provide what is sometimescalled "reverse polarity protection". That is, it permits normal
http://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Image:Rectified_waves.pnghttp://en.wikipedia.org/wiki/Image:Diodebridge3.pnghttp://en.wikipedia.org/wiki/Image:Diodebridge2.pnghttp://en.wikipedia.org/wiki/Current_(electricity)


44/55

functioning when batteries are installed backwards or DC input-power supply wiring "has its wires crossed" (and protects thecircuitry it powers against damage that might occur without thiscircuit in place).

Prior to availability of integrated electronics, such a bridgerectifier was always constructed from discrete components.

Since about 1950, a single four-terminal component containingthe four diodes connected in the bridge configuration became astandard commercial component and is now available withvarious voltage and current ratings.

How Bridge Rectifier works

When four diodes are connected, the circuit is called a BRIDGERECTIFIER. The input to the circuit is applied to the diagonallyopposite corners of the network, and the output is taken from theremaining two corners.

One complete cycle of operation will be discussed to help youunderstand how this circuit works. We have discussed transformers inprevious modules in the NEETS series and will not go into theircharacteristics at this time. Let us assume the transformer is working
http://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/Battery_(electricity)


45/55

properly and there is a positive potential at point A and a negativepotential at point B. The positive potential at point A will forward biasD3 and reverse bias D4. The negative potential at point B will forwardbias D1 and reverse bias D2. At this time D3 and D1 are forwardbiased and will allow current flow to pass through them; D4 and D2are reverse biased and will block current flow. The path for current

flow is from point B through D1, up through RL, through D3, throughthe secondary of the transformer back to point B. This path isindicated by the solid

arrows. Waveforms (1) and (2) can be observed across D1 and D3.

One-half cycle later the polarity across the secondary of thetransformer reverses, forward biasing D2 and D4 and reverse biasingD1 and D3. Current flow will now be from point A through D4, upthrough RL, through D2, through the secondary of T1, and back topoint A. This path is indicated by the broken arrows. Waveforms (3)and (4) can be observed across D2 and D4. You should have notedthat the current flow through RL is always in the same direction. Inflowing through RL this current develops a voltage corresponding tothat shown in waveform (5). Since current flows through the load (RL)during both h

sound energy to electrical energy

Documents