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BUCK - BOOSTTRANSFORMER

BYCH RAJENDER

(07915A0208)

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Introduction

It is a type of auto transformer used to

make small adjustments to the voltageapplied alternating current equipment.

Buck-Boost means that these transformers areused to buck (lower) or boost (increase) line

voltage to match required load voltage.

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Necessity

For large adjustments in voltage (more than 15%

to 20%), usually a two-winding transformer isused with the required voltage ratio, for example240V to 120V.

These transformers are more costly than buck

boost transformers since both windings mustcarry the full power delivered to the load,whereas the buckboost winding must only carrya fraction of the load power.

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Types

There are two basic types,

1.self adjusting (active)2.passive designs.

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1.Self adjusting (active)

The active types monitor incoming voltagesand will adjust the outgoing voltage to bewithin an acceptable range.

This is typically between 115 & 225V forcomputer UPS systems.

In an active buckboost transformer, a

control circuit selects which tap to use tomaintain the output voltage within the desiredrange, over a range of input voltages.

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2.Passive designs

Passive transformers are used for larger

equipment where the amount of buck or boost

is fixed.

The passive transformers are rated in volt-

amperes and are rated for a percent of voltage

drop or rise.

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For example, a buckboost transformerrated at 10% rise at 208V will raiseincoming voltage of 210V to 231V.

A rating of 5% drop at 240V will yield theresult of 233V if the actual incoming voltageis 245V.

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Frequency

All transformers only operate withalternating current. Transformers onlychange voltage, not frequency.

Equipment that uses induction motors willoperate at a different speed if operated atother than the design frequency.

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Some equipment is markedon its nameplate to run ateither 50Hz or 60Hz, and

would only need the voltageadjusted with a buckboosttransformer.

http://localhost/var/www/apps/conversion/current/tmp/scratch25663/wiki/File:Buck-Boost_Powerline_Transformers_320x240_23sec_noaudio_vidqual_0.ogv

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Application inelectric power

distribution Power traveling long distances in electric power

grids can experience a condition known as

voltage drop due to the slight resistance of themetallic conductor having acumulative(increasing) effect over tens tohundreds of miles/kilometers.

Distant customers may experience a drop of 5%to 10% of rated nominal line voltage.

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To combat(fight) these effects, largeboost transformers are placed on poles inremote locations to increase system

voltage and bring the voltage back up toacceptable levels.

The boosting consumes amperage

capacity from the unboosted main line,reducing the main line current carryingcapacity for all customers.

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On three-phase power lines, the verylarge and heavy transformers areoften spaced apart across three

separate consecutive poles on thepowerline, each boosting one of thethree phases.

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Applications

A typical buck- boost application is 120 voltsin, 12 volts out for low voltage lighting orcontrol circuitry.

In most applications, this low voltagetransformer is field connected as anautotransformer.

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Buckboost connectionsare used in several

places such asuninterruptible powersupply (UPS) units for

computers,

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First, you should have this information

before selecting the buck-boost

transformer. Line voltage

Load voltage

Load KVA or Load amps Frequency

Phase

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Advantages

More efficient

Smaller & lighter

5-10 times increase in

KVA

Versatile, many

applications

Lower cost.

Buck-Boost transformers

have capacities of .050

kVA to 5.0 kVA.

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Disadvantages

No circuit isolation

Cannot create a neutral Application voltages and KVA dont match the

nameplate voltages and KVA

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Conclusions

In AC power systems the fluctuating voltages maydamage the power system equipment.

So, in order to avoid these circumstances & toprotect the system equipments from thefluctuations Buck Boost Transformer is used.

The buck boost transformer maintains the voltageconstant in case of external voltage variations.

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References

www.wikipedia.com

www.acmepowerdist.com

www.howstuffworks.com

http://www.wikipedia.com/http://www.acmepowerdist.com/http://www.howstuffworks.com/http://www.howstuffworks.com/http://www.acmepowerdist.com/http://www.wikipedia.com/

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