TransformersTransformerAnA.C.deviceusedtochangehighvoltagelow current A.C. into low voltage high current A.C. and vice-versa without changing the frequencyIn brief,1.Transferselectricpowerfromonecircuitto another. It does so without a change of frequency!. It accomplishes this by electromagnetic induction".#herethetwoelectriccircuitsareinmutual inductive in$uence of each other.%rinciple of operationItisbasedon principleof &'T'A( I)*'CTI+). Accordingto which an e.m.f. is inducedinacoil whencurrentin theneighbouring coilchanges.Constructional detail , Shell type Windings are wrapped around the center leg of a laminated core.Core typeWindings are wrapped around two sides of a laminated square core.-ectional view of transformersNote: High voltage conductors are smaller cross section conductors than the low voltage coilsConstruction of transformer from stampingsCore typeFig1: Coil and laminations of core type transformerFig: !arious types of cores-hell typeThe ./ and (/ windings are split into no. of sections#here ./ winding lies between two (/ windingsIn sandwich coils lea0age can be controlledFig: Sandwich windingsCut view of transformer Transformer with conservator and breather#or0ing of a transformer1. When current in theprimary coil changes "eing alternating in nature# a changing magnetic field is produced. $his changing magnetic field gets associated with the secondary through the soft iron core%. Hence magnetic flu& lin'edwith the secondary coilchanges.(. Which induces e.m.f. in the secondary.-ingle-%hase TransformersTransformer SymbolsNP = number of turns in the primary NS = number of turns in the secondaryEP = voltage of the primaryES = voltage of the secondaryIP= current in the primaryIS= current in the secondary-ingle-%hase TransformersTransformer FormulasEP / ES = NP / NSEPNS = ESNPEPIP = ESISNPIP = NSISIdeal TransformersZero leakage flux:)Flu&es produced "y the primary and secondary currents areconfined within the coreThe windings have no resistance:) *nduced voltages equal applied voltagesThe core has infinite permeability) +eluctance of the core is ,ero) Negligi"le current is required to esta"lishmagnetic flu&Loss-less magnetic core) No hysteresis or eddy currentsIdeal transformer!1 - supply voltage .*1) noload input current . !) output voltgae.*

) output current*m) magnetising current. /1)self induced emf ./

) mutually induced emf1&2 equation of a transformer#or0ed out on board34efer pdf 5le, emf-equation-of-tranformer voltage load ) novoltage load ) full voltage load ) noregulation !oltage==1

1 NNV VpspsNN!!=recallSecondary voltage on no)load!

is a secondary terminal voltage on full load =1

1

1

1regulation !oltageNNVVNNVSu"stitute we haveTransformer Efficiency1lectrical &achinesTransformere6ciencyisde5nedas7appliestomotors, generators and transformers8,0 111 =inoutPP0 111 +=loss outoutP P PTypes of losses incurred in a transformer,Copper I

4 losses.ysteresis losses1ddy current lossesTherefore, for a transformer, e6ciency may be calculated using the following,0 111coscosxI V P PI VS S core CuS S+ +=(osses in a transformer!ore or Iron loss"!opper loss"Condition for ma9imum e6ciencyContd.,The load at #hich the t#o losses are e$ual =All day e6ciencyhours2 ( 3'Wh in*nput 'Wh inoutput in watts input in watts putout efficiency commercial ordinary dayforall==%ll day efficiency is al#ays less than the commercial efficiency