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Earthing Transformers for Power Systems

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  EARTHINGTRANSFORMERSFOR POWER SYSTEMS  ABSTRACT:-  Normally power systems and net works are operated under variable complex stresses.n power systems t!e aults are not avodable even a ter takin# utmost care at every sta#e- rom plannin# to maintainance. T!e #roundin# o a circuit reduces potential stressesunder ault condition. $ower eedin# rom delta delta or i t!ere is no accessibility or star connected trans ormers occasionally s!orted to #round is very common-un-intentional#roundin# occurs any w!ere rom t!e eedin# system to utili%ation e&uipment T!e mainob'ective o #roundin# neutral is to make a s!ort circuit current su icient in ma#nitude or t!e relay action. T!is article restricted to %i#-%a# type wit! oil illed trans ormers. T!eneutral point is usually available at every volta#e level rom #enerator to trans ormers. nt!e absence o a power trans ormer o suitable capacity( connection and desi#n a separate#roundin# trans ormer can be used .T!ey are inductive devices intended primarily to provide a neutral point or #roundin# purpose. T!e main purpose o t!is paper is to discuss about t!e di erence between)art!in# trans ormer and $ower trans ormer and to discuss about t!e desi#nin# o eart!trans ormers. NTR*+,CT*N:- A trans ormer is a device w!ic! electroma#netically trans ers A.C. volta#e rom onelevel to anot!er level. An eart!in# trans ormer is a trans ormer primarily to provide aneutral point or #roundin# purpose. T!e sole duty o t!e #roundin# trans ormer is to pass#round current durin# an eart! ault.( and it carries no use ul load. T!e desirable &uantities o an eart!in# trans ormer are low %eroimpedance and low losses no load losses.  /,NCT*N */ )ART0N1 TRANS/*R2)RS:- ã Apart rom providin# an easy pat! to #round current durin# an eart! ault( t!e ollowin# additional unctions are also to be ac!ieved ã 0oldin# t!e neutral s!i t wit! in t!e limits ã $ermittin# t!e circulation o unbalanced load current in t!e neutral ã To limit t!e current durin# line to eart! aults ã To eart! t!e system ã To provide sin#le p!ase line to neutral load ã Can be used wit! resistance 3reactance3arc suppression coil C*2$ARS*N B)T4))N )ART0N1 AN+ $*4)R TRANS/*R2)RS:- T!e selection any trans ormer mainly by two actors-namely( primary volta#eand load ./or an eart!in# trans ormer load is s!ort time or s!ort duty  only at t!e time o ault (normally rom a ew seconds to one minute  COMPARISION CHARACTERISTICS  2.29MVA (S.C) 6.6KV 600 Amps(ET@) 2MVA110.! KV #$%& 1 (PT@)  )T5$T5$urposeTo provide a neutral point or eart!in#Raidin# or lowerin#volta#es67A ratin#S!ort timeContinuous7olta#es in #eneral,p to 88kv0i#!er volta#eseven9967 and above No o windin#s*ne3two*ne3two3t!ree  +irection o power low,ni directionB-directionalS.C wit! stand duration;sec.to ; min9 sec<ossesNo load lossesNo load losses and loadlosses2a#neti%in# current7ery lessNormal$riority or impedance=ero se&uence impedanceS!ort circuit impedanceS!ort circuit current+epends on system rom ew !undred amperes to ewt!ousand amperes,p to 9> times normalcurrent<eaka#e reactance<ittle 2oreType o volta#e mixedConstantin #eneralConstant3variable3re#ulationTransportationRoadRoad3RailS!ort circuit temperature n de#rees centi#rade9>9>0armonic residuals reeexist<oad actor<ow 0i#!nsulation,ni orm,ni orm3#raded) iciency2ore<essCost<ess2ore  ã 4ei#!ts( losses( dimensions and cost actors are muc! lower. ã Rise o oil 3windin# temperature is very less.
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