17595278 Power System Protection Recent Trends by Jdm Latest

8/12/2019 17595278 Power System Protection Recent Trends by Jdm Latest

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POWER SYSTEM PROTECTION ANDRECENT TRENDS

BYBY

J DAKSHINA MURTHYJ DAKSHINA MURTHY

SENIOR CONSULTANT, ESCISENIOR CONSULTANT, ESCI

&&

FORMER CHIEF ENGINEER,FORMER CHIEF ENGINEER,

AP TRANSCO, HYDERABADAP TRANSCO, HYDERABAD


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Developments in Relay Technology

Till 1980 Electromagnetic Relays

1980 1986 Static Relays

1986 1990 Microprocessor based relays

1990 Numerical relays


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Solid State Relays

nput !uantities ad"usted to le#els suitable $ornput !uantities ad"usted to le#els suitable $or

electronic circuits%electronic circuits%

&urrent signals con#erted to #oltage signals%&urrent signals con#erted to #oltage signals%

'ecision ta(en based on recti$ied '& !uantities%'ecision ta(en based on recti$ied '& !uantities%


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Solid State Relays)

T*ese are semiconductor de#ices composed o$T*ese are semiconductor de#ices composed o$

electronic components li(e resistors+ diodes +electronic components li(e resistors+ diodes +

transistors etc%transistors etc%

No mo#ing partsNo mo#ing parts

,ig*ter and smaller t*an electromagnetic relays,ig*ter and smaller t*an electromagnetic relays


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Solid State Relays)

-er$orm t*e same $unction as electromagnetic relays-er$orm t*e same $unction as electromagnetic relays

e.cept t*at t*ey need less #oltage to operatee.cept t*at t*ey need less #oltage to operate

S/itc*ing can be per$ormed in #ery s*ort timesS/itc*ing can be per$ormed in #ery s*ort times

$$ected by transients+ /*ic*+ i$ present in t*e inputs+$$ected by transients+ /*ic*+ i$ present in t*e inputs+

may cause t*em to mal$unctionmay cause t*em to mal$unction


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Solid State Relays)

Reliable but electronic components may dri$t due toReliable but electronic components may dri$t due to*ig* ambient temperature and aging*ig* ambient temperature and aging

Energie trip circuits using electronic de#ices suc* asEnergie trip circuits using electronic de#ices suc* assilicon control recti$iers% 2ence no arcing duringsilicon control recti$iers% 2ence no arcing durings/itc*ings/itc*ing

S/itc*es in solid state relays *a#e lea(age currentsS/itc*es in solid state relays *a#e lea(age currentsirrespecti#e o$ t*e $act /*et*er t*e s/itc*es are openirrespecti#e o$ t*e $act /*et*er t*e s/itc*es are openor closedor closed


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Digital Relays

3iltered signals con#erted to S!uare /a#es

E#aluation is done based on -*ase ngle &omparison

Eit*er discrete logics or Microprocessors are used


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'igital Relays)

-o/er system protection *as c*anged a lot since t*e-o/er system protection *as c*anged a lot since t*e

e#olution o$ microprocessorse#olution o$ microprocessors

4ery large integration made it possible to put toget*er4ery large integration made it possible to put toget*er

numerous components in a single c*ipnumerous components in a single c*ip

Today+ digital tec*ni!ues are implemented to protectToday+ digital tec*ni!ues are implemented to protect

all components o$ po/er systemall components o$ po/er system

5asically+ digital tec*ni!ues use t*e same logic t*at is5asically+ digital tec*ni!ues use t*e same logic t*at is

used in electromec*anical and solidused in electromec*anical and solidstate relaysstate relays


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'igital Relays *a#e many ad#antages o#er

electromec*anical relays )

Economical))Ma"or reason $or t*e acceptance o$Ma"or reason $or t*e acceptance o$

digital relays is t*at t*ey present many $eatures atdigital relays is t*at t*ey present many $eatures atreasonable price%reasonable price%

3ast operation) T*ere are t/o reasons $or t*eir $astT*ere are t/o reasons $or t*eir $ast

operation% ne+ digital relays barely use anyoperation% ne+ digital relays barely use any

mec*anical parts% T/o+ t*e use o$ *ig* speedmec*anical parts% T/o+ t*e use o$ *ig* speed

processors *a#e made t*ese relays #ery $ast%processors *a#e made t*ese relays #ery $ast%


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Sel$7 Monitoring) Monitor t*emsel#es continuously+) Monitor t*emsel#es continuously+

/*ereas electromec*anical relays must be tested by/*ereas electromec*anical relays must be tested bypersonnel at regular inter#als% Sel$7 Monitoringpersonnel at regular inter#als% Sel$7 Monitoring

$eature sa#es time as /ell as money$eature sa#es time as /ell as money

Multiple 3eatures ) Relays+ Meters+ &ontrol) Relays+ Meters+ &ontrol

S/itc*es+ ndicators and &ommunication de#ices canS/itc*es+ ndicators and &ommunication de#ices can

be integrated into a single microprocessor basedbe integrated into a single microprocessor based

protecti#e relay% Substation System sc*ematics andprotecti#e relay% Substation System sc*ematics and/iring diagrams are easy to generate due to reduced/iring diagrams are easy to generate due to reduced

number o$ de#ices and related /iringnumber o$ de#ices and related /iring


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Reduced &ommissioning Time ) Microprocessor

based relays *a#e metering $eatures and remote

capabilities /*ic* ma(e commissioning simple and

less time consuming

,ess utage Time )3ast operation and $ault locationcapability o$ microprocessor based relays $or

transmission line protection reduce t*e po/er outage

time considerably% *en relays+ /it*out a $ault

locator capability+ detect a $ault+ cre/ spends a lot o$time in $inding t*e location o$ t*e $ault by patrolling

t*e line%


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3le.ibility ) 'igital relays can be designed and built

using general purpose *ard/are % relay can be used

to protect di$$erent po/er system components byloading di$$erent so$t/are programs

Small Sie ) 'igital relays are lig*ter in /eig*t andneed less space t*an t*e electromec*anical and solid

state relays% East to transport%

Easy Replacement )'ue to economical ad#antage+

digital relays+ i$ $ail it can be replaced in $ull% T*is

sa#es time and labor needed $or repairs


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Numerical Relays :

Signals are $iltered using an nti aliasing $ilterSignals are $iltered using an nti aliasing $ilter

Sampled signals are con#erted to numerical #alues atSampled signals are con#erted to numerical #alues ateac* sampling pointeac* sampling point

&alculations are carried out in real time using one or&alculations are carried out in real time using one orse#eral microprocessorsse#eral microprocessors


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Numerical Relay

Structure o !u"er#c$% re%$'(Structure o !u"er#c$% re%$'(

numerical relay consists o$ t*e $ollo/ing main numerical relay consists o$ t*e $ollo/ing main

subsystems)subsystems)

MicroprocessorMicroprocessor

nalog input systemnalog input system

'igital output system'igital output system

-o/er supply-o/er supply


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5loc( 'iagram o$ a Typical Numerical Relay


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Numerical relays operate on sampled signals andumerical relays operate on sampled signals andadopt digital computations% Sampling is t*e processadopt digital computations% Sampling is t*e process

o$ con#erting analog input signals+ suc* as curreno$ con#erting analog input signals+ suc* as current

and #oltage+ into digital input signals% T*ese analogand #oltage+ into digital input signals% T*ese analog

input signals+ in case o$ electromec*anical and staticinput signals+ in case o$ electromec*anical and static

relays+ are directly $ed into t*e electromagneticrelays+ are directly $ed into t*e electromagnetic

/inding or electronic circuits% n order to protect t*e/inding or electronic circuits% n order to protect t*e

relay $rom large transients o$ t*e input signals arelay $rom large transients o$ t*e input signals asurge $ilter is used%surge $ilter is used%


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n anti7aliasing $ilter is used to a#oid possible errorsn anti7aliasing $ilter is used to a#oid possible errors

in reconstructing input signal carried out a$ter t*ein reconstructing input signal carried out a$ter t*e

' Sample 2old section% ny signal *a#ing' Sample 2old section% ny signal *a#ing

*armonic components o$ order N*armonic components o$ order N:1+ ;N :1+


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T*e ' con#erts t*e sample #alues t*at represent t*eT*e ' con#erts t*e sample #alues t*at represent t*eanalog input signals into t*e digital input signals%analog input signals into t*e digital input signals%2o/e#er+ t*e con#ersion is not instantaneous+ and $o2o/e#er+ t*e con#ersion is not instantaneous+ and $or

t*is reason+ t*e ' system typically includes at*is reason+ t*e ' system typically includes asample7and7*old circuit% T*e sample7and7*oldsample7and7*old circuit% T*e sample7and7*oldcircuit pro#ides ideal sampling and *olds t*e samplecircuit pro#ides ideal sampling and *olds t*e sample#alues $or !uantiation by t*e ' con#erter%#alues $or !uantiation by t*e ' con#erter%

T*e microprocessor containing t*e relay algorit*m isT*e microprocessor containing t*e relay algorit*m ist*e controller o$ t*e numerical relay% T*et*e controller o$ t*e numerical relay% T*emicroprocessor most o$ten per$orms all control+microprocessor most o$ten per$orms all control+

computation+ sel$7test and communication $unction%computation+ sel$7test and communication $unction%T*e algorit*m $unctions as a digital $ilter to e.tracT*e algorit*m $unctions as a digital $ilter to e.tractt*e $undamental component o$ t*e input signal+ basedt*e $undamental component o$ t*e input signal+ basedon /*ic* t*e relay operation is carried out%on /*ic* t*e relay operation is carried out%


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T*e signal $rom t*e digital $ilter is compared /it* t*e pre7T*e signal $rom t*e digital $ilter is compared /it* t*e pre7

set t*res*old in t*e digital output system% T*e relayset t*res*old in t*e digital output system% T*e relay

operation is decided based on t*is comparison%operation is decided based on t*is comparison%

Re%$ $%)or#t*"Re%$ $%)or#t*"

T*e algorit*m is designed to remo#e as muc* as possible allT*e algorit*m is designed to remo#e as muc* as possible allo$ un/anted components $rom t*e input signals suc* aso$ un/anted components $rom t*e input signals suc* as

*armonic+ '&+ etc% T/o common algorit*ms+ t*e 'iscrete*armonic+ '&+ etc% T/o common algorit*ms+ t*e 'iscrete

3ourier Trans$orm >'3T? and t*e Root Mean S!uare >RMS?3ourier Trans$orm >'3T? and t*e Root Mean S!uare >RMS?

algorit*m are generally used%algorit*m are generally used%


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T*e '3T can e.tract any $re!uency $rom t*e signal% SinceT*e '3T can e.tract any $re!uency $rom t*e signal% Since

t*e '3T is capable o$ re"ecting e#eryt*ing e.cept t*et*e '3T is capable o$ re"ecting e#eryt*ing e.cept t*e

$re!uency being measured+ it *as a good response to$re!uency being measured+ it *as a good response totransient o#ers*oot%transient o#ers*oot%

Root Me$! S+u$re RMS-Root Me$! S+u$re RMS-

T*e Root Mean S!uare is a met*od o$ calculating t*eT*e Root Mean S!uare is a met*od o$ calculating t*e

magnitude o$ a periodically #arying !uantity% t can bemagnitude o$ a periodically #arying !uantity% t can be

calculated $or a series o$ discrete #alues or $or acalculated $or a series o$ discrete #alues or $or a

continuously #arying $unction%continuously #arying $unction%


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Numerical Technique Advantages

nalogue Tec*ni!ue Numerical Tec*ni!ue

More comple. *ard/areMore comple. *ard/are Simple *ard/are Simple *ard/are

Slo/ly 'ecreasingSlo/ly 'ecreasing bruptly 'ecreasing bruptly 'ecreasing

accuracyaccuracy per$ormance per$ormance

'i$$icult to modi$y'i$$icult to modi$y Simple to modi$y Simple to modi$y

Simple to #eri$ySimple to #eri$y 'i$$icult to #eri$y'i$$icult to #eri$y

'ata manipulation'ata manipulation 'ata manipulation 'ata manipulation di$$icultdi$$icult simple simple

'ata storage di$$icult'ata storage di$$icult 'ata storage simple 'ata storage simple

Sel$ Super#ision di$$icultSel$ Super#ision di$$icult Sel$ Super#ision simpleSel$ Super#ision simple


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Numerical Tec*ni!ue d#antages

,ess space,ess space 5etter $unctionality 5etter $unctionality

,ess /iring,ess /iring dapti#e $unctions dapti#e $unctions

,ess terminations,ess terminations 5etter per$ormance5etter per$ormance

,ess components,ess components Sa#ings in ci#il /or(s Sa#ings in ci#il /or(s

,ess aging problems,ess aging problems Sa#ings in erection+Sa#ings in erection+

Sel$ Super#isionSel$ Super#ision cabling and commissioning cabling and commissioning

&ommunication&ommunication Sa#ings in maintenanceSa#ings in maintenance

@reater $le.ibility Sa#ings in cost$unction@reater $le.ibility Sa#ings in cost$unction


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POWER

TRANSFORERPROTE!T"ON


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Ge!er$% r$t#!)' o Po.er tr$!'or"er' u'e/0

1% A00;;0 B4 =1C M4 uto Trans$ormers

;% ;;01=; B4 100M4 uto Trans$ormers

=% ;;0== B4 C0 D =1%CM4 Trans$ormers

A% 1=;66 B4 A0 D ;%CM4 Trans$ormers

C% 1=;== B4 C0+ =1%C+ ;C+ 16+ 1C M4 Trans$ormers

6% 1=;11 B4 16+ 1C D %C M4 Trans$ormers

% ==11 B4 8+ C+ =%1C M4 Trans$ormers


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Most o$ t*e -o/er trans$ormers o$ 1=;11B4 and

abo#e are o$ Star7Star #ector grouping /it* t*e

neutral solidly eart*ed% T*ere are a $e/ trans$ormers

/it* delta7star on 24 side?% T*e ==11B4 and 11B4A1C4 Trans$ormers are o$ delta7star >delta on

24 side?%


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T*e types o$ $aults t*at t*e trans$ormers are sub"ected to

are classi$ied as )7

T*roug* 3aults)7T*ese are due to o#erload conditions

and e.ternal s*ort circuits% Time graded & D E3

relays are employed $or e.ternal s*ort circuit conditions% 3uses are pro#ided $or 'istribution trans$ormers%

nternal 3aults)7 1? Electrical 3aults ) 73aults /*ic* cause immediate

serious damage suc* as p*ase to eart* or p*ase to


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p*ase $aults+ s*ort circuits bet/een turns o$ 24D,4p*ase $aults+ s*ort circuits bet/een turns o$ 24D,4

/indings+ etc%/indings+ etc%

;?;? ncipient 3aults) 77*ic* are initially minor $aults+*ic* are initially minor $aults+

causing slo/ly de#eloping damage+ suc* as a poorcausing slo/ly de#eloping damage+ suc* as a poor

electrical connection o$ conductors or brea(do/n o$electrical connection o$ conductors or brea(do/n o$

insulation+ etc%insulation+ etc%


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&onser#ator larmlarm

Trip

Tr$!'or"erTr$!'or"er

T$!1T$!1


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T*e $ollo/ing relays are employed to protect t*e

trans$ormer against internal $aults%

i? 5uc**ol relays

iii?'i$$erential relays

iii? RE3 relays+

i#? #er $lu.ing relays


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#uchhol$ Relays: -

*ene#er a $ault in trans$ormer de#elop slo/ly+*ene#er a $ault in trans$ormer de#elop slo/ly+

*eat is produced locally+ /*ic* begins to*eat is produced locally+ /*ic* begins to

decompose solid or li!uid insulated materialsdecompose solid or li!uid insulated materials

and t*us to produce in$lammable gas and oiland t*us to produce in$lammable gas and oil

$lo/% T*is p*enomenon *as been used in t*e gas$lo/% T*is p*enomenon *as been used in t*e gasprotection relay or popularly (no/n as 5uc**olprotection relay or popularly (no/n as 5uc**ol

relay% T*is relay is applicable only to t*e so7calledrelay% T*is relay is applicable only to t*e so7called

conser#ator type trans$ormer in /*ic* t*e trans$ormerconser#ator type trans$ormer in /*ic* t*e trans$ormer

tan( is completely $illed /it* oil+ and a pipe connectstan( is completely $illed /it* oil+ and a pipe connects

t*e trans$ormer tan( to an au.iliary tan( or F&onser#atorGt*e trans$ormer tan( to an au.iliary tan( or F&onser#atorG

/*ic* acts as an e.pansion c*amber%/*ic* acts as an e.pansion c*amber%


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3igure s*o/n as 5uc*ol relay connected into t*e pipe leading to

t*e conser#ator tan( and arrange to detect gas produced in t*e

trans$ormer tan(% s t*e gas accumulates $or a minor $ault

t*e oil le#el $alls and+ /it* it a $loat H3I /*ic* operates amercury s/itc* sounding an alarm% *en a more serious

$ault occurs /it*in t*e trans$ormer during /*ic* intense

*eating ta(es place+ an intense liberation o$ gases results%

T*ese gases rus* to/ards t*e conser#ator and create a rise in

pressure in t*e trans$ormer tan( due to /*ic* t*e oil is $orced

t*roug* t*e connecting pipe to t*e conser#ator% T*e oil $lo/de#elops a $orce on t*e lo/er $loat s*o/n as J4J in t*e $igure

and o#ertrips it causing it contacts to complete t*e trip circuit o$

t*e trans$ormer brea(er% peration o$ t*e upper $loat indicates

an incipient $ault and t*at o$ t*e lo/er $loat a serious $ault%


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5uc**ol relay peration ) &ertain -recautions)

T*e 5uc**ol relay may become operati#e not onlyduring $aults /it*in t*e trans$ormer% 3or instance+

/*en oil is added to a trans$ormer+ air may get in

toget*er /it* oil+ accumulate under t*e relay co#er and

t*us cause a $alse operation o$ t*e gas relay% 3or t*is

reason /*en t*e I@asI alarm signal is energied+ t*e

operators must ta(e a sample o$ t*e gas $rom t*e relay+

$or /*ic* purpose a special cloc( is pro#ided% @ases

due to $aults al/ays *a#e colour and an odour and are

in$lammable%


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T*e lo/er $loat may also $alsely operate i$ t*e oil

#elocity in t*e connection pipe+ t*oug* not due to

internal $aults+ is su$$icient to trip o#er t*e $loat% T*is

can occur in t*e e#ent o$ an e.ternal s*ort circuit /*en

o#er currents $lo/ing t*roug* t*e /indings o#er*eat t*ecopper and t*e oil and cause t*e oil to e.pand% $ mal7

operation o$ 5uc**ol relay due to o#erloads or e.ternal

s*ort circuits is e.perienced+ it may be necessary t*at

t*e lo/er $loat is ad"usted $or operation $or still *ig*er

#elocities%


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n installing t*ese relays t*e $ollo/ing re!uirements

s*ould be $ul$illed%

a? T*e conductors connecting t*e contacts to t*e

terminals on t*e co#er must *a#e paper insulation+ as

rubber insulation may be damaged by t*e oil%

b? T*e $loats must be tested $or air tig*tness+ $ore.ample+ by submerging t*em in *ot oil to create a

surplus pressure in t*em%

c? T*e relay co#er and t*e connection pipe s*ould *a#e aslope o$ 1%C to = percent and not *a#e any protruding

sur$ace to ensure unrestricted passage o$ t*e gases into

t*e conser#ator%


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Di%%erential Relays :&

'i$$erential relay compares t*e currents on bot* sides

o$ t*e trans$ormer% s long as t*ere is no $ault /it*int*e protected e!uipment >Trans$ormer?+ t*e current

circulates bet/een t*e t/o &Ts and no current $lo/s

t*roug* t*e di$$erential element% 5ut $or internal $aults

t*e sum o$ t*e &Ts secondary currents /ill $lo/ t*roug*

t*e di$$erential relay ma(ing it to operate%

T/o basic re!uirements t*at t*e di$$erential relayconnections are to be satis$ied are )

a? t must not operate $or load or e.ternal $aults%

b? t must operate $or internal $aults%


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s on7load tap c*ange $acilities are in#ariably

pro#ided in t*e grid trans$ormers+ any departure $rom

t*e nominal tap position /ill result in spill currents int*e relay circuits%

3urt*er+ t*e &Ts are o$ten o$ di$$erent types and *a#e

dissimilar magnetiation c*aracteristics+ again result7ing in spill current during *ea#y t*roug* $ault

conditions%

To a#oid un/anted relays operation under t*e abo#e

t/o conditions+ a J-ercentage 5iasJ di$$erential relay

is used%


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T*e operating c*aracteristics o$ percentage bias di$$erential

relay is s*o/n in t*e $igure%

T*e current $lo/ing t*roug* t*e operating coil o$ t*e relay

s*ould be nearly ero during normal operating conditions and /*en

e.ternal s*ort circuit occurs%

*ile setting t*e di$$erential relay on a trans$ormer+ t*e

>mismatc*? current t*roug* di$$erential element at normal tap and

positi#e and negati#e e.treme taps are to be computed% 'i$$erential

element pic(up setting andor bias settings is adopted based on

ma.imum percentage mismatc* adding some sa$ety margin%

'i$$erential &urrent K L 17;L

| I1-I2|

5ias Setting K 777777777777

(I1+ I2) / 2


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& T Ratios and connections $or di$$erential relay

=% simple rule o$ t*umb is t*at t*e &Ts on any ye>Star? /inding o$ a -o/er trans$ormer s*ould be

connected in delta and t*e &Ts on any delta /inding

s*ould be connected in ye >Star?%

C% a? $ t*e &Ts are to be connected in Star+ t*e &%T

Ratio /ill be n l /*ere in is trans$ormer $ull load

current%

b? $ t*e &Ts are to be connected in 'elta+ t*e &%T

Ratio /ill be n0%CC %


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D#ere!t#$% Re%$ I"2ro3e"e!t

'i$$erential Relay *as impro#ed a lot /it* t*e'i$$erential Relay *as impro#ed a lot /it* t*e

introduction o$ numerical relayintroduction o$ numerical relay

Numerical relays use tec*ni!ues suc* as *armonicNumerical relays use tec*ni!ues suc* as *armonic

bloc(ing+ /a#e s*ape recognitionbloc(ing+ /a#e s*ape recognition

n case o$ electromagnetic and static relays+ in an case o$ electromagnetic and static relays+ in atypical delta7/ye po/er trans$ormer+ t*e currenttypical delta7/ye po/er trans$ormer+ t*e current

trans$ormer /ould be connected as /ye7delta%trans$ormer /ould be connected as /ye7delta%


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not*er $eature in#ol#es correction $or currentnot*er $eature in#ol#es correction $or current

trans$ormer ratios+ /*ic* may re!uire e.ternaltrans$ormer ratios+ /*ic* may re!uire e.ternalau.iliary current trans$ormer%au.iliary current trans$ormer%

n t*e ot*er *and+ /it* t*e numerical relays+ alln t*e ot*er *and+ /it* t*e numerical relays+ all

current trans$ormers are connected in /yecurrent trans$ormers are connected in /ye

con$iguration and p*ase compensations are done incon$iguration and p*ase compensations are done in

t*e relayt*e relay

T*e magnitude compensation in numerical relays isT*e magnitude compensation in numerical relays is

also done in t*e relayalso done in t*e relay


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Restricted Earth Fault Protection (REF) : -

T*is relay is operati#e only $or t*e internal $aults o$t*e trans$ormer and t*us $ast operating time can be

ac*ie#ed%

1% n e.ternal $ault on t*e star side /ill result in current

$lo/ing in t*e line &T o$ t*e a$$ected p*ase and a

balancing current in t*e neutral &T and current in t*e

relay is ero and *ence relay is stable% 'uring an internal$ault+ t*e line current on t*e line &T gets re#ersed and

*ence relay operates%


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;% T*e arrangement o$ residually connected &Ts on t*e

delta side o$ a trans$ormer is only sensiti#e to eart*

$aults on t*e delta side because ero se!uence currents

are bloc(ed by t*e delta /inding%

3or e.ternal $aults no current $lo/s t*roug* RE3 unless

a &T gets saturated% 2ence minimum pic(up currentsetting is adopted >10 or ;0 n? on RE3 relay% 5ased

on t*e t*roug* $ault current+ t*e stabiliing resistor is set

suc* t*at t*e relay /ill not operate $or e.ternal $ault

/*en a &T gets saturated% T*is relay operates only $or

internal eart* $aults+ instantaneously%


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3 l $ l $ l $ ;C00 > ?


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3ault current $or e.ternal $ault $ K ;C00 >assume?

&%T%Ratio >line and neutral? 7 =001

;C00

Secondary $ault current K 777777 K 8% == >Sec%?

=00

R&T K &%T% Resistance

T, K ,ead Resistance K %A1 *msBm >;%C s! mm&u?4oltage de#eloped across &T >Saturated?

>4(? K $ >R&T ;R,?

K 8%==>C =?

K 66%6A 4oltsRelay burden K l 4

Relay perating

&urrent K 0%; >Set #alue?

Relay perating 4oltage


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Relay perating 4oltage4R K

Relay burden 777777777777777777

Relay perating currentK 10%; K C 4olt

Stabiliing Resistor SR K 4B 7 4R

77777777777

Set K 66%6A 7 C%0

777777777777777

0%; K =08%; *ms

Set SR K =10 *ms

$ t*e calculated #alue o$ SR e.ceeds t*e e.isting range+ t*e

current settings can be raised accordingly and arri#ed at suitable


52/152


53/152

Over%lu'ing Protection:

=% #er$lu.ing condition in a trans$ormer can occur during

system o#er #oltage andor under $re!uency

conditions >43?%

;% T*e #er$lu.ing condition does not call $or *ig* speed

tripping% T*e tripping can be delayed depending on t*e

o#er$lu. /it*stand capability o$ t*e trans$ormer%

11%Relays /it* de$inite time delay >nearly =0Sec%? and in#erse

c*aracteristic are being employed%


54/152

Other Protective devices employed

-ressure Relie$ 4alue >-R4?-ressure Relie$ 4alue >-R4?

inding Temperatureinding Temperature il Temperatureil Temperature

,T& 5uc**ol,T& 5uc**ol


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Transmission (ineProtection


56/152

D#'t$!ce Re%$'( 4

ntroduction)

T*e impedance relays also called distance relays areT*e impedance relays also called distance relays are

employed to pro#ide protection to transmission linesemployed to pro#ide protection to transmission linesconnected in a net/or( as t*ey are economic andconnected in a net/or( as t*ey are economic and

possess se#eral tec*nical ad#antages% T*ey arepossess se#eral tec*nical ad#antages% T*ey are

comparati#ely simple to apply+ operate /it* e.tremelycomparati#ely simple to apply+ operate /it* e.tremely

*ig* speed+ and bot* primary and bac(up protection*ig* speed+ and bot* primary and bac(up protection$eatures are in*erent in t*em%$eatures are in*erent in t*em%


57/152

D#'t$!ce Re%$'( 4 co!t5/-

Moreo#er+ t*ey can be easily modi$ied to /or( as unitMoreo#er+ t*ey can be easily modi$ied to /or( as unit

sc*emes by coordinating t*em /it* po/er line carriersc*emes by coordinating t*em /it* po/er line carrier

$acilities and are suitable $or *ig* speed reclosing%$acilities and are suitable $or *ig* speed reclosing%

T*e impedance relay is made to respond to t*eT*e impedance relay is made to respond to t*eimpedance bet/een t*e relay location and t*e pointimpedance bet/een t*e relay location and t*e point

/*ere $ault is incident% T*e impedance is proportional/*ere $ault is incident% T*e impedance is proportional

to t*e distance to t*e $ault+ >*ence t*e name Idistanceto t*e distance to t*e $ault+ >*ence t*e name Idistance

relayI? and is t*ere$ore independent o$ t*e $aultrelayI? and is t*ere$ore independent o$ t*e $aultcurrent le#els%current le#els%

i l i i i l


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'istance Relaying -rinciple)

distance relay compares t*e currents and #oltagesat t*e relaying point /it* &urrent pro#iding t*e

operating tor!ue and t*e #oltage pro#ides t*e

restraining tor!ue% n ot*er /ords an impedance relay

is a #oltage restrained o#ercurrent relay%

T*e e!uation at t*e balance point in a simple

impedance relay is B14; K B;; or 4 K B= /*ereB1+ B; and B= are constants% n ot*er /ords+ t*e

relay is on t*e #erge o$ operation at a constant #alue

o$ 4 ratio+ /*ic* may be e.pressed as an impedance


59/152

Since t*e operating c*aracteristics o$ t*e relay dependSince t*e operating c*aracteristics o$ t*e relay depend

upon t*e ratio o$ #oltage and current and t*e p*aseupon t*e ratio o$ #oltage and current and t*e p*ase

angle bet/een t*em+ t*eir c*aracteristics can be bestangle bet/een t*em+ t*eir c*aracteristics can be best

represented on an R7O diagram /*ere bot* 4 ratiorepresented on an R7O diagram /*ere bot* 4 ratio

and t*e p*ase angle can be plotted in terms o$ anand t*e p*ase angle can be plotted in terms o$ an

impedance R"O% 3urt*er+ t*e po/er systemimpedance R"O% 3urt*er+ t*e po/er system

impedance li(e $ault impedance+ po/er s/ings+ loadsimpedance li(e $ault impedance+ po/er s/ings+ loads

etc% can also be plotted on t*e same R7O diagram%etc% can also be plotted on t*e same R7O diagram%

T*ere$ore response o$ a particular relay during po/erT*ere$ore response o$ a particular relay during po/er

s/ing+ $aults and ot*er system disturbances can easilys/ing+ $aults and ot*er system disturbances can easilybe assessed%be assessed%

T $ 'i R l


60/152

Types o$ 'istance Relays)

>1?>1? mpedance relaympedance relay

>;?>;? Reactance relayReactance relay>=?>=? M*o relayM*o relay

>C?>C? Modi$ied impedance relayModi$ied impedance relay

mpedance relay)

&*aracteristics o$ an impedance relay on R7O&*aracteristics o$ an impedance relay on R7O

diagram is s*o/n in $igdiagram is s*o/n in $ig

peration o$ t*e impedance relay is independent o$peration o$ t*e impedance relay is independent o$

t*e p*ase angle bet/een 4 and % T*e operatingt*e p*ase angle bet/een 4 and % T*e operating

c*aracteristic is a circle /it* its center at t*e origin+c*aracteristic is a circle /it* its center at t*e origin+

and *ence t*e relay is non7directional%and *ence t*e relay is non7directional%


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&*aracteristic o$ 'irectional mpedance Relay)

&*aracteristic o$ a directional impedance relay in t*e&*aracteristic o$ a directional impedance relay in t*e

comple. R7O p*ase is s*o/n in $ig%comple. R7O p*ase is s*o/n in $ig%

T*e directional unit o$ t*e relay causes separation o$T*e directional unit o$ t*e relay causes separation o$

t*e regions o$ t*e relay c*aracteristic s*o/n in t*et*e regions o$ t*e relay c*aracteristic s*o/n in t*e

$igure by a line dra/n perpendicular to t*e line$igure by a line dra/n perpendicular to t*e line

impedance locus% T*e net result is t*at tripping /illimpedance locus% T*e net result is t*at tripping /illoccur only $or points t*at are bot* /it*in t*e circlesoccur only $or points t*at are bot* /it*in t*e circles

and abo#e t*e directional unit c*aracteristic%and abo#e t*e directional unit c*aracteristic%


63/152


64/152

T*e Reactance7type 'istance Relay)

Reactance relay measures 4 SinReactance relay measures 4 Sin PP>i%e% Q sin>i%e% Q sin PPK O?%K O?%*ene#er t*e reactance measured by t*e relay is less*ene#er t*e reactance measured by t*e relay is less

t*an t*e set #alue+ t*e relay operates% T*e operatingt*an t*e set #alue+ t*e relay operates% T*e operating

c*aracteristic on R7O diagram is s*o/n in $igc*aracteristic on R7O diagram is s*o/n in $ig

T*e resistance component o$ impedance *as no e$$ectT*e resistance component o$ impedance *as no e$$ect

on t*e operation o$ reactance relay+ t*e relay respondson t*e operation o$ reactance relay+ t*e relay responds

solely to reactance component o$ impedance% T*issolely to reactance component o$ impedance% T*isrelay is in*erently non7directional% T*e relay is mostrelay is in*erently non7directional% T*e relay is most

suitable to detect eart* $aults /*ere t*e e$$ect o$ arcsuitable to detect eart* $aults /*ere t*e e$$ect o$ arc

resistance is appreciable%resistance is appreciable%


65/152

M*o relay)


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M*o relay)

T*is is a directional impedance relay+ also (no/n asT*is is a directional impedance relay+ also (no/n as

admittance relay% ts c*aracteristic on R7O diagram is aadmittance relay% ts c*aracteristic on R7O diagram is a

circle /*ose circum$erence passes t*roug* t*e origin ascircle /*ose circum$erence passes t*roug* t*e origin asillustrated in $igure s*o/ing t*at t*e relay is in*erentlyillustrated in $igure s*o/ing t*at t*e relay is in*erently

directional and it only operates $or $aults in t*e $or/arddirectional and it only operates $or $aults in t*e $or/ard

direction%direction%

Modi$ied impedance relay)

lso (no/n as o$$set M*o relay /*ose c*aracteristic encloses t*elso (no/n as o$$set M*o relay /*ose c*aracteristic encloses t*e

origin on R7O diagram as s*o/n in $igorigin on R7O diagram as s*o/n in $ig

T*is o$$set m*o relay *as t*ree main applications) 7T*is o$$set m*o relay *as t*ree main applications) 7

i?i? 5usbar one bac(up5usbar one bac(up

ii?ii? &arrier starting unit in distancecarrier bloc(ing sc*emes%&arrier starting unit in distancecarrier bloc(ing sc*emes%

iii? -o/er S/ing bloc(ing%iii? -o/er S/ing bloc(ing%


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M i 3 i 'i S *


68/152

Main 3eatures in 'istance Sc*eme

'istance sc*emes consist o$ t*e $ollo/ing ma"or

components)7i? Starters%

ii? Measuring units%

iii? Timersi#? u.iliary relays

Starters) 7T*e starting relay >or starter? initiates t*e distance

sc*eme in t*e e#ent o$ a $ault /it*in t*e re!uired

reac* >more t*an one7=?%

Starters) 7Starters) 7


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Starters) 7Starters)

t*er $unctions o$ t*e starter are) 7t*er $unctions o$ t*e starter are) 7

a?a?

Starting o$ timer relays $or second and t*ird ones%Starting o$ timer relays $or second and t*ird ones%

b?b? Starting o$ measuring elements%Starting o$ measuring elements%

T*e starters are generally o$ M*o or impedance type%T*e starters are generally o$ M*o or impedance type%

it* M*o type starters) 7

Measuring units $or p*ase and eart* $aults can be eit*erMeasuring units $or p*ase and eart* $aults can be eit*er

directional or non7directional as M*o starter isdirectional or non7directional as M*o starter is

in*erently directionalin*erently directional

it* impedance type starters)


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it* impedance type starters) 7

Measuring units *a#e to be directional as impedancestarters are non directional%

T*e under impedance relay can be used in

con"unction /it* t*e directional relay as starter /*ic*

/ill t*en $unction similar to t*e M*o starter%

Measuring units) 7

T*ey are generally o$ a m*o or reactance or acombination o$ m*o+ reactance and resistance types%


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Eart* 3ault nits)


72/152

Eart* 3ault nits) 7

T*ese measuring units utilie line to neutral #oltage>4an+ 4bn 4cn? and p*ase currents >a+ b+ c?% norder to ma(e t*ese units measure t*e positi#ese!uence impedance correctly+ a ero se!uence

current compensation is to be pro#ided /*ic* isobtained by)

BN K >Q07Q1? =Q1 >/*ere Q1 K positi#e se!uenceimpedance o$ line%

Q0 K Qero se!uence impedance o$ line? n t*e current circuit >1BN? a /ill be $ed $or t*e

abo#e measurement%


73/152

Timers) 7

Timer relays /*en initiated by starters pro#ide t*eTimer relays /*en initiated by starters pro#ide t*e

time lag re!uired $or ones% T*ey also /ill be usedtime lag re!uired $or ones% T*ey also /ill be used

$or one e.tension purpose /*ene#er re!uired%$or one e.tension purpose /*ene#er re!uired%

u.iliary relays) 7

'istance sc*eme comprises o$ se#eral au.iliary'istance sc*eme comprises o$ se#eral au.iliary

relays+ /*ic* per$orm $unctions suc* as $lagrelays+ /*ic* per$orm $unctions suc* as $lagindications+ trippings+ signaling+ alarm etc%indications+ trippings+ signaling+ alarm etc%

A//#t# % F t # /# t *


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A//#t#o!$% Fe$ture' #! /#'t$!ce 'c*e"e'( 4

i? -o/er S/ing bloc(ing relay

ii? 4T $use $ailure relay%

iii? S/itc* onto $ault relay

i#? 3ault locator

#? uto7reclosing sc*eme%

#iii?&arrier communication sc*eme%

P S # 6% 1#


75/152

Po.er S.#!) 6%oc1#!)( 4

'istance relay /*ic* respond to balanced =7p*ase'istance relay /*ic* respond to balanced =7p*asec*anges in t*e impedance /ill be a$$ected by po/erc*anges in t*e impedance /ill be a$$ected by po/er

s/ings% T*ese s/ings or oscillations occur $ollo/ings/ings% T*ese s/ings or oscillations occur $ollo/ing

a system disturbance suc* as ma"or load c*ange or aa system disturbance suc* as ma"or load c*ange or a

dip in #oltage due to delayed $ault clearance%dip in #oltage due to delayed $ault clearance%

n case o$ $ault+ t*e transition $rom period on case o$ $ault+ t*e transition $rom period o

impedance locations >;C to == o$ starter impedance?impedance locations >;C to == o$ starter impedance?to $ault impedance >starter impedance? is suddento $ault impedance >starter impedance? is sudden

/*ereas during po/er s/ings% T*e -S5 relays use/*ereas during po/er s/ings% T*e -S5 relays use

t*is di$$erence to bloc( t*e tripping during s/ings%t*is di$$erence to bloc( t*e tripping during s/ings%


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7T u'e $#%ure re%$( 4

T*e distance relays being #oltage restraint &T*e distance relays being #oltage restraint &

relays+ loss o$ #oltage due to main -T $use $ailure orrelays+ loss o$ #oltage due to main -T $use $ailure or

inad#ertent remo#al o$ $use in one or more p*asesinad#ertent remo#al o$ $use in one or more p*ases

/ill cause t*e relay operation% T*e $use $ailure relay/ill cause t*e relay operation% T*e $use $ailure relay

/ill sense suc* condition by t*e presence o$ residual/ill sense suc* condition by t*e presence o$ residual

#oltage /it*out residual current and bloc(s t*e relay%#oltage /it*out residual current and bloc(s t*e relay%

S.#tc* o!to $u%t(


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S.#tc* o!to $u%t( 4

*en t*e line is s/itc*ed on to a close by $ault >saya$ter line clear /it* eart* s/itc* closed?+ t*e #oltage att*e relaying point /ill be ero% 3aults o$ t*is type /illnormally be cleared by bac(up ones%

T*e #oltage applied to t*e relay is lo/ and t*iscondition occurring simultaneously /it* t*e operationo$ starter /ill cause instantaneous trip by ST3

relay% T*is ST3 $eature /ill be e$$ecti#e only $orabout 17; seconds a$ter t*e line is c*arged% 3aultsoccurring a$ter t*is time /ill be measured in t*enormal /ay%


78/152


79/152

F$ctor' $ect#!) /#'t$!ce re%$ o2er$t#o!(4

iii? 3ault resistance%

#? n$eed e$$ect%

iii? 5ranc*ing7o$$ e$$ect%

i#? ,oad encroac*ment%


80/152

F$u%t re'#'t$!ce(4

3ault resistance *as t/o components)73ault resistance *as t/o components)7

a? rc resistance%a? rc resistance%

b? @round resistance%b? @round resistance%

n a $ault bet/een p*ases+ only arc resistance is in#ol#ed%n a $ault bet/een p*ases+ only arc resistance is in#ol#ed%3or a $ault at 3+ t*e actual line impedance3or a $ault at 3+ t*e actual line impedance

K R O K Q,K R O K Q,

'ue to t*e presence o$ $ault resistance+ t*e impedance'ue to t*e presence o$ $ault resistance+ t*e impedance

measured by t*e relaymeasured by t*e relay

K R O R3 K QR >/*ere QR U Q,?K R O R3 K QR >/*ere QR U Q,?


81/152

3ault arc resistance is gi#en by arringtonIs3ault arc resistance is gi#en by arringtonIs$ormula)$ormula)

Rarc K 8C0 O l 1%ARarc K 8C0 O l 1%A

/*ere/*ere l K lengt* o$ arc in $tl K lengt* o$ arc in $t K $ault current in mps K $ault current in mps


82/152


83/152

T*e arc resistance *as little e$$ect on accuracy o$T*e arc resistance *as little e$$ect on accuracy o$

one71 unit as it operates instantaneously be$ore t*eone71 unit as it operates instantaneously be$ore t*e

arc can stretc* appreciably e.cept in case o$ s*ortarc can stretc* appreciably e.cept in case o$ s*ort

lines% Reactance relays are t*ere$ore used $or s*ortlines% Reactance relays are t*ere$ore used $or s*ort

lines /*ere t*e $ault resistance may be comparablelines /*ere t*e $ault resistance may be comparable

/it* t*at o$ t*e protected lines and also $or ground/it* t*at o$ t*e protected lines and also $or ground$aults /*ere t*e ground resistance is *ig*%$aults /*ere t*e ground resistance is *ig*%

T*e arc resistance /ill *a#e greater impact onT*e arc resistance /ill *a#e greater impact on

accuracy o$ bac(up ones >time delayed? as t*e arcaccuracy o$ bac(up ones >time delayed? as t*e arc

stretc*es appreciably%stretc*es appreciably%

n$eed e$$ect)7


84/152

n$eed e$$ect)

T*e e$$ect o$ intermediate current source bet/eenT*e e$$ect o$ intermediate current source bet/een

relay location and $ault point is termed as in$eedrelay location and $ault point is termed as in$eede$$ect% &onsider t*e s(etc* indicated in $ig 777e$$ect% &onsider t*e s(etc* indicated in $ig 777

$ault at 3 on t*e line 5& is at a distance o$ Q1Q; $ault at 3 on t*e line 5& is at a distance o$ Q1Q;$or t*e relay at station % 5ut /*en current ; $lo/s$or t*e relay at station % 5ut /*en current ; $lo/s

$rom bus '+ t*e impedance to t*e $ault as seen by t*e$rom bus '+ t*e impedance to t*e $ault as seen by t*erelay at isrelay at is

Q1 Q; Q; . >;1?%Q1 Q; Q; . >;1?%

T*us t*e $ault is seen by t*e relay as $art*er t*an /*atT*us t*e $ault is seen by t*e relay as $art*er t*an /*at

it really is+ i%e%it really is+ i%e% distance relay under reac*es due to t*edistance relay under reac*es due to t*ein$eed e$$ect%in$eed e$$ect%

T*e e$$ect o$ in$eed becomes more pronounced /it*T*e e$$ect o$ in$eed becomes more pronounced /it*more interconnections at station 5%more interconnections at station 5%


85/152

Br$!c*#!)4o eect( 4


86/152

)

&onsider t*e s(etc* indicated in $ig 777

$ault at 3 is at t*e distance o$ Q1Q; $or t*e relay atstation % 5ut /*en current 1 gets distributed as ;

D = at station 5+ t*e impedance to $ault seen by t*erelay at station /ill be >Q1 =1 Q;? /*ic* isless t*an >Q1Q;?%

T*en t*e $ault is seen by t*e relay as nearer t*an /*atit really is i%e% distance relay o#erreac*es due to

branc*ing7o$$ e$$ect% T*is o#erreac*ing tendency/ill cause t*e relay to loose its selecti#ity%

Lo$/ e!cro$c*"e!t( 4


87/152

Lo$/ e!cro$c*"e!t(

*ile protecting long lines t*e necessary reac*ile protecting long lines t*e necessary reac*may be so large t*at t*e minimum ser#icemay be so large t*at t*e minimum ser#iceimpedance >or load impedance? $alls /it*in t*eimpedance >or load impedance? $alls /it*in t*eregion o$ t*e starter% T*is /ould result iregion o$ t*e starter% T*is /ould result in

tripping /it*out t*ere being any $ault% T*e t/otripping /it*out t*ere being any $ault% T*e t/oconditions i%e% operation at *ea#y load and s*orconditions i%e% operation at *ea#y load and s*ortcircuit di$$er by #irtue o$ p*ase angle bet/eecircuit di$$er by #irtue o$ p*ase angle bet/een#oltage and current% 3or t*e load impedance+#oltage and current% 3or t*e load impedance+

t*e p*ase angle /ill be /it*in =0 to 7=0 'eg%t*e p*ase angle /ill be /it*in =0 to 7=0 'eg%*ile during s*ort circuits+ t*e $ault impedance*ile during s*ort circuits+ t*e $ault impedance*as a p*ase angle o$ 60 to 80 deg% >i%e% line*as a p*ase angle o$ 60 to 80 deg% >i%e% lineangle?%angle?%


88/152

,oad encroac*ment problem is more pronounced,oad encroac*ment problem is more pronouncedin case o$ under impedance starters and getsin case o$ under impedance starters and getslessened in case o$ m*o+ elliptical+ lens etc+ typelessened in case o$ m*o+ elliptical+ lens etc+ typeo$ starters% Relays /it* suitable c*aracteristic oo$ starters% Relays /it* suitable c*aracteristic onR7O diagram *a#e to be care$ully c*osen toR7O diagram *a#e to be care$ully c*osen toprotect long and *ea#ily loaded lines+ and t*isprotect long and *ea#ily loaded lines+ and t*isbecomes easily possible /it* microprocessorbecomes easily possible /it* microprocessor

based numerical relays%based numerical relays%


89/152

No!4'.#tc*e/ 'c*e"e 3' '.#tc*e/ 'c*e"e( 4

n an ideal Non7s/itc*ed sc*eme+ t*ere /ill be 6

starters+ = $or p*ase $aults and = $or ground $aults%

T*ere /ill be independent measuring units $or bot*

p*ase $aults and eart* $ault $or eac* p*ase+ $or all

t*ree ones+ totaling to 18 units% T*is sc*eme is

$aster and more accurate but is costly%


90/152

n t*e s/itc*ed sc*eme+ only one measuring unit /illbe used $or all types o$ $aults% T*is single measuring

unit is s/itc*ed to t*e correct $ault loop impedanceby s/itc*ing7in t*e respecti#e #oltages and currentsby t*e starter%

T*e reac* o$ t*e measuring element gets e.tended toone7; and one7= a$ter t*e elapse o$ correspondingtimings t*roug* one e.tension process% S/itc*edsc*eme is relati#ely slo/ in operation and *as t*e ris(

o$ total sc*eme $ailure in t*e e#ent o$ $ailure o$ t*eonly one measuring unit a#ailable%

8o!e e9te!'#o! 'c*e"e'(


91/152

8o!e e9te!'#o! 'c*e"e'( 4

s a #ia media bet/een non7s/itc*ed and s/itc*eds a #ia media bet/een non7s/itc*ed and s/itc*edsc*emes+ t*ere are sc*emes /it* one e.tensionsc*emes+ t*ere are sc*emes /it* one e.tension$acility >suc* as EE ma(e MM=4 D MR=4 relays?%$acility >suc* as EE ma(e MM=4 D MR=4 relays?%T*ese sc*emes consists o$ = measuring units $orT*ese sc*emes consists o$ = measuring units $or

p*ase $aults and = measuring units $or eart* $aultsp*ase $aults and = measuring units $or eart* $aults>apart $rom = starters?%>apart $rom = starters?%

T*e reac* o$ t*e measuring unit gets e.tended toT*e reac* o$ t*e measuring unit gets e.tended to

one7; and one7= a$ter elapse o$ correspondingone7; and one7= a$ter elapse o$ correspondingtimings t*roug* a one e.tension process%timings t*roug* a one e.tension process%


92/152

Ot*er O2er$t#!) C*$r$cter#'t#c'(

Earlier /*en electromagnetic relays /ere in use+ t*e

c*aracteristics in#ol#ing straig*t lines and or circles

on R7O diagram /ere only possible% it* t*e ad#ent

o$ static relays+ microprocessor based relays and

presently o$ numerical relays+ any desiredre!uired7

operating c*aracteristic is possible gi#ing /ider

c*oice $or selection o$ relays% n$act t*ere are relays+/*ic* can be programmed remotely%

A22%#c$t#o! o /#'t$!ce re%$'(


93/152

A22%#c$t#o! o /#'t$!ce re%$'(

Since t*e distance relays are $ed $rom t*e secondaries oSince t*e distance relays are $ed $rom t*e secondaries oline &Ts and bus -Tsline &4Ts+ t*e line parameters areline &Ts and bus -Tsline &4Ts+ t*e line parameters are

to be con#erted into secondary #alues to set t*e relay asto be con#erted into secondary #alues to set t*e relay as

per re!uirements%per re!uirements%

Qsecy K Qprimpedance ratioQsecy K Qprimpedance ratio

>/*ere mpedance ratio K -%T%Ratio&%T%Ratio?>/*ere mpedance ratio K -%T%Ratio&%T%Ratio?

2ence any c*anges in &%T %ratio *as to be e$$ected2ence any c*anges in &%T %ratio *as to be e$$ected

along /it* re#ision o$ relay settings only%along /it* re#ision o$ relay settings only%

3or t*e lines+ t*e impedance in *ms per BM is appro.imately as3or t*e lines+ t*e impedance in *ms per BM is appro.imately as

d


94/152

under)under)

7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

B4B4 Q1 >K Q; ?Q1 >K Q; ? ,ine ngle,ine ngle7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

1=; B41=; B4 0%A0%A 60 to 0 'eg%60 to 0 'eg%

;;0 B4;;0 B4 0%A0%A 0 to 80 'eg%0 to 80 'eg%

A00 B4A00 B4 0%=0%= 80 to 8C 'eg%80 to 8C 'eg%77777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

T*e line impedance is to be computed depending on line con$igurationT*e line impedance is to be computed depending on line con$iguration

conductor sie and clearness% T*e #alues in t*e table are onlyconductor sie and clearness% T*e #alues in t*e table are only

representati#e%representati#e%

distance relay is stepped $or eit*er = ones or A ones to pro#ide distance relay is stepped $or eit*er = ones or A ones to pro#ide

protection%protection%


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To ensure proper coordination bet/een distance relays in po/er system+ itTo ensure proper coordination bet/een distance relays in po/er system+ itis customary tois customary to


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is customary tois customary to

c*oose relay o*mic setting as $ollo/s) 7c*oose relay o*mic setting as $ollo/s) 7

777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

S%No% QonesS%No% Qones ReactanceReactance Time Time777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

1%1% Qone71Qone71 80 o$ Q,80 o$ Q, nstantaneousnstantaneous

>no intentional time delay?%>no intentional time delay?%

;%;% Qone7;Qone7; 100 o$ Q, A07C0100 o$ Q, A07C0 0%= to 0%A seconds 0%= to 0%A seconds

o$ QS,o$ QS,

=%=% Qone7=Qone7= 100 o$ Q, 1;0100 o$ Q, 1;0 0%6 to 0%8 seconds0%6 to 0%8 secondso$ QS,o$ QS,

A%A% Qone7AQone7A 100 o$ Q, 1;0100 o$ Q, 1;0 0%9 to 1%C seconds 0%9 to 1%C seconds

o$ Q,,o$ Q,,

777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777

/*ere Q, K -ositi#e se!uence impedance o$ line to be/*ere Q, K -ositi#e se!uence impedance o$ line to be


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/*ere Q, K -ositi#e se!uence impedance o$ line to be/*ere Q, K -ositi#e se!uence impedance o$ line to be

protected%protected%

QS, K -ositi#e se!uence impedance o$ ad"acent s*ortestQS, K -ositi#e se!uence impedance o$ ad"acent s*ortestline%line%

Q,, K -ositi#e se!uence impedance o$ ad"acent longestQ,, K -ositi#e se!uence impedance o$ ad"acent longest

line%line%

Note)Note)

l *ere a t*ree one relay only is a#ailable+ t*e one =*ere a t*ree one relay only is a#ailable+ t*e one =

/ill be set to co#er t*e ad"acent longest line%/ill be set to co#er t*e ad"acent longest line%

""?""? T*e onal timings /ill be care$ully selected to properlyT*e onal timings /ill be care$ully selected to properly

grade /it* t*e relays on all t*e $eeders emanating $romgrade /it* t*e relays on all t*e $eeders emanating $rom

t*e ad"acent bus%t*e ad"acent bus%

Nor"' o 2rotect#o! $/o2te/ or tr$!'"#''#o! %#!e' #!


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A0P0S'te"(4

i? 1=; B4 ,ines) 7

s/itc*ed type distance sc*eme supplemented by t*ree

numbers directional , relays and 1 No% directional

E, relay%

ii?;;0 B4 ,ines) 7

T/o 'istance Sc*emes) 7

Main7) 7 Non7s/itc*ed sc*eme $ed $rom bus -T%

Main7) 7 s/itc*ed sc*eme $ed $rom line &4T%

pro#ision is generally made $or t*e c*angeo#er o$l l $ * di * $ * b


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#oltage supply $or t*e distance sc*emes $rom t*e bus-T to line &4T and #ice7#ersa%

Eac* distance sc*eme is $ed $rom independent &Tsecondary cores%

iii? A00 B4 ,ines)7

T/o 'istance Sc*emes)7

Main7)7 Non7s/itc*ed or Numerical distance

sc*emesMain7)7 Non7s/itc*ed or Numerical distancesc*emes


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R7O diagram is indicated

Setting range in o*ms $or Qone71

77777777777777777777777777777777777777

0%8=A to =0

1%==C to A8

1%668 to 60

Q; K 1 to =%C times Q1

Q= K 1 to C times Q1

777777777777777777777777777777777777777Some o$ t*e sc*emes are pro#ided /it* a Qone7A timer to

ma(e t*e sc*eme /or(s as a A one relay+ t*e starter itsel$

being t*e At* one%


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MR:7( 4


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t is an electromagnetic relays /it* = m*o units $orp*ase $aults+ = reactance units $or eart* $aults% = m*ostarters+ eac* being associated /it* one p*ase $or alltypes o$ $aults and one o$$set m*o unit $or po/ers/ing bloc(ing%

Setting ranges same as in MM=4%

R7O diagram $or p*ase $aults is same as t*at $orMM=4 relay and $or eart* $aults it is indicated in$igure


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SHPM ;u$/r$ "*o-( 4


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t is a non7s/itc*ed static sc*eme /it* 18 measuring m*o

units% T*e one7= measuring elements /ill act as starters+

/*ic* *a#e eit*er m*o or a lenticular c*aracteristic% T*e

operating c*aracteristic on R7O diagram is indicated in $igure

T*e lenticular c*aracteristics allo/s *ealt*y o#erloads and*ence pre#ents tripping on load encroac*ment%

Setting range) 7 0%; to ;A0 *ms%

t *as built7in $eature o$ continuous sel$ monitoring >on

demand and periodic sel$ testing?% ll t*e additional $eatures pro#ided by relay can be enabled

or disabled /it* t*e *elp o$ s/itc*es pro#ided $or t*em%


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PYTS( 4


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t is a static s/itc*ed sc*eme /it* modular plug7in construction

>/it* built in test points?%

t *as = under impedance starters and a single m*o measuringunit% ne unit $or po/er s/ing bloc(ing% R7O diagram is

indicated in $igure

Setting range) 0%0C to A0 *ms+ /it* starter *a#ing range o$ ;0

to 0 *ms%

t *as an uncompensated starter+ /*ic* *as become a

problem due to load encroac*ment $or long lines%

T*e 47 c*aracteristic o$ t*e starter is indicated in abo#e $igure%

*en t*e #oltage is less t*an 6C rated+ t*e starter operates at a

current greater t*an 0%;C n% it* lo/ #oltages at some o$ t*e

stations+ t*is $eature *as caused relay to operate unnecessarily%


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112/152


113/152


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PD < =>?( 4


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t is a numerical protection relay /it* polygont is a numerical protection relay /it* polygonc*aracteristics%c*aracteristics%

t consists o$ $our impedance ones /it* independent Rt consists o$ $our impedance ones /it* independent Rand O #alues $or eac* oneand O #alues $or eac* one

Qone A can be utilied as a special one $or cabieQone A can be utilied as a special one $or cabieprotection%protection%

R O diagram as indicated in $igure%R O diagram as indicated in $igure%

T*roug* MM+ one can enter and edit t*e settings >T*eT*roug* MM+ one can enter and edit t*e settings >T*e

settings are pass/ord protected?settings are pass/ord protected? Setting RangeSetting Range )) 0%1 to ;000 *ms%0%1 to ;000 *ms%

TimersTimers )) 0 to 10 Secs%0 to 10 Secs%


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Qone - -rogrammable% Selectable as aQone - -rogrammable% Selectable as a

directional $or/ard or re#erse one%directional $or/ard or re#erse one%

Qone7A 'irectional re#erse one% Note t*atQone7A 'irectional re#erse one% Note t*at

Qone7= and Qone7A can be set toget*er to gi#eQone7= and Qone7A can be set toget*er to gi#e

e$$ecti#ely a $or/ard one /it* a re#erse o$$set%e$$ecti#ely a $or/ard one /it* a re#erse o$$set%


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E$rt* F$u%t Protect#o!(


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Eart* $ault !uadrilateral c*aracteristics is similar tot*e p*ase $ault !uadrilateral c*aracteristics as

s*o/n belo/% Resisti#e reac*es can be set

independently $or p*ase and eart* $ault protections%

ll eart* $ault elements are !uadrilateral s*aped+

and are directionalised similar to t*e p*ase $ault

elements% T*e impedance reac*es o$ eart* $ault

elements use residual compensation o$ t*e

corresponding p*ase $ault reac*es%


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REL84?@@(


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t is a numerical relay /it* !uadrilateral impedanceunits $or p*ase and eart* $aults% Eac* measuring

unit *as indi#idual and independent setting o$ t*e

reac* in resisti#e and reacti#e directions+ as /ell as

$or t*e ero se!uence compensation $actor+ BN%Entire Qone7= reac* >in $or/ard direction? is

a#ailable in re#erse direction /it* a separate timer

T=R% R7O diagram is as indicated

3our groups o$ setting parameters are possible to suit3our groups o$ setting parameters are possible to suitdi$$erent system conditions% nly one o$ t*e groupsdi$$erent system conditions% nly one o$ t*e groups


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y y g py y g p/ill be in ser#ice by c*oice% t *as continuous sel$/ill be in ser#ice by c*oice% t *as continuous sel$

monitoring and sel$ testing $eature and indicate t*emonitoring and sel$ testing $eature and indicate t*esame by e.tinguis*ing JRelay #ailableJ ,E' on t*esame by e.tinguis*ing JRelay #ailableJ ,E' on t*erelay% T*roug* MM+ one can enterW edit t*e settings+relay% T*roug* MM+ one can enterW edit t*e settings+read t*e mean ser#ice #alues o$ line #oltage+ current+read t*e mean ser#ice #alues o$ line #oltage+ current+

real+ reacti#e po/er and $re!uency% t stores data o$real+ reacti#e po/er and $re!uency% t stores data o$latest = disturbances occurred% >T*e settings are notlatest = disturbances occurred% >T*e settings are notpass/ord protected?%pass/ord protected?%

Setting rage)Setting rage) 0%1 to 1C0 *ms%0%1 to 1C0 *ms%

Timers)Timers) 0 to 10 Secs%0 to 10 Secs% t *as a $eature /*ic* does o#erload super#ision andt *as a $eature /*ic* does o#erload super#ision and

unsymmetrical load condition+ /*ic* can be used $orunsymmetrical load condition+ /*ic* can be used $oralarm or trip%alarm or trip%


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M$1e( 4 Se#"e!' Lt/0

SA=?? %


127/152

SA=?? re%$(

t is a numerical protection sc*eme /it* 16 bit

microprocessor% it* t*ree #ersion o$ detectors%

i? -*ase selecti#e o#ercurrent $ault detector%

ii? 4oltage controlled >under7impedance? $ault detector >/it*

independent R D O reac*es? and

iii? -olygonally s*aped angle7dependent impedance $ault

detector%

t *as $i#e ones >t/o o$ /*ic* can be used $or communication

sc*emes?%

R7O diagram is indicated belo/%

part $rom common $eatures+ it pro#ides Emergencypart $rom common $eatures+ it pro#ides Emergencyo#ercurrent $unction+ /*ic* comes into picture /*en maino#ercurrent $unction+ /*ic* comes into picture /*en main


128/152

o#ercurrent $unction+ /*ic* comes into picture /*en maino#ercurrent $unction+ /*ic* comes into picture /*en maindistance sc*eme is bloc(ed due to 4T $use $ailure conditions%distance sc*eme is bloc(ed due to 4T $use $ailure conditions%

t pro#ides t/o user de$ined logic $unctions% t *as continuoust pro#ides t/o user de$ined logic $unctions% t *as continuoussel$ monitoring and sel$ testing $eature% t stores data o$ latestsel$ monitoring and sel$ testing $eature% t stores data o$ latestt*ree $aults and measures #alues o$ load current+ operatingt*ree $aults and measures #alues o$ load current+ operating#oltage+ po/er and $re!uency continuously%#oltage+ po/er and $re!uency continuously%

Setting range)0%1 to ;00 *ms /it* 0%0 to =; sec >in step oSetting range)0%1 to ;00 *ms /it* 0%0 to =; sec >in step o0%01 sec? timers%0%01 sec? timers%

3our groups o$ settings are possible to suit di$$erent system3our groups o$ settings are possible to suit di$$erent systemconditions% nly one o$ t*e groups /ill be in ser#ice byconditions% nly one o$ t*e groups /ill be in ser#ice byc*oice%c*oice%


129/152

SEL < :>?( 4

t is numerical relay /it* 3our M*o ones $or p*ase


130/152

t is numerical relay /it* 3our M*o ones $or p*ase

$aults /it* independent p*ase to p*ase o#ercurrent

super#ision%

3our ground $aults $or M*o and Xuadrilateral ones

/it* independent p*ase and residual o#ercurrent

super#ision and ero se!uence compensation% T/o Xuadrilateral ones $or po/er s/ing bloc(ing%

,oad7encroac*ment c*aracteristics%

nstantaneous+ 'e$inite time and 'MT o#ercurrentc*aracteristics%

Si. >6? setting groups are a#ailable in t*e sc*eme%

Setting ranges)7


131/152

3or M*o ones ) 0%;C to =;0 *ms

>Secondary?

3or Xuadrilateral Qones )

Reactance ) 0%;C to =;0 *ms

>Secondary?

Resistance ) 0%;C to ;C0 *ms

>Secondary?

Timers ) 07;000 &ycles


132/152


133/152

BUS BAR PROTECTIONBUS BAR PROTECTION


134/152

T*e current trans$ormer secondaries are added toget*erT*e current trans$ormer secondaries are added toget*er

i * $ * i ll $ li d *i * $ * i ll $ li d *


135/152

to gi#e t*e sum o$ t*e currents in all $our linesW and t*eto gi#e t*e sum o$ t*e currents in all $our linesW and t*e

sum is sent to t*e di$$erential relay% n case a $aultsum is sent to t*e di$$erential relay% n case a $ault

occurs t*at is e.ternal to t*e &T connections+ say at t*eoccurs t*at is e.ternal to t*e &T connections+ say at t*e

point 1 in t*e 3igure+ t*e total current $lo/ing to t*atpoint 1 in t*e 3igure+ t*e total current $lo/ing to t*at

$ault /ill be e.actly e!ual to t*e total current entering$ault /ill be e.actly e!ual to t*e total current entering

t*e bus on lines ;+=+A and no current /ill $lo/ to t*et*e bus on lines ;+=+A and no current /ill $lo/ to t*edi$$erential relay% 2o/e#er+ i$ a $ault occurs on t*e bus+di$$erential relay% 2o/e#er+ i$ a $ault occurs on t*e bus+

bet/een p*ases or $rom p*ase to ground+ t*e sum o$ t*ebet/een p*ases or $rom p*ase to ground+ t*e sum o$ t*e

line currents /ill e!ual t*e total bus $ault current andline currents /ill e!ual t*e total bus $ault current and

t*e relay /ill correctly measure t*is !uantity%t*e relay /ill correctly measure t*is !uantity%


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5us di$$erential protection5us di$$erential protection


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2ig* impedance circulating current sc*eme2ig* impedance circulating current sc*eme

5iased di$$erential or lo/ impedance5iased di$$erential or lo/ impedancecirculating sc*eme%circulating sc*eme%

S0 No0 Det$#%' H#)* #"2e/$!ce c#rcu%$t#!)

curre!t re%$

Lo. #"2e/$!ce 6#$'e/

/#ere!t#$% re%$


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1% -rinciple T*e currents entering and

lea#ing t*e busbar arecompared conti7nuously% t

in#ol#es c*oosing o$

impedance *ig* enoug* to

stabilise t*e relay $or *ea#y

e.ternal $aults%

t *as di$$erential and bias

setting% T*e resultant biasis proportional to

arit*metic sum o$ all

currents+ /*ereas t*e

operating current is

#ector sum o$ all circuit

currents%

;% &Ts t re!uires all identical &T

ratios

t can /or( /it* &Ts o$

une!ual ratios also%

=% 5urden mposes comparati#ely *ig*burden on &Ts% u.iliary

&Ts reduce t*e

per$ormance o$ sc*eme

mposes less burden on&Ts% u.iliary &Ts

*a#e no e$$ect on

per$ormance o$

sc*eme

S0No0 Det$#%' H#)* #"2e/$!ce

c#rcu%$t#!) curre!t re%$

Lo. #"2e/$!ce 6#$'e/

/#ere!t#$% re%$


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A% &T Saturation peration o$ sc*eme e#en

/*en &Ts get saturatedduring internal $aults

peration o$ sc*eme e#en /*en

&Ts get saturated during internal$aults%

C% -er$ormance 2ig*ly sensiti#e $orinternal $aults and

completely stable $or

e.ternal $aults

2ig*ly sensiti#e $or internal$aults and completely $or

e.ternal $aults

6% Relays in %-

System

@E& ma(e &@=A+

-5'&5

@E& ma(e M5&Q

55 ma(e R'SS


140/152

3or some *ig* impedance sc*emes+ only 4oltage


141/152

g p + y g

Setting Z4Y /ill be set% >T*e calculations are similar

to t*at o$ Restricted Eart* 3ault relay setting $or t*eTrans$ormer protection?%

Lo. I"2e/$!ce Bu'6$r Sc*e"e(4 T*is relay operates on circulating current principle

and di$$erential current setting > ;0 n? is adopted

on t*e relay% T*e bias setting is generally set by t*erelay manu$acturer based on bus $ault le#els%

Bu'6$r Protect#o!

? &* ( 3 t


142/152

a? &*ec( 3eature) 7

To pre#ent incorrect tripping due to damage to /iringTo pre#ent incorrect tripping due to damage to /iringand e!uipment $rom e.traneous sources+ c*ec( relayand e!uipment $rom e.traneous sources+ c*ec( relay

is pro#ided% T*is c*ec( relay is pro#ided byis pro#ided% T*is c*ec( relay is pro#ided by

duplication o$ primary protection using a second setduplication o$ primary protection using a second set

o$ current trans$ormers cores on all circuits ot*er t*ano$ current trans$ormers cores on all circuits ot*er t*anbus section and bus couple units% T*e c*ec( system isbus section and bus couple units% T*e c*ec( system is

arranged in a similar manner o$ t*e primaryarranged in a similar manner o$ t*e primary

protection+ but $orms one one only co#ering t*eprotection+ but $orms one one only co#ering t*e

/*ole o$ t*e busbars >in case o$ single sectionalied/*ole o$ t*e busbars >in case o$ single sectionalied

busbar or bot* t*e buses >in case o$ double busbarbusbar or bot* t*e buses >in case o$ double busbar

arrangement?%arrangement?%

b? Super#ision


143/152

*en a &T secondary /inding or connectionsbet/een &T and t*e relay circuit become open

circuited+ t*e relay may maloperate $or load or

t*roug* $aults depending on t*e e$$ecti#e primary

setting% T*is condition o$ an open circuit can bedetected by using super#ision >o#er #oltage? relay+

/*ic* is arranged to gi#e alarm%

T*e super#ision must be time delayed to a#oid a $alse

alarm during genuine $ault conditions+ typically t*ree

seconds is adopted%

Numerical 5usbar -rotection


144/152

2ig*ly stable $or e.ternal $aults2ig*ly stable $or e.ternal $aults

2ig*ly sensiti#e $or internal $aults2ig*ly sensiti#e $or internal $aults perating speed around C0 msecperating speed around C0 msec

daptability to t*e dynamically c*anging topology o$ t*edaptability to t*e dynamically c*anging topology o$ t*e

busbarbusbar

&entralied or distributed arc*itecture&entralied or distributed arc*itecture

Support easy maintenance+ operation and $uture e.pansion o$Support easy maintenance+ operation and $uture e.pansion o$

t*e busbart*e busbar

&an operate /it* di$$erent o$ &Ts&an operate /it* di$$erent o$ &Ts

3iber optic cable used $or communication bet/een central and3iber optic cable used $or communication bet/een central and

perip*eral unitsperip*eral units

Ensure *ig* communication speedEnsure *ig* communication speed

Numerical 5usbar -rotection>contYd?


145/152

Management 3unctions)

n addition to t*e protection and control elements+ numerical

busbar protection pro#ides a /ide range o$ measurement+

monitoring+ post $ault analysis and sel$7diagnostic $eatures%

&ircuit brea(er control

Trip circuit super#ision>using -S,?

nline measurements

-lant status monitoring 3our alternati#e setting groups

-rogrammable sc*eme logic >-S,?

Se!uence o$ e#ent recording >SE?

Numerical 5usbar -rotection>contYd?


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Management 3unctions) &ompre*ensi#e disturbance recording >/a#e$orm capture? ser con$igurable ,E's

,ocal and remote communication ports

Time sync*roniation 3ully customiable menu te.ts

Multile#el pass/ord protection

Test $acilities

-o/er7 up diagnostics and continuous sel$7monitoring o$ relay

ser $riendly setting and analysis so$t/are


147/152

E.amples o$ numerical busbar protectionE.amples o$ numerical busbar protection))

M&M -A0 >re#a?M&M -A0 >re#a?RE5 C00 >55?RE5 C00 >55?

BREAKER FAILURE RELAY LBB PROTECTION-


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Main protecti#e sc*emes pro#ided $or linetrans$ormerMain protecti#e sc*emes pro#ided $or linetrans$ormergenerator are re!uired to operate and clear t*e $aultgenerator are re!uired to operate and clear t*e $ault

immediately+ isolating t*e $aulty section o$ t*e system%immediately+ isolating t*e $aulty section o$ t*e system%

t is t*en important t*at t*e circuit brea(er operatest is t*en important t*at t*e circuit brea(er operates

correctly+ clearing t*e $ault !uic(ly by tripping%correctly+ clearing t*e $ault !uic(ly by tripping%

2o/e#er t*ere is a ris( t*at brea(er may not trip >eit*er2o/e#er t*ere is a ris( t*at brea(er may not trip >eit*er

due to mec*anical sluggis*ness or due to inability todue to mec*anical sluggis*ness or due to inability to

interrupt *ea#y $ault current?% T*en t*e $ault getsinterrupt *ea#y $ault current?% T*en t*e $ault getscleared by bac(up relays at remote stations%cleared by bac(up relays at remote stations%

ncreasing po/er system comple.ity demands s*ortencreasing po/er system comple.ity demands s*orter

$ault clearing times t is t*ere$ore necessary to$ault clearing times t is t*ere$ore necessary to


149/152

$ault clearing times% t is t*ere$ore necessary to$ault clearing times% t is t*ere$ore necessary to

pro#ide brea(er $ailure relay >also called F,ocalpro#ide brea(er $ailure relay >also called F,ocal

brea(er bac(up relayG or FStuc( brea(er protectionG?%brea(er bac(up relayG or FStuc( brea(er protectionG?%

T*is sc*eme /ill isolate t*e bus to /*ic* t*e stucT*is sc*eme /ill isolate t*e bus to /*ic* t*e stuc(

brea(er is connected+ $aster% t comprises o$ , Dbrea(er is connected+ $aster% t comprises o$ , D

E, relays /it* a timer% T*e ,55 relay is energiedE, relays /it* a timer% T*e ,55 relay is energiedby trip command o$ main protection sc*emes andby trip command o$ main protection sc*emes and

t*us initiate master trip relay o$ t*e busbar protectiont*us initiate master trip relay o$ t*e busbar protection

sc*eme a$ter elapsing o$ de$ined time% T*en t*e entiresc*eme a$ter elapsing o$ de$ined time% T*en t*e entire

brea(er connected to t*e bus get tripped+ t*usbrea(er connected to t*e bus get tripped+ t*usisolating $aulty element%isolating $aulty element%


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n %- System+ 55 ma(e R&+ @E& ma(en %- System+ 55 ma(e R&+ @E& ma(e

&T@=9 type brea(er $ailure relays are commonly&T@=9 type brea(er $ailure relays are commonly


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yp y y

used% T*e general practice is to set t*e current settingused% T*e general practice is to set t*e current setting

K ;0 o$ n and Time setting K ;00 m %Sec% T*eK ;0 o$ n and Time setting K ;00 m %Sec% T*esc*ematic diagrams $or t*e application o$ t*e ,55sc*ematic diagrams $or t*e application o$ t*e ,55

relay >type &T@? are indicated in t*e $igure%relay >type &T@? are indicated in t*e $igure%

E#en i$ t*e busbar protection sc*eme is not a#ailable+E#en i$ t*e busbar protection sc*eme is not a#ailable+

t*e ,55 sc*eme can be made use o$ by pro#idingt*e ,55 sc*eme can be made use o$ by pro#iding

special trip circuits and trip relays similar to t*at o$special trip circuits and trip relays similar to t*at o$

bus protection trip circuits $or eac* line% sc*ematicbus protection trip circuits $or eac* line% sc*ematic$or suc* application is indicated in $igure$or suc* application is indicated in $igure


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17595278 Power System Protection Recent Trends by Jdm Latest