Distance protection schemes€-qil&

't2.1

12.212.312.412.512.6

lntroductionZone 1 extension scherneTransfer trip schemesBlocking schemeDirectional comparison unblocking schemeApplication to weak infeed terminals

12.1INTRODUCTIONOne of the main disadvantages bf conventional time-stepped distance protection, as illustrated in Figure 12.1, isthe fact that the instantaneous Zohe 1 of the protection ateach end of the protected line iannot be set to cover thewhole of the feeder length and is usually set to a6out 80%.This leaves two 'end zones', each being about 20% of theprotected ieeder lengih; in which faultslre cleared instan-taneously (Zone -t tirile) by the protection at one end of thefeeder but in Zone 2 time (0.3 to 0.4 seconds typically) bythe protectioh at the other end of the ferjder.

ln some applications this siituation cannot be tolerated, fortwo main reasons:

i; Faults remaining on the feeder for Zone 2 time maycause the system to become unstable.b. Where high speed auto-reclosing is used, Jhe non-simultaneous opening of the circuit bredkers at both endsof the faulted section results in no 'dead time' during theauto-reclose cyole for the fault to be extinguished and forionizid gases tcj clear. This results in the possibility that atransient fuult will cause permanent lockout of the circuitbreakerS at each end. of thri line section.

Unit schemes of protection which compare the conditionsat the two ends of the protected feeder simultaneously canpositively identify whether the fault is internal'or external tothe protected section, and are capable of providing highspeed,protection f6r the whole feeder length. This advan-tage is balanCed by the fact that the unit scheme does notprovide the back up protection to adjacent feeders given bya distance scheme.

The most desirable scheme is obviously one which com-bines the best features of both arrangements, that is, in-slantaneous tripping over the whole feeder length plusback-up protection to adjacent'feeders. This ean beachieved by interconnecting the distance protections ateach end of the protected feeder by a signalling channel.The signalling chdnnel may be high fiequency (hf) operat-ing over the overhead line conductors, voice freqrency(vf) using either pilots or a power line carrier communica-tions channel. a radio link. microwave channel or a fibreoptic link. These communication techniques are describedin detail in Chapter 8.

The purpose of the signalling channel is to transmit in-formation about the s)r6tem conditions from one end of the'protected line to the other; it can also be arranged to initiate

12,7 Operational comparison of transfer trip andblocking relaying schemes

12.8 Application to three-terminal lines12.9 Scheme requirements

213

. . ror prevent trippiog sf the rernotecircui't breaker. The former' arangernent:isv.gene.rally' r.efened to as a .lransier trip

:.. :scheni€:;wtiite the latler is known asa 'blocking scheme'.Wh€h cefiiei ol'sibn'alling'''equib*'tent is not dvailable, fasttripiiing for all lind fadtslsdd be achieved by dxtending theZone 1 r6abfi of'dislAnce f6taY3'under':control ot an'ass'6Ciat'ed' auto -?iclose "sEfrdme" The resu lti n g d istancescheme is referred to as a 'lone 1 Extensibri'S'Chemd and

:''its appti cati os,is;o qrrna lly'l i m ited'to d istri bu rion systerns o r: to'.intergbnneg&d power', sy$ernQ'nrhenr-lcarrier,, is'tem-

porarily takenrout of.tsilrviog.r',.i:'! , r:rji '?i, i4i :t ' ...

zoNE .t..lr-i: ' ,: 'i : --(a} STEPPEO TIME/OISTANCE Cil!flAgTERISTjG$.,-

'-As

(aI OISTANCE/TIME CHARACTERISTICS

Ranqe chanqe relay(bl TRIP CIRCUIT (CONTACT LOGIC) (Z,eit reachl

when energised).

Figure 12.1 Conventional diitance scH6iid.. . *....--,*.,..--,.,-,",.,* .,,i::.1*, ,r; ',"when the Lliltor:recfos'e''fscility islbut of service.

12.2 { ,'-r26rue I ExrENsroru.scHEME,, l:J,ig:,UJ:*iJiiTtj#!,f "i$ffi."i1:1t*T::ffi#iThe scheme is intended for use with an auto-reilose relav. during the lreclaim time iS'adbject to the discriminationThe-Zone 1-units.of.the.distancerelav-havc-two settinq obtained with normal Zone 1 and Zone 2 settings. Thecontrols; one,'as ini'ttre' bbsic"distanc6'schdine, is set t5 .€R9,{I.t"..i" lhoqn 13f,isu19,,1.}*1' nu ,^cover 80% of the protected line length and-the other, The disadvantage of the Zone 1 extension scheme is thatknown as 'Extended Zonell, is set to cover l2ogfr of the extErnalrfdults,:tietrrteeri'ttxi far end of the line and the first

'"''protectdd tln'e:TnEZtn6l rbjchis nbtiTstlfebdirbhed by''''2Wo bf the-nexi line;.result"in rlie tripping of the circuitthe exended.frgne;Niqglting and iqreset to $g basic value bre-bkers'€iternal td"ther{aulted s'bction, increasing thewfien,a gorqgrand. fr,om the.agto*eblose relqyis .rgceived. : binount cif bleakirmCintenance nebded. This is illustrated

' Oh erctrefice of a fftrltidt ar4rpoint within ttrs exrended in Figure 12.3 (a) forb Sihgie circuit line where three circuit,Z6ri€,'t'^fbdch, the reldy ilpgrat'ei,in'Zone,.1;.time, trips the : '$eafer; opeffe,and,in Figure 12:3 (b) for a double circuit

. Circrjrit"bfeaker and'lnitiatei auto..reslo$Jre.tA cdntact from line,'.whore. fiv.ecircuit 'breakers Operate.

" thg.€uto:reclos€ relay,ig.rised;to'reset-the Zons.lrl€ach ol:'i"'Sirrce ttr.i u'sbbfsiiirt-allihg'bquipment is not necessary. this' ttrb distance rdtby to'the tbasic=vatue'$f,80%:.Th6'auto- scheme is ofteii"useddsia t'einporary replacement for carrier-ir're€lose coittact used for thig purpose:operatesrbefore the' r aided setrennes":whea: the signalling equipment is out of' c$osirigpulseisappliedrtoths.breakg4andreseiisor|tiatthe-',r,!elvi@r; J.r:-,:.1 :;,".1v1,..i, , d ,,' i

214

TZ3"

T?2

ZONE 1 ext

it{fiiFf^iiii'} ; Irrli t1.t!i,n r. . "t"+b* F

-Z1c- Z1 extc

6 i.3-:.. '- *-'1..$,1-----n!{tZ1 ext n'rf z1H1 H 3 ' * z'tnz '-'-7't-en n2---'-#

I

Ereakers .21 extJ Zlp-. . . *... . .marked thusauto'reciose' r-, r; r. .,:.- ; irr --,.ii',1, cr l*:(a} FAULT WITHIN ZONE 1 EXTENSION REACH OF

OISTANCE RELAYS (SINGLE CIRCUIT L|NES),{hen t.lte."qfrQuit breaker at oqe qfd ig opcn, insranqapeousclearance cannot be aehieved fer end-zone faults-;;ir the'breaker open' terpjnal.

Z1 extJ

P I'ZlextN r'

{bI FAULT WITHIN ZONE 1 EXTEIISION'.{d.&}+'OF$srANeE R€LJ6nS"{OOUSrF€If,€t +r,I,t&Sl " I

Figure 12.3 Performance of distance relays fitted with ZonE l

I

II

J.I

i

I

exrcnsion when used with a4tglgelose telays ansi n g I e a nd d ou b te "i,",, tt {!*i:i= -li

-i 'i""' :"':r'::'; u-.*-"_*'12.3

TRANSFER TRIP.€CHEMES12.3.1 . 'trtrD i rect transfar triil Gndar- reachl ng ) lch.rneThe simplesi "raay of;S6eding-up fault .dibidnce at thoterminal which clears anpnd zone fault in Zone 2 tirne is toadopt a direct transf,er,{rip or intertrip technique as shownin Figure 12.4:. AZnAe.f ionracrjs-aranged$$jisnd a signalto the remote end arld,,alreceive relay contmt at that end isconnected in the tripping circuit. The schenre in which theZone l relay is used tS"siriifi'sbriit i6f$b rcmore end ofthe feeder in this rna,nner is termed a 'transfur trip under-reaching scheme'.Considering now.a-fuult F in-fhe end.zone atend H inFigure '12.1(a), operati{t'r.}. of the.Zonertr Rlay*al.;gnd ,ry

Sbteced {kr#fi:{€€dte€&fti al{}iifdnripping sigiilet.to theTi m e de t ayed resetting,o*'ttre-d6"rui"Ji'#"nt il: "' rrir,i:f,-€ifJldtl*efidJ*fr ihh c*q ttoil*ailerr r* ir-mmri* t*at the;{1ffii;;i.i:"#Xffi''i"iffi:;ffi;['ii:!*:' ;ffi#g$tffit i*?l?lend fed faulted lineof a

cpn ept fio rnslaa dta$-ulpotngd,geF.npl,'q.ke,9lase.wrless.tjrne to.

. . *,c *arri:is *"itdio;6 ilffi;a;;;ffi [;":lfi,l,|'e:i 2.t.trip when the fault, i$*loie'p*if. n4gnC,.lrJo #,.,"r0 : r r :Tfietnttffialosl$contao6cr{tb ZqogejfRita$ arangeddvi.ryyw*r *!ry -4ry 4ti.\r erY' q}.r 9r rveu

L!"_ i"".o, for the 66e;ijlaved rnnifinsFntat( baar#ained, ,-*o,snddrsmbrd;;d er, nacfu*tgtr6su;;rdisoduvbyconsideringafault'F'inadoublecircuit'lilw,as.i*rown'. ?{zoscS;spaenioq";ilurgu;ia;ulre€jp,t-lit6,"iisUirn"

(cr srMpuFrd S&ibtft*&LiH& t Stg$-l' ;,i _i {

215

zi

-T.22 RRX

HC

*.:1RECE!VE.. -..: RELAYCONTACT

(AI TRIP CIRC,UIT {COi\TACT LOGIC)

(al Fault occurs - bus barvoll€ge low sonegligiblb far,r-li cuiierii:vi6. end H.

i;l2. ,lUt.f nO.CreTal ilearB*..fault and current' startileedingtno'ir efid H.

f isui'i2:6 Single end, fed cte-$e.qp fa.ytq-g1 double circuit line.

{c} 9€UDSTATELOGTC'',,:;r:

The need for sush a time delayed q€itis, best explained bythe parallel feeder arrangemen+shs#n in Figure 12.8. lf afault occurs near circuit breaker( o(treeder JK, the protec-tion at ( will clell ihE fau.tt faster ttrdn,-the protection at J.As sociri aS ffea lid! tr'.ogn*r s' thedircction'of c u?ie n t f I owdown the healtliflTeeder r:everses. The Zbne 2 units at endG. whieh operated arrrl sent ttre si{nal to end H when thefault at ( started; reset wli&6€ker'K.opens.The Zone, 2. u nits at end" H,,wiich,re6trai ned when the f a u ltat K starGd; operate when-breaker ,( opens. lf the Zone 2units at' end ll.operate before Zsne 2 at end G resets,tripping of the breakers at G and H may take place.

'11UItEI

sizl#l6L

JuGU(JzF@6

sc heme i s lh en kn own as' a' peml issiVe over. reach'tra nsf ertrip scheme: or'directional comparison seheme'.

S i n ce th e, si g n aUindi.$.dt&.f. ii;keyed, by over- reachi n gTone 2 units, the scherne rcqtfies.duplex signalling chan-nels - one frequency for each'tlliptiorlofsignalling.lf distance relay,s with mho characler{stics are used thescheme is better suited thao the permigsive under-reaching,scherne for protectins shqrt lines, becquse :ll?e'.'resistiveiovera-Se of that Zone 2 u-nit

-is' gr.€Eter tbaa that af Zone 1.

To prevent operation under current reversal conditions. ina parallel feeder circuit. it is necessary-fo UsdA'tt'l,ie:$elayedur,rit ip the permissive tlip c!lggi!. Thjs current reversalguard is.necessary only".whdii-the .{i.r14 ?,ipaqfr is setgreater than 1507o of the piotected line, irDp€d?ince;

signal send circuit by the time the current reversaldescribed above'takes glace. ';'j '":" : '

The time,delayed unit is de-energized if the Zone 2 units-opsrate-or thr signd r*eived- -etemerlt resets. The resettime ddlqlr:(td)Ydf theilindldelav itnit is set to cover anyoverlap'in time caused by Zbne 2 units operating and the

i:1:r:''sigitdf ?esdt?in g,at and //.. $thenns!€r cu rrent in th e h ea lt h y,'rx{c€dg*;&vdges.r Using, a*irne ile.fa*.unit,in'this manner, that:'elswith 6 tidiedelardn pieh,upatdrcsefting, means that no

-extralfmO.detaf isaddcdin thepermisslve trip circuit for an, iRternaf fatilt. ,- : r r.-i.. . .

': rn tti'6 hiriiurdperntnEliive dvdrlrb#tt' scheme, as with the'' J'permi$Sivs:imtleri'r@eh so*iemcit i nsta nta n eou s c I ea ra n c e

eahFot hreuachieved'for end zba€'faults near the 'breaker:';,"6fpgrf{,1ffiinaf.: tJswevet, to :achioie fast clearance forlthesb'ifaultel addftisnal circuit?y ;ban'- be included in the

scheme to echother'received signal'to the remote terminal,as shown in Figure 12.10. An'auxiliary contact of the localcircuit breaker is connected to the distance protectionscheme to show when the circdtbteakOr is open or closed.

'sFN*€IREUIT--lfTl

SIGNAIUNG

216

$$'?olzz*ol-

[OREI@TETER,MINAL

{b} srcNALLr NG SiNU SnqNGE[d{l GdlrrAcT rocrc)

(c| stMpLtFtEDtoli.b€idiiiJiije,f ' r*r$ ''r',.b jn;.: j l: r.cEE.=t:T", r:o.rr.. f_a'.4,. :1i: f*r,.:1. r.r:af--. I tF

" 1".*i.,4 tnlrt ^+{t: |}!.:t-:: /{ii: )if.r t'le ii ii:::j!:r,:r'r. -J' 1r. .g '-. n. ;r.lrtdtl:, :,t . l: 1,.:!.:..-.,

4r{ ;I:4 t/:-Jr;.T: !;-i?f", ,.ii, ,

l;;.)r,;i{& }t.ii.'r:. :,:j.r.l i:€,i.: t;-i r

j : ,,. ;:x;iii"'atih:i it'j,".: :{l. .t:. '1.. :

r+ ;l;i6'1.hii", t:rii;i",{: <ga' i;*tii: r3,.!

1: lfi.ai|* ::. i;;;i;:itsftr *f-d, ti :r,'r:t:ir )'$ :r'.i".a:G,:fr f r,. , ;

F::'"r. Isr;tv, {}.!{r&.:;';l de i. . .'+:'-

",;.1*;... ii' ;JlT.$ Er{\

., ;ii':i' .,. ; lU;]. :':i ::. !I':*: . ",;:; ,., :": trHi::*'.it.A ti m e del ay, /S//. is*eqoi red i fi...the eahA ebg*t it de p{e\rentt r i p p i n g of t h e r€qng.tg{efi d' braakel, rsh e r} ttrg,!g-ca&,F-eak eris tri pped by the "busbra pro$efition. or bnealcer Jail".pr@c-ti on associated wittno$er.tueders{sno*ed.:to.tt}ebqpbar.The time delay ensures that the remote end agfla&sni{willreset by the time Qgec.QqedsignnljXrF$Qivfid gJ.lWsend.S i g n a I tra nsmission'-can,tehe.plac€Fevsni aft€!, tbq.f ernoteend breaker has trjpped; !o-tal€\4gidrgonIi$Jogs Bans.mission due to lpc,k:U,F o{ both*.gignalgr the:tirne'.delayc i rc u it ( T 2 ) is used. f ft er !h e ti me.deh#;/ I3' leierp+,sertd:iS blOCked.'i,.,r,'.,r. :jrJp.] :.i!;riC,*ti.::::,;+,::.^.}.ii,.i.:

.. ' :r:-: ;. "r.;. .: i'i j1'l*'sii:i 1:. :riu;..- ::1:' .'';:

12.3.4 .- .rr*;iqri1i,r,,,. : 1g;4;;11y; .;,.Jr ,.:i.

Acceleration s€ltF.mQ : i,':-e!.+rlraqit.;'. .illii{'.il {,,}: :.i,.-* -.ii

Th i s sc hem e i s s idt'i I ar bo tlie bermis6iG',lha#: riaHti" iia ns-fer trip scheme in'itS 'brifrii'6ie'rdf j6F&'l+i;n',''tuFt is

Fi-a d ii' 12.9 C1ftb1i-rdf 6isb|A n eid ciicu ft' = Dcrrh issi ve- L i' wir-'ibdcf schdine FOil " 1'..:-' "-' ri'

(bl FAULT CUfi REI&T'U|STRIaUI|oNwlTI{' CIRCUIT BFEAKER X*OPEN

[il5i'Y:'l'n::-i I]i ;" '. ' EHU'#*:$-'" ti'1": ,r''L, -.{.y ,t . ,.,.:

(dl Sl G NALLI NG ARRANGEME!3r,j$:' tlrg' t! rrir "f o t19.L l1r.:-:€

' E nzl. "f$

o" i :"ii it n a t 6c n ii' c, rcii i -'6v'arftaffi#idifi€.r r: c'..r' '

'. -, lrnR .n' 4

r:,;.....;1,3* 1,;.q1:; .j,n :.r': ..1r:r*:j

'217

applicab'le only to zone switched distance relays whichshaie thetamer' measuring uriiti for both Zone 1 andZorie 2.ln these relays the reach of the measuring units is exteridedfrom Zone 1 to Zone2 by means of a range change relay; afterZone2time....ln this 5cheme; t{reu.nder-reachr,ng Zone l unit is arrangedto sefid d sign_al to ihe'remoie end of the feedEi in additi6nto tri pBih€ :ifi 6 loca I ci rc u it bre6ker- The.receive. rel,ay con -taci i5,6nsnged io:operate the' range changb.-relay whictiexterids the reach of the'mea$uri-nS-unit_frpm-Zene 1 to.'Z.ond:2 immediatirly instead' ot:ai:tii" enJ ot'Z6ne

"Z time

delay. This accelerates the fault.olear5npes'at the remoteend. The schbme is shown in ;iguri!'fZ.itT h e 9f .lierng ls nqt- q,uite.'bs: f as,t.

rin.-o peratien . as tli.b per -

missiiie intertiip scheftes, since trme is reciuired for thedistance. m,eaSi.ripg_u1it to operate after the reach has beenchaqied fi'orn Zohe 1 to Zone 2. lt may be argued. though,

. A that the sligfiff_:fg,ryy;gryraligl'_wiit resuti in inc-reasld-] I

secunry rrom matopcratton. -, . i .

12.4, '

B[oeKtNG' Scit-E tut€i-The alternatlve'anangements so far described have usecr--thE signalling,Channel to trdnsmit'a-tripping instruction. lfthe signalling channel _failq€r.there is no infeed from oneend, end:of-zofie faults will taRe longer to be cleared.The,. bkxking .aeherne,uses.- jnverse logic. Signalling isinltiated only foi external faults and signalling transmissiontakesplace over healihf linir sectipns. Fast fault clearanceoccurs when.no siSn6f is"r6c"lved and the over-reachingclistsncs-rtfraa$rring units (22) looking into the lineoperate. The signallingchannel is keyed by reverse lookingdistance units (23). An idedl''bfocking scheme is shown inFigure'12.12i

Thb signblling'chartrtel us€d need only be of the singlefrequificy type thst'operates both local and remote receiverelays when a.block signal is initiated at any end of theprofected s"etiqtrA biockifig in3tfrctfon has to be seniOy the reverse lookingZonb 3.bnlti to ptoven't' iristantaneous tripping of tnereniote relay for 2one'2 faults ex€Fi-al to the protectedsection. To achierre:this. the reverse looking Zone 3 unitsand: ttt6 signalling, channel rnust operate faster than theforlVard"lci,oking Zone 2 units. ln practice this is seldom th'ca$e and to ensiJr€ discrimination a-short time delay is--grer{era$y introduced' i nto{$eb_locklng h od e tri p ci rc u i i, a sillusrratg{'irF figure-, 1!,J3j.

-t t

- -- lThe'fiults'i*rbwn"at:fl S"ana / in Figure 12.12 are nowconsidereelA fauft at Ai$ seerr bry-the Zone 1,"relays at both ends G andend H; as a reiult the-'fault is cl,eafg_.d instantaneously atboth ends of'the fotectbdfi#e. Si$rialling is conlrolled byth€ Zone 3 units looking away from the protected section,so'no$ansmissiron takes place thus giving fast back-uptripping via the foisvard.looking Zone 2 units.n fauir at S is seen'irry titd fbqrvaid iooking Zone 2 units atends G end,#'arTdoy*lhe"&ng1 0nfts at'end H. No signal$ansmission taks plact;'sitfcsrhe fault is internal and thefault is cleared in lone f time at end H and after the shorttime lag{ST!) * el6 G. .'. 1.'-. , 'A fault at lis seen by the reverse looking Zone 3 units atend H and the forward looking Zone 2 units at end G. Thefault at f would normally be cleared by the Zone 1 unitsassociateil-with"'iine"secii;A gl.to pievent thd Zone 2units at end 6 frorn tripping the reverse looking Zone 3,units at end H send a blocking signal to end G. lf the fau'is not cleared instanfaneouiTy 67 ttre protections on lin+--ssction HJ,the trip stgtiat vni#be.lineh at end G after thenormal Zorrc 21inr9.[apse. . .,The 3biiirtg-of tfie i6Verse bokiiig Zone 3 units must begreater than tharof Zone 2 trnits at the remote end of thefeeder, otherwise there iS the possibility of Zone 2 unitsinitiating tripping and the reveQg looking Zone 3 unitsfailing to see an external fauk, Thib would result in instan-taneous tripping for 6n externa! fagtt.When the signalling channLl'is used for a stabilizing signal.as in the above case, transmission takes place over ahealthy line section. The signalling channel should then bemore reliable yrhen used in the blocking mode, especiallyif "therffanhel is power line carrier. lt is essential that theoperatfgrg".iiFres .oi ihc varioui-"relays be skillfully co-ordinateci for allsy3tern conditions, so that sufficient timeid atways alloiryed;for the receipt of a blocking signal fromthe rei-mote-en'd.OJ-ffie feeder. lf this is not done accurately,the scherhe may*tlip, for an external fault or alternatively,the end zone.trippiag times may be delayed fuither than isnecessary.

,-.

lf the signalling channel fails. definite action must be tak,to revert the scheme to conventional basic distance protec*tion. Normally, the blocking mode trip circuit is supervised.by -a 'channel-in-service' contact so that the blocking

Z2c-

(tt tRip crncur{coNTACT LoGtc) ;-

218

;i{i .i1..j. .r

H"

i SIGI:rAfLlNGfii3.*; i':1,- :'r.1EOUTPMENT ,..!... -j., 1<. END

''l' . ,'ii.r . lllllitf{lj:i. Si' :

, i:!':.'i.3i.l.? 9ii-j .'i.!:i; at:.': ::-i t:i: 1jt61;i"r;6 .1,;1

J:- 't 4*r;:, ,:

-y-.,I-y rt'l'w t- .-.4:l;llbl '.\'"AH|/B rS :. r."--

(b) TRrP CTRCUJT

SIGNAL"LING .:' .rEOUIPMENT

.ENO G- 1.,-t

(el SIGNALLING ARRANGEMENI;.'

i.;:' i,.:*it avr-:i".itfu6: :il.+r*tl+;"..:+*,t +:,., \j :.ril ; Lr.l.3+ td5&i€i .'::;lg1d.r!d[..;'I

4i.t'*''i:,-:s

;t.. -, .ir.,!Blr i'*j\^t" 'r+irhf';:!"tl:t,, *'--.nti,.'il'" +::, IfrP{€LAj. -.g;f 1' ': + -- ' '

*. *+:. ':1..

, i. j1.' . ,i.;;-:. ga: :'1il+ .li=. "r .{-,.t .i 'r 4i.;de;r')h-.},:'r :

,fi'.rl

t,t _r,oi..t tJ"r jri",-{t' E i, .9; l:,..:

r:" i l':: .. :*'& ii.]"r/: -.;;-i' rh,'r't: { ..'.qr-*";'ei}

ti.'i -

.':.r;.ri; tr !r:1"+ 34 p 1, ,lrl*; F {,i , ii. nt:,iirf!*.k t'*t-:*ii: li;:l &'tr} ?:'i ,!,ii rt&;.l"*:'

i? .ji;rrqt:l]g riFl:. _li

'*i. G{,:C;ti stiriti; ,.:,;r ii:11::I4 ?rf, r?:': t: r;t'i;,.;l

'.,:;iiryl;!-.,Ii .ii:_6 j c it.t5 i ii .' r;1*.'ill .ri.:.i; ...-:'i tir'-".:.., ':ril:i f;rti:.-.r

. cal {fi{f ClffFl4l"lcpfrrTAcrm$Ci".:-

trrulc' .

rN SERV|C€

{d SIMPUF|ED SOUOSTATT LOOE

z3

t .i: li-ir,r+'.{:-) I F .- j.] ift. -fi.r -s..:j$$.,r .i(dlslMPLlFlED SOLTD STATE LOGTC

. 3t:i ij :r 19! .: ''ll i: L .13:l .,' I i;J"' r. i-"i.-r;-+.r .- ! - ..4

show$ reverse looking Zone {.units,that initirdie tha block-ing signal. ln practiCe, the 2onij'3"unifs irie sii with af oruvard offFgt Eh.?facJ6riilic ro provi{ie back - u p prgtectio nfor busbar faultd aftei lhe'Zones:timnUehy. Thisinakes itnec.essary to.stop.the tjlbtking 9,.S€tUUing sent ior tnleinai3rUIGI

-l(J<zl<tEL

f a u lts.. .This is achieve{*lv;r,nqhi lC3tt";,b" a I se nd ci rcu itcanditioas[.upg!-Jtgi - -o'pdtffi tof 1fu f orwa rd I ook in gconditbaat.'.r!pp4_Ire.ti -o'pdffi .of

' tlfoZorie 2 units;.as shown'in Sigure'ii.i4.As for the perrnissi"" o*r-i*i"h ssherxa.:.th*-blockingscheme also is affected hyfhe current reverbal in.the beal-thy feed€r'il.ueJoafault in atouble circuit |ine.lf the fauli tondition;slxbriiin- iii'Fr gurd'l 2.8 occurs. therevels€ looking Zone 3 unirs qt eAd H.Wil! hav-e+pptjed theblocking signal.to the prcitecrtiiin aib;rd'6 of ihd neatttry

-.- -.line .GH :..the reverse.Jaoking-Zon€ 3"-u nits at. end. H*resetwhen breaker ( opens. T,he.Qrwatd lookiftS:Zgie ?1u.nitsat end G, which operated when the fault at ( started, also

219

z2

T-4r

i{ t' --: - ,: 1.'' '.. :i iil- r' ' l : -,'- ' .

'BECE?t/FfigtAFli: . : tl:t. *.i.-11:f.*' {!$1;

t# f*f S.*i;io A.}r;o'i : +-,.: P

Figure 12.12 ldeal blocking scheme,

i' l2

t 216c;- H ':.'i.''

-^T^-^t..::::::::T.\-_--=----:-,\-r .\- - .

Zlu I

z2u '

t Z3s

(al DISTANCE/TIME CHARACTERISTTCS

-,''.1:'i ,]

{b} sTcNALLtNG CHarurfr r-GErrro dfrnarucenierur: tcorulacr loctct ' ''

received. This arrangement gives the scheme better secur-ity than that of the blocking scheme, since tripping f/external faults is possible only if the fault occurs within thr_-''-laboVe time'interval of channel failure.

-,'14 tliis viiayJh6"scheme has the dependability of a btocking.EchHnig and the security of a permissive over-reachgg"he.op.-The scheme is geneially preferred when powerlirle ca,.friet is.used; elcept when continuous transmission

- of .Signal is not acceptable.

(c} SOLID STATE LOGIC OF SENO CIRCUIT

12.6APPLICATION TO WEAK TNFEEDrenumuetsA weak jqfeed tqrminal cannot contribute sufficient faultc.yqr€qt .Cufing jpteeaat fpij-lt conditions to operate theprotecti.6n.fl pp1 ied at thit tertiii nal. H owever, it is n ecessa ryto open the circuit breaker at the weak infeed terminal.sjncr even tJgw F{it infeeO can maintain the fault. Wirhpermissive transfer trip and acceleration schemes, theprotectiqn at the strong infeed terminal will be unable tocleqr end-zone faults instantaneously unless a signal isreceived frqm, tharemqte {ias'.end.

-To md i ntEi.l :ste bitl{y.i.o/,alrr ieve h ig h s peed a u to - rec I o'

ing, it is essential that both the strong and weak infe.__',r te{rninal Srea&erF. lre opened instantaneously for fau lt.

anywhere within the line section.Tlre operatign of each of the schemes described above is

' epnsidered below, fgweak infeed conditions at one termi-* lrvla.l.rt, _ f'i..,. ':n:.:.r .t':.,:.: :'j r,. :

,.,r,,..fifiUry lf,:ilt

t*l

220

(al OISTANCE/TIME CHARACTERIST1CS

ir,:..;;ii,&' '"

Figure 12.15 Weak infeed in permissive bverg,pch sbheme.

atH,aat6

t'o the

6,b'r',o. ri'*,i t

.'FROM S?ANDARO

POR SCHEME

"*fs*(' TI

i

I

4rlid

"$p€n framJo have

plo-speed

rird,*t{reffitectiongnd se-iiipping ofefldirect intertrip-

P i s dat*.ls tild!;i&dbtititf ti ulkiosiifSi ii]i.f

221

f ,,

,rt''tl

r-lI

.:ile : i' r.i r:i. ,:.1

{ lr'.ij .L. '! ',,, "'

Figure 12.1V Typiaal three-er,Eninal line.. r,

6:6, "ZbNFTREACFTOF:REIAYSAT G -H-H' ZOIIIE 1 RE;ACT+OFf,EtAYS.AI HJ.J' ZONE l REACH OF REHYS AT JH'.J'.J'FAULT ZONE IN WHICH HIGH SPEED CLEARANCE,,.. , .. TBAil!.ALLTERMLNALS IS ACHIEVEDWITHOUT CARRIER I

Figure 12.18 Coverage of typicat rhree terminal line with'*' distanc7 refaw. *- nr -\l

the'trip signal isltceived rdith only one guard signal. Thisis necessary because thbtripping signal is initlqted and theguarrd signal retnoved by the operation of the Zone 1 relayof the distance. schenie ?t^any end. lf a common guardsignal were rlsed, it would be necessary for the Zone 1

'retays at twd ends of,tlfl; feeder to operate before tripping' cguld'ttrke'pltrcg'at:ttg ttt*d\errnind for a fault outside' Zond-1 at th'at enh: Tfii$i6 niit:always possible, because of-. varying fee.der len.Stf-li aad u.odgf -rqaching by the distance

measurjng relays caused by infeeds.

lf a+'q\$i.L-Eashing*tr-etl^s.b!:trip scheme. that is, one in'':"" lVhich the tarrieriin$.iating relay is set to over-reach the

section. Wereused, ft would be necessary to use a duplexcarrier iin[ uetween.each pair of stations.This is necessary te fflsyre that tripping does not take plaeat one end until it i! certain that the carrier starting relay--at both the remaihing terminals have operated, haking

' -c6nailithatthe"fault is within the line section.

..fhrsmelho'{.qf-ggA".qlli{tg -is nol only expensive but alsooccerpies a relativply large bandwidth;-because of theshortage of avbjlablecariei ftequencies this is not usuallyacceptable.

Flu,qtgJS:y_.c'an.ofrc1 ,r:::Un{t*,e:Sib rraGfehtl.ip:soh€rnes,,:a btocking scheme need

[e8-'qiStait'e6-scherfe ' ohty riie a Simple oiilott sinetc sinier c-hannel. as theti!"ti!,tt0nl.Or overlAp. - funCtion of .the.:sighal ir ts btock fiipping rather than to

- qi ttreiiiStst"ade o*i6tiiffig'insilhanbdrr:5'irftipir{(i is usuattv' ' ,d;;l;i: t*ffi;:A;nL+ mus(.bs taken to ensure that the,f, lfltliilcn"smaifBtttlai\rmtmsf 9tt'[e'.two'tqdtih.dline.This'.'; bcfity:d6rived Signa{Uoes nqt.under any circumstances:i' r' i3.tlly..stititeattnhgrtte t.?.iE;'Ueo=irladiof,dhilrfre.use of:a l;a-ffi;l'fr'l;E;ii"'J.iGo.trriithe far end. tn the case of..caiiiBFflht<tilil'drtrBsmbt6.ikiFiinbfl|'.:-'-'..1.'..;.'.

.;".,.,'"iiiliBld.r<j-i"lltniYiri6ltd"tf,{f,i-ti,p;if{fd-tiffi 6fsiftntE'ir infjuenced L ; mined'iiiditvpeffbcfieihe'is influenced '' rnitted. sigir'dl b daote-d,bi'reflection at.the 'tee' junction

rigt-i6iil,?h$;ifude'of 'opriration.of ,:'arrd, ifr oiderio ebtap"fiaxlrlur.n.reliable operation, tlelg lstr,EtvstiriijtridVjiioriiSlvantasiesairU disadvdriiages bre ,1'an adriHritage"in,using a"slocking:scheme where trans-

'' aidC.uss'dd'int,iiei'it's.tibh$iitlfits-elrhptel.. ': .:.r '''mission'fsalrarays,ovsa',hpsHhylineandattenuationduetad Sv-ste-r$'flie:-taisc.sgsed in'.l.d.tq

,",e.tb;.ii*li,i$liXi*ifr*;ii"qltilaq'r'dulibinenrs of thb ": io dn'internalifsutt ds€s'not'have to be considered.' ;;dti;s s;;;;es itlii';;fif;";".iltii"Jdlilirrrirtte.Lcrii", , t'1" .oroolUrnlitc b'e'bverco'me"'ilitn" pro,tection.or thSe;r"riti 6itn" iionajfino cnar,*t. lf a frjquencv Sf,it carri€r r,'.terminal lines'btenumerous; it isfar'more diff icult to protect

is used. .witn'i..pbrnfi9givgrrr1416qy.ieh'trlnSii'ttansfer tiip :,"S"!itr€ of'this ratuepatisfactotiiy forall configuralions:scheheit is necd3sjrv%'us"aalOlft6ffrit'OuaibtreEuencfai 'i sittern conditioirs thm it is-tb'do.the same for the sin, --each of the three t"rihi}iJfil ld tfibtih'd]:sidnats from iWo tiv6-tlrhitneliiim.'Tha.riarior.is fettures of transfer trip and

tetrinlfs can be identified definitely at th; third. A cpm; i 'b}bcking'scffemiit rrvill$s.cansidered in relation to these

mon trip frequency iS employed, triiping being allOwid ii: I prob{eCrs::r'nI'irrirl'r'"r,':.1 r1,::-'::/" '"

222

tlte Zone 2witn ilre

at all

of thet?lpping

\ \ tit':ir. ;* 2f.i.;t1. ;i.t?.lless

'ihi moreoffeeder,

ln thers un-

Lfita worstto be

not

From the'relaying thero arf'advantages in theblocking and the ince the

hiUh'lhfeeds.

Whert one of ttre tixminals hae no intesd infeed.livith the

et

min the

rs'intemal

otherwould

titre-fauit

bim&orEat"trther line

3

,(

6itir0Fli,'"tF*.i,{,;l{."i" *

" it S,:,.:r.r.fi;S; .ii.r.r.

There are twocaeegfupflit-bf frisdeu*mflilolthc fiFf" 'is shown in'Figre"t*.l& lc$blors* f,cca*ga of @ :;rel ative f e€der :iortg{J$'.ir ifof the reaches.d tlt$fthf$a section,bf tfie{sr#itZone 2 tiimetia I Zo ne 2 cl earan*-{K'q.$S s#i itsginf eeds. 16s-s66i1d*iissfi,*qrilh$pg *tis assu med eitherthlUdpSn#Srn*is no infeed at th€tbr$lsS. :slltno i ntertri p, signal . €6fi.rW{SSSqbecause it can not,opeflte*Sin second zoneitimerhy tt*g rehf*FWhere the more,u$galis used, athe protected,'scctiwl,sback in at anotharr il

Tni

6.G' ZONE 1 REACFI OF RETAYS AT G ,'

H.H' ZONEI REACHOFRELAYSAT H -

J.J' ZONE 1 REACH OFRELAYSAT-Jbi r'-.r' ZouE ruoi c-ovEneo:av€o+i5-'1 Reuavs ATANY TEfiMINALS.

t&fu$ l +Y":,ti.i.s,jrrg;x{,t i:i,.; J:..ir?gr: ;

'4;:Li)$ :i ar &zuo.'nr*> | qi..tl€ 4Fg.t'f',fJrr,.iitfiEdssrliffir c*i-.:ilii-, t'if; ',"' :{,i. lXLl r'}I44 ti: Fiitr:,, xrgi.:|!e 4:f :.

Figure 12,2OThtgp,clos&.tqA,

tta!'F the SigFl to noigl$l*

Fioure 12.21 exbkai df ntramii'fra$foi dt

this happens ther, fallB*dtFatffi#,ro."lffiter,received tripping signal may not operatehifti&;ieJhe uJ

^.r'.rtr.d ji:.;1r,a"' ..,.,.r":.,

223