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INSTRUCTIONSGEI-83950

Su PER SED E 5 GE I .25363

C A R R IE R - C U R R E N T P I L O T

WITH MHO TYPE DlSTANCE RELAYS

GENERALf) ELECTRIC

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GEI-S3950 Carrier-Current Pilot Relaying with MHO-Type Distance Relays

CONTENTS

PAGE

INTRODUCTION.. 3

CARRIER-CURRENT RELAYING 3

FAULT LOCATION 3

METHOD OF COMMUNICATION 3

DESCRIPTION 4

CARRIER-CURRENT FUNCTION ,................ 4

Starting Carrier-Current Transmitter 00... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Contact Co-Ordination ..... .... ... 4

Stopping Carrier-Current Transmitter 5

Reserve Signal Test ... 5

Relay Preference ... 5

Carrier-Current Reception 5

Carrier Alarm 5

Carrier Trip Circuits 6

BLOCKING AND RECLOSING FUNCTIONS 6

Out-of-Step Blocking During Power Swings 6

Initiating Reclosing 7

MANUAL FEATURES 8

Carrier Test Switch 8

Carrier Trip Cut-off Switch 8

FUNCTIONS AND SETTINGS 8

Basic Rules for Settings 8

Backup Ground Relays 8

Carrier Ground Relays 8

Carrier Ground Relays on 3-Terminal Lines 8

Carrier Phase Relays 9

Back-up Phase Relays ,..................................... 9

General 10

1.

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WITH

CARRIER-CURRENT

DISTANCE

INTRODUCTION

The load carrying ability of a trans-on line depends on the stability limite line, beyond which limit power cannotansmitted and sti ll have the generationd the two terminals of the line inhronism. There are two types ofity limits; the steady-state limit, andransient limit. In reaching the steady-limit the power transmitted over the

if' increased gradually so that the gen-on is able to take up the increases inwith no tendency to overshoot due to

hanical inertia ofmoving parts ingener-or governing equipment. Thetransientity limit can be reached by a disturb-to the system which brings inertia

ions into play.

Continuity of service depends on keep-all parts of a transmission system Intion or at least inan operable condition

a maximum percentage of the time.ersely, the amount of time a trans-on line is out of service for main-ce or due to a short circuit must beto a minimum.

The longer the transmission system iscted to the disturbance of a fault, theer is the possibility of transient in-ity, and the greater is the damage toelectrical equipment. Thus it is impor-from both the standpoints of stabilitycontinuity of service that faults be

ed as quickly as possible. It is equallyr tant that the faul t be cleared by takingnimum of the system out of service, or,her terms, that the protective relay bective" to the highest possible degree.

For non-persistent faults , high-speedsing is an invaluable aid toboth systemity and continuity of service, but thisct deserves more emphasis than caniven here and consequently will only beioned briefly.

CARRIER-CURRENT RELAYING

Pilot relaying is characterized by ancommunication system between two or

terminals of a transmission line,which information is t ransfer red fromnal to terminal. The information ob-d from anyone terminal is in itselfquate for high-speed selectivity, buttotal information received from allnals is suff icient to produce a relayingm of maximum selectivi ty and speed.

By using a channel of high-frequencynt (30 to 200 kilocycles/second) theer conductors themselves can be usedarry effiCiently the required relayingmation. Coupling capacitors with safeation to high voltage can be used toto and draw from the power conductors

PILOTMHO-TYPE

the high-frequency current with low im-pedance to this current and high impedanceto the power frequency current. Parallelresonant circuits called "traps" turned to

the carrier frequency confine this high-frequency current to the section of thepower l ine between the relaying terminalswithout introducing any appreciable im-pedance to the power line current. Thesetraps prevent the carrier signal from beingdrained off by an external fault, which wouldrender the carrier current relaying ineffec-tive at the time when it is most needed.

Thus, the use of high-frequency car-rier current to convey the necessary relay-ing information allows the power conductorsthemselves to be used to effectively transmitthis information.

FAULT LOCATION

As described in the subsection "Car-rier-Current Relaying" it is necessary forthe relays at the terminals of a protectedline to compare via the carrier-currentchannel what each terminal ofrelays "sees"under fault conditions. It i s obviouslynecessary that any relay Which is used todetermine in what direction a fault occursmust have a sense of direction, that is,U must be a directional relay. Therefore,directional relays are used at each ter-minal to determine whether the fault isinternal (in the protected section) or ex-ternal (outside the protected section). Whenan internal fault occurs, the line should bede-energized completely and quickly bytripping the line circuit breakers at eachterminal. When the fault is external thecircuit breakers should not be tripped im-mediately but should allow time for the

breakers on the faulted external line sectionto trip.

Considering the directional relays ateach end of the protected section, let usexamine their basic operat ion in a carrier-

RELAYING

RELAYS

current relaying scheme. Please refer toFig. 1.

Fig. 1 represents three adjacent trans-

mission line sections, with circuit breakersA, B, C, D, E, and F, and faults s,hown inlocations X, Y, and Z. Let us consider thesection between the breakers C and D as thesect ion to be protected by carr ier-currentrelays. The directional relays at breakerC operate only for faults to the r-ight ofbreaker C, and direct ional relays at breakerD operate only for faults to the left ofbreaker D. This means that the only faultsthat can operate both the directional relaysat C and D are those faults that occur be-tween C and D (internal faults). Faultssuch as Y and Z will operate onlyone of thedirectional relays, e.g., fault Y operatesonly the directional relays at 0; fault Zoperates only the directional relays at C.

Thus, we have a distinguishing char-

acteristic between internal and externalfaults . Internal faul ts cause the direct ionalrelays at both terminal C and D to operate,external faults operate the directional relaysat only one terminal. It is the function ofthe carrier channel to indicate instantan-eously to both terminals whether or not thedirectional relays at both terminals C andD have operated.

METHOD OF COMMUNICATION

Briefly, if the fault is external, car-rier-current is transmitted for the dura-tion of the fault from one terminal to blocktripping at each terminal. If the fault isinternal, carrier-current transmission isstopped instantaneously at both terminals,and both breakers are tripped. Also, if

there is no fault carrier-current is nott ransmitted from ei ther terminal. Speakingin terms of the directional units, thedirectional unit causes carrier-currenttransmission from the local transmitter tostop whenever the directional unit operates.

Fig. I Typical Transmission Line (6~00721 Sh.I-2)

Th e se i n s tr u ct i o ns do n ot p ur po rt ~o c ov er a ll d et ai ls or v ar ia ti on s i n e qu ip me nt n or to p ro vi de f orevery possible contingency to be met in connect ion with insrallat ion, operation or maint en an ce . S ho uldrurther infor~tion be desired or sho uld pa rt icula r prob lems ar is e whi ch ar e no t co ve red su ffi ci en tl y rorthe p urch aser ' s purpo ses , th e ma tter sho uld be ref erred to the Ge nera l El ec tr ic Compa ny.

To the extent required the products de scribed here in meet applicable ANSI, IEEE and NEHA s tandards ;bu t no such assurance is g iven wi th re spect to loca l codes and ordinances because they vary g reat ly .

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GEI-83950 Carrier-Current Pilot Relaying with MHO-Type Distance Relays

If carrier-current transmission is offunder normal unfaulted condi tions, and thedirectional units operate to stop carrier-current transmission, it is obvious thatsomething is needed to start transmission.This function is performed by additionalelements which must be sensitive to faultsand very fast, but need not be directional.It is vital to start carrier and block trippingfor every external fault. Therefore, thecarrier-star ting fault detectors must oper-ate faster and be more sensitive than thedirectional units. More will be said aboutthis co-ordination later.

Let us summarize the basic facts ofcarrier-current pUot relaying:

1. The transmission of carrier-currentfrom any terminal prevents trippingofeach terminal ofthe protected section.

2. Carrier-current is transmitted for ex-ternal faults by the operation of faultdetectors.

3. Carrier-current transmission is stop-

ped at each terminal for internal faultsby the operation of the directionalrelays at each terminal, thereby allow-ing tripping at each terminal.

4. The carrier-current transmission isoff under normal, unfaulted cond1t1ons.

Referring back to Fig. 11etusexaminethe relay operations for an internal and anexternal fault noting the approximate ac-cumulative times in the sequence in cycleson a 60 cycle per second basis.

For an internal fault:

1. (0 cycles) Fault occurs at X.

2. (1/2 cycle) Fault detectors at C and

D operate, starting carrier currentat C and D.

3. (1 cycle) Dtrectional relays at C andD operate, stopping carrier currentat C and D.

4. (2 cycles) Trip colls of breakers atC and D are energized.

5. (5 to 10 cycles) Breakers at C and Dopen, de-energtzingfaulted line section.

For an external fault:

1. (0 cycles) Fault occurs at Y.

2. (1/2 cycle) Fault detectors at C andD operate, starting carrier currentat C and D.

3. (1 cycle) Directional Relay at D oper-ates, stopping carrier current at D.Carrier current at C is not stopped,it is received at both C and Dand trip-ping is prevented at both C and D.

4. (Some time after 5 cycles) BreakersA and B open, due to the operation ofthe relays at A and B, de-energizingfaulted line section.

DESCRIPTION

The directional units of the standardcarrier terminal are of high-speed induc-tion cylinder construction. The phase units

4

1

)

P H A S ECA RR I E RS TA RTCON TA C T S

CO N TRO L SP OWERA II PL I F I E R

GD2 X

F i g . 2 C a r r i e r S t a r t i n g C o n t r o l o f t h e C S 2 7 ( 0 1 6 5 A 6 0 7 7 S h . 2 -0 )

are provided withvoltage restraint to enablethem to distinguish between fault conditionsand normal operating conditions. Forreasons which are of no particular interesthere, the resulting unit is called a mhounit.

The fol lowing paragraphs will discussthe functions of all the elements of the

standard carrier-relaying terminal.

CARRIER-CURRENT FUNCTION

STARTING CARRIER-CURRENTTRANSMITTER

In the Type CS-27 General Electricrelaying transmitters, transmission is con-trolled by means of the voltage bias on thebase of" a transistor in the keying unit.When this base has a negattve bias theintermediate amplif ier is de-energized andtherefore it supplies no input to the poweramplifier, and there is no carrier signaltransmitted. When this base is biasedpositively, the transistor switches the inter-mediate }mpllfier on, and it supplies asignal to the power amplifier, so a carrier

signal is sent out onthe power transmissionline. The connections are arranged so thatthe carrier-starting contacts, which areclosed under normal conditions, maintain anegative bias on the base of the carrierstarting transistor. Fig. 2 shows theseconnections for the phase carrier startingrelays.

In the symbols for transistors Q251and Q252, the electrode with the arrow isthe emitter, and the direction of the arrowshows the forward direction of current f lowfrom emitter to base. The base connectionis shown at the left of the transistor in thispar ticular diagram, and the remaining con-nection, at the lower r ight, is the collector.Since the current flows from positive emitter

to negative base, these are PNP transistorWhen the base is biased negatively, theemitter-base circuit conducts, and thiscauses the emitter-collector circuit alsoto conduct, and in this condition the tran-sistor acts as a closed switch. When thebase is positively biased, no current flowsfrom the emitter to the base, and thereforeno current flows from the emitter to the

collector, and the transistor acts like anopen switch. Tracing these relations inFig. 2, when the carrier starting contactsare closed, the base of Q251 is biasednegatively so Q251 is on. This biases tnebase of Q252positively, so Q252 is off, andthere is no signal past that point.

Conversely, when any of the carrier-start contacts are open, the base ofQ251 isat its most positive potential and Q251 isoff, so that the base of Q252 is negativelybiased and Q252 is on. This supplies powerto the intermediate amplifier, and thereforea carrier signal is sent out on the powertransmission line.

In any of these carrier terminals, MXis controlled by a mho unit with a setting,long enough to respond to any internal faulton the protected section. In the GXC17, thisis the zone-3 unit (M) which gives the relayits directional properties. In the otherforms, MX is controlled by the zone-zmho unit (M2), or in some cases by a mhounit which is not used lor anyother purpose.

The characteristics of the carrier-starting units are shown referred to animpedance diagram in Fig. 3. This diagramrepresents the impedance values for onephase of a transmission line as determinedfrom the ratio of the phase-to-phase voltagedivided by the vector difference of the cur-rents in the two corresponding conductors.In both cases the units operate for conditionsinside the circle.

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R -X CHARACT ER I ST I C O FC AR R I E RS T A RT I NG U N I TS

Car-rier=Cur rent F:l.::t Relaying with MHO-Type Distance Relays GEI-S;;"'5,}

x

68CB(CEB17)

2 11 l 1 . 1 3(CEB17 )

.1l.OM)

( G CY& G C X Y )

- x

F i g . 3 C a r r i e r S t a r t i n g R e l a y C h a r a c t e r i s t i c s ( 6 i j 0 0 1 2 1 S h . 3 - 2 )

In Fig. 3 the characteristic of thedance unit 68 (CFZ) is shown as ah~with its center a t the orig in .

In the diagram the line CDrepresentsconditions for various faults on themission line between C and D. It willoticed that with carrier-startingrelaysng offset-mho character is tics , faultsoccur near D for which carrier will

be started at C. This makes no differ-in the opera tion since the direc tionals at C would immediately stop theer signal for a fault within the pro-

d section.It should be emphasized, however,in relaying terminals using carrier-ng relays having offset-mho charac-cs, the carrier starting unit must bereversed and offset as the character-of Fig. 3 indicates. The unit must besed in order to insure start ing carr ierexternal faults which would be in theng direction for the remote terminal.unit must be offset so as to maintaincarrier signal for a zero-voltage ex-l fault behind the terminal after theory action of the unit has expired.

Sinee the units described above willgenerally operate on single line-to-nd faults it is necessary to provideadditional unit to start carrier forfaults. This unit is called Gl and is

ly a low-set instantantaneous over-nt unit. In other words it operatestart carrier whenever ground faultnt is flowing at the particular terminalr cons ideration. This requires a nor-y closed contact in series with theer starting contacts of the phases as shown in Fig. 2.

TACTCO-ORDINATION

Referring to the elementary diagramill be seen that the CLPG relay inchide~

an auxiliary relay GDIXwhose contacts arealso in the carrier control circuits. This isa telephone-type relay with a 2 cycle timedelay pickup and a 5 cycle time delay drop-out. The purpose of this relay is to preventaccidental tr ipping, by continuing to send acarrier signal when the clearing of an ex-ternal ground fault removes or reversesthe fault current in the GDunit, and causesthe poss ibility of the contacts reboundingdue to the removal of restraining torque.There is no similar unit for phase faultsbecause the phase relays have a voltagerestraint which hold them open after thefault is cfeared,

STOPPING CARRIER-CURRENTTRANSMITTER

In order that the carrier-current con-tro lled relays shall trip the circuit breakersfor an internal fault, it is necessary toprovide a means for stopping the transmitterfor such a fault. This is done, a s explainedpreviously, by directional. units looking intothe protected section. The directinal unitsstop carrier tr ansmtsston through auxili-aries MXand GD2Xwhichmay beconsider-ed merely as repeaters for the directionalunits. These auxiliaries are of the tele-phone type and stop carrier by re-apply ingnegative potentia l to the base of transis torQ252 through resistor R253, as shown inFig. 2. The BCA relay contains theseauxiliaries.

To perform the carrier-s topping func-tion, MX is controlled by the mho units ofthe CEY16A, GCX (the M unit), or GCY(the M2unit).

The GD2X unit is controlled by twounits, GD and G2, connected in the groundcarrier trip circuit. The GD unit is con-nected to pick up for internal faults. TheG2 unit is a residual overcurrent unit:this has been found desirable in order toavoid tripping on extraneous currents such

as the zero sequence charging current e:.-countered when a parallel line is faulted.

The two sets of units , (M, M2,e tc.) andGD, are thus the co-operating fault-locating"observers" mentioned before under "FaultLocation". Identical equipment to thatdescribed above is, of course, provided ateach terminal of the protected line section.

RESERVE SIGNALTEST

The reserve signal test is made byoperating the transmitter at a power levelsufficiently reduced to operate the receiverat the other terminal within the linearportion of its output range, and thereby itis possible to get an indication of the at-tenuation of the carrier current channel.This reduced level of transmitter output isobtained by limiting the input to the inter-mediate amplifier by means of a "reservesignal" (R.S_) contact of the test switch asshown at the right of Fig_ 4. For thepresent, it is sufficient to assume thatpower from the pos itive bus is being sup-plied to the R.S. rheostat through transistorQ254. Switch 8251 in paral le l with the R.S.rheostat circuit, is located in the carriertransmitter assembly and is used to turnon the transmitter at full power, for testpurposes. The transmitter modulator forthe telephone is also supplied throughtransistor Q254, to -33 volts.

RELAY PREFERENCE

In case of an internal fault, it is neces-sary to have some means for turning offany signal that may have been started forR.S. test or by S251 or by the modulatorfor the telephone, so as to provide high-speed tripping rather than permit falseblocking by this signal. This feature isprovided by resis tor R259 and transistorsQ253 and Q254. This group of componentsacts similarly to R252, Q251, and Q252, sothat when R259 is connected to the negativesupply, transistor Q254 is turned off. Re-ferring to Fig. 4, it will be seen that thecarrier-s top contacts control trans istorsQ251 and Q252 for the relay carrier s ignalby means of R253, and they also controltransistors Q253 and Q254 for the testsignal etc. by means of R259. This con-stitutes relay preference, and it operatesinstantaneously without the delay of anytelephone relay.

CARRIER-CURRENTRECEPTION

The transmitted signal is received ina receiver similar in operation to a homeradio, and the output of the receiver is putto work through the medium of a receiverrelay. This receiver relay, R, is energizedby the output of the receiver and whenenergized picks up to open "a" contacts inthe carrier trip circuit and thus preventstr-ipping,

CARRIER ALARM

Relay RAis a telephone-type receiveralarm relay connected in series with thepilot coil of the receiver relay. It picks upwhenever carrier current is received, tooperate a bell and a lamp for test or signal-l ing purposes . Its p ickup is higher than thatof the R relay so that if a test s ignal picksup RA the carrier receiver output will begreat enough to reliably operate the Rrelay.

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GEI-83950 Carrier-Curren t Pilot Relay ing with MHO-Type Distance Relays

R259

T S

C AR R I E RS TA RT

C A R R I E RS T O P

48.125 OR 250V.

CONTRCLSP O W E RA MP L I F I E R

CARRIER TRIP CIRCUITS

F i g . ~ C S 2 7 K e y i n g C o n t r o l a n d S t a n d a r d K e y i n g C o n t a c t C o n n e c t i o n s ( O I 6 5 A 6 0 7 7 S h . I - O )

The carrier trip circuits are thosewhich energize the trip coil of the circuitbreaker if carrier-current is off duringthe fault, and do not trip the breaker ifcarrier current is received for the durationof a fault. Other protective relays may tripthe same breaker, but tripping by theserelays is not primarily dependent on thereception or absence of carrier current.

Fig. 5 shows the carrier trip circuitsand associated auxiliary equipment. Thephase carrier trip circuits are controlledby mho unit contacts M and by the receiverrelay R. Fig. 5 shows how the auxiliariesMX and GD2X are controlled directly bythe mho unit and carrier ground relay.

In these carrier-current re lay schemes,targets are provided to indicate all pos-sibilities of fault tripping. These targetlocat ions and funct ions are as below:

1. A target in the receiver relay indicateswhen a carrier trip occurs.

2. A target in the ground relay indicateswhen ground is involved.

3. A target in the phase relay (s) indi-cate (s) the operation of a phase relay.

4. In the case of distance relays used alsofor backup, targets in the RPM timerindica te the t ime zone involved.

5. Targets in the ground back-up relayinc!ica te a ground back-up t rip .

In order to prevent a "race" betweenthe opening of the receiver relay contact Rdue to the reception of a carrier signal and

the closing of the phase or ground faultdetecting relay contacts uponthe occurrenceof an external fault, the contact R of the'receiver relay is held in the open positionfor unfau lted condi tions. This precludes theposs ibility of tripping the breaker throughthe carrier trip circuit while carrier isbeing started. This is accomplished by anaddHtonal d-e holding coil on the receiverrelay. This coil is controlled by the con-tacts GD2Xand MXa s shown in Fig. 6.

Thus we have two coils controllingthe R relay, one energized from the carrierreceiver and the other energized from thed-e control bus. When e ither one, or bothof these coils are energized, the R relayopens the carrier trip circuits shown inFig. 5. When a fault occurs in the directionof the pro tec ted section, the faul t de tec tingrelay operates, and the auxiliary unit MXor GD2Xopens the contacts shown in Fig. 6to de-energize the R holding coil . However,the fraction of a cycle (60 cycle basis) re-qui red to opera te MXor GD2Xis sufficientto insure that the receiver relay R does notdrop out before carrier current is receivedto energize the other coil of R, which willkeep the R contact open and thus preventincorrect carrier tripping for an externalfault. Of course, if the fault is internal,carrier current will be received to hold theR relay in the operated position after theholding coi l i s de-energized and Rwil l dropout, permitt ing tripping through the circuitsof Fig. 5.

BLOCKINGAND RECLOSINGFUNCTIONS

OUT-OF-STEP BLOCKINGDURINGPOWER SWINGS

These carrier-current relayingschemes recognize out-of-step and powerswing conditions by using more sens itiverelays which will operate earlier on theseconditions, but which will be by-passedunder fault conditions. The MB unitFig. 7 is an offset mho unit in a Type CEBrelay and is connected to operate in thedirection of the protected section. This unitis placed in only onephase of t he line since itis probable That a power swing or out-of-step condition will appear the same in allphase's. The Z units in Fig. 7 u sed in theGCX scheme are impedance units in aType CFZ relay and they perform thefunction of fault detection in addition toout-of-step blocking; consequently, theyare present. in all three phases.

T-SI T~S! T-SI

b. M HO UNIT S

;---"----,..

1lSI lSI lS I to ~_1 I

u" T,\'~)( Gf)2){

1

~ I ' R

! it

M X

~ j>GIl2X

F i g . ~ C a r r i e r T r i p C i r c u i t s a n d A s s o c i a t e d A u x i l i a r y E q u i p m e n t ( 0 1 6 5 A 6 0 7 7

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Carrier-Current Pilot Relaying with MHO-Type Distance Relays GEI-83950

(+) -- -- -- -- -

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GEl-83950 Carrier-Current Pilot Relaying with MHO-Type Dtst~nce Relays

MANUAl FEATURES

(aJ T I shunts the reserve signal micro-"!':,meter except when it is in the REC

posttton to receive a test signal.

(c) It inserts the micro-ammeter for meas-uring a signal from the remote trans-mitter, REC.

(d) It introduces an attenuating resistorinto the transmitter supply so thatthe receiver output current at the otherterminal (s) is made to vary with thereceived signal voltage. Since thereceived signal voltage depen.ds on theattenuation over the power conductors,this is often used to detect and roughlymeasure the amount of sleet on thepower conductors.

CARRIER TRII' CUTOFF SWITCH

This switch, deSignated as CCS,is usedto open the carrier trip circuits in casean essenttal part of the carrier-current B.relaying equipment is out of service formaintenance or other reasons. Undersuch conditions protection is provided bythe distance relays with their zones ofprotection, and by the time-delay groundback-up relays.

This switch should be turned to the"OFF" position whenever the carrier-start-ing relays at another station are out ofservice for any reason, as otherwise afault external to the other terminal maycause false tripping of this terminal.

F UNCTIONSAND SETTINGS

Table A lists the tables showing thefunctions and settings of devices used inthe several schemes. Tables I and VtIcover the devices commcn to all theschemes.

It is important to note that protectiverelay settings depend on system condi-tions and the circuit to be protected. Forthis reason, the information supplied inthe attached tables can only be quaUtativeand not quanttttve. The user must calculatehis own relay settings and these must beappUed to the relays by the user beforethe relays are put into service.

BASIC RULES FOR SETTINGSIn order to insure proper operation

of the protective schemes covered by theseinstructions the following general rulesmust be followed with regard to relaysettings. They are stated here for betterunderstanding.

A. BACK-UP GROUNDRELAYS

1. The pickup setting of the high speedurnts must be high enough to insurethat these unlts do not ptck up forany ground fault external to theprotected line section.

TAELE "A"

2. The pickup setting of the time delaywits must be low enough to insurepositive operation for all single-phase-to-ground faults on the pro-tected line for all practical systemoperating conditions. Unless localbackup is provided at the terminal (s)leading out ,of the opposite station (s)the setting should be low enough toprovide backup for all adjacent linesections in the forward direction, atleast sequentially. The time-dialsetting must provide for time co-ordination with similar relays onall adjacent lines tn the forwarddirection.

CARRIER GROUNDRELAYS

1. Since high-speed carrier stoppingand tripping depends on the oper-ation of the ~irecttonal units of thecarrier ground relays, these direc-tional units (GD) at all terminalsmust pick up for all single-phase-to-ground faults in the protectedline secnoi, for all practical systemoperating conditions. Dual polar-izatior. provides for maximum sen-sitivity and should be used wherefa-:H1ttes are avattsble,

2. Since high-speed carrier trippingalso depends on the operation ofthe overcurrent wits (G2), theseunits at all terminals must pick upfor all single-phase-to-ground faultsin the protected line section for allpractical system operating condi-tions.

3. Stnce proper carrier blocking forexternal ground faults is necessaryfor blocking false t ripping, the over-

A

CARRIER TiST SWITCH TABLE NUMBERS FUNCTIONS I SETTINGSThe carr te r test switch, TS, performs i SCHEME tELEM. DIAGI,'.TERMfl _ ! j _ ,II :,ImIvi V I, Vi vnlvm IX Ix iXI~,xrr!,Xm

the follcwing functions: ~ I 'I CEY-CEB i '1021B99CA 2 x' x' i ; : ! x I xii : ii : 3~ x' X I X _+,. . : :x : . . ; . . . '-+_':__-+_-+Gc""EY-'iCEBf7138B42CA 2 I - x I

IGCr -I 7021B81CA! _3 -x---I--;-(b) It starts the transmitter for testing, I GCX17 i 7021B82CA 2 xSEND. 1 GCXY ! 7021B83CA 2 x, x . x

t_ I 3 XI X i x

l

C.

current units (G1), which start car-rter, .nust be set more sensitivethan the over current units (G2) atthe remote terminals of the pro-tected line seUon. In general,magnitudes of zero-sequence cur-rents flowing in all three terminalsof a three-terminal line for au ex-ternal ground fault are different.Because of this, the ratio of G1 set-ting to G2 setting will depend on thenumber of terminals that the pro-tected line has. This has been re-flected tn the suggested settings for01 and G2 in Table VII.

CARRIER GROUND RELAYS ON 3-TERMINAL LINES

With an external tie between two ter-minals of a 3-terminal line as showntn Fig. 9, it is possible to haveconsiderable magnitude of ground cur-rent flowing out of terminal B for aninternal fault near terminal C. Thiswill cause blocking of the other ter-minals, so no tripping can occur untilback-up relaying trip:' the breakernearest to the fault. T)epending onthe system configuration and the faultlocation. thp. current magnitudes andd+r ec+ion may vary from this situation, all the way to the normal situa-tion of current f lowing into the faultedline at all terminals, in four stagesas outlined below. The same typeof situation can exist on phase faults,but it is a li.ttle easier to deal witbecause the vcltage restraint in thedistance relays used as phase fault de-tectors compensates them for changesin source Impedance, and thereforetheir reach changes less than thatof the ground relays, with systemconditions.

BJ

___ IS c

Fig . 9 Three Termina l Line (0165A6077 Sh. i j -O)

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1. Out-flowing CurrentAboveGI-Pickup

For this case (as mentioned above)Gl will start carrier at B, thusblocking A and C. The primaryrelaying cannot operate, so the clear-ing depends initially on the back-uprelaying at C. Since the minimumcleartng time at C is about four

cycles, and the pickup time of GDIXat B is the pickup time of Gl plustwo cycles, GDIX will probably beset up, and therefore the carrierrelaying at A and B still cannot re-spond until the five cycle dropouttime of GDIX at B has expired.

This is delayed sequential tr ipping,and as far as a blocking systemof relaying is concerned, there isno " ~medy for this situation if thesetting of Gl is already the highestthat c-an be used with sufficientmar~n for blockinr; A in case ofan eXternal fault l:ieyond C. (Forthe margin necessary for this lattersituation, see Case 4, below.)

2. Out-flOwinj or In-flowing CurrentBelow Gl tckUp

Note that for any system configura-tion where Case 1 can arise, Case2 will arise instead, if the faultlocation is further away from C.

For this case, Gl does not operate,so carrier is not started at B,GDIX does not pick up, and trippingat A and C is normal. B will tripas soon as C has cleared.

This is instantaneous sequential trtp-ping, and.as far as a blocking systemof relaying is concerned; there isno remedy for this situation if thesetting of GD is already the lowestthat can be obtained.

3. In-flOWin~Current Above 01 Pick-up But Be ow G2 PlckUp

Note that for any system configura-'ion where Case 1 and 2 can arise,Case 3 can arise instead, if thetault location is still further away{com C.

For this case, G1 starts carrierat B, thus blocking A and C. Asin Case a , the primary relayingcannot operate, so the clearing de-pends initially on the back-up re-laying. at C. However, unlike Case 2,

GD picks up, so GDIX does notpick uP. and therefore the primaryrelaying will trip A and B as soonas C trips by back-up relaying.

This is instantaneous sequential trip-ping of terminals A and B. Forthe narrow range of ground faultcurrents, or of ground fault locations,represented in Case 3, it is possibleto have an auxiliary relay at Bwhichwill respond to the operation of GDand will bypass G1 contact in thecarrier starting circuit, thus makingthe pr imary relaying again effective

Carr ier-Current Pilot Relaying with MHO-Type Distance Relays GEI-83950

at A and C, and eliminating the In-stantaneous sequential tr ipping of A.However, terminal B will still haveonly instantaneous sequential trip-ping, and this must be taken intoaccount in choosing the dead timeof the breakers at A and C in caseof instantaneous reclosing. There-fore the only practical advantageobtained by the added auxiliary relayat B is that in the current rang"between G1 and G2 it keeps theprimary protection at A and C ef-fective rather than having to dependon the back-up relaying to trip C.It does not improve the performancefor Case 1 or 2, if either of thesecases can exist for any fault locationon the protected line.

4. In-flowing Current Above G2 Pickup

For this case, operation is normalat all terminals ii the proper mar-gin has been taken in choosing thesettings. An internal fault will becleared correctly, and the only con-cern necessary is the result of an

internal fault. Considering Fig. 9,an external fault at the right maydraw equal currents out of terminalsB and C, but the sum of these cur-rents will flow in through A ifthere is no ground current suppliedfrom any other line or groundedbank at B. In order, to insureblocking at A for a fault whichwould draw currents just below Glpickup at Band C, it is necessaryto set the pickup of G2 at A for atleast 2.5 times the pickup of Gl at Bor C, rather than only 1.25 times.Unless fault data are available toprove it unnecessary, the usual mesh-ed system {... .th external intercon-nections possible among each pairof terminals) requires a similar2.5:1 ratio of G2 pickup at any ter-minal to the Gl pickup at each of theoth!lr two terminals.

D. CARRIER PHASE RELAYS

1. In most of the schemes under con-sideration, the same phase relaysthat provide carrier protection alsoprovide back-up protection. Thus,these relays must be set to providefor both functions. In general, therequirements do not conflict. How-ever, it is well to remember that thecarrier portions of this scheme pro-vide the best part of the overall lineprotection and this should greatlyinfluence the relay settings.

2. Since high-speed carrter stoppingand tr ipping depend on the operationof the carrier-stopping and trippingunits, these units at all terminalsmust be set to pick up for all multi-phase faults in the protected linesection for all practical system con-ditions. It should be noted that onthree-terminal lines, an internal faultnear. one terminal will appear to befar ther away, impedance-wise, f romthe relay terminal than it actually isbecause of the current infeed fromthe second remote terminal. Thismust be considered when setting

the reach of the carrier stop andtrip units.

ZA-C ZA-J + (1 + IB) ZJ-CIA

where A, B, C are the three ter-minals, and ,1 is the junction of thethree branches as shown in Fig. 9.

S. Because successful carr ier blockingfor external phase faults is essentialto prevent false tripping, the car-rier starting units for externalfaultsmust reach farther than the reachof the carrier-stopping and trippingunits at the remote terminals. Anoffset setting is required ona ll mho-type carrier-starting units to insurethat these units will pick up and staypicked up to maintain carrier trans-mission on nearby, zero-voltage ex-ternal faults.

4. Out-of-step blocking is obtained byvirture of the sequence of opera-tion between the measuring unitof the out-of-step blocking relayand the carrier "tripping unit. Thissequence of operation is measuredby the time-delay auxiliary OB unitin the out-of-step-blocking relay.The OB unit has a four-cycle timedelay on pickup. The measuringunit of the out-of-step-blocking relaymust be set so that its character isticis larger. than, and encircles, thatof the carrier tripping unit at thesame terminal. Its characteristicmust be sufficiently large so thatthe apparent impedance resultingfrom a system swing or out-of-stepcondition will require more thanfour cycles (on a 60-cycle base) totraverse the distance from the per-iphery of the blocking relay char-acteristic to that of the tripping unitcharacteristic. This will permitQut':'.oi-step blocking to get set up.It is Important to note that theproper setting for _the measuringunit of the out-of-step bloc1tingrelaywill depend on the rate of the fast-est swing and the setting of thecorresponding tripping unit.

5. The PJC overcurrent fault detectorsthat are recommended when line-side potentials are employed, arenot mechanically capable of beingoperated in the picked-up positioncontinuously. For this reason, theyshould be set above maximum fullload current. However, the setting

should be as low as possible to in-sure fast operation during fault con-ditions. Note, CHC fault detectorrelays are available that are suitablefor operation continuously pickedup. These may be set below fullload current.

E. BACK-UP PHASE RELAYS

1. The high-speed, first-zone unitsmust be- set short enough so thatthey do not reach beyond any of theremote terminals, even under con-ditions of minimum infeed.

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GEI-B39110 Carrier-Current Pilot Relaying with MHO-Type Distance Relays

2. The second-zone, time-delay unitsshould be set with a reach that tslong enough to insure that they willoperate for phase faults anywherein the protected line section. Onthree-terminal Hnes the effects ofinfeed must be considered. Seesection D-2 above. I'he second-zone time setting of the RPM relayshould be as short as posslble butlong enough to insure timecoordlna-tton for faults in adjacent line sec-tions as far away as the reach oftheir second-zone units.

3. The third-zone time-delay units ofthe GCX17A and B relays controlthe RPM timer. For this reason,the reach should be at least some-what longer than the associated sec-ond-zone uni ts . In GCXY and

10

GCY12A and CEB17 relay applica-tions, the third-zone units "look"in the reverse direction; and whilethey control the associated RPMtiming relay, so do the second-zone units. For this reason, thereach setting is based on the re-quirements to start carrier. Seesection D-3 above. The third-zonetime setting of the RPM relay shouldbe set to insure time coordinationwith relays on the adjacent linesections, with due regard to thereach settings of those relays.

F. GENERAL

1. Under no conditions should the set-tings of any of the phase relays,including the out-of-step-blocking

relay, be such that load can causethem to operate.

2. All phase relays employed in theseschemes are supplied with phase-to-phase potent ia ls and the currentsof the same 2 phases. Thus, theyreach the same distance for alltypes of mul ti -phase faul ts .

3. In no case should any relay be setoutside of the rated ranges as givenin the instruct ion book .

4. All values of ohms, amperes andvolts used in these tables are interms of secondary quant it ies ; ohmsare phase-to-neut ra l va lues .

A well-planned and coordinated relayingsystem will provide secure and reliableprotection.

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Carrier-Current Pilot Relaying with MHO-Type Distance Relays GEI-83950

- - - - - - - - ~ - - . - - - - - - r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ' - - - - - - - -D_E_VI_C_E t--D_:_ci_:-t!_UN_I_T_t- --:- F_ .UN_C_T_.I_O_N--:- .__

CAllAV' 85 I GD2_X_-+~",,~;_. ~l~l;~~ ;o:J~fu'1~'nl~e~~f~~n:edi~~~~r~~~.~ H~5:~.:-~~~~l~i~~;Y~~~ ; ~~ t a~ : ; :~~~ . r,t is_~~!M X Controlled by 21/M20r Zl_/.M or 21-22 depending on scheme used, In turn it pr-ovides the samefunctions as GDX exeept for multi-phase faults. -------- .. --------------1

R PicKs up on receipt of a carrier signal to block local tripping. Has fast pick-up and drop-out t!~~~IRH Drops out for faults in tripping direction. RH & R are wound on same core. The normally closedIi contacts labelled R are closed when both R & RH are de-energized, and they are open when either

R or RH or both are energized. _ I

T Provides target indication for carrier trip. '1

1I GDY Purchased only for a terminal, on a 3-terminaJ line, where current flowing in toward an internalfault is above G1 pickup but below G2 pickup. Controlled by 67GD. In turn it by-passes G1 contactI to remove carrier started by Gl, thus permitting tripping of other terminals if cur-rent is flowing

Iin at both of them. _

RA Picks up on receipt of a carrier to give an alarm. Has fast pick-up and drop-out hmes. ~IRI Initiates Automatic Reciosing. Holds off carri.er {or approximately 8 cycles after a trip. Hasi fast pick-up and 7-9 cycle drop-out times

GA15B 85Y

AA22L B5XOptional

TABLE I

FUNCTIONS THAT ARE COMMONTO ALL SCHEMESf.----- ----- ----- tI

6SB1CB4B21 I TS

0328 IMicroammeter

'Identifies source of carrier signal if more than 1 carrier terminal is connected to same alarm bell.hite Lamp!

el Jack

6SBlDB211

BCG51E orBCG53E orBCG77E

LPG12C

I

.Switch for testine: the carrier channel. _

i Rheostat Provides reserve signal (RS) test of carrier channel in R.S. position of switch. _I 'Reads strenath of received signal in REC position of switch, during RS test.

For voice communication.~ ~ ~ - - - + - - - - + - - - - - ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - . - - - - - - - - - - - - - - - - - - - - - - - - - - -Channel cutout switch for removing directional comparison . .nd instantaneous reclostng from service.

------+--+------+. B=a::::c::ku.=.lPl:....:rc::e:.::la"'lvLii:!;n:..Q..;gr:.;e~m=a:!!in:!!s~in::....::s:.::e:.:.r_'_v.:::ic::.:e::.!.'-- _Directional unit. Provides directional control for IOC & TOC listed dire~tly below. _

Directional Instantaneous Overcurrent Unit. Provides high-speed back-up protection on ground !faults. J.Directional Time Overcurrent Unit. Provides time delay back-up protection on ground faults. IGround Directional Unit in Carrier Scheme. With G2 it operates on ground faul ts in the tripping Idirection to control GD2X and initiate carrier tripping. Also operates tn conjunction with 67GC/G1forground faults in the non-t ripping direction to control 67GC/GDIX. II

Non-directional overcurrent unit that starts carrier on ground faults. It also operates in conjunction

with 67GC/GD to control 67GC/GDlX. .

CCS I67GB I D

IOC

TOC

67GC GD

IG1

G2

GDIX

T

-

Non-directional overcurrent unit. It operates in conjunction with 67GC/GD to provide carrie~stopping and tripping for ground faults in the tripping dire",c",ti""o""n=-. --\

Auxiliary relay with 1-2 cycle pick-up and 5 cycle drop-out time. Controlled by 67GC/GD and I67GC/Gl to prolong carrier transmission on stngle-phase-to-ground faults in the non-trippingdirection. - __

Target to indicate a ground fault carrier trip. I

i

TABLE IT

IAPPLIES TO CEY16B - CEB17A-2- OR 3-TERMINAL LINE APPLICATIONS DWG. 7021B99CA ICEY16B 21 M Directional Mho Distance Relay. Operates in conjunction with 85/MX to stop carrier t ransmission

and provide for carrier tr tpptng,

CEBl7B 68 RM Offset Mho Distance Rela!. Operates to start carrier t ransmission.

CHC12A 50 Non-di rect ional Instantaneous Overcurrent Relay. Fault detector to supervise all tripplng by 21.May safely be set below load current and picked up continuously. With line-side potential, use thisor PJC. --

PJC31C 50 Non-directional Instantaneous Overcurrent Relay. Fault detector to supervise all tripping by 21.Should not be set below maximum load current. With ltne-side potential, use this or CHC. _j

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GEI-83950 Carrier-Current PUot Relaying wi th MHO-Type Distance Relays

TABLE III

APPLIES TO CEY-CEB PHASE RELAYS IN 2- OR 3-TERMINAL LINE APPLICATIONS DWG. 7381B42CA

~---- ~----; ---- r. ----i DEVICE 1 DEV. UNIT \, ' NO. I I

. CEY15A I 21-M11 iDirectional Mho Distance RelayI Iphase faults.

FUNCTION

Operates to provide first zone back-up protection for

CEY16A

t CEB17A

21-M2 i Directional Mho Distance Relay - Operates in conjunction with 85/MX to stop carrier transmission! Iand provide for carrier tr ipptng, Controls 21X/TX to initiate operation of RPM timing rela! l Operates in conjunction with 21X/TU-2 to provide second zone back-up protection for multi-phase

! faults.

21-M3 IOffset Mho Distance Relay - Operates to start carrier transmission. Controls 21X/TX to initiateI operation of RPM Timing Relay Operates in conjunction with 21X/TU-3 to provide reversed third

II zone back-up protec tion for mul ti -phase faul ts.

I.

CHC12A I 50 Non-directional Instantaneous Overcurrent Relay. Fault detector to supervise all tripping by 21.I

IMay safely be set below load current and picked up continuously. With l ine-s ide potent ta l, use

1 this or PJC.PJC31C I 50

[Non-directional Instantaneous Overcurrent Relay. Fault detector to supervise all tripping by 21.

I Should not be set below maximum load current. With line-side potential use this or CHC.RPM21D i 21X I TX I Auxiliary Unit which energizes the timing unit 21X/TU. Operated from phase-distance relays 21-M2I TU

Ilor 21-M3. Timing unit operated from 21X/TX. Has contacts TU-2 and TU-3 for second and third

i zone time dela! tri l2Eing in conjunction with I2hase-distance rela!s.

CEB12BI

68 i ME Operates in conjunction with 68/0B to provide out-of-step blocking of t ripping. Auxi lia ry uni t for!

iI

OB out-of-step blocking. Has 4 cycle time delay pickup. Operates in conjunction with 68/MB to blockzone 1, zone 2 and carrier tripping by phase relays on system swings and out-of-step conditions.

I This blocking is prevented in the event that 21-M2 contacts close and short down 68/0B before68/0B gets picked up, as in the case of an internal fault.

TABLE IV

APPLIES TO GCY12A 2- OR 3-TERMINAL LINE APPLICATIONS - DWG. 7021BBICA

GCYI2A 21 Mi Directional Mho Distance Unit - Operates to provide first zone back-up protection for multi-phasefaults.

M2 Directional Mho Distance Unit - Operates in conjunction with 85/MX to stop carrier transmissionand provide for carrier tripping. Controls 21X/TX to initiate operation of RPM timing relay.IOperates in conjunction with 21X!TU-2 to provide second zone backup protection for multi-phasefaults.

I OM3 IOffset Mho Distance Unit - Operates to start carrier transmission. Controls 21X/TX to initiate1

l operattoa of RPM timing relay. Operates in conjunction with 21X/TU-3 to provide reversed thirdzone back-u.ll.J>.rotection for multi-phase faults.

, CHC12A 50 I Non-di rect ional Instantaneous Overcurrent Relay.Fault detector to supervise all tripping by 21.

IMay safely be set below load current and picked up continuously. With line-side potential, use

i this or PJC.I PJC31C 50 I INon-directional Instantaneous Overcurrent Relay. Fault detector to supervise all tripping byI

\i Should not be set below maximum load current. With line-side potential, use this or CHC.

\

I RPMllD 21X I TX IAuxil iar:t : Unit which energizes the t iming unit 21X/TU. Operated from 2hase-dis tance relays .TU

CEB12B 68

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Carrier-Current Pilot Relay ing with MHO-Type Distance Relays GEI-83950

TABLE V

APPLIES TO GCX17AOR -B 2-TERMINAL LINE APPLICATIONS - DWG.702IB82CA

VICEDEV. UNIT FUNCTIONNO.

X17A, 21 M 'Directional Mho Distance Unit . Operates in conjunction with 85!MX to stop carrier transmissi on-M, and provide for carrier tripping. Controls 21X!TX to initiate operation of RPM timing relay.-N

IOperates in conjunction with 21X;TU-3 to provide third zone back-up protection for multi-phasefaults. Operates in conjuction with 21!0 to provide first zone back-up protection for multi-phasefaults. Operates in conjunction with 21X/TU-2 to energize 21/0X which in turn switches the reachof 21/0 from zone 1 to zone 2.

I

0 Non-directional Reactance Distance Unit. Operates in conjunction with 211M to provide firs t-zoneback-up protection for multi-phase faults. Also operates in conjunction with 21/M, 21/0X and21X/TU-2 to provide second zone back-l1ll_protection for multi-phase faults.

OX Auxiliary Transfer Unit. Operates in conjunction with 21Mand 21X/TU-2 to switch the reach of21/0 from firs t to second zone.

S Auxiliary Coordinating Unit. Purpose and operation described in GCX17A Instruction Book.

DC Non-directional Overcurrent Unit. Acts as a fault detector to supervise operation of all multi-[phase-fault tripping. Should not be set below maximum load current. Present only in GCXl7B or N.

MllD 21X TX Auxiliary Unit which energizes the timing unit 21X/TU. Opera ted from Phase-distance relays.

TU Timing Unit operated from 21X/TX. Has contacts TU-2 and TU-3 for second and third zone timedelay tripping in conjunction ith phase-distance relays.

Tl,T2,T3 Targets used in conjuncti on with zones 1 2 and 3 of the l Ihase-distance relavs .Z17A 68 Z31 -Z23 Non-direct ional Ix~Ic:edanceDistance Units . Start carrier on multi-phase faults. Also operate in

Z12 conjunction with 68 OB to provide out-of-s tep blocking of t ripping.

OB Auxutar} Unit for Ot't-of-stey: blocking. Has 4 cycle t ime delay pick-up. Opera tes in conjunctionwith 68 Z31, 68/Z23 and 68 Z12 to block zone 1, zone 2 and carrier triPPin!J by phase relayson system swings and out-of-step. This blocking is prevented in the event that 21 M contacts closeand short down 6a/OB before 6a/OB gets picked up, as in case of an internal fault.

TABLE VI

APPLIES TO GCXYON 2- OR 3-TERMINAL LINE APPLICATIONS - DWG.7021Ba3CA

IXY 21 OM3 Offset Mho Distance Unit - Operates to start carrier transmission. Controls 21X/TX to initiate !

operation of RPM timing relay. Operates in conjunction with 21X/TU-3 to provide reversed third izone back-up protection for multi-phase faults.

M2 Directional Mho Distance Unit - Operates in conjunction with 85/MX to stop carrier transmission ,and provide for carrier tripping. Controls 21X/TX to initiate operation of RPM timing relay. 'Operates in conjuncti on wit h 21/01 to provide firs t zone back-up protection for multi-phase faults .Operates in conjunction with 21X/TU-2 to provide second zone back-up protection for multi -phasefaults.

01 Non-direct ional Reactance Dis tance Unit - Operates in conjunction with 21/M2 to provide firstzone back-up protection for multi-phase faults.

S Auxiliary Coordinating Unit - Pur_l)_osend operation described in GCXYinstruction book.

MllD 21X TX Auxi liary Uni t which energ izes the t iming uni t 21X/TU. Operated from phase-distance relays.

TU Solenoid Timing Unit operated from 21X/TX. Has contacts TU-2 and TU-3 for second and thirdzone t ime delay t ripp ing in conjunct ion with phase-d is tance relays .

Tl,T2 T3 Targets used in conjunction with zones 1 2 and 3 of the phase-distance relays.B12B 68SB MB Operates in conjunction with 6aSB/OB to provide out-of-step blocking of tripping.

OB Auxiliary Unit for out-of-step blocking. Has 4 cycle t ime delay pickup . Opera tes in conjunct ionwith 68SB/MB to block zone 1, zone 2, and carrier tripping by phase relays on system swingsand out-of-stit conditions. This blocking is prevented in the event that 21/M contacts close andshort down 68 OB before 68/0B gets picked up, as in case of an internal fault.

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GEI-83950 Carrier-Current Pilot Relaying with MHO-Type Distance Relays

~-- -- -- - -.--.

or I remote terminal with the remote breaker closed. I relay for a ground fault at the second remoteJBCG7HE I terminal. Then assume only the second remote

II terminal breaker to be open and determine themaximum current in the relay for a ground

Ifault at the first remote terminal. Set the

Ipickup no lower than 125%o f the greaterthe two values obtained.

! TOC Set pickup no higher than 67% (If the minimum single-phase-to-ground-fault current in the relayI

with the remote breaker closed, Unless local backup is provided at the terminal (s) leading out ofthe opposite station (s), the settings should be low enough to provide backup for all adjacent line

I sections in th e forward direction, at least sequentially. Set time dial to coordinate with otherL___ ground relays on the system.

CLPG12C 67GC GD Set for minimum pickup (maxtmum sensitivity). Set for minimum pickup (maximum sensitivity).

ICheck to insure pickup for all single-phase-to- Check to insure pickup for all stngle-phase-ground faults on the protected line with line to-ground faults on the protected line with thebreakers closed on both terminals. Use dual line breakers closed at all three terminals.

I polarization where facilities permit. Use dual polar ization where facilities permit.

I G2 Set piCkup no higher than 67% of the minimum Set pickup no higher than 67%of the minimuI single-phase-to-ground-fault current in the re- single-phase-to-ground-fault current In tI lay with the remote breaker closed. Lower lay with both remote line breakers closed.

Ipick-up settings are permissible and in most Lower pick-up settings are permissible and incases desirable for increased speed of opera- most cases desirable for increased speed oftion. However. do not set pickup lower than operation. However, do not set pickup lower

I 125% of the Gl pick-up setting at the remote than 250% of the Gl pick-up settings at the twoend of the line. remote terminals.

l Gl Set pickup no higher than 80% of the pickup of Set pickup no higher than 40% of the lowerthe opposite terminal's G2 unit. settings of the two opposite terminals G2 units.

TABLE vnGROUNDRELAY SETTINGS - ALL SCHEMES

UNIT I TWO TERMINAL LINESf..--Q____;No adjustment Available

, IOC i Set pickup no lower than 125%of the maximumcurrent ill the relay for a ground fault at the

r----;r---., DE"iC~~~E6.'

I JBCG52E I 67GBI or

I JBCG54E I

THREE TERMINAL LINES

Assume one of the remote terminal breakersopen and determine the maximum current in the

TABLE vmPHASE RELAY SETTINGS -- CEYI6A-CEBI7A RELAYS -- 2-TERMINAL LINES -- DWG. 7021B99CA

DEVICE DEV. UNIT SETTINGSNO.

CEY16A 21 M Set to reach 125-150% of the ohms to the opposite terminal, taking the line impedance angle intoconsideration. 125% tends to give slow operation for end-zone faults, so it would be usedto avoid false operation on swings, or operation of 68SB on maximum load with the setting whichresults from the setting chosen for 21-:M.

CEB17A 68CB RM Set for 0.5 ohm offset. Set ~j. reach for not less than 1.25 x [

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Carrier-Current Pilot Relaying with MHO-Type Distance HdaYIi (,EI 6:l l:l50

------ -----. -- ------- _.. -TABLE IX

PHASE RELAY SETTINGS -- CEY16A-CEB17A RELAYS -- 3-TERMINAL LINES -- DWG. 7021B99CA

VICE

-----I

UNITi SETTINGS I

Y-1-6-A-+-----+--M--t- S -e -t-t-o-reach 125-150% of the maximum apparent impedance to either of the other terminals,~cluding the effect of infeed and line-impedance angle. 125% tends to give slow QPeration for end- I

. zone faults so it would be used only to avoid false operation on swings 150% is the preferred

! ~ettings. However, the setting should not be long enough to require a setting on 68SB so high that !lit will be picked up by maximum load. ~RM For each terminal, make the following calculation of desired reach for each of the other terminals ,

with the opposite one of the other terminals open, and use the greater of the 2 values of desiredreach. Minimum r:~h = 1.25 [(Setting of M at opposite end) + 0.5-(ohms of line section betweenthe 2 closed termtnals) ]. i

17A

12B MB This setting should be chosen by means of a graphic solution on an R-X diagram, including swing

:~~:~v~~~ ~~f~f:et :~s~~~ f~~~~~\iO::{n~h(~~ge~~ ~~~~::~:n~f:;:'~) ~~:i: : : : .~~d~~~~ha~r~~~~ :should exceed the reach of 21 by an amount sufficient to allow at least 4 cycles (.067 sec.) along the Iswing line intersecting the 2 characteristics. If no swing study is available as a basis for these Isettings, the setting should be at least 150%of the setting of M, subject to the limitation due to load Icurrent, mentioned below. The offset tap of 68SE should be the available value nearest to half thedifference between the ohmic settings of 68SE and 21. The reach of 68SE must not be great enough to 'cause operation by maximum load current. If this requirement cannot be met, the setting of 21 ,must be reduced {which will result in sequential tripping), and the CEB14 should be substituted to Iprevent 68SE/OB getting set up for a particular range of fault locations. -1

12A The setting with a phase-to-phase test connection should be not more than 58%of the minimum i3-phase fault current. This insures at least 150% of pickup for phase-to-phase faults, or more Ifor 3-phase faults. .

31C

50

50 The setting should be not more than 69%, or preferably 58%, of the minimum 3-phase fault current;but not less than 110% of the maximum load current. The 69%value insures at least 125% of pickupfor phase-to-phase faults.

---------------------------------------~

TABLE X

PHASE RELAY SETTINGS -- CEY15A-CEY16A-CEB17A RELAYS -- 2-TERMINAL LINES -- DWG. 7381B42CA

OR GCY12 RELAYS -- 2-TERMINAL LINES -- DWG. 7021B81CA

1:,A 21-Ml Set for 80-90% of the impedance to the remote end of the line, taking account of the impedanceGCY12 21 Ml angle of the line.

16A 21-M2 The minimum setting is 125% of the impedance of the protected line section, taking account of theGCY12 21 M2 line impeaance angle. The maximum setting is the least of 3 maximums, determined as follows:

The first maximum is 80% of the total impedance (not reactance) ohms to the end of the shortestzone-l reach on any other line out of the opposite statton, taking, account of the line-impedanceangle.The second maximum is a setting such that the unit will not trip on the maximum swing from whichthe system might recover (usually considered 120 0 ).The third maximum is a setting which will permit choosing a setting of ME such that MB will not

, operate due to maximum load.

IThe best setting is (approximately) the square root of the product of the (greater ) minimum andthe least maximum.

17A 21RM3

II The setting cf this unit depends on the setting of the M2u nit at the other terminal. Set CEB17 for

or I 0.5 ohm offset, or GCY for 1 ohm offset. Set the reach fur not less than 1.25 [(Setting of M2 at12 21 OM3 i opposite end) + (offset ohms) - (ohms of protected line seL tton) l.M2lD 21X TU2 i Set for a long enough delay to permit clearing of any fault on any other line out of the oppositeor I station within reach of this 21-M2 plus the desired margtn,MllD

ITU3

I

Set for a long enough delay to permit clearin, of any Iault on any other line out of the station! II i where relays arc, within reach of this 21R3 or 21 OMS, plus the desired margin (margin usuallyI I 10 cycles).

12B I 68 ME This setting should be chosen by means of a graphic solution on an R-X diagram, including swinglines for different system conditions, showing the successive values of apparent impedance at knownintervals of time as the fastest sWin~ (for each system condition) progresses. The reach of 68should exceed the reach of 21-M2 or 1/M2 by an amount sufficient to allow at least 4 cycles (.067sec.) along the swing line intersecting the 2 characteristics. If no swing study is available as a basisfor these settings, the setting should be at least 150%of the setting of M subject to the limitation dueto load current, mentioned below. The offset tap of 68 should be the available value nearest to half

Ithe difference between the ohmic settings of 68 and 21. The reach of 68 must not be great enough tocause operation by maximum load current.

C12A ! 50 The setting with a phase-to-phase test connection should be not more than 58%of the minimum3-phase fault current. This insures at least 150%of pickup for phase-to-phase faults, or more for3-ohase faults.

31C 50 The setting should be not more than 69%, or preferably 58%, of the minimum 3-phase fault current;

Ibut not less than 110% of the maximum load cur-r-ent, T he S9%value insures at least 125%of pickupfor phase-to-phase faults.

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GEI-83950 Carrier-Current Pilot Relaying with MHO-T)'I,eDistance Relays

TABLE XI

PHASERELAY SETTINGS -- CEYI5A-CEYI6A-CEBI7A RELAYS -- 3-TERMINAL LINES -- DWG.7381B42CA

OR GCY12 RELAYS -- 3-TERMINAL LINES -- DWG.7021B81CA

DEVICE DEV. UNIT SETTINGSNO.

CEY15A 21-Ml Ml Set for 80-90% of the impedance to the nearer remote terminal, taking the line impedance angle intoor GCY 21 consideration. Do not include the effects of infeed.

CEY16A 21-M2 Set to reach 110-150%of the maximum apparent tmpedance to either of the other terminals includingor I the effects of infeed and line-impedance angle. 110%gives slow operation for end-zone faults; so itI GCY12 21 M2! would be used only to prevent false operation on swings or to avoid excessive reach from the stand-

point of coordination with relays on other lines out of the other stations. 150%is the preferredsetting. However, the setting should not be long enough to require a setting on 68SB so high that itwill be picked up by maximum load.

CEB17A 21RM3 .For each terminal, make the following calculation of desired reach for each of the other terminals ,or with the opposite one of the 0eer terminals open, and use the greater of the two values of desired

GCY12 reach. Minimum reac~) J 1.25 (Settings of M at opposite end) + 0.5 - (ohms of line section between )the two closed terminals

RPM21D 21X TU2 Set for a long enough delay to permit clearing of any fault on any other line out of ei ther of the othr two stations, ~~thin reach of M2 (omitt ing the effect of infeed), plus the desired margin (margin

RPMllD ually 10 cycles

TU3 Set for a long enough delay to permit clearing of any fault on any other line out of this station, withinreach of OM3 (omitting the effect of infeed) Dlus the desired margin (margin usually 10cycles).

CEBI2B 68 ME This setting should be chosen by means of a graphic solution on an R-X diagram, including swinglines for different system conditions, showing the successive values of apparent impedance at known

intervals of time as the fastest swing (for each system condition) progresses. The reach of 68 shouldexceed the reach of 21-M2 or 211M2 byan amount sufficient to allow at least 4 cycles (.067 sec.) alonthe swing line intersecting the two characteristics. If no swing study is available as a basis for thesesettings, the setting should be at least 150%of the setting of M, subject to the limitation due to load,mentioned below. The offset tap of 68 shouuld be the available value nearest to half the differebetween the ohmic settings of 68 and 21. The reach of 68 must not be great enough to cause operationby maximum load. If this requirement cannot be met, the setting of 21 must be reduced (which willresult in sequential tripping), and the CEB14 should be substituted to prevent 68/0B getting sefor a part icular range of fault locat ions.

CHC12 50 The setting with a phase-to-phase test connection should be not more than 58%of the minimum3-phase fault current. This insures at least 150%of pickup for phase-to-phase faults, or more for3-phase faults.

PJC31C 50 The setting should be not more than 69%, or preferable 58%of the minimum 3-phase fault current;but not less than 110% of the maximum load current. The 69%value insures at least 125%of pickupfor phase-to-phase faults.

TABLE XlI

PHASE RELAY SETTINGS-- GCXI7-CFZI7 RELAYS -- 2-TERMINAL LINES -- DWG.7021B82CA

GCX17 21 M Set for at least 125% of the impedance to the opposi te terminal, taking account of the line impedanceangle. However, 125%tends to give slowoperation for end-zone faults, so at least 150%is prefer red.The setting must not be large enough to permit operation by maximum load, or to permit response toa severe fault on an adjacent phase. The setting is also influenced by the fact that if there is no localback-up relaying on other lines out of the opposite-terminal, it i s desi rable to have M provide zone-3protection out to 80% of the shortest zone-2 reach on any of those lines, taking account of only theminimum reliable infeed at the opposite station.

01 Set for 80-90% of the reactance to the opposite terminal for zone-l protection.

02 Set for 80% of the total reactance to the end of the shortest zone-l reach on any other line out of theopposite station taking account of only the minimum reliable infeed at the opposi te station.

OC The setting should be not more than 69%,or preferably 58%9of the minimum 3-phase faul t current;but not less than 110%of the maximum load current. The 6 %value Insures at least 125%of pickupfor phase-to-phase faults.

CFZ17 68 ZI-2 The maximum set ting is one which wUlpermit the relay to reset at maximum load, following a swing;therefore the maximum suggested setting is 80%of the impedance corresponding to maximum load.If out-of-step blocking is not used, the minimum setting = 1.25 [ (Setting of M at opposite end) -

Z2-3 (ohms of protected section)]. If out-of-step blocking is used, the minimum setting for that purposeshould be determined by means of a graphic solution on an R-X diagram, including swing lines fordifferent system conditions, showing the successive values of apparent impedance at known intervals

Z3-1 of time as the fastest swing(for each system condition) progresses. The reach of 68 should exceed thereach of 211M by an amount suff icient toallow at least 4 cycles (.067 sec.) along the swing l ine inter-

I secting the 2 characteristics. If no swing study is available as a basis for these settings, the settingshould be at least 150% of the setting of 211M. Then use the higher of the minimums found for thecarrier starting function and for the out-of-step blocking function, subject to the maximum determinedbv the load, mentioned above.

RPMllD 21XI

TU2 Set for a long enough dela~ to permit clearing of any fault on any other line out of the oppositestation within reach of this 21 02. plus the desired margin.

TU3 Set for a long enough delay topermit clearing of any fault on any other line out of the opposite station,within reach of this 211M plus the desired margin (margin usuallv 10 cvcles).

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Carrier-Current Ptlot Relaying with MHO-Type Distance Relays GEl-83950

TABLE XIII

PHASE RELAY SETTINGS -- GCXY -- 2TERMINAL LINES -- DWG. 7021B83CA I----------------- ---.-- ------1

VICE i DN~?_:___.Jf__-UN_::_~IT___.J_=___,_-~._=_=.",,__,_.,__----:__:.,__--_:_c_S_,E-T-T-IN.,.._G..,.S_:_--___::____,.--,..,--__ IXY ,21 01

I M2

TABLE XIV

PHASE RELAY SETTINGS -- GCXY -- 3-TERMINAL LINES -- DWG. 7021B83CA

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