hand book-1(revised).doc

7/21/2019 Hand Book-1(REVISED).doc

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HANDBOOK

FOR

PROTECTION ENGINEERS

Authored by

M.V.S. BIRINCHI, BE., FIE C.VENKATESWAR!, M.E, PGDIEME".D#re$tor %Te$h$'() Ch#e* E&+#&eerProte$t#o&

APTRANSCO APGENCO

1


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2

HANDBOOK

FOR

PROTECTION ENGINEERS


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3


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ACKNOWEDGEMENTS

The Hand Book covers the Code of Practice in Protection Circuitry including

standard lead and device numbers mode of connections at terminal stri!s colour codes in

multicore cables "os and "onts in e#ecution$ %lso !rinci!les of various !rotective relays

and schemes including s!ecial !rotection schemes like differential restricted directionaland distance relays are e#!lained &ith sketches$ The norms of !rotection of generators

transformers lines ' Ca!acitor Banks are also given$

The !rocedures of testing s&itchgear instrument transformers and relays are

e#!lained in detail$ The close and tri! indication and alarm circuits for variety of Circuit

breakers indicating ferrule numbers are also included$ %ll relevant information and circuit

diagrams necessary for trouble shooting are also given$

(e have more than 2) years e#!erience each in !rotective relaying and included a

lot of information by &ay of original contribution a!art from collection of usefulinformation from a large number of reference books manuals of manufacturers etc$ and it

is ho!ed that this Hand Book &ill serve as a useful guide for all !racticing *ngineers$

(e thank +ri B$Babu +!ecial ,fficer -Protection. +ri /ivekananda and +ri

+achidanandam "ivisional *ngineers %P0*C, +ri $0o!al ao Chief *ngineer +ri

4$$+astry and +ri 5$"akshina urthy +u!erintending *ngineers %PT%+C, for their

valuable advise in !re!aration of this book$ (e also thank +arvasri 0$ +eshagiri ao

"ivisional *ngineer $5agan ohan ao %ssistant "ivisional *ngineer 6$+rinivasa ao

/$/enkates&arlu and rs$+hil!a %ssistant *ngineers of %PT%+C, +ri /$$ao and+ri "iganta of P0C74 for !atiently going through the Hand Book and for their valuable

suggestions in bringing out this Book$ (e s!ecially thank "r$Bhuvanaika ao %P0*C,

for his contribution of the cha!ter on *#citation ' /oltage Control$ ,ur s!ecial thanks to

+ri $ +reenivasa eddy and +ri %$Bhaskar 5$P$,s &ho has !rovided com!uter aided

assistance in bringing out this Hand Book$

M.V.S. BIRINCHI C. VENKATESWAR!

INDE-

1$ Code of Practice

1$1 +tandard number for devices

1$2 Ty!es of Panels

1$3 Protective elay 8 Connection ' 9ones of Protection

1$: orms of Protection for 0enerator Transformers ' 4ines

:


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1$) Current Transformers

1$; /oltage Transformers

1$< *nergy eters

1$= +ynchronising Panel

2$ 0enerator and their Protection3$ Transformers and their Protection

:$ "istance elays in %$P$+ystem relay indications ' their eanings

)$ Busbars 8 %rrangements ' Protection

)


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;


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;$ ,>4 ' *>? relays


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THE F!NCTIONA RE/!IREMENTS OF THE REA01

i. eliability The most im!ortant reuisite of !rotective relay is reliability since

they su!ervise the circuit for a long time before a fault occursD if a

fault then occurs the relays must res!ond instantly and correctly$

ii. +electivity The relay must be able to discriminate-select. bet&een those

conditions for &hich !rom!t o!eration is reuired and those for &hich no

o!eration or time delayed o!eration is reuired$

iii. +ensitivity The relaying eui!ment must be sufficiently sensitive so that it

o!erates reliably &hen reuired under the actual conditions that

!roduces least o!erating tendency$

iv. +!eed The relay must o!erate at the reuired s!eed$ 7t should neither be too

slo& &hich may result in damage to the eui!ment nor should it be too fast

&hich may result in undesired o!eration$

HEATH0 TRIP CIRC!T

IMPORTANT EEMENTS

S2#t$h +e'r Circuit breaker Bulk oil inimum oil +?; %irblast /acuum etc$ de!ending on

medium used for uenching the arc$ "ifferent o!erating mechanisms such as

solenoid s!ring !neumatic hydraulic etc$ are em!loyed$

=

Trip Coil

Relay Contact

High ResistancePush Button

Lamp

+ Ve

- Ve

Battery


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Prote$t#3e +e'r1 elays -current voltage im!edance !o&er freuency etc$ based on o!erating

!arameter definite time inverse time ste!!ed etc$ as !er o!erating characteristic

logic &ise such as differential over flu#ing etc$

St't#o& B'ttery1 % +tation battery containing a number of cells accumulate energy during the

!eriod of availability of %$C su!!ly and discharge at the time &hen relays o!erate

so that relevant circuit breaker is tri!!ed$

@

C,"*

,?

P%CT7C*


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CODE OF PRACTICE 1 PROTECTION

1$AA Circuitry

1$A1 The entire &iring of circuitry for indications alarms metering and !rotection should be

!ermanent &iring$

1$A2 There is no !lace for tem!orary &iring or adhocism in elay circuitry$

1$A3 The leads should be identified by ferrules near terminals$

1$A: *very lead should end at a terminal !oint and no Eunctions by t&isting is allo&ed$ 7f t&o &ires are

to be terminated at same terminal they may be connected at t&o different terminals and a loo!

!rovided$1$A) The &iring should be by co!!er leads for C$T secondaries for all cores -i$e$. metering as &ell as

!rotection$

1$A; The &iring should be by co!!er leads for PT secondaries also &herever they are intended for

!rotection$

1$A< The co!!er lead for 1$A) ' 1$A; above should be stranded but not single lead ty!e$

1$A= %luminum leads can be used for indication alarms and PT secondaries for metering but stranded

&ires only are to be used$ Ho&ever &here PTs are em!loyed for commercial metering stranded

co!!er &ires are to be used$

1$A@ The terminations should be lugged by ring sha!e , lugs$ F sha!e lugs should be avoided$

1$1A ?or CT +econdary terminations t&o nuts &ith one s!ring &asher and t&o flat &ashers to be

com!ulsorily used$1$11 The terminal stri!s should be stud ty!e &ith nuts and not scre&GinGty!e$

1$12 (herever t&o batteries are available the !rimary !rotection and backGu! !rotection should be

from different batteries$

1$13 (here there is only one battery at a Po&er +ubstation the !rimary and backGu! !rotections

should be given "$C su!!ly through t&o individual circuits &ith inde!endent fuses run from "$C

bus$

1$13% (hen CBs have t&o tri! coils both main !rotection and backu! !rotection &ill energise both the

tri! coils$

1$1: "$C and %$C su!!lies should not be taken through different cores of the same cable$

1$1) 7nde!endent "$C cables should be run to every eui!ment in the yard and loo!ing of "$C su!!ly

either in the yard or in the control room from one eui!ment to the other is not !ermitted$1$1; The "$C yard lighting for emergency lighting should be through inde!endent cables and not

mi#ed u! &ith !rotection and other circuitry$

1$1< ?or indications alarms annunciations controls -closing coil tri! coil etc$ negative -Gve. is

al&ays given direct and !ositive -ve. is su!!lied only on commands like close tri! relay tri!

etc$

1$1= (here "$C !rotection su!!ly is at 2: volts or 32 volts the battery units should be very near the

eui!ment and not in the control rooms$

1$1@ 7n cases of 1$1= above each tri!!ing units -2: volts or 32 volts battery &ith charger. should not

be used for more than t&o circuit breakers or eui!ment$

1$2A +tandard colour codes for leads in control cable of different siIes should be as denoted on the

cover !age$

1A


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1$21 The lead numbers are also standardised as follo&s so that any T *ngineer can easily identify

the !ur!ose for &hich the lead is connected by noting the lead number$

5 +eries "$C 7ncoming 51 52 etc$

6 +eries Control G Closing Tri!!ing etc$ 61 62 63 etc$

4 +eries %larms indications and annunciations 41 42 43 etc$

* +eries Potential transformer secondaries *1 *2 *3 etc$H +eries 4T %$C +u!!ly H1 H2 H3 etc$

% +eries C$T secondary for s!ecial !rotection %1 %2 %3 etc$

B +eries Bus bar !rotection B1 B2 B3 etc$

C +eries Protection Circuits C1 C2 C3 etc$

" +eries etering Circuits "1 "2 "3 etc$

1$22 CTs &ith 1 am! secondary rating should be used com!ulsorily &here meters !rotective devices

etc$ are remotely situated &ith reference to eui!ment$

1$23 The CT ratios available and ado!ted &ith number of cores shall be dis!layed on each !anel as

follo&s -&ith underlined !osition as ado!ted.$

:AA G 2AA G 1AA > 1G1G11$2: (herever CT cores are not used J+H,T70 4,,P+K should be !rovided near CT secondary

terminals and not in marshaling bo#es or at !anels$

1$2) The Cable entries near eui!ment marshaling bo#es and !anels should be by use of a!!ro!riate

siIe glands$

1$2; The (iring inside the !anels should be clear and neatly fastened avoiding loose &ires$

1$2< %ll &ires not in use should not only be disconnected but removed from !anels$

1$2= PT secondaries should have grou! ,CBs &ith "$C alarm$ ?uses at different !anels should not

be used$

1$2@ ?e& cells from a battery of cells should not be used for se!arate lo& voltage "$C circuits$ "$C G

"$C converters only should be em!loyed utilising full "$C voltage of the entire battery as in!ut$

2$AA STANDARD EAD N!MBERS

Certain lead numbers are standardised as follo&s and should be com!ulsorily ado!ted &ith

ferrules at terminations of leads$

51 G Positive

52 G egative

Controls ' %larms

emote Close 61) emote Tri! 6)

4ocal Close 61)4

4ocal Tri! 6)4

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Re('y F'4#(y

Re('y

E(e$tro M'+&et#$ St't#$ Me$h'$'(

Ty5e6 o* Co&tro( P'&e(6

1 Control Panels 12 arshalling Bo#es

2 elay Panels 13 %0 Panels

3 Control ' elay Panels 1: achine Panels

: +ynchronising Panel or

Trolley

1) "u!le#-H/4/. Panels

) Communication Panels 1; Bus 9one Protection Panels

; %nnunciation Panels 1< TC Panels -,4TC.

< "$C$ "istribution Board 1= T7 Panels -tem!.

= %$C$ "istribution Board 1@ 7ndoor Panels

@ Charger Panels 2A ,utdoor Panels

1A elay 0alleries 21 Panels &ith dra&n u!11 %u#iliary Control Panels mimics ' isolator cum

breaker status indication

-+ema!hores. etc$

13

B'6ed o& Ch'r'$ter#6t#$

1$ "efinite time elays

2$ 7nverse time elays &ith

definite minimum time -1 "T.

3$ 7nstantaneous elays

:$ 7"T &ith inst$

)$ +te!!ed Characteristic

;$ Programme +&itches


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DEVICE N!MBERS AND THEIR NOMENCAT!RE

2 Time delay relay

3 Checking or 7nterlocking relay

21 "istance relay

2) Check synchroniIing relay

2< Fndervoltage relay3A %nnunciator relay

32 "irectional !o&er -everse !o&er. relay

3< 4o& for&ard !o&er relay

:A ?ield failure -loss of e#citation. relay

:; egative !hase seuence relay

:@ achine or Transformer Thermal relay

)A 7nstantaneous ,vercurrent relay

)1 %$C 7"T ,vercurrent relay

)2 Circuit breaker

)2a Circuit breaker %u#iliary s&itch Jormally o!enK -a contact.)2b Circuit breaker %u#iliary s&itch Jormally closedK -b contact.

)) Po&er ?actor relay

); ?ield %!!lication relay

)@ ,vervoltage relay

;A /oltage or current balance relay

;: *arth fault relay

;< "irectional relay

;= 4ocking relay


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*>f$ Tri! L elay tri! 63 aster tri!

"iffl$Tri! L

,+>,4TC tri! 1;3T

BucholI tri! ;3T

,$T tri! 2;T

($T tri! :@T

,ver flu#ing tri! @@

P$$/ tri!

Ter$%la Tri! 1:@T

BucholI %larm ;3%

($T %larm :@%

,$T %larm 2;%

Ter$%larm 1:@%

Busbar !rot$ Tri! @;

Pole discre!ancy tri! 1;2

7ndication ve 41,?? 43, 4)+ema!hore ,?? 4eui!mentG,?? 41)

, 41< , 41@ ,?? 421

NORMS OF PROTECTION TO BE FOOWED AS PER A.P.E.R.C. ORDERS

?or Transmission ' "istribution 4ines

S.No. Vo(t'+e Prote$t#o& S$he4e

1$ :AA 6/ 4ine ainG7 on s&itched or umerical "istance +cheme

ainG77 on s&itched or umerical "istance +cheme

2$ 22A 6/ 4ine ainG7 on s&itched distance scheme -?ed from Bus PTs.

ainG77 +&itched distance scheme -?ed from line C/Ts.

1)


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(ith a changeover facility from bus PT to line C/T and

viceGversa$

3$ 132 6/ lines ain Protection +&itched distance scheme -fed from bus

PT.$

Backu! Protection 3 os$ directional 7"T ,>4 elays

and 1 o$ directional 7"T *>4 relay$

:$ 33 6/ lines onGdirectional 7"T 3 ,>4 and 1 *>4 relays$

)$ 11 6/ lines onGdirectional 7"T 2 ,>4 and 1 *>4 relays$otes

i$ ,n some of the old 22A6/ lines one distance scheme &ith backu! directional 7"T 3 ,>4 '

*>4 relays &ere !rovided$

ii$ ,n some of the 1326/ grid lines only distance scheme is available

iii$ /ery fe& ;;6/ lines are in service -&hich are also being !hased out.

Busbars %ll 22A 6/ busbars &ill have busbar !rotection scheme &ith main and check

Ione$

1;


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1


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NORMS OF PROTECTION FOR EHV CASS POWER TRANSFORMERS

POWER STATIONSVo(t'+e r't#o 7

$'5'$#ty

HV S#de V S#de Co44o& re('y6

i$ 11>132 6/ 0T 3GonGdir ,>4

1GonGdir *>4

relay and>orstandby *>?

*?

GG "ifferential or ,verall

differential ,verflu#

BuchholI,4TC BuchholI

P/ ,T (T

ii$ 13$=>22A 6/

1)$22A 6/

1=>:AA 6/

21>:AA 6/

0enerator T>?s

3GonGdir ,>4

1GonGdir *>4

relay and>or

standby *>?

*?

GG "ifferential or ,verall

differential ,verflu#

BuchholI

,4TC BuchholI

P/ ,T (T

iii$ 22A >;$;6/

+tation T>?s

3GonGdir ,>4

1GonGdir *>4

relay and>or

standby * >? *?

3GonGdir$ ,>4

relays

"ifferential ,verflu#

BuchholI

,4TC BuchholI

P/ ,T (T

iv$ 0enGvolt>;$;6/

F%T

3GonGdir$ ,>4

relays

3GonGdir$ ,>4

relays


BuchholI

,4TC BuchholI

P/ ,T (T

S!BSTATIONS

v$ 132>33>116/ u!to

= /%

3 ,>4 relays 1

*>4 relay

2 ,>4 relays 1

*>4 relay

BuchholI ,4TC

BuchholI ,T (T

vi$ 132>33>116/

above = /% and

belo& 31$) /%

3 ,>4 relays 1

dir$ *>4 relay

3 ,>4 relays 1

*>4 relay

"ifferential

BuchholI ,4TC

BuchholI ,T (T

vii$ 132>336/ 31$)

/% ' above

3 ,>4 relays 1

dir$ *>4 relay

3 ,>4 relays 1

*>4 relay


BuchholI ,4TC

P/ ,T (T

viii$ 22A>33 6/

31$)/% '

)A/%

22A>1326/ 1AA

/%

3 ,>4 relays 1

dir$ *>4 relay

3 ,>4 relays 1

dir$ relay


BuchholI ,4TC

P/ ,T (T

i#$ :AA>22A6/

31)/%

3 directional ,>4

relays -&ith

dir$highset.

1 directional *>4

relays$ estricted

*>? relay

3 "irectional

,>4 relays for

action

3 directional ,>4

relays -&ith

dir$highset.1

directional *>4

relays$ estricted

*>? relay


BuchholI ,4TC

P/ ,T (T and

overload -alarm. relay

Breaker failure !rotection The 4BB !rotection scheme &ill be !rovided for all 22A6/ stations -along

&ith busbar !rotection scheme.

Transformers

1=


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i$ o BuchholI relay for transformers belo& )AA 6/% ca!acity

ii$ Transformers u!to 1)AA 6/% shall have only Horn ga! !rotection

iii$ Transformers above 1)AA 6/% and u!to =AAA 6/% of 33>116/ ratio shall have one grou! control

breaker on H/ side and individual 4/ breakers if there is more than one transformer$

iv$ Transformers above =AAA 6/% shall have individual H/ and 4/ circuit breakers$

v$ The relays indicate above shall be !rovided on H/ and 4/

vi$ 4%s to be !rovided on H/ ' 4/ for transformers of all ca!acities and voltage class$

vii$ ,4TC out of ste! !rotection is to be !rovided &here aster follo&er scheme is in o!eration

viii$ ?ans failure and !um!s failure alarms to be connected$

i#$ %larms for ,$T$ ($T$ BuchholI -ain tank ' ,4TC. should be connected$

Po#&t6 to be $he$8ed 2h#(e dr'2#&+ CT6

1$ /oltage class

2$ 7ndoor >,utdoor

3$ ,il filledMesin castM ing ty!eM

:$ +hort Circuit rating

)$ %vailable ratios

;$ +econdary Current values

,utdoor

3$ Nuencing Bulk oil or in$ ,il or +?; or /acuum or %ir blast

:$ "$C Control voltage or 2:/ or 32/ or 11A/ or 22A/

)$ ated current -make ' break.

1@


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;$ u!turing ca!acity

Break time closing time limit

C.T. RATIOS AND REA0 SETTINGS TO BE ADOPTED

The C$T ratios and relay settings for all eui!ment at *HT substation u!to 4$/ breakers of Po&er

transformers shall be a!!roved by +*>Protection$

The C$T ratios and relay settings for all 336/ 116/ ' ;$; 6/ feeder breakers at *HT substations

shall be finalised by "*>* ' T$

The relay settings so finalised by +*>Protection or the concerned "* shall not be altered by any other

officer$

The officers above are res!onsible for relay CoGordination and gradation$

IMITS OF ERRORS IN CT6

ClassA$1to1$A The Current *rror and !hase dis!lacement *rror at the rated freuency shall not e#ceed the

values given belo& &hen the secondary burden is any value from 2)O to 1AAO to the

rated burden$

#4#t6 o* 9 error 't 9 o* r'ted

Curre&t

Ph'6e d#65('$e4e&t #& 4#&ute6 't

9 o* r.$t

C('66 :;


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C('66 =7> >;9 :;;9

3 3 3

) ) )

21


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A55(#$'t#o& St'&d'rd6

IS BS

Precession etering A$1or A$2 B4 B4

Comml$ or 7ndl$metering A$) or 1$A % B C

%mmeters !o&er meter 1$A or 3$A C"elays )P1Aor )P2A +TF

+elective !rotection P+

Com!osite *rror for Protection 7++ 2


24/167

?or !rotection of various eui!ment of *HT class the +tar !oint on secondaries of CT should be

made as follo&s for ensuring correct directional sensitivity of the !rotection scheme

1$ ?or Transmission 4ines G 4ine side

2$ ?or Transformers G Transformer side

3$ ?or Bus bar G Bus side

:$ 0enerator Protection G 0enerator +ide

The above method has to be follo&ed irres!ective of !olarity of CTs on !rimary side$ ?or

e#am!le in line !rotection if P1 is to&ards bus then +2s are to be shorted and if P2 is to&ards bus

then +1s are to be shorted$

The C$T secondary connections for Transmission line Transformer and Busbar are indicated in

the figures$

B!SBAR CT@6 CONNECTIONS

GENERATOR CT@6 CONNECTIONS

2: GeneratorProtectionScheme

GeneratorProtectionScheme

GENERT!R STT!R"#N$#NGS

P% P& P& P%S% S& S& S%


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2)


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C.T POARIT0 TEST

*ach current transformer should be individually tested to verify that the !olarity markings on the

!rimary and secondary &indings are correct$ The follo&ing figure sho&s the test unit for this$

The ammemeter % is a robust moving coil !ermanent magnet centre Iero ty!e instrument$ %lo& voltage battery is used to energise the !rimary &indings through a single !ole !ush button$ ,n

closing the !ushGbutton &ith above C$T ammeter markings the ammeter should give a !ositive flick

indicating correct !olarity of the C$T

PRIMAR0 INECTION TEST

This test is carried out to ensure the C$T ratio of current transformers$ 7f this test is carried out

after C$T secondary &iring is com!leted it ensures not only the correct ratio of C$Ts but also the

correctness of the entire C$T secondary &iring com!rising !rotection and metering !ortions$ The testing

eui!ment consists of a loading -inEection. transformer controlled by a variable transformer to get the

reuired current on the !rimary side of the C$T under test$

?or carrying out the ratio test on C$Ts the follo&ing circuit is made use of$

Current is !assed through the !rimary &indings of the standard C$T and C$T under test$ The ratio

of the C$T can be determined by com!aring the currents in ammeters %1 and %2$

VOTAGE TRANSFORMERS

C('66 o*

A$$ur'$y

A55(#$'t#o& IMITS OF ERROR

At ;9 to :;;9 o* r'ted At ;:;;9 o*

2;


27/167

burde& 7 ; to :;;9 o*

r'ted burde& !PG

burde& :; to

PF Ph.d#65('$e

4e&t

R't#o Ph.d#65('

$e4e&t

R't#o

A$2

% +ubGstandard 7ndication meters A$) 2A A$) 2A

B 1stgrade indicating in!uts &att

meter 7ndl ' +ynchronising

1$A 3A 1$A *'T Concerned

e. (henever directed by Chief *ngineer>+u!erintending *ngineer>Protection > /idyut +oudha >

Hyderabad$

2$ 7t is the res!onsibility of %sst$"ivisional *ngineer -Protection to maintain a Calendar and ensure

testing of relays.

3$ The %sst$*ngineer -Protection. is res!onsible for the accuracy of test results noted in the Test

ecord$:$ Breaker o!ening and closing times should be checked$

a. at the time of commissioning

b. annually during service

c. (henever tri! or closing coils are changed

d. (henever maEor re!airs to o!erating mechanism are done

e. (henever breaker contacts are changed$

)$ +tation earth resistance of earth !its and combined value should be taken

a. annually

b. (henever directed by "*-*'T.

;$ The %ssistant "ivisional *ngineer -aintenance. in charge of the +ubstation is res!onsible for

measurement and record of +ubstation earth resistances and carrying out im!rovements &herenecessary$

2


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2=


29/167

GENERATOR

PROTECTION

2@


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3A


31/167

31


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GENERATOR AND ITS PROTECTION

The core of an electrical !o&er system is the generator$ There are !o&er units based on steam

gas na!htha &ater !o&er diesel engine drive and &ind mills$ The range of siIe e#tends from a fe&

hundred 6/% -or even less. for engineGdriven and hydro sets u! to turbine driven sets e#ceeding

)AA/% in rating$

+mall and medium siIed sets may be directly connected to the distribution system$ % larger unit is

usually associated &ith an individual transformer transmission system$ o s&itchgear is !rovided

bet&een the generator and transformer may be ta!!ed off the interconnection for the su!!ly of !o&er to

au#iliary !lant$ Provision of a breaker in bet&een 0enerator and Transformer makes it !ossible to dra&

!o&er for the au#iliaries through the F%T from the *H/ bus even &hen machine is not in service$

Ty!ical arrangements are given in figure$$$$$$$$$$$$

32


33/167

Protection of ;$; 6/ system in generating stations

aEor Thermal +tations au#iliaries are fed from ;$; 6/ bus &hich is connected by a 22A>;$;6/

+tation Transformers and 0eneration voltage>;$; 6/ Fnit %u#iliary Transformers$

+tation Transformers

The vector grou! of these transformers is +tarG"elta i$e$ the ;$; 6/ system is delta connected$

,r

The vector grou! of these transformers is +tarG+tar &ith the ;$;6/ side grounded through a high

resistance$

Fnit %u#ilary Transformers

The vector grou! of these transformers is "elta 8+tar -ungrounded +tar on ;$;6/ +ystem.$

%ny earth fault on the ;$; 6/ system cannot be seen by any *>4 relay -since the ;$; 6/ system

is delta connected or high resistance grounded or ungrounded +tar.$Ho&ever 3G,>4 relays are

!rovided on the ;$;6/ side of the +tation Transformers and Fnit %u#ilary Transformers $ %n

o!enGdelta voltage of the ;$; 6/ bus PT is connected to an over voltage relay &ith a very lo&

setting$ %ny earth fault on the ;$; 6/ system &ill cause the !resence of o!enGdelta voltage and

make the voltage relay o!erate &hich is connected to give alarm$ The faulty ;$; 6/ feeder can

be identified by tri!!ing the ;$; 6/ outlets one after the other$

33


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Ge&er'tor Prote$t#o& V'r#ou6 Fu&$t#o&6

0enerating units are the source of the !o&er system and their security against any adverse

conditions is most im!ortant in the system$ The generator !rotection must ensure a fast and selective

detection of any fault in order to minimiIe their dangerous effects$

Protection of !assive elements like transmission lines and transformers is relatively sim!le &hich

involves isolation of faulty element from the system &hereas !rotection of generators involves tri!!ing

of generator field breaker generator breaker and turbine$

0enerator Protections are broadly classified into three ty!es$

C4%++ 8 % G This covers all electrical !rotections for faults &ithin the generating unit in &hich

generator field breaker generator breaker and turbine should be tri!!ed$

C4%++ 8 BG this covers all mechanical !rotections of the turbine in &hich turbine &ill be

tri!!ed first and follo&ing this generator &ill tri! on reverse !o&er > lo& for&ard

!o&er !rotections$

3:


35/167

3)


36/167

C4%++ 8 CG This covers electrical !rotection for faults in the system in &hich generator &ill be

unloaded by tri!!ing of generator breaker only$ The unit &ill come to house load

o!eration and the F%T &ill be in service$ /arious !rotections of this class are

i. 22A 6/ -H/ side of 0enerator Transformer. busbar !rotection$

ii. 0enerator Transformer H/ side breaker !ole discre!ancy$

iii. 0enerator negative !hase seuence !rotection

iv. 0enerator Transformer over current > *arth fault !rotection

v. everse !o&er !rotection &ithout turbine tri!$

1. Ge&er'tor D#**ere&t#'( Prote$t#o& % G)1

7t is unit ty!e !rotection covering the stator &inding for !hase to !hase faults due to breakdo&n

of insulation bet&een stator !hase &indings$ This relay is not sensitive for single line to earthfaults as the earth fault current is limited due to the high neutral earthing resistance$

3;


37/167

7f CTs of identical ratios are used on neutral and line side of generator an o!erating current

setting of 2AO it can be ado!ted$ 7t is instantaneous in o!eration and it tri!s the generator breaker

-Class 8 %. to eliminate the system in 8 feed to the fault along &ith field breaker and turbines$

?or all machines of ratings 1A /% and above this !rotection shall be !rovided$

OVERA DIFFERENTIA REA0

32G Time delay S 1 +ec$

G Fnder voltage relay S 11A 8 11)O of

generator rated current

1A. o2 For2'rd Po2er Re('y %=G)1

7n thermal machines &hen the steam flo& through turbine is interru!ted by closing the *+/s or

the governor valves the remaining steam in the turbine generates -lo&. !o&er and the machine

enters to motoring conditions dra&ing !o&er from the system$ This !rotection detects lo&for&ard !o&er conditions of the generator and tri!s generator breaker after a time delay avoiding

motoring of generator$

The lo& for&ard !o&er relay &ill be !rovided &ith turbine tri! interlock in thermal machines$

% setting of A$)O of rated active !o&er of generator &ith a time delay of 2$A +ec$ shall be

ado!ted$

11. Re3er6e Po2er re('y %=


42/167

dra&ing !o&er from the system$ everse !o&er relay !rotects the generators from motoring

condition$ 7n thermal machines reverse !o&er condition a!!ears subseuent to lo& for&ard

!o&er condition$

?or reverse !o&er relay a setting of A$)O of rated active !o&er of generator &ith 2 stage timer as

given belo&$

i. St'+e I1 (ith turbine tri! interlock a time delay of 2 +ec$ shall

be ado!ted$

ii. St'+e II1 (ithout turbine tri! interlock a time delay of about

2A +ec$ can be ado!ted to avoid unnecessary tri!!ing of unit during system

disturbance causing sudden rise in freuency or !o&er s&ing conditions$

:2


43/167

:3


44/167

12. Rotor e'rth *'u(t 5rote$t#o&1

This !rotection shall be !rovided for machines of all siIes$ This !rotection shall be connected for

alarm and the o!erator may take the machine at the earliest o!!ortunity after the first earth fault

has occurred$

This !rotection &ill have a sensitive voltage function o!erating on bridge measurement basis &ith

au#iliary eui!ment$ 7t &ill have t&o levels one for alarm and one for tri!$ The settings ado!ted

in general are

i. ?or alarm 2) 65 ,hm 1$A +ec$

ii. ?or tri! ) 6 ,hm A$) +ec$

% modern generating unit is a com!le# system com!rising the generator stator &inding and

associated transformer and unit transformer the rotor &ith its field &inding and e#citers and the

turbine and its associated condenser and boiler com!lete &ith au#iliary fans and !um!s$ ?aults of

many kinds can occur &ithin this system for &hich diverse !rotection a!!lied &ill be governed by

economic considerations taking into account the value of the machine and its im!ortance to the!o&er system as a &hole

13. Pole +li! elay -@= 0.G

The !ole sli!!ing relay is designed to !rotect synchronous generators against the !ossibility of the

machine running unstable region of the !o&er angle curve &hich &ould result in !o&er

oscillations and !ole sli!$ Pole sli!!ing of generators &ith res!ect to the system leading to an

increase in rotor angular !osition beyond the generator transient stability limits$ +ome of the

causes for !ole sli!!ing are as follo&s$

i. 4arge net&ork disturbanceii. ?aults on the net&ork close to the generator$

iii. 4oss of generator field$

iv. ,!erating the generator in an e#cessive under e#cited mode$

v. 4oss of evacuation$

+etting recommendationsG

a. 7f the source of oscillation lies bet&een generator>transformer unit the machine has to be isolated

from the net&ork after the first sli!$

::


45/167

?or&ard reach of relay characteristics shall cover generator>generator transformer$ Tri!!ing in

this Ione shall be in the first !ole sli!$ The reach of this Ione is SA$f. of the generator -large overflu#ing for short times.$

The stator under freuency relay measures the freuency of the stator terminal voltage$

:)


46/167

+etting ecommendationsG

?or %larm :=$A HI 2$A +ec$ time delay$

?or Tri! :


47/167

+mall ca!acity induction generators also are in service mostly mini hydel and &indmills of

ca!acity of 2AA6( to 2AAA6( &hich de!end on the system for e#citation$ Their !rotection

reuirements are very sim!le such as overcurrent relays$

The !rotective relays generally used for the synchronous generators are listed at in the follo&ing

!age$

7nstead of inde!endent relays for each function micro!rocessor based numerical relay &hich can

take care of the entire 0enerator !rotections the latest entry$

:


48/167

PROTECTIVE SCHEMES FOR VARIO!S GENERATORS

Fu&$t#o&6 Ste'4 7

G'6 Turb#&e6

Hydro

Turb#&e6

S4'((

%J:;

MVA)

Med#u4

%:;:;;

MVA)

'r+e

%:;;

MVA)

S4'((

%J:;

MVA)

Med#u4

%:;:;;

MVA)

'r+e

%:;;

MVA)

"ifferential Q Q Q Q Q Q@)O +tator *>? Q Q Q Q Q Q

1AAO +tator *>? Q> Q Q> Q

7nterturn ?aults Q Q Q Q Q Q

Backu! 7m!edance Q Q Q Q

/oltage controlled ,>C Q Q

egative +euence Q Q Q Q Q Q

?ield ?ailure Q Q Q Q Q Q

everse Po&er Q Q Q Q Q Q

Pole +li!!ing Q Q

,verload Q Q Q

,ver voltage Q Q Q Q Q QFnder freuency Q Q Q Q Q Q

"ead machine Q Q

otor *arth ?ault Q Q Q Q Q Q

,verflu#ing Q Q Q Q

:=


49/167

:@


50/167

TRANSFORMER PROTECTION

)A

T%+?,*

P,T*CT7,


51/167

The rating of Po&er transformers used in %$P +ystem$

1$ :AA>22A 6/ 31) /% %uto Transformers

2$ 22A>132 6/ 1AA/% %uto Transformers

3$ 22A>33 6/ )A ' 31$)/% Transformers

:$ 132>;; 6/ :A ' 233 6/ )A 31$) 2) 1; 1) /% Transformers

;$ 132>11 6/ 1; 1) ' 116/ and above are of +tarG+tar vector grou!ing &ith the

neutral solidly earthed$ There are a fe& transformers &ith deltaGstar -delta on H/ side.$ The 33>116/ and

116/>:1)/ Transformers are of deltaGstar -delta on H/ side.$

)1


52/167

The ty!es of faults that the transformers are subEected to are classified asG

1. Through ?aultsG These are due to overload conditions and e#ternal short circuits$

Time graded ,>C ' *>? relays are em!loyed for e#ternal short circuit conditions$ ?uses are

!rovided for "istribution transformers$

2. 7nternal ?aultsG

a. *lectrical ?aults G ?aults &hich cause immediate serious damage such as !hase to earth or

!hase to !hase faults short circuits bet&een turns of H/'4/ &indings etc$

b. 7nci!ient ?aults G (hich are initially minor faults causing slo&ly develo!ing damage$ +uch asa !oor electrical connection of conductors of breakdo&n of insulation etc$

The follo&ing relays are em!loyed to !rotect the transformer against internal faults$

i. BuchholI relays

ii. "ifferential relays

iii. *? relays$

iv. ,verflu#ing relays

)2

Trans*ormer Tan

Conser,ator

larm

(

Trip


53/167

i. Bu$hho(L Re('y61

(henever a fault in transformer develo!s slo&ly heat is !roduced locally &hich begins to

decom!ose solid of liuid insulated materials and thus to !roduce inflammable gas and oil flo&$ This

!henomenon has been used in the gas !rotection relay or !o!ularly kno&n as BucholI relay$ This relay is

a!!licable only to the soGcalled conservator ty!e transformer in &hich the transformer tank is com!letely

filled &ith oil and a !i!e connects the transformer tank to an au#iliary tank or U ConservatorU &hich acts

as an e#!ansion chamber$ ?igure sho&n as BucholI relay connected into the !i!e leading to the

conservator tank and arrange to detect gas !roduced in the transformer tank$ %s the gas accumulates for a

minor fault the oil level falls and &ith it a float V?V &hich o!erates a mercury s&itch sounding an alarm$

(hen a more serious fault occurs &ithin the transformer during &hich intense heating takes !lace an

intense liberation of gases results$ These gases rush to&ards the conservator and create a rise in !ressure

in the transformer tank due to &hich the oil is forced through the connecting !i!e to the conservator$ The

oil flo& develo!s a force on the lo&er float sho&n as U/U in the figure and overtri!s it causing it contacts

to com!lete the tri! circuit of the transformer breaker$ ,!eration of the u!!er float indicates an inci!ient

fault and that of the lo&er float a serious fault$

Bu$ho(L re('y O5er't#o& 1 Cert'#& Pre$'ut#o&61

The BucholI relay may become o!erative not only during faults &ithin the transformer$ ?or

instance &hen oil is added to a transformer air may get in together &ith oil accumulate under the relay

cover and thus cause a false o!eration of the gas relay$ ?or this reason &hen the V0asV alarm signal is

energiIed the o!erators must take a sam!le of the gas from the relay for &hich !ur!ose a s!ecial clock is

!rovided$ 0ases due to faults al&ays have colour and an odour and are inflammable$

The lo&er float may also falsely o!erate if the oil velocity in the connection !i!e through not due

to internal faults is sufficient to tri! over the float$ This can occur in the event of an e#ternal short circuit&hen over currents flo&ing through the &indings overGheat the co!!er and the oil and cause the oil to

)3


54/167

e#!and$ 7f malGo!eration of BucholI relay due to overloads or e#ternal short circuits is e#!erienced it

may be necessary that the lo&er float is adEusted for o!eration for still higher velocities$

7n installing these relays the follo&ing reuirements should be fulfilled$

a. The conductor connection the contacts to the terminals on the cover must have !a!er insulation as

rubber insulation may be damaged by the oil$

b. The floats must be tested for air tightness by for e#am!le submerging them in hot oil to create a

sur!lus !ressure in them$

c. The relay cover and the connection !i!e should have a slo!e of 1$) to 3 !ercent and not have any

!rotruding surface to ensure unrestricted !assage of the gases into the conservator$

##) D#**ere&t#'( Re('y61

% "ifferential relay com!ares the currents on both sides of the transformer$ %s long as

there is no fault &ithin the !rotected eui!ment -Transformer. the current circulates bet&een the

t&o CTs and no current flo&s through the differential element$ But for internal faults the sum ofthe CTs secondary currents &ill flo& through the differential relay making it to o!erate$

T&o basic reuirements that the differential relay connections are to be satisfied are

a. 7t must not o!erate for load or e#ternal faults$

b. 7t must o!erate for internal faults$

%s onGload ta! change facilities are invariably !rovided in the grid transformers any de!arture

from the nominal ta! !osition &ill result in s!ill currents in the relay circuits$ ?urther the CTs are often of

different ty!es and have dissimilar magnetiIation characteristics again resulting in s!ill current during

heavy through fault conditions$

):

!'C

R'C

#%

#&TRNS(!R)ER

Percentage Differential Relay in a Two Terminal Circuit


55/167

To avoid un&anted relays o!eration under the above t&o conditions a UPercentage BiasU

differential relays is used$

The o!erating characteristics of !ercentage bias differential relay is sho&n in the figure$

The current flo&ing through the o!erating coil of the relay should be nearly Iero during normal

o!erating conditions and &hen e#ternal short circuit occurs$

(hile setting the differential relay on a transformer the -mismatch. current through differential element

at normal ta! and !ositive and negative e#treme ta!s are to be com!uted$ "ifferential element !icku!

setting and>or bias settings is ado!ted based on ma#imum !ercentage mismatch adding some safety

margin$

"ifferential Current S W 71G72 W

W71G72 W

Bias +etting S GGGGGGGGGGG

-7172.>2

C$T atios and connections for differential relay

1$ % sim!le rule of thumb is that the CTs on any (ye -+tar. &inding of a Po&er transformer should be

connected in delta and the CTs on any delta &inding should be connected in (ye -+tar.$

2$ a. 7f the CTs are to be connected in +tar the C$T atio &ill be 7n>1%

(here 7n is transformer full load current$ b. 7f the CTs are to be connected in "elta the C$T atio &ill be 7n>A$)


56/167

);


57/167

)


58/167

)=


59/167

Re6tr#$ted E'rth F'u(t Prote$t#o& %REF)1

This relay is o!erative only for the internal faults of the transformer and thus fast o!erating timer

can be achieved$

1$ %n e#ternal fault on the star side &ill result in current flo&ing in the line CT of the affected !hase and

a balancing current in the neutral CT and current in the relay is Iero and hence relay is stable$ "uring

an internal fault the line current on the line CT gets reversed and hence relay o!erates$

2$ The arrangement of residually connected CTs on the delta side of a transformer is only sensitive to

earth faults on the delta side because Iero seuence currents are blocked by the delta &inding$

?or e#ternal faults no current flo&s through *? unless a CT gets saturated$ Hence minimum !icku!

current setting is ado!ted -1AO or 2AO 7n. on *? relay$ Based on the through fault current the

stabilising resistor is set such that the relay &ill not o!erate for e#ternal fault &hen a CT getssaturated$This relay o!erates only for internal earth faultsinstantaneously$

)@


60/167

?ault current for e#ternal fault 7fS 2)AA % -assume.

C$T$atio -line and neutral. S 3AA>1 %

2)AA

+econdary fault current S GGGGGG S =$33 % -+ec$.

3AA

CT S C$T$esistance

T4 S 4ead esistance S 6m -2$) s mm Cu.

/oltage develo!ed across CT -+aturated.

-/k. S 7f-CT 24.

S =$33 -) 3.

S ;;$;: /olts

elay burden S 1 /%

elay ,!erating

Current S A$2 % -+et value.

elay ,!erating /oltage

elay burden

/ S GGGGGGGGGGGGGGGGGGGGGGGGGGGGG

elay ,!erating Current

S 1>A$2 S ) /olts

/6G/+tabilising esistor + S GGGGGGGGGGGGG

7+et

S ;;$;:G)$A

GGGGGGGGGGG

A$2

S 3A=$2 ,hms

+et + S 31A ,hms

7f the calculated value of + e#ceeds the e#isting range the current settings can be raised accordingly and

arrived at suitable + value$

;A


61/167

;1


62/167

,verflu#ing Protection

1$ ,verflu#ing condition in a transformer can occur during system over voltage and>or under freuency

conditions -/>?.$

2$ The ,verflu#ing condition does not call for high s!eed tri!!ing$ The tri!!ing can be delayed

de!ending on the overflu# &ithstand ca!ability of the transformer$

3$ elays &ith definite time delay -nearly 3A+ec$. and inverse characteristic are being em!loyed$

,ther Protective devices em!loyed

Pressure elief /alue -P/.

(inding Tem!erature

,il Tem!erature,4TC BuchholI

;2


63/167

;3

TRANSMISSION INES

PROTECTION


64/167

Tr'&64#66#o& #&e Prote$t#o&

D#6t'&$e Re('y61

7ntroduction

The im!edance relays also called distance relays are em!loyed to !rovide !rotection to transmission

lines connected in a net&ork as they are economic and !ossess several technical advantages$ They arecom!aratively sim!le to a!!ly o!erate &ith e#tremely high s!eed and both !rimary and backu! !rotection

features are inherent in them$ oreover they can be easily modified to &ork as unit schemes by

coordinating them &ith !o&er line carrier facilities and are suitable for high s!eed reclosing$ The im!edance

relay is made to res!ond to the im!edance bet&een the relay location and the !oint &here fault is incident$

The im!edance is !ro!ortional to the distance to the fault -hence the name Vdistance relayV. and is therefore

inde!endent of the fault current levels$

"istance elaying Princi!le

% distance relay com!ares the currents and voltages at the relaying !oint &ith Current !roviding the

o!erating torue and the voltage !rovides the restraining torue$ 7n other &ords an im!edance relay is a

voltage restrained overcurrent relay$

The euation at the balance !oint in a sim!le im!edance relay is 61/2S 627

2or />7 S 63 &here 61

62and 63are constants$ 7n other &ords the relay is on the verge of o!eration at a constant value of />7

ratio &hich may be e#!ressed as an im!edance$

+ince the o!erating characteristics of the relay de!end u!on the ratio of voltage and current and the

!hase angle bet&een them their characteristics can be best re!resented on an G diagram &here both/>7 ratio and the !hase angle can be !lotted in terms of an im!edance E$ ?urther the !o&er system

im!edance like fault im!edance !o&er s&ings loads etc$ can also be !lotted on the same G diagram$

;:


65/167

Therefore res!onse of a !articular relay during !o&er s&ing faults and other system disturbances can easily

be assessed$

Ty!es of "istance elays

-1. 7m!edance relay

-2. eactance relay

-3. ho relay

-:. odified im!edance relay

-1. 7m!edance relay

Characteristics of an im!edance relay on G diagram is sho&n in fig

,!eration of the im!edance relay is inde!endent of the !hase angle bet&een / and 7$ The o!erating

characteristic is a circle &ith its center at the origin and hence the relay is nonGdirectional$

Characteristic of "irectional 7m!edance elay

Characteristic of a directional im!edance relay in the com!le# G !hase is sho&n in fig$

The directional unit of the relay causes se!aration of the regions of the relay characteristic sho&n in the

figure by a line dra&n !er!endicular to the line im!edance locus$ The net result is that tri!!ing &ill occur

only for !oints that are both &ithin the circles and above the directional unit characteristic$

;)


66/167

The eactanceGty!e "istance elay

eactance relay measures />7 +inA -i$e$ 9 sin A G .$ (henever the reactance measured by the relay is less

than the set value the relay o!erates$ The o!erating characteristic on G diagram is sho&n in fig

The resistance com!onent of im!edance has no effect on the o!eration of reactance relay the relay

res!onds solely to reactance com!onent of im!edance$ This relay is inherently nonGdirectional$ The relay is

most suitable to detect earth faults &here the effect of arc resistance is a!!reciable$

ho relay

This is a directional im!edance relay also kno&n as admittance relay$ 7ts characteristic on G diagram is acircle &hose circumference !asses through the origin as illustrated in figure sho&ing that the relay is

inherently directional and it only o!erates for faults in the for&ard direction$

odified im!edance relay

%lso kno&n as offset ho relay &hose characteristic encloses the origin on G diagram as sho&n in fig

This offset mho relay has three main a!!lications G

i. Busbar Ione backu!

ii. Carrier starting unit in distance>carrier blocking schemes$

;;


67/167

iii. Po&er +&ing blocking$

ain ?eatures in "istance +cheme

"istance schemes consist of the follo&ing maEor com!onentsG

i. +tarters$

ii. easuring units$

iii. Timers

iv. %u#iliary relays

i. +tarters G

The starting relay -or starter. initiates the distance scheme in the event of a fault &ithin the

reuired reach -more than IoneG3.$

,ther functions of the starter are G

a. +tarting of timer relays for second and third Iones$

b. +tarting of measuring elements$

The starters are generally of ho or im!edance ty!e$

(ith ho ty!e starters G

easuring units for !hase and earth faults can be either directional or nonGdirectional as ho

starter is inherently directional$

(ith im!edance ty!e starters G

easuring units have to be directional as im!edance starters are non 8 directional$

The under im!edance relay can be used in conEunction &ith the directional relay as starter

&hich &ill then function similar to the ho starter$

ii. easuring units G

They are generally of a mho or reactance or a combination of mho reactance and resistance

ty!es$

Phase ?ault FnitsG

These measuring units are fed &ith line to line voltages -such as /ab /bc. and difference

bet&een line currents -7aG7b.$ They measure the !ositive seuence im!edance from the relay

location to the fault !oint$ Three such relays res!ond correctly to all !ossible single line to

ground faults line to line faults double line to ground faults and 3G!hase faults$ They

ho&ever do not res!ond correctly to earth faults$

;


68/167

*arth ?ault Fnits G

These measuring units utiliIe line to neutral voltage -/an /bn /cn. and !hase currents -7a

7b 7c.$ 7n order to make these units measure the !ositive seuence im!edance correctly a

Iero seuence current com!ensation is to be !rovided &hich is obtained by

6 S -9AG91.> 3R91 -&here 91 S !ositive seuence im!edance of line$

9A S 9ero seuence im!edance of line.

7n the current circuit -16. 7a &ill be fed for the above measurement$

iii. Timers G

Timer relays &hen initiated by starters !rovide the time lag reuired for Iones$ They also

&ill be used for Ione e#tension !ur!ose &henever reuired$

iv. %u#iliary relays G

"istance scheme com!rises of several au#iliary relays &hich !erform functions such as flag

indications tri!!ings signaling alarm etc$

Add#t#o&'( Fe'ture6 #& d#6t'&$e 6$he4e61

i. Po&er +&ing blocking relayii. /T fuse failure relay$

iii. +&itch onto fault relay

iv. ?ault locator

v. %utoGreclosing scheme$

vi. Carrier communication scheme$

#) Po2er S2#&+ b(o$8#&+1

"istance relay &hich res!ond to balanced 3G!hase changes in the im!edance &ill be affected by

!o&er s&ings$ These s&ings or oscillations occur follo&ing a system disturbance such as maEor load

change or a di! in voltage due to delayed fault clearance$

7n case of fault the transition from !eriod of im!edance locations -2) to 33O of starter im!edance.

to fault im!edance -starter im!edance. is sudden &hereas during !o&er s&ings$ The P+B relays use

this difference to block the tri!!ing during s&ings$

##) VT *u6e *'#(ure re('y1

The distance relays being voltage restraint ,>C relays loss of voltage due to main PT fuse failure or

inadvertent removal of fuse in one or more !hases &ill cause the relay o!eration$ The fuse failure

relay &ill sense such condition by the !resence of residual voltage &ithout residual current and

blocks the relay$

###) S2#t$h o&to *'u(t1

;=


69/167

(hen the line is s&itched on to a close by fault -say after line clear &ith earth s&itch closed. the

voltage at the relaying !oint &ill be Iero$ ?aults of this ty!e &ill normally be cleared by backu!

Iones$

The voltage a!!lied to the relay is lo& and this condition occurring simultaneously &ith the

o!eration of starter &ill cause instantaneous tri! by +,T? relay$ This +,T? feature &ill be

effective only for about 1G2 seconds after the line is charged$ ?aults occurring after this time &ill be

measured in the normal &ay$

#3) F'u(t (o$'tor1

7t measures the distance bet&een the relay location and fault location in terms of 9 in ,hms or

length in 6 or !ercentage of line length$

This relay gets same in!uts as the distance relay -connected in series &ith one of the main relays.$

The measurement is initiated by tri! signal from distance relays$

The fault locator gives the e#act location of the fault thereby reducing the time of restoration$

3) Auto Re$(o6#&+ S$he4e61

Ty!es of ?aultsG

i. Transient ?aultsG

These are cleared by the immediate tri!!ing of circuit breakers and do not recur &hen the line is reGenergised$

ii. +emiG!ermanent ?aultsG

These reuire a time interval to disa!!ear before a line is charged again$

iii. Permanent ?aultsG

These are to be located and re!aired before the line is reGenergised$

%bout =AG@AO of the faults occurring are transient in nature$ Hence the automatic reclosure of

breaker -after tri!!ing on fault. &ill result in the line being successfully reGenergised thereby

a. "ecreasing outage time

b. 7m!roving reliability

c. 7m!roving system stability

d. educes fault damage and maintenance time

De'd T#4e1

The time bet&een the %utoGreclosing scheme being energised and the 1streclosure of the circuit breaker $

This is normally set at 1 +ec$

Re$('#4 T#4e1

;@


70/167

The time follo&ing a successful closing o!eration measured from the instant the autoGreclosing relay closing

contacts making &hich must ela!se before the autoGreclosing relay initiated another reclosing attem!t$ 7n

other &ords it may be said to be the time bet&een 1stand 2ndreGclosure$

Ty5e6 o* Autore$(o6#&+ 6$he4e6 %b'6ed o& 5h'6e)1

') Three 5h'6e Autore$(o6#&+1

This ty!e of autoGreclosing causes an immediate drift a!art of the t&o systems and hence no

interchange of synchroniIing !o&er can take !lace during the dead time$

b) S#&+(e Ph'6e Autore$(o6#&+1

7n this only the faulty !hase -&hich already has tri!!ed on +40 fault. is reclosed &ithout causing

interru!tion in interchange of synchronising !o&er bet&een t&o systems through other t&o healthy

!hases$

Ty5e6 o* Autore$(o6#&+ 6$he4e6 %$'6e o& 'tte45t6 o* re$(o6ure)

') S#&+(e Shot Autore$(o6#&+1

7n this scheme breaker is reclosed only once on a given fault before lockout of circuit breaker

occurs$ High s!eed autoGreclosing for *H/ system is invariably single shot$

b) Mu(t#6hot Autore$(o6#&+1

7n this scheme more than one reclosing attem!t is made for a given fault before lockout of the circuit

breaker occurs$ e!eated closure attem!ts &ith high fault level &ould seriously affect the circuitbreaker eui!ment and system stability$ The factors that must be taken into accountG

i. Circuit Breaker 4imitationsG

%bility of circuit breaker to !erform several tri! close o!erations in uick succession$

ii. +ystem ConditionsG

7n the !ercentage of the semiG!ermanent faults -&hich could be burnt out. is moderate for

e#am!le on the lines through the forest multishot autoGreclosing is follo&ed$


71/167

Ty5e6 o* Autore$(o6#&+ %de5e&d#&+ o& 65eed)1

7. H#+h 65eed Autore$(o6#&+1

This aids in fast restoration of su!!ly but should be done by taking into account the follo&ing

factorsG

i. +ystem disturbance time can be tolerated &ithout loss of system stability$

ii. Characteristics of !rotection schemes and circuit breaker$

77$ o2 S5eed or De('yed Autore$(o6#&+1

This is suitable for highly interconnected systems &here the loss of a single line is unlikely to cause

t&o sections of the system to drift a!art and loose synchronism$

For EHV Sy6te461

') Cho#$e o* De'd T#4e1

4o&er limit is decided by deionising time of circuit breaker$

F!!er limit is decided by transient stability and synchronism$

4ong transmission lines reuire longer dead time for single !hase faults$

The dead time for high s!eed autoGreclosing scheme &ith *H/ system is A$3GA$= +ec$

b) Cho#$e *or re$('#4 t#4e1

This should not be set to such a lo& value that the o!erating cycle of breaker is e#ceeded &hen t&o

fault incident occurs close together$ The reclaim time &ill be in the range of 1AG3A +ec$ de!ending

on the breaker o!ening and closing mechanisms$


72/167

vi.

C'rr#er Co44u$'t#o& S$he4e61

The main disadvantage of conventional timeGste!!ed distance !rotection is that the instantaneous

9oneG1 of the !rotective scheme at each end of the !rotected line is set to cover =AO of the line and

hence faults in the balance 2AO of the line -at each end. are cleared in 9oneG2 time &hich isundesirable$

The desirable scheme is the one &herein the relays clear the faults on the 1AAO of the !rotected line

instantaneously and also !rovide backu! for uncleared faults on adEacent lines$ This can be achieved

by interconnecting the distance relays are each end of the line by a signaling channel -&hich can be

either !ilots a !o&er line carrier communication channel a radio link or a micro&ave channel.$

The !ur!ose of the signaling channel is to transmit the information about the system conditions at

one end of the !rotected line to the other end and initiate or !revent tri!!ing of the remote circuit

breaker$ The former arrangement is referred to as a JTransfer tri! schemeK &hile the latter is kno&n

as JBlocking schemeK

') Tr'&6*er tr#5 6$he4e1

7n this scheme the distance relay at one end of the !rotected lines sends a carrier signal to the

relay at other end of the line for interGtri!!ing thereby clearing the faults on entire line

instantaneously$


73/167

Transfer tri! is of t&o ty!esG

#) !&derre'$h#&+ 6$he4e1

The scheme in &hich the 9oneG1 relay -set to cover about =AO of 94. is used to send a signal

to the remote end of the feeder for interGtri!!ing is termed as transfer tri! underGreaching

scheme$ To avoid malGo!eration due to recei!t of false signal the receiving end relay

o!eration is interGlocked &ith its 9oneG3>starter o!eration i$e$ the scheme o!erates either by

its o&n 9oneG1 relay o!eration or by recei!t of carried and its 9oneG3>starter o!eration$

##) O3erre'$h#&+ 6$he4e1

This scheme is suitable for short lines &here an underreaching 9oneG1 &ould be too short tobe of any !ractical use$ 7n this scheme the relay set to reach beyond 1AAO of the line is

used to send an interGtri!!ing signal to the remote end of the line$ 7t is essential that the

receive relay contact be monitored by a directional relay to ensure that tri!!ing does not take

!lace unless the fault is &ithin the !rotected section$ The disadvantage of this scheme is that

there is no inde!endent 9oneG1 tri!!ing$ The fast tri!!ing therefore relies entirely on

signaling channel$

The disadvantages of these schemes is that the signal is transmitted over the fault line section$

"istortion of the signal may occur due to attenuation introduced into the line by the fault$


74/167


75/167

F'$tor6 '**e$t#&+ d#6t'&$e re('y o5er't#o&1

i. ?ault resistance$

ii. 7nfeed effect$

iii. BranchingGoff effect$

iv. 4oad encroachment$

i. ?ault resistanceG

?ault resistance has t&o com!onentsG

a. %rc resistance$

b. 0round resistance$

7n a fault bet&een !hases only arc resistance is involved$

?or a fault at ? the actual line im!edance

S 5 S 94

"ue to the !resence of fault resistance the im!edance measured by the relay

S 5 ? S 9 -&here 9 X 94.

?ault arc resistance is given by (arringtonVs formula

arcS = 71$:

&here l S length of arc in ft

7 S fault current in %m!s


76/167

The arc resistance has little effect on accuracy of IoneG1 unit as it o!erates instanteously before the

arc can stretch a!!reciably e#ce!t in case of short lines$ eactance relays are therefore used for short

lines &here the fault resistance may be com!arable &ith that of the !rotected lines and also for

ground faults &here the ground resistance is high$

The arc resistance &ill have greater im!act on accuracy of backu! Iones -time delayed. as the arc

stretches a!!reciably$

ii. 7nfeed effectG

The effect of intermediate current source bet&een relay location and fault !oint is termed as infeed

effect$ Consider the sketch indicated in fig GGG

% fault at ? on the line BC is at a distance of 9192 for the relay at station %$ But &hen current 72

flo&s from bus " the im!edance to the fault as seen by the relay at % is

91 92 92 # -72>71.$

Thus the fault is seen by the relay as farther than &hat it really is i$e$ distance relay under reaches

due to the infeed effect$

The effect of infeed becomes more !ronounced &ith more interconnections at station B$


77/167

iii. BranchingGoff effect G

Consider the sketch indicated in fig GGG

% fault at ? is at the distance of 9192 for the relay at station %$ But &hen current 71 gets

distributed as 72 ' 73 at station B the im!edance to fault seen by the relay at station % &ill be -91

73>71 R 92. &hich is less than -9192.$

Then the fault is seen by the relay as nearer than &hat it really is i$e$ distance relay

overreaches due to branchingGoff effect$ This overreaching tendency &ill cause the relay to loose its

selectivity$

iv. 4oad encroachment G

(hile !rotecting long lines the necessary reach may be so large that the minimum service im!edance

-or load im!edance. falls &ithin the region of the starter$ This &ould result in tri!!ing &ithout there

being any fault$ The t&o conditions i$e$ o!eration at heavy load and short circuit differ by virtue of

!hase angle bet&een voltage and current$ ?or the load im!edance the !hase angle &ill be &ithin

3A to G3A "eg$ (hile during short circuits the fault im!edance has a !hase angle of ;A to =A deg$

-i$e$ line angle.$

4oad encroachment !roblem is more !ronounced in case of under im!edance starters and gets

lessened in case of mho elli!tical lens etc ty!e of starters$ elays &ith suitable characteristic on G diagram have to be carefully chosen to !rotect long and heavily loaded lines and this becomes

easily !ossible &ith micro!rocessor based numerical relays$


78/167


79/167

No&62#t$hed 6$he4e 36 62#t$hed 6$he4e1

7n an ideal onGs&itched scheme there &ill be ; starters 3 for !hase faults and 3 for ground faults$

There &ill be inde!endent measuring units for both !hase faults and earth fault for each !hase for all

three Iones totaling to 1= units$ This scheme is faster and more accurate but is costly$

7n the s&itched scheme only one measuring unit &ill be used for all ty!es of faults$ This

single measuring unit is s&itched to the correct fault loo! im!edance by s&itchingGin the res!ective

voltages and currents by the starter$

The reach of the measuring element gets e#tended to IoneG2 and IoneG3 after the ela!se of

corres!onding timings through Ione e#tension !rocess$ +&itched scheme is relatively slo& in

o!eration and has the risk of total scheme failure in the event of failure of the only one measuring

unit available$

o&e e"te&6#o& 6$he4e61

%s a via media bet&een nonGs&itched and s&itched schemes there are schemes &ith Ione e#tension

facility -such as ** make 3/ ' 3/ relays.$ These schemes consists of 3 measuring units for !hasefaults and 3 measuring units for earth faults -a!art from 3 starters.$

The reach of the measuring unit gets e#tended to IoneG2 and IoneG3 after ela!se of corres!onding

timings through a Ione e#tension !rocess$

,ther ,!erating Characteristics

*arlier &hen electromagnetic relays &ere in use the characteristics involving straight lines and >or circles on

G diagram &ere only !ossible$ (ith the advent of static relays micro!rocessor based relays and !resently

of numerical relays any desired>reuiredGo!erating characteristic is !ossible giving &ider choice forselection of relays$ 7nfact there are relays &hich can be !rogrammed remotely$

A55(#$'t#o& o* d#6t'&$e re('y61

+ince the distance relays are fed from the secondaries of line CTs and bus PTs>line C/Ts the line

!arameters are to be converted into secondary values to set the relay as !er reuirements$

9secyS 9!ri>7m!edance ratio

-&here 7m!edance ratio S P$T$atio>C$T$atio.

Hence any changes in C$T $ratio has to be effected along &ith revision of relay settings only$


80/167

?or the lines the im!edance in ,hms !er 6 is a!!ro#imately as under

GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG

6/ 91 -S 92 . 4ine %ngle

GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG

132 6/ A$: ;A to


81/167

-no intentional

time delay.$

2$ 9oneG2 1AAO of 94 :AG)AO A$3 to A$:

of 9+4 seconds

3$ 9oneG3 1AAO of 94 12AO A$; to A$=

of 9+4 seconds

:$ 9oneG: 1AAO of 94 12AO A$@ to 1$)

of 944 seconds$

GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG

&here 94 S Positive seuence im!edance of line to be !rotected$

9+4 S Positive seuence im!edance of adEacent shortest line$

944 S Positive seuence im!edance of adEacent longest line$

ote i. (here a three Ione relay only is available the Ione 3 &ill be set to cover the adEacent longest

line$

EE. The Ional timings &ill be carefully selected to !ro!erly grade &ith the relays on all the

feeders emanating from the adEacent bus$

=1


82/167

=2


83/167

orms of !rotection ado!ted for transmission lines in %$P$+ystemG

i. 132 6/ 4ines G

% s&itched ty!e distance scheme su!!lemented by three numbers directional ,>4 relays and 1 o$

directional *>4 relay$

ii. 22A 6/ 4ines G

T&o "istance +chemes G

ainG7 G onGs&itched scheme fed from bus PT$

ainG77 G % s&itched scheme fed from line C/T$

% !rovision is generally made for the changeover of voltage su!!ly for the distance schemes from

the bus PT to line C/T and viceGversa$

*ach distance scheme is fed from inde!endent CT secondary cores$

iii. :AA 6/ 4inesG

T&o "istance +chemesG

ainG7G onGs&itched or umerical distance schemes

ainG77G onGs&itched or umerical distance schemes

"etails of distance relaysG

1. ake G 0*C %lstom 4td$

=3


84/167

i. 3/ G 7t is an electromagnetic ty!e distance relay &ith

3Gmho measuring units for !hase to !hase faults$

3Gmho measuring units for !hase to earth faults$

3Gmho starting units each starter being associated &ith one !hase and o!erating for

all faults associated &ith that !hase and one offset mho unit for !o&er s&ing

blocking$

G diagram is indicated

+etting range in ohms for 9oneG1

GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG

A$=3: to 3A

1$33) to :=

1$;;= to ;A

92 S 1 to 3$) times 91

93 S 1 to ) times 91GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG

+ome of the schemes are !rovided &ith a 9oneG: timer to make the scheme &orks as a : Ione relay

the starter itself being the :th Ione$

ii. 3/ G

7t is an electromagnetic relays &ith 3 mho units for !hase faults 3 reactance units for earth faults$ 3

mho starters each being associated &ith one !hase for all ty!es of faults and one offset mho unit for

!o&er s&ing blocking$

+etting ranges same as in 3/$

G diagram for !hase faults is same as that for 3/ relay and for earth faults it is indicated infigure

iii. 3/ GY

7t is an electromagnetic relay &ith 3 os$ reactance units for !hase faults 3 reactance units for earth

faults and 3 mho starters !er !hase for all ty!es of faults and one offset mho unit for P+B$ G

diagram is indicated in figure

iv. ++3/ G

=:


85/167

7t is an electromagnetic s&itched scheme &ith t&o version i$e$ &ith mho or under im!edance starter

and available in lo& and high range$

3 under im!edance starters directionalised by mho element or 3 mho element starters and for all ty!es of

fault one reactanceGmeasuring unit for !hase and earth faults$

4o& range relay 91 S A$) to


86/167

?e& versions do not have se!arate IoneG: timer$ 7n such relays IoneG: time S IoneG3 time 1)A msec

-fi#ed builtGin delay.$

v. +HP -Nuadra mho. G

7t is a nonGs&itched static scheme &ith 1= measuring mho units$ The IoneG3 measuring elements &ill act

as starters &hich have either mho or a lenticular characteristic$ The o!erating characteristic on G

diagram is indicated in figure

The lenticular characteristics allo&s healthy overloads and hence !revents tri!!ing on load encroachment$

+etting range G A$2 to 2:A ,hms$

7t has builtGin feature of continuous self monitoring -on demand and !eriodic self testing.$

%ll the additional features !rovided by relay can be enabled or disabled &ith the hel! of s&itches

!rovided for them$

vi. PQT+ G7t is a static s&itched scheme &ith modular !lugGin construction -&ith built in test !oints.$

7t has 3 under im!edance starters and a single mho measuring unit$ ,ne F>7 unit for !o&er s&ing

blocking$ G diagram is indicated in figure

+etting range A$A) to :A ,hms &ith starter having range of 2A to 7 starter &hich has become a !roblem due to load encroachment for long

lines$

The /G7 characteristic of the starter is indicated in above figure$

(hen the voltage is less than ;)O rated the starter o!erates at a current greater than A$2) 7n$ (ith

lo& voltages at some of the stations this feature has caused relay to o!erate unnecessarily$

=;


87/167

vii. ,PT7H,

,!timho distance relay is a nonGs&itched !rotection scheme having 1= com!arators and u!to five

Iones of !rotection -three basic Iones of measurement and t&o for Ione e#tension schemes.

The relay has !artially cross !olarised sha!ed mho characteristics for IoneG1 and IoneG2 !hase units$The IoneG3 for !hase faults have offset lenticular characteristics &hich !ermit the relay to be a!!lied to long

heavily loaded transmission lines &ithout encroachment into the load im!edance$

?or earth faults IoneG1 and IoneG2 units have uadrilateral characteristics &ith inde!endent reaches

in resistive and reactive a#es$ The IoneG3 units are offset uadrilateral$

The IoneG3 units for !hase and earth faults can be chosen for offset or to see in reverse direction$ The

relay characteristic is indicated in ?ig$

,n event of failure of uadrilateral com!arators mho>lenticular com!arators are automatically

enabled but vice versa is not !ossible$ The relay has self testing facility$ 7t has = grou!s of settings and anyone grou! can be set active$

=


88/167

==


89/167

P" 8 )21 G

a. 7t is a numerical !rotection relay &ith !olygon characteristics$

b. 7t consists of four im!edance Iones &ith inde!endent and values for each Ionec. 9one 8 : can be utiliIed as a s!ecial Ione for cabie !rotection$

d. 8 diagram as indicated in figure$

e. Through 7 one can enter and edit the settings -The settings are !ass&ord !rotected.

+etting ange A$1 to 2AAA ,hms$

Timers A to 1A +ecs$

=@


90/167

7C, "7+T%C* *4%Q -%lstom make.

7C, P::A series is a distance scheme &ith advanced numerical technology$ 7C, P::1 and

P::2 relays have five Iones of !hase fault !rotection and five Iones of earth fault !rotection$

a. Ph'6e *'u(t 5rote$t#o&

Phase fault uadrilateral characteristics is sho&n in the figure$

i. 9ones 12 ' 3 8 directional for&ard Iones as used in conventional three Ione distance

schemes$ ote that 9oneG1 can be e#tended to 9oneG1 &hen reuired in 9oneG1 e#tensionscheme$

ii. 9one P 8 Programmable$ +electable as a directional for&ard or reverse Ione$

iii. 9oneG: 8 "irectional reverse Ione$ ote that 9oneG3 and 9oneG: can be set together to give

effectively a for&ard Ione &ith a reverse offset$

@A

one-%

one-%.

one-&

one-/

one-P0programma1le2

one-3

R%ph R&Rp

R/

R3ph

one-%

one-%.

one-&

one-/

one-P0programma1le2

one-3

R%G R& Rp R/

R3G


91/167

$) E'rth F'u(t Prote$t#o&1

*arth fault uadrilateral characteristics is similar to the !hase fault uadrilateral characteristics as

sho&n belo&$ esistive reaches can be set inde!endently for !hase and earth fault !rotections$

%ll earth fault elements are uadrilateral sha!ed and are directionalised similar to the !hase fault

elements$ The im!edance reaches of earth fault elements use residual com!ensation of the

corres!onding !hase fault reaches$

@1


92/167

2. ake G BBC>HBB

i. 49@;

7t is a nonGs&itched scheme &ith 3 underim!edance measuring units common for ground and

3G!hase faults$

3 os$ under im!edance -offset mho. starters one underGim!edance unit for all !ossible

!hase to !hase faults$ G diagram is indicated in figure

?or&ard and reverse reach can be selected inde!endently in starters -&ith IoneG: time

setting.$

+etting range A$1 to 1AA ,hms$

ii. 479; G

7t is a s&itched scheme &ith 3 underGim!edance starters 3 overcurrent starters and one

neutral current starter$ 7t has one reactance measuring unit for all faults$ (ith the !rovision

of angle re!lica unit the relay has s!ecial o!erating characteristic on G diagram indicated

in figure &hich !ermits high loading on long lines$ This being the initial versions of static

relays there have been number of com!onent failure and are being !hased out$

iii. 43 relays G

a. 43(Q+

This relay consists of 3 under im!edance starters and a single directional reactance measuring

unit -C relay.$

7t is four Ione relay the IoneG: starter ste! being nonGdirectional$ Time settings for all the

four Iones -including 9oneG1. can be varied from A$1 to ) seconds$ G diagram is indicated

in figure$

@2


93/167

b. 43&yas G

This is similar to 43(Q+ relay e#ce!t that the F>7 starters are !rovided &ith com!ounding

chokes thereby shifting the circle making it an offset mho as indicated in figures$

7t is also su!!lemented by Qi>4 G !o&er s&ing blocking unit$

iv. 4;ft G

7t is high s!eed single ste! distance relay usually su!!lemented to 43&yas or 43&ys$ 7t is set to

!rotect =AO of line and &ithout any time delay$

@3


94/167

v. Qke>l relay G

This consists of three under im!edance starters used in conEunction &ith 43&yas relays$ By

!rovision of com!ounding chokes the o!erating region of the Qke>l relay is shifted much above the

origin of the G diagram$ The o!erating characteristic of the combination of 43&yas and Qke>l

relay is indicated in figure$

7t may be seen from the diagram that this combination !ermits much higher loading and

!rotects longer lines &ithout any !roblem of load encroachment$

@:


95/167

3. ake %BB G

i. Q9?C G

7t has come into service in the initial stage of the advent of static relays has 3 mho measuring units

for earth faults one mho unit for !hase faults and 3 under im!edance starters$

7n addition this relay has negative seuence current starter &ith a fi#ed setting of 2AO of 7n &hich

causes the relay to tri! in 9oneG:$ The starter can be made to o!erate either as a circle or as oval$

G diagram is indicated in figure$+etting range G 1$= to 2AA ,hms$

a. This relay is found to lose its directional sensitivity for closeby reverse faults and hence not

recommended for use on feeders emanating from generating stations$

b. %lso the negative !hase seuence starter is found to res!ond to very far end faults$

ii. %9,0 G

7t is a s&itched scheme &ith 3 under im!edance starters and one reactance measuring unit$ 7t has

uadrilateral characteristic$

G diagram is indicated in figure$

+etting range A$2) to ;: ,hms$

The starter can be made to o!erate either as a circle or oval$

@)


96/167

iii. %9?*

7t is static three Ione nonGs&itched scheme$

?or ground and 3G!hase faults the distance relay has a reactance like o!erating characteristic the

reactance line being inclined by a fe& degrees to&ards resistance a#is on G diagram &hich!rovides e#cellent margin for high resistance faults and minimises effects of load current and remote

ends infeed on distance measurement G diagram is indicated belo&$

To avoid load encroachment !roblem the relay is !rovided &ith blinder &hich has inde!endent

settings in resistive and reactive directions$

?or !hase to !hase faults mho units are used$

+etting rage A$2) to ;: ,hms$

@;


97/167

iv. %9,% G

7t is a static scheme having 3 under Gim!edance starters and one measuring unit$ The directional

measuring unit has got uadrilateral characteristic &ith inde!endent settings in resistive and reactive

directions$ G diagram is as indicated$

The F>7 starter can be made to o!erate &ith a circle or oval characteristic &ith a selectable

s&itch -+3 1 , for circle ,?? for oval in 09B module.$

0+B odule

"irectional +1 1 G ,??

onGdirectional +1 1 G ,

+etting range A$1; to ;: ,hms$

@


98/167

-v. *49G1AA

7t is a numerical relay &ith uadrilateral im!edance units for !hase and earth faults$ *ach measuring

unit has individual and inde!endent setting of the reach in resistive and reactive directions as &ell as

for the Iero seuence com!ensation factor 6$ *ntire 9oneG3 reach -in for&ard direction. is

available in reverse direction &ith a se!arate timer T3$ G diagram is as indicated

?our grou!s of setting !arameters are !ossible to suit different system conditions$ ,nly one of the

grou!s &ill be in service by choice$ 7t has continuous self monitoring and self testing feature and

indicate the same by e#tinguishing Uelay %vailableU 4*" on the relay$ Through 7 one can

enterD edit the settings read the mean service values of line voltage current real reactive !o&er and

freuency$ 7t stores data of latest 3 disturbances occurred$ -The settings are not !ass&ord !rotected.$

+etting rage A$1 to 1)A ,hms$

Timers A to 1A +ecs$

7t has a feature &hich does overload su!ervision and unsymmetrical load condition &hich can beused for alarm or tri!$

@=


99/167

vi. %"+4 G

This !ilot &ire !rotection scheme used for !rotection of short lines$ 7t is very fast o!erating relay

clearing the faults in 1AAO of line &ithout any time delay$ This is commissioned on 22A 6/ 6T+ VCV

+tation G 6T+ / +tage tie lines 1 ' 2 at both ends as ainG1 !rotection scheme -ainG77 being

*49G1AA relay.$

4ike&ise 0*C make ?%C3: !ilot &ire differential relays are !rovided on 22A 6/ TPC G

%%0F"% tie lines 1 ' 2 &ith backu! ,>4 *>4 relays$

:. ake G Fniversal *lectric

i. "T:)B

7t is a nonGs&itched 3GIone distance scheme &ith 1= measuring units 3 os$ lo& set starters

94 and 3 os$ high set starters 9H$ 7t is available in t&o ranges lo& and high$


a. ?or 4o& rangeeactance easuring units for 9oneG1 ' 9oneG2$

b. ?or High range

ho measuring units for 9oneG1 ' 9oneG2$

@@


100/167

ii. "TB1A1

7t is s&itched scheme &ith 3 im!edance starters one neutral overcurrent starter and one mho

measuring unit$


This relay has a /G7 characteristic similar to that of PQT+ relay$ (hen the voltage is less than

;)O rated the starter o!erates at a current greater than A$2) 7n$

?or 22A 6/ lines the settings on ainG7 distance relay must be on !ar &ith that of ainG77

relay and viceGversa$

?or 132 6/ lines distance relay along &ith directional ,>4 *>4 relays are used$ The

o!erating time of ,>4 *>4 relays for adEacent bus faults are set eual to or more than IoneG2

time of distance relay$

1AA


101/167

). ake G *asun eyrolle G

i. TH:P*2: G

7t is static nonGs&itched scheme &ith 3 for&ard Iones and 1 reverse Ione consists of a total of

2: measuring units$ 12 os$ mho units for IoneG1 ' IoneG2 for !hase and earth faults$ ;

os$ offset mho units for IoneG3 ; os$ ho units for reverse reach$ G diagram is

indicated in figure$

7t has reverse reach set to -c # IoneG1. for !hase faults and -c # IoneG1. -16. for earth

faults 6 being com!ensation factor$ 0enerally c is set eual to V1V$

ii. TH:P*1 G7t is static s&itched scheme &ith 3 offset mho starters and one mho measuring unit$ G

diagram is indicated in the figure$

7t is available in lo& and high ranges G

+etting range G

4o& range G A$A= to @$) ,hms -&ith %A$= to @$;.

High range G A$: to :


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ake G +eimens 4td$


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+*4 8 321 G 7t is numerical relay &ith

a. ?our ho Iones for !hase fau

hand book-1(revised).doc

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