Transmission Line Protection Setting Calculation

7/23/2019 Transmission Line Protection Setting Calculation

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Copyright © SEL 2014

Transmission Line SettingCalculations − Beyond the Cookook

Michael J. Thompson and Daniel L. Heidfeld,

Schweitzer Engineering Laboratories, Inc.



!ntroduction

• Calculations may have 20+ yeas of life

• !tandadi"ed calculations help you

do #ood $o%

• &ou ae moe effective if you undestand

'ac%#ound and philosophies

!denti"y #hen to look eyond the

cookook



$elay Setting %undamentals&e"ining 'er"ormance

• !electivity

• !peed

• !ensitivity



$elay Setting %undamentals&e"ining $eliaility

• Dependa'ility

• !ecuity

• Dependa'ility and secuity♦ (sually invesely elated

♦ )ette schemes can impove 'oth



(E$C )isoperations $eport

• * of misopeations

esulted in false tips

• The est $eefailues to tip o

slo$ tips

• -oal is to educefalse tips $ithout

inceasin# failues

to tip

See "ull report at

nerc*com



The +rt and Science o" Line 'rotection

• e have t$o /%no's to ad1ust♦ !ensitivity each, pic%up, and so on3

♦ Delay

• 4vey settin# affects pefomance

and elia'ility

♦

!et sensitive 'ut not too sensitive♦ !et fast 'ut not too fast



The +rt and Science o" Line 'rotection

• !cience 5 find the limits♦ Dependa'ility

♦ !ecuity

• 6t 5 apply ma#ins

♦ (se appopiate ma#ins fo pecision of

calculation and element♦ 7no$ $hich ma#ins can 'e sacificed and

$hich should not



Contingencies

• 8otection must 'e elia'le fo ♦ Loss of any sin#le element o component 9 5 :3

♦ Hi#h;po'a'ility dou'le contin#encies 9 5 23

• !ome conditions ae altenate nomal,

not contin#encies

• &ou must identify contin#encies appopiatefo chec% at hand



,ood Calculations

• Documentation may have 20+ yea life♦ Desci'e the citeia and contin#encies

♦ <$n evey $od=even if usin# a template

• T$o styles

♦ Calculate a settin# and chec% it

♦

Calculate secuity and dependa'ility limits andchoose a settin#

• 8ut fault study data $ith each element

• !epaate phase and #ound calculations



Line $elaying Schemes +re &esigned

+round %ault Types

• 8hase faults

♦ Loada'ility is a concen

♦

!ystem is 'uilt fo positive;se>uence load flo$

• -ound faults most common3

♦ 8ossi'le hi#h fault esistance

♦ Hi#he ?0 impedance



Transmission Line $elay Schemes

• !tep distance♦ (ndeeachin# elements $ith no delay

♦ <veeachin# elements $ith delay

• Diectional pilot schemes

♦ <veeachin# elements $ith si#nalin#

♦ !i#nals that eithe 'loc% o pemit opeation

• Diffeential



,eneral Calculations

• CT@ selection

• !ouce impedance

atio !A@3

♦ Chec% 9;0

♦ Chec% 9;:

• Loada'ility citeia



(E$C Loadaility



'hase &istance -ones

• !tep ?one :B typically 05*0(ndeeachin#, instantaneous

• !tep ?one 2B typically :205:0<veeachin#, end;"one covea#e $ith delay

• !tep ?one EB typically 200+<veeachin#, time;delayed emote 'ac%up

• 8ilot tippin# "oneCommon to com'ine $ith ?one 2 o ?one E

• 8ilot 'loc%in# "one

Must coodinate $ith emote pilot tippin# "one



'hase &istance -ones.hy &o .e (eed )argin/

• Lines ae typically not physically 'alanced

• !hot lines have moe eo fo an

out;of;"one fault• (ndeeachin# elements must neve

oveeach

• <veeachin# elements must neveundeeach



.hen &o .e &isregard

Cookook )argins/

• !tep ?one :

♦ !hot lines

♦ @adial lines

• !tep ?one 2

♦ Lines $ith tapped 'anches

♦

Lon# F shot line aan#ements

• !tep ?one E

♦ )anch 'eyond a emote shaed 'ea%e

♦ !hot lines



Tapped Branch Eample

• Chec% ? 688 at each tap 'us

• Chec% system nomal and 9 5 : fom

each teminal



Tapped Branch Eample-+'' at Station &



Long Short Line Eample

• Coo%'oo% each on shot lines could causeeGcessive coodination delays

• &ou must incease each on shot line to

assist coodination



'hase &istance 'ilot Tripping -one

• 9um'e of elay elements is limited• !tep ?one 2 o !tep ?one E can 'e eused

as pilot tippin# "one

• Andependent distance element can 'e used

fo moe feedom in settin# each



'hase &istance 'ilot Blocking -one

• 8ilot 'loc%in# "one must 'e moe sensitiveto evese faults than emote elay pilot

tippin# "one

• Coodination is 1ust as impotant fohy'id 8<TT as DC)

• &ou must coodinate cuent supevision

pic%up if CT@s ae diffeent



,round &istance -ones

• !tep ?one :B typically 050(ndeeachin#, instantaneous

• !tep ?one 2B typically :25:0<veeachin#, end;"one covea#e $ith delay

• !tep ?one EB 9F6)ac%up functions ely on I- T<C

• 8ilot tippin# "oneB typically 200+@each same as phase pilot tippin# "one

• 8ilot 'loc%in# "one

Must coodinate $ith emote pilot tippin#



,round &istance -ones.hy &o .e (eed )ore )argin Than 'hase/

• ?eo;se>uence impedance is %no$n $ith

less pecision

• Can 'e difficult to find $ost;case mutual

couplin# effect

• ault esistance can cause oveeach



.hen &o .e &isregard

Cookook )argins/

• !ame as fo phase distance@echec% usin# #ound faults 'ecause EA0 $ill

have diffeent disti'ution than phase cuent

• hen line is mutually coupled



)utual Coupling +""ects $each



)utual Coupling ,round &istanceCheck Conditions "or $emote Bus %ault

• Minimum chec%s

♦ ? 688 unde nomal conditions

♦

? 688 $hen mutually coupled line is out♦ ? 688 $hen mutually coupled line is out

and #ounded

• Conside 'ute foce method♦ (se fault study to un 9;: cases t$o ties out

♦ Chec% fo minimums and maGimums



,round 3ercurrent

• Most uncetainty in "eo;se>uence net$o%• Hi#he "eo;se>uence line impedance

• Hi#h fault esistance possi'le

• !peed dichotomy

♦ Little impact on sta'ility and po$e >uality

♦ Hi#h impact on pu'lic safety



,round 3ercurrent Elements

• Anstantaneous ovecuent♦ !ecuityB :0 of maGimum eGtenal fault

cuent 9 5 23

♦ Dependa'ilityB :0 pic%up fo close;in fault

• Anvese;time ovecuent

♦ !ecuityB a'ove :0 $inte eme#ency

♦ Dependa'ilityB 200KE00 pic%up fo minimum

intenal fault

• 6utomated coodination fo time dial



'ilot ,round 3ercurrent

• 8ilot 'loc%in# element 5 set it lo$ 'uta'ove :0 $inte eme#ency

• 8ilot tippin# element

♦ !ecuityB 200 ma#in $ith emote pilot

'loc%in#

♦ Dependa'ilityB 200 pic%up fo minimum

intenal fault

• Ma#in ad1ustment if lo$e pic%up

is needed



!mpedance5Based &irectional Element

• 4lement measues souce impedanceto fault

• o evese faults, impedance is in font

of elay♦ Measued value is at least the line impedance

♦ )ounday 'et$een fo$ad and evese is half

line impedance



&o (ot 6se +utomatic Settings .hen7

• Thee is lo$ o no line impedance• 8ilot tippin# o pilot 'loc%in# pic%ups ae

'elo$ default cuent thesholds

• 6 pilot scheme is used and CT@s ae

diffeent at each teminal

•&ou ae potectin# seies;compensated othee;teminal lines



Summary

• Detemine if coo%'oo% settin#s can 'eapplied to potected line

• Calculate appopiate secuity and

dependa'ility limits

• 7no$ $hen to not use 6(T< diectional

settin#s

• (se thoou#h documentation to ecod

you easonin#



8uestions/

Transmission Line Protection Setting Calculation

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