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Copyright © AEP and SEL 2015

Case Study: Achieving Selectivity ona Critical Distriution !et"or#

Jim Thomas American Electric Power 

 Andrew K. Burich, Michael J. Thompson,and Sneha Vasudevan

Schweitzer Engineering Laboratories, Inc.

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Agenda

• Introduction to AE distri!ution networ"

• #etwor" desi$n challen$es and $oals

•Implemented protection s%stem♦ &ircuit protection

♦ Bus protection

• &ontin$enc% anal%sis

• &onclusion

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$ntroduction to Distriution !et"or#

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Design Challenges and %oals

• T%pical overcurrent radial '(eeder)protection

• *ead+loop networ"

• ault current ma$nitude as (unction

o( location

• rotection $oals♦ Selectivit%

♦ Speed

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Location& Location& Location

Sin$le+-ine+to+round

ault on &ircuit /

Sin$le+-ine+to+round

ault on &ircuit /'Brea"er 0 1pen)

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Circuit Protection Syste'

• 1TT 2 *TT primar% microprocessor+!ased rela%s

•  Alternate microprocessor+!ased and

electromechanical rela%s

• 1TT 2 *TT rela%s consistent with e3istin$

alternate rela%s

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(elay Coordination

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!eed )or Speed

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*us Di))erential Protection

• 4eplacement o( e3istin$ !us protection withtwo+restraint, dual+slope, microprocessor+

!ased rela%s at Su!stations B and &

• Various &+ratin$s on !rea"er &Ts

• -ar$e+ma$nitude (ault currents 5

&T saturation

• 4ecommendations

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E+isting Connections at Sustation *

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(eco''ended Connections

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$n)inite $ncrease in (estraint

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*us Di))erential %oalsDependaility

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*us Di))erential %oalsSecurity

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Sensitivity o) *us ProtectionLarge Slope Settings (esult in

Sacri)ice o) Sensitivity

• aults in volta$e re$ulator 

• 6i$h+impedance !us (aults

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Contingencies

• -oss o( (i!er+optic communications

• -oss o( potential '-1)

• Brea"er (ailure

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!et"or# Co''unications Layout

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L,P at Sustation A -as !o E))ect

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L,P at Sustations * or C A))ects All

(elays at Sustation

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L,P at Sustations * or C A))ects All

(elays at Sustation

• -oss o( all directional elements

• 4eliance on *TT to clear (ault

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*rea#er .ailure

• ro$ramma!le lo$ic+implemented!rea"er (ailure

• -ocal !rea"er (ailure

• *TT to isolate remote end

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! / 2 ContingencyLoss o) .ier,ptic Co''unications and L,P

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Conclusion

• Selectivit% 5 "e% $oal o( protection scheme• &ontin$encies

• Bus di((erential up$rade

♦ &T saturation challen$e

♦ Sensitivit% compromise

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uestions