Negative Sequence Protection

7/24/2019 Negative Sequence Protection

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Copyright © SEL 2014

Negative-Sequence

Differential Protection

Principle!" Sen!itivity" an# Security

Bogdan Kasztenny

Normann Fischer

Héctor J. Altuve

Schweitzer Engineering Laboratories, Inc.



$he Nee# for Sen!itivity

• High-resistance line faults

• urn-to-turn faults

♦ ransformers

♦ !enerators

♦ "hunt reactors

• #a$acitor %an& failures



Stator an# %otor $urn-to-$urn &ault!

• "tator turn-to-turn faults

♦ "$lit-$hase $rotection 'hydro(

♦ )ero-se*uence overvoltage 'steam(

• No electrical $rotection for rotor turn-to-turn faults

• +i%ration sensors



'ren(t Stator $urn-to-$urn

&ault! )*plau!i+le,#onstruction indicates that

turn-to-turn faults are im$lausi%le

,e do not $rotect againstturn-to-turn faults

urn-to-turn faults evolve until

detected as ground or $hase faults

,e never see turn-to-turn faults



./ Principle

• "ensitive• Fast

• nherently secure



$he Secret to Sen!itivityDifferential Current,

athematically

/*uivalent

No 012 differential 3 no 014 differential



./ Li*itation



enerator

o#el

• 5igital model

ca$a%le of

simulating stator

turn-to-turn faults

• 67.0 &+8 9:: ,8

!";-connected

• A+< and s$eed

controls



Sa*ple enerator &ault!Stator $urn-to-$urn &ault 35

9

$resent

69: Hz

$resent



Sa*ple enerator &ault!E6ternal &ault

9

$resent

69: Hz

$resent



' %otating $ran!for*er,

"tator 6= ω'rotor( > ω'field( 3 : • ω ? dc in F

"tator 9= ω'rotor( @ ω'field( 3 9 • ω ? 69: Hz in F



Sa*ple enerator &ault!E6ternal &ault

9':Hz(

F'69:Hz(

67

9':Hz(

F'69:Hz(



Sa*ple enerator &ault!Stator $urn-to-$urn &ault

9':Hz(

F'69:Hz(

1 C 67

9':Hz(

F'69:Hz(



)&120 785 9er!u! )2:0 785

<otor

urn-to-urnFaults



Stator &iel# Current ;n+alance



Evolving &ault E6a*ple2refault /Dternal E urn



Evolving &ault E6a*ple :0S&5

9':Hz(

F'69:Hz(



Stator &iel# Current Differential



Evolving &ault E6a*ple .S&5

9':Hz(

F'69:Hz(



Evolving &ault E6a*ple .S&5



Phy!ical achine o#el

• 99: +8 9: &+A8 7 $oles• 9 Gindings $hase8 6:: turns each

• EI slots8 6I60 $itch

• 68 98 78 E8 and 6: turn-to-turn faults

• 2rime mover > induction motor



E6ternal &ault E6a*ple

9':Hz(

F'69:Hz(

IE

9':Hz(

F'69:Hz(



E6ternal &ault E6a*ple

9':Hz(

F'69:Hz(



Stator $urn-to-$urn &ault E6a*ple <5

9':Hz(

F'69:Hz(

E: C IE

9':Hz(

F'69:Hz(



Stator $urn-to-$urn &ault E6a*ple <5

9':Hz(

F'69:Hz(



Conclu!ion!

• Negative-se*uence differential♦ s eDcellent for $rotecting lines and transformers

♦ Needs security for # saturation

♦ #annot detect turn-to-turn faults in stators and

reactors

• :"F and 01"F $rovide very sensitive stator

and rotor turn-to-turn fault $rotection



/ue!tion!,



$he Secret to Sen!itivity%e!training Current,

012 014

oGer restraint $rovides sensitivity %ut challenges security



%e!training Current Purpo!e

<eflect the stress on $rotection systemcom$onents8 #s in $articular8 that can cause

s$urious differential current

=he magnitude of every current that

contri%utes to the differential signal must

contri%ute to the restraining signal

=

Negative-se*uence restraining current

does not meet this re*uirement for

%alanced faults



$he Secret to Sen!itivity'##re!!ing C$ Saturation>

• "ecurity $ro%lems under # saturation

• Need for eDternal fault detection logic



' %otating $ran!for*er,



$urn-to-$urn &ault Protection ?ith <2/



$urn-to-$urn &ault Protection ?ith <2/

urn-to-urn Fault

"ystem Fault



Stator &iel# Current Differential

#om$ensation

Fre*uency Angle



Evolving &ault E6a*ple :0S&5

Documents

Negative Sequence Protection