Transient recovery voltage and rate of rise

Transient recovery voltage

1. INTERNATIONAL COUNCIL
ONLARGE ELECTRIC SYSTEMS
Transient Recovery Voltage (TRV) and Rate of
Rise of Recovery Voltage (RRRV) of Line
Circuit Breakers in Over Compensated
Transmission Lines
Presenter Mark McVey
C4/B5.41

2. This paper will focus on the unique effects
over compensation of transmission lines has
on the Transient Recovery Voltage (TRV) and
Rate of Rise of Recovery Voltage (RRRV) of
Line Circuit Breakers and possible mitigation
techniques.
The findings of this paper are based on time
domain simulations performed on a sample
over compensated system with varying
degrees of compensation levels to
demonstrate how the level of compensation
affects the level TRV and RRRV.
Introduction:

3. As the grid of the future is becoming more complex,
and many countries have issues with adding extra
overhead transmission lines, a solution to add series
compensation to the existing lines has become a
necessity. Series Capacitors allow Transmission System
Owner/Operator to increase the amount of power
transmitted without adding additional lines. The series
capacitors also allows the system to be more stable.
Series Compensation however does have certain
negative effects on the transmission line where it does
increase the Transient Recovery Voltage (TRV) and
also the Rate of Rise of Recovery Voltage (RRRV).
Depending on the level of compensation selected
Series capacitors increase the impact of TRV on Circuit
Breakers. Over compensation of lines while needed,
can make TRV impact challenging.
Certain mitigation techniques can be applied to
overcome these issues. This paper deals with TRV,
RRRV and the results of a system study on this
phenomenon.

4. `
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Different Designs Compensation M ore Than 60 % Or May Be > 100 %
Gapless Triggered Gap

5. Overcompensation:
Degreeofcompensationdefinedintermsofthecapacitivereactanceofthe
S/Ccomparedtotheinductivereactanceoftheline.
Asimpletransmissionlinewithseriescompensationispresentedinfigure1.
Thedegreeofcompensation(KC)inpercentistheratioofthecapacitorreactanceoverline
reactanceasshowninequation(1.1).
Where:
X
c:Totalcapacitiveseriesreactanceinstalledinthelinefromonelineendbreakertothenextlineendbreaker
X
L:Totalinductivelinereactancefromonelineendbreakertothenextlineendbreaker
TransmissionlineovercompensatedwhencompensationdegreeKCisgreaterthan100% .
Figure 1
Eq1.1

6. TheTransientRecoveryVoltage(TRV)is:
•Voltagethatappearsbetweenthecontactsofthecircuitbreakerafterarcextinction
duringopeningprocesswhileclearingafault.
•TheRateofRiseofRecoveryVoltage(RRRV)isdefinedaspeaktransient
recoveryvoltagedividedbythetotaltimefromzerovoltagetopeakvoltage.
•LevelofTRVandtheRRRVarekeyfactorsindeterminingwhetherthefaultcan
beclearedsuccessfully

7. TransientRecoveryVoltage:
TheadditionofseriescapacitorsinatransmissionlinemayaffecttheTransientRecovery
Voltage(TRV)ofLineCircuitBreakers(LCB)inmultipleways:
•Duringfault,seriescapacitorcompensatesthetransmissionlinereactance,
•Loweringtheoverallfaultimpedance
•Increasingthefaultcurrentflowingthroughtheline.Increasesthevoltagerisefromfaulted
endtofarendofline,changinglineSusceptancetohighervoltagelevelsjustbeforecurrent
break,increasingtheTRVontheline-sideoftheLCB.
•TheLCBwillnormallybreakcurrentatazero-currentcrossing,
•IfS/Cnotbypassed,willleavetrappedDCchargeontheS/Cbankwhichwilloffset
theline-sideTRVbytheamountofthattrappedvoltage,increasingthepeakTRV
acrosstheopeningcontactsoftheLCB.
•Thelevelofseriescompensation,expressedasapercentageoftheoveralllinereactance,
affectstheleveloftrappedDCcharge.
•Highercompensationlevel,higherleveloftrappedDCchargethushigherTRV.

8. 0
50000
100000
150000
200000
250000
300000
0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010
Time (Seconds)
Voltage (Volts) TRV Straigtline Envelope
Bypass Switch Recovery Voltage
TRV Recover Voltage Of Bypass Breaker

9. DC Offset During Faults

10. Studysystemandmethodology:
•EHVtransmissionlinesstretchoverhundredsofkilometres.
•InChinatheyreachupto2000km.
•Duetofinitewavetravelingtimes,distinctvoltageshapessuchasTRVmaytravelforth
andbackaline,producingaharmonic/subharmonicoscillationonitsown(e.g.trappedline
charge).
•RepresentingS/Casjustacapacitor,isoversimplifyingtheactualdetails,
•itcanbevarioustypesegFSCorTPSCwithallmethodsbeingequippedwithfurther
protectivedeviceslikeMOV’s,asparkgapandabypassbreaker.
•AsTRVoccursduringtheprocessoffaultclearing,mostoftheseprotectivedeviceshave
alreadyrespondedtothefaultsituation–dependingonlevelandlocationoffault.
•ResponsehastremendousimpactontheTRVlevels:e.g.abypassedS/Cdoesnotinteract
withtheharmonicsinthecircuit.
•Faultsequence:
•Timeoffaultoccurring, instantaneousvoltagesandcurrentsinthesystempriortothefault
needtobeconsidered.
•Faultlocationalsoinfluencesthefaultcurrentsandthecontributingcurrentsacrosstheline
breakers,thereforeeffectsTRV.
•Importanttoconsiderthefaulttype,i.e.single-phase-toground, three-phase,phase-to-phase
withorwithoutground.
•Multipletypesoffaultdevelopmentcanoccur,e.g.asingle-phasefaultthatevolvesintoa
threephasefault.
•Durationofthefaultbeforethecircuitbreakercontactsstartopeningalsohaveaneffect .

11. SC1
39 4
SC1
65 10
25 km 10 km
110 km
55 km
110 km
165 km
12
11
10 km 25 km
Bus A Bus B
Line 2
Line 1
Tap 5
Tap 6
L1SC-A L1SC-5 L1-5 L1-B
L2SC-A L2SC-5 L2-5 L2-B

12. Sampleofresultsandsimulations:
•Asampleofthesimulationsresultsisbelow.Fromthetableand
figures,asthelevelofcompensationisincreased,thepeakTRValso
increased.
•ItcanalsobeseenisthattheaverageRRRVisrelativelyconsistentas
thelevelofcompensationisincreased.
Breaker CompensationLevel MaxTRV(kVpk)
L1SC-A 0% 396.8
60% 648.9
100% 777.5
140% 931.9
L1SC-5 0% 374.0
60% 519.0
100% 550.1
140% 831.4
L2SC-A 0% 467.4
120% 755.3
200% 922.8
280% 1001.1
L2SC-5 0% 356.1
120% 455.7
200% 626.8
280% 797.3

13. Figure 02 –L1SC-A TRV Plot – 0% Compensation
Figure 03 –L1SC-A TRV Plot – 60% Compensation

14. Recommendations and Mitigation:
1.Fastbypass of SC
•Whenfaultdetectedbytheprotectionsystem,acommandtotheCBtoopen
andsimultaneouslytotheSCequipmenttoperformafastSCbypass
operation.
•Uponreceivingthebypasscommand,SCgapwouldbetriggeredtoperform
thebypass–thiswouldoccurifthevoltagebetweenGapcontactsarehigh
enough.
•IntheeventofbypassingtheSCthroughGAPtriggeringTRVcausedby
capacitorimpactcanbereduced.
•ThismeasureisonlyeffectiveifthefaultislargeorclosetotheSCbanks.
2.Reducingthe degreeof Compensation
•Calculationsandtestsshowsthatreducingdegreeofcompensationwill
restrictthepeakvalueofTRV.
•Oneexampleofthisduringopeningofasinglephasetogroundfaultat
BeijingdongSubstation,reducingcompensationfrom40%to25%anduse
ofthefastbypassmeasure,theTRVpeakatXimengCBwasreducedfrom
2440kV to2171kV .
•Thebreakingcurrentisbelow1/4oftheratedCBbreakingcurrentof50
kA
rmsandtheRRRVisbelow1.54kV/µs.

15. RecommendationsandMitigation:
•Dividingthe SC into twoparts –one SC at every terminal
•Use of openingresistorson the CB
`
`
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Pre-Insertion Contact
Shorting Contact
.
(repeated for phases B & C)
R
p
L
p
t
p
t
s
Phase A

16. Over Compensated Series Capacitor High TRV
TRV MOV ArresterMitigation
RecommendationsandMitigation:
MOVandCBinParallel
Bypass SW
Bypass Arrester or Gap
Line Breaker

17. Recommendations and Mitigation:
Changing test requirements of CB TRV amplitude
•CurrentChineseandIECEHV/UHVCBstandard,requiresCB’stowithstandaTRV
peakvalueof2.5p.u.andRRRVof1.54kV/µswheninterrupting25%ofrated
breakingcurrent. ForSClineCB’s,theTRVpeakvalueacrossCBmayexceed2.5
p.u.duringcertainfaultconditions.
•SomeCBmanufacturesdesignedCB’swithhigherTRVwithstandcapabilityand
appliedit.Eg.inTurkeysomeCB’sTRVcapabilityareenhancedtowithstandthe
TRVpeakvalueof3.2p.u.andRRRVof1.54kV/µsforbreakingcurrentof12.5
kA
rms.InCanada’s735kVSCsystem,CB’sareabletowithstand2.8p.u.TRVpeak
valueinordertosatisfythesystemsoperationalrequirements,whichishigherthan
IECstandards.InwesternCanada’s500kVsystem,several500kVSClineCB’scan
withstandTRVpeakvalueof3.3p.u.forbreakingcurrentof6kA
rms.
•FortheChineseUHVSClinesCB’s,whenclearingasinglelinetogroundfault,the
maximumTRVpeakvalueis2.5p.u.,RRRVis1.3kV/µsandsteadystatebreaking
currentislessthan8.5kA
rms.
•Withreferencetotheabovesimulationresults,thehigherTRVtestconditionforEHV
CB’saresuggestedforCB’susedinseriescompensatedtransmissionlines.

18. Conclusionsandfuturework :
Asthelevelofseriescompensationincreasesonagiventransmissionlinesegmenttheseverity
oftheTRValsoincreasesproportionallyandmayexceedthecircuitbreakercapabilityleading
todamageorfailureofthebreakerandpossiblyfurtherdamagetothesystem.Mitigation
approachesareavailablethatcansuccessfullylimitTRV.
Breakingcurrentwillalsoincreasewiththeincreaseindegreeofcompensation.Thisallneeds
tobeincludedinthedesignoftheseriescompensatedsystem
ExtensiveresearchonthissubjecthasbeenperformedbyHydroQuebecandsuggestionswere
madetoincludedmodifiedClassBcircuitbreakerTRVspecificationsw.r.t.testdutiesfor
circuitbreakersusedinseriescompensatedlines.

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