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I
A
SEMINAR
ON
“SURGECURRENTPROTECTIONUSINGSUPERCONDUCTOR”
Submittedinpartialfulfillmentforbachelorof
technologyDegreeat
RajasthanTechnicalUniversity,Kota
BACHELOROFTECHNOLOGY
IN
ELECTRICALENGINEERING
SUPERVISEDBY: SUBMITTEDBY:
Prof.ASADZAI SARFARAZKHAN
RollNo.-13EVEEE051
Enrl.No.-13E1VEEEM3XP051
DEPARTMENTOFELECTRICALENGINEERING
VYASINSTITUTEOFENGINEERINGANDTECHNOLOGY,JODHPUR
RAJASTHANTECHNICALUNIVERSITY,KOTA
II
2017
CERTIFICATE
ThisistocertifythatthestudentMr.SarfarazKhanoffinalyear,have
successfullycompletedtheseminarpresentationon“SURGECURRENT
PROTECTIONUSINGSUPERCONDUCTOR”towardsthepartialfulfillment
ofthedegreeofBachelors ofTechnology(B.TECH)intheElectrical
EngineeringoftheRajasthanTechnicalUniversityduringacademicyear
2017undermysupervision.
Theworkpresentedinthisseminarhasnotbeensubmittedelsewherefor
awardofanyotherdiplomaordegree.
Prof.AsadZai
Supervisor
Professor
Deptt.ofElectricalEngineering
VIET,Jodhpur.
CounterSignedby:
Prof.ManishBhati
Head
Deptt.ofElectricalEngg.
VIET,Jodhpur.
III
ACKNOWLEDGEMENT
FirstIwanttothankmy
“ALLAH”
who neverleavesmealonein bad circumstances,help me
alwayswiththeirwellblessings.
Thereareanumberofpeoplewhodeserverecognitionfortheir
unwavering supportand guidance throughoutthis seminar
presentation.Iwouldliketotakethisopportunitytothankthem.
Firstandforemost,Iwanttothankmywell-wisheradvisorandas
aguide,Mr.AsadZaiSirforhissupport,constructivecriticism,
andnew technicalupdates.Thispresentationcouldhavenot
beencompletedwithouthisenthusiasmanddirection.
IagainwanttothankMr.AsadSirforgivingmethistypeof
technicaltheorytopicbywhichIcanunderstandmycorebranch
efficiently.
IwillbealwaysthankfultoOurHODMr.ManishBhatiSirfor
expandingmyunderstandingofglobalinequalitiesthroughout
historyandherconstantmentorship.
Iwanttothankmyfriendswhohaveencouragedmeoverthe
studyofthispresentation.
Finally,Iwanttothankmyfamily.Myparents,especially,have
beenasourceofstrengthandsupportforme.Theycontinually
pushmetothinkcriticallyandneversettleforanythinglessthan
mybest.Theykeptmefocused,ontrackandfedinthefinal
stretchofmycollegestudy.
Fortheircontinualsupport,Iamforevergrateful.
IV
ABSTRACT
ModernPowerSystemsaregrowingfastwithmoregenerators,
transformersandlargenetworkinthesystems.Theinstallation,
runningandmaintenancecostsofthepowersystem equipment
aremore.Wheneverafaultoccurs,thereisaneed forthe
protection ofthese systems.PowerSystem Protection is a
branch ofelectricalpowerengineering thatdeals with the
protectionofelectricalpowersystemsfrom faultsthroughthe
isolationoffaultedpartsfrom therestoftheelectricalnetwork.
Superconductorsareoneofthelastgreatfrontiersofscientific
discovery.Here,in thispaperwediscusstheuseofSuper
ConductorsasprotectivedevicesforSurgeCurrentProtection.
Superconductors conductelectricity offering zero resistance
below certaintemperatures.Westudydifferenttypesofsuper
conductorfaultcurrentlimitersandtheirworking.
V
LISTOFFIGURES
Fig.-(1.2)-Graphb/winrushcurrentand
time.........................................10
Fig.-(2.6)-Faultcontrolwithafault-current
limiter................................13
Fig.-(2.7.1)-Fault-currentlimiterinthemain
position...........................14
Fig.-(2.7.2)-Fault-currentlimiterinthefeeder
position.........................15
Fig.-(2.7.3)-Fault-currentlimiterinthebus-tie
position.........................15
Fig.-(2.8.1)-Fault-currentlimiterwithHTStrigger
coil.........................19
Fig.-(2.8.2)-Inductivefault-current
limiter.............................................20
Fig-(2.9.1)-SchematicdiagramoftheCRIEPIinductive
FCL..............22
Fig.-(2.9.2)-ConfigurationofcoilsintheTEPCO/Toshiba
FCL............23
Fig.-(2.9.3)-Exteriorviewofthe6.6kV2,000A-classcurrent
limiter..24
VI
Fig.-(2.9.4)-CurrentlimitingcharacteristicsofToshiba
FCL.................24
Fig.-(3.1)-Lightening
surge....................................................................26
Fig.-(4.1)-Powerratingoftheinductivelimitermodels
built/tested
atHydro
Quebec.....................................................................33
CONTENTS
INNERTITLE………………………………………………………………...I
CERTIFICATE……………………………………………………………….II
ACKNOWLEDGEMENT…………………………………………………...III
ABSTRACT…………………………………………………………………..IV
LISTOF
FIGURES...........................................................................................V
CONTENTS………………………………………………………………VI-VII
Chapter1:Introduction………………………………………………………8
1.1:Introduction…………………………………………………….8
1.2:SurgeCurrent…………………………………………………..9
VII
Chapter2:Superconductor…………………………………………………..11
2.1:Superconductor………………………………………………...11
2.2:MeissnerEffect…………………………………………………11
2.3:FaultCurrentLimiter…………………………………………12
2.4:FaultCurrentProblem………………………………………...12
2.5:FaultControlProblem…………………………………………13
2.6:SuperconductiveFcl……………………………………………13
2.7:FaultCurrentLimiterApplications…………………………..14
2.8:SuperconductiveFaultCurrentLimiterConcepts…………..16
2.8.1:SeriesResistiveLimiter………………………........................16
2.8.2:InductiveLimiter………………………………......................19
2.9:FclProgram……………………………………………………..20
Chapter3:LighteningProtection…………………………………………….25
3.1:ComponentsOfLighteningProtectionSystem……………….25
3.1.1:RodsOrAirTerminals……………………………………….25
3.1.2:ConductorCables……………………………………………..25
3.1.3:GroundRods……………………………………......................25
3.2:LighteningProtectionSystem…………………………………..26
3.2.1:HowALighteningProtectionSystemWorks……………….27
3.2.2:LighteningProtectionFacts…………………………………..28
3.2.3:LighteningDissipationMyths………………………………...28
3.3:FuturePlans……………………………………...........................30
3.4:FaultCurrentLimiter……………………………………...........30
3.5:FclPrograms……………………………………………………..31
Chapter4:AdvantagesDisadvantagesAndLimitationsOf
Superconductor.33
4.1:Advantages……………………………………...............................33
4.2:Limitations……………………………………...............................35
4.3:Disadvantages……………………………………..........................35
Chapter5:Applications…………………………………………………………38
VIII
5.1:BasicApplications……………………………………...................38
5.1.1:LowTemperatureSuperconductivity…………………………38
5.1.2:ParticleAcceleratorsAndMagneticFusion
Devices…………39
5.1.3:HighTemperatureSuperconductivity………………………..39
5.1.4:HtsBasedSystems……………………………………...............40
Chapter6:FutureAspects………………………………………………………41
6.1:SuperconductivityTransmissionLines………………………….41
6.2:PowerApplications,HighTc……………………………………..41
6.3:FaultCurrentLimiter…………………………………….............42
6.4:SuperconductingMotors……………………………………........42
6.5:SuperconductingMaglevTrains…………………………………42
CONCLUSION:
....................................................................................................46
REFERENCES:
....................................................................................................47
CHAPTER-1
Introduction
1.1Introduction
Beforeknowinghowthesuperconductorsactsassurgecurrentprotectors
9
letus
concentrateonwhatissurgecurrent?Whatitdoestothepowersystem?And
whatare
superconductors?MeissnerEffectanddifferenttypesofsuperconductor
faultcurrent limiters.
Electricpowerdistributionsystemsincludecircuitbreakerstodisconnect
powerincaseofafault,buttomaximizereliability,theywishtodisconnect
thesmallestpossibleportionofthenetwork.Thismeansthateventhe
smallestcircuitbreakers,aswellasallwiringtothem,mustbeableto
disconnectlargefaultcurrents.
A problem arises ifthe electricitysupplyis upgraded,byadding new
generationcapacityorbyaddingcross-connections.Becausetheseincrease
theamountofpowerthatcanbesupplied,allofthebranchcircuitsmust
havetheirbusbarsandcircuitbreakersupgradedtohandlethenewhigher
faultcurrentlimit.
Thisposesaparticularproblem whendistributedgeneration,suchaswind
farmsandrooftopsolarpower,isaddedtoanexistingelectricgrid.Itis
desirabletobeabletoaddadditionalpowersourceswithoutlargesystem-
wideupgrades.
Asimplesolutionistoaddelectricalimpedancetothecircuit.Thislimitsthe
rateatwhichcurrentcanincrease,whichlimitsthelevelthefaultcurrentcan
risetobeforethebreakerisopened.However,thisalsolimitstheabilityofthe
circuittosatisfyrapidlychangingdemand,sotheadditionorremovaloflarge
loadscausesunstablepower.
Afaultcurrentlimiterisanonlinearelementwhichhasalowimpedanceat
normalcurrentlevels,butpresentsahigherimpedanceatfaultcurrentlevels.
10
Further,thischangeisextremelyrapid,beforeacircuitbreakercantripafew
millisecond later.(High-powercircuitbreakers are synchronized to the
alternatingcurrentzerocrossingtominimizearcing.)
Whilethepowerisunstableduringthefault,itisnotcompletelydisconnected.
After the faulting branch is disconnected,the fault current limiter
automaticallyreturnstonormaloperation.
1.2SurgeCurrent
Themaximum instantaneousinputcurrentdrawnbyanelectricaldevice
whenfirstitisturnedonisdefinedassurgecurrent.Itisalsoknownas
InrushcurrentorInputSurgeCurrentorSwitch-onSurge.Alternatingcurrent
electricmotorsandtransformersmaydrawseveraltimestheirnormalfull-
loadcurrentwhenfirstenergized,forafew cyclesoftheinputwaveform.
Powerconvertersalsooftenhaveinrushcurrentsmuchhigherthantheir
steadystatecurrents,duetothechargingcurrentoftheinputcapacitance.
Theselectionofovercurrentprotectiondevicessuchasfusesandcircuit
breakersismademorecomplicatedwhenhighinrushcurrentsmustbe
tolerated.Theovercurrentprotectionmustreactquicklytooverloadorshort
circuitbutmustnotinterruptthecircuitwhenthe(usuallyharmless)inrush
currentflows.
11
Fig.-(1.2)-Graphb/winrushcurrentandtime
Theonlylimitsofthesurgecurrentarethelineimpedance,inputrectifierdrop
andthecapacitorequivalentseriesresistance.Highinrushcurrentcanaffectthe
electricalsystemsbytrippingfusesandcircuitbreakersunnecessarily.Ifinrush
protectionisnotinplace,relaysandcircuitbreakersmustberatedthatarerated
higherthananypossibleinrushcurrent.InrushCurrentcanalsocausepitted
contactsonswitchesandrelaysduetoarcingofthecontacts.InrushCurrent
canbeashighas100timesthenormalsteadystatecurrentandlastsforless
thanhalfanormal60hertzcycle.Thissurgecurrentcancausecomponent
damageand/orfailurewithintheequipmentitself,blownfuses,trippedcircuit
breakersandmayseverelylimitthenumberofdevicesconnectedtoacommon
powersource.
12
CHAPTER-2
SUPERCONDUCTOR
2.1Superconductor
Anelement,inter-metallicalloyorcompoundthatwillconductelectricity
without
resistance below a certain temperature.The Dutch Physicist Heike
KamerlinghOnnesofLeidenUniversitywasthefirstpersontoobserve
superconductivityinmercury.
Superconductivityisaphenomenonofexactlyzeroelectricalresistance
certainmaterialswhencooledbelowacharacteristiccriticaltemperature.It
isaquantummechanicalphenomenon.
TypesofSuperconductors:
LowTemperatureSuperconductor
HightemperatureSuperconductors
LTSarethesubstancesthatloseallresistivitycloseto4K,atemperature
attainableonlybyliquid helium.HTS arethesubstancesthatloseall
resistancebelowtemperaturemaintamablebyliquidnitrogen.
 ExamplesofLTS:LeadandMercury
 ExamplesofHTS:YBCO,BSCCO,LSCO,etc.
2.2MeissnerEffect
The Meissner effectis the expulsion ofthe magnetic field from a
superconductor
duringitstransitiontothesuperconductingstate.TheGermanphysicists
13
Walther
MeissnerandRobertOchsenfelddiscoveredthephenomenonin1933by
measuringthemagneticfielddistributionoutsidesuperconductingtinand
leadsamples.Themagneticfluxisconservedbythesuperconductor,when
theinteriorfielddecreasedtheexternalfieldisincreased.
2.3FaultCurrentLimiter
AFaultCurrentLimiterisadevicewhichlimitstheprospectivefaultcurrent
whenafaultoccurs.Generallyfaultcurrentlimitersaresuperconductorfault
currentlimiters.SuperconductingFaultCurrentLimitersaredescribedas
beinginoneofthetwomajorcategories:
Resistive
Inductive
FirstapplicationsforFCLsarelikelytobeusedtohelpcontrolmedium-
voltage
electricity distribution systems,followed by electric-drive ships:naval
vessels,
submarinesandcruiseships.LargerFCLsmayeventuallybeemployedin
highvoltagetransmissionsystems.
Fault-currentlimiters using high temperature superconductors offera
solution to controlling fault-current levels on utility distribution and
transmissionnetworks.Thesefault-currentlimiters,unlikereactorsorhigh-
impedancetransformers,willlimitfaultcurrentswithoutaddingimpedance
tothecircuitduringnormaloperation.Developmentofsuperconductingfault
-currentlimiters is being pursued by severalutilities and electrical
manufacturersaroundtheworld,andcommercialequipmentisexpectedto
beavailablebytheturnofthecentury.[1]
14
2.4Fault-CurrentProblem
Electricpowersystem designersoftenfacefault-currentproblemswhen
expanding
existingbuses.Largertransformersresultinhigherfault-dutylevels,forcing
the
replacementofexistingbusworkandswitchgearnotratedforthenewfault
duty.
Alternatively,theexistingbuscanbebrokenandservedbytwoormore
smaller
transformers.Anotheralternativeisuseofasingle,large,high-impedance
transformer,resultingindegradedvoltageregulationforallthecustomerson
thebus.Theclassictradeoffbetweenfaultcontrol,buscapacity,andsystem
stiffnesshaspersistedfordecades.
2.5FaultControlProblem
Insomeareas,suchastheUnitedStates,additionalgenerationfrom co
generators
andindependentpowerproducers(IPPs)raisesthefaultdutythroughouta
system
olderbutstilloperationalequipmentgraduallybecomesunderratedthrough
system growth;someequipment,such astransformersin underground
vaultsorcables,canbeveryexpensivetoreplacecustomersrequestparallel
servicesthatenhancethereliabilityoftheirsupplybutraisethefaultduty.
2.6SuperconductiveFCL
Superconductorsofferawaytobreakthroughsystem designconstraintsby
presenting
15
impedanceto theelectricalsystem thatvariesdepending on operating
conditions.
Superconductingfault-currentlimitersnormallyoperatewithlowimpedance
andare
"invisible"componentsintheelectricalsystem.Intheeventofafault,the
limiterinsertsimpedanceintothecircuitandlimitsthefaultcurrent.With
currentlimiters,theutilitycanprovidealow-impedance,stiffsystem witha
lowfault-currentlevel.
Fig.-(2.6)-Faultcontrolwithafault-currentlimiter
Alarge,low-impedancetransformerisusedtofeedabus.Normally,theFCL
doesnotaffectthecircuit.Intheeventofafault,thelimiterdevelopsan
impedanceof0.2perunit(Z=20%),andthefaultcurrentISCisreducedto
7,400 A.Withoutthelimiter,thefaultcurrentwould be37,000 A.The
developmentofhigh temperature superconductors (HTS)enables the
developmentofeconomicalfault-currentlimiters.Superconductingfault-
currentlimiterswerefirststudiedovertwentyyearsago.Theearliestdesigns
used low temperature superconductors (LTS),materials thatlose all
resistanceattemperaturesafewdegreesaboveabsolutezero.LTSmaterials
aregenerallycooledwithliquidhelium,asubstancebothexpensiveand
16
difficult to handle. The discovery in 1986 of high temperature
superconductors,whichoperateathighertemperaturesandcanbecooledby
relativelyinexpensiveliquidnitrogen,renewedinterestinsuperconducting
fault-currentlimiters.[2]
2.7Fault-CurrentLimiterApplications
Fault-currentlimiters can be applied in a numberofdistribution or
transmissionareas.
The fault-currentlimiterFCL protects an individualcircuiton the bus.
Underratedequipmentcanbeselectivelyprotectedasneededinthismanner.
Fig.-(2.7.1)-Fault-currentlimiterinthemainposition
17
Fig.(2.7.2)-Fault-currentlimiterinthefeederposition
Thetwobusesaretied,yetafaultedbusreceivesthefullfaultcurrentofonly
onetransformer.Thetwobusesaretied,yetafaultedbusreceivesthefull
faultcurrentofonlyonetransformer.
Fig.-(2.7.3)-Fault-currentlimiterinthebus-tieposition.
Themostdirectapplicationofafault-currentlimiterisinthemainpositionon
abusBenefitsofanFCLinthisapplicationincludethefollowing:
 Alargertransformercanbeusedtomeetincreaseddemandonabuswithout
breakerupgrades
 A large,low impedance transformercan be used to maintain voltage
18
regulationatthenewpowerlevel
 I
2
tdamagetothetransformerislimited
 Reduced fault-currentflows in the high-voltage circuitthatfeeds the
transformer,whichminimizesthevoltagedipontheupstream high-voltage
busduringafaultonthemedium-voltagebus
AnFCLcanalsobeusedtoprotectindividualloadsonthebus(Fig.4.7).The
selectiveapplicationofsmallandlessexpensivelimiterscanbeusedto
protectold
oroverstressedequipmentthatisdifficulttoreplace,suchasunderground
cablesor
transformersinvaults.AnFCLcanbeusedinthebus-tieposition(Fig.4.8).
Suchalimiterwouldrequireonly
Asmallloadcurrentratingbutwoulddeliverthefollowingbenefits:
 separatebusescanbetiedtogetherwithoutalargeincreaseinthefaultduty
on
eitherbus.
 duringafault,alargevoltagedropacrossthelimitermaintainsvoltagelevel
on
theunfaultedbus.
 theparalleledtransformersresultinlowsystemimpedanceandgoodvoltage
regulation;tap-changingtransformerscanbeavoided.
 excesscapacityofeachbusisavailabletobothbuses,thusmakingbetter
useof thetransformerrating.
2.8SuperconductiveFault-CurrentLimiterConcepts
2.8.1TheSeriesResistiveLimiter
19
Thesimplestsuperconductinglimiterconcept,theseriesresistivelimiter,
exploitsthe
nonlinearresistanceofsuperconductorsinadirectway.Asuperconductoris
insertedinthecircuit.Forafull-loadcurrentofIFL,thesuperconductorwould
bedesignedtohaveacriticalcurrentof2IFLor3IFL.Duringafault,thefault
currentpushesthesuperconductorintoaresistivestateandresistanceR
appearsinthecircuit.
Superconductingfaultcurrentlimitersexploittheextremelyrapidlossof
superconductivity (called "quenching)above a criticalcombination of
temperature,currentdensity,andmagneticfield.Innormaloperation,current
flows through the superconductor without resistance and negligible
impedance.
Ifafaultdevelops,thesuperconductorquenches,itsresistancerisessharply,
andcurrentisdivertedtoaparallelcircuitwiththedesiredhigherimpedance.
(Thestructureisnotusableasacircuitbreaker,becausethenormally-
conducting superconductive materialdoes not have a high enough
resistance.Itisonlyhighenoughtocausesufficientheatingtomeltthe
material.)
Superconductingfaultcurrentlimitersaredescribedasbeinginoneoftwo
majorcategories:resistiveorinductive.
InaresistiveFCL,thecurrentpassesdirectlythroughthesuperconductor.
Whenitquenches,thesharpriseinresistancereducesthefaultcurrentfrom
whatitwouldotherwisebe(theprospectivefaultcurrent).AresistiveFCLcan
beeitherDCorAC.IfitisAC,thentherewillbeasteadypowerdissipation
from AClosses(superconductinghysteresislosses)whichmustberemoved
20
bythecryogenicsystem.AnACFCLisusuallymadefrom wirewoundnon-
inductively;otherwisetheinductanceofthedevicewouldcreateanextra
constantpowerlossonthesystem.
InductiveFCLscomeinmanyvariants,butthebasicconceptisatransformer
witharesistiveFCLasthesecondary.Inun-faultedoperation,thereisno
resistanceinthesecondaryandsotheinductanceofthedeviceislow.Afault
currentquenchesthesuperconductor,thesecondarybecomesresistiveand
theinductanceofthewholedevicerises.Theadvantageofthisdesignisthat
thereisnoheatingressthroughcurrentleadsintothesuperconductor,and
sothecryogenicpowerloadmaybelower.However,thelargeamountofiron
required meansthatinductiveFCLsaremuch biggerand heavierthan
resistiveFCLs.
Thequenchprocessisatwo-stepprocess.First,asmallregionquenches
directlyinresponsetoahighcurrentdensity.Thissectionrapidlyheatsby
Joule heating,and the increase in temperature quenches adjacent
regions.
[promotional language]
GridON Ltd has developed the firstcommercial
inductiveFCLfordistribution&transmissionnetworks.Usingauniqueand
proprietary concept of magnetic-flux alteration - requiring no
superconducting or cryogenic components - the self-triggered FCL
instantaneouslyincreasesitsimpedancetenfold upon faultcondition.It
limitsthefaultcurrentforitsentiredurationandrecoverstoitsnormal
conditionimmediatelythereafter.ThisinductiveFCLisscalabletoextrahigh
voltageratings.
Thesuperconductorinitsresistivestatecanalsobeusedasatriggercoil,
pushingthe
bulkofthefaultcurrentthrougharesistororinductor.Theadvantageofthis
21
configuration,showninFig.4.9,isthatitthelimitstheenergythatmustbe
absorbedbythesuperconductor.Thefault-currentlimiterFCLnormallyisa
shortacrossthecopperinductiveorresistiveelementZ.Duringafault,the
resistancedevelopedinthelimitershuntsthecurrentthroughZ,which
absorbsmostofthefaultenergy.
Fig.-(2.8.1)-Fault-currentlimiterwithHTStriggercoil
Thetriggercoilapproachisappropriatefortransmissionlineapplications,
wheretensofmegawatt-secondswouldbeabsorbedinaseriesresistive
limiter.Thetriggercoil
configurationalsoallowsanimpedanceofanyphaseangle,from purely
resistiveto
almostpurelyinductive,tobeinsertedintheline.
2.8.2TheInductiveLimiter
Anotherconceptusesaresistivelimiteronatransformersecondary,withthe
primaryinseriesinthecircuit.Thisconcept,illustratedinFig.4.10,yieldsa
limitersuitableforhigh-currentcircuits(IL>1000A).Onephaseofthelimiter
22
isshown.AcopperwindingWCuisinsertedinthecircuitandiscoupledtoan
HTSwindingWHTS.Duringnormaloperation,zeroimpedanceisreflectedto
theprimary.ResistancedevelopedintheHTS windingduringafaultis
reflectedtotheprimaryandlimitsthefault.
Fig.-(2.8.2)-Inductivefault-currentlimiter
Theinductivelimitercanbemodeledasatransformer.Theimpedanceofthis
limiterinthesteadystateisnearlyzero,sincethezeroimpedanceofthe
secondary(HTS)windingisreflectedtotheprimary.Intheeventofafault,
thelargecurrentinthecircuitinducesalargecurrentinthesecondaryand
thewindinglosessuperconductivity.Theresistanceinthesecondaryis
reflectedintothecircuitandlimitsthefault.
2.9FCLProgram
ThedrivingfactorsforcurrentlimitersinJapanaresomewhatdifferentfrom
thoseintheUnitedStates,giventhatIPPsandcogeneratorsarenotas
prevalentinJapan.Rather,thedemandforpowerinJapanesemetropolitan
areas continues to grow because ofeconomic growth and increased
23
consumeruseofelectricity.Inaddition,industrialuseofcomputersandother
power-quality-sensitiveequipmenthasforcedtheutilitiestoprovidehigher
qualityandmorereliablepower.Thequitesuccessfulapproachtoimproved
powerqualityinJapanhasbeentoincreaseconnectionsbetweenvarious
powersystems and to concentrate generation capacityin larger,more
efficientunits.
Increasing interconnection does,however,increase the maximum fault
currentavailableatanypointinthesystem,andthisisrapidlyleadingtothe
need forbreakerupgradesand system reconfigurations.Adding to the
complexityofthesituationinJapanisthelimitedroom atsubstationsites,
whichcanprecludebreakerupgrades.
Theprimaryneed,asexpressedbymanagementoftheTokyoElectricPower
Company (TEPCO),is fora limiterforthe nucleus ofthe Japanese
transmissionsystem,the500kVtransmissiongrids.Inresponsetothisreal
marketpulltherehasbeenaseriesofprogramstodevelopfaultcurrent
limitersusingavarietyofmethods,withrecentfocusonsuperconducting
limiters(Nakade1994).AlthoughFCLsarenotacomponentoftheNEDO
budget,TEPCOhasreportedthatitspendsabout¥100millionperyear(~$1
million)onthisprogram,andsomeresistiveFCLworkisapparentlyincluded
intheNEDObudgetunderthetopic"ResearchofSuperconductingMaterials
andDevices”.Inthelate1980s,SeikeiUniversitymanufacturedasmall-scale
three-phasecurrentlimitingreactoranddemonstratedsuccessfuloperation.
Thisthree-phasesystem introducesalargeunbalancedreactanceinthe
system tolimitcurrentsinthecaseofasingle-phaseshortandquenchesto
introduceresistanceinthecircuitinthecaseofathree-phasefault.
24
MitsubishiElectricCompany(MELCO)hasbeenparticipatinginaMITI/NEDO
FCL
programsince1990.ThisisaresistivelimiterapproachusingHTSfilmsona
strontiumtitanatesubstratethathasdemonstratedlimitingof400Acurrents
to11.3A.TheCentralResearchInstituteoftheElectricPowerIndustry
(CRIEPI)hasdevelopedtheinductivelimitershowninFig.4.11(Ichikawaand
Okazaki1995).Thisapproach,similartothoseofABBandSiemens-Hydro
Quebec,usesacylinderofbulkBSCCO-2212orBSCCO-2223toseparatea
normalcoppercoilfrom anironcore.Innormaloperation,thefieldfrom the
coppercoildoesnotpenetratethesuperconductor;underfaultconditions,
however,thecurrentinducedinthesuperconductorissufficienttodriveit
normal,andthemagneticfieldlinkstheironyoke.Thisgreatlyincreasesthe
inductanceofthecoppercoil,thusprovidingcurrentlimiting.CRIEPIwork
hasfocusedonacmagneticshieldingperformanceofbulksuperconductors
andtheirresponsestofaultcurrents.
Inaddition,introductionofa"controlring"inthesystem toabsorbsomeof
theenergydepositedduringafaulthasreducedthecooldowntimeofthe
shieldfollowingafaultedstate.ThemostextensiveFCLprogram inJapan
hasbeenthecollaborationbetweenTEPCOandToshiba.Thelong-term goal
ofthisprogram isthedevelopmentofa500kVlimiterwitharatedcurrentof
8,000A.Initialdevelopmenthasbeenfocusedonadistributionlevellimiter
designedfor6.6kV.
25
Fig.(2.9.1)-SchematicdiagramoftheCRIEPIinductiveFCL
AsshowninFig.4.12,theFCLisformedbyconnectingfoursuperconducting
coilsinaseries-parallelconfigurationsothetotalinductanceisminimized.
Onesetofcoilsisused foreach phaseofthedevice,and limiting is
accomplishedbyquenchingthecoils.
ThecurrentversionoftheFCLshowninFig.4.13usesaspeciallowacloss
Nb-Ti
conductor.Testsinacircuitwithanominalshortcircuitcurrentof25.8kA
havesuccessfullydemonstratedlimitingtoabout4,000amps(Fig.4.14).
26
Fig.(2.9.2)-ConfigurationofcoilsintheTEPCO/ToshibaFCL
RecentworkhasincludedtheintroductionofHTScurrentleadstoreducethe
refrigerationloadofthesystem tolevelsthatcanbehandledbya4KGifford
McMahonrefrigerator.[3]
Fig.(2.9.3)-Exteriorviewofthe6.6kV2,000A-classcurrentlimiter
27
Overthreegenerationsofthedevice,theheatleakhasbeenreducedfrom
13.8wattsto3.4watts,whichisnearingtherequiredlevel.
Fig.(2.9.4)-CurrentlimitingcharacteristicsofToshibaFCL
CHAPTER-3
LighteningProtection
3.1Componentsofalightningprotectionsystem
Lightningrodsor'airterminals'areonlyasmallpartofacompletelightning
protectionsystem.Infact,therodsmayplaytheleastimportantroleina
system installation.Alightningprotectionsystem iscomposedofthreemain
components:
3.1.1RodsorAirTerminals
Thesmall,verticalprotrusionsdesignedtoactasthe'terminal'foralightning
28
discharge.Rodscanbefoundindifferentshapes,sizesanddesigns.Most
aretoppedwithatall,pointedneedleorasmooth,polishedsphere.The
funtionalityofdifferenttypesoflightningrods,andeventheneccessityof
rodsaltogether,aresubjectsof
manyscientificdebates. 
3.1.2ConductorCables
Heavycables(right)thatcarrylightningcurrentfrom therodstotheground.
Cablesarerunalongthetopsandaroundtheedgesofroofs,thendownone
ormorecorners
 ofabuildingtothegroundrod(s).
3.1.3GroundRods
Long,thick,heavyrodsburied deep into theearth around a protected
structure.The conductorcablesareconnectedtotheserodstocompletea
safepathforalightningdischargearoundastructure.
Theconductorcablesandgroundrodsarethemostimportantcomponents
ofa lightning protection system,accomplishing the main objective of
diverting lightning currentsafely pasta structure.The 'lightning rods'
themselves,thatis,thepointyvertically-orientedterminalsalongtheedgesof
roofs,donotplaymuchofaroleinthefunctionalityofthesystem.Afull
protectionsetup,givengoodcablecoverageandgoodgrounding,wouldstill
worksufficientlywithouttheairterminals.
29
Fig.(3.1)-Lighteningsurge
3.2Lightningprotectionsystems-Whattheydoanddon'tdo
Alightningprotectionsystem'sonlypurposeistoensuresafetytoabuilding
anditsoccupantsiflightninghappenstohititdirectly,ataskaccomplished
byprovidingagood,safepathtogroundforthelightningtofollow.Contrary
tothemyths,lightningprotectionsystems:
 Don'tattractlightning
 
 Don'tandcannotdissipateorpreventlightningby'draining'astormofits
charge
 
 Mostdon'toffersurgeprotectionforsensitiveelectronics
 
 Doofferfireprotectionandstructuraldamageprotectionbypreventingahot,
explosivelightningchannelfrompassingthroughbuildingmaterials
3.2.1Howalightningprotectionsystemworks
Withoutadesignatedpathtoreachground,alightningstrikemaychooseto
insteadutilizeanyconductoravailableinsideahouseorbuilding.Thismay
30
includethephone,cable,orelectricallines,thewaterorgaspipes,or(inthe
caseofasteel-framedbuilding)thestructureitself.Lightningusuallywill
followoneormoreofthesepathstoground,sometimesjumpingthroughthe
airviaasideflashtoreachabetter-groundedconductor(watchanimation
above).Asaresult,lightningpresentsseveralhazardstoanyhouseor
building.
 Fire
Firecanstartanywheretheexposedlightningchannelcontacts,penetrates
orcomesnearflammablematerial(wood,paper,gaspipes,etc)inabuilding
-includingstructurallumberorinsulationinsidewallsandroofs.When
lightningfollowselectricalwiring,itwilloftenoverheatorevenvaporizethe
wires,creatingafire.
 Sideflashes
Sideflashescanjumpacrossrooms,possiblyinjuringanyonewhohappens
tobeintheway.Theycanalsoignitematerialssuchasagasolinecanina
garage.
 
 Damagetobuildingmaterials
Theexplosiveshockwavecreatedbyalightningdischargecanblow out
sectionsofwalls,fragmentconcreteandplaster,andshatternearbyglass.
 
 Damagetoappliances
Televisions,VCRs,microwaves,phones,washers,lampsandjustabout
31
anythingpluggedintoanaffectedcircuitmaybedamagedbeyondrepair.
Electronicdevicesandcomputersareespeciallyvulnerable.
Addingaprotectionsystem doesn'tpreventastrike,butgivesitabetter,
saferpathtoground.Theairterminals,cablesandgroundrodsworktogether
tocarrytheimmensecurrentsawayfrom thestructure,preventingfireand
mostappliancedamage.
3.2.2Lightningprotectionfacts
Rodsandprotectionsystemsdon'tattractlightning,nordotheyinfluence
wherelightningwillstrike.Rodsorprotectionsystemsdonotandcannot
preventlightning,norcanthey'discharge'thunderstorms.
Lightning protection systems(including placementofrods,cables,and
groundings)are custom-designed forindividualstructures and require
complexengineeringtofunctionproperly.Theyshouldonlybeinstalledby
qualifiedcontractors.
Lightningprotectionsystemsdonotalwayspreventdamagetoelectronicsor
computers.Youshouldstillunplugsuchdevicesduringthunderstormsto
ensuresufficientprotection.
3.2.3Lightningdissipation/eliminationmyths
Productscalled'lightningelimination'or'lightningdissipation'deviceshave
arisenasaresultoftwomyths:one,thatathunderstorm'schargecanbe
drainedorotherwiseaffectedbyobjectsontheground,andtwo,cloud-to-
groundlightningdischargesbeginfrom theground.Theseproducts,thatare
stillbeingsoldtoday,claim tobeabletopreventadirectlightningstriketo
anyobjectonwhichtheyareinstalled.Thedeviceshavewidelyvarying
32
appearances,butusuallyarecharacterizedbyametallicframewithhundreds
ofsharp-pointedbristles,needlesorthinrods.Theframedesignsrangefrom
comb-liketoumbrella-shaped.
Thedevicesaresaidtopreventorreducedirectlightningstrikestoobjects
onwhichtheyareinstalled,usingcoronadischargetoperformoneormoreof
thefollowing:1.)todrainastorm ofitschargebeforelightningcanoccur,2.)
tocreatealocalized'spacecharge'overtheprotectedareathatdiverts
lightningstrikes,or3.)tomakeinitiationofupwardleadersfrom theobject
moredifficult,therebyreducingthechancesofadirectsteppedleader-
groundleaderconnection.
Aswediscussedinourarticleaboutthunderstorm chargedissipation,the
problemwiththesedevicesisthatwhiletheydocreatecoronadischarge,the
rateofcharge'leakage'iscompletelyinsignificantincomparisontotherate
of charge generation in the 10-mile-high,15 to 25 mile-diameter
thunderstorm overhead!Noamountofman-madecoronadischargeonsuch
asmallscalehastheslightestchanceofdrainingchargefasterthana
gargantuanthunderstorm cloudisproducingit.Andalthoughsmall-scale
coronadoeshelppreventtheinitiationoflaboratory-generatedsparks(such
asfromVandeGraaffgenerators),thiscannotbeextrapolatedtoapplytofull
-sizedlightningdischarges,whichareseveralthousandtimeslargerthanthe
artificalcounterparts(seeourarticleoncomparingartificialandnatural
lightning).Coronadischargefrom small'dissipators'isinsignificanttoafull-
sizedthunderstorm andwilldonothingtoaltertheoccurenceorbehaviorof
lightninginitsgeneeralvicinity.
Cloud-to-groundlightningstrokesinitiatehighinthunderstorms,milesabove
thesurfacewheregroundobjectshavenoeffect.Evenafterinitiationofthe
33
discharge,thedownward-movingsteppedleaderis'blind'toobjectsonthe
grounduntilitisveryclosetotheground,within50to100feet.Atthat
distance,lightning willstrike within the very smallarea itis already
descendingin,regardlessofanydevicesnearbythatclaim todivertor
preventthestrike.Forexample,aphotographexistsofalightningstriketo
theMerchandiseMartbuildingindowntownChicago.MerchandiseMartis
veryclosetothe1,700foottallSearsTower,yetnoteventheSearsTower
influencedthegroundconnectionofthisclosecloud-to-groundstroke.
Inadditiontotheobviousscientificflawswiththeconceptoflightning
'dissipation'and'elimination'devices,theyhavebeenproventobeineffective
inreal-worldinstallations.Many'lightningdissipation'devicesontowersand
buildingshavebeenstruckdirectly.Despitetheevidence,theycontinuetobe
sold,installedandpromoted.
3.3FuturePlans
TEPCOwilldevelopathree-phaselimiteroverthenextthreetofouryearsand
testitinthegridwithinthiscentury.Therearefew distribution-levelFCL
applicationsseenintheTEPCO grid,however,andthecurrentplanisto
introduce solid state breakers for distribution before installing
superconductiveFCL.Thetrueapplicationforthe
superconductingFCLisattransmissionvoltagesof500kV.Theview of
TEPCOresearchersisthatthisvoltagerangewillrequiretheintroductionof
HTScoils(rather
thanLTS)toeliminatethehelium gasfrom thesystem.Introductionofa
transmissionlevelFCLonthegridisanticipatedabout2010.
3.4Fault-CurrentLimitersInEurope
34
By farthe mostcomprehensive FCL program in Europe is thatbeing
conductedby
collaboration between Electricité de France,GEC Alsthom,and Alcatel
Alsthom
Recherché.Theprogram'smaingoalistoprovideFCLsforthe225kVgridin
France.ThegrouphaschosenaresistivelimiterbasedonLTSmaterialand
hasdemonstratedeffectiveoperationat40kV (rms),withanindustrial
demonstrationontheFrench63kVgridexpectedin1998.Evaluationofthe
Frenchprogram isbeyondthescopeofthisWTECstudy,sonovisitwas
madetothisproject.Verhaegeetal.(1996)provideanoverview ofthe
technologyandprojectstatus.
3.5FCLPrograms
TwositestheWTECpanelvisitedinEuropeaddressedFCL:ABBinBaden-
Daetwil,
Switzerland,andSiemensinErlangen,Germany.ABBispursuingafault-
currentlimiterconceptverysimilartothatdescribedabovefortheCRIEPI
program.Itisreferredtoasthe"shieldedironcoreconcept."Itusesawarm
ironcoreenclosedbyasuperconductingshieldinafiberglassDewar.The
copperprimarycoiliswoundexternaltothisDewar.ABBhasconstructed
andtesteda100kWprototypeusingastackoffourBi-2212rings8cm long,
and20cm indiameter.Operationwasat480Vwithfaultcurrentsof8kA.A
newABBthree-phase1.2MW FCLisnowinoperationinapowerstationin
Löntsch,Switzerland.
SiemensisfollowingtworoutesforFCLinacollaborativeprogram with
Hydro-QuebecCanada.AttheSiemenscorporatelabsinErlangen,thefocus
hasbeenonresistivelimitersusingYBCOthinfilm meanderlinesonYSZor
onYSZandsapphire(Gromolletal.1996).Theadvantageofthisapproachis
35
thattheYBCOfilm hasahighnormalstateresistanceandisnotshuntedby
normalmetal,as would be the case in a composite powder-in-tube
conductor.Thefilm alsohasverylow heatcapacity,whichleadstorapid
switchingtothenormalstate(<1ms)andthepossibilityofrapidcooldown.
Analysisasof1996hasdeterminedthatbothpeaklet-throughcurrentand
steadystatelimitingcurrentdecreaseasJcisraised.Inaddition,thedesign
ofalimiterofusablesizedependsstronglyonJc--higherJcenablesamore
compactdesign.
Themajorfocusoftheprogram has,therefore,beenthefabricationof
uniform high-Jc films ofYBCO.Techniques investigated have included
pulsed laserdeposition (PLD),thermalco evaporation,and magnetron
sputteringonbufferedp-YSZ,unbufferedp-YSZ,andsapphire.Biaxially
textured YSZ bufferlayershavebeen fabricated on partofthep-YSZ
substratesbyionbeam assisteddeposition.Currentdensitiesupto3x106
A/cm2havebeenachieved,ashavegoodlimitingperformanceandrecovery
timeson theorderof1 second.Thenextmilestonefortheprojectis
constructionofa100KVAlimiterusingacrycooler.Furtherdetailsofthis
programaregivenintheSiemenssitevisitreport(AppendixD).
TwoadditionalGermanFCLprojectsbeganinJanuary1997.Thefirstisa
system studythatwillbefollowedbyconstructionofademonstrationFCL.
ThisprojectisajointeffortbytheGermanutilitiesRWE,VEW,andBadenwerk,
andbyEUSGmbHandFZK.Thesecondprojectinvolvingthedevelopmentof
a smallinductive limiteris underthe auspices ofthe German Israel
Foundation.TheGermanparticipantsareFZK,HoechstAG,andtheutility
Badenwerk;theIsraeliparticipantsareTelAvivandBenGurionUniversities.
TheworkatHydro-Quebechasresultedintheconstructionandtestofa
36
numberofdevicessince1992(Fig.4.15).Thelatestsystem operatedat450
Vand95ampsforanominalpowerof43KVA.Twodifferentmaterialswere
evaluatedforthesuperconductingshield:melt-castBi-2212from Hoechst,
andcompositereactiontextured(CRT)materialfrom Cambridge.Although
successfulcurrentlimiting wasdemonstrated,thelimiterthatused the
Hoechstmaterialfailedduringa480Vshortcircuittestduetoafractureof
thesuperconductor(Caveetal.1996).SubsequentanalysisbyHydro-
Quebecindicatedthatthermalstressinthebulksuperconductorgaveriseto
thefailure.Thenear-term futuredirectionofthisprogram willbeconcerned
withimprovingthehomogeneity,criticalcurrentdensity,andresistivityofthe
bulksuperconductor.
CHAPTER-4
ADVANTAGES,DISADVANTAGESAND
LIMITATIONS
4.1ADVANTAGES
37
Fig.(4.1)-Powerratingoftheinductivelimitermodelsbuilt/testedatHydro-Quebec
 Relativelynarrow superconducting wirescan beused to carryhuge
currents.
 Lessfuelrequiredtogenerateelectricitywhichwillleadtoareductionin
costs
 Superconductingcableswillbesmallerandcanfitintoexistingconduits
for expansionofthepowersupply.
 Environmentalbenefits from less pollution and more efficentpower
production
4.1.1TransformingtheElectricityGrid
38
Theelectricpowergridisamongthegreatestengineeringachievementsof
the20thcentury.Demand,however,isabouttooverwhelm it.Forexample,
thenorthAmericanblackoutof2003,whichlastedaboutfourdays,affected
over50millionpersonsandcausedabout$6billionineconomicloss.
Superconductor technology provides loss-less wires and cables and
improvesthereliabilityandefficiencyofthepowergrid.Plansareunderway
toreplaceby2030thepresentpowergridwithasuperconductingpowergrid.
Asuperconductingpowersystem occupieslessrealestateandisburiedin
theground,quitedifferentfrompresentdaygridlines.[13]
4.1.2ImprovingWide-BandTelecommunication
Wide-bandtelecommunicationstechnology,whichoperatesbestatgigahertz
frequencies,isveryusefulforimprovingtheefficiencyandreliabilityofcell
phones.Suchfrequenciesareverydifficulttoachievewithsemiconductor-
based circuitry.However,they have been easily achieved by Hypres's
superconductor-basedreceiver,usingatechnologycalledrapidsingleflux
quantum,orRSFQ,integratedcircuitreceiver.Itoperateswiththeaidofa4-
kelvincryocooler.Thistechnologyisshowingupinmanycellphonereceiver
transmittertowers.
4.1.3AidingMedicalDiagnosis
Oneofthefirstlarge-scaleapplicationsofsuperconductivityisinmedical
diagnosis. Magnetic resonance imaging, or MRI, uses powerful
superconductingmagnetstoproducelargeanduniform magneticfields
inside the patient's body.MRIscanners,which contain liquid helium
refrigerationsystem,pickuphow thesemagneticfieldsarereflectedby
organs in the body.The machine eventually produces an image.MRI
machinesaresuperiortox-raytechnologyinproducingadiagnosis.Paul
39
LeuterburandSirPeterMansfieldwereawardedthe2003Nobelprizein
physiology or medicine,"for their discoveries concerning magnetic
resonanceimaging,"underlyingthesignificanceofMRI,andbyimplication
superconductors,tomedicine.
4.2LIMITATIONS
 Thereisamaximumcurrentthatsuperconductingmaterialscancarry.
 Costisprohibitiveforimmediatereplacementofexistingtechnologies.
 DevelopingcountrieswillnotbeabletoaffordthetechnologyAboveacritical
currentdensity.
 superconductivitybreaksdownlimitingcurrent.
 Low criticaltemperaturesaredifficult,expensiveandenergyintensiveto
maintain.
 Thematerialsareusuallybrittle,notductileandhardtoshape.
 Theyarealsochemicallyunstableinsomeenvironments.
 ItcannotfunctionwithACelectricity,astheswitchinginACdestroysCooper
pairs.
 Thereisa"limit"tothecurrentpassingthroughthematerialbeforeitlosesits
superconductingproperties.
4.3DISADVANTAGES
 Superconductingmaterialssuperconductonlywhenkeptbelow agiven
temperaturecalledthetransitiontemperature.
 Forpresentlyknownpracticalsuperconductors,thetemperatureismuch
below77Kelvin,thetemperatureofliquidnitrogen.Keepingthem belowthat
40
temperatureinvolvesalotofexpensivecryogenictechnology.[13]
 Thus,superconductorsstilldonotshow upinmosteverydayelectronics.
Scientistsareworkingondesigningsuperconductorsthatcanoperateat
roomtemperature.
 Thegreatestdrawbackofsuperconductorsisthattheyonlyfunctionassuch
attemperatureslowerthanitscriticaltemperature.
 Thistemperaturevariesbutistypicallyaround70Kelvinformostcommonly
usedsuperconductors.
 Thereforeanysuperconductingapplicationisgenerallycoupledwithsome
sortofactiveorpassivecryogeniccooling.
 Otherdrawbacksincludeprice,materialhandling,maximum currentcarrying
capacityEtc.butthecryogeniclimitationmustbethebiggest.
 This is why the search for the near-mythical ‘room temperature
superconductor’ is so important for the future of superconducting
applications.
4.3.1Highertier
Atthemoment,superconductorsonlyworkatverylowtemperatures.They
havetobekeptverycoldwithliquidnitrogenorliquidhelium.Alotofworkis
goingintodevelopingsuperconductorsthatwillworkatnormaltemperatures.
Untilthishappens,theiruseswillbelimited.
4.3.2Highmeltingandboilingpoints
Metallicbondsarestrongandalotofenergyisneededtobreakthem.Thisis
whymetalshavehighmeltingpointsandboilingpoints.
4.3.3Conductingelectricity
41
Metalscontainelectronsthatarefreetomoveinthemetalstructure,carrying
chargefromplacetoplaceandallowingmetalstoconductelectricitywell.
4.4.4Metallicbonding-Highertier
Metallicbondingisthestrongattractionbetweencloselypackedpositive
metalionsanda'sea'ofdelocalisedelectrons.Theattractionbetweenthe
metalionsandthedelocalisedelectronsmustbeovercometomeltortoboil
ametal.Someoftheattractionsmustbeovercometomeltametalandallof
them mustbeovercometoboilit.Theseattractiveforcesarestrong,so
metalshavehighmeltingandboilingpoints.
Thedelocalisedelectronsareabletomovethroughthemetalstructure.
Whenapotentialdifferenceisapplied,theywillmovetogether,allowingan
electriccurrenttoflowthroughthemetal.
42
CHAPTER-5
APPLICATIONS
5.1BasicApplications
 Theproductionofsensitivemagnetometersbasedonsquids
 Fastdigitalcircuits(includingthosebasedonJosephsonjunctionsandrapid
singlefluxquantumtechnology),
 Powerfulsuperconductingelectromagnetsusedinmaglevtrains,Magnetic
ResonanceImaging(MRI)andNuclearmagneticresonance(NMR)machines,
magnetic confinementfusion reactors (e.g.Tokamaks),and the beam-
steeringandfocusingmagnetsusedinparticleaccelerators
 Low-losspowercables
 RFandmicrowavefilters(e.g.,formobilephonebasestations,aswellas
militaryultra-sensitive/selectivereceivers)
 Fastfaultcurrentlimiters
 Highsensitivityparticledetectors,includingthetransitionedgesensor,the
superconductingbolometer,thesuperconductingtunneljunctiondetector,
thekineticinductancedetector,andthesuperconductingnanowiresingle-
43
photondetector
 Railgunandcoilgunmagnets
 Electricmotorsandgenerators
5.1.1Lowtemperaturesuperconductivity
Thebiggestapplication forsuperconductivityisin producing thelarge
volume,stable,andhighmagneticfieldsrequiredforMRIandNMR.This
represents a multi-billion US$ marketforcompanies such as Oxford
Instruments and Siemens.The magnets typically use low temperature
superconductors(LTS)becausehigh-temperaturesuperconductorsarenot
yetcheapenoughtocost-effectivelydeliverthehigh,stableandlargevolume
fieldsrequired,notwithstandingtheneedtocoolLTSinstrumentstoliquid
helium temperatures.Superconductorsarealsousedinhighfieldscientific
magnets.
5.1.2Particleacceleratorsandmagneticfusiondevices
ParticleacceleratorssuchastheLargeHadronCollidercanincludemany
highfieldelectromagnetsrequiringlargequantitiesofLTS.Toconstructthe
LHCmagnetsrequiredmorethan28percentoftheworld’sniobium-titanium
wireproductionforfiveyears,withlargequantitiesofNbTialsousedinthe
magnetsfortheLHC’shugeexperimentdetectors.
[2]
Asmallnumberofmagneticfusiondevices(mostlytokamaks)haveusedSC
coils.ThecurrentconstructionofITERhasrequiredunprecedentedamounts
ofLTS(eg.500tonnes,causinga7foldincreaseinworldsannualproduction
capacity).
[3]
5.1.3High-temperaturesuperconductivity(HTS)
44
Thecommercialapplicationssofarforhightemperaturesuperconductors
(HTS)havebeenlimited.
HTScansuperconductattemperaturesabovetheboilingpointofliquid
nitrogen,which makes them cheaper to coolthan low temperature
superconductors(LTS).However,theproblem withHTStechnologyisthat
thecurrentlyknownhightemperaturesuperconductorsarebrittleceramics
whichareexpensivetomanufactureandnoteasilyformedintowiresorother
usefulshapes.
[4]
ThereforetheapplicationsforHTShavebeenwhereithas
someotherintrinsicadvantage,e.g.in
 LowthermallosscurrentleadsforLTSdevices(lowthermalconductivity),
 RFandmicrowavefilters(lowresistancetoRF),and
 Increasinglyinspecialistscientificmagnets,particularlywheresizeand
electricityconsumptionarecritical.
 WhileHTSwireismuchmoreexpensivethanLTSintheseapplications,this
canbeoffsetbytherelativecostandconvenienceofcooling.
 Theabilitytorampfieldisdesired(thehigherandwiderrangeofHTS's
operatingtemperaturemeansfasterchangesinfieldcanbemanaged);or
cryogenfreeoperationisdesired(LTSgenerallyrequiresliquidhelium thatis
becomingmorescarceandexpensive).[14]
5.1.4HTS-basedsystems
HTShasapplicationinscientificandindustrialmagnets,includingusein
NMR andMRIsystems.Commercialsystemsarenow availableineach
category.
[5]
AlsooneintrinsicattributeofHTSisthatitcanwithstandmuchhigher
magneticfieldsthanLTS,soHTSatliquidhelium temperaturesarebeing
45
exploredforveryhigh-fieldinsertsinsideLTSmagnets.Promisingfuture
industrialand commercialHTS applications include Induction heaters,
transformers,faultcurrentlimiters,powerstorage,motorsandgenerators,
fusionreactors(seeITER)andmagneticlevitationdevices.
Earlyapplicationswillbewherethebenefitofsmallersize,lowerweightor
theabilitytorapidlyswitchcurrent(faultcurrentlimiters)outweighsthe
addedcost.Longer-term asconductorpricefallsHTSsystemsshouldbe
competitiveinamuchwiderrangeofapplicationsonenergyefficiency
groundsalone.(ForarelativelytechnicalandUS-centricviewofstateofplay
ofHTS technology in powersystems and the developmentstatus of
Generation2conductor.
CHAPTER-6
FUTUREASPECTS
6.1SuperconductingTransmissionLines
Since10%to15%ofgeneratedelectricityisdissipatedinresistivelossesin
transmissionlines,theprospectofzerolosssuperconductingtransmission
lines is appealing.In prototype superconducting transmission lines at
BrookhavenNationalLaboratory,1000MW ofpowercanbetransported
withinanenclosureofdiameter40cm.Thisamountstotransportingthe
entireoutputofalargepowerplantononeenclosedtransmissionline.This
couldbeafairlylowvoltageDCtransmissioncomparedtolargetransformer
banksandmultiplehighvoltageAC transmissionlinesontowersinthe
46
conventionalsystems. The superconductor used in these prototype
applications is usually niobium-titanium,and liquid helium cooling is
required.
Current experiments with power applications of high-temperature
superconductorsfocusonusesofBSCCOintapeformsandYBCOinthinfilm
forms.Currentdensitiesabove10,000amperespersquarecentimeterare
considerednecessaryforpracticalpowerapplications,andthisthresholdhas
beenexceededinseveralconfigurations.
6.2PowerApplications,HighTc
Powerapplicationsofhightemperaturesuperconductorswouldhavethe
majoradvantageofbeingabletooperateatliquidnitrogentemperature.The
biggestbarriertotheirapplicationhasbeenthedifficultyoffabricatingthe
materialsintowiresandcoils.CurrentdevelopmentfocusesonBSCCOand
YBCOmaterials.
6.3Fault-CurrentLimiters
High fault-currents caused by lightning strikes are a troublesome and
expensivenuisanceinelectricpowergrids.Oneofthenear-term applications
forhigh temperaturesuperconductorsmaybetheconstruction offault-
currentlimiterswhichoperateat77K.Theneedistoreducethefaultcurrent
toafractionofitspeakvalueinlessthanacycle(1/60sec).
Arecentlytestedfault-currentlimitercanoperateat2.4kVandcarryacurrent
of2200amperes.ItwasconstructedfromBSCCOmaterial.
47
6.4SuperconductingMotors
Superconductingmotorsandgeneratorscouldbemadewithaweightof
aboutonetenththatofconventionaldevicesforthesameoutput.Thisisthe
appealofmaking such devicesforspecialized applications.Motorsand
generatorsarealreadyveryefficient,so thereisnotthepowersavings
associatedwithsuperconductingmagnets.Itmaybepossibletobuildvery
large capacity generators for power plants where structuralstrength
considerationsplacelimitsonconventionalgenerators.
In1995theNavalResearchLaboratorydemonstrateda167hpmotorwith
high-Tcsuperconductingcoilsmadefrom Bi-2223.Itwastestedat4.2Kand
atliquid neon temperature,28K with 112 hp produced atthe higher
temperature.
6.5SuperconductingMaglevTrains
Whileitisnotpracticaltolaydownsuperconductingrails,itispossibleto
constructasuperconductingsystem onboardatraintorepelconventional
railsbelowit.Thetrainwouldhavetobemovingtocreatetherepulsion,but
oncemovingwouldbesupportedwithverylittlefriction.Therewouldbe
resistivelossofenergyinthecurrentsintherails.Ohanianreportsan
engineeringassessmentthatsuchsuperconductingtrainswouldbemuch
saferthanconventionalrailsystemsat200km/h.
AJapanesemagneticallylevitatedtrainsetaspeedrecordof321mi/hin
1979 using superconducting magnetson board thetrain.Themagnets
inducecurrentsintherailsbelowthem,causingarepulsionwhichsuspends
thetrainabovethetrack.
48
 FutureApplicationsofSuperconductivity
With such features as zero resistivity and high current density,
superconductivity provides low-loss operation and high magnetic field,
featuresinconceivablewithnormalconductivity.Accordingly,expectations
arehighthatsuperconductivitywillimprovetheperformanceofelectrical
appliances.
Thesuperconductingstateoccurswithinlimitedtemperature,magneticfield
and current density ranges. Thanks to the discovery of oxide
superconductorsofhighcriticaltemperatures*1andtheincreasedcritical
current density*2 of superconducting wires made from them,
superconductivityisexpectedtobeusedinabroaderrangeofcommercial
fields.
Futuristicideasfortheuseofsuperconductors,materialsthatallowelectric
currenttoflow withoutresistance,aremyriad:long-distance,low-voltage
electricgridswithnotransmissionloss;fast,magneticallylevitatedtrains;
ultra-high-speed supercomputers;superefficientmotors and generators;
inexhaustiblefusionenergy–andmanyothers,someintheexperimentalor
demonstrationstages.
Butsuperconductors,especiallysuperconductingelectromagnets,havebeen
around for a long time.Indeed the first large-scale application of
superconductivity was in particle-physics accelerators,where strong
magnetic fields steerbeams ofcharged particles toward high-energy
collisionpoints.
49
Accelerators created the superconductorindustry,and superconducting
magnetshavebecomethenaturalchoiceforanyapplicationwherestrong
magneticfieldsareneeded– formagneticresonanceimaging(MRI)in
hospitals,forexample,orformagneticseparationofmineralsinindustry.
Otherscientificusesarenumerous,from nuclearmagneticresonancetoion
sourcesforcyclotrons.
Someofthestrongestandmostcomplexsuperconductingmagnetsarestill
builtforparticleacceleratorslikeCERN’sLargeHadronCollider(LHC).The
LHC uses over1,200 dipole magnets,whose two adjacentcoils of
superconducting cable create magnetic fields thatbend proton beams
traveling in opposite directions around a tunnel 27 kilometers in
circumference;theLHCalsohasalmost400quadrupolemagnets,whose
coilscreateafieldwithfourmagneticpolestofocustheprotonbeamswithin
thevacuumchamberandguidethemintotheexperiments.
TheseLHCmagnetsusecablesmadeofsuperconductingniobium titanium
(NbTi),andforfiveyearsduringitsconstructiontheLHCcontractedformore
than 28 percentofthe world’s niobium titanium wire production,with
significantquantitiesofNbTialsousedinthemagnetsfortheLHC’sgiant
experiments.
What’smore,althoughtheLHCisstillworkingtoreachtheenergyforwhichit
wasdesigned,theprogram toimproveitsfutureperformanceisalreadywell
underway.
 Designingthefuture
“Enablingtheacceleratorsofthefuturedependsondevelopingmagnetswith
muchgreaterfieldstrengthsthanarenowpossible,”saysGianLucaSabbiof
50
BerkeleyLab’sAcceleratorandFusionResearchDivision(AFRD).“Todothat,
we’llhavetousedifferentmaterials.”
Fieldstrengthislimitedbytheamountofcurrentamagnetcoilcancarry,
whichinturndependsonphysicalpropertiesofthesuperconductingmaterial
suchasitscriticaltemperatureandcriticalfield.Mostsuperconducting
magnetsbuilttodatearebasedonNbTi,whichisaductilealloy;theLHC
dipolesaredesignedtooperateatmagneticfieldsofabouteighttesla,or8
T —hundredsofthousandsoftimeshigherthanEarth’smagneticfield.
TheLHCAcceleratorResearchProgram (LARP)isacollaborationamong
DOElaboratoriesthat’sanimportantpartofU.S.participationintheLHC.
SabbiheadsboththeMagnetSystemscomponentofLARPandBerkeley
Lab’s Superconducting MagnetProgram.These programs are currently
developing acceleratormagnetsbuiltwith niobium tin (Nb3Sn),abrittle
materialrequiringspecialfabricationprocessesbutabletogenerateabout
twicethefieldofniobium titanium.Yetthegoalformagnetsofthefutureis
alreadysetmuchhigher.
“Amongthemostpromisingnewmaterialsforfuturemagnetsaresomeof
thehigh-temperaturesuperconductors,”saysSabbi.“Unfortunatelythey’re
verydifficult
51
CONCLUSION
Thepurposeofthispresentationwasthestudyofsurgecurrentprotection
usingSuperconductors.TheSuperconductorFaultCurrentLimitersoffers
efficientadvantagestopowersystemsandopensupamajorapplicationfor
superconductingmaterials.
Surge suppressors should be used as a mailer of habit with all
semiconductorbased
electronicandcomputerhardwareincludingperipheralssuchasprinters
monitors,
externaldiskdriversandothers.Butitcan’tbereliedupontoprovide
protectionagainstlightninginducedtransients.Sothesafestprocedureto
ensurethatallsusceptiblehardwareistounplugthesuppressormainpower
cordduringlightning.
52
References
[1] KEGray,DEflower–superconductingfaultcurrentlimiters
[2] IEEEtransactiononappliedsuperconductivity,march1997
[3] HMRosenberg–TheSolidState.http://www.amazon.co.uk/Solid-State
Introduction-MaterialsEngineering
[4] CPPoole,HAFarachandRJCreswick,Superconductivity(Academic
PressInc,
[5] SanDiego,California,1995(~
£40)http://www.amazon.co.uk/SuperconductivityCharles-PPoole/
[6] SuperconductivitybyW.Buckel,ReinholdKleiner
[7] Superconductivity:PhysicsandApplicationsbyKristianFossheim,Asle
Sudboe
[8] Superconductivity:fundamentalsandapplicationsbyWernerBuckel
[9] ieeexplore.ieee.org›...›Spectrum,IEE
[10]http://www.scribd.com/doc/115890153/surge-current-protection-using-
superconductors
[11]http://jntuhome.com/surge-current-protection-using-superconductors-
seminardownload-full-paper-eee-seminar-topics/
53
[12]http://kguru.info/t-surge-current-protection-using-superconductors-ppt--
55999
[13]http://en.wikipedia.org/wiki/Surge_protector
[14]http://www.edaboard.com/thread126937.html
[15]http://image.slidesharecdn.com/surgesupressor2bypratyashapatra-
140216062041-phpapp02/95/surge-supressor-21-638.jpg?cb=1392531698

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Surge current protection Seminar Report