I

A

SEMINAR

ON

“SURGECURRENTPROTECTIONUSINGSUPERCONDUCTOR”

SubmittedinpartialfulfillmentforbacheloroftechnologyDegreeat

RajasthanTechnicalUniversity,Kota

BACHELOROFTECHNOLOGY

IN

ELECTRICALENGINEERING

SUPERVISEDBY: SUBMITTEDBY:

Prof.ASADZAI SARFARAZKHANRollNo.-13EVEEE051Enrl.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”whoneverleavesmealoneinbadcircumstances,helpmealwayswiththeirwellblessings.

Thereareanumberofpeoplewhodeserverecognitionfortheirunwavering supportand guidancethroughoutthisseminarpresentation.Iwouldliketotakethisopportunitytothankthem.Firstandforemost,Iwanttothankmywell-wisheradvisorandasaguide,Mr.AsadZaiSirforhissupport,constructivecriticism,andnewtechnicalupdates.Thispresentationcouldhavenotbeencompletedwithouthisenthusiasmanddirection.IagainwanttothankMr.AsadSirforgivingmethistypeoftechnicaltheorytopicbywhichIcanunderstandmycorebranchefficiently.IwillbealwaysthankfultoOurHODMr.ManishBhatiSirforexpandingmyunderstandingofglobalinequalitiesthroughouthistoryandherconstantmentorship.

Iwanttothankmyfriendswhohaveencouragedmeoverthestudyofthispresentation.

Finally,Iwanttothankmyfamily.Myparents,especially,havebeenasourceofstrengthandsupportforme.Theycontinuallypushmetothinkcriticallyandneversettleforanythinglessthanmybest.Theykeptmefocused,ontrackandfedinthefinalstretchofmycollegestudy.Fortheircontinualsupport,Iamforevergrateful.

IV

ABSTRACT

ModernPowerSystemsaregrowingfastwithmoregenerators,

transformersandlargenetworkinthesystems.Theinstallation,

runningandmaintenancecostsofthepowersystemequipment

aremore.Wheneverafaultoccurs,thereisaneedforthe

protectionofthesesystems.PowerSystem Protectionisa

branchofelectricalpowerengineeringthatdealswiththe

protectionofelectricalpowersystemsfrom faultsthroughthe

isolationoffaultedpartsfromtherestoftheelectricalnetwork.

Superconductorsareoneofthelastgreatfrontiersofscientific

discovery.Here,inthispaperwediscusstheuseofSuper

ConductorsasprotectivedevicesforSurgeCurrentProtection.

Superconductorsconductelectricityofferingzeroresistance

belowcertaintemperatures.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.

Aproblem arisesiftheelectricitysupplyisupgraded,byaddingnew

generationcapacityorbyaddingcross-connections.Becausetheseincrease

theamountofpowerthatcanbesupplied,allofthebranchcircuitsmust

havetheirbusbarsandcircuitbreakersupgradedtohandlethenewhigher

faultcurrentlimit.

Thisposesaparticularproblemwhendistributedgeneration,suchaswind

farmsandrooftopsolarpower,isaddedtoanexistingelectricgrid.Itis

desirabletobeabletoaddadditionalpowersourceswithoutlargesystem-

wideupgrades.

Asimplesolutionistoaddelectricalimpedancetothecircuit.Thislimitsthe

rateatwhichcurrentcanincrease,whichlimitsthelevelthefaultcurrentcan

risetobeforethebreakerisopened.However,thisalsolimitstheabilityofthe

circuittosatisfyrapidlychangingdemand,sotheadditionorremovaloflarge

loadscausesunstablepower.

Afaultcurrentlimiterisanonlinearelementwhichhasalowimpedanceat

normalcurrentlevels,butpresentsahigherimpedanceatfaultcurrentlevels.

10

Further,thischangeisextremelyrapid,beforeacircuitbreakercantripafew

millisecondlater.(High-powercircuitbreakersaresynchronizedtothe

alternatingcurrentzerocrossingtominimizearcing.)

Whilethepowerisunstableduringthefault,itisnotcompletelydisconnected.

Afterthe faulting branch is disconnected,the faultcurrentlimiter

automaticallyreturnstonormaloperation.

1.2SurgeCurrent

Themaximum instantaneousinputcurrentdrawnbyanelectricaldevice

whenfirstitisturnedonisdefinedassurgecurrent.Itisalsoknownas

InrushcurrentorInputSurgeCurrentorSwitch-onSurge.Alternatingcurrent

electricmotorsandtransformersmaydrawseveraltimestheirnormalfull-

loadcurrentwhenfirstenergized,forafewcyclesoftheinputwaveform.

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 PhysicistHeike

KamerlinghOnnesofLeidenUniversitywasthefirstpersontoobserve

superconductivityinmercury.

Superconductivityisaphenomenonofexactlyzeroelectricalresistance

certainmaterialswhencooledbelowacharacteristiccriticaltemperature.It

isaquantummechanicalphenomenon.

TypesofSuperconductors:

LowTemperatureSuperconductor

HightemperatureSuperconductors

LTSarethesubstancesthatloseallresistivitycloseto4K,atemperature

attainableonlybyliquidhelium.HTSarethesubstancesthatloseall

resistancebelowtemperaturemaintamablebyliquidnitrogen.

ExamplesofLTS:LeadandMercury

ExamplesofHTS:YBCO,BSCCO,LSCO,etc.

2.2MeissnerEffect

The Meissnereffectis 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

electricitydistribution systems,followed byelectric-drive ships:naval

vessels,

submarinesandcruiseships.LargerFCLsmayeventuallybeemployedin

highvoltagetransmissionsystems.

Fault-currentlimitersusing high temperaturesuperconductorsoffera

solution to controlling fault-currentlevels 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,suchastransformersinunderground

vaultsorcables,canbeveryexpensivetoreplacecustomersrequestparallel

servicesthatenhancethereliabilityoftheirsupplybutraisethefaultduty.

2.6SuperconductiveFCL

Superconductorsofferawaytobreakthroughsystemdesignconstraintsby

presenting

15

impedancetotheelectricalsystem thatvariesdependingonoperating

conditions.

Superconductingfault-currentlimitersnormallyoperatewithlowimpedance

andare

"invisible"componentsintheelectricalsystem.Intheeventofafault,the

limiterinsertsimpedanceintothecircuitandlimitsthefaultcurrent.With

currentlimiters,theutilitycanprovidealow-impedance,stiffsystemwitha

lowfault-currentlevel.

Fig.-(2.6)-Faultcontrolwithafault-currentlimiter

Alarge,low-impedancetransformerisusedtofeedabus.Normally,theFCL

doesnotaffectthecircuit.Intheeventofafault,thelimiterdevelopsan

impedanceof0.2perunit(Z=20%),andthefaultcurrentISCisreducedto

7,400A.Withoutthelimiter,thefaultcurrentwouldbe37,000A.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.

Thefault-currentlimiterFCLprotectsanindividualcircuitonthebus.

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 impedancetransformercanbeusedtomaintainvoltage

18

regulationatthenewpowerlevel

I2tdamagetothetransformerislimited

Reducedfault-currentflowsinthehigh-voltagecircuitthatfeedsthe

transformer,whichminimizesthevoltagedipontheupstreamhigh-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 superconductorwithoutresistance and negligible

impedance.

Ifafaultdevelops,thesuperconductorquenches,itsresistancerisessharply,

andcurrentisdivertedtoaparallelcircuitwiththedesiredhigherimpedance.

(Thestructureisnotusableasacircuitbreaker,becausethenormally-

conducting superconductive materialdoes nothave a high enough

resistance.Itisonlyhighenoughtocausesufficientheatingtomeltthe

material.)

Superconductingfaultcurrentlimitersaredescribedasbeinginoneoftwo

majorcategories:resistiveorinductive.

InaresistiveFCL,thecurrentpassesdirectlythroughthesuperconductor.

Whenitquenches,thesharpriseinresistancereducesthefaultcurrentfrom

whatitwouldotherwisebe(theprospectivefaultcurrent).AresistiveFCLcan

beeitherDCorAC.IfitisAC,thentherewillbeasteadypowerdissipation

fromAClosses(superconductinghysteresislosses)whichmustberemoved

20

bythecryogenicsystem.AnACFCLisusuallymadefromwirewoundnon-

inductively;otherwisetheinductanceofthedevicewouldcreateanextra

constantpowerlossonthesystem.

InductiveFCLscomeinmanyvariants,butthebasicconceptisatransformer

witharesistiveFCLasthesecondary.Inun-faultedoperation,thereisno

resistanceinthesecondaryandsotheinductanceofthedeviceislow.Afault

currentquenchesthesuperconductor,thesecondarybecomesresistiveand

theinductanceofthewholedevicerises.Theadvantageofthisdesignisthat

thereisnoheatingressthroughcurrentleadsintothesuperconductor,and

sothecryogenicpowerloadmaybelower.However,thelargeamountofiron

requiredmeansthatinductiveFCLsaremuchbiggerandheavierthan

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 orcryogenic components - the self-triggered FCL

instantaneouslyincreasesitsimpedancetenfolduponfaultcondition.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.ResistancedevelopedintheHTSwindingduringafaultis

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

areascontinuestogrow becauseofeconomicgrowthandincreased

23

consumeruseofelectricity.Inaddition,industrialuseofcomputersandother

power-quality-sensitiveequipmenthasforcedtheutilitiestoprovidehigher

qualityandmorereliablepower.Thequitesuccessfulapproachtoimproved

powerqualityinJapanhasbeentoincreaseconnectionsbetweenvarious

powersystemsandtoconcentrategenerationcapacityinlarger,more

efficientunits.

Increasinginterconnectiondoes,however,increasethemaximum fault

currentavailableatanypointinthesystem,andthisisrapidlyleadingtothe

needforbreakerupgradesandsystem reconfigurations.Addingtothe

complexityofthesituationinJapanisthelimitedroomatsubstationsites,

whichcanprecludebreakerupgrades.

Theprimaryneed,asexpressedbymanagementoftheTokyoElectricPower

Company(TEPCO),isfora limiterforthenucleusoftheJapanese

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

systemtolimitcurrentsinthecaseofasingle-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

normalcoppercoilfromanironcore.Innormaloperation,thefieldfromthe

coppercoildoesnotpenetratethesuperconductor;underfaultconditions,

however,thecurrentinducedinthesuperconductorissufficienttodriveit

normal,andthemagneticfieldlinkstheironyoke.Thisgreatlyincreasesthe

inductanceofthecoppercoil,thusprovidingcurrentlimiting.CRIEPIwork

hasfocusedonacmagneticshieldingperformanceofbulksuperconductors

andtheirresponsestofaultcurrents.

Inaddition,introductionofa"controlring"inthesystemtoabsorbsomeof

theenergydepositedduringafaulthasreducedthecooldowntimeofthe

shieldfollowingafaultedstate.ThemostextensiveFCLprograminJapan

hasbeenthecollaborationbetweenTEPCOandToshiba.Thelong-termgoal

ofthisprogramisthedevelopmentofa500kVlimiterwitharatedcurrentof

8,000A.Initialdevelopmenthasbeenfocusedonadistributionlevellimiter

designedfor6.6kV.

25

Fig.(2.9.1)-SchematicdiagramoftheCRIEPIinductiveFCL

AsshowninFig.4.12,theFCLisformedbyconnectingfoursuperconducting

coilsinaseries-parallelconfigurationsothetotalinductanceisminimized.

Onesetofcoilsisusedforeachphaseofthedevice,andlimitingis

accomplishedbyquenchingthecoils.

ThecurrentversionoftheFCLshowninFig.4.13usesaspeciallowacloss

Nb-Ti

conductor.Testsinacircuitwithanominalshortcircuitcurrentof25.8kA

havesuccessfullydemonstratedlimitingtoabout4,000amps(Fig.4.14).

26

Fig.(2.9.2)-ConfigurationofcoilsintheTEPCO/ToshibaFCL

RecentworkhasincludedtheintroductionofHTScurrentleadstoreducethe

refrigerationloadofthesystemtolevelsthatcanbehandledbya4KGifford

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

systeminstallation.Alightningprotectionsystemiscomposedofthreemain

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)thatcarrylightningcurrentfromtherodstotheground.

Cablesarerunalongthetopsandaroundtheedgesofroofs,thendownone

ormorecorners

 ofabuildingtothegroundrod(s).

3.1.3GroundRods

Long,thick,heavyrodsburieddeepintotheeartharoundaprotected

structure.The conductorcablesareconnectedtotheserodstocompletea

safepathforalightningdischargearoundastructure.

Theconductorcablesandgroundrodsarethemostimportantcomponents

ofalightningprotectionsystem,accomplishingthemainobjectiveof

divertinglightningcurrentsafelypastastructure.The'lightningrods'

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

Theexplosiveshockwavecreatedbyalightningdischargecanblowout

sectionsofwalls,fragmentconcreteandplaster,andshatternearbyglass.

 

Damagetoappliances

Televisions,VCRs,microwaves,phones,washers,lampsandjustabout

31

anythingpluggedintoanaffectedcircuitmaybedamagedbeyondrepair.

Electronicdevicesandcomputersareespeciallyvulnerable.

Addingaprotectionsystem doesn'tpreventastrike,butgivesitabetter,

saferpathtoground.Theairterminals,cablesandgroundrodsworktogether

tocarrytheimmensecurrentsawayfromthestructure,preventingfireand

mostappliancedamage.

3.2.2Lightningprotectionfacts

Rodsandprotectionsystemsdon'tattractlightning,nordotheyinfluence

wherelightningwillstrike.Rodsorprotectionsystemsdonotandcannot

preventlightning,norcanthey'discharge'thunderstorms.

Lightningprotectionsystems(includingplacementofrods,cables,and

groundings)arecustom-designedforindividualstructuresandrequire

complexengineeringtofunctionproperly.Theyshouldonlybeinstalledby

qualifiedcontractors.

Lightningprotectionsystemsdonotalwayspreventdamagetoelectronicsor

computers.Youshouldstillunplugsuchdevicesduringthunderstormsto

ensuresufficientprotection.

3.2.3Lightningdissipation/eliminationmyths

Productscalled'lightningelimination'or'lightningdissipation'deviceshave

arisenasaresultoftwomyths:one,thatathunderstorm'schargecanbe

drainedorotherwiseaffectedbyobjectsontheground,andtwo,cloud-to-

groundlightningdischargesbeginfromtheground.Theseproducts,thatare

stillbeingsoldtoday,claimtobeabletopreventadirectlightningstriketo

anyobjectonwhichtheyareinstalled.Thedeviceshavewidelyvarying

32

appearances,butusuallyarecharacterizedbyametallicframewithhundreds

ofsharp-pointedbristles,needlesorthinrods.Theframedesignsrangefrom

comb-liketoumbrella-shaped.

Thedevicesaresaidtopreventorreducedirectlightningstrikestoobjects

onwhichtheyareinstalled,usingcoronadischargetoperformoneormoreof

thefollowing:1.)todrainastormofitschargebeforelightningcanoccur,2.)

tocreatealocalized'spacecharge'overtheprotectedareathatdiverts

lightningstrikes,or3.)tomakeinitiationofupwardleadersfromtheobject

moredifficult,therebyreducingthechancesofadirectsteppedleader-

groundleaderconnection.

Aswediscussedinourarticleaboutthunderstorm chargedissipation,the

problemwiththesedevicesisthatwhiletheydocreatecoronadischarge,the

rateofcharge'leakage'iscompletelyinsignificantincomparisontotherate

ofcharge generation in the 10-mile-high,15 to 25 mile-diameter

thunderstormoverhead!Noamountofman-madecoronadischargeonsuch

asmallscalehastheslightestchanceofdrainingchargefasterthana

gargantuanthunderstorm cloudisproducingit.Andalthoughsmall-scale

coronadoeshelppreventtheinitiationoflaboratory-generatedsparks(such

asfromVandeGraaffgenerators),thiscannotbeextrapolatedtoapplytofull

-sizedlightningdischarges,whichareseveralthousandtimeslargerthanthe

artificalcounterparts(seeourarticleoncomparingartificialandnatural

lightning).Coronadischargefromsmall'dissipators'isinsignificanttoafull-

sizedthunderstormandwilldonothingtoaltertheoccurenceorbehaviorof

lightninginitsgeneeralvicinity.

Cloud-to-groundlightningstrokesinitiatehighinthunderstorms,milesabove

thesurfacewheregroundobjectshavenoeffect.Evenafterinitiationofthe

33

discharge,thedownward-movingsteppedleaderis'blind'toobjectsonthe

grounduntilitisveryclosetotheground,within50to100feet.Atthat

distance,lightningwillstrikewithintheverysmallareaitisalready

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.Therearefewdistribution-levelFCL

applicationsseenintheTEPCOgrid,however,andthecurrentplanisto

introduce solid state breakers for distribution before installing

superconductiveFCL.Thetrueapplicationforthe

superconductingFCLisattransmissionvoltagesof500kV.Theviewof

TEPCOresearchersisthatthisvoltagerangewillrequiretheintroductionof

HTScoils(rather

thanLTS)toeliminatethehelium gasfrom thesystem.Introductionofa

transmissionlevelFCLonthegridisanticipatedabout2010.

3.4Fault-CurrentLimitersInEurope

34

ByfarthemostcomprehensiveFCLprogram inEuropeisthatbeing

conductedby

collaborationbetweenElectricitédeFrance,GEC Alsthom,andAlcatel

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-2212rings8cmlong,

and20cmindiameter.Operationwasat480Vwithfaultcurrentsof8kA.A

newABBthree-phase1.2MWFCLisnowinoperationinapowerstationin

Löntsch,Switzerland.

SiemensisfollowingtworoutesforFCLinacollaborativeprogram with

Hydro-QuebecCanada.AttheSiemenscorporatelabsinErlangen,thefocus

hasbeenonresistivelimitersusingYBCOthinfilmmeanderlinesonYSZor

onYSZandsapphire(Gromolletal.1996).Theadvantageofthisapproachis

35

thattheYBCOfilmhasahighnormalstateresistanceandisnotshuntedby

normalmetal,aswould bethecasein acompositepowder-in-tube

conductor.Thefilm alsohasverylowheatcapacity,whichleadstorapid

switchingtothenormalstate(<1ms)andthepossibilityofrapidcooldown.

Analysisasof1996hasdeterminedthatbothpeaklet-throughcurrentand

steadystatelimitingcurrentdecreaseasJcisraised.Inaddition,thedesign

ofalimiterofusablesizedependsstronglyonJc--higherJcenablesamore

compactdesign.

Themajorfocusoftheprogram has,therefore,beenthefabricationof

uniform high-JcfilmsofYBCO.Techniquesinvestigatedhaveincluded

pulsedlaserdeposition(PLD),thermalcoevaporation,andmagnetron

sputteringonbufferedp-YSZ,unbufferedp-YSZ,andsapphire.Biaxially

texturedYSZbufferlayershavebeenfabricatedonpartofthep-YSZ

substratesbyionbeamassisteddeposition.Currentdensitiesupto3x106

A/cm2havebeenachieved,ashavegoodlimitingperformanceandrecovery

timesontheorderof1second.Thenextmilestonefortheprojectis

constructionofa100KVAlimiterusingacrycooler.Furtherdetailsofthis

programaregivenintheSiemenssitevisitreport(AppendixD).

TwoadditionalGermanFCLprojectsbeganinJanuary1997.Thefirstisa

systemstudythatwillbefollowedbyconstructionofademonstrationFCL.

ThisprojectisajointeffortbytheGermanutilitiesRWE,VEW,andBadenwerk,

andbyEUSGmbHandFZK.Thesecondprojectinvolvingthedevelopmentof

asmallinductivelimiterisundertheauspicesoftheGermanIsrael

Foundation.TheGermanparticipantsareFZK,HoechstAG,andtheutility

Badenwerk;theIsraeliparticipantsareTelAvivandBenGurionUniversities.

TheworkatHydro-Quebechasresultedintheconstructionandtestofa

36

numberofdevicessince1992(Fig.4.15).Thelatestsystemoperatedat450

Vand95ampsforanominalpowerof43KVA.Twodifferentmaterialswere

evaluatedforthesuperconductingshield:melt-castBi-2212fromHoechst,

andcompositereactiontextured(CRT)materialfrom Cambridge.Although

successfulcurrentlimitingwasdemonstrated,thelimiterthatusedthe

Hoechstmaterialfailedduringa480Vshortcircuittestduetoafractureof

thesuperconductor(Caveetal.1996).SubsequentanalysisbyHydro-

Quebecindicatedthatthermalstressinthebulksuperconductorgaveriseto

thefailure.Thenear-termfuturedirectionofthisprogramwillbeconcerned

withimprovingthehomogeneity,criticalcurrentdensity,andresistivityofthe

bulksuperconductor.

CHAPTER-4

ADVANTAGES,DISADVANTAGESAND

LIMITATIONS

4.1ADVANTAGES

37

Fig.(4.1)-Powerratingoftheinductivelimitermodelsbuilt/testedatHydro-Quebec

Relativelynarrow superconductingwirescanbeusedtocarryhuge

currents.

Lessfuelrequiredtogenerateelectricitywhichwillleadtoareductionin

costs

Superconductingcableswillbesmallerandcanfitintoexistingconduits

for expansionofthepowersupply.

Environmentalbenefitsfrom lesspollutionandmoreefficentpower

production

4.1.1TransformingtheElectricityGrid

38

Theelectricpowergridisamongthegreatestengineeringachievementsof

the20thcentury.Demand,however,isabouttooverwhelmit.Forexample,

thenorthAmericanblackoutof2003,whichlastedaboutfourdays,affected

over50millionpersonsandcausedabout$6billionineconomicloss.

Superconductortechnology provides loss-less wires and cables and

improvesthereliabilityandefficiencyofthepowergrid.Plansareunderway

toreplaceby2030thepresentpowergridwithasuperconductingpowergrid.

Asuperconductingpowersystemoccupieslessrealestateandisburiedin

theground,quitedifferentfrompresentdaygridlines.[13]

4.1.2ImprovingWide-BandTelecommunication

Wide-bandtelecommunicationstechnology,whichoperatesbestatgigahertz

frequencies,isveryusefulforimprovingtheefficiencyandreliabilityofcell

phones.Suchfrequenciesareverydifficulttoachievewithsemiconductor-

basedcircuitry.However,theyhavebeeneasilyachievedbyHypres'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

insidethepatient'sbody.MRIscanners,which contain liquid helium

refrigerationsystem,pickuphow thesemagneticfieldsarereflectedby

organsinthebody.Themachineeventuallyproducesanimage.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.Keepingthembelowthat

40

temperatureinvolvesalotofexpensivecryogenictechnology.[13]

Thus,superconductorsstilldonotshowupinmosteverydayelectronics.

Scientistsareworkingondesigningsuperconductorsthatcanoperateat

roomtemperature.

Thegreatestdrawbackofsuperconductorsisthattheyonlyfunctionassuch

attemperatureslowerthanitscriticaltemperature.

Thistemperaturevariesbutistypicallyaround70Kelvinformostcommonly

usedsuperconductors.

Thereforeanysuperconductingapplicationisgenerallycoupledwithsome

sortofactiveorpassivecryogeniccooling.

Otherdrawbacksincludeprice,materialhandling,maximumcurrentcarrying

capacityEtc.butthecryogeniclimitationmustbethebiggest.

This is why the search for the near-mythical‘room temperature

superconductor’is so importantforthe future ofsuperconducting

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,

magneticconfinementfusionreactors(e.g.Tokamaks),andthebeam-

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

Thebiggestapplicationforsuperconductivityisinproducingthelarge

volume,stable,andhighmagneticfieldsrequiredforMRIandNMR.This

representsamulti-billion US$ marketforcompaniessuch asOxford

InstrumentsandSiemens.Themagnetstypicallyuselow temperature

superconductors(LTS)becausehigh-temperaturesuperconductorsarenot

yetcheapenoughtocost-effectivelydeliverthehigh,stableandlargevolume

fieldsrequired,notwithstandingtheneedtocoolLTSinstrumentstoliquid

heliumtemperatures.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 cheaperto 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(LTSgenerallyrequiresliquidheliumthatis

becomingmorescarceandexpensive).[14]

5.1.4HTS-basedsystems

HTShasapplicationinscientificandindustrialmagnets,includingusein

NMRandMRIsystems.Commercialsystemsarenow availableineach

category.[5]

AlsooneintrinsicattributeofHTSisthatitcanwithstandmuchhigher

magneticfieldsthanLTS,soHTSatliquidhelium temperaturesarebeing

45

exploredforveryhigh-fieldinsertsinsideLTSmagnets.Promisingfuture

industrialand commercialHTS applicationsincludeInduction heaters,

transformers,faultcurrentlimiters,powerstorage,motorsandgenerators,

fusionreactors(seeITER)andmagneticlevitationdevices.

Earlyapplicationswillbewherethebenefitofsmallersize,lowerweightor

theabilitytorapidlyswitchcurrent(faultcurrentlimiters)outweighsthe

addedcost.Longer-term asconductorpricefallsHTSsystemsshouldbe

competitiveinamuchwiderrangeofapplicationsonenergyefficiency

groundsalone.(ForarelativelytechnicalandUS-centricviewofstateofplay

ofHTS technologyinpowersystemsandthedevelopmentstatusof

Generation2conductor.

CHAPTER-6

FUTUREASPECTS

6.1SuperconductingTransmissionLines

Since10%to15%ofgeneratedelectricityisdissipatedinresistivelossesin

transmissionlines,theprospectofzerolosssuperconductingtransmission

linesisappealing.Inprototypesuperconductingtransmissionlinesat

BrookhavenNationalLaboratory,1000MW ofpowercanbetransported

withinanenclosureofdiameter40cm.Thisamountstotransportingthe

entireoutputofalargepowerplantononeenclosedtransmissionline.This

couldbeafairlylowvoltageDCtransmissioncomparedtolargetransformer

banksandmultiplehighvoltageACtransmissionlinesontowersinthe

46

conventionalsystems.The superconductorused in these prototype

applicationsisusuallyniobium-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

Highfault-currentscausedbylightningstrikesareatroublesomeand

expensivenuisanceinelectricpowergrids.Oneofthenear-termapplications

forhightemperaturesuperconductorsmaybetheconstructionoffault-

currentlimiterswhichoperateat77K.Theneedistoreducethefaultcurrent

toafractionofitspeakvalueinlessthanacycle(1/60sec).

Arecentlytestedfault-currentlimitercanoperateat2.4kVandcarryacurrent

of2200amperes.ItwasconstructedfromBSCCOmaterial.

47

6.4SuperconductingMotors

Superconductingmotorsandgeneratorscouldbemadewithaweightof

aboutonetenththatofconventionaldevicesforthesameoutput.Thisisthe

appealofmakingsuchdevicesforspecializedapplications.Motorsand

generatorsarealreadyveryefficient,sothereisnotthepowersavings

associatedwithsuperconductingmagnets.Itmaybepossibletobuildvery

large capacity generators forpowerplants where structuralstrength

considerationsplacelimitsonconventionalgenerators.

In1995theNavalResearchLaboratorydemonstrateda167hpmotorwith

high-TcsuperconductingcoilsmadefromBi-2223.Itwastestedat4.2Kand

atliquid neon temperature,28K with 112 hp produced atthehigher

temperature.

6.5SuperconductingMaglevTrains

Whileitisnotpracticaltolaydownsuperconductingrails,itispossibleto

constructasuperconductingsystem onboardatraintorepelconventional

railsbelowit.Thetrainwouldhavetobemovingtocreatetherepulsion,but

oncemovingwouldbesupportedwithverylittlefriction.Therewouldbe

resistivelossofenergyinthecurrentsintherails.Ohanianreportsan

engineeringassessmentthatsuchsuperconductingtrainswouldbemuch

saferthanconventionalrailsystemsat200km/h.

AJapanesemagneticallylevitatedtrainsetaspeedrecordof321mi/hin

1979usingsuperconductingmagnetsonboardthetrain.Themagnets

inducecurrentsintherailsbelowthem,causingarepulsionwhichsuspends

thetrainabovethetrack.

48

FutureApplicationsofSuperconductivity

With such features as zero resistivity and high current density,

superconductivityprovideslow-lossoperationandhighmagneticfield,

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

currenttoflowwithoutresistance,aremyriad:long-distance,low-voltage

electricgridswithnotransmissionloss;fast,magneticallylevitatedtrains;

ultra-high-speedsupercomputers;superefficientmotorsandgenerators;

inexhaustiblefusionenergy–andmanyothers,someintheexperimentalor

demonstrationstages.

Butsuperconductors,especiallysuperconductingelectromagnets,havebeen

around fora long time.Indeed the firstlarge-scale application of

superconductivity was in particle-physics accelerators,where strong

magneticfieldssteerbeamsofcharged particlestoward high-energy

collisionpoints.

49

Acceleratorscreatedthesuperconductorindustry,andsuperconducting

magnetshavebecomethenaturalchoiceforanyapplicationwherestrong

magneticfieldsareneeded–formagneticresonanceimaging(MRI)in

hospitals,forexample,orformagneticseparationofmineralsinindustry.

Otherscientificusesarenumerous,fromnuclearmagneticresonancetoion

sourcesforcyclotrons.

Someofthestrongestandmostcomplexsuperconductingmagnetsarestill

builtforparticleacceleratorslikeCERN’sLargeHadronCollider(LHC).The

LHC uses over1,200 dipole magnets,whose two adjacentcoils of

superconductingcablecreatemagneticfieldsthatbendprotonbeams

traveling in opposite directions around a tunnel27 kilometers in

circumference;theLHCalsohasalmost400quadrupolemagnets,whose

coilscreateafieldwithfourmagneticpolestofocustheprotonbeamswithin

thevacuumchamberandguidethemintotheexperiments.

TheseLHCmagnetsusecablesmadeofsuperconductingniobiumtitanium

(NbTi),andforfiveyearsduringitsconstructiontheLHCcontractedformore

than28percentoftheworld’sniobium titanium wireproduction,with

significantquantitiesofNbTialsousedinthemagnetsfortheLHC’sgiant

experiments.

What’smore,althoughtheLHCisstillworkingtoreachtheenergyforwhichit

wasdesigned,theprogramtoimproveitsfutureperformanceisalreadywell

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’sSuperconductingMagnetProgram.Theseprogramsarecurrently

developingacceleratormagnetsbuiltwithniobium tin(Nb3Sn),abrittle

materialrequiringspecialfabricationprocessesbutabletogenerateabout

twicethefieldofniobiumtitanium.Yetthegoalformagnetsofthefutureis

alreadysetmuchhigher.

“Amongthemostpromisingnewmaterialsforfuturemagnetsaresomeof

thehigh-temperaturesuperconductors,”saysSabbi.“Unfortunatelythey’re

verydifficult

51

CONCLUSION

Thepurposeofthispresentationwasthestudyofsurgecurrentprotection

usingSuperconductors.TheSuperconductorFaultCurrentLimitersoffers

efficientadvantagestopowersystemsandopensupamajorapplicationfor

superconductingmaterials.

Surge suppressors should be used as a mailerofhabitwith 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