High-Resolution, Fast Start-Up, Delta-Sigma ADC-Based AFE for Air Circuit Breaker

82 Pages·2016·3.65 MB·English

by  Texas Instruments, Incorporated

TI Designs
High-Resolution, Fast Start-Up, Delta-Sigma ADC-Based
AFE for Air Circuit Breaker (ACB) Reference Design
TIOverview DesignFeatures
Thisdesignhighlightsasignalprocessingfrontendfor • ThreeVoltageandFiveCurrentInputsInterfaced
anelectronictripunit(ETU)forusewithanaircircuit to8-Channel,SimultaneousSampling,24-Bit ∆∑
breaker (ACB).Thissubsystemusesahigh-resolution ADCADS131E08SWithFastStart-Up(<3ms)
delta-sigma(∆∑)ADCformeasuringwidecurrentand
• MeasurementofACCurrentInputsWithDynamic
voltageinputswithinaspecifiedaccuracy;the
Rangeof ≤500Within ±1%WithFixedPGA Gain
subsystemcanmeasureuptoeightsimultaneous
• MeasurementofACInputFrom10Vto750 V
inputswith24-bitresolution.TheADCinterfaceswith
Within±1%WithFixedPGAGain
anMSP430MCUforinputprocessing.Thisdesignis
poweredwithrectifiedcurrentinputorauxiliaryDC • OnboardPotentialDivider toMeasureVoltage and
inputpower supplies.Thedesignofferstwooptionsto BurdenResistorsfor CurrentMeasurement
generatepositive andnegativepowersupplies,one
• TotalStart-upTimeof <4msfor ∆∑ADC
usingtheLM5017andtheotherwiththeLM5160
(ADS131E08S)toMeasureWithin±2%ofInput
configuredinFly-Buckmode.Thepurposeofusingan
VoltageAfterApplicationofAuxiliaryDCInput
ETUinanACB istoachievefastandrepeatabletrip
• CurrentMeasurementAccuracyof ±0.2%Achieved
performanceforwidecurrentinputsandwide
WithADS131E08for 0.2-to100-AACInput
temperatureinputs.TheACBtripswithin <mswhen
poweredwithafault. • VoltageMeasurementAccuracyof ±0.2%Achieved
WithADS131E08for 5-to1000-VACInput
DesignResources
• DC-DCConvertersConfiguredinFly-Buck™
ConfigurationtoGenerateSupplyOutputs
TIDA-00661 ToolFolderContainingDesignFiles
• AccuracyMeasurementWithLowPowerCurrent
ADS131E08S ProductFolder
Transformer(LPCT)From0.6mVto333V(>500
MSP430F5969 ProductFolder
DynamicRange)Within±0.2%
LM5160 ProductFolder
• SubsystemConfigurablefor 2-or8-WPower
LM5017 ProductFolder
Output
TPS73201-Q1 ProductFolder
• ProvisiontoMeasureThreeCurrentInputsWith
TPS72301-Q1 ProductFolder
SingleGainInterfacedto12-Bit InternalADCof
TPS73230-EP ProductFolder
MCUfor EarthCurrentMeasurement
TPS7A6533-Q1 ProductFolder
• ModularDesignProvidesOptiontoInterfaceADC
LMV614 ProductFolder
BoardtoADS131EVMorMSP430MCU
LM2903 ProductFolder
LMT87 ProductFolder • OnboardLDOstoGenerate3.3Vand5VforMCU
andADCBoards,±2.5Vand3Vfor ADCAnalog
LM4041-N ProductFolder
Supply
LM8364 ProductFolder
ADS131E08 ProductFolder • ADCInputsProtectedAgainstESD
FeaturedApplications
• ACB
ASKOurE2EExperts
• MCCB
• Recloser
• FeederProtectionRelay
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VDC_PRI TPS7A6550 5.0 V_REG
ENBCRLEOASKUERR E (CLoMmp2a9ra0to3r) 12.0 V (LDO) 12.0 V_RELAY
TPS7A6533 3.3 V_DVDD
AUCOXR.T DC RECTIFIER CS(DN 1C8h.5 M3o7sFNEKT)CS L(SMtep5 D1o6w0n D(8C -WDC)) 5.5 V (LDO)
MOSFET based LM5160 (2 W) TPS73201 2.5 V_AVDD
Shunt Regulation (Step Down DC-DC) TP(SLD7O3)230 3.0 V_AVDD
(LDO)
–5.5 V TPS72301–2.5 V_AVSS
(LDO)
On MSP430 Board On ADS131E08S Board
ADS131E08S Board AVDDAVSS 3.3 V_DVDD
ADS131E08S
Current Input RBE1US6RI.S5DT E(cid:159)ON(cid:3)R V i n = - V - -D2-I-F-F-- E PPGGAA ßß(cid:8)(cid:8)(cid:3)(cid:3)
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5V VoRlMtSa tgoe 7 5I0n pVRuMtS PO1T.E2N 0T(cid:159)IA(cid:3):L 1 D.2IV .ID(cid:159)E(cid:3)R V i n = - V - -D2-I-F-F-- MNDUAX PPGGAA ßß(cid:8)(cid:8)(cid:3)(cid:3) SPI +5.+0-53 V..53_ RVVEG (TMLPM STEN8S7OR)
PGA ß(cid:8)(cid:3)
2.4I NVT o Rr E4.F0 V CLK EXCTLEORCNKAL
MSP430 Board 3.3 V_DVDD 3.3 V_DVDD
3.3 V_DVDD
LMV614 MSP430F5969IRGZ
(L1.M65-4V0 R4E1F) V i n = - -V -2-D-D-- (xA1) (opamp) EVMSPI/ I2C (+SI5NPA.5TID, E VIC2R,C /–MF, A5CG.C5UP E IVO,
B 3.3 V, 5V_REG)
(x5.7)
EaCruthrr Fenatult (xC5.7) 1AS2DA-BRCit UGAPRIOT C(EOxNpNaEnCsiToOnR)
D CLK CRYSTAL
(x5.7)
RST (ULLMV D8e3te6ct4or)
NOTE 1: Voltage & Current input is converted to ±1.2-V peak at Max input
NOTE 2: ADC PGA Gain Setting = 2 for all inputs JTAG CONNECTOR
NNOOTTEE 34:: OA/PDA c (oBn,nCe,Dc)t sG taoi nM =C U5. 7board through the ADC/MCU Interface connector A (14 PIN)
AnIMPORTANTNOTICEattheendofthisTIreferencedesignaddressesauthorizeduse,intellectualpropertymattersandother
importantdisclaimersandinformation.
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1 Design Theory—Circuit Breaker
Acircuitbreakerisanautomatically-operatedelectricalswitchthat hasbeendesignedtoprotectan
electricalcircuitfromdamagecausedbyoverload.Anoverloadoccurswhentoomanydevicesare
operatingonasinglecircuit,orwhenforcingapieceofelectricalequipmenttoworkbeyonditsdesigned
capabilities.Ashortcircuitoccurswhentwobareconductorstouch.Whenashortcircuit occurs,
resistancedropstoalmostzero.Short-circuitcurrentcanbethousandsoftimeshigher thananormal
operatingcurrent).Thebasicfunctionof acircuit breakeristodetectafaultconditionand,byinterrupting
continuity,immediatelydiscontinueelectricalflow. Breakersareavailableindifferent types.
• Low-voltagecircuitbreakers:These breakersarecommonlyusedindomestic,commercial,and
industrialfields.Miniaturecircuitbreakers(MCB),molded-casecircuit breakers(MCCB), andaircircuit
breakers(ACB)arecommonexamplesoflow-voltagecircuit breakers.
• Medium-voltagecircuitbreakers:Thesebreakerscanbeassembledintometal-enclosedswitchgear
lineupsforindoorapplicationsorasindividualcomponentsfor outdoorapplicationslikesubstations.
Vacuumcircuitbreakers,aircircuitbreakers,andSF6circuit breakersareexamplesofmedium-
voltagecircuitbreakers.
• High-voltagecircuitbreakers:Thesebreakershelptoprotectandcontrolelectricalpower transmission
networks.Thesebreakersareusesolenoidsfor operationandemploytheuseofcurrentsensing
protectiverelaysthatfunctionthroughcurrent transformers. Vacuum circuit breakersandSF6circuit
breakersareexamplesofhigh-voltagecircuit breakers.
Circuitbreakersperformthefollowingfunctions:
• Sensing–Whenanovercurrentoccurs
• Measuring– Theamountofovercurrent
• Acting– Bytrippinginatimelymannertoprevent damagetothecircuit breakerandtheconductors
thatthe breakerprotects
Thecurrent-carryingcapacity(inA)ofthebreakermust behigher thantheexpectedloadinthecircuit.
1.1 Circuit Breaker Construction
Circuitbreakersareconstructedfromthefollowingfivemajorcomponents:
• Frame(moldedcase)
• Contacts
• Arcchuteassembly
• Operatingmechanism
• Electronictripunit(ETU)
TheconstructionandoperationofACBsandMCCBssharecommon features,suchasacontactsystem
withanarc-quenchingmechanismtooperatethebreakerandanelectronicsystemtoprovideprotection,
control, andindication.
MCCBsareavailableupto4000Abutbecomelesscost-effectivefor verylargeratings(2000Aand
above). TheadvantageofMCCBswithlargeratingsisacompactsize. Inashortcircuit,thecontactsof
MCCBsopenbeforethefirstpeakofthecurrent waveform(withinfivemsina50-Hzsystem).The fault
currentflowingthroughanMCCBneverreachesitspeakandthefaultenergyalloweddownstreamis
limited. Thisfaultlimitationprotectssensitiveequipmentthat isnotratedtowithstandfaults.
AnACBisphysicallylargerbutmorecost-effectivefor higher ratings.ACBsareselectedbecausethey
havetheabilitytowithstandfaultcurrent ratherthanlimitit.AtypicalACBopensashort circuit within
40msto50ms,allowingbetweenoneandtwocyclesoffaultcurrent throughbeforeopening. Aload
protectedbyanACB(transformersorbusbars, for example)must beratedtowithstandfaultcurrentfora
shortduration.
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1.2 Circuit Breaker—Sensor Selection
Circuitbreakerscombinethefollowingsensorsfor operation:
• Ironcoresensorforthepowersupplytotheelectronics
• Air coresensor(Rogowskicoils)formeasurement,whichguaranteeshighaccuracy
Considerthefollowingparameterswhenselectingbreakers:
1. Ratedcurrent – Thisisthemaximumvalueofcurrentthat acircuit breaker(fittedwithaspecified
overcurrenttrippingrelay)cancarryindefinitelyatanambienttemperaturestatedbythemanufacturer
withoutexceedingthespecifiedtemperaturelimitsofthecurrentcarryingparts.
2. Short-circuitcurrent(faultcurrent) – Theshort-circuitcurrent-breakingratingofacircuit breakeristhe
highest(prospective)valueofcurrentthat thecircuit breakeriscapableofbreakingwithoutbeing
damaged.Thevalueofcurrentquotedinthestandardsistheroot meansquare(RMS)value of theAC
componentofthefaultcurrent,thatis,theDCtransientcomponent,whichisalwayspresent inthe
worstpossiblecaseofshortcircuit.Whencalculatingthestandardizedvalue, theDCtransient
componentisassumedtobezero.
3. Ratedvoltage– Thisisthevoltageatwhichthecircuit breakerhasbeendesignedtooperateinnormal
orundisturbedconditions.
4. Systemfrequency– Thesystemfrequencyisnormally50Hzor60Hzandcanevenbe400Hzin
someapplications.Thenextsubsectionprovidesfurtherinsightonthefaultcurrent.
Thesystemfrequencyisnormally50Hzor60Hzandcanevenbe400Hzinsomeapplications.The next
subsectionprovidesfurtherinsightonthefaultcurrent
1.2.1 FaultCurrent
Acircuitbreakermustbecapableofsafelyinterruptingthemaximumratedshort-circuitcurrentat their
locationinthecircuit.Notethatthecostofcircuit breakersislowerwithalowerbreakingcapacity.
Potentialshort-circuitcurrentisdeterminedby:
1. Theavailablepowerfromthetransmissionnetwork
2. Transformercharacteristics
3. Impedanceofconductorsinthedistributionsystem
Afaultlevelstudythataccountsfortransformer characteristicsandconductorimpedanceatallcircuit-
breaker installationpointsallowsforaselectionofbreakerswithanoptimumbreakingcapacity.
1.3 Next-Generation Circuit Breakers
Thepreviousgenerationsofbreakershavebeenthermal-magneticbreakers. Thenewgenerationof circuit
breakersisbasedontheETU.CircuitbreakersbasedonETUprovidehighlyaccurateprotectionwith
widesettingrangesandcanintegratemeasurement,metering,andcommunicationfunctions.Designers
cancombinethesecircuitbreakerswithaswitchboarddisplayunit toprovideallofthefunctionsof a
powermeteraswellasoperatingassistance.Throughdirectaccesstoin-depthinformationand
networkingthroughopenprotocols,thesebreakersallowoperatorstooptimizethemanagementof their
electricalinstallations.
Thenewgenerationofcircuitbreakershasbeenspecificallydesignedtoprotectelectricalsystemsfrom
damagecausedbyoverloads,shortcircuits,andequipmentgroundfaults.Circuitbreakersaredesigned
toopenandcloseacircuitmanuallyandtoopenthecircuit automaticallyatapredeterminedovercurrent
setting. Circuitbreakerscanalso:
• Enhancecoordinationbecauseoftheir levelofadjustability
• Provideintegralground-faultprotectionfor equipment
• Providehighinterruptingratingsandwithstandratings
• Providecommunicationsandpowermonitoring
• Provideprotectiverelayingfunctions
• Providezone-selectiveinterlocking(ZSI),whichcanreducedamageintheeventofafault
• Provideameansofconnectiontoanexternaltest device, allowingfor periodicaltestsofthestatusof
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theETUusedinbreakers
• Allowallsettingstobeprogrammedinthefield, without theuseofanyexternaldevice
• AllowtheETUtosealuponadjustment (keylockorseal) behindatransparentdoororplate,which
allowstheusertoviewthesettingsandprotect against unauthorizedtampering
1.3.1 ElectronicTripUnit(ETU)
Thetripunitsintegratedintocircuitbreakersarecalledelectronictripunits(ETUs).ETUsintegrateinto the
circuitbreakerasanadd-onsystemtomaintain thecompactsizeofacircuit breaker. ETUsare
microcontroller(MCU)basedandareusedtomeet abroadrangeofmonitoringandprotection
requirements,suchascurveshaping,zoneselectiveinterlocking,arcflashreduction,diagnostics,system
monitoring,andsystemcommunications.TrueRMSsensingoffersincreasedaccuracyandreliability.
Tripunitsusingdigitalelectronicsarefasterandmore accurate.Designedwithsignalprocessing
capabilities,ETUscanprovidemeasurement informationanddeviceoperatingassistance.Someof the
functionsthatETUsofferare:
• MCUandmicroprocessorunit(MPU)basedtrueRMSmeasurement
• Fourtofivecurrentsensing
• Optionalvoltagemeasurement
• Protectionfunctionsandpowermeasurements
• Self-poweredwhenphasecurrent> 20%to25%nominalcurrent (In)orauxiliarypowered(DCinput)
• Makingcurrentrelease(MCR)
• Fault recordingandeventlogging
• Digital outputsandinputsforcoordination
• Parameterizationanddisplay
• Networkcommunication
• Thermalmemoryandovertemperatureprotectivetrip
• Zoneselectiveinterlocking(ZSI)andisolatedalarmsprovision
• Unitstatuslight-emittingdiodes(LEDs) andcauseoftripLEDs
• Liquidcrystaldisplay(LCD),resetpush-button,andtest push-button
• Discreterotary orkey-basedprogrammablesettings
• Auxiliary modulesincluding
– Analogoutput
– Digital input
– Tripcircuitsupervision(TCS)module
– Powersupplymodule
1.4 Summary of Electronic Trip Unit (ETU) Features
1.4.1 Measurements
TheETUcalculatesalltheelectricalvaluesinrealtime,suchastheV,A,W,VAR,VA,Wh,VARh,VAh,
andHzpowerfactors.TheETUalsocalculatesdemandcurrentanddemandpower overanadjustable
timeperiod.Intheeventoftrippingonafault,theinterruptedcurrentisstored.Theoptionalexternal
powersupplyenablestheETUtodisplaythevaluewiththecircuit breakeropenornotsupplied.
Instantaneousvalues
Thevaluedisplayedonthescreenisrefreshedatsomefixedtimeinseconds.Minimum andmaximum
valuesofmeasurementsarestoredinmemory.
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Demandmetering
Thedemandiscalculatedoverafixedorslidingtimewindow,whichcanbeprogrammedfrom5min to
60min.Accordingtothecontractsignedwiththepower supplier, anindicatorassociatedwithaload
sheddingfunctionenablestheETUtoavoidorminimizethecostsofoverrunningthesubscribedpower.
Maximumdemandvaluesaresystematicallystoredandtimestamped.
1.4.2 FaultRecording,EventLogging,andDisplay
Eventlogsandtablesarecontinuouslyactivated.Providingawealthofinformation,thesemetricsenable
userstoensurethattheinstalledequipmentbaseoperatescorrectlytooptimize settingsandmaximize
energyefficiency.
Localorremotedisplaysoffereasyaccesstooperatorsandprovidethemainelectricalvalues:I,U,V,f,
energy, power,totalharmonicdistortion, andsoforth.Theuser-friendlyswitchboarddisplayunitwith
intuitivenavigationismorecomfortabletoreadandoffersquickaccesstoinformation.
1.4.3 Communication
Fourlevelsofcommunicationfunctionalitiesexist:
• Devicestatus:onandoffposition,tripindication,andfault-tripindication
• Commands:open,close,andreset
• Measurements:mainlyI,U,f,P,E,andTHD
• Operatingassistancedata:settings,parameters,alarms,histogramsandeventtables,and
maintenanceindicators
CommoncommunicationinterfacesincludeEthernet,RS485,Profibus,andRS232.
1.4.4 I/OModules
Inputandoutput(I/O)modulesareavailabletoexpandthecapabilitiesofthecircuit breaker. Thefollowing
descriptionssummarizethecapabilitiesofthesemodules:
• Thedigitaloutputmoduleallowstheconnectionofuptosixbinarysignalstoexternalsignaling
devices.Themodulecanbealternativelyutilizedtocontrolother equipment.Solid-stateandrelay
outputversionsofthismoduleareavailable.
• Thedigitalinputmodulecanconnect toamaximumofsixdigital(24-VDC)inputs.Thisspecification
enablesthestatusofaswitchorthecubicledoortobecommunicatedtothecircuit breaker.
• Theanalogoutputmodulecanbeusedtooutput avarietyofmeasuredvalues(amps, volts,power,
powerfactor,andsoforth)toanalogdisplaydevicesonthecubicledoor.
• Zoneselectiveinterlocking(ZSI)isamethodthat allowstwoormore circuit breakerstocommunicate
witheachothersothatashortcircuitorgroundfaultisclearedbythebreakerclosest tothefaultinthe
minimumamountoftime.
SomeoftheothercommonlyusedI/Omodulesinclude:
• Communicationmodule
• Powersupplymodule
• Analoginputmoduleforinputmeasurementofresistance-temperaturedetectors(RTDs)
• Communicationmodule
• Displaymodule
• EarthLeakagemodule
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1.4.5 Time-CurrentCurvesandCircuitBreakerAdjustments
Time-currentcurvesshowhowfastabreakertripsatanymagnitudeofcurrent.AnETUprocessesthe
inputsignals(voltageandcurrent)andprovidesthetripsignalstoasolenoidorfluxshiftdevice(FD)
basedontheconfiguredtripsettings.Someofthetripcurvesthat canbeconfiguredare:
• L=Longtime
• S=Shorttime
• I=Instantaneous
• G=Groundfault(equipment)
1.4.6 CircuitBreakerAdjustments
Table1.BreakerTripParameters
FUNCTION DESCRIPTION
Variesthelevelofcontinuouscurrentthecircuitbreakercarrieswithouttripping.The
Continuousampere(Ir) continuouscurrentisadjustablefrom20%to100%ofthecontinuousampereratingofa
breaker(Ir=%ofIn).Thisisalsoknownaslong-timepickup.
Referredtoasthe"overload"position,thisfunctioncontrolsthe"pause-in-tripping"timeofa
Long-timedelay breakertoallowlowlevelortemporaryoverloadcurrents.Thisfunctionallowsadjustable
settingsfrom3sor25sat6×Ir.
Determinesthelevelatwhichthecircuitbreakertripswithoutanintentionaltimedelay.The
instantaneouspickupfunctionisadjustablefrom2to40timesthecontinuousamperesetting
Instantaneouspickup
(Ir)ofabreaker.(Anytimeanoverlapexistsbetweentheinstantaneousandshort-timepickup
settings,theinstantaneousautomaticallytakesprecedence).
Controlstheamountofhighcurrentthebreakerremainsclosedagainstforshortperiodsof
Short-timepickup time,whichallowsbettercoordination.Thisfunctionisadjustablebetween1.5to10timesthe
continuousamperesetting(Ir)ofacircuitbreaker.
Controlstheamountoftime(from0.05to0.2sinfixedtime,or0.2sat6×IrintheI2tramp
mode)abreakerremainsclosedagainstcurrentsinthepickuprange.Thisfunctionisusedin
Short-timedelay conjunctionwiththeshort-timepickupfunctiontoachieveselectivityandcoordination.(A
predeterminedoverrideautomaticallypreemptsthesettingat10.5timesthemaximum
continuousamperesettingIn).
Controlsthelevelofgroundfaultcurrentthatcausescircuitinterruptiontooccur.Thisfunction
Groundfaultpickup
isadjustablefrom20%to70%ofthemaximumcontinuousamperesetting(In)ofabreaker.
Addsapredeterminedtimedelaytothetrippointwhenthegroundfaultpickuplevelhasbeen
Groundfaultdelay reached.AninverseI2trampisstandardandprovidesabettertrippingselectivitybetweenthe
mainandfeederorotherdownstreambreakers.
1.4.7 ElectricMotor Operator
Theelectricmotoroperatorisdesignedtoopen,close,andremotelyreset acircuit breaker. Theelectric
motoroperatorismountedonthefaceofacircuit breakersothat itcanengagetheoperatinghandleof a
breaker.Thebuilt-inmotorisconnectedtoremotepushbuttonsorcontacts.Pressingthe “ON”pushbutton
orclosingthe“ON”contactscausestheelectricmotortomovethecircuit breakertothe “ON” position.
Pressingthe “OFF”pushbuttonorclosingthe “OFF” contactscausestheelectricmotortomovethe circuit
breaker to the“OFF” position.Toresetthecircuit breakerfromthetrippedposition, theelectricmotormust
first movethecircuitbreakerhandletothe “OFF”positionandthentothe “ON”position, just asthisaction
isperformedmanually.
1.4.8 Discriminatoror Making CurrentRelease(MCR)
Thediscriminator(alsoknownasamakingcurrent release(MCR)),isasettingprovidedwitheachtripunit
andisbasedonthespecificcircuitbreakersizeandprotectsthecircuit against closingonhighmagnitude
faults. TheMCRfunctionimmediatelytripsandopensthecircuit breakerifhigh-magnitudefaultcurrentis
sensedat theinstantthecircuitbreakercloses.
Thediscriminatorissetat ≥tentimestheratingplugampereratingandisenabledfor approximatelythe
first tencyclesofcurrentflow.Incaseswhereafaultconditionexists,thebreakertripswithnointentional
timedelayonclosing,whichprotectstheuserfromapotentiallyunsafecondition.
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1.4.9 InstantaneousOverride
Instantaneousoverrideisafixedcurrent levelatwhichanadjustablecircuit breakeroverridesallsettings
andtripsinstantaneously.Theinstantaneous(INST)tripfunctiontripstheMCCBorACBwhentheshort-
circuitcurrentexceedsthepickupcurrentsetting,irrespectiveofthestate.Theinstantaneousoverride is
factorysetnominallyjustbelowthebreakerwithstandrating.
1.4.10 TripUnitOvertemperature
Electronictripunitscanoperatereliablyinambienttemperaturesthat rangefrom –20°Cto70°C.Breakers
arederatediftheyareabove70°C.Intheunlikelyeventthat temperaturesexceedthisambient
temperaturerange,thetripunithasabuilt-inovertemperature triptoprotectthetripunit.
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2 ACB Ratings
Avoltageratingcircuitbreakerhasavoltageratingthat designatesthemaximumvoltageitcanhandle.
Thevoltageratingofacircuitbreakercanbehigher thanthecircuit voltage,butneverlower. Forexample,
a480-V ACcircuitbreakercanbeusedina240-VACcircuit,buta240-VACcircuit breakercannot be
usedina480-VACcircuit
Table2.CommonBreakerVoltageRatings
ACVOLTAGE
230 380 400 415 440 500 525 690
RATINGS(V)
Continuouscurrentrating
Everycircuitbreakerhasacontinuouscurrentrating,whichisthemaximumcontinuouscurrentacircuit
breaker isdesignedtocarrywithouttripping.Theratedcurrentfor acircuit breakerisoftenrepresented as
In.Thisdesignationisnottobeconfusedwiththecurrentsetting(Ir), whichappliestothosecircuit
breakersthathaveacontinuouscurrentadjustment.Ir isthemaximumcontinuouscurrent that acircuit
breaker cancarrywithouttrippingforthegivencontinuouscurrentsetting.Ir maybespecifiedinampsor
asapercentageofIn.
Table3.CommonBreakerCurrent Ratings
ACCURRENT
200 250 400 630 800 1000 1250 1600 2000 2500 3200 4000 5000 6300
RATINGS(A)
80 100 160 250 320 400 500 630 800 1000 1280 1600 2000 2500
IrTHRESHOLD
to to to to to to to to to to to to to to
SETTINGS(A)
200 250 250 630 800 1000 1250 1600 2000 2500 3200 4000 5000 6300
Pickup(A)=Irx…1.5 – 10
Currentsetting(A)Ir=Inx …0.4 –1.0
NOTE: ThepickupcurrenthastheoptiontobeIr×15orIr×20.
• ICW is theshort-circuitwithstandratingofaparticularcircuit breakerinamperes.Thewithstand rating
isdefineddifferentlywithindifferentstandards, butitisalwaysthevalueofcurrent that acircuitbreaker
canwithstandforsomeperiodoftimewithout interrupting.
• ICS,ortheservicebreakingcapacityperIEC60947-2,isthebreakingcapacitythat abreakercan
safelyinterruptandbeoperationalafterinterruptingatleastonetime.
• ICU,ortheultimatebreakingcapacityperIEC60947-2,isthebreakingcapacitythat abreakercan
safelyinterrupt,butmaynotremainoperationalafterinterruptingonetime.
Interruptingrating
Circuitbreakersarealsoratedaccordingtothemaximumlevelofcurrenttheycaninterrupt.Thisisthe
interruptingratingorampereinterruptingrating(AIR).Theinterruptingratingsfor acircuit breakerare
typicallyspecifiedinsymmetricalRMSamperesfor specificrated voltages.Thetermsymmetrical
indicatesthatthealternatingcurrentvaluespecifiediscenteredaroundzeroandhasequalpositive and
negativehalfcycles.
Circuitbreakershaveinterruptingratingsasfollows:
• 25kA– Standard,lowshort-circuitlevelapplications(forexample:servicebusinesses)
• 36kAto50kA –Standardapplications(forexample:industrialplants,buildings,andhospitals)
• 70kAto100kA– Highperformanceatcontrolled cost
• 150kA– Demandingapplications
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2.1 Air Circuit Breaker (ACB)—Operating Time
AnimportantspecificationforACBsistheoperatingtime.Thespecificationsfor operatingtimeinclude
breakingtimeandclosingtime.Breakingtimeincludesthemeasurementofinput current andprocessing
ofthesamplestoprovidethesolenoidtripcommand,whichbreaksthefaultcurrent.
Breaking(maximum)time(instantaneousbreaktimeatshort-circuitinterruptioncurrent):If theload current
isgreaterthanthesetinstantaneouspickupvalueisdetected,theACB-electronictripunit willinitiatea
trippulsewithinMaximumbreaktimeofhavingseenthecurrent.Themaximumbreakingtimeisspecified
bydifferentACBmanufacturersintherangeof 30msto50ms.
Toachieveafasterbreakingtime,theETU(includingthepower supply, MCU, andADCs)must have a
faststart-upcapability.
2.2 TIDA-00661 Advantages
ThisTIDA-00661designprovidesasolutiontosomeofthecriticalrequirementsofanACB,suchas:
1. Fast start-up:ACBsarespecifiedtotripwithin35msto40mswhentheyarepoweredwithafault.The
start-uptimeincludesthesystempowerup,ACinput currentmeasurement,andbreakingofthefault
current.
2. Wideinputmeasurement:Thefaultcurrentinput rangevariesfrom0.3Into12Inormoreforagiven
currentbreakerrating.Thecircuitbreakersareavailableinmultiplecurrent ratings.AnADCwith high
resolutionensurestheuseofthesametripunit for multiplecurrentratings.
3. Accuratemeasurementofvoltageandcurrent inputs:Theaccuratemeasurementofinput current
ensuresarepeatabletriptimeperformancefor protectionandanaccuratemeasurementofdifferent
parametersformetering.
4. Increasedreliabilityandtemperatureperformance:Theintegrationofreferenceandprogrammable
gainamplifier(PGA)reducestheexternalcomponentsrequirement,improvestemperature
performance,andincreasesreliability.
TheTIDA-00661designprovidesasolutionfor alloftheabovecriticalrequirementsofacircuit breaker.
ThedesigncontainsanAFEboardandaninterfaceboard.
2.3 TIDA-00661 System Description and Functionality
2.3.1 AFEBoard(With ADCandLDOsforAnalogSupply)
Theanalogfrontend(AFE)boardusesafast start-up ∆∑ADCwithastart-uptimeof <3ms. The ∆∑
ADChaseightsimultaneoussamplingADCswith24-bitresolution.Additionally,theADChasaPGA,
whichcanbeusedtoimproveaccuracywhilemeasuringwideinput currents.TheAFEhasaprovisionto
measurethreevoltagesandfivecurrents. TheAFEboardusestheinternalreferenceoftheADC.A
provisionforanexternalclockhasbeenprovidedinthisdesigntomeetthemeasurementaccuracy
requirementoverawidetemperaturerange.TheADCinput hasbeenconfiguredfor a ±2.5-Vinputrange.
ThePGAhasbeensetforafixedgainof2for most measurementapplications.Anexternal,onboard
temperaturesensorhasbeenprovided.Thedigitalinterfaceispoweredby3.3-Vsupply. TheADCis
interfacedtoanMSP430F5969basedinterfaceboardorMMB0DSPboard.
TheAFEboardfortheTIDA-00661designfeaturesthefollowing:
1. Fast start-up(<3ms)∆∑ADCADS131E08Switheight simultaneousinputsfor measuringupto five
currentsandthreevoltages;onboardpotentialdividerfor measuringupto900V
2. LDOtogenerate ±2.5V,3VforADCanaloginput
3. Temperaturesensortomeasurelocalonboardtemperature
4. ExtensionconnectorsforinterfacingtoMMB0digitalsignalprocessor(DSP)boardofan
MSP430F5969interfaceboard
10 High-Resolution,FastStart-Up,Delta-SigmaADC-BasedAFEforAirCircuit TIDUB80B–January2016–RevisedSeptember2016
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