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RT 3 b

RT 3 b. Smart Grid Protection SMART GRIDS: new possible approaches to adapt protection and automation systems and to match electric system security, quality of supply needs and generators features Alberto Cerretti ENEL DISTRIBUZIONE ITALY.

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RT 3 b

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  1. RT 3 b Smart Grid Protection SMART GRIDS: new possible approaches to adapt protection and automation systems and to match electric system security, quality of supply needs and generators features Alberto Cerretti ENEL DISTRIBUZIONE ITALY

  2. MainproblemsforDSOsrelatedto high penetrationof DG – Impact on protection and automation system • Short circuitcurrentvaluesincrease • Problems • Limitedproblemsfor short termwithstandcurrent (maintainingprevious network configuration) due to wide adoptionofinvertersto interface generatorswithdistribution network. Max Icc  1,2 In • Problemswith MV feedermaximumcurrentprotections (50-51). Invertersmaybecomparedtocurrentgenerators (short circuitcurrentconstantduring fault, completelydifferentfrombehaviourofsynchronousgenerators). Short circuitcurrent direction inversionmayresultwith non correcttripping (expeciallywith 50 relays) • Possiblesolutions • Adoptionofdirectionalprotectionsagainstovercurrents (67) (bothfeeder and CustomerGeneralProtectionRelay) • Introductionof a minimum timedelaytoavoid non correcttripping and toallowlogicselectivity • Wide adoptionofinvertersasgenerators interface with the distribution network ? Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  3. Incompatibilitywith MV network automation system • Problems • Non correct fault detection fromFPIswith short circuits (with no directional detection) • Possibleislandoperation (reductionofeffectivenessofautomaticreclosingcycle or ofautomationcycle, worseningofqualityofsupply, possibledamagestogenerators/inverters in case ofautomaticreclosingwithexcessivephaseshift) • Problemsof network security: automationcyclehastodisconnect minimum amountof DG during fault selection, i.e. fault selection and clearing hastobeperformed, preferably, opening SwitchDisconnector or Circuit Breakers just upstream the faultysection • Possiblesolutions • Adoptionofdirectionalprotectionfunctionagainstovercurrents (67) on FPIsbesidesagainstphasetoearth fault (67N) • Adoptionof innovative FPIscompletelycoordinated (detection algorithms, sensitivity, etc) withprotectionrelays and with IEC 61850 protocol, withoutconfirmationof the fault fromvoltageabsence detection (causedfrom CB tripping in HV/MV substation) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  4. Incompatibilitywith MV network automation system • Possiblesolutions • AdoptionoflogicselectivityamongFPIsalong the feeders and amongFPIs and MV feederprotections (logicselectivityalsoextendedtointernalCustomerplantprotections ?) • Adoptionof transfer trip amongFPIs / MV feederprotectionrelays and Interface ProtectionRelayof DG connected in MV besides wide adoptionofCBsinsteadofswitchdisconnectoralong the feeders ? • Wide adoptionofCBsalong MV feedersinsteadofSDs, so to open directly the faultysection, notonly in case of a phasetoearth fault (possibleonly in MV compensatedneutralnets), butalso in case of short circuits, toincrease network securititylevelbesidesQualityofSupply. Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  5. Transfer trip schemeadoptedby ENEL (protectionrelays and FPIs) Logicselectivityalong a MV feeder Logicselectivityalong a MV feeder and inside a MV Customerplant Withlogicselectivity and CBsinsteadofSDsonlyfaultysectionof the feeder and sectionsdowstreamresultinterestedfromaninterruption (transient or short or long) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  6. Interface ProtectionRelay and possibleislandoperation • Problems • Usually IPR are installed at DG’s PCC and based on local measurements. In Italy: • Main loss of mains protections are 81> & 81< • A Non Detective Zone (NDZ) isalwayspresent: in case of real power balance betweenload and generation, relay’sthresholds (whateverloss of mains detectionprincipleis) maybe not violatedduringislandingdepending on thresholdsregulations and waiting time for fastreclosingoperation (if present) • More restrictedregulation of the thresholdsmayresult in a worsening of electric system security (nuisance tripping, withunnecessarryloss of large amount of DG) • Lessrestrictedregulation of the thresholdsmaybedangerous for generators: damages to axys for rotating machines – due to excessive toques – and damages to electronic components of invertersresultatFastReclosingOperation (ENEL standard FRO waiting time is 400 ms at the moment, 600 ms in the next future) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  7. Interface ProtectionRelay and possibleislandoperation • Problems • Frequency and voltage for LV Customers during island operation may exceed limits of Standard (EN 50160) and of Contract with important damages • Possiblesolutions • Adoptionof transfer trip amongFPIs/feederprotectionrelays and Interface ProtectionRelayof DG asmain Loss ofMainsprotection. Disconnectiontimeofgeneratorsnotlongerthan 500 ms, including CB operationtime, withwaitingtimefor first reclosingoperation = 600 ms (100 ms for fault self extinguishment) • Loss ofmains back up protectionrealizedwithanimprovedversionofactual IPR, withless sensitive regulationsof the frequencythresholds • Withabsenceofcommunication network (eventemporary) automaticchangeof IPR frequencythresholdsregulations so toassurehighersensitivity (no island) • Coordinationof IPR voltagethresholdsregulationswithgenerator LVFRT (it is the capability of the generators to overcome voltage sags due to a network contingency or a short-circuit) toavoid nuisance tripping Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  8. Generator LVFRT and IPRvoltagethresholdsregulations • zone of normal operation, • zone in which DG unit has to remain connected to the grid, at worst without supplying energy; once the voltage reaches 90% of rated value generator has to restart to inject power into the network, • zone where DG plants can be isolated from the network by means of each own protections, • zone in which the generator has to remain connected to the grid and to absorb reactive power until its own power factory limits, • zone in which internal protections have to act in order to disconnect generator from the grid. Zone of 27/59 IPR thresholdsintervention Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  9. NDZ of Interface ProtectionRelay - possibleislandoperation Voltage and frequency oscillations during islanding Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  10. Interface ProtectionRelay and possibleislandoperation • Possible IPR (with transfer trip) scheme Transfer trip 0,2 Vn Voltage at Pcc IPR trip (gen. disconnectionwithin 500 ms) 81.S2 47,5 – 51,5 Hz 81.S2 49,7 – 50,3 Hz Communication network presence Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  11. Interface ProtectionRelay and possibleislandoperation • Logicselectivity complete scheme (transfer trip + network automation) Production Supervision System alsoreceives and trasmittogeneratorsrequestfrom DSO forP&Q set points Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  12. Interface ProtectionRelay and possibleislandoperation • Logicselectivity complete scheme (transfer trip + network automation) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  13. Interface ProtectionRelay and possibleislandoperation • Logicselectivity complete scheme (transfer trip + network automation) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  14. Interface ProtectionRelay and possibleislandoperation • Logicselectivity complete scheme (transfer trip + network automation) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  15. Interface ProtectionRelay and possibleislandoperation • Comments • ENEL Distribuzione solution (for MV net only, at present time) guarantee Quality of Supply, security of electric system and generators (non island operation/damages after FRO) • Nevertheless, other subjects are defining requirements with consequences on Distribution networks, taking into account only some points of the whole problem

  16. Interface ProtectionRelay and possibleislandoperation

  17. Network safety vs qualityofsupply/damagestogenerators As a functionof 81>/81< thresholdsregulations and ofwaitingtimefor FRO anequivalent short circuitvoltagemayappear at generatorterminals, causing short circuitcurrentslimitedonlybyinternalimpedanceof the generators and mechanicaltorques on rotatinggenaratorsaxys. Seriousdamagesmay derive. Do productstandards (allgenerators, includinginverters, PV, wind, etc., correctly deal this ? Manydamagesoccur on rotatingmachinesalso in case ofsimplyvoltagedips ! Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  18. Network safety vs qualityofsupply/damagestogenerators In case of SD/CB intentional opening, no automatic FRO ispresent, butislandoperationispossiblefor long time. In case of short circuits on the feeder IPR should trip for 27 thresholdbefore FRO. In case ofphasetoearthfaultsislandoperationispossiblefor long time and FRO maybepresentforqualityofsupplyreasons. Will distributorshaveto eliminate FRO in case ofphasetoearthfaultstoallow IPR tripping ? Will Regulatorsallowthis ? Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  19. Network safety vs qualityofsupply/damagestogenerators In case ofintentionaloperations on the net, no significative electricparameterdisturbancemayappear (itdependsonlyfrom the unbaslancebetween generation and load) withoutisland detection from IPR (whateveris the adoptedalgortithm). Long islandoperationispossible. Considering PV inverters, no fullystandardized loss ofmainsprotectionfunctionisdefined, aswellasproper test procedurestakinginto account the mutualinfluenceofdifferentgenerators. Embedded IPR isnot at alltestedlike a traditionalprotectionrelay (under TC 95 responsibility). In addition, loss ofmainsshouldhavetobedetectedBEFORE FRO, and thisispeculiarofeach single distributor. Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  20. Network safety vs quality of supply/damages to generators • Furtherconsiderations • Itseemsthatneedsofelectric system security maybe in contrastwithneedsofqualityofsupply set by some Regulators and, possibly, with some productstandards (generators, expecially PV ones). More cooperation and integrationamongall the involvedSubjects and TechnicalCommitteesisnecessary ? On featuresofeachkindofgenerators, on typetests and procedures (includingpossibleembedded IPR on inverters), etc ? • In case ofphasetoearthfaultsitwouldbepossibleto eliminate FRO or toperformitwith some tenssecondsofdelay (toincreaseislandcondition detection from IPR - embedded or not) without significative decreaseofqualityofsupplylevelonlywithcompensatednetworks (more than 90% oftransientinterruptions due tophasetoearthfaults are eliminate by the coil). In case ofinsulatednetworks (or earthedthroughresistors), some reclosingoperations are necessarytoavoid long interruptions. In thesenets a decreaseofQoSwillappear. Isitpreferrabletoaccept a decreaseofQoS (withpropoermodificationsof the rules set by the Regulators) or towidelyadoptcompensatedneutral MV net ? Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  21. Network safety vs quality of supply/damages to generators • Furtherconsiderations • In case of wide regulationoffrequency/voltagethresholds, safetyproblemsmaybepresent in case of non expectedislandoperationof network parts • IPR thresholdsregulations and LVFRT coordinationimpliesthatalleventualgeneratorprotections (includedembeddedones in PV inverters) havetobeproperly set (type test on LVFRT withallembeddedprotectionfunctionsactivated !) • LV net iseven more subjecttopossibleislandcondition, PLC seemtobe a propercommunication system , buttimes are non compatiblewith a 600 ms delayfor FRO. Whichsolution ? • Island operation: isitbettertoallow and correctly deal it or isitpreferrableto continue avoidingit? In Italy, cumulative durationof long interruptions fo LV Customers due tofaultsisabout 45,1 minutes. Makeitanyanysensetoconsider a possibleislandoperationto face a conditionwhichrepresent  0086% of the total yearduration ? Nothingisdefined, at the moment, concerningsubjectsresponsibleofQualityofSupply and/or ofrespectofcontractparamentersduringislandoperation Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  22. Voltage/cos regulation Vs hosting capacity • Problems • Regulationlaw on on-loadtapchanherof HV/MV TR • Slow voltagevariations: mainlimitto hosting capacityalong a feeder(expecially medium/high lenght and overhead) ! • PossiblerequestsfromTSOstohave a cos   0,9 lagging at PCC on HV net • Possiblesolutions • Cos  in the range 0,95 leading ÷ 0,9 laggingforrotatinggenerators (at the moment 0,95 leading ÷ 0,98 lagging) • Cos  AT LEAST in the range 0,9 leading ÷ 0,9 laggingforinverters (expecially PV ones) (at the moment cos  = 1) • Adoption, fromDSOs, of a DMS usingrealtimevoltagemeasurementstocalculateloadflows and sendproper P & Q set pointstomaingenerators. Communication network maybe the sameforlogicselectivity and transfer trip • Failsafevoltagecontrolalgorithm: localcontrollaw in absence (eventemporary) ofcommunication net Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  23. Voltage/cos regulation Vs hosting capacity • Possiblesolutions • Wideningof cos  regulationrangereducingalsoactivepower ? On demand ? In automatic ? • Are productstandardsofgenerators (rotating and/or inverters, expecially PV ones) compliantwithnetworks cos  needs ? • Are generatorscontrolsystemsableto deal controlsignalsfromDSOs DMS ? Ifnot, havetheytobeable ? In whichtime ? Withwhichprotocol (IEC 61850 ?) • Are possiblerequestsfromTSOstohave a cos   0,9 lagging at PCC with HV net tobeconsidered or a newapproachhastobedefinedtoincrease hosting capacity in the respectofcontractuallimitsconcerningvoltage and of EN 50160 standard ? • Haveinverters (expecially PV ones) toabsorbreactivepowerduring night to compensate reactivepowerof underground cables ? (no load, possible cos  ≤ 1 leading at PCC with HV, excessivevoltage on MV net Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  24. Voltage/cos regulation Vs hosting capacity • Possiblesolutions • Have DG on MV net tobeconnecteddirectlyto HV/MV substation MV bus (to produce reactivepowerwithnegliglibleeffect on voltage) or may DG tobeconnected on existingfeeders ? (withreductionoflosses) • Have DSO toinstallcompensationsystems (Inverters ?) on HV/MV substation MV bus toregulate cos  at PCC with HV net ? Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  25. Voltage/cos regulation Vs hosting capacity Effect of cos on voltage regulation is quite different between overhead feeders and MV underground feeder If GD isconnectedalonganexistingoverheadfeeder (with passive load), itisnecessarythatgeneratorsabsorbreativepowertolimitvoltageincrease and tomaximizeHosting Capacity. With cos  in the range 0,9÷0,92 itispossibletouse the conductor up toitsthermallimit Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  26. Voltage/cos regulation Vs hosting capacity If GD produces reactive power (for instance cos = 0,9 leading) HC results drastically reduced (43% of previous condition, 3,34 MW against 7,74 MW) Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  27. Anyway, ifgeneratorsabsorbreativepowertolimitvoltageincrease, HC ismaximized. With cos  in the range 0,9÷0,92 itispossibletoreachmaximumadmissiblelimit in Italy (bothforStandards and Regulations) for GD in MV nets (10 MW), withexcellentvoltagecontrol. Voltage/cos regulation Vs hosting capacity With a MV underground cable, effect on voltage regulation of cos results reduced. Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  28. If GD produces reactive power (for instance cos = 0,9 leading) HC results reduced (76% of previous condition, 7,63 MW against 10 MW) Voltage/cos regulation Vs hosting capacity Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  29. New distribution network operationschemestoincrease network security and tolimitvoltagevariations (fast and slow) Introductionof a meshedoperationschemeinsteadof a traditionalradialonemaytrasformaninterruption (transient, short and long, depending on protection and automation system) in a simplevoltagedip. In addition, a meshedschemereducesvoltagevariations and allow a higher security levelfor the electric system: 2 connectionsfromeachgeneratorto a HV/MV substationswouldbepresent, so a (n-1) contingencyshouldhave no relevanteffect Manyimportantproblems, anyway, are present: • Problems • In a realmeshed network, short circuitcurrentwouldsurelyresultmuchhigherthan the valueconsidered in a radial network (more currentinfeedsfromdifferent HV/MV TRs and fromall the GD connectedto the meshednetworks. In Italy all MV net isrealizedwith a short withstandcurrent = 12,5 kA, 1 s. • Cross sectionof the MV feederconductors are notconstantalong the feeder, i.e. a complete 2 ways connection of GD to a HV/MV susbsationwouldnotbegenerallypresent. As a conclusion, the whole network wouldhavetobecompletelyrenewed Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  30. Problems • Manyproblemswouldaffect MV network protection and automationsystemsusing a meshedconfiguration: • Phasetoearthfaults: • on compensatednetworks, directional WATTMETRIC protectionswouldnotbeabletodetect the fault, aswellasFPIs • on compensatednetworks, controller in chargeofresonancepointcalculation and consequentcoiltuningwouldnotbeableto do itany more. At the moment about 2 controller in the same HV/MV substationsmaycorrectly deal the parallel situation (bothcreated in the SS, closing bus coupler, and along the MV net) of the MV netsthey are in chargeof • Short circuits: • Depending on the levelofmeshedoperation, it can beextremelydifficultto individuate a precise fault currentpath and todisconnectonly the faultysectionwithproper timing As a conclusion, the wholeprotection and automationsystemswouldhavetobecompletelyrenewed Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  31. Possiblesolutions • Adoptionof a solidgroundedconfigurationfor MV net and installationofdistancerelays (21). • MV net automation system wouldhavetobedismatled • Distancerelaywouldnotwotkcorrectly on a MV net, due tolimitedlenghtof the feeders, the continuouschangeof conductor tipology (overhead, cable) and the high presenceofundregroundcablewithvery low reactancevalue and, finally, the continuouspresenceofinfeedpoints, withcompletelydifferentfeatures • Adoptionofdifferentialprotections • A proper and realiable communication network would be necessary, to maintain the advantages of MV net automation systema, an enormous number of differential relays would be necessary. What would happen in case of changes in the network operation scheme ? As a conclusion, both the whole MV distribution net and protection and automationsystemswouldhavetobecompletelyrenewed. Performancesobtainablewith a traditionalradialdistribution net, provideditisequippedwith a high performance protection and automation system, are verysimilar, withneedofextremelylowerinvestments ! Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  32. Possiblesolutions • Adoptionof a “partial” meshedscheme, consisting in a closedloopconfiguration (2 MV feedersfrom the same HV/MV substation MV busbaroperatedwith the “border” SD/CB normallyclosed): • Maximum short circuitcurrentlevelwillremain the sameas in traditionalradialoperation • Protection and automationsystemsmaybemaintianed, besidesresonantgrounding • Minimum intervention on the feedersmaybenecessary, in case ofpartsoffeedersrealizedwithsectionshavingtoo low cross sections or too low thermallimit May bethissolution a good compromise betweeneffectiveness and costs ? Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  33. FPR1 FPR2 MVLV FPI MVLV FPI GPR SCHEMA Project (closedloop on the same MV busbar) • FPR 1&2: protectionrelays s of the twofeederof the closedloop (67 & 67N, WATT-VAR) • MV/LV FPI: FPIsinstalled on CBsalong the MV/LV subs. of the twofeederofclosedloop (67 & 67N, WATT-VAR) • GPR: CustomerGeneralProtectionRelay (51/67, 51N/67N, WATT-VAR) • Direction of “redloop”, forovercurrents, phasetoearthfaults and cross countryfaults • Direction of “blueloop”, forovercurrents, phasetoearthfaults and cross countryfaults • Direction oflogicselectivitylocksignal on “redloop”, forovercurrents, phasetoearthfaults and cross countryfaults • Direction oflogicselectivitylocksignal on “blueloop”, forovercurrents, phasetoearthfaults and cross countryfaults GPR GPR MVLV FPI MVLV FPI MVLV FPI MVLV FPI GPR GPR MVLV FPI MVLV FPI MVLV FPI MVLV FPI GPR MVLV FPI MVLV FPI Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  34. Smart Grids Key components in ENEL vision Smart Protections SmartMeters SmartComponents Advanced SCADA Smart Sensors Distribution Management System Communications GIS Security Storage Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

  35. …. anyquestion.…? Thanksforyourattention Alberto Cerretti– Italy– RT3b – Papers 463, 465, 507, 1134

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