Kema_Memo 1_Physical Infrastructure and DG Interconnection

7/30/2019 Kema_Memo 1_Physical Infrastructure and DG Interconnection

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memo

To: IEPR Committee (Chair Weisenmiller and CommissionerDouglas)

Date: April 29, 2011

From: KEMA, Inc. Karin Corfee, David Korinek, WilliamCassel, Christian Hewicker, J org Zillmer, Miguel PereiraMorgado, Holger Ziegler, Nellie Tong, David Hawkins, and

J orge Cernadas

Copy: Otto Tang

Subject: Distributed Generation in Europe PhysicalInfrastructure and Distributed Generation Connection

KEMA is pleased to submit the attached memo (Memo #1) on distributed generationapplications in Europe. This memo specifically focuses on the physical infrastructure anddistributed generation connection. This memo is the first of three memos that will serve asinterim deliverables for the European Distributed Generation Infrastructure Study. The threememos will eventually be rolled into one consultant report.


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TABLE OF CONTENTS

Introduction...............................................................................................................................................

1

SECTION1: PhysicalInfrastructureinGermany.............................................................................. 2RegionalandQuantitativeAllocationofRenewableEnergyinGermany.................................... 2WindEnergy....................................................................................................................................... 4SolarEnergy........................................................................................................................................ 4BiomassinCogenerationPlants...................................................................................................... 4HydroPower...................................................................................................................................... 5

Network

Structures

in

Germany

..........................................................................................................

5

GridandVoltageLevels................................................................................................................... 5TransmissionGrid............................................................................................................................. 6

ConclusionforGridConnectionofDistributedGeneration.......................................................... 10ImplicationsofDGonGridPlanningandOperation................................................................ 10GridDimensioning.......................................................................................................................... 11GridOperation................................................................................................................................. 11

GeneralandTechnicalRequirementsinGermany......................................................................... 12GeneralRequirements..................................................................................................................... 12TechnicalRequirements.................................................................................................................. 13

TechnicalOptionstoEnsureSecureGridOperation...................................................................... 15General.............................................................................................................................................. 15MostFrequentApplicationofOptionsinGermany................................................................... 18

RecentNetworkPlanningPoliciesandStudies............................................................................... 19SECTION2:PhysicalInfrastructureinSpain................................................................................... 21OverallSystemPlanningandDevelopment.................................................................................... 22NetworkStructuresinSpain.............................................................................................................. 22GridandVoltageLevels................................................................................................................. 22TheSpanishTransmissionSystem................................................................................................ 23TheSpanishDistributionSystem.................................................................................................. 26


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HVDistributionGrid...................................................................................................................... 26MVDistributionGrid...................................................................................................................... 27LVDistributionGrid....................................................................................................................... 30

RenewableEnergySources(RES)inSpain....................................................................................... 31DistributedGeneration................................................................................................................... 32RegionalandQuantitativeAllocationofRenewableEnergy.................................................... 33

RESCompensationArrangementsinSpain..................................................................................... 36InterconnectionTechnicalRequirementsinSpain...................................................................... 37

ImplicationsonPowerGridOperation............................................................................................ 38ConnectionProcesstoTransmissionNetworkinSpain................................................................. 38ConnectionApplicationPhase....................................................................................................... 38

ConnectionProcesstoDistributionNetworkinSpain................................................................... 40RESInstallations(Nonsolar)......................................................................................................... 40PhotovoltaicInstallations................................................................................................................ 41

MainReasonsforSuccessofRESinSpain....................................................................................... 42RemainingBarrierstoDevelopmentofDGinSpain...................................................................... 43ImpactofDGonSpainsNetworkInfrastructure........................................................................... 44

SECTION3: ComparisontoGridInfrastructureinCalifornia..................................................... 46SECTION

4:

Summary

of

Key

Lessons

Learned

..............................................................................

51

ListofFigures

Figure1:GenerationMixinGermanyatEndof2009(AllDatainPercentages)............................. 2Figure2:RelationshipbetweenNetworkConnectionLevelandTechnologyforInstallationsEligibleunderthe2008RenewableEnergyAct..................................................................................... 3Figure3:MediumvoltageGridLayouts a)NormallyopenLoops;b)CircuitswithTwoSourceStationsandNormallyopenContactatOneStation............................................................................ 7Figure4:TypicalUrbanLowvoltageGridLayout............................................................................... 9Figure5:TypicalRuralLowvoltageGridLayout.............................................................................. 10Figure6:VoltageIncreaseCausedbyDistributedGeneration......................................................... 14Figure7:SpanishTransmissionSystem................................................................................................ 25Figure8:LoopedHVGrid(SingleSourcePoint)................................................................................ 26


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Figure9:BridgeConfiguration(HVGridFedfromTwoPoints)..................................................... 27Figure11: UrbanMVGrid:ReflectionPointandSupportCircuitDesign..................................... 28Figure12:UrbanMediumVoltageGrid:DistributionPointdesign................................................ 29Figure

13:

Rural

MV

Grid

Structure

......................................................................................................

30

Figure14:LVGridStructure.................................................................................................................. 31Figure15:BreakdownoftheTotalInstalledCapacitybyTechnologyattheEndof2010............31Figure16:AnnualGrowthofSpainsInstalledPowerGeneration(GW)........................................ 32Figure17:BreakdownoftheTotalRenewableInstalledCapacitybyTechnologyattheEndof2009............................................................................................................................................................ 33Figure18:WindCapacityGeographicDensityinSpain................................................................... 34Figure

19:

Installed

Solar

Power

(MW)

in

the

Autonomous

Communities

of

Spain

by

End

2009

a)PVandb)SolarThermal..................................................................................................................... 35Figure20:DGConnectionProcess........................................................................................................ 40

ListofTables

Table1: GeneralRulesforSelectingtheVoltageLevelofthePointofCommonCoupling,accordingtotheRatedPowerofGenerationPlants............................................................................. 3Table2:HydroPowerPlantsinGermany,CategorizedbyNumberandInstalledPower............5Table3:OverviewofVoltageLevelsinGermany................................................................................. 6Table4:MostFrequentlyUsedOptionstoIntegrateDistributedGenerationinGermany..........18Table5:OverviewofVoltageLevelsinSpainperIECDefinitions.................................................. 23Table6:ComparisonofACVoltageLevelsinCaliforniaandEurope............................................ 46


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INTRODUCTION

AsreflectedintheEnergyCommissionspreviousIntegratedEnergyPolicyReportproceeding,theEnergyCommissionwantstodeterminehowcertainEuropeancountriesintegratelargequantitiesofintermittentrenewableelectricityintotheirelectricdistributionsystemswhilestill

maintainingsystemcontrolandreliability.ThismemoaddressesthisissuebyprovidingacomparisonbetweentheelectricdistributionsystemsinEuropeandCaliforniawiththeultimategoalofcapturingkeylessonslearnedtofacilitateCaliforniasintermittentrenewabledistributedgeneration(DG)intoitselectricdistributionsystem.

ThismemodescribesthephysicaldistributioninfrastructureandtherequirementsandprocessesforinterconnectingDGtothedistributioninfrastructureinGermanyandinSpain.ItcomparestherelevantcharacteristicsintheseEuropeancountriestothecorrespondingcharacteristicsinCalifornia.Theanalysisfocusesonmedium andlowvoltagedistributiongridsandoutlinesrelevantaspectsandimpactsofrenewablegenerationathighervoltagelevels.

Theresearchfocusedonaddressingthefollowingquestions:

HowaretheelectrictransmissionanddistributionsystemsconfiguredinGermanyandSpain?DoesthistopologyincreaseopportunitiesforrenewableDGintegration?

HavegridoperatorschangedtheconfigurationoftheirdistributionsystemstoallowforgreaterpenetrationofrenewableDG?Whatarethechangesfromaqualitativesense(whathavetheydone)andaquantitativesense(howmuchofithavetheydone,howaretheytreatingcostallocation,whatisthequantitativerelationshipbetweenchangesininfrastructureandDGpenetration)?

Do

grid

operators

use

ancillary

technologies

(i.e.,

battery

storage,

flywheel)

and

policy

leversthatallowforgreaterbackflowsonthedistributionsystemwithoutthreateninggridstability(e.g.,protectiondevices,curtailment)?Ordotheysimplyallowgreaterpenetrationundersomecircumstanceswithoutconcern?

IshigherpenetrationofrenewableDGlikelytocausevoltageissuesandpotentialbackfeedissues?HowdoestheelectricdistributionsystemofGermanyandSpainaddressthebackfeedissueinlightofactivepowerflowfromthemediumvoltagecircuitsuptothetransmission/subtransmissionhighvoltagecircuits?

Thismemoisorganizedasfollows:

Section

1

reviews

the

current

state

of

physical

infrastructure

in

Germany.

Section2reviewsthecurrentstateofphysicalinfrastructureinSpain.

Section3providesacomparisontogridinfrastructureinCalifornia.

Section4providesasummaryofkeylessonslearned.


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SECTION 1:Physical Infrastructure in Germany

Atoftheendof2009about16percentoftheGermanelectricalenergyproductioncamefrom

renewableenergysources.1ThegrowthofrenewableDGinGermanycontinuesunabated.Germangridoperatorshavedealtwiththechallengeofsignificantrenewableintegrationforthelastfiveto10yearsandhavedevelopedtechnicalrulesandguidelinestoensuresecurenetworkoperation.AnexaminationoftheGermanpowersystemisthereforeusefulforacomparativeanalysis.

Regional and Quantitative Allocation of Renewable Energy inGermany

Theextentofdeploymentofeachtypeofrenewablegenerationdependsonmanyfactorssuchaslocalclimateconditions,landutilization,andpopulationlevels.AcomparisonofalltypesofinstalledgenerationcapacityinGermany,includingbothrenewablesandconventionalgenerationisshowninFigure1.

Figure 1: Generation Mix in Germany at End of 2009 (All Data in Percentages)

Source: BDEW: German Energy Market, 2010

1GermanStatisticsofRenewableEnergySources,December2010.

13

13

18

15

12

29

Generation capacity(total: 153.8 GW net)

Nuclear Lignite

Hard coal Natural gas

Oil, Pump storage hydro, other Renewables

23

24

18

13

6

16

Net electricity generation(total: 561 TWh net)

56

10

10

21

3

Renewable generation capacity(total: 44.6 GW)

Wind

Biomass

Hydro

Solar

others


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Thetypeofrenewableenergysourceoftenaffectsthesizeofthegenerationplantsandtherebythetype(voltagelevel)ofthegridconnection.AsageneralrulefortheGermangrid,thevoltagelevelatthepointofcommoncouplingforDGplantsfollowstheschemashowninTable1.

Table 1: General Rules for Selecting the Voltage Level of the Point of Common Coupling,according to the Rated Power of Generation Plants

Rated power of the generation plant Voltage level of grid connection

Up to 30 kW Low-voltage grid without verification

30 to 200 kW Low- or medium-voltage grid

0.15 to 20 MW Medium-voltage grid

15 to 80 MW High-voltage grid

80 to 400 MW Extra-high voltage grid

Source: Potentialermittlung fr den Ausbau der Wasserkraftnutzung in Deutschland, Bundesministerium fr Umwelt, Naturschutzund Reaktorsicherheit (BMU), September 2010 [Capacity of hydro power in Germany, September 2010]

InactualpracticetherecanbedeviationsfromthegeneralrulebasedontheresultsofspecificstudiesforDGinterconnection.Figure2showsthebreakdownofgenerationtypesinstalledateachvoltagelevelasapercentageofthetotalgenerationcapacityinstalledatthatvoltage.Thesizeofthegeneratorisakeyparameterasitrequiresacorrespondingcapacitybothatthenetworkconnectionpointandfortransportingtheelectricityproducedfromthatpointtothesystem.Forinstance,solarpowerinstallationstendtoberathersmall(mainlyroofbasedinstallations)andaremostlyconnectedtothelowvoltagenetwork.Ontheotherhand,windprojectsaredevelopedoveramuchwiderrangeofsizes(e.g.,windfarms)andthereforeareconnectedatmanydifferentvoltagelevels.

Figure 2: Relationship between Network Connection Level and Technology for InstallationsEligib le under the 2008 Renewable Energy Act

2

Source: Bundesnetzagentur EEG-Statistikbericht 2008 (Translated Regulators EEG Statistical Report, 2008)

2Installedgeothermalcapacityisnegligible.Gasesreferstowastegasprojects(e.g.,minegas,etc.)

0% 20% 40% 60% 80% 100%

Extra high voltage

Extra high/ high voltage

High voltage

High / medium voltage

Medium voltage

Medium/ low voltage

Low voltage

Hydro

Biomass

Gases

Geothermal

Wind

Solar


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AdditionalgeneralobservationsinregardtonetworkintegrationofDGontheGermannetworkareasfollows:

Wind Energy

Ahighconcentrationofwindenergyplantsappearsinrural,sparselypopulatedareasinnorthernGermany.Theindividualgeneratingunitsmostlyhavearatedpowerfrom1MWto3MW.Hence,thepointofcommoncouplingismostoftenlocatedonamediumvoltagegrid.However,whenindividualunitsarecollectedintowindfarmswithratedpowerfrom20MWto80MW,theyareusuallyconnectedtothehighvoltagegrid.Afewlargewindfarmsgenerate80to400MWofelectricpowerapieceandaredirectlyconnectedtotheextrahighvoltagegridviaseparatesubstations.

Solar Energy

Eventhoughthepercentageofelectricalenergygeneratedbysolarpowerwasonlyabout

7

percent

of

all

renewable

energy

by

the

end

of

2009,

solar

power

has

had

the

strongest

growth

rateforthelasttwoyears.AsignificantamountofsolarenergygeneratingunitshasbeeninstalledparticularlyinsouthernGermany.Theinstalledsolargenerationcapacityincreasedby3,800MWin2009andbyabout6,500MWin2010,bringingthetotalinstalledsolarcapacitytoapproximately10GW.

Inurbanareas,smallsolargenerationplants(photovoltaicmodulesandconverters)areinstalledonroofsofresidentialhomes(ratedpower3kWto5kW)orcommercialandpublicbuildings(100kWto1MW).Accordingtogridcode,smallunitsupto5kWpeakcanbeconnectedasasinglephasecustomerataservicepoint.3Unitsupto30kWareallowedtoconnectasathreephasecustomeratanypointontheLVgridwithouttechnicalverification.

However,thepresenceofmultipleDGprojectswithinanindividualrurallowvoltagegridcancauseseverevoltageorpowerqualityissues(seeMemo#2forfurtherdiscussion).

Biomass in Cogeneration Plants

Bytheendof2009,thefractionofrenewableelectricalenergygeneratedfrombiomasswasroughly30percentofallrenewableenergyproduction.Hence,biomassisthenextmostimportantrenewableenergysourceafterwindinGermany,andalsohashighgrowthrates.CogenerationplantsforbiomassareinstalledalloverGermany,particularlyinruralareas.Smallunitswithelectricpowerupto150kWareconnectedtothelowvoltagegrid.Themajorityofunitsrangesfrom500kWto5MWandisconnectedtothemediumvoltagegrid.Largeunitswithconsiderablymorethan5MWexistandareconnectedtothemedium orhighvoltagegrid

3EigenerzeugungsanlagenamNiederspannungsnetzRichtliniefrdenAnschlussundParallelbetriebvonEigenerzeugungsanlagenamNiederspannungsnetz;VWEWEnergieverlagGmbH;September2005[GermanTechnicalGuidelineGeneratingPlantsConnectedtotheLowVoltageNetwork,September2005]


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accordingtotheirratedpower.Sincebiomassisconsistentlyavailable,itislesscriticalfornetworkoperationthanfluctuatingresourcessuchaswindandsolarpower.

Hydro Power

HydropowerresourcesareconsideredtobewelldevelopedinGermany.Therefore,the

amountof

hydro

power

has

remained

nearly

constant

over

the

last

few

decades

since

most

of

thepotentiallocationsarealreadyutilized.HydropowerstationsofvarioussizeshavebeeninstalledinmountainousareasandalongriversincentralandsouthernGermany.Currently,hydrogenerationisabout25percentofallGermanrenewableenergygeneration.

Severallargepumpedstoragepowerplantsconnectedtotheextrahighvoltagegridcontributetotheloadbalancingandfrequencycontrolofthetransmissionsystem.Table2providesanoverviewofthenumberofgenerationplantsinseveralpowercategoriesandtheinstalledpower.

Table 2: Hydro Power Plants in Germany, Categorized by Number and Ins talled Power

Hydro power unitswith less than 1 MW

Hydro power unitswith more than 1 MW

Pumped- storageplants

Number of units ~6,500 ~400 ~30

Installed Power ~600 MW ~3,400 MW ~6,600 MW

Network Structures in Germany

Inthenextpartofthememo,thebasictechnicallayoutsandconfigurationsofGermantransmissionanddistributiongrids,includingsubstationsandsecondarysubstationsaredescribed.ThenthegeneralandtechnicalrequirementsfortheinterconnectionofDGfroma

Germanperspectivearethenconsidered.Finally,themostcommonnetworkupgradeoptionstomanagetheintegrationofrenewableenergysourcesandcomplywithtechnicalrequirementsareexamined.

Grid and Voltage Levels

TheEuropeanpowergridisathreephasealternatingcurrentgridoperatedatafrequencyof50Hertzatallvoltagelevels.4Fourcommonvoltagegroups(EHV,HV,MV,andLV)havebeenestablishedintheGermanpowergridperInternationalElectrotechnicalCommissiondefinitions.TheexistinggridvoltagesforeachofthesegroupsinGermanyareshowninTable3.

4Therailwaypowergridisdistinguishedfromthepublicpowergridbyfrequencyandgeneration.ItisatwophaseACgridoperatedat16.7Hz.


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Table 3: Overview of Vol tage Levels in Germany

Name(IEC Definition) Abbreviation Rated Voltage Role

Extra-high voltage EHV 380 kV, 220 kV Transmission grid

High voltage HV 110 kV

Distribution gridMedium voltage MV 30 kV, 20 kV,15 kV, 10 kV

Low voltage LV 400 V

Transmission Grid

TheEuropeantransmissiongridisoperatedprimarilyat380kVandpartiallyat220kV,butthelatterisonthedeclineandprovidesthebasisfortheelectricalenergytransportbetweenlargescalepowerplants,theconnecteddistributiongrids,andneighboringcountries.TheEuropeantransmissiongridisanintegratednetworkdesignedtoensurereliable,efficient,andsecureelectricalenergysupplybasedontherulesoftheOperationHandbookoftheEuropean

Network

of

Transmission

System

Operators

for

Electricity

(ENTSO

E).5

According

to

the

GermanTransmissionGridCode,6themaintaskofthetransmissiongridoperatorsistoassumeresponsibilityforthewholesystemofelectricalenergysupply,including:

Thebalanceofloadwithinacontrolarea,especiallyincaseofaresourcecontingency,andtherebymaintainingsystemfrequencystability

Networksecurity,i.e.,thesecurityofsupply,secureoperation,thecompliancewithvoltageandotheroperationallimitsandthe(n1)criterion

Theongoingevaluationofsystemoperatingconditionsandinitiationofrequiredcorrectivemeasuresthatwillinvolvetheassociateddistributiongridoperatorsasneeded

Thetransmissiongridisameshedsystemwithhighstandardsforsystemstability(frequency,voltage,dynamicstability)andsecurityofsupply.ThetransmissioninfrastructureinGermanyispredominatelyoverheadconstruction.

Distribution Grid at the High Voltage Level

The110kVhighvoltage(HV)gridservesasthetransportgridformediumdistancesandcarriestheelectricenergyfromexchangepointsonthetransmissiongridtowardsurbanorruralmediumvoltagegrids.Therequirementsconcerningsecurityofsupplyareagaincoveredbycompliancetothe(n1)contingencycriterion.Thegridismeshedandconsistsmainlyofoverheadlines.Inurbanareas,undergroundcablesareofteninstalledat110kV.Highloads

5UCTEOperationHandbook(OH),version2.5,levelE,dated24.06.2004,UnionfortheCoordinationofTransmissionofElectricity(UCTE);Brussels.

6TransmissionCode2007,Netz undSystemregelnderdeutschenbertragungsnetzbetreiber,Version1.1,August2007,VerbandderNetzbetreiberVDNe.V.beimVDEW,Berlin[TransmissionCode2007,NetworkandSystemRulesoftheGermanTransmissionSystemOperators,August2007]


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withhighdemands(e.g.,largeindustrialloads)andgeneratingunitsexceedingapowerlimitofabout20MWareprimarilyconnectedtothisgridlevel.

Distribution Grid on Medium Voltage Level

Themediumvoltagegrid(MVgrid)mainlycomprisesthevoltagelevels30kV,20kV,15kV,

and

10

kV.

Urban

and

rural

medium

voltage

grids

significantly

differ

in

their

characteristics.

Ahighdensityofloadsandrelativelyhighdemandthatcauseshighutilizationoftheequipment(transformers,cables)istypicalforurbanareas.Appropriatefortheserequirements,urbanmediumvoltagegridsinGermanyconsistlargelyofcableswithatypicalcablecrosssectionof150to300mm(nominallyequivalenttoarangeof300kcmilto636kcmil)andwithacomparablyshortcablelength.TheurbanMVgridsaregenerallyoperatedatvoltagelevelsof10kVand20kV.Theyaresetupasloopednetworkswithopenloopsundernormaloperatingconditions(seeFigure4),wherethesmallercirclesrepresentnormallyopenswitchgearandthelargercirclesrepresentsubstationtransformers.

a) b)

Figure 3: Medium-voltage Grid Layoutsa) Normally-open Loops; b) Circuits w ith Two Source Stations and Normally-open Contact at One

Station

Source: KEMA

TheMVgridsareconnectedtothehighvoltagegrid(110kV)viasubstationswithtwoormoreHV/MVtransformersinaratedpowerrangefrom31.5MVAto63MVA.Thepowertransformersaretypicallyequippedwithtapchangersandautomaticvoltagecontrolto

110 kV

110 kV

20 kV20 kV

20 kV20 kV


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guaranteeafixedvoltageatallmediumvoltagebusbars.Aslinktothelowvoltagegrids,thesecondarysubstationsmainlyconsistofsingleMV/LVtransformersinaratedpowerrangefrom400to1,000kVA.Fordirectcustomerconnections,transformersupto1,600kVAcanbeused.Asaresultofthehighinstalledpowertransformercapacityandtherelativelyshortcableswithlargecrosssections,thenetworkimpedanceiscomparablylowthroughoutthewhole

urbanmediumvoltagegrid.Hence,voltagedropandpowerqualityissuesrarelyoccur.

RuralMediumvoltageGridsRuralareasarecharacterizedbylargergeographyandlowloaddensity.Thisresultsinlonglines,highnetworkimpedances,andlowutilizationoftheequipment.InruralmediumvoltagegridsinGermany,undergroundcablesandoverheadlinesareinstalledinnearlyequalshares.Typicalundergroundcablecrosssectionsrangefrom120to240mm(nominallyequivalenttoarangeof4/0AWGto400kcmil).Thecrosssectionsofoverheadlinesrangefrom70to120mm(nominallyequivalenttoarangeof2/0AWGto4/0AWG).

RuralMVgridsareoperatedatvariousvoltagelevels;mostcommonare10kV,15kV,20kV,

and30kV.Likeurbanareas,ruralMVgridsaresetupasloopednetworkswithopenloopsundernormaloperatingconditionsorinsomecases,linesareconnectedbetweentwostationswithanormalopencontactatoneend(seeFigure1).Usually,thegridsareconnectedtothehighvoltagegrid(110kV)viasubstationswithtwoHV/MVtransformersinaratedpowerrangefrom16to40MVA.Thepowertransformersaretypicallyequippedwithtapchangersandautomaticvoltagecontroltoguaranteeafixedvoltageatallmediumvoltagebusbars.ThesecondarysubstationsconsistofsingleMV/LVtransformersinaratedpowerrangefrom100to400kVA.

Inafewcases,intermediate30kVgridsoperatetosupplyremote,lightlyloadedareas.These30kVdistributiongridsformclosedloopsandsupplylowervoltage10kVgrids.

Duetothelonglines,smallcrosssectionsandthecomparablylowinstalledtransformercapacity,thenetworkimpedanceincreasessignificantlytowardstheremotelineterminal.Voltagedropandpowerqualityissuesfrequentlyoccur(seefurtherdiscussioninMemo#2).

Low Voltage (LV) Distribution Grid

Thelowvoltagegrid(LVgrid)isa400Vnetworkandremainsathreephasegrid(orthreephaseplusneutralphase)uptotheservicepoints(endcustomers).Ingeneral,outgoingcableunitsinsecondarysubstationsarefusedbyalowvoltage,highloadbreakingcapacityfuse.Servicepointconnectionsareprotectedforamaximumpermissiblecurrentof63A(equalto25kVA).Similartomediumvoltagegrids,urban,andrurallowvoltagegridshavedifferentgrid

characteristics.

UrbanLowvoltageGridsAccordingtothehighspatialdensityofurbanloads,lowvoltagegridsintheseareasconsistofrelativelyshortgridcableswithtypicalcablecrosssectionsof150to240mm(nominallyequivalenttoarangeof300kcmilto400kcmil).Fromthegridcables,servicepointcableswitha


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crosssectionof3550mm(nominallyequivalenttoarangeof#2AWGto#1AWG)branchofftocustomers.

TheurbanLVgridsareoperatedasmeshedgridsconnectedbymeansofcabledistributionboxes.TheLVgridscanbefedbyasinglesecondarysubstationorbyoneortwoMVcircuits

(see

Figure

4).

The

urban

secondary

substations

contain

about

10

outgoing

cable

units.

The

meshedgridstructureensureshighservicereliability,allowsforhighutilization,andreducesvoltagedropsandpowerqualityissues.Unfortunately,thegridassemblyisunclearandthemaintenanceeffortisrelativelyhigh.

Figure 4: Typical Urban Low-voltage Grid Layout

Source: KEMA

RuralLowvoltageGrids

Withrespecttotheexpansionofthesupplyzoneandthelowloaddensity,rurallowvoltagegridsinGermanyaremainlyradiallystructuredcableoroverheadlinegrids.Forthegridlines,typicalcablecrosssectionsrangefrom95mmto150mm(nominallyequivalenttoarangeof3/0AWGto300kcmil).Thecrosssectionsofoverheadgridlinesrangefrom50to95mm(nominallyequivalenttoarangeof#1AWGto3/0AWG).Theservicepointconnectionsaretypicallyrealizedthrough35mmcables(nominallyequivalentto#2AWG).Occasionally,overheadlineswithcrosssectionof25to35mm(nominallyequivalenttoarangeof#4AWG

to

#2

AWG)

are

used.

Theruralsecondarysubstationscontainuptoeightoutgoingcableunits.TheruralLVgridsareoperatedasradialgridsfedbyasinglesecondarysubstation(seeFigure5).Thelonglinesanddecreasingcrosssectionstowardsthelineendscausehighnetworkimpedances.Thus,thesensitivitytovoltagedeviationandsystemperturbations(powerqualityissues)significantlyrises.


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Figure 5: Typical Rural Low-voltage Grid Layout

Source: KEMA

Inadditiontothestandardtaskofsupplyingendusecustomersthedistributionoperators(DSO)mustconnectdistributedgeneratingunitsinthemostcostefficient,technicallysecureway.Therefore,theDSOfirstutilizesanyexistingreservecapacityinthegridforconnectingaDG.Ifthesereservesareexhausted,thepointofcommoncouplingcaneitherbemovedtoahighervoltagelevelgrid(dependingontheDGsize),orthelowervoltagegridmustbeupgradedtoaccommodatethenewDG.Inthecaseofagridextensionorupgrade,thegridplannerconsidersexistinggridexpansionrequirementsandnetworkplanningdirectivesin

conjunction

with

the

technical

rules

for

the

grid

connection

of

distributed

generation

in

order

to

comeupwiththeoveralllowestcostgridexpansionplan.

Conclusion for Grid Connection of Distributed Generation

Implications of DG on Grid Planning and Operation

Eventhoughtheincreasingproductionofrenewableenergyfromdistributedgeneratingunitsaffectsthegridatallvoltagelevels,nofundamentalchangesinthegridstructureandplanningstandardshavebeenmadeinGermany.However,duetothescaleofdistributedgenerationgrowthinthelastdecade,thelevelofDGoutputonmedium andlowvoltagegridsnowexceedslocalloadinmanyplacesinGermany.Hence,backfeedconditionsoccurinsomeregionsofthenetwork.Ingeneral,backfeedsarepermittedinGermany.Themeteringandprotectionhastobedesignedforbidirectionalflow.Afourquadrantmeterisnecessaryandtheprotectionsystemhastoallowbackfeeds.

Networkconnectionsandupgradesareplanned,basedontheexpectedlevelofbackfeed,sothatthisconditioncausesnooverloads.Therefore,abackfeedconditionduringnormal


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operationsshouldnotleadtocurtailmentortrippingtheDG.Infact,undertheGermanrules,TSOsmustfirstexhaustallotheravailablemarketoptionsbeforecurtailingrenewableDG.RulesapplyingtoDGcurtailmentbyDNOsarenotasclear,andtheDNOsalsohavefeweroptionsthantheTSOs.However,ifarenewableDGiscurtailedbyeitheraTSOoraDNO,theDGstillreceivesitsnormalfeedintariffremunerationforanycurtailedenergy(i.e.,itdoesnot

reducetheDGsrevenue).

SincethecostsofnetworkupgradesinGermanyaresocialized,networkplannersseekthelowestcostplanofupgradetosatisfyDGintegrationneeds.Uptonow,theplanningforDGintegrationhasgenerallybeendoneaspartoftheregulargridexpansionplanningprocesswithnormalexpansionplanningandreplacementneedsconsideredfirst,thenDGintegrationsecond.

Grid Dimensioning

Inthepast,medium andlowvoltagegridsweredesignedanddimensionedbasedonthepeakloadscenario.Thegriddimensioningandoperationnowhavetoaccountforthefollowingfour

scenariosforloadandDGoutput:

Peakload/lowDGoutput

PeakDGoutput/lowload

Peakload/peakDGoutput

Lowload/lowDGoutput

Thefirsttwoscenarioshavebecomethemostcriticalcasesforgridplanningandoperation.Thepowerlinesandtransformersofeachvoltagelevelofthegridmustbesizedtomanagetheemergingrenewablepowerproduction.

Protectionaspects

TheprotectiondevicesandsettingsinGermandistributiongridsgenerallyallowforbackfeeds.Theoverloadprotectiondependsontheloadinglimitsoftheassetsandisindependentoftheflowdirection.

Distributedgenerationplantshavetobeequippedwithovervoltageandundervoltageprotection.ThetimedelayoftheprotectiondeviceshastobeadjustedtoallowforthetimedelayoftheautomatictapchangersonHV/MVpowertransformerssupplyingthatpartofthenetwork.Additionally,distributedgenerationplantsinmediumvoltagegridsandabovemustbeequippedwithunderfrequencyandoverfrequencyprotection.Furthermore,apowercircuitbreakerwithintheDGplantmustguaranteethedisconnectionofthedistributedgenerationprojectfromthegridincaseofashortcircuitintheplant.

Grid Operation

OperationalissuesduetothehighconcentrationofwindandphotovoltaicgenerationplantsthataremanagedmainlyatthehighvoltageandextrahighvoltagelevelinGermanyinclude:

Theloadforecastandgenerationschedules,definedinthetraditional15minuteschedulingintervals,getperturbedbyfluctuatingrenewableoutput.


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Theconsiderablebackfeedsfromlowload/highDGareasmustbetransportedtolargeloadcentersandcancausecongestioninthetransmissiongrid.

Thecurtailedutilizationofconventionalpowerplantsreducestheavailablefrequencycontrolandshortcircuitdutyandaffectsthedynamicstabilityofthesystemduetoareductioninrotationalinertiaconnectedtothesystem.

AccordingtotheGermanlawEnWG,gridoperatorsatallvoltagelevelscaninvokegenerationcurtailmenttocopewithcongestionandothercriticaloperationalsituationsthatjeopardizethenetworksecurity.Forthispurpose,distributedgenerationplantswithratedpowerofmorethan100kWmustbeequippedwithremotecontrolcapabilitytocommunicatetheirrealtimeoutputtothegridoperatorandallowforthegridoperatortosendautomaticpowerdispatchcontrolinstructionstothegenerators.Whilesuchtelecommunicationfacilitiesarenothighvoltagefacilities,theystillareanessentialcomponentoftheinfrastructurerequiredforreliableoperationandcontrolofthehighvoltagegridinGermany.

General and Technical Requirements in Germany

General Requirements

TheimplementationofrenewableenergysourcesisanimportantpoliticaltargetoftheGermangovernment.Inthiscontext,thefederalgovernmenthasdevelopedlegalboundaryconditionsforthedevelopmentofdistributedgeneration.Asaresult,importantnewlaws(EnWG7andEEG8)wereenacted.TheselawsdefineapriorityofrenewableenergysourcesincontrasttoconventionalenergysourcesandobligatetheGermangridoperatortoconnectdistributedgeneration.Thegridoperatorhastoensurethatdistributedgeneratingunitsareabletofeed

into

the

grid

and

that

the

total

installed

power

can

be

transmitted

under

normal

conditions.

Furthermore,thepointofcommoncouplingshouldbeascloseasreasonabletothelocationoftheindividualdistributedgeneratingunit,giventechnicallimitations.

Anexceptionisdefinedfordistributedgeneratingunitswithaninstalledpowerlowerthan30kW.Fortheseunitsthepointofcommoncouplingissimplydefinedasthelowvoltagegridclosesttotheserviceconnectionoftheownerofthegeneratingunit.

7EnWG ZweitesGesetzzurNeuregelungdesEnergiewirtschaftrechtsvom7.Juli2005;BundesgesetzblattJahrgang2005TeilINr.42,ausgegebenzuBonnam12.Juli2005[SecondGermanLawontheEnergyIndustry,July2005]

8EEGGesetzzurNeuregelungdesRechtsderErneuerbarenEnergienimStrombereichundzurnderungdamitzusammenhngenderVorschriftenvom25.Oktober2008;BundesgesetzblattJahrgang2008TeilINr.49,ausgegebenzuBonnam31.Oktober2008[GermanLawontheRenewableEnergySources,October2008]


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Regardingtheevaluationofthetechnicallyreasonablepointofcommoncoupling,differenttechnicalnormsandrulesweredevelopedinthepast.Theserulesweredevelopedinconsiderationofthefollowingtargets:

ThepointofcommoncouplingshouldbeclosetothelocationoftherespectiveDG.

Asecure

grid

operation

must

be

maintained

under

all

conditions,

including

the

full

outputofthedistributedgenerator.

TheoperationofDGshouldhavenegligibleimpactonothercustomers.

Specificpowerqualityparametershavetobemaintained.

Giventhiscontext,distributedgenerationplantsareconnectedatvariousvoltagelevelsdependingonthetypeofenergysourceandtheinstalledpower.Thefollowingsummarydescribesthetechnicalnormsandrulesregardingdistributedgenerationconnectedtomediumvoltageandlowvoltagegrids.

Technical Requirements

Toensureasecureoperationofthegridunderallconditionsthefollowingmainpointsshouldbeconsidered:

Allcomponentsusedintheinterconnectionshouldbeproperlydimensionedforthesizeoftherenewableproject.

Thevoltagelevelatthepointofconnectionshouldbewithinanacceptablerange.

Utilization and Overload

Theutilizationoftheelectricalinterconnectioncomponentsmustnotexceedtheratedcurrentoftheelectricalcomponents.Theratedcurrentsofthecomponentsaredefinedthroughindustrynorms.Inaddition,gridoperatorsinGermanyhavedefinedrelatedrules.Distributedgeneratingunitsthatareconnectedtothemediumvoltageorlowvoltagegridsshouldnotcauseoverloads,undervoltages,orovervoltages.

Permissible Voltage Range

Thepermissiblevoltagerangeformedium andlowvoltagegridsisdefinedinthenormDINEN50160.9Ontheonehand,themaximumvoltageshouldnotexceedtheinsulationleveloftheelectricalcomponents.Ontheotherhand,theminimumvoltageateachserviceconnectionpointmustallowanundisturbedoperationofallconnecteddevices.Inthiscontext,thevoltageateachserviceconnectionpointshouldbeinarangeof10percentoftheratedvoltageundernormaloperatingconditions.

9DINEN50160MerkmalederSpannunginffentlichenElektrizittsversorgungsnetzen;April2008[GermanNorm50160VoltageCharacteristicsofElectricitySuppliedbyPublicDistributionNetworks,April2008]


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Power Quality

Additionally,distributedgenerationplantsshouldnotinterferewithothercustomers(consumersorgeneratingunits).Toensureacceptablepowerqualityparameters,thefollowingsystemperturbationsassociatedwithaDGshouldbeconsidered:

Voltage

increase

at

point

of

connection

Flicker

Harmonics

Admissiblelimitsforvoltagedeviation,nonsymmetry,flicker,andharmoniclevelsarealsodefined(seeMemo#2).Technicalrulesexistforthegridconnectionofgeneratingunitstothemediumvoltagegrid10andtothelowvoltagegrid11,respectively.

The Most Critical Issue: Voltage Increase

Generally,voltageincreaseisthemostcriticalissueatthepointofcommonconnectionfordistributedgeneratingunits.Voltageincreasesarecausedbytheinjectedpowerofgenerating

units.Thepowertransmissionoverthenetworkimpedancecausesavoltagedropfromthefeedingtothereceivingend.Themagnitudeofthevoltagedeviationrelatestothesizeoftheimpedance.Asaresult,thevoltagedeviationsinthegridvarydependingontheDGsize.ThiseffectisillustratedinFigure6.

Figure 6: Voltage Increase Caused by Distributed Generation

Source: KEMA

10.ErzeugungsanlagenamMittelspannungsnetzRichtliniefrdenAnschlussundParallelbetriebvonErzeugungsanlagenamMittelspannungsnetz;VWEWEnergieverlagGmbH;Juni2008[GermanTechnicalGuidelineGeneratingPlantsConnectedtotheMediumVoltageNetwork,June2008]

11.EigenerzeugungsanlagenamNiederspannungsnetzRichtliniefrdenAnschlussundParallelbetriebvonEigenerzeugungsanlagenamNiederspannungsnetz;VWEWEnergieverlagGmbH;September2005[GermanTechnicalGuidelineGeneratingPlantsConnectedtotheLowVoltageNetwork,September2005]

servicepoint

load

G

distributedgenerationplant

circuitlinetransformer

voltage

lengthpeakload

peakfeedin

voltageincrease


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15

ThemaximumdifferencebetweenreceivedvoltageswithandwithoutDGoperationaredefinedintheGermangridrules(seeMemo2).Alldistributedgeneratingunitsthatareconnectedonacommonsectionofgridhavetobeconsidered.

Theshortcircuitdutyatapointofcommoncouplingservesasameasureforthenetwork

impedance.

High

short

circuit

duty

reflects

a

low

network

impedance

and

vice

versa.

Therefore,

inareaswithlowshortcircuitpower(i.e.,ruralareas),theoccurringvoltageincreaseishigherthaninareaswithahighershortcircuitpower(i.e.,urbanareas).Ifthevoltageincreaseexceedsthelimitvalue,eithergridupgradesarerequiredtoreducethenetworkimpedance,orthedistributedgeneratingunithastobeconnectedtoanotherpointofcommoncoupling.

Inaddition,othertypesofsystemperturbations(i.e.,flicker,harmonics,etc.)arealsoevaluatedinregardtotheshortcircuitpoweratthepointofcommoncoupling.AlloftheperformancerulesareconsideredbytherespectiveTSOorDNOduringplanningstudiesforeachDGconnectionandappropriateplanningoptionsareemployed,asdiscussedinthenextsection.

Technical Options to Ensure Secure Grid Operation

General

Becauseofthedistinctelectricalcharacteristicsofeachmedium andlowvoltagegrid,themaximumacceptablelevelofDGcapacitycanbelimitedatanygivenpointinthenetwork.Toensuresecuregridoperationdifferentgridplanningoptionscanbeusedtoincreasetheacceptableamountofconnecteddistributedgenerationinagivenpartofthenetwork.However,Germannetworkplannersconsiderallpossibilitiesinordertodeterminetheminimumlevelofgridinvestment.Generally,whentheconnectionpointisinadequate,the

technical

options

include:

DirectlyconnectingtheDGintoasubstation

UpgradingofthenetworkcircuitthermalcapabilitytotheDGlocation

Upgradingofupstreamtransformercapacity

Reroutingthecircuittoreducecircuitlength

Relocationofthenetworkloopnormallyopendisconnectpoint

Setpointadjustmentofautomaticvoltagecontrolonnetworktransformers

Usingreactivepowercapabilitiesofdistributedgeneratingunits

Constructionof

anew

substation

Changestonetworktopology

Upgradeofthenetworksratedvoltagelevel

Installationofsupplementalreactivepowercompensationequipment

Implementationofrotatingandnonrotatingenergystoragesystems


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Thesepossibilitiesaredescribedinmoredetailbelow.

Direct Connection at a Substation

Ifthevoltageincreaseexceedsthelimitvalue,otherpointsofcommoncouplingshouldbejustified.Inthiscontext,thedirectconnectionofadistributedgeneratingunittoanetwork

substation

is

one

of

the

most

commonly

used

solutions

in

Germany.

This

option

can

also

be

usedifothersystemperturbationfactorsexceedthepermissiblelimits.ItrequiresrelocationoftheplannedDGtoasiteadjacenttothenetworksubstationorconstructionofagentielinefromtheDGsitetothenetworksubstation.

Upgrade of Conductor Size

AnupgradeofgridundergroundcableoroverheadlinescanbeusediftheconnectionoftheDGtothenearestgridlineexceedscriticalperformanceparameters.Dependingonthegridload,thisapproachmayallowadditionaldistributedgeneratingunitstobeintegratedintothegrid.InGermany,thissolutionisoftenusedforoldergridlines,andconductorreplacementneededduetotheageofthegridlinecansometimesbecombinedwithintegrationof

distributedgeneration.Thissolutionisalsousedinordertoraiseshortcircuitdutyatthepointofcommoncoupling.Therefore,thisoptioncanalsobeusedtosolveproblemsregardingcriticalvoltageincreases.However,Germanyavoidsupgradingofthedistributiongridsolelyforintegratingdistributedgenerationmany.DependingontheamountofDGprojectsaddedtoaportionofthegrid,upgradeoflineconductorsmayonlybeashorttermoption.Inallcases,relevantneartermandlongtermgridplanningfactorsshouldbetakenintoaccount.

Upgrade of Transformer Capacity

Similartolineupgrades,theupgradeofupstreamtransformercapacityisalsousedinGermanyforsomeDGinterconnections.Thisoptionmaybepreferable,especiallyforoldertransformersandallowsmorepoweroutputbydistributedgeneration.

Reduction of the Circuit Length

Thisoptioncanberealizedbyreplacinggridline(s)totheDGsitewithanalternativeroutethatcreatesashortercircuitlengthandlowernetworkimpedance.However,thefeasibilityofthisoptiondependsonthegeographyofthespecificgridarea.Moreover,theresultantbenefitsinmanycasesarerelativelylow.

Relocation of the Network Normally-Open Disconnect Point

Ashorttermoptiontoreducevoltageincreasesongridlinescanbetherelocationofthenormallyopendisconnectpointofagridloop.12

In

Germany

this

option

is

only

a

short

term

solution

and

is

used

more

from

the

grid

operation

side.Theimpactoftherelocationofthedisconnectionpointontheabilitytointegratedistributedgenerationiscomparablylowandmayincreasethenetworkelectricallosses.Withrespecttothedynamicgrowthofrenewableenergygeneration,therearesuperioroptionsformediumtermorlongtermgridplanning.

12Thedisconnectionpointdefinesthenormallyopenpointinanetworkloop(seeFigure1a).


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Adjustment of Automatic Voltage Control Set Point on Transformers

Anadjustmentofthetransformervoltagecontrolsetpointisalsoconsideredashorttermoption,butinsomecasescanbeusedtokeepthevoltagelevelatadownstreamDGconnectionpointwithinthepermissiblerange.

ThisoptioncanonlybeusedinmediumvoltagegridsinGermanybecauseonlytheHV/MVpowertransformersareequippedwithautomaticvoltagecontrolsystems(tapchangingunderload).Therefore,applicationislimitedtolargerDGfacilitiesthatneedtoconnecttoMVnetworks.ThisoptionisoccasionallyusedinGermany.

Using Reactive Power Production Capabilities of Distributed Generation Plants

Somedistributedgeneratorsareequippedwithautomaticvoltageregulatorsthatcanabsorbreactivepowerfromthegrid(underexcitedoperation)orprovidereactivepowertothegrid(overexcitedoperation)UnderexcitedDGoperationcanbeusedtodecreaseconnectionvoltage,whileoverexcitedoperationcausesvoltageincrease.InGermany,thisoptionisbeing

usedwithincreasingfrequencyaspartofthelongtermgoalfordistributedgeneratingunitstocontributetothevoltagecontrolofthegrid.Inthepast,numerousDGunitswerenotcapableofproducingreactivepower.Therefore,differenttechnicalruleshavebeendevelopedthatincludetherequirementforDGcapabilitytoprovidereactivepowerandtocontrolvoltage.

Construction of a New Substation

AnewsubstationcanbenecessaryifseveralcomponentstransformersandgridlinesreachcriticalutilizationlevelsduetoDGintegration.Theconstructionofanewsubstationimpliesextensivegridextensionmeasures.ItisthemostcostlyoptionandisthereforeavoidedinGermany.However,thisoptionmaybenecessaryinareasexperiencingacomparablyhighlevelofDGinstallationconcentratedinonelocation.ThishasbeenthecaseinthenorthernpartofGermanywheresomeHV/MVsubstationshavebeenconstructedexclusivelyfordistributedgeneration(windfarmconnection).

Change to the Network Structure

ChangestoexistingnetworkstructuresarecarriedoutinGermanyonlyifneededaspartofacomprehensivegridexpansionplan.WhiledistributedgenerationaloneisnotconsideredthemainreasonforchangingnetworkstructureinGermany,itisoneofthemanyfactorsconsideredinlongtermgridexpansionplanning.

Upgrade of the Rated Voltage Level

TheratedvoltagelevelofmediumvoltagegridsinGermanyhasbeenupgradedinsomeareas.

Inmostcases,theupgradewasfrom10kVto20kV.Theseupgradesallowforagreaterpenetrationofdistributedgeneration.However,whenthisoptionhasbeenuseditwasselectedduetoitscompatibilitywiththeoverallgridexpansionplanningneeds.DistributedgenerationwasnotbeenusedasthesoledriverforthisoptioninGermany.


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Installation of Supplemental Reactive Power Compensation

Theimplementationofsupplementalreactivepowercompensationsystems(e.g.,shuntreactors,FACTS),ishardlyeverusedformediumvoltageandlowvoltagegridsinGermany.Testsregardingtheimplementationofreactivepowercompensationsystemsarebeingcarriedout.Whethertheinstallationofmorereactivepowercompensationsystemsinmediumvoltage

andlowvoltagegridswilltakeplaceinGermanyisunclearatthistime.

Implementation of Rotating and Non-rotating Energy Storage Systems

Energystoragesystemscanstoreoutputfromfluctuatingrenewableenergysourcesattimeswhentheyexceedtheneedsofthegrid,andthestoredenergyisreleasedbackintothegridatalatertimewhenneeded.However,storagesystemshavenotbeenusedinmediumvoltageandlowvoltagegridsinGermanyforDGintegrationtodatebecausethecostsofsuchtechnologiesarenoteconomicallyjustified.However,pumpedstoragehydroprojectshavebeenusedextensivelyontheEHVgridforregulatingpurposes.

However,implementationofstoragesystemsforrenewableintegrationonHVandMVgridsis

consideredtobealongtermpossibilityinGermany.

Most Frequent Application of Options in Germany

ThemostfrequentlyusedoptionsaresummarizedinTable4andarecategorizedaccordingtothemostcommonfieldsoftheirapplication.

Table 4: Most Frequently Used Options to Integrate Distributed Generation in Germany

Option Grid overloadCritical voltage

variationPower quality

issues

Direct connection

to a substation

Upgrade of gridcircuit conductors

Upgrade of upstreamtransformer capacity

Reduction of thegrid circuit length

Relocation of the loop normally-open disconnect point

Set point adjustment of transformerautomatic voltage control (tap changer)

Using reactive power capabilitiesof distributed generation plants

Construction ofa new substation


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Automatic Curtailment Option

Ingeneral,thegridoperatorsofmedium andlowvoltagegridsinGermanyhavenotusedautomaticcurtailmentofDGasanoptionforexpansionplanning.However,thisoptionhasrecentlybeenunderdiscussion.Inthisscenariothedistributedgenerationplantwouldneedtobecapableofautomaticallyreducingtheiroutputintheeventofspecificovervoltageor

overloadcondition,evenwithoutaremotecontrolsignalfromthegridoperator.Technicalruleshavenotyetbeenestablishedforthispotentialoption,butitmightbeimplementedinthefutureasanoption.

Recent Network Planning Policies and Studies

Eventhoughtheincreasingproductionofrenewableenergyfromdistributedgeneratingunitsaffectsthegridatallvoltagelevels,nofundamentalchangesintheapprovedgridstructureandplanningdirectiveshavebeenmadetodate.Technicalguidelineshavebeendevelopedto

ensureasecure

operation

of

the

grid

under

all

conditions

while

connecting

distributed

generationinaneconomic,leastcostmannerfromtheperspectiveofgridexpansionoptions.Anylargescalegridexpansionandredesignmeasuresinthepasthavebeendrivenprimarilybyoveralllongtermgridplanninggoals,andnotprimarilybydistributedorrenewablegeneration.However,recentpolicyinitiativesandstudiesinGermanysuggestthatanewgridinvestmentparadigmmaybedeveloping.ThisisdueperhapsinparttoconcernsoverthelevelofdependenceonnuclearresourcesinGermanyslongtermenergyplanandthepossibilityofsignificantlyreducingthisdependencethroughintegrationofevenhigherlevelsofrenewables.

MostrelevanttothecurrentKEMAinvestigation,recentlypublishedGermanstudyreportsconcludethatamajorincreaseinthescopeofdistributedandrenewablegenerationwould

requireconsiderableexpansionofexistingtransmissionanddistributionnetworks.Accordingtoonemajorwindresourceexpansionstudy13completedin2010,inthebaserenewableexpansionscenariostudiedupto3,600kmofnewtransmissionlinesareneededtoaccommodaterenewablegrowth,particularlylargeoffshorewind,by2020.Thiswouldrequireapproximately1billion/yearinadditionalgridexpansioncostsfornewtransmissionlines.Anotherexpansionscenarioconsideredincreaseduseofhightemperaturetransmissionconductorswhichwouldreducethemileageofnewlinestosome1,700km,butwouldalsorequiresome5,700kmofexistinglinestobemodified.Thisscenariowouldincreasetheexpansioncoststo1.6billion/year,whichisthehighestofallthescenariosanalyzed.

TheseresultsarecomplementedbyanotherdraftstudybyamajorGermanindustryassociation

(BDEW)whichquantifiesthenetworkexpansionnecessarytomeetmidtermrenewablepolicygoalsandforecast.14Whilethegovernmentsenergystrategypublishedin2010envisionsatotal

13DeutscheEnergieAgenturNetworkStudyIIPlanningoftheGridIntegrationofWindEnergyinGermanOnshoreandOffshoreuptotheYear2020(DenaGridstudy),2010.

14DraftreportbytheFederalAssociationoftheGermanEnergyIndustry(BDEW),March2011.


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installedsolarpowercapacityofapproximately33GWin2020(i.e.,doublingthecurrentinstalledsolarpowercapacity),theFederalMinistryofEnvironmentestimatesthatby2020therewillbeanother52GWofinstalledcapacityaddedfromsolarpowerandsmalleronshorewindparks.Giventhisforecast,theBDEWdraftstudyconcludesthatby2020theywouldneedtobuild195,000kmto380,000kmofadditionallinesontheGermanHVandMVdistribution

voltagenetworks.Theassociatedcapitalcostisestimatedtobe13billionto27billion.

Duetothedelayandconsiderableamountoftimeneededofthepermittingprocedureforplannedandnewtransmissionlines,theGermangovernmenthasalsorevealedpotentiallegalchangesinordertoaccelerateandsimplifytheplanningandpermittingprocedure.


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SECTION 2:Physical Infrastructure in Spain

Inrecentyearsdistributedgeneration(DG)hasreceivedincreasingattentionasitcancontribute

tothevariousgoalsofEUenergypolicy.Enhanceddiversityofsupply,areductioningreenhousegasemissions,efficiencygainsandmoreflexibilityininvestmentsaresomeofthemajorbenefitsassociatedwithDG.However,whentheamountofdistributedelectricitysupplyofrenewableenergysources(RES)surpassesaparticularlevel,itcannolongerbeignoredinplanningandoperationoftheelectricitysupplysystem.Therefore,improvementsoftheregulatoryframeworkoftheelectricitysupplysystemsarerequiredalongwiththegrowthoftheelectricitysupplyfromdistributedgeneration.

Basicprinciplesforachievingsustainabledevelopmentfromaneconomic,social,andenvironmentalpointofviewinSpaintodayincludereducingdependenceonforeignenergy,betteruseofavailableenergysources,andagreaterawarenessoftheenvironment.Thesegoals

increasinglydemandthedeploymentofrenewablesourcesofenergy,increasedefficiencyinelectricgenerationandareductioningreenhousegasesinaccordancewiththecommitmentsacquiredonsigningtheKyotoprotocol,bymeansofasearchforenergyefficientgenerationofelectricity.

CreationofthespecialregimeforthegenerationofelectricitymeantanimportantmilestoneinSpainsenergypolicy.TargetsforrenewableenergyandcombinedheatandpowerarecoveredintheRenewableEnergyPlan20052010andintheStrategyforEnergySavingandEfficiencyinSpain(E4),respectively.Inviewoftheabove,althoughgrowthinthespecialregimeforelectricitygenerationhasbeenoutstanding,incertaintechnologiesthetargetsarestillfarfrombeingreached.

Attheendof2010Spainhadatotalinstalledelectricpowerproductioncapacityof97.5GW(peninsularsystem).Thetotalinstalledcapacityinsolarandwindpowerproductionwas23.8GW(24percentofthetotalinstalledcapacity).Thistotalincludesapproximately9GWfromwindprojectsand4GWfromsolarPVprojectssmallerthan20MW.Continuedgrowthofdistributedrenewablegenerationseemsunabated.

Therefore,Spanishgridoperatorsinrecentyearshavedevelopedtechnicalrulesandguidelinestomaintainsecurenetworkoperationwithlargeamountsofrenewables.AccordingtotheseextensiveexperiencestheSpanishpowerdistributionsystemissuitableforacomparativeanalysis.

TheSpanishMinistryofIndustrythroughtheInstituteforEnergyDiversificationandSaving(IDAE)hasdevelopedthewebsiteRenovables(Renewables)MadeinSpain,http://www.renovablesmadeinspain.com/withtheobjectivetoinformtheworldaboutthesignificantpenetrationofrenewableenergiesinSpainandtheleadershipofSpanishcompaniesandorganizationsthathavemadethispossible.


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InthefollowingsectionstheresearchteampresentsthemainvoltagesofthetransmissionanddistributionnetworksinSpain.Thenwedescribetherelevanttypesofrenewableenergysourcesbyregion,alongwiththecharacteristicsofthegenerationplantsandtheirimplicationsforthegrid.Finally,weaddressthemostfrequentlyusedtechnicaloptionsandfacilitiestomanagetheintegrationofrenewableenergysourcesandtherebytocomplywithtechnical

requirementsandguidelines.

Overall System Planning and Development

InMay2008,theSpanishMinistryofIndustry,TradeandTourismpassedthe20082116planningdocumentforthegasandelectricitysectorstoensurethesafetyandqualityoftheenergysupply.Thisplansetsoutasubstantialprograminvolvingtheconstructionofnewpowerinstallations.

In2009RedElctricadeEspaa(REE),theSpanishcorporationthatoperatesthenationspower

transmissionsystemandelectricitygrid,continuedtodrawupforecaststudies,bothforpowerdemandandcover.REE,asoperatoroftheinsularandextrapeninsularsystems,likewisedrawsupboththedemandandpowerpeakforecastsandtheestimatesofgeneratingequipmentneedsforthesesystems.

REEiscarryingoutinvestmentsaimedatreinforcingthegridmeshinordertocoverincreasesindemandinsomeareasofthemainlandandtofacilitatetheestablishmentofthenewgenerationinstalled,mainlycombinedcyclesandwindpowerplantsand,toaneverincreasingextent,solarthermalplants.

Network Structures in Spain

ThispartofthereportdescribesthebasictechnicalconfigurationsofSpanishdistributiongridsincludingsubstationsandsecondarysubstations.Theanalysisfocusesonmedium andlowvoltagedistributiongrids.ItalsooutlinesrelevantaspectsofdistributedgenerationathighervoltagelevelsinSpain.

Grid and Voltage Levels

TheSpanishpowergridatallvoltagelevelsisathreephasealternatingcurrentgridoperatedatafrequencyof50Hertz.FourcommonvoltagelevelshavebeenestablishedintheSpanish

powergrid

as

shown

in

Table

5.

This

classification

of

voltages

is

according

to

the

IEC

definitions.


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23

Table 5: Overview of Voltage Levels in Spain per IEC Definitions

System Name

(IEC Definition)Abbreviation Rated Voltage Role

Extra-high voltage EHV 400 kV, 220 kV15 Transmission grid

High voltage HV132 kV, 110 kV

66 kV, 45 kV

Distribution gridMedium voltage MV

30 kV, 20 kV,15 kV, 13.2 kV,

11 kV

Low voltage LV 400 V

Spanishlegislation(RoyalDecree223/2088)givesasimilarclassificationforlinesabove1kV:

Specialcategory:Linesofnominalvoltageaboveorequalto220kV,ortheonesoflower

voltagethatareoperatedbytheTSO. Firstcategory:Linesofnominalvoltagebelow220kVandabove66kV

Secondcategory:Linesofnominalvoltageequaltoorbelow66kVandabove30kV

Thirdcategory:Linesofnominalvoltageequaltoorbelow30kVandabove1kV.

Thecharacteristicsandfunctionsofthemainvoltagelevelsarediscussedbelow.

The Spanish Transmission System

ThetypicalvoltagelevelsforthetransmissiongridinSpainare400kVand220kV.The

internationalconnectionsarealsoconsideredasapartofthetransmissionsystem.REEistheTransmissionSystemOperator(TSO)andownsabout99.8percentofthe400kVpowerlinesand98.5percentofthe220kVpowerlines.AccordingtocurrentSpanishregulationsall220kVmustbetransferredtotheTSO.

TheElectricitySectorAct54/1997confirmedtheroleofREEasacornerstoneofsystemoperation.Thislawcreatedawholesalepowermarketthatrequiredaneffectivelymanagedtransmissiongridtoworkproperlyandacoordinatedoperationofthegenerationtransmissionsystemtoensurethatdemandwouldbesatisfiedatalltimes.

Act17/2007of4JulyinSpainamendedthepreviouslawtoadaptittoEuropeanDirective

2003/54/CEwhich

established

the

common

guidelines

for

the

domestic

power

market.

This

law

hasresultedinthedefinitiveconsolidationoftheREEsTSOmodel.Inthisregard,REE,asthesystemoperator,guaranteesthecontinuityandsecurityofthepowersupplyandtheproper

15Inthepast,theDSOscontrolledpartsofthe220kVnetwork,butithasmostlybeenmovedtotheTSO.


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coordinationoftheproductionandtransmissionsystem,performingitsfunctionsbasedontheprinciplesoftransparency,objectivity,andindependence.

REEisnotjustthemanager(operator)ofthetransmissiongridbutlikewisehasexclusiveresponsibilityfordevelopmentandmaintenanceofthegrid.Thisisquitedifferentfromthe

German

case

where

several

transmission

grid

owners

and

operators

coexist.

LikeGermany,SpainispartoftheEuropeanNetworkofTransmissionOperatorsforElectricity(ENTSOE),andthereforeoperatesaccordingtorulesintheOperationHandbookofENTSOE.Thetransmissiongridisameshedsystemwithhighstandardsforsystemstability(frequency,voltage,dynamicstability)andsecurityofsupply.Overheadlinesdominatethegridinfrastructure.Figure7illustratestheSpanishtransmissionsystemwith400kVlinesrepresentedinredand220kVlinesrepresentedingreen.


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Figure 7: Spanish Transmission System

Source: REE (http://www.ree.es/transporte/mapa_red_transporte.asp)


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The Spanish Distribution System

ThetypicaldistributionvoltagelevelsinSpainare132kV,110kV,66kV,45kV(highvoltage),30kV,20kV,15kV,13.2kV,11kV(mediumvoltage),and380V(400Vinthelatestregulation,RD842/2002,lowvoltage).

InSpain

the

main

distribution

companies

are

Iberdrola,

Endesa,

Gas

Natural

Fenosa,

Hidrocantbrico,andE.Onwithamarketshareof40percent,39percent,15percent,2.5percent,and2.5percenteach,whichcombinedrepresent99percentofthetotaldistributionactivity.

HV Distribution Grid

SpanishHVgridsareofmeshedtopology(moreorlesscomplex)andcanbeoperatedalsoinameshedphilosophy(closedloop)orradial(openloop).Theexceptionareafewradialbuiltnetworksinruralareas,butevenintheseareasthemostcommontopologyistheopenloop,sothereispossibilityofsupportthroughasecondline.ThisgridisusedtofeedthedistributionsubstationsthatareconnectedtotheMVgrid.ThelayoutoftheHVbusbarofthese

distributionstationsdependsontheareatheyarebuilt.MostoftheHVgridcomplieswithn1securitycriterion(fortransformersandlines).Securitycriterian2canbeappliedforHVgridsassociatedtourbanareas,whenthereareforexamplesubstationsfedbycriticaldoublecircuitlines.Figures8through10illustratedifferentnetworktopologiesappliedattheHVlevelinSpain.

Figure 8: Looped HV Grid (Single Source Point)

Source: KEMA


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Figure 9: Bridge Configuration (HV Grid Fed from Two Points)

Source: KEMA

Figure 10: HV Mesh Configuration

Source: KEMA

MV Distribution Grid

TheSpanishmediumvoltage(MV)grid)inSpainisdifferentiatedbyurban,semiurban,and

ruralareasthathavedifferentpowerquality,reliability,andcontinuityofsupplyrequirements.

Urban Medium-voltage Grids

UrbanMVgridsinSpainservehighdensityurbanareasfedbyundergroundcables.Thetypicalcablecrosssectionis240to400mm(nominallyequivalenttoarangeof400kcmilto750kcmil),butthereisasignificantheterogeneityofcrosssectionespeciallyinthelargecitiesduetodecadesofdifferentplanningcriteriaandnetworkdevelopmentcriteria.


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ThedesignphilosophyofMVgridsinSpainistoservetheMV/LVstationsinawaytheycanalwaysbefedfromatleastfromtwodifferentpoints.ThereshouldnotbeMV/LVstationsonsingle,radialMVsources.Thisisachievedbyapplyingmainlytwostandardnetworkdesigns:

Reflectionpointandsupportcircuit

Distributionpoint

Figure11illustratestheconceptbehindthereflectionpointandsupportcircuitdesign.Theideaistohaveanormallyopenbackupcircuit(CircuitodeApoyo)thatincaseoffaultinoneofthemainfeederswillbeabletocloseintothereflectionpointandfeedtheloadonthehealthyportionofthefaultedfeederafterthefaulthasbeenisolatedbyremotecontrolledswitches.TheseswitchesareassociatedtoRMUs(RingMainUnits)intheMV/LVstations(circlesinthefigure).IntheexampleshowninFigure11,afault(indicatedbythelightningbolt)hasoccurredonthefirstsectionofCircuit1nearthesourcestation(ST),whichhasbeenisolatedandtheremainderofthecircuitloadpickedupfromthereflectionbusviathebackupcircuit(greenindicatesaclosedbreaker,andwhiteindicatesanopenbreaker).

Figure 11: Urban MV Grid: Reflection Point and Support Circuit Design16

Source: Universidad Pontificia Comillas: Master Thesis by Trinidade Moya

Figure12illustratesthedistributionpointdesignthatisusedmainlyinhighdensityloadareas.Reliabledistributioncentersarebuiltascloseaspossibletotheloadcenterandtwoormorehighcapacitytrunkfeeders(circuitosallementadores)areconstructedfromtheremoteHV/MVtransformationsubstationstothedistributioncenters.Noloadisconnecteddirectlytothetrunkfeeders.MultipledistributioncircuitsemanatefromeachdistributioncenterandfeedmultipleMV/LVstationswithinthehighloaddensityarea.Figure12illustratesaconfigurationwithtwosuchdistributioncenters,butothercombinationscanbeused.TheMV/LVstationsnormally

consist

of

transformers

above

400

kVA,

with

one

or

more

transformers

per

station.

16STmeanssubstation.CircuitodeApoyomeansbackupcircuit.CXmeansreflectionpoint;abuswithcircuitbreakersandgroundswitchesusedtogroundthecircuitswhenthebreakersareopen.


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Figure 12: Urban Medium Voltage Grid: Distribution Point design17

Source: Universidad Pontificia Comillas: Master Thesis by Trinidade Moya

Rural Medium-voltage Grids

Spainhasmadeadifferentiationbetweenconcentratedanddispersedruralareas.Botharefed

mainly

by

overhead

lines,

though

dispersed

rural

areas

have

longer

lines,

commonly

causing

voltagedropproblemsrelatedtothelargeimpedanceofthelongoverheadlines.Thedesignnormallyconsistsofamainfeederwiththesameconductorcrosssectionoveritsfulllength,

17CentrodeRepartoCR1and2meansDistributionCentersNo.1and2,SubestaciaonTranformadorameansTransformationSubstation,TrafoT1andT1meanBank1and2.


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fromwhichseveralderivativefeeders(branches)aresuppliedtypicallywithsmallerconductors.

SimilarlytotheUnitedStates,theruralnetworksinSpainareequippedwithswitchesalongthelines(reclosersandsectionalizers)inordertomoreefficientlyisolatefaultysectionsandrestore

the

supply

to

the

healthy

ones.

The

main

feeders

of

the

rural

network

can

be

fed

from

two

alternativesubstationsoperatinginanopenloopmanner(makinguseofanormallyopenpointbymeansofaswitch),resemblingtheloopconnectedwithnormalopencontactphilosophythatisusedinGermany.Thisallowstheuseoflooprestorationschemesincaseoffaults.ThetypicalSpanishruralMVgridstructureisillustratedinFigure13.Unlikeurbanareas,MV/LVstationsinruralareasareusuallysuppliedfromasinglecircuit.

Figure 13: Rural MV Grid Struc ture

Source: KEMA

LV Distribution Grid

Thelowvoltagegrid(LVgrid)isathreephase400V,comprisingalsoaneutralwire.Thesegridsarebuiltandoperatedinaradialway,regardlessofbeingurbanorrural.Urbangridsaredominatedbyundergroundcables,whileruralgridsaredominatedbyoverheadlines.Ruralgridsaremoreexposedtovoltagedeviations(droporrise)duetotheirhigherperunitimpedancecombinedwithlongerlength.ThetypicalSpanishLVgridstructureisillustratedinFigure14.


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Figure 14: LV Grid Structure

Source: KEMA

Renewable Energy Sources (RES) in Spain

Electricityproducers

in

Spain

are

subjected

to

different

legislation

depending

on

the

technology

andenergysourceused.Producersareclassifiedintwomaingroups:specialregime(ex:renewableenergysources)andordinaryregime(ex:conventionalpowerplantssuchasnuclearpowerstations).Figure15showsabreakdownofthetotalinstalledcapacitybytechnologyattheendof2010.Figure16showstheannualevolutionoftheinstalledpowerbytechnologyfrom2005to2010.

Figure 15: Breakdown of the Total Installed Capacity by Technology at the End of 201018

Source: REE (Red Elctrica de Espaa)

18ThecategoryOtherSpecialRegimeincludescogenerationandwastetoenergyplantsbelow50MW.

Installed Pow er (GW)

Combined cycle; 25,2

Fuel/Gas; 2,9

Coal; 11,4

Nuclear; 7,7Hydro; 16,7

Wind; 19,8

Solar; 4,0

Other Special Regime;9,8


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Spainhadatotalinstalledcapacityinelectricpowerproductionof97.5GW(peninsularsystem)bytheendof2010.Thetotalinstalledcapacityinsolarandwindpowerproductionwas23.8GW(24percentofthetotalinstalledcapacity)attheendof2010.Nexttocombinedcycleplantsat25.2percentofthetotalresourcecapacity,windwasthenextlargestblockat19.8percentoftotal.

Figure 16: Annual Growth of Spains Installed Power Generation (GW)


Distributed Generation

Generally,distributedgenerationcomprisesgenerationplantsthatareconnectedtolow and

mediumvoltagedistributiongridsclosetoenergyconsumersandgenerationplantsforselfsupply.However,thisdefinitionassuchisnotusedinpracticeinSpain.Althoughtherearedifferentremunerationschemesforgeneratorsofdifferentsize,whichthereforewillbeconnectedtodistinctvoltagelevels,themainsplitinSpainismadebetweenthesocalledordinaryandthespecialregime.Thetechnologieseligibleforspecialregimearecogeneration,renewableenergysourcesandwaste.AccordingtotheSpanishlawRD661/2007,therenewableenergysourcesgroupisdividedineightsubgroupsasfollows:

b.1:solarenergy

b.2:windenergy

b.3:waves,geothermic,tides

b.4:andb.5:hydropower

b.6,b.7,andb.8:biomassandbiogas

Installationswithaninstalledcapacitylargerthan50MWarenotincludedinthespecialregime.However,iftheseinstallationsproducerenewableenergytheyreceiveapremiumequal

Installed Pow er (GW)

12,2

15,5

21,0

21,7

23,1

25,2

6,6

6,6

4,8

4,4

3,0

2,9

11,4

11,4

11,4

11,4

11,4

11,4

7,9

7,7

7,7

7,7

7,7

7,7

16,7

16,7

16,7

16,7

16,7

16,7

8,7

11,6

14,8

16,2

18,7

19,8

8,4

9

9,7

12,6

13,3

13,8

0 10 20 30 40 50 60 70 80 90 100

2005

2006

2007

2008

2009

2010

Combined cycle Fuel/Gas Coal Nuclear Hydro S.R. Wind S.R. Other


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tothatpaidtosmallerrenewableprojects(i.e.,thoselessthan50MW),butdiscountedby2080percent.DuetothisfinancialdisincentivetherearenoindividualrenewableenergyprojectsinSpainwithinstalledcapacityover50MW.

Point of Common Coupling

The

definition

of

point

of

common

coupling

in

Spain

is

similar

to

Germany,

i.e.

it

is

the

grid

connectionpointofagenerationplant.Itslocationdependsontheratedpowerofthegenerationplantandtechnicalandeconomicaspectsofthepowergrid(voltagelevel,utilizationofassets,networkimpedance,etc.).

Regional and Quantitative Allocation of Renewable Energy

In2009,thegeneratorsoperatinginthespecialregimesupplied32percentofthegrosselectricalconsumptioninSpain.Windfarmsalonesupplied14.5percentofSpainsgrosselectricalconsumptionin2009.

Figure17showstheshareofthedifferentrenewabletechnologiestothetotalinstalledcapacity

in

renewable

electricity

production

for

the

special

regime

(S.R.).

Figure 17: Breakdown of the Total Renewable Installed Capacity by Technology at the End of 2009


Wind Energy

WindpoweristherenewablesourcethathasexperiencedthelargestdevelopmentinSpain.ThepopulationdensityinlargeareaswithgoodwindresourceismuchlowerthaninGermany,

whichhas

provided

opportunities

to

build

larger

wind

farms.

The

development

has

taken

place

throughlargeinvestorssuchaselectricityandconstructioncompanies.Recently,thetrendisfornonelectriccompaniestoselltheirinstallationsduetotheincreasingtechnicalrequisitesinthissector.Thedevelopmentofthewindpowersectorgoesinthedirectionoflargerwindfarmsconnecteddirectlytothetransmissiongridduetothetechnicaldevelopmentofwindturbinestechnologyandtheavailablecapacityinthetransmissiongridtotransportmoreelectricpower,gettingbetterprices.Whentheinstallationcapacityislargerthan50MW,promotersdivideintoseveralinstallationsunder50MWinordertogetthehighestpayment.About60percentofthe

Installed Power (% Total Renewable i nstalled Power)

S.R. Hydro 7,8%

S.R. Wind 75,1%

S.R. Solar 13,9%S.R.Biomass 2,6%


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totalinstalledwindpowerisconnectedtothetransmissiongrid.Oftheremaining40percentconnectedtodistributionthelargemajorityisconnectedtothe132/110/66kVgrids.Only25percentisconnectedtotheradialoperateddistributiongrids(30kVandbelow).Windpowerisdistributedalloverthecountry,butthereissignificantincidenceoflargewindfarmsinthenorthernregionsofGaliciaandtothesoutheastinCastillaLaMancha.Figure18showsthe

installedwindcapacitydensity(kW/km2)inSpain.

Figure 18: Wind Capacity Geographic Density in Spain


Spainswindproductionishighlyvariablebothhourbyhouranddaytoday.Forexample,Spainsrecordhighwindproductionwasabout11:00amonFebruary24,2010at12,916MW,andtherecordlowwasonJune3,2009at164MWintheearlyafternoon.Onmostdays,windproductionpeaksatnight,andreachesaminimumbetweennoonand2:00pm.Downwardrampsinwindproductioninthemorningsoftenincreasemorningrampupsofconventionalgenerationinthesummeralongwithdispatchofpumpedhydroplants.SomekeyfactsaboutwindpowerinSpain:

RenewableenergyplanforSpain(20052010):~20,000MW(accomplished)

Officialnetworkplanningfor2016:29,000MW

Furtherincreaseexpectedfor2020incompliancewithproposedECinitiatives Productionrecords:54percentofdemand at3:50amonDecember30,2009

Solar Energy

Spainleadstheworldinthedevelopmentofsolarenergy,asitisoneofthesunniestcountriesinEurope.Morethan95percentofthetotalPVinstalledcapacityisconnectedtothe


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distributiongrid(below220kV)aswellasabout35percentofthetotalthermal(conventional)installedgeneratingcapacity.

Figure19showsthedistributionofsolarPVandsolarthermalpowerintheSpanishautonomouscommunities,byend2009.Atthistimetherewereabout3.3GWofsolarPVwere

connected

to

the

grid.

While

solar

thermal

is

present

only

in

the

communities

of

higher

solar

radiationexposure,suchasAndalucia,solarPVismuchmoreuniformalongthecountry,althoughstilldominatedbythesoutherncommunities.

a) b)

Figure 19: Installed Solar Power (MW) in the Autonomous Communities of Spain by End 2009a) PV and b) Solar Thermal

Source: REE and ASIF (Associacion Industrial Fotovoltaica)

AtpresenttheTSOhasnoremotemonitoringorremotecontrolcapabilityforanyofthe3.3GWofPVpowergenerationbecausetelemetrytotheTSOisonlyrequiredforDGprojectsof10MWorlarger,andtherearenoPVprojectsofthissizeinSpain.AstheinstalledMWofsolarPVexpands,thelackoftelemetryontheseprojectswillcreategreateroperatingproblemsfortheTSO.Also,SpainswinterpeakdemandisintheeveningwhenPVmakesnocontribution.Inthewintertheuseofmoltensaltenergystorageandhybridizationwithnaturalgas19canenablesuchsystemstoproduceduringthepeakdemandhours.Ontheotherhand,concentratingsolar

thermalhasapositivecorrelationwithSpainssummerpeakdemand.

19HybridizationwithnaturalgasislimitedbySpanishregulationsto15percentofsolarthermalplantcapacity,whereashybridizationwithbiomassorbiogasisallowedupto50percent.


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RES Compensation Arrangements in Spain

RESrevenuescanbedeterminedbyoneofthetwofollowingalternatives:

Feedintariff:thepricepaidpereachkWhproducedbyaRESinstallationisregulatedandfixedtoaconstantvalue,independentofmarketfluctuations.TheannualevolutionofthistariffdependsontheevolutionoftheaveragereferenceelectricitytariffinSpain(RT),asfeedintariffs(FIT)aresetasapercentageoftheRT.Thetariffisfixedforacertaincontractduration(e.g.,15years).TheregulatedfeedintariffforeachREStechnologydependsonthetypeofthetechnologyandontheyearwhentheinstallationisputonservice.Thisalternativeisaheritageofthepreviousregulation.RESfacilitiesgreaterthan10MWarecommittedtogivetodistributioncompanies(DISCOs)aproductionschedule30hoursinadvance,beingallowedtoadjustsuchschedule1houraheadofeachintradailymarket(sixcallsduringaday).HourlyenergydeviationsfromtheproductionschedulearepenalizedatapriceperkWhdeviatedequalto10percentoftheRT.Thispenalizationdoesnotapplyinadeadbandof20percentoftheproduction

scheduledforRESfacilities.Thisrule,whichimpliesabigchangeinRESregulationfromthepreviousframework,willapplytowindfarmsonlysinceJanuary1,2006.AsthegovernmentREStargetsarereached,theFITdecreases.WhentheFITcontractperiodforagivenRESprojectisover,itsenergyissoldatthemarket(pool)price.

Wholesalemarket:RESaregivenincentivestojointhewholesalemarket,followinginthiscasepracticallythesamerulesasordinarygenerators.AstheRESwillfacenewtechnicalandeconomicconstraintsbydoingso,theirremunerationschemeprovidesanadditionaleconomicincentive.Thetotalincomeisthesumofthemarketsellingprice,plusapremiumthatrepresentstheexternalitiesinasimilarwaytopreviousregulation,plustheabovementionedadditionalincentivetoaccessthemarket.Thepremiumand

theadditionalincentivearesetalsoasapercentageoftheRT.AsRESareintegratedinthewholesalemarket,theyhaveaccesstoalltherestofelectricitymarkets(daily,intradaily,ancillaryservices,etc.).Theycanearnmoneyiftheyareabletoparticipateinsuchmarketsorpayiftheyusesuchservices,beingthemostimportantthecostofproductiondeviationsfromthepredictions.Inthiscase,thereisnodeadband,andthepriceissettledthroughmarketmechanisms.

REShaveanadditionalincomeassociatedtoreactivepowerthatdependsonthetimeperiod(peak,flat,orvalleyhours)anditcanbepositiveornegativedependingonthepowerfactorthe

unit

is

providing.

This

income

encourages

RES

to

consume

reactive

power

(lagging

power

factor)invalleyhoursandtosupplyreactivepower(leadingpowerfactor)inpeakhours.Inpreviousregulationstherewasanincentivetokeepthepowerfactorequaltoone.

AninterestingaspectofcurrentSpanishlegislationistheeconomicincentivethathasbeenfixedforwindfarmstobeabletocopewithvoltagedipswithouttripping.Thisisoneofthemaintechnicalproblemsforwindgenerationexpansion,withhighpenetrationlevelsofwindgenerationthatcanalltripatonceifthereisavoltagedipinthetransmissionnetwork,


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threateningsystemstability.Thereisaneconomicincentiveof5percentofRTtoeachkWhsoldbyeachimmunizedwindparkagainstvoltagedipsduringaperiodoffouryears.

Interconnection Technical Requirements in Spain

RESproducersthatwishtoconnectattheEHVlevelmustconnectaminimumcapacityof100

MWat

any

one

point

of

interconnection

to

the

220

kV

grid

or

at

least

250

MW

at

any

one

point

ofconnectionwithtothe400kVgrid.ItispossibleseveralforsmallerprojectdeveloperstomakeajointapplicationtotheTSOtofulfillthisrequirement.RD436/2004definesadditionalcriteriaandareagainstatedagainintheRD661/2007(annex11)withsomemodifications:

1. Thecombinedcapacityofallspecialregimegeneratorsconnectedtoonelineofthedistributiongridcannotexceed50percentofthecapacityoftheline.

2. Thecombinedcapacityofallspecialregimegeneratorsconnectedtoonesubstationorsubstationtransformercannotexceed50percentofthecapacityoftherespectivesubstationortransformerservingthatvoltagelevel.

3. Forproducerswithoutstoragecapabilitiesornotabletodirectlymanagetheiroutput,

suchaswindpowerandPVproducers,itisalsoestablishedthattheMWcapacityoftheproducerorgroupofproducerssharingaconnectionpoint(pointofcommoncoupling),willnotexceed5percentofthegridshortcircuitduty(atthatpointonthesystem)expressedinMVA.Fordispatchablegenerators(biomass,solarthermal),theMWcapacityshallnotexceed10percentofthegridshortcircuitduty(atthatpoint)expressedinMVA.ThisisintendedtolimitthemaximumvoltagedeviationduetoDGoperationtotherangeof510percentofthelocalgridsnominalvoltage.

BecauseoftheabovelimitationsingridimpactsduetoDG,veryfewbackfeedsituationshave

developed

in

Spain.

In

practice,

the

criteria

above

only

restrict

the

connection

to

the

distributiongridandarenottheconnectiontothetransmissiongrid.Basedonutilityexperienceregardingconnectiontothedistributiongrid, criteria1and2fromthelistabovelimitthecapacitythatcanbeconnectedinabout10percentofthecases,whilecriteria3islimitinginapproximately90percentofthecases.DGprojectsinSpaindonothavemuchexperienceconnectingtotheMVdistributiongrid,sotheselimitationsmayneedtobereviewedinthecomingyearsaswell.Distributioncompaniesgenerallyconsiderthesecriteriatobeadequate,althoughtherehavebeensuggestions/discussionsontheinclusionoflocalloadasalimitingfactorfortheinterconnectionofspecialregimegenerationduetoconcernaboutbackfeedintoHVandthetransmissiongrid.

Photovoltaicplants

smaller

than

100

kVA

and

connected

to

low

voltage

networks

(below

1kV)

havespecificconnectionrequirementsenactedintheRoyalDecree1663/2000.Themostrelevantrequirementsofthislegislationaretheobligationstomaintainvoltageattheinterconnectionpointat5percentofthenominalvoltageandoperateatapowerfactorascloseaspossibletounity.


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Implications on Power Grid Operation

REE(TSO)has,alongtheyears,beenexperiencingwindgenerationtripsduetovoltagedips.Asaresult,ithasbeenmonitoringvoltageandgeneratorperformancesince2005.AnoperationalprocedurehasbeenimplementedaspartoftheSpanishgridcodethatestablisheswhen

generatorsmustremainconnectedinordertoallowridethroughintheeventofafault.StartingJanuary1,2008,allnewwindfacilitieshadtocomplywiththisvoltageridethroughregulation.Mostexistingplantshavemadethenecessaryretrofitstocomply,andonlysome1,000MWto1,500MWplantsstillneedtobeadapted.REEnowrunsrealtimesimulationtomodelscenariosofthreephasefaultsin70ofits400kVsubstations.ThesesimulationsallowtheTSOtotakeactionsfromadedicatedcontrolcentreinordertoensuresafesystemoperationandavoidfurthergenerationtripping.

Voltagecontrolforconventionalgenerationistypicallydoneatthesubstation.Thatisnotsufficientwherealargepenetrationofrenewablegenerationexists.REEhasinstitutedasystemtoincentiverenewablegeneratorstoprovidereactivepower:Generatorsreceiveabonusor

sufferapenaltyfor+8percentto 4percentof78.44perMWh,dependingonthepowerfactor.Thesystemoperatorissuesinstructionstomodifythepowerfactorsettings.

SinceApril1,2009,REEhasorderedallDGunitsabove10MWtooperateatpowerfactorsbetween0.98and0.99inductiveinordertoeliminatesuddenchangesinthevoltageprofileandavoidhighvoltages.REEbelievesthattheultimatesolutionistoenablevoltageschedulingcapabilityforallgeneratorsgreaterthan10MW.AkeyissueremainsastowhenandhowtoautomateDGvoltagecontrolandwhetherthisrequiresalocal,regional,ornationalstructure.

Connection Process to Transmission Network in SpainConnection Application Phase

Therearetwodifferentstages,accordingtoP.O12.2ofREE:

1 Requestforaccesstothetransmissiongrid.

2 Requestforconnectiontothetransmissiongrid.

Forstage1,thegeneratormustsubmitarequestforaccesstoaspecificnetworklocation(node)andsupplyavarietyoftechnicaldataaboutitsgeneratingplantfromratedpowertoPSS/E

controlblock

models

for

dynamic

analysis.

REE

also

requests

the

seasonal

generation

patterns.

Itisacompletesetofdataonthegeneratingunit,whichiscomplementedwithdataoninterconnectionlinesandalsowithdataonstepuptransformers.Furthermoretherearedifferentrequestsdependingonthegenerationtechnology.REEP.O12.1annexeslistallthenecessarydatafordifferentgenerationtechnologies.Afterreceivingtherequestforaccessaccompaniedbythegeneratordata,theSpanishTSOhastwomonthstodetermineifthesystemcapacitywillsupporttheconnection.Ifso,thegeneratoradvancestostagetwo.


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Atstagetwothegeneratormustsubmitthebasicdesignofitsinstallation,theconstructionprogramandareportshowingthattheinstallationfulfillsalltheconnectionrequirementsinInstalacionesconectadasalareddetransporte:Requisitosminimosdediseoyequipamiento.Thisdocumentdefinesprotectionrequirements,groundingrequirements,switchgeararrangements,etc.Thegeneratorhasonemonthtodeliverthesedocumentsafter

receivingapositivestage1approval.Initsturn,theTSOhasonemonthtodecideifthegeneratorsdocumentationisadequate.

Thegeneratordoesnothavetoperformanystudiesitself,sincethestudiesarecarriedoutbytheTSOusingdatasuppliedbythegenerator.ThegeneratorisfreetoasktheTSOforinformationaboutaparticularlocationornodeofthegridifhewishestoperformhisownstudiestoevaluatethefeasibilityoftheinterconnectioninagivennode.The[decidingauthority]usestheTSOstudiesforitsdecision.

Ifthestateoneproposalfails,thegeneratorcanproposealternativeconnectionpointsorrequestinformationonthegridreinforcementcostsnecessarytoeliminatetherestrictions.Ifthe

developeris

willing

to

pay

for

these

reinforcements,

while

advancing

to

stage

two,

he

must

pay

upfrontfor20percentofthesecosts.

Commissioning Phase

Twomonthsbeforetheplannedinterconnectiondate,thegeneratormustprovidetheTSOwithat

Kema_Memo 1_Physical Infrastructure and DG Interconnection

Documents

Transcript of Kema_Memo 1_Physical Infrastructure and DG Interconnection