Christian Winter – Minnesota Power Minnesota Power

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Transmission Lessons Learned from theDecarbonization of Minnesota’s North ShoreChristian Winter – Minnesota PowerMinnesota Power Systems ConferenceNovember 13, 2019

Overview Background Issues– Voltage Support & System Strength– Power Delivery Capability– Redundancy Summary2

What is the North Shore Loop?20152015-2016U1: 2016U2: 20193

Transmission Impacts from Fleet Transition Voltage Support & System Strength––– Power Delivery Capability–– Redundancy––4

Transmission Impacts from Fleet Transition Voltage Support & System Strength– Steady state voltage regulation– Dynamic reactive support (Voltage Stability, Damping)– Short circuit capability Power Delivery Capability–– Redundancy––5

Illustration: Voltage SupportImagine the power system in Minnesota being supported by columns, representingbaseload generators that supply voltage support and system strength.Major Load Centers6Removing columns weakensthe support systemCONCLUSION: Voltage Support & System Strength presentlyprovided by baseload generators needs to be retained orreplaced. Location matters.6

North Shore Loop Reactive Resources (2014)Tac Harbor4627244224Laskin42423825Silver Bay27SwitchedCapacitor Banks(MVAr)7DynamicVoltageSupport(MVAr)27Voltage Support Resources in the North Shore Loop2014: Before Fleet TransitionTotal Static: 127 MVARTotal Dynamic: 237 MVAR

North Shore Loop Reactive Resources (2015)Tac Harbor4627244224Laskin42423825Silver Bay27SwitchedCapacitor Banks(MVAr)8DynamicVoltageSupport(MVAr)27Voltage Support Resources in the North Shore Loop2015: Laskin Conversion & Tac Harbor Unit 3 ShutdownTotal Static: 127 MVAR (No Change since 2014)Total Dynamic: 147 MVAR (-90 MVAR since 2014)

North Shore Loop Reactive Resources (2016)Tac Harbor4627244224Laskin42423825Silver Bay27SwitchedCapacitor Banks(MVAr)9DynamicVoltageSupport(MVAr)27Voltage Support Resources in the North Shore Loop2016: Silver Bay & Tac Harbor Units IdledTotal Static: 127 MVAR (No Change since 2014)Total Dynamic: 25 MVAR (-212 MVAR since 2014)

Taconite Harbor Voltage Regulation (2016)Fewer reactive resources less voltage regulationWeaker system voltage more affected by changes on system10

North Shore Loop Reactive Resources (2017)Babbitt12Tac Harbor4624274224Laskin20ETCO4242North Shore40Capacitor banks placed wherelow voltages were identified4020203825Silver Bay27SwitchedCapacitor Banks(MVAr)DynamicVoltageSupport11 (MVAr)27Voltage Support Resources in the North Shore Loop2017: North Shore, ETCO, Babbitt Cap Banks InstalledTotal Static: 279 MVAR ( 152 MVAR since 2014)Total Dynamic: 25 MVAR (-212 MVAR since 2014)

North Shore Loop Reactive Resources (2019)Babbitt12Tac Harbor4624274224Laskin20ETCO4242North Shore *Dynamic reactive supportinstalled to prevent postcontingent voltage collapse401752020203825Silver Bay* North Shore Cap Banks controlledby STATCOM to increase dynamiccapacitive range of STATCOM27SwitchedCapacitor Banks(MVAr)DynamicVoltageSupport12 (MVAr)27Voltage Support Resources in the North Shore Loop2019: Silver Bay Unit Idled, STATCOM OnlineTotal Static: 159 MVAR ( 32 MVAR since 2014)Total Dynamic: 175 MVAR (-62 MVAR since 2014)

Taconite Harbor Voltage Regulation (2019)13

Silver Bay Voltage Regulation (2019)Last North Shore LoopGenerator Idled14

North Shore Loop Voltage StabilityAcceptable Voltage RangeVoltage StabilityMust provide sufficient dynamic(fast-responding) reactive supportto ensure system voltage canrecover after a fault eventAcceptable Voltage RangeNorth Shore Loop FaultWithout North Shore STATCOMVoltage CollapsedNorth Shore Loop FaultWith STATCOMVoltage Recovered

North Shore Loop Reactive Resources (2020 )Babbitt12Mesaba Jct46282427Tac Harbor284224Laskin20ETCO4242North Shore *Additional capacitor banks toboost voltage along a heavilyloaded transmission path401752020203825Silver Bay27SwitchedCapacitor Banks(MVAr)DynamicVoltageSupport16 (MVAr)27Voltage Support Resources in the North Shore Loop2020 : Mesaba Junction Cap Banks (Planned)Total Static: 215 MVAR ( 88 MVAR)Total Dynamic: 175 MVAR (-62 MVAR)

Transmission Impacts from Fleet Transition Voltage Support & System Strength– Steady state voltage regulation– Dynamic reactive support (Voltage Stability, Damping)– Short circuit capability Power Delivery Capability– Increased reliance on external sources– Increased power flow on incoming transmission lines Redundancy––17

Illustration: Power Delivery CapabilitySources of PowerToday, a certain amount of power is provided bybaseload generators at particular locationsDemand forPowerWhen this power is no longer supplied at the samelocations, a “hole” is created that must be filled18CONCLUSION: Replacement of power provided by existinggenerators may cause a need for transmission upgradesDemand forPower

Power Provided by Baseload GeneratorsNSL Local Generation 455 MWNSL Local Peak Load -250 MWNSL Net Export 205 MWTac Harbor557555Laskin7050Silver Bay7575

Increased Reliance on External SourcesNSL Local Generation 455 MWNSL Generation Retired -455 MWNSL Local Peak Load -250 MWNSL Net Export -250 MWMinntacTac Harbor2x 373 MVA557555Laskin1x 373 MVAForbes7050Silver BayExisting230/115 kVTransformersArrowhead2x 373 MVA7575

Strengthening the Forbes SourceForbes

Forbes: Critical ContingencyLow Voltage ViolationLine OverloadedForbesPost-ContingencyForbes source lostMinntac source weakenedVoltage depression affecting a wide areafrom Hibbing all the way to Babbitt

Solution: Forbes Transformer AdditionPROBLEM SOLVED: Re-establish a second230/115 kV transformerat Forbes NOW the connectionbetween 230 kV and115 kV remains intact ALSO adds muchneeded transformercapacity to supportincreased reliance on230/115 kV connectionCONCEPTUAL

Forbes: Critical Contingency (Pre-Project)Low Voltage ViolationLine OverloadedPROBLEMForbes source lost andMinntac source weakenedVoltage depression affecting a wide areafrom Hibbing all the way to Babbitt

Forbes: Critical Contingency (Post-Project)Low Voltage ViolationLine OverloadedSOLUTIONPost-contingent voltages look great afterForbes 230/115 kV Transformer Addition

Strengthening the Minntac SourceMinntac

Minntac: Critical ContingencyInternal fault or failure of a230 kV breaker at MinntacMinntacLow Voltage ViolationLine OverloadedMinntac source lostPower rerouted onto 115 kVPost-ContingencyLow voltages in Virginia & Babbitt areasTransmission lines to Virginia area overloaded

Solution: Minntac Bus ReconfigurationPROBLEM SOLVED: Add 3 new breakers & replace theexisting breaker with a newer one Expand the Minntac 230 kV businto a more reliable “ring” bus Relocate a transmission line to adifferent position on the bus NOW for any single breaker failure,one transmission line and one230/115 kV transformer are stillconnectedCONCEPTUAL

Minntac: Critical Contingency (Pre-Project)Internal fault or failure of a230 kV breaker at MinntacLow Voltage ViolationLine OverloadedMinntac source lostPower rerouted onto 115 kVPROBLEMLow voltages in Virginia & Babbitt areasTransmission lines to Virginia area overloaded

Minntac: Critical Contingency (Post-Project)Internal fault or failure of a230 kV breaker at MinntacLow Voltage ViolationLine OverloadedSOLUTIONVoltages in Virginia & Babbitt areas look greatOverloaded transmission lines are relieved (mostly)

Increased Flow on Incoming LinesNSL Local Generation 455 MWNSL Generation Retired -455 MWNSL Local Peak Load -250 MWNSL Net Export -250 MWMinntacTac Harbor2x 373 MVA557555Laskin2x 373 MVAForbes75757050Silver BayExisting230/115 kVTransformersArrowhead2x 373 MVAIncoming Lines: Capacity UpgradesThermal Upgrades: 226 milesRebuild/Reconductor: 40 milesNew Transmission Line: 5.5 milesTerminal Equipment at 10 Substations

Transmission Impacts from Fleet Transition Voltage Support & System Strength– Steady state voltage regulation– Dynamic reactive support (Voltage Stability, Damping)– Short circuit capability Power Delivery Capability– Increased reliance on 230/115 kV Sources– Increased power flow on 115 kV system Redundancy– Fewer sources available in the area– Limited options for mitigating issues32

Redundancy: Hoyt Lakes EndSingle Points of Failure leave theentire North Shore Loop servedonly from the Duluth end(140 miles away)Low VoltagesWeak System“Baseload Issues”RedundancyTransmission Overloads33Baseload Support

Mesaba Junction 115 kV ProjectNew Mesaba JunctionHoytLakesLaskinSolution: Mesaba Junction 115 kV ProjectNew Parallel 115 kV LineNew34 Switching StationVoltage ConversionRedundancy, CapacityRedundancy, Voltage SupportEliminate Single Points of Failure

Redundancy: Duluth EndMaintenance/Prior Outagecontingencies leave the entireNorth Shore Loop served onlyfrom the Hoyt Lakes end(140 miles away)3590 MW

Duluth 115 kV Loop Solution AlternativesCTDGDGDGDG?Duluth 115 kV Loop Alternatives36New Parallel 115 kV TransmissionNew Parallel 230 kV TransmissionNew Distributed Generation/StorageNew Peaking Generation

North Shore Loop Transmission ProjectsBabbitt Capacitor BankMinntac ReconfigurationMesaba Junction115 kV ProjectHoyt Lakes38 LineReconductorForbes 37 Line UpgradeLaskin – Taconite HarborVoltage Conversion43 LineUpgradeSpare 138/115 kVTransformerNorth ShoreSwitching StationETCO Capacitor BankForbes Transformer Addition18 Line ReconductorNorth ShoreSTATCOMSILVER BAYForbes 3T Breaker ReplacementForbes Tie Breaker Addition42 LineUpgrade145 LineReconductor57 Line UpgradeDuluth Loop 115 kV Project3758 Line UpgradeDULUTHTwo Harbors115 kV ProjectColbyville TerminalEquipment201620172018LegendLocal Baseload Generators115 kV Lines/Substations138 kV Lines/Substations230 kV Lines/Substations20192020

Christian Winter – Minnesota Power Minnesota Power Systems Conference November 13, 2019 Transmission Lessons Learned from the Decarbonization of Minnesota’s North Shore Background Issues – Voltage Support & System Strength – Power Delivery Capability – Redundancy Summary Overview. 2. What is the North Shore Loop? 3

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