New Technologies for Microgrid Protection - IEEE.CH€¦ · IEC60909 §Usually settings ... §Microgrid protection strategies ideally should be generic such that they could be:

Microgrid ProtectionIEEE PES Swiss Chapter Workshop: MicrogridsEvolution and Integration in Modern Power Systems

Alexandre Oudalov, ABB Switzerland Ltd., Corporate Research, 2014-04-30

© ABB GroupMay 2, 2014 | Slide 2

Microgrid ProtectionOutline

§ What is a microgrid?§ Traditional distribution grid protection§ Problems caused by DER and islanded operation§ Potential solutions

§ Adaptive protection concept§ Hailuoto microgrid§ Distributed adaptive protection approach


MicrogridsExpected evolution of distribution system

Central generation includingrenewables 50-25’000 MW

HV grid a backbone for longdistance bulk powertransmission at 110-1200 kV(AC or DC)

MV grid for a local powerdistribution at 6-69 kVDistributed generation includingrenewables1-25 MW

LV grid for the “last mile” powerdistribution at 110-1000 VSub-utility generation includingrenewables0.005-1 MW







Microgridsare electricity distributionsystems containing loadsand distributed energyresources, (such asdistributed generators,storage devices, orcontrollable loads) thatcan be operated in acontrolled, coordinatedway either whileconnected to the mainpower network or whileislanded.

CIGRE C6.22 workingdefinition














MicrogridsGlobal markets

§ Navigant Research says:§ There are >400 projects currently in operation or

under development worldwide§ The global market may reach 4’000 MW of deployed

annual capacity and B$40 in annual revenue by 2020


Microgrid protectionGrid connected and islanded modes

Protection mustrespond to bothutility grid andmicrogrid faultsutility grid faults:protection isolatesthe microgridfrom the utilitygrid as rapidly asnecessary toprotect themicrogrid loads.microgrid faults:protection isolatesthe smallestpossible section ofthe feeder.


Microgrid protectionGrid connected and islanded modes

Protection mustrespond to bothutility grid andmicrogrid faultsutility grid faults:protection isolatesthe microgridfrom the utilitygrid as rapidly asnecessary toprotect themicrogrid loads.microgrid faults:protection isolatesthe smallestpossible section ofthe feeder.


Faults in traditional distribution networksCauses and damages

§ Unintentional short circuits mayoccur between phases, phase(s)and neutral/earth and are usuallycaused when a wire's insulationbreaks down, or when anotherconducting material is introduced

§ A large current causes:§ rapid buildup of heat,

potentially resulting inoverheat and damage to thewire's insulation, or a fire

§ vibration due to magneticforces, deformation ofbusbars

Initiated by:§ Lightning§ Dirt/salt on

insulators§ Flashover line-

line (wind)§ Flashover to tree§ Tower/pole or

conductor falls§ Objects fall on

conductors§ Cable insulation

failure§ Excavation work


Protection devices used in distribution networksFuses and Circuit Breakers

§ Objectives of unit protection:§ Protect faulted part from damage:

§ Detect fault§ Selectively isolate faulted component

§ Continued supply for rest of system§ Apparatuses

§ Fuses§ Circuit breakers – CBs (operated by relays)

Unit protectionprotectsgenerator, line,transformer… butweakens systemwhen tripping CB

System protectionacts to avoidsystem blackoutse.g. sacrifice someload to save therest

All protections arebased onknowledge aboutnormal andabnormaloperation andlimits of thesystem


Digital protection relaysSolutions for MV and LV networks

§ Control the tripping of CBssurrounding the faulted part of thenetwork

§ Large variety of protection functions:§ Over-current (OC)§ Directional over current§ Earth fault§ Under/over voltage§ Under/over frequency§ Reverse power flow§ Phase unbalance§ etc.

§ Remote configuration, monitoring andcontrol via a communication link


Protection settingsOver-current protection

§ Measured values are compared with pre-calculated settings and relay generates atripping command when the measured valueexceeds the thresholds

§ Settings are usually calculated at thedesign/planning stage either manually orwith software tools based on standards, e.g.IEC60909

§ Usually settings are not touched afterwards§ Multiple setting groups are possible today

(switching by means of an externalcommand) but not actively used


Protection settingsOver-current protection

§ Measured values are compared with pre-calculated settings and relay generates atripping command when the measured valueexceeds the thresholds

§ Settings are usually calculated at thedesign/planning stage either manually orwith software tools based on standards, e.g.IEC60909

§ Usually settings are not touched afterwards§ Multiple setting groups are possible today

(switching by means of an externalcommand) but not actively used


Protection settings

§ Selective operation is when only theCB immediately on the supply side ofthe fault is tripped and continuity ofservice for the rest of the system isensured

§ It requires a coordination ofprotection devices between thesource and the fault. The selectivityis obtained by current and/ortripping time discriminating

Coordination between multiple protection devices

Load A

CB A

Load B Load C

CB B CB C


Protection settings

§ Selective operation is when only theCB immediately on the supply side ofthe fault is tripped and continuity ofservice for the rest of the system isensured

§ It requires a coordination ofprotection devices between thesource and the fault. The selectivityis obtained by differentiating thecurrent values and the trip times

Coordination between multiple protection devices

Load A

CB A

Load B Load C

CB B CB C

in in inout outout

Blocking signal Blocking signal No signal


Microgrid Protection

§ DERs and isolated operation from maingrid imposes new challenges for thetraditional distribution grid protection§ Changes in the magnitude and

direction of short circuit currents§ Reduction of fault detection

sensitivity and speed in tappedDER connections

§ Unnecessary tripping of utilitybreaker for faults in adjacent linesdue to fault contribution of the DER

§ Auto-reclosing of the utility linebreaker policies may fail

Main challenges


Utility grid


§ In the grid connected mode theutility provides a significant faultcurrent during the fault

§ After isolation from the utilitygrid the local generator (DG) isthe only fault current source inthe island

§ Fault current level depends ontype, size and location of DG butit is lower than the fault currentfrom the utility grid

§ CB1 operation will be delayedand if the time delay exceeds alimit of DG under voltageprotection CB2 will disconnectDG unit and the island will beshut down

Main challenges

DG

Fault

CB1

CB2


Utility grid






Main challenges

DG

Fault

CB1

CB2







Main challenges

Utility grid

DG

Fault

CB1

CB2


Microgrid protection

§ Microgrid protection strategies ideally should be genericsuch that they could be:§ Applicable for both grid and islanded operation§ Adapted to any DER type§ Scalable so that the strategy does not need to be

redefined with each new DER connection§ May include requirements for:

§ Modifying/replacing protection devices§ Use of advanced protection functions§ Add new/upgrade existing fault current sources§ Dynamic protection settings management

New Strategies

Fault Current SourceEnsure fault level in inverter dominated microgrids

§ Do not enforce sophisticated protection incustomer’s premises. Use classical fuses

§ At least one resource must deliver a faultcurrent high enough to ensure operation andselectivity of protections

§ High-power storage is an ideal candidate fora Fault Current Source (FCS)

§ An FCS is connected to the “main” LV bus inparallel to the network and contains:§ A slow-charge, rapid-release electricity

storage§ An inverter in idle mode, rated to deliver

a high current for a few seconds§ A short-circuit detection unit (measure

local voltage)§ A charging circuit to restore the status of

energy storage device



§ Adapt protection settings to the actualstate of the microgrid based on the presetlogic

§ Accomplished by monitoring of actualprotection settings and DER/networkconnectivity information

§ A programmable logic application is calledto perform after changes in CB status. Noon-line setting calculations are needed inthis application.

§ Suggestions for practical implementation:

Dynamic protection settings management

§ Use of IEDs with directional over-current protection function and withmultiple setting groups

§ Use of communication infrastructure and standard protocols to exchangeinformation between IEDs and a central setting coordination unit (e.g.substation computer or RTU)


Centralized microgrid adaptive protection exampleGrid connected mode

Load

DG

1 2

ActiveSetting Group

Utility Grid

3Load

1 2 3 1 2 3

IEDCB

Central controller CommunicationNetwork


Centralized microgrid adaptive protection exampleTransition to islanded mode

DG

1 2

Utility Grid

3 1 2 3 1 2 3

1. Data (CB status) are transmitted from the end devices using unsolicited messages as conditionschange. The central controller also polls each end device periodically to ensure that the end deviceis still healthy


Centralized microgrid adaptive protection exampleTransition to islanded mode

DG

1 2

Utility Grid

3 1 2 3 1 2 3


2. The central controller analyzes the network state and if necessary adapts protection settings to fitthe new network configuration


Centralized microgrid adaptive protection exampleIslanded mode

DG

1 2

Utility Grid

3 1 2 3 1 2 3

3. The central controller sends control messages (to switch settings) to the field devices




Centralized microgrid adaptive protection exampleIslanded mode

DG

1 2

Utility Grid

3 1 2 3 1 2 3

3. The central controller sends control messages (to switch settings) to the field devices




Microgrid protectionCentralized adaptation scheme lab tests

§ Centralized approach has been tested in thelab (focus on data exchange) with arealization for MV (IEC61850) and LV(Modbus) grids

§ In addition a real-time HIL simulations havebeen conducted for the MV case

§ Adaptation process is limited bycommunication system/protocol capabilityand takes <100 ms in the MV case and ~700ms (per circuit breaker) in the LV case

§ Both systems have demonstrated goodperformance and operated properly indifferent conditions (including situationwhen settings have been forced manually tothe wrong setting group)


Hailuoto microgrid

§ Goal is to develop anddemonstrate in the fieldan active microgridmanagement

§ Active managementfunctionalities include:§ Protection settings

changing based onmicrogrid topology(e.g. grid connectedó island)

Hailuoto is theFinnish island inthe Northern Gulfof Bothnia in theBaltic Sea. It has~1000 regularinhabitants and600 holidayhouses

Practical demonstration of adaptive protection

§ Transition between grid connected and islanded operation modes:§ Unintentional islanding via black-start§ Intentional islanding via SCADA§ Re-synchronization to the utility grid


Hailuoto microgridSystem configuration






Hailuoto microgridAutomation system configuration

§ Off-line process§ “Trusted” settings are

uploaded to IEDs asmultiple setting groups

§ IEC 61850 is used as amaster protocol forcommunications with theIEDs

§ IEC 61131 programminglanguages are used in thePLC application whichallows easy cross-platformtransfer of the application


Hailuoto microgridOn line operation and control logic

§ OPC Data Access mechanism provides a way tosupply the IED data received from the fielddevices to the IEC 61131 Logic Processor

§ OPC Client/Server architecture allows feeding thecontrol actions back to the IEDs

§ Additional OPC server instance can be used tomap and broadcast the IED data upstream to thedistribution network control center via SCADA



§ Aimed to simplify animplementation for amicrogrid with a large numberof circuit breakers

§ Protected system is split intosmall areas being delimited bythe adjacent switchingdevices coordinated by locallogic units (LL)

§ Each LL communicates withunits in directly adjacent areasand exchange information onlocal short circuit levels (SCL)

Distributed adaptation scheme



§ Configuration change in anarea triggers re-evaluating of alocal SCL using the MVAmethod

§ Each protection setting groupcorresponds to a specific rangeof available SCLs

§ LL decides on switch/keep anactive setting group

§ SCL information is sent toneighbouring areas where it isfurther used to re-evaluatelocal SCLs

§ The adaptation processprogressively advances throughthe microgrid

MVA method:each networkcomponent isreplaced by ablockrepresenting thecontribution orthe reduction ofthe SCL expressedin MVA

Distributed adaptation scheme



§ High penetration level of DER and islanded operationmode pose main protection challenges in microgrids

§ Ideally protection system must follow microgridconfiguration changes

§ Adaptive protection may increase availability of localgeneration and reduces customer outages

§ At the moment it looks like a switching between the pre-calculated “trusted” setting groups is a preferred solution

§ Centralized adaptive protection scheme based on fullconnectivity model can be suitable for small scalemicrogrids

§ For large scale microgrids a distributed adaptive protectionscheme with a limited connectivity model can be morepertinent

Key take away points



§ A. Oudalov, A. Fidigatti, “Adaptive Network Protection inMicrogrids”, International Journal of Distributed EnergyResources, Vol.5, No.3, pp.201-226, July-September 2009

§ W. Zhao, A. Oudalov, B. Su, Y. Chen, “Research on Close-LoopSimulation for Centralized Coordination of Protection Settings”,in Proc. of China International Conference on ElectricityDistribution, Shanghai, 2012

§ A. Oudalov, L. Milani, E. Ragaini, A. Fidigatti, “SampleImplementation of Adaptive Protection for LV Networks”, PACWorld Magazine, Vol.20, pp.28-33, June 2012

§ D. Ishchenko, A. Oudalov and J. Stoupis, "ProtectionCoordination in Active Distribution Grids with IEC 61850," inProc. of IEEE T&D conference, 2012, Orlando, FL, USA.

§ H. Laaksonen, D. Ishchenko, A. Oudalov, “Adaptive Protectionand Microgrid Control Design for Hailuoto island”, IEEE Trans onSmart Grids, March, 2014

Further reading

Documents

New Technologies for Microgrid Protection - IEEE.CH€¦ · IEC60909 §Usually settings ... §Microgrid protection strategies ideally should be generic such that they could be: