impact of distributed generation units on short circuit capacity calculations by shabanzadeh

In the name of Allah, Most Gracious, Most Merciful

Impact of Distributed Generation Unitson Short-Circuit Capacity (SCC) Calculations

By : Morteza ShabanzadehSupervisor : Professor Mahmoud-Reza Haghi-Fam

Morteza Shabanzadeh & TMU 2013

P t ti O tliPresentation Outline

Introduction Introduction SCC Calculation According to IEC 60909 Standard Impact of DGs on Fault Locating Methods DGs Effects in Different Types of Dis. Networks Limitation of Short-Circuit Power due to DGs

2/72MortezaShabanzadehandTMU2013

IntroductionIntroduction

Short-Circuit Currents : Initial symmetrical short-circuit current ( ) Peak short-circuit current ( ) Steady state short-circuit current ( )



Peak Short-Circuit Currents ( ):

Ip causes high dynamic and mechanical stresses on the components.

It ill b h d ithi 10 ft f th f lt It will be reached within 10 ms after occurrence of the fault.

Conventional circuit breakers in the network will not be fast enough tointerrupt this current and therefore components have to be designed suchinterrupt this current and therefore components have to be designed such

that they are able to withstand these currents.



Initial & Steady-state Short-Circuit Currents ( , ):

They will result in large losses , And therefore cause thermal overloading.g



Fault level calculations are indispensable tools during the Grid Design Phase.

The purpose of short-circuit calculations is to determine: Thermal effect of fault currents on grid components.g p Mechanical stresses on grid components. Coordination of protection devices.



Distribution networks are characterized by: Max acceptable fault current (related to the switchgear) Thermal withstand capability (of the equipment) Mechanical withstand capability (of the equipment and constructions)



Main inhibiting factor for the interconnection of DGs: Combined Isc contribution of the upstream grid and DGs should remain

below the network design value.

SCC of existing distribution network (esp. MV) is close to the design value(little margin for the connection of DGs).



DGs Isc depends on : DGs size DGs control mode (Technology) The number of connection points of DGs in the system


Overview of the IEC 60909 StandardOverview of the IEC 60909 Standard

o Basic Principles: Equivalent Voltage Source Method Several simplifications in calculation procedures Isc Calculation using Vn and rated values of the equipment Various correction factors Network neutral is earthed



o Short-circuit current definitions: Initial Symmetrical Short-Circuit Current ( ):

rms value of the ac symmetrical component of a prospective

short-circuit current

Initial Symmetrical Short-Circuit Power ( ):

hasnophysicalmeaning



o Short-circuit current definitions: Peak Short-Circuit Current ( ):

Max instantaneous value of the fault current.

Decaying aperiodic component ( ):



o Short-circuit current definitions: Steady-state Short-Circuit Current ( ):

The rms value of the current after the decay of the transient

components.

For far-from-generator faults :



o Calculation of : Equivalent Voltage Source :

Voltage of an ideal source applied at the short-circuit location in positive

sequence system, whereas all other sources in the system are ignored

(short-circuited)(short-circuited).



o Short-circuit Impedances :



o Short-circuit Impedances :1) Equivalent impedance of the upstream network :

Fornetworkswithanominalvoltagehigherthan35kV,theIECStandardsuggestsRQ=0. Inallothercases,itrecommendsRQ/XQ=0.1asasafeassumption.



o Short-circuit Impedances :2) Equivalent impedance of a Transformer:

These Eqs are also applicable to shortcircuit current limiting reactors


TheseEqs.arealsoapplicabletoshort circuitcurrentlimitingreactors.


o Short-circuit Impedances :3) Equivalent impedance of Lines:

Theimpedanceofoverheadlinesandcables iscalculatedfromconductorandlinegeometrydataanditistypicallyknownforstandardlinetypes.



o Short-circuit Impedances :4) Equivalent of Synchronous Generators:

Xd isthesubtransientreactance.



o Short-circuit Impedances :5) Equivalent of Power Station units with Syn. Generators:

TheimpedanceisreferredtotheHVside.

tr istheratedtransformationratiooftheunittransformer.



o Short-circuit Impedances :6) Equivalent of Asynchronous Motors:

ILR/IrM istheratiooflockedrotor toratedcurrentofthemachine..



o Short-circuit Impedances :

Shuntcapacitorsandnonrotatingloadsareignored.



o Correction factors:

IEC60909introducesimpedancecorrectionfactorsfor:

Transformers(KT) Synchronousgenerators(KG) Powerstationunits(KS)

whichmultiplytherespectiveimpedancesinallcalculationformulae.



o Fault level calculation in networks with DG:

o Resultingfaultlevelisthephasorsumofthemaxfaultcurrentsfrom: UpstreamGrid Step down Transformer StepdownTransformer VariousDGs

o AccordingtoIEC60909:Thegridcontributioniseasilycontributed,butThecontributionofnovelDGtypesisnotaddressedinthisStandard.



DG

Directly coupled

Decoupled via converter interface

Asynch. Generator

Synch. Generator

Static Conversion

Rotating Conversion

SCIG & DFIG wind generators

CHP Fuel CellPVDirect drive WTs

-CHP


g


o Fault level calculation in networks with DG:1) Contributionoftheupstreamgrid



o Fault level calculation in networks with DG:2) ContributionoftheDGstations

Type ITypeI TypeII TypeIII TypeIV




Type I :Synch.Generatorsdirectlycoupledtothegrid

Type ISHEP, CHP




Type II :ASynch.Generatorsdirectlycoupledtothegrid

Type IISmall SHEP,

constant speed WTs




Type III:DFIG,withpowerconvertersintherotorcircuit

Type IIIDFIG

(variable speed WTs)




Type III:DFIG,withpowerconvertersintherotorcircuit

LimitedovercurrentcapabilityofRotor Statorcurrentisdominant Crowbar protectionCrowbarprotection RoughlyapproximatedasTypeII Statorisdisconnectedafter30~50ms Isc(max)



Type IV:Powerconverterinterfacedunits,withorwithoutrotatinggenerator

Type IVPVs, -Turbines

variable speed WTs




Type IV:Powerconverterinterfacedunits,withorwithoutrotatinggenerator

AretreatedasASynch.Machines

orort isthedurationofthecontribution(100msmaybeadoptedhereaswell)


Case StudyCase Study

PLOAD =35MVA

T II

Type IV

PDG =17.16MW

Type I

Type II

Type III



Type IV

Type III

Type II


Type I


Results

Asexpected,thecontributionofTypeIVDGunitsismuchlowerthanallotherTypes.

Type IV

Type III


Case StudyCase StudyResults

Type II

Type I



Resulting fault level at the MV busbars :

Algebraic sum

Phasor sum (with contribution of WF1 added algebraically)(with contribution of WF1 added algebraically)


DGs short-circuit current SimulationDGs short-circuit current Simulation

Technical Softwares to simulate DGs Protection behavior:

DIgSILENTPowerFactory PSCAD ATPEMTP


Example (2) :Example (2) :

Resulting fault level in Netherland test network:

Peak Short Circuit Current (KA)


Solutions for fault level reductionSolutions for fault level reduction

1. Increasethedesignmaximumfaultlevel

2. Reducetheprospectiveshortcircuitcurrentofthegrid Reconfigurationofthenetwork Increasetheshortcircuitimpedanceofthetransformers Reduce the prospective shortcircuit current of the DGReducetheprospectiveshort circuitcurrentoftheDG

3.ReducetheprospectiveshortcircuitcurrentoftheDG Selectequipmentwithincreasedshortcircuitimpedance Installation of current limiting reactors Installationofcurrentlimitingreactors Connectionviapowerelectronicsconverters

4.Activelimitationoftheshortcircuitcurrent


Impact of DGs on Fault Locating MethodsImpact of DGs on Fault Locating Methods

o Effect of DG on Impedance Measurement Based Method :

Single-line diagram of network DG unit placed at upstream DG unit placed at downstream



o Simulation Result :

Scenario (2): Inverter based DG = 5 MW

Scenario (1): Synchronous DG = 30 MW


single-phase to ground fault


o Simulation Result :Calculation error with DG at upstream of fault Calculation error with DG at downstream of fault

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1. InverterbasedDGsinjectless shortcircuitcurrenttothefault.


2. UpstreamDGshavemorenegative effectsonfaultlocatingmethodsincomparisontodownstreamDGs.

DGs Effects in Different Types of Dis NetworksDGs Effects in Different Types of Dis. Networks

o Three types of distribution systems:

RadialL Loop

Network



A. RadialC (1) C (2)C (3)Case(1) Case(2)Case(3)



A. RadialDGat7,PF

DGat7,VC

DGat2~7,

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,5MW,PFDGat2~7,5MW,VC

B

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B #


Bus#


A. Radial

Isc (KA)

We can see that the more connection points of DG in the system, the lower values


of short circuit currents.


B. Loop

h f h d d d b f l d


The case of shared sized DG at two connection points provides better profile around 1.0 p.u.


B. Loop

Isc (KA)

d f l d h f l l f f h d


As expected, fault currents decrease as the fault location gets far away from the grid.


C. Network

55/72MortezaShabanzadehandTMU2013 34.5 kV network type test system


C. Network



Dispersedlylocated DGresultsinbettervoltageprofilecomparedtosinglespotlocatedDG.

If di t ib ti t h t id ti f lt t t Ifadistributionsystemhasastronggridconnection,faultcurrentsmaynotsignificantlyincreasewiththeadditionofDG.

AnumberofDGhavingaunitarypowerfactorcontrolshouldbelocatedalongg y p f gdistributionsystemsothatbettervoltageprofileisobtained.


Limitation of Short-Circuit Power due to DGsLimitation of Short-Circuit Power due to DGs

Fault Current Limiters (FCLFCL) :

The most important requirements of an FCL are1) Limitation of peak current (Ip) within 10ms.

(The minimum opening time of the circuit breakers is much longer

, and therefore they are not able to protect the components)

2) Ratio between nominal current and limited short-circuit current.

3) Low impedance and low losses in normal situation.



The most important types of FCLFCL :

1. Choke coil

2. Superconductorsp

3. Semiconductors

4. Magnetic fault current limiter

5. Is Limiter




1. Choke coil

(high) impedance( g ) p simple and robust voltage drop & losses during normal operation big size




2. Superconductors

use the relationship between the resistance and temperature to limit Ip, Ik.

R = 0 (when they are cooled below their critical temperature)

During fault, due to losses their temperature will increase and FCL will get a much higher R.

low losses very fast response (Ip can be limited quite well) very expensive are still in development stage (not commercially available yet) are still in development stage (not commercially available yet)




3. Semiconductors

use semiconductor switches

good controllability fast response losses in the semiconductors




4. Magnetic fault current limiter

Based on the fact that a coil, or transformer, has a very low impedance when it is in saturation At the moment a fault occurs the large fault current forces the coil out of saturation, implying a muchAt the moment a fault occurs the large fault current forces the coil out of saturation, implying a much

higher impedance.

reliable operation gradual and smooth change of impedance good limiting capabilities (R8) commercially available large dimensionsg high price




5. Is Limiter consists of two conductors in parallel.

The main conductor carries the nominal current

(up to 5kA).

After tripping the parallel fuse limits Ip in a very short time

( 1 )(< 1 ms).




5. Is Limiter very fast good R-ratio small size low losses after each operation fuses have to be replaced;

h lThis implies :

relatively high costs longer interruption times incorrect operation incorrect operation


Limitation of Short Circuit Power due to DGsLimitation of Short-Circuit Power due to DGs

SelectionofFCLFCL:

ThegoaloftheprocedureistofindaconfigurationforwhichCtot isaslowaspossible(i.e.findingmin[Ctot]):

thecostsofrepairing orreplacing componentswhichhavebeendestroyedbecauseoftohighfaultcurrents,butalsothecostsof


customerminuteslost.


SelectionofFCLFCL:10 d l h b FCL10stepproceduretoselectthebestFCL:

Step1. Createalistofpossiblefaultlocations;Step2. Foreachofthepossiblefaultlocations,

conductashortcircuitcalculationusingIEC(60)909;

Step7.Determinepossiblefaultcurrentlimiterlocations;Step8.Foreach(combination)ofthelocations:calculate

thetotalcostsofafault,usingthetwodifferentco duc a s o c cu ca cu a o us g (60)909;Step3. Removethefaultlocationsforwhichnopeakfault

currentproblemoccurs;Step4. Foreachoftheremainingfaultlocations:

Determinetheprobabilityofafaulttooccur;St 5 S l t th f lt l ti ith th hi h t f lt

e o a cos s o a au , us g e o d e etypesoffaultcurrentlimitersatthelocation(s);

Step9.Selectthesituationwiththelowesttotalcostscausedbyafaultandpermanentlyaddthefaultcurrentlimiter.

St 10 R th f lt l ti f th li t dStep5. Selectthefaultlocationwiththehighestfaultoccurrenceprobability.

Step6.Calculatethetotalcostsofafaultatthislocation,withoutaddingfaultcurrentlimiting.

Step10.Removethefaultlocationfromthelistandrestartfromstep2,repeatinguntilthereisnofaultlocationleftinthelist



SelectionofFCLFCL: CHP

CHP

The rated Ipeak of the substation is 50kATheratedIpeak ofthesubstationis50kA


ArealnetworkinthesouthwesternpartoftheNetherlands


SelectionofFCLFCL:Theresultsaccordingto10stepprocedure:


th h t l ithose who struggle in our cause, we will surely guide them to our ways;

and Allah is with those who do good.

AL ANKABOOT (6 )AL-ANKABOOT (69)


impact of distributed generation units on short circuit capacity calculations by shabanzadeh

Documents

interconnection of dgs

methods dgs effects

standard impact of dgs

current peak

grid components

current definitions

current steady state

equipment mechanical