23 stability and control
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Room 6.2
.Wednesday, 14th September(8. 30 - 10.30)
Rpt: Costas Vournas
231 Volt/Var control for active distribution networks - L.A. Kojovic, C.A. Colopy, D.
Arden
232 Stability enhancement and blackout prevention by VSC based HVDC -Y. Jiang-Hfner, M. Manchen
233 Effectiveness of a supplementary MLQG power oscillation damping controllerinstalled at an HVDC line within a meshed network - R. Preece, A.M. Almutairi,O. Marjanovic, J.V. Milanovic
234 Voltage stability, loss reduction and dynamic stability studies of an integratedsystem - P. Pesoti, S.O. Souza, F. Terra, A.C. Zambroni de Souza, B. Isaias Lima
Lopes, R. Coradi Leme
mar a gor ms o accommo a e s r u e genera on n e gr -H.T. Yip, C. An, G. Millar, G.J. Lloyd
236 Optimization strategy applied to DG reactive power for decentralized voltage
- . . , . , .
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BOLOGNA 2011
Volt/Var Control
for
Active
Distribution
Networks
LjubomirA.KOJOVIC CraigA.COLOPY DanielARDEN
CooperPower
Systems
USA
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DistributedVoltVar AutomationandOptimization
CapacitorBanks
Voltage
Regulators
Substation
LoadTapChanger
Voltage
RegulatorsDistributionTransformer
LTCome
DisadvantagesofDistributedAutomation
DistributedAutomation
LTC,CapacitorBanks,andVoltageRegulators
Controlbasedonlocalmeasurements:
Isnotcontinuouslymonitored
Doesnotadequatelyrespondtochangingconditions
outonthedistributionfeeders canmisoperate
Voltage
Current
Power
real
reactive
followingautomaticreconfiguration
Operationmaynotbeoptimalunderallconditions
Cannotoverridetraditionaloperationduringpower
systememergencies
Temperature,and
Timeofday
Maymisoperate whenDGarepresent reverse
powerflowfromDGcancausestandalonecontrolsto
believefeederhasbeenreconfigured
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IntegratedVoltVar AutomationandOptimization
YukonIVVC
Server
SCADA
GIS/mapping
CustomerCare&Billing
OMS
EngineeringAnalysis
Administrativeand
Operations
InternalOperationsand
CustomerService
ExternalOperationsor
TCP/IP
(BPL,FiberOptic,WiFi)
Cellular
(GSM/GPRS,
x
AMINetworks
900MHz
VHF
Voltage
Sensors
LTC
Controls
Meters
CapacitorBank
Controls
VoltageRegulator
Controls
Recloser
Controls
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IntegratedVoltVar AutomationandOptimization
FeederVoltageManagementSoftware
Capacitor
Control
Var orPowerFactorManagement
Software
Minimizing Var Flow
FlatteningtheVoltageProfile
ConservationVoltageReduction
CommunicationsNetworks
TCP/IP(BPL,fiber,WiFi)
DNP3.0(RadiosviaRS232port)
900MHz,VHF,PLC
CommunicationtoFeederCapacitorBanks: 1 or2waycommunicationnetwork
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IntegratedVoltVar AutomationandOptimization
Upper
Voltage
Limit
FlattenedVoltageProfile
agnitude
LoweredVoltage(afterflattening)
Vo
ltageM
FeederLength
Regulated
by
100
%]
90
we
rFactor
Unregulated80P
o
TwoDayMeasurementData12
a.m. 12
p.m. 12
a.m. 12
p.m. 12
a.m.
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IntegratedVoltVar AutomationandOptimization
BusinessDrivers Business
Objectives
Regulationimposesnewrequirementswiththe Unitypowerfactorminimizeslosses
Energypurchasesavings
IncreasedkWh
sales
on
improved
voltage
profile
ReducedvoltageminimizespurchasedkW:
1%reductioninvoltageresultsin0.5to0.8%
reductioninkW
Stimulusbilldrivenenergyefficiencyprojects
FunctionalObjectives Technical
Requirements Monitorandcontrolsubstationvoltageregulators
orLTC
Managefeedervoltagedowntosettabletargets
Monitorandcontrolsubstationandfeeder
capacitorbanks
Monitorend
of
line
voltages
to
avoid
excursions
Flatvoltageprofile
fromthespecifiedranges
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IntegratedVoltVar AutomationandOptimization
thatneedrepair
Traditionallyutilitiesvisiteverycapacitorbanksiteannuallytofind
the20%thatneedrepair
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IntegratedVoltVar AutomationandOptimization
CurrentCapacitorBankStatusReport
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C
opyrightyearABB.
All
rightsreserved.-1-
9/23/2011,YingJiang-Hfner
Stabil ity Enhancement and
Blackout Prevention by
VSC Based HVDC
2011 08 14, Italy
Ying J iang-Hfner (speaker)
ABB AB, HVDC, Sweden
Manfred Manchen
NamPower, Namibia
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C
opyrightyearABB-2-
9/23
/2011,
YingJiang-H
fner
Summary
Caprivi link project
Technical Challenges
Field experiences and Factory tests
Comparison between interconnected grids with AC and DC
Conclusions
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C
opyrightyearABB-3-
9/23
/2011,
YingJiang-H
fner
Caprivi link, a VSC HVDC transmission,
is a 300 MW HVDC Light with OH-line 950 km
interconnects the national grids
of Namibia and Zambia
has trading of electricity as main purpose
Enhances stability of two national grids
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C
opyrightyearABB-4-
9/23
/2011,
YingJiang-H
fner
330 kV AC400 kV AC
Gerus
Converter
station
Nambia
HVDC Line 950 km
Zambezi
Converter
station
Zambia- 350 kV DC
+ 350 kV DC
Electrode Lines50 km
Capriv i link, a planned Bipole
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C
opyrightyearABB-5-
9/23/2011,
YingJiang-H
fner
- Overhead line and long distance,Re-start after DC-line faults within 500 ms after clearing
- Configured as a bipole, starting with monopole
- Connecting two changable AC network configurations. Any one of them can be completely out of generation. Any one of them can be a small islanded grid. Both of them can be extremely weak SCR
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C
opyrightyearABB-6-
9/23/2011,
YingJiang-H
fner
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C
opyrightyearABB-7-
9/23/2011,
YingJiang-H
fner
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C
opyrightyearABB-8-
9/23/2011,
YingJiang-H
fner
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C
opyrightyearABB-9-
9/23/2011,
YingJiang-H
fner
Conclusion
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C
opyrightyearABB-10-
9/23/2011,
YingJiang-H
fner
Conclusion
Impact to Interconnected Grids
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C
opyrightyearABB-11-
9/2
3/2011,
YingJiang-H
fner
Impact to Interconnected Grids
Interconnected by AC
+ Increased spinning capacity+ Increased availability by
coordinating maintenance+ Energy trading- Complexity in operation- Risk of uncontrolled power flow- Risk of spreading failures- Stability related to SCC
Interconnected by DC (VSC based)
+Increasedspinning capacity+ Increasedavailabilityby
coordinatingmaintenance+ Energy trading+ Simple in Operation
- Risk of uncontrolledpower flow- Risk of spreadingfailures- Stability relatedto SCC
Conclusion
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C
opyrightyearABB-12-
9/2
3/2011,
YingJiang-H
fner
Conclusion
Field experiences from Caprivi link project have proven HVDC Light
Operate in extremely weak AC systems with SCR down to zero
Enhance the stability of weak AC systems
Prevent black out under critical contingencies- function as a super UPS to feed passive loads- stabilize the voltage and frequency of small island grid
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EFFECTIVENESS OF A SUPPLEMENTARY MLQG
POD CONTROLLERINSTALLED AT AN HVDCLINE WITHIN A MESHED NETWORK
R. Preece A. M. AlmutairiO. Marjanovic J. V. Milanovi
Manchester, United Kingdom
School of
Electrical &
Electronic
Engineering
Overview
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Development and comparison of two Power Oscillation
Damping (POD) controllers for application with a
VSC-HVDC link.
Completed within a large heavily meshed network.
Completed a thorough probabilistic evaluation of the
controllers performances across a wide range of
operating points and outage contingencies.
Wide Area Measurement System (WAMS) based
controller shown to outperform local Power System
Stabiliser (PSS) design.
2
OverviewWhat has been done?
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
P t ti O tli
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Aims and motivation.
Introduction of test network.
Why we need POD.
Discussion of POD controller designs (PSS & MLQG).
Probabilistic Assessment Method.
Results.
Comparisons and conclusions.
3
Presentation Outline
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
Aims & Motivation
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Future transmission grids will feature more HVDC links
in parallel with existing AC lines.
HVDC links can provide effective POD capabilities
with various controller designs available.
The robustness of these POD controllers to varying
network conditions is rarely assessed:
Varying generation and load operating points. n-1 outages on generators and key tie-lines.
4
Aims & MotivationWhat are we looking at and why?
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
Test Network
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5
Test NetworkNETS & NYPS 16 machine, 68 bus with 400 MW VSC-HVDC
Mode 1 Mode 2 Mode 3 Mode 4
Frequency (Hz) 0.40 0.51 0.63 0.79
Damping (%) 4.66 4.18 4.21 4.87
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
POD Options: PSS & MLQG
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Observer
Modal Form
Optimum
FeedbackMultiple
Inputs
Single
Output
Network
Modes
6
POD Options: PSS & MLQG
WashoutPhase
CompensationGainSingle
Input
Single
Output
Power System Stabiliser (PSS)
Modal Linear Quadratic Gaussian (MLQG)
Tuned for most controllable mode (Mode 1 lowest frequency)
Targeted action on specific network modes
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
Small Signal Analysis
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7
Small Signal AnalysisFollowing the controller designs which looks better?
With no POD, all inter-area modes have damping less than 5%.
5% Damping
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
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Small Signal Analysis
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9
Small Signal AnalysisFollowing the controller designs which looks better?
With MLQG POD, damping is vastly improved for all modes.
5% Damping
4.9%
4.8%
5.4%
7.1%18.9%
15.4%
14.3%
11.7%
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
Probabilistic Assessment
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10
Probabilistic AssessmentMethodology for Establishing Controller Robustness
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
Random variation in generation and loads.
Generators and loads are normally distributed.
Loads have constant power factor.
HVDC varies with uniform distribution (50 MW steps).
Generator outage contingencies.
Outages on small generators.
Large equivalent generators set to half power.
Line outage contingencies.
Outages on 4 key inter-area ties.
Probabilistic Assessment
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11
obab st c ssess e tFull Process Flowchart
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
Generate operating point based upon current contingency
Loadflow?
Linearise open loop system (no POD controllers)
Identify
critical modes?
Evaluate closed loop dynamic equation with MLQG POD & shortlist eigenvalues
Create features sets and pass to Nave Bayes Classifier
Stable?
Save results and repeat at new operating point
Yes
No
Yes
Yes
Linearise closed loop system with PSS POD
Identify
critical modes?
Yes
No
No
No
Results: Modal Variation
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12R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
0.2
0.4
0.6
0.8
-1.5 -1 -0.5 0
Frequenc
y,
Hz
Real part , p.u.
0.2
0.4
0.6
0.8
-1.5 -1 -0.5 0
Frequency,
Hz
Real part , p.u.
MLQG PSS
Results: Modal Variation
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13
Improvements over no POD
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
0.2
0.4
0.6
0.8
-1.5 -1 -0.5 0
Frequenc
y,
Hz
Real part , p.u.
0.2
0.4
0.6
0.8
-1.5 -1 -0.5 0
Frequency,
Hz
Real part , p.u.
MLQG PSS
100%
100%
95%
96%
94%
97%
90%
98%
Results: Modal Variation
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0.2
0.4
0.6
0.8
-1.5 -1 -0.5 0
Frequency,
Hz
Real part , p.u.
0.2
0.4
0.6
0.8
-1.5 -1 -0.5 0
Frequency,
Hz
Real part , p.u.
MLQG PSS
14
Improvements of MLQG over PSS
R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
MLQG outperforms PSS: 100%
100%
98%
88%
Conclusions
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POD controller performance can vary greatly withchanging network conditions or topology.
WAMS based design shown to outperform local-PSS design
significantly.
Probabilistic assessment can demonstrate strengths
and weaknesses of different controller designs.
Can be used to identify situations when performancemay be detrimental (e.g. particular generator or line
outages) in order to help with further mitigation.
15R ob in P re ec e | C ig r S ym po si um | B ol og na 2 01 1
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Voltage Stability, Loss Reduction andVoltage Stability, Loss Reduction andDynamic Stability Studies of anDynamic Stability Studies of anIntegrated SystemIntegrated System
Paulo Murinelli Pesoti, Silas O. SouzaPaulo Murinelli Pesoti, Silas O. Souza, Felipe Terra,, Felipe Terra,
A. C. Zambroni de Souza, Isaias L. Lopes, Rafael C. LemeA. C. Zambroni de Souza, Isaias L. Lopes, Rafael C. Leme
Federal University at ItajubFederal University at Itajub,,
BrazilBrazil
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MotivationMotivation
Interaction of a microInteraction of a micro--grid and a powergrid and a power
grid considering loss reduction, voltagegrid considering loss reduction, voltage
and dynamic stability.and dynamic stability.
Loss Sensiti it Based on Tangent VectoLoss Sensitivity Based on Tangent Vector
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Loss Sensitivity Based on Tangent VectorLoss Sensitivity Based on Tangent Vector
Losses given by:Losses given by:
PPsyssys= Vi= Vikk VjVjkk (G(Gkk(cos((ij)(cos((ij)kk)+ cos((ji))+ cos((ji)kk))))--GGkk(V(Vikik22 +V+Vjkjk
22))
Deriving in relation to system parameterDeriving in relation to system parameter ::
k
nl
=
1
== GGkk (( VVjkjk ++ VVjkjk ) A +) A +
VVjkjk VVjkjk -- 2 G2 Gkk (V(Vjkjk + V+ Vjkjk ))
d Pd
system
k
nl
=1dVd
ik
dV
djk
dV
d
jk
dVd
ik
dA
d
L S i i i B d T VL S iti it B d T t V t
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Loss Sensitivity Based on Tangent VectorLoss Sensitivity Based on Tangent Vector
Main points:Main points:
Shows losses variation with respect toShows losses variation with respect to ..
Derivatives all known from tangent vector.Derivatives all known from tangent vector.
Computationally cheap.Computationally cheap.
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Dynamic Stability StudiesDynamic Stability Studies Based on a unified computational tool recentlyBased on a unified computational tool recently
proposed:proposed:
Transient period is integrated by incorporating theTransient period is integrated by incorporating theintegration step into the Jacobianintegration step into the Jacobian (Newton).(Newton).
After this period, quaseAfter this period, quase--dynamic approach employed.dynamic approach employed.
( ) [ ]0 0 0, ( , ) ( , )2
i i i i i
hF x y x x f x y f x y= + + +
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MethodologyMethodology The critical buses and the buses most sensitiveThe critical buses and the buses most sensitive
to loss reduction are identifiedto loss reduction are identified (tangent vector).(tangent vector).
A disturbance is considered, which consists ofA disturbance is considered, which consists ofthe outage of the wind farm generation. Thethe outage of the wind farm generation. The
radial part of the system becomes an importer.radial part of the system becomes an importer.
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Test SystemTest System
The wind farm generation and the loadThe wind farm generation and the loadconnected to the radial system are given by:connected to the radial system are given by:
Load=20+j10 [MVA]Load=20+j10 [MVA]
Generation=40+j20 [MVA]Generation=40+j20 [MVA]
grid
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Wind farm trips outWind farm trips out
Tangent Vector NorBefore 2.811After 3.051
Variation 8.562%
Losses variation shown in Table below.
Tangent vector norm increases after the contingency
Loss Active Power Reactive Power
Before 1.9251[pu] 192.51[MW] -2.7354[pu] -273.34[MVAr]
After 1.9830 [pu] 198.30[MW] -2.3346[pu] -233.46[MVAr]
Wind farm trips outWind farm trips out
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Wind farm trips outWind farm trips out
Critical buses: Bus 43: connects the grid to the microCritical buses: Bus 43: connects the grid to the micro--
grid. Bus 119 contains the microgrid. Bus 119 contains the micro--grid load.grid load.
BusesRank
Before After
1 41 41
2 39 39
3 117 117
4 2 119
5 3 2
6 19 37 13 43
8 14 19
9 33 33
10 15 13
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Long Term SimulationLong Term SimulationVoltage at load buses of interest.Voltage at load buses of interest.
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Long Term SimulationLong Term Simulation Voltage level at the synchronous machinesVoltage level at the synchronous machines
ConclusionsConclusions
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ConclusionsConclusions
The problem of connecting a grid to a radial microThe problem of connecting a grid to a radial micro--gridgridconsisting of a wind farm and a load is addressed.consisting of a wind farm and a load is addressed.
The wind farm tends to enhance the system voltageThe wind farm tends to enhance the system voltagesecurity. The outage of this source may change the voltagesecurity. The outage of this source may change the voltage
stability scenario, since the critical buses may change.stability scenario, since the critical buses may change.
The dynamic simulation is executed in order to completeThe dynamic simulation is executed in order to completethe analysis. This paper employed a recent methodologythe analysis. This paper employed a recent methodologythat combines the transient and long term studies into athat combines the transient and long term studies into asingle computational tool.single computational tool.
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SMART ALGORITHMS TO ACCOMMODATE
Tony Yip, Chang An, Graeme Lloyd ALSTOM GRID UK
Introduction
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Introduction
Wind farms tend to be located at the extremes of the
rated to carry the full output of the wind farm in allcircumstances causing the standard winter and summer
Instead of applying fixed summer and winter line ratings,load management based on a dynamically derived line
More wind means :
of the wind.
More generation
More current through the line
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
P341 Dynamic Line Rating
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P341 Dynamic Line Rating
The DLR calculates the rating ofthe line dynamically from some ora o e oca wea er measurements such as windspeed, wind direction, ambienttemperature and solar radiation
inputs based on CIGRE or IEEEstandard equations.
The rela has 6 definite time DLRstages which can be set as a
percentage of the line ampacity.
If the load current exceeds a DLR
used to send commands to theDG to reduce their output . As aback-up, in case for some reason
reduced, the relay can initiatelocal tripping of the DG or line.
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
Protection Algorithm
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Heat balance equation in CIGRE 207/IEEE 738 Standards
where
wrCiSMJ PPPPPPP
PJ = Joule heating (due to current flow)
M
PS = solar heating
Pi = corona heating
Pc = convective cooling
s
Pr = radiative cooling
Pw = evaporative cooling
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
PM, Pi and Pw are neglected.
Dynamic Line Rating load management and protection -Site trial of a 132kV double-circuit line between Skegness and Boston (North
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Site trial of a 132kV double circuit line between Skegness and Boston (North
Wind generation at Skegness is expected to increase
Generation can cause power flow from Skegness to Boston.Rating of 40km 132kV line may be exceeded
E.ON Central Networks decided to apply Dynamic Line Rating asa cos e ec ve a erna ve o ren orc ng e nes as analternative to spending 5m to reinforce the existing 132kVnetwork
50-70MW Skegness
180MW
Onshore
ratings are based onEngineering
Boston
P27 assumes - ambient
temperature =2C
n er ,(Summer), 9C
(Spring/Autumn), wind
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
spee = . m s, so ar
radiation = 0)
Skegness Dynamic Line Rating
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Weather monitoring equipment at Skegness and Bostonrelays data back to the NMS control system. Wind
NMS to calculate a real-time line rating based on theCIGRE 207 methodology
Solar Radiation 890W/m2 (Eng. Recommendation P27assumes none)
TempSola
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
Skegness Dynamic Line Rating
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S eg ess y a c e a g
Ambient Temperature
Wind
Speed
ne
Current
Local
Offshore 132kV
Wind Farms33kV Wind Farms relay
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
Curtail if >95% Trip if >99%
Skegness Dynamic Line Ratings
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g y g During the first year of operation the actual line temperature
has been monitored by sensors (Power Donuts) fitted directlyto the conductors.
These sensors have been fitted on the bottom conductor at
three locations along the line. The results are sent by GPRScomms an compare wt t e ca cuate va ues n rea tme.This will allow the theory to be verified.
ALSTOM 2010. All rights reserved. Information contained in this document is provided withoutliability for information purposes only and is subject to change without notice. No representation or warranty isgiven or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosureto third parties, without express written authority, is strictly prohibited.
Comparison of conductor temperature (Tc) at Sk calculatedfrom CIGRE standard and measured by Power DonutTM for
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from CIGRE standard and measured by Power Donut forthe continuous period of 1 Day 13 Min from 24/04/2009
Verification of Conductor Temperature (Tc)25 600
20
400
450
500Tc, CIGRE
10
15
oC
orm/s
200
250
300
350
Amps
, u
Ambient Temp
Wind Speed
5
50
100
150Line Current
24/04 04:00 24/04 08:00 24/04 12:00 24/04 16:00 24/04 20:00 25/04 00:00 25/04 04:00
The results show a very good match between Power DonutTM and CIGRE calculatedconductor temperature.
The minimum and maximum differences are -1.24oC and 0.96oC respectively and for 90%of the time the absolute difference is less than 1.00oC.
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correctness of the CIGRE equations.
P27 vs. Ampacity with each weather parameter at SK 23,24/04/09
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/ /
P27 vs. each weather parameter
1100
1200
Ampaci ty w ith
WindSpeed&WindAng
800
900
1000
mps
500
600
700
Amp aci ty with
Wind Speed
Amp aci ty w ith
all parameters
300
400
23/04 00:00 23/04 06:00 23/04 12:00 23/04 18:00 24/04 00:00 24/04 06:00 24/04 12:00 24/04 18:00 25/04 00:00
P27 Spring/Autumn RatingAmpaci ty w ith
Solar Radiation
Ampacity with
Amb ien t Temp
The graph shows that the weather parameters having a significant impact one ne ra ng, are n e or er rom owes o g es : so ar ra a on -
501A, max +0% compared to P27), ambient temperature (438-528A, max+5%), wind speed (450-985A, max +97%) and wind speed + wind angle (457-1161A, max +132%).
P27 assumes zero solar radiation which is why the solar radiation ampacity isalways below the P27 ampacity.
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e prng u umn ra ng or e - s ne s .
Ampacity Level Distribution a from all weather parametersat SK Spring 2009, 20/04/2009 27/04/2009
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at SK Spring 2009, 20/04/2009 27/04/2009
400
Ampacity Level Dis tr ibution, Spring. Avg=753.8A, stdev=117.73
300
350
200
250
(times)
100
150n
0
50
Amps
For the majority of the time the ampacity is greater than the
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P27 Spring/Autumn rating of 501A.
Conclusions
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A protective relay has been developed which calculates the dynamic line ratingbased on weather conditions
DLR could facilitate the widespread and cost-effective connection of renewableenergy sources thus allowing the associated environmental, social and costbenefits to be captured.
DLR maximizes the usable capacity of overhead line assets by 50% or more
DLR avoids upgrading or replacing existing transmission lines (save significantcapital investment) For example the cost of installing 40km of 132kV upgraded line is approx 5M.
DLR increases energy yields, so improving the cost effectiveness of renewableenergy projects and reducing greenhouse gas emissions
capacity to the DG project. Assuming that the project is a wind generation project andthat it achieves a 25% load factor the extra energy exported would be 11 GWh perannum (5907 tonnes C02saving) and the extra revenue to the developer could be up to600k per annum
The relay provides easy and flexible integration to the control system with a largechoice of industry standard communication protocols and easy schemecustomization with Programmable Scheme Logic (PSL)
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Conclusions
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Analysis of the data obtained from site shows a close co-ordinationbetween the actual and the theoretical calculations of the conductortemperatures
The analysis also shows that the weather parameters having a significant
im act on the line ratin are in the order from lowest to hi hest: solar radiation ambient temperature wind speed .
Variation of the weather parameters along the line is unavoidable and thisneeds to be considered for each application. To cope with this variation therela includes correction factors which can be a lied for each weatherparameter.
The conservative approach of using only the wind speed and ambient
tem erature as var in uantities and the assum tions made about winddirection and solar radiation (wind direction is 20, solar radiation is890W/m2) are shown to provide a good safety margin in the Skegness-Boston application while providing some increase in the line rating.
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ACCUMULATED PHASE ANGLE DRIFT
MEASUREMENT
Loss of Grid Problem
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Loss of grid is where a
inadvertently isolatedfrom the grid andcon nues o suppylocal load
oss o gr can e
caused by:
ro ec on rppng
Accidentally due to
reconfiguration
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Loss of Grid Problem
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Safety risk - for example, through personnel working
the network are energised
-
Loss of system earth where the earth is on the starwinding of a network transformer. This can causeproblems for existing earth fault protection to detectearth faults if the system is unearthed.
(frequency and voltage ) to local demand.
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Existing LOG Methods Performance Assessment
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Loss of grid performance can be assessed in terms of sensitivity and
Sensitivity
ma es poss e msma c e ween oca genera on an e eman a einstant of islanding.
Also referred to as non-detection zone
Stability
Stability for different fault types with varying duration and retained voltage at thepoint of measurement
When designing loss of grid method objective is to have a small nondetection zone and be stable for as many fault characteristics as
STABILITY
Network faults
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Generator/demand Imbalance
Existing Loss of Grid Methods
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Passive Methods
Under/over frequency and voltage
Df/dt rate of change of frequency
o age vec or s
Direct inter-tripping
Active Methods
Active frequency drift
Reactive Error export
There is an abundance of active methods proposed in the technicalliterature, however, their application in practice has been limited todate. The traditional protection philosophy of independence from other
systems ma es t e ntro ucton o t ese met o s cu t.
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Novel Loss of Mains Protection - Phase Angle
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Aim: improve LOM stability without sacrificing
PAD: frequency difference between grid and island
will ive rise to a measurable hase an le drift Local island frequency is measured by the relay Grid frequency estimated based on linear extrapolation of
recorded historical data The PAD algorithm is based on a threshold comparison of
an accumulated voltage phase angle derived from thedifference between the current measured frequency and the
fnest
fn-Df - -
f[n]
fn
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nTW TD
RTDS Testing
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Two main network case studies have been used
connected to a 33kV network The second scenario tests the operation of relays protecting a synch generator
connected to a 11kV network.
These models are sim lified versions of the full network su lied b a UKDNO with appropriate aggregations made to reduce their complexity wherenecessary. Each scenario consists of a grid source, simplified network, pointof isolation, local captured load and generator (including a step-up transformerwhere appropriate).
For DFIG generators shortly after disconnection from the grid and the loss of the
reference signal the controller becomes unstable and identification of the islandingevent is therefore relatively easy.
or ync ronous mac nes e con ro er oes no s gn can y mpac on edynamic response to a loss of grid, the inertia of the machine is the primary factor.
Islanding & fault conditions considered
RTDS testing include: Sensitivity for a range of settings 0%, 2.5%, 5%, 10% power imbalance Stability for a range of settings 1/2/3 phase faults with retained voltage of
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, ,
RTDS Testing
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Fault Position A (20%Retained Gen Voltage)
Fault Position B (50%Retained Gen Voltage)
Fault Position C (80%Retained Gen Voltage)
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11kV network model and fault locations.
RTDS 33kV SM Sensitivity Testing (PAD)PAD Sensitiv it Settin s fo r 30MVA SM Assume a max imum o eratin timeo f 500ms
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35
40
45
ree)
The protection exhibitsgood sensitivity for smallimbalances of down to
10
15
20
25
MaxSettings(Deg
PAD Active
PAD Reactive
.
To detect all imbalances asuitable setting is 10
0
5
10 5 2.5 0 -2.5 -5 -10
Imbalance Ratio (% of Gen Rating )
Max sensitivity settings
based on 500ms trip timePAD Sensitiv ity Settings for 1.5MVA SM (Assume a maximum operating time of 500ms)
35
40
increased if trip time criteriaincreased
15
20
25
30
ttings(Degree)
PAD Active
0
5
10
10 5 2.5 0 -2.5 -5 -10
MaxS
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Imbalance Ratio (% of Gen Rating )
11kV SM Maximum Sensitivity Setting for PAD
RTDS 11kV SM Stability Testing (PAD)
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11kV Stabil ity Test Results - ABCG fault
250
150
200
m
s)
80% retained Voltage
50% retained Voltage
20% Retained Voltage
50
100
TripTime(
.
-50
0
0 5 10 15 20 25 30 35 40
PAD Angle sett ing ()
11kV SM Stability (Retained Voltage 20%/50%/80%, Three-phase
fault).
or e ne wor mo e e pro ec on s s a e or a au ypesthe setting is >100.
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Conclusion
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The use of an accumulated phase angle drift method has beendemonstrated to be an effective method for detecting loss of grid
It has been shown to possess good levels of sensitivity at near
It has also been shown to possess a high degree of stability undersevere faultconditions
An open loop trial is planned in the near future to confirm itsperformance under practical conditions
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www.alstom.com
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1
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INTRODUCTIONVoltage control is an im ortant as ect to be ro erl accounted for in theinteraction of DG with the Smart Grid (SG) operation and control.
The aim of the voltage control is to assure an adequate
.
In existing MV distribution system, voltage regulation isperformed by HV/MV substation, using a On Load TapChanger (OLTC). Large DG devices, can be equippedwith local voltage/reactive power control system.
The interaction between OLTC and DG devices maycause over or undervoltages along the feeders.
To overcome such problems, new voltage control structures have been proposed,based on centralised and decentralised/coordinated approaches requiring:
additional measurements
additional data communication
Such an impact on the distribution system willbecome economically viable in the far-awayfuture. Nowadays, the main technical challengeis to define road maps to update the existing
2
control systems.
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In this paper a completely decentralised approach is adopted to develop aAIM OF THE PAPER
voltage/reactive power control scheme for DG devices connected todistribution networks
keeping the existing control structures of DG device
avoiding any real-time data exchange among
using only local measurements of voltage and currentat the Point of Common Coupling (PCC)
so as to improve the voltage profi le along the feeder in presence ofvariationsboth of loads and ofthe HV/MV substation o eratin conditions.
REFERENCE SYSTEM
Radial distribution network
HV/MV substation with OLTC regulator
DG device: synchronous generator
3
w reac ve power regu a or
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REACTIVE POWER CONTROL SCHEME
The classical
enriched with anOptimisationStrategy.
OPTIMISATION
STRATEGY
In this paper attention isfocused only on theSubstation Voltage &Load Estimation block.
4
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SUBSTATION VOLTAGE & LOAD ESTIMATIONThe ado ted scheme for the Substation Voltage & Load Estimation block isdeveloped in the following assumptions:
distribution network configuration is known;
su s a on s mo e e y a vo age genera or n seres w a ea age mpe ance; a echanges of the operating conditions of the HV/MV substation are modeled by variations of thevoltage generator;
nodal loads are modeled by shunt admittances and are subject to homothetic variations.
extract f rom time-varying
signals the corresponding
phasors at fundamental
estimates the Thevenin
equivalent circuit of the
distribution system as
determines
the shunt admittancesof the nodal loads
computes the value of
the vol tage of the HV/MVsubstation
5
frequency seen from the PCC
SUBSTATION VOLTAGE & LOAD ESTIMATION
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SUBSTATION VOLTAGE & LOAD ESTIMATION
How is it ossible to se arate the effects of the variations of loads from
In the above modeling assumptions the distribution system
the ones of HV/MV substation?
Once the Thevenin
equivalent circuit is known
- the equivalent impedance depends onunknown load admittances and the
presents the following electrical equivalent ci rcuit:
nown su s a on mpe ance;- the no-load voltage depends onunknown load admittances, the known
HV/MV substation impedance and the
6
unknown HV/MV substation voltage.
CASE STUDY
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The distribution system has been simulated by using PSCAD/EMTDC and the proposed
C S S U
Substation Voltage & Load Estimation block has been implemented in Matlab.
Radial feeder with 4 busbar: line data & loaddata
132/20 kV transformer with OLTC data
The OLTC has a vol tage
2.4 MW-3MVA synchronous generator data
re erence equa o . p.u.
DG is equipped with a
classical reactive ower
7
regulator with Qref(t)=0
CASE STUDY
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Three cases have been considered characterized with different values ofloads and ofHV vol tage at the substation:
rated loads and 1.0 p.u. HV voltage;Case A
rated loads and 1.01 .u. HV volta e.
load increased of 10 % and 1.0 p.u. HV voltage;Case B
Case C
CaseActual values Estimated values
A
B
termsofaccuracy,althoughthevariationsoftheloadsandoftheHV
C voltagearequitesmall!! The actual value of vsub does not change because the OLTC regulation acts to keep constant the
8
voltage at the transformer MV busbar.
CONCLUSIONS
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A reactive ower control scheme for DG devices has been ro osed that uaranteesan optimal voltage profile in MV distribution systems in presence of both load and HV/MVsubstation variations.
The proposed scheme keeps the existing control structures of DG device, uses onlylocal measurements of voltage and current at PCC and avoids any data exchange withOLTC regulator.
Attention has focused on the eculiar Substat ion Volta e & Load Estimation rocedureand its validity has been tested by numerical simulations in open loop configuration.
FUTURE RESEARCH STEP
completing the Optimisation strategy development with the Voltage Profile
Optimisation oc ; analysing the performance of the closed-loop reactive power control scheme;
investigating the possibility of including other DG devices and load models.
9
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10
Question 3
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,are, the higher the achievable performance is.
- reactive power: it is controllable for some electric machines andeec ronc n er aces.
- active power: it is controllable for DG devices using dispatchableprimary energy sources.
If the increase of DG penetration is essentially based on renewable energyconversion s stems, then the control of active ower must be achieved b
promoting Active Demand so as to introduce new command signals to beused by the control system.
Q ti 4
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Question 4
Information about the distribution networkand DG operating conditions are gathered
APPROACH
The control action is performed by local
rom e su s a on.
On the basis of such information, at theHV/MV substation level, an optimal
controllers and information exchange is onlyused forcoordinationpurposes.
On the other hand, this approach does notsys em con ro s ra egy s e ne anactuated by sending adequate commands
to the OLTC and to the DG devices.
optimise the overall system operation butonly guarantee that specific voltage
constraints are fulfilled.
Concerning the optimisation functions, they can include the classical technical-economical objectives (such as flat voltage profile, distribution loss reduction, control actionminimisation) and additional new objectives. In particular it should be accounted for the costs
rea e o e servces prov e y c ve eman an y or exampe, y e re uc onof generation from renewable energy in response to a specific request from the controlsystem).
The com arison between different control structures should account both for theperformance evaluated in terms of optimisation functions and for the investment costs.
Question 5
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reduces the power flows along the feeder.
Problems of volta e stabilit limit ma arise if the lar e enetration of DG fromrenewable energy sources:- causes significant reverse power flows towards the HV network,- is trusted as a substitution of the necessary reinforcement of the feeder whennew loads are connected.
Concerning dynamic stability of the voltage control scheme proposed in the paper#236, the new optimisation strategy is designed to change the reference value ofreactive power with a settling time equal to 60-100 s. Such loop is very slower thatthe reactive power control loop which presents a settling time of 5-10 s. In this way
t e two oops are ecoupe an t e r sta e operaton s guarantee .
Further studies will concern the interaction with the OLTC control loop and witho er con ro sys ems w en presen .
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