Risk Based Assessment of Subsynchronous Resonance in AC/DC Systems

233 Pages·2017·22.46 MB·English

by  Atia Adrees (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Atia Adrees

Risk Based
Assessment of
Subsynchronous
Resonance in
AC/DC Systems
Springer Theses
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Atia Adrees
Risk Based Assessment
of Subsynchronous
Resonance in AC/DC
Systems
Doctoral Thesis accepted by
the University of Manchester, UK
123
Author Supervisor
Dr. Atia Adrees Prof. Jovica V.Milanović
Schoolof Electrical andElectronic Schoolof Electrical andElectronic
Engineering Engineering
University of Manchester University of Manchester
Manchester Manchester
UK UK
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-319-44946-3 ISBN978-3-319-44947-0 (eBook)
DOI 10.1007/978-3-319-44947-0
LibraryofCongressControlNumber:2016949599
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To my family
’
Supervisor s Foreword
Futuretransmissionnetworkswillbecharacterizedbyincreasednumberofheavily
compensated lines due to vast proliferation of renewable energy sources and
efficient operation of the electricity market. In many cases to secure rights of the
way for new transmission lines is becoming increasingly difficult. In order to
facilitatebulkpowertransferbetweendifferentareasofthenetworkandtotransfer
remotely generated power by renewable generation to consumer centers as well as
to facilitate efficient electricity market operation future transmission networks are
expectedtoincludemediumlengthorevenshortheavilycompensatedAClinesand
HVDC lines operating in parallel with existing AC lines.
Fixed series compensation is a highly effective and economical means of
improving power transfer by reducing transfer reactance of a transmission line.
Presence of series capacitors in transmission lines also enables a decrease in the
angular separation of the end voltages, contributing towards an increase in the
angular stability. In 1971 following the turbogenerator shaft failure, it was dis-
covered that series compensation can create adverse interactions between series
compensated electrical system and turbine generator mechanical system leading to
shaft fatigue or ultimate shaft damage. The phenomenon is known as subsyn-
chronousresonance(SSR)sinceitistheresultofaresonantconditionwithanatural
frequency below the synchronous frequency of the system. Following this, it has
beendemonstratedinnumerousstudiesthatcompensatedAClinesandHVDCline
controls pose a risk of SSR. Self excitation or dynamic instability due to SSR
produces very high amplitude mechanical torques in turbine generator shaft that
couldleadtoshaftdamage.TransienttorqueamplificationproblemcausedbySSR
yields high amplitude mechanical torque following electrical disturbances that
could result in shaft fatigue and ultimately shaft breakdown. The studies also
demonstrated thatthegenerators connectedradiallytothecompensatedAClineor
HVDC line are at higher risk of SSR than the generators in highly meshed power
networks. There can be a range of circumstances, however, (e.g., outage of AC
lines,nearbygeneratoroutofservice,changeofcompensationlevel,etc.)thatcould
change the degree of exposure to SSR in meshed networks.
vii
viii Supervisor’sForeword
In addition to fixed series capacitors, thyristor controlled series capacitors
(TCSC) have been increasing used for line compensation. Subsynchronous fre-
quency characteristics of the power system with thyristor controlled series capac-
itorshowever,differsignificantlyfromfixedseriescapacitorscompensatedsystem.
Flexibility of changing the compensation level and ability to effectively damp
subsynchronous resonance and electromechanical oscillations make TCSCs an
attractive and versatileseries compensation option. These additional benefitscome
with considerable higher costs. Therefore, future transmission networks will have
many instances where thyristor series capacitor will be used in conjunction with
fixed series capacitors due to reliability and economical reasons.
Powersystemloadsthatalwayshadadegreeofuncertaintyassociatedwiththem
will further diversify in the future due to new type of devices connected to the
networkandparticularlyduetoproliferationofelectricvehicleswhosecontribution
will be characterized by both spatial and temporal uncertainty. Finally, integration
of new types of generators in the network (mainly stochastic and intermittent) will
add another layer of uncertainty to system operation. This uncertain, to a large
extent probabilistic, behavior of power system is the root origin of risk. Risk
management and quantification of risk have become increasingly important when
discussing and assessing operation of power system.
Most of the past SSR studies adopted deterministic approach to analyze SSR
problem.Primaryobjectiveofthisresearchwastodevelopanapproachtoevaluate
SSR risk associated with different compensation levels in various contingencies
taking into account the combination of probability of occurrence of each contin-
gency,probabilitiesofdifferent operatingconditionsandseverity ofSSR problem.
SSRriskevaluationcanassistintheselectionofbestmitigationschemeforagiven
transmissionsystembyprovidinginformationabouttheseverityandprobabilityof
SSR occurrence.
Theworkpresentedwithinthisthesisisverytimely,extremelyrelevantandtoa
large extent pioneering as it uses for the first time risk based assessment tools to
analyzetheinteractionbetweenelectricalandmechanicalsystemsinmixedAC/DC
power networks at subsynchronous frequencies. The research first developed SSR
indices to assess the severity of SSR problem the generators in the network are
exposedto.ItthenmovedtoinvestigatetheeffectofVSC-HVDClinesondynamic
instabilityoftorsionalmodes(oneofthefirst,ifnotthefirstworkinthefield)and
finally it developed a methodology based on risk evaluation methods for SSR
studies. The application of the developed methodology in a large network for the
assessment and optimal SSR mitigation (combination of fixed capacitors and
TCSCs) demonstrates that risk evaluation can assist in the selection of the best
mitigationschemesforagiventransmissionsystembyprovidinginformationabout
the severity and probability of SSR occurrence. This is one of the pioneering
applications of risk based assessment in power system dynamic studies. The
research also addressed the issue of assessment of the effect of uncertainties in the
mechanical parameters of a turbine generator on SSR in a meshed network with
bothtypesofcompensationschemessymmetricalandasymmetricalcompensation.
Supervisor’sForeword ix
Substantial research contributions can be found throughout this thesis and it
shouldprovetobeanexcellentreferenceforallinterestedinthetopic.Thecontent
is readily accessible and easy to follow, as the methodical progression with each
chapter develops on the ideas found before it, and makes excellent reading on a
fascinating subject.
July 2016 Prof. Jovica V. Milanović, CEng, FIET, FIEEE
Deputy Head of School and Director of External
Affairs & Business Engagement
in the School of Electrical and Electronic Engineering
at the University of Manchester, UK
Visiting Professor at the University of Novi Sad, Serbia
University of Belgrade, Serbia and Conjoint Professor
at the University of Newcastle, Australia.
Parts of this thesis have been published in the following journal articles
and conference proceedings:
(cid:129) J. V. Milanovic and A. Adrees, “Identifying Generators at Risk of SSR in
MeshedCompensatedAC/DCPowerNetworks,”IEEETransactionsonPower
Systems, vol. 28, pp. 4438–4447, 2013.
(cid:129) A. Adrees and J. V. Milanovic, “Methodology for Evaluation of Risk of
Subsynchronous Resonance in Meshed Compensated Networks,” IEEE
Transactions on Power Systems, vol. 29, pp. 815–823, 2013.
(cid:129) A.Adrees andJ.V.Milanovic,“OptimalCompensation ofTransmission Lines
Based on Minimisation of the Risk of Subsynchronous Resonance,” IEEE
Transactions on Power Systems, vol. 31, pp. 1038–1047, 2015.
(cid:129) A. Adrees and J. V. Milanovic, “Subsynchronous resonance in meshed net-
works with HVDC lines,” IEEE Innovative Smart Grid Technologies Europe
(ISGT) 2011, Manchester, U.K, 5–7 Dec. 2011.
(cid:129) A. Adrees and J. V. Milanovic, “Effects of uncertainties in shaft mechanical
parameters on maximum torsional torques in meshed networks with HVDC
lines,” IEEE Transmission and Distribution Conference and Exposition (T&D)
2012, Orlando, U.S.A, 7–10 May 2012.
(cid:129) A. Adrees and J. V. Milanovic, “The Effects of Uncertainties in Mechanical
Parameters on SSR in Meshed Power Networks with Different HVDC
Technologies,” IEEE International Conference on Probabilistic Methods
Applied to Power Systems 2012, Istanbul, Turkey, 7–10 May 2012. Best
Student Paper Award
(cid:129) A. Adrees and J. V. Milanovic, “Index for ranking generators based on risk of
subsynchronous resonance in the network,” IEEE PowerTech (POWERTECH)
2013, Grenoble, France, 16–20 June 2013.
(cid:129) A.AdreesandJ.V.Milanovic,“Studyofsubsynchronousresonanceinmeshed
compensated AC/DC network,” 2013 IREP Symposium Bulk Power System
DynamicsandControl-IXOptimization,SecurityandControloftheEmerging
Power Grid (IREP) 2013, Crete, Greece, 25–30 Aug. 2013.
(cid:129) R. Preece, A. Adrees, and J. V. Milanovic, “Risk-based framework for
assessment of operational constraints for power systems focusing on
small-disturbance stability and sub-synchronous resonance,” IEEE Innovative
Smart Grid Technologies Europe (ISGT) 2013, Copenhagen, Denmark, 6–9
Oct. 2013.
(cid:129) R. Preece, A. Adrees, and J. V. Milanovic, “Risk-based framework for
Establishing And Visualising Operational Constraints of power systems,”
Power Systems Computation Conference (PSCC) 2014, Wroclaw, Poland, 18–
22 Aug. 2014.
xi