Power System Security ConceptsEE 521 Analysis of Power SystemsChen-ChingLiuBoeing Distinguished Professorhi i i Washington State UniversityReliability Definitions (NERC)Reliability The degree of performance of the elements of the bulk electric system that results in electricity being delivered to customers within accepted standards and in the amount desired. Reliability may be measured by the frequency duration andmagnitudeof adverseeffectsontheelectricsupply frequency, duration, and magnitude of adverse effects on the electric supply. Electric system reliability can be addressed by considering two basic and functional aspects of the electric system Adequacy and Security.Adequacy The ability of the electric system to supply the aggregate electrical demand and energy requirements of the customers at all times, taking into account scheduled and reasonably expected unscheduled outages of systemelements. system elements.Security The ability of the electric system to withstand sudden disturbances such as electric short circuits or unanticipated loss of system elements.System Security The ability of a power system in normal operation to undergo a likely disturbancep g ywithout entering an emergency or a restorative state. The objective of security control is to keep thepower systeminthenormal state the power system in the normal state.Power System Constraints Dy Liacco framework considers the power system as being operated under two types ofy g p ypconstraints: Load constraints- Demandsmust bemet by Load constraintsDemands must be met by the system. Operating constraints Maximal and Operating constraints - Maximal and minimal operating limits, steady-state and stabilitylimitations stability limitations.System Operating States Normal - Load and operating constraintssatisfied Emergency - Operating constraints not completelysatisfied completely satisfied. Restorative - Load constraints not completelysatisfied completely satisfied. Security Assessment / ControlNormalSECURENormalPreventiveControlINSECURERestorative ControlPreventive ControlEMERGENCY RESTORATIVE EMERGENCY RESTORATIVEEmergency Control g ySecurity Assessment The operating state of a power system is SECURE if no disturbance in the next contingency list leads to an emergency operating condition and isINSECUREth i otherwise. Needs a list of next contingencies N-1 or N-2 security criteriaSecurity Assessment and Control Security monitoring - limit checking Securityanalysis- contingencyevaluation Security analysiscontingency evaluation Preventive control - how sure, impact?E l Emergency control Fault diagnosis Restorative controlMEASUREMENTSDataFILTERINGSTATE ESTIMATION NETWORK TOPOLOGY DataAcquisitionAndProcessingSTATE ESTIMATION NETWORK TOPOLOGYSECURITY MONITORINGEMERGENCYCONTROLEMERGENCYSTATELOAD FORECAST UPDATESTATEEXTERNAL EQUIVALENTUPDATESecurityAnalysisCONTIGENCYEVALUATION ON-LINE LOAD FLOWEXIT PREVENTIVE CONTROLSecurity Related Software State estimation Securitymonitoring Security monitoring Network topology E l i l d l External system equivalent model On-line power flow Optimal power flow (OPF) Contingencyevaluation Contingency evaluationAlarmProcessing Alarm ProcessingyesnoNormal?Security analysisEnergytransactionsFault diagnosisEnergy transactionsP ti t lRemedial controlsPreventive controlsMaintenance actionsRemedial controlsRestorative actionsNERC: Available Transfer Capability (ATC)MW A->BTotal TransferA->BTotal TransferCapability (TTC)Transmission Reliability MarginTRMTRMNonrecallableNonrecallable ATCATCRecallable Recallable Recallable ScheduledRecallable ReservedNonrecallable ReservedNonrecallable Available Transfer CapabilityATCATCReservedNonrecallable ScheduledNonrecallable ReservedTimeOperating Horizon Planning Horizon