Authors: Dinesh Salem-Natarajan, Mani Subramanian Hsiao-Dong Chiang,

1. State Estimator for CA ISO Market and Security Applications – Relevance and ReadinessIEEE PES General Meeting 2008PITTSBURGH, PENNSYLVANIA, USAJuly 20-24, 2008 Authors: Dinesh Salem-Natarajan, Mani Subramanian Hsiao-Dong Chiang, Liang Zhao, Wei Shao, Gordon Lin, Hua Li Matthew Varghese, & (ABB, Sugar Land, TX) (Bigwood-Systems, Ithaca, NY) Soumen Ghosh (CaISO, Folsom, CA)

2. Overview • Introduction • CAISO Network Model (EMS Model) footprint; • The Market Model footprint, Full Network Model (FNM); • The models in Common Information Model/eXtensible Markup Language (CIM/XML) format; • The relevant EMS applications; • The implementation of Voltage Stability Analysis (VSA); • Orthogonal State Estimator (SE) and its comparison with Fast Decoupled SE; • The relevance of SE solution in Real Time Nodal Market and VSA; • The SE Readiness Metrics adopted at CAISO and the proposed acceptable range of the metrics. • Conclusion

3. Introduction • Reliability tools and market systems depend on the results produced by the SE • Monitoring & Analyzing the quality and availability of every SE solution • At CAISO, the SE solution is used for Real Time Power Flow and Contingency Analysis, Real Time Nodal Market, and for Voltage Stability Analysis. • In the evaluation of SE readiness, • Several metrics used by the Midwest ISO (MISO) and Southwest Power Pool (SPP) were reviewed • Several new SE performance metrics of the SE solution at the CAISO have been identified • The new SE performance metrics are to identify an unreasonable SE solution even if the solution is valid. • Our hope is to set up a framework for all stake holders to work collectively in identifying a standard set of SE metrics to determine the quality of the SE solution

4. CAISO Network Model footprint

5. Network Model • EMS Network Model:This includes the detailed system (including sub-transmission) for the state of California and for all other WECC areas, the system is represented for voltage levels at 161 KV and above. • Market Full Network Model: Detailed Network Model, mostly derived from the EMS Network Model, • The power system model for the CAISO footprint, • Fictitious injections on inter-ties to areas not part of CAISO markets and • Commercial data for the market participants (ex: an association between a set of electrical buses to a specific LMP pricing node) • CIM/XML Model Format: A common model format that can be used and understood by different platforms provided by a variety of vendors.

6. PSLF Model

7. CIM/XML Model </cim:ACLineSegment><cim:ACLineSegment rdf:ID="Conductor_2003"> <cim:Naming.name>POEPH-RIOOSO_230_BR_1_1</cim:Naming.name> <cim:Naming.description>30280_POE _230_30330_RIO OSO _230_BR_1 _1</cim:Naming.description> <cim:Conductor.x>43.8911</cim:Conductor.x> <cim:Conductor.r>7.41658</cim:Conductor.r> <cim:Conductor.bch>16.234</cim:Conductor.bch> <cim:ACLineSegment.MemberOf_Line rdf:resource="#Line_7448"/> <cim:ConductingEquipment.BaseVoltage rdf:resource="#230_BV"/>

8. Detailed Model

9. EMS Relevant applications • STATE ESTIMATOR • State Estimation processes telemetered system power measurements to obtain an estimate of ‘State’ - the magnitudes and phase angles of bus voltages in the actual power systems. • This calculation is based on the telemetered analog quantities (MW, MVAr, and KV) and the most current topology of the power system. • Knowing the state of the power system, it calculates the MW, MVAr, and MVA flows through all the transmission lines and transformers and the MW and MVAr injections for all the loads and generation sources. • These calculated voltage and power values provide useful operational information in cases when no telemetry is available. When valid telemetry does exist, the calculated quantities can be used to identify measurement errors. • REAL TIME LOAD FLOW & CONTINGENCY ANALYSIS • Real Time Load Flow provides the system operator with grid information like voltage and line flows for different short-term study conditions. • Real Time Contingency Analysis provides the system operator with the information on the ‘system state’ for different ‘what if’ conditions on the existing system. • CAISO OUTAGE MODELING TOOL (COMT) • The COMT application is a Web-based tool which allows the users to search the CAISO Outage database and identify scheduled outages that impact the network topology. The tool allows the users to develop switching instructions (based on Network Model components) that need to be automatically applied to the network model at the appropriate time. • In the Real-Time COMT is used to update the status of non-telemetered points and the status points with failed telemetry.

10. Voltage Stability Analysis (VSA) Tool • VSA Real-Time Mode (VSA/RT) • VSA Real-Time Look-Ahead Mode (VSA/LA) • VSA On-line Study Mode (VSA/OS)

11. VSA Tool Input and Output

12. VSA-User Interface, RT/LA System Load Margin: the maximum total real power transferred from source to sink before the system hits the voltage collapse point under a proposed stress pattern. Interface flow: the power flowing through an interface flow gate. The Interface Margin is the portion of the total power transferred that flows through the Interface.  If the interface is defined properly in relation to the stress pattern a sizable portion of total power transferred will flow through the defined interface

13. VSA -User Interface, OS Study mode VSA runs as a stand-alone process, which can be launched directly from the workstation as well as from the Viewer. Study mode VSA can retrieve an archival case from the VSA viewer or a Dispatcher Load Flow case directly from the data bridge.

14. Orthogonal vs. Fast Decoupled Comparisons Stage 1 Run with existing ‘Convergence Tolerance’ Run with existing ‘Global Measurement Errors’ Stage 2 Set MW/ MVAR convergence tolerance for all Areas to 0.05 Revise the MW/ MVAR mismatch on ‘Zero Injection Buses’ measurement error tolerance to 0.1 Stage 3 Re-set convergence tolerance to values before Stage 2 Reduce the minimum values for ‘Global Measurement Errors’ For Voltages, use decrements of 0.001 For Circuits, use decrements of 0.5 (then) .05 For gen/loads, use decrements of 0.1 (then) .01 Stage 4 Repeat steps of Stage 2 with parameters of Stage 3 COMPARISON : INVALID RUNS for ORTHOGONAL vs. FAST DECOUPLED

15. State Estimation & Real Time Market • Real Time Market • Real Time Pre Dispatch (RTPD) • Executes every 15 minutes • Real Time Interval Dispatch (RTID) • 5 Minutes dispatches • RTPD & RTID • Utilizes the Full Network Model updated by the real time State Estimator solution to get the current operating conditions to initialize the power flow. State Estimator Solution resides in Enterprise Integration Bus to be used by RTPD and RTID.

16. State Estimation & Market • In the RTM environment the static model is updated with dynamic data based upon real time operations that comes from the State Estimator application which is merged with commercial Market and Supplemental Market Data Maintenance (SMDM) system data for the various Market runs. • The static market model from the GDB and the dynamic model of the power system are exported from the EMS to the RTM system. • For the RTM analysis, the State Estimator solution along with Topology Information from the EMS is transmitted to the RTM System and used to initialize the Power Flow.

17. SE/ DLF Solution Quality Monitor

18. SE/ DLF Solution Quality Monitor

19. Conclusion • Importance of the quality of the information provided by the SE to the various reliability and market tools • At the California ISO, the SE solutions are required for (1) The Real Time Market and for (2) Security Applications such as Voltage Stability Analysis. • This paper proposes the formulation of metrics to study the availability and quality of the SE solution.

20. Questions and Answers