Experiences at California ISO in supporting State Estimator solution accuracy due to
external model for reliability and market operations
Ankit Mishra, Veera Raju Vinnakota, James Bonham, Sirajul Chowdhury, Brian Cummins
California ISO, USA
IEEE PESGM 2014 July 27-31, Washington D.C.
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Presentation Overview
Abstract
1. Introduction
CAISO overview
2. Existing State Estimator (SE) related processes
DB updated process
ensuring SE availability
ensuring SE solution Quality
3. Metrics driven approach for supporting SE solution quality
need for higher quality of SE solution in external areas
quality driven process adjustment for external areas
details of quality driven initiatives
4. Summarization and Conclusions
Acknowledgements
References
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Abstract
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State Estimator (SE) is critical for CAISO market and reliability
higher quality of SE solution in CAISO internal areas has been in
place
external area solution need better quality
metrics refined to guide SE quality improvement
processes amended to support quality driven approach
PI tracking of metric computations, posting monthly averages from
five-minute averages
a model measurement based stations’ connectivity graph is introduced
to quickly identify SE related measurement problems
graph further helps guide certain corrective actions for supporting SE
solution quality
CAISO Overview - Independent System Operators and Regional Transmission Organizations
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Control flow of electricity on transmission grid Regulated by FERC Serve 66% of the U.S. & more than 50% of Canada Do not own generation or transmission infrastructure
CAISO Overview – Main Office in Folsom, California
CAISO Overview – CAISO is part of Western Interconnection
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encompasses western half of North America -- 14 states, British Columbia, Alberta and parts of Mexico
Western Electricity Coordinating Council (WECC) coordinates regional reliability and planning — governed by 32 board members
California — ≈ 40% of WECC peak demand
no ISO or California investor-owned utility representatives on WECC board
CAISO Overview – Grid Operations
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60,703 MW of power plant capacity (net dependable capacity)
50,270 MW record peak demand (July 24, 2006)
27,589 market transactions per day
26,024 circuit-miles of transmission lines
30 million people served
246 million megawatt-hours of electricity delivered annually
Model Size for State Estimator (SE)
* Between CAISO and external areas
SE runs every half a minute
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Internal External
Number of Areas 4 41
Number of Buses 5087 7820
Number of Branches 2679 5941
Number of Switches 29046 41468
Number of Analogs 16591 24498
Number of Ties 78* 546
Peak Load approx. 45,000 MW -
CAISO Network Model Process
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SCOPE Data
Request
PSLF/
GDB
Validation
Checks
Build
Model
QAS
Testing
QA &
Market
Testing
Promotion
EMS Displays
Errors to Correct
• changes to the network model are provided by participating transmission owners (usually from existing planning models)
• the modeling tool can import PSLF or PSSE data formats
• PTOs provide incremental changes in PSLF data format
• the modeling tool imports PSLF bus branch data
• the model is then detailed into a node-breaker model manually by the modeler using a graphical user interface
• the modeler can assign coordinates to equipment and make the one-line aesthetically pleasing
• SCADA is manually added and linked to the detailed model
EMS Model Update Process 1 - Conventional
– changes to network model captured from participating transmission owners typically in bus-branch model of PSLF or PSSE data formats
– import PSLF or PSSE data files of PTOs using vendor supplied modelling tool
– bus-branch model detailed into a node-breaker model manually using vendor supplied graphical user interface
– the modeler can assign coordinates to equipment and make the one-line aesthetically pleasing
– SCADA data definitions are manually added and linked to the detailed model
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EMS Model Update Process 2 – CIM Based Model Exchange
Bulk Model Update: when the incoming CIMXML model is significantly different from the existing model
– identify and cutout the buses to be replaced – import CIMXML models based on areas – fix issues related to incoming CIM model and system specific modeling
nuances – clean the incoming model with respect to naming conventions that
meet in-house business processes – remove inconsistencies between existing tie stations and the tie
stations in the incoming model – the SCADA measurements are imported with the new CIM model – clean-up auto-generated one-lines to meet display requirements
Incremental Model Update – use of existing Database tools to identify incremental changes based
on CIM description fields – use third party software(CIMSPY) to identify incremental changes
based on CIM RDFIDs
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New SE Quality Metrics
• primarily for tracking and improving external area solution
• metrics to guide on problem area to go after and monitor improvements
NEW METRICS*
Generation, Load and Interchange Estimate Delta = Abs(Meas Load – Est Load) + Abs(Meas Gen – Est Gen) + Abs(Meas Intch – Est Intch) /(Meas Gen + Meas Load + Meas Intch)
Load Estimate Delta = Abs(Meas Load – Est Load) /Meas Load in MW
Generation Estimate Delta = Abs(Meas Gen – Est Gen) /Meas Gen in MW
Interchange Estimate Delta = Abs ( Meas Intch – Est Intch) / Meas Intch in MW
Meas : Measured; Est : Estimated; Gen : Generation
IMPLICIT ASSUMPTION : LOADS AND GERATIONS ARE POSITIVE VALUES
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*Ref : Presentation at 12th International Electric Power Control Centers (EPCC) Workshop June 2-5, 2013 Bedford Springs, Pennsylvania, U.S.A.
Area Load Calculation *
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SCADA / AGC Area Load = (G1 + G2) – (T1+T2+T3) in MW SE Estimated Load = ( L1 + L2 + L3 + Losses ) in MW computed from State (V Magnitude and V Angle), using real-time measurements and real-time network model
AREA
G1 G2
L1
L2
L3
T1
T2
T3
Elements Contributing to Percentage Delta
Internal Areas
• load not modeled
• generation not modeled
• generation behind meters (e.g., oil refineries)
• auxiliary loads of generation not modeled
• inaccuracy of estimate impacting load calculation
External Areas
• All the Above
• Balancing Authority area misalignment with EMS area
• inadequate network model and telemetry
• inaccurate pseudo measurement calculation
• out-of-date AGC computed load point available in EMS
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Metrics Monitored By Area
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% Generation Delta % Load Delta % Interchange Delta total negative generations total negative load Chi-Square-P Chi-Square-P Threshold Chi-Square-Q Chi-Square-Q Threshold
Typical EMS Displays Helpful To Fix Problems
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negative loads
buses with large MW / MVAR estimates, mismatches
negative generations
out-of-bound load estimates
large mismatches between measurements and estimates
gross measurement errors
Tracking the Metrics at CAISO
• values computed every SE run, tracked on PI
• metric value helps choose target quality level and track if improvements work
• need for tools with improved visuals to enhance external area solution quality
– to help topology adjustments in external areas matching real time conditions
– to provide better visuals on measurements, estimates, errors, etc.
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Model-Measurement Graph (in-works)
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- provides visual assessment of extent of spread of measurements and local redundancy - provides visual opportunity of line-flow measurements based spanning tree - graph generated from an SE solution using scripts and open source GraphViz tool - station connectivity graph with flow measurements superposed Dashed: out of service lines Oval Bubbles: stations White Boxes: area/station names
Line Color: measurement available Red: measurement could not be used
Orange Bubbles: tie stations — color of bubble represents voltage level
SE Solution Quality Improvement Outlook Time Frames
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Short Term Outlook (daily basis)
o ‘On-Call’ person looks at the error contributing elements on a daily basis
o improves SE solution quality and reduces number of real-time issues of maintenance
Medium Term Outlook o error contributing elements are reviewed by staff in assigned areas
o improves SE solution quality in near term time frames
Long Term Outlook ( 8-16 week cycle times)
o model deficiencies identified and enhancements made
o telemetry inadequacies identified and data requested
On-Going Support and Efforts of SE Solution Quality
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enhancement of certain EMS displays with area (pslf or ba) as an attribute
a couple of additional PI process book displays and their upkeep
PI tracking of metrics and ongoing maintenance support monthly computation and posting of metrics’ averages daily efforts for upkeep of solution driven by quality metrics and identified target
requirements
tools to support easier identification of problems and for reporting quality summary
Summary and Conclusions
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State Estimator is critical for CAISO market and reliability
higher quality of SE solution in CAISO internal areas has been in place
external area solution need better quality
metrics identified to guide SE quality improvement
processes amended to support quality driven approach
o data base promotion approach amended
o SE support team re-aligned based on geographic area basis
o external area model/telemetry enhancement driven by long term SE quality improvement
targets for metrics defined
graphs generated to help identify measurement related problems
metrics driven medium term Solution improvement by tracking metrics on monthly basis
PI based displays to track metrics by areas
SE availability improves due to reduction in invalid solutions
Acknowledgement
• To CAISO for support and encouragement to present some of the works carried out at CAISO
• To Timothy Willenberg for extensive support on PI calculations
• To Jose Sanchez Alvarez, Trevor Ludlow for trying out the new processes and helping to tune and support SE solution quality
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References
• State Estimator for Market and Reliability – Need for EMS Support Tools to fix Topology Errors and for External Model Maintenance: Veera Raju Vinnakota, Sirajul Chowdhury, Brian Cummins, Ankit Mishra, Hani Alarian, California ISO, presented at 12th International Electric Power Control Centers (EPCC) Workshop June 2-5, 2013 Bedford Springs, PA, U.S.A.
• Dinesh Salem-Natarajan, Wei Shao, Mani Subramanian, Hsiao-Dong Chian, et.al., “State Estimator for CAISO Market and Security Applications – Relevance and Readiness,” presented at IEEE PES General Meeting 2008, Pittsburgh, PA, U.S.A. July 20-24, 2008
THANK YOU Contact
Veera Raju VINNAKOTA ([email protected]) or
James BONHAM ([email protected])
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