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ERCOT’s Experiences in Using ERCOT’s Experiences in Using Pseudo Measurements in State
EstimationMurali Boddeti, Diran Obadina, Freddy
Garcia, N. D. R. Sarma, Yang Wu*, Venkata KanduriKanduri
El t i R li bilit C il f T IElectric Reliability Council of Texas, Inc.*Alstom Grid
IEEE PES Panel session on‘State Estimation Pseudo Measurements’
July 2011, Detroit
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ERCOT - Introduction
Single Interconnection, with no synchronous ties to any other region in North America
Responsible for all transmission equipment operating at 60 kV and above (69, 138, 345 kV)
Five DC Ties to external regions Five DC Ties to external regionso 1 in North Texas, 1 in East Texas, 3 to Mexico
Utilizes Alstom’s EMS for its Real-Time Network Security Analysis applications
Facilitates competitive markets to help achieve reliabilityreliability
Operates as Nodal Market as of 1st Dec, 2010
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About ERCOT
85% f T l d 85% of Texas load 550 generating units, ~6000 buses; ~7000 branches Peak demand: 65778 MW (08/23/2010) Peak demand: 65778 MW (08/23/2010)Wind capacity: 9500 MWWind generation record: 7355 MW (06-19-2011), d ge e at o eco d 355 (06 9 0 ),
~15% of load at that time
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ERCOT
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KEY SE Role
Filters redundant real time measurements –eliminates incorrect measurements
Produces a Real Time Network modelo Allows determination of power flows in areas not directly
meteredo Used for real time monitoringo Used for real time Market and congestion managemento Used to uncover potential operational problems related to n-1o Used to uncover potential operational problems related to n-1
security, voltage and transient stability
Results used for adapting the load parameterso Used for Day-Ahead Market and other forward marketso Off-line power flows and stability studies
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ERCOT SE
Conventional State Estimator , i.e., RT modeling decomposed into (1) Processing statuses of
it h (2) P i f l d t iswitches (2) Processing of analog data, given network topology and parameters
Uses MW/MVAR, KV, tap. Uses MW/MVAR, KV, tap. Executes periodically (5 mins); on demand; or grid
event RT measurements collected via ICCP links with TSPs
every 10 secs Network observability of over 99% Network observability of over 99% Measurement redundancy of about 2.0
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ERCOT SE
Unobservable buses result from– Temporary loss of ICCP link– Temporary loss of measurement point (from the RTU)– Unavailable/inadequate measurements
Unavailable/inadequate measurements typically at lower KV level (69KV); typically affecting radial lines and tap loadsp
SE extended to unobservable buses through the addition of Pseudo measurements
Challenge is to avoid corrupting the states estimated from telemetry
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Handling Temporary Loss of Telemetered Data
Continue to use old telemetered values for a configurable number of SE executions
l ( l i t )cycles(several minutes)
Progressively reduced measurement confidence Progressively reduced measurement confidence values (increased measurement variance)
Stale measurements subsequently dropped and replaced with pseudo measurements based on load predictions and generation schedulespredictions and generation schedules
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Pseudo Measurements
Calculated based on telemetered valueso Predefined Calculated point in SCADA (RTMONI)
C (C C )o Topology-based Calculated Point (CALCM)
Load Schedules Load Schedules
Operator Overrides
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RTMONI Calculation
Short-term SCADA calculation tool
Used until the telemetry is available at calculated Used until the telemetry is available at calculated point
Can be defined online without DB load
Ease of use made a tool for pseudo measurement Ease of use made a tool for pseudo measurement modeling by the shift engineer
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RTMONI Calculation
Fig1 Example without RTMONI CalculationsFig1. Example without RTMONI Calculations
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RTMONI Calculation
Fig2. Example with RTMONI Calculations
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CALCM Function
Addition of calculated measurements using network topology information
Accurate than RTMONI
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CALCM Function
Fig 4: CALCM Calculations
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Load Schedules
Classified into various weather zones in Texas Conforming and non conforming classification Conforming and non-conforming classification Used as pseudo measurement when telemetry
is unavailable Adapted in real-time with SE results Adapted parameters used in study applications
and foward marketsand foward markets
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Load Schedules
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Fig 6: Load Schedules and Bus Load Forecast
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Operator Overrides
Breaker and Switch status Analog values
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Measurement Relative Confidence Values -
Zero Injection Bus 0.001
True measurement 0.01
Pseudo Measurement 0.1
Stale measurement 0 01*3K (K=SE execution Stale measurement 0.01*3K (K=SE execution count since declared stale)
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Conclusions
Pseudo Measurements used to extend SE solution to unobservable parts of the networko Derived from load predictions & generation p g
scheduleso Derived as calculations from telemetry
Operator entryo Operator entry Old measurements used to maintain
observability in the event of temporary loss of telemetry
Appropriate confidence factor weightings used to avoid corrupting states estimated from p gtelemetry data
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Questions ?
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