PS ERC DISTRIBUTED STATE ESTIMATION A. P. Sakis Meliopoulos Georgia Power Distinguished Professor School of Electrical and Computer Engineering Georgia Institute of Technology IEEE-PES – Greek Chapter, May 2007 Atlanta, Georgia 30332 1
Outline PS ERC • Background Data • Limitations of Traditional SE • Distributed State Estimation/SuperCalibrator • Implementation and Demonstration • Next Step: System Wide Implementation • Future Applications 2
The Electric Power Grid PS ERC Recognition: The Power Grid is a Critical Infrastructure Vulnerabilities Resulting from System Complexity Vulnerabilities Resulting from Severe Weather Vulnerabilities from the Cyber Space Vulnerabilities from Fuel Supply Lines 3
Power Grid Vulnerability PS ERC What Did We Learned from Blackouts? 1965: Relay Mis-operation/Lack of Real Time System Info 1989: Vulnerability From Solar Storms 2003: Lack of Situational Awareness/Relay “mis-operation” or “Zone 3: Yes or No” 2005: Dynamic Interactions of Electric Loads Etc. Etc. 4
Power Grid Vulnerability PS ERC Consensus: Real Time Knowledge of the Operating Conditions of the Grid Drastically Contributes to Grid Security 5
Basic Operational Tool PS ERC August 14, 2003 Report : Lack of Situational Awareness Power Grid Visibility Basic Tools: SCADA (unfiltered) and SE (filtered) The objective of SE is to provide a reliable real time model How well is it done? Historical performance of SE suggests an Average reliability of 95% Is this performance acceptable? Is this performance acceptable? 6
Motivation: Present Operating Model PS ERC Real Time Model State Estimation Applications Load Forecasting Optimization (ED, OPF) VAR Control Available Transfer capability Security Assessment Congestion management Dynamic Line Rating Transient Stability EM Transients, etc. Visualizations Markets: Day Ahead, Power Balance, Spot Pricing, Transmission Pricing (FTR, FGR), Ancillary Services 7
Traditional State Estimation PS ERC Power System SE: Basic Assumptions • Positive Sequence Model • P, Q, V measurement set • Near-Simultaneous Measurements • Single Frequency Implications: • Balanced Operation • Symmetric Power System • Biased SE • Iterative Algorithm 8
PS ERC Errors from Imbalance and Asymmetry 9
Bus Voltage Magnitude and Phase Errors – Estimated minus Measured Value Magnitude is Normalized, Phase is Magnified 100 times PS ERC Measurement Data: Phase A Only Displayed Data: Phase A Max magnitude error: 0.006 pu Phase error: (-0.110 to 0.096) Example of Imbalance Bias Measurement Data: Phase A Only Displayed Data: Phase B Max magnitude error: 0.018 pu Phase error: (-0.360 to 0.329) 10
Instrumentation Errors: PS ERC Voltage Measurement Example Voltage Measurement IC Substation A, 115 kV Bus Van = 62.53 kV / 27.52 Deg Van = 62.19 V / 27.51 Deg Van = 61.63 V / 27.11 Deg Vbn = 62.96 kV / -92.68 Deg Vbn = 62.61 V / -92.70 Deg Vbn = 63.09 V / -92.85 Deg Vcn = 62.33 kV / 147.46 Deg Vcn = 61.99 V / 147.45 Deg Vcn = 61.72 V / 148.00 Deg NORTHBUS3 NBUS3M S NBUS3M SI RG-8 Cable, 500 ft Phase A Magnitude Error: 1.46% Phase A Magnitude Error: 1.46% Phase A Phase Error: 0.41 degrees Phase A Phase Error: 0.41 degrees 69kV:69V Wound Type VT 11
Elimination of State Estimator Biases PS ERC Eliminates Model Biases (Full Three-Phase Model with Neutrals, etc.) Eliminates Imbalance Biases (Three Phase Measurements) Biases From Instrumentation Channel Errors (Augment Model with Instrumentation) Robustness (Model Quadratization) 12 12
Keeping Things in Perspective… PS ERC (a) SCADA Transducers: 1 to 3% (b) Modern Relays: 0.1 to 1% (c) GPS-Synchronized Equipment: Magnitude 0.1% to 1%, Phase: 0.01 to 0.05 Degrees at 60 Hz. (Systematic Errors Can Be Easily Accounted for) (b) System Asymmetries (4 to 6% differences among phases) (c) System Imbalance (0 to 12% among phases – based on personal observations) (d) Instrumentation Channel Errors (0.02 to 3%) 13
The SuperCalibrator Concept PS ERC The SuperCalibrator is conceptually very simple. The basic idea is to provide a model based error correction of substation data and in particular RELAY DATA. The SuperCalibrator is facilitated by the substation automation technology that makes all substation data readily accessible at a common point. The basic idea is to utilize a detailed model of the substation, (three-phase, breaker-oriented model, instrumentation channel inclusive and data acquisition model inclusive). Then all substation data obtained with any device, PMU, meter, relay, SCADA, etc. is expressed as a function of the state of the detailed substation model. An estimation algorithm determines the best estimate of the substation model state. GPS Synchronized Relays Make the Process Robust and the Results Globally Valid 14
Important Point PS ERC GPS-Synchronized Measurements Make it Possible to “Distribute” the State Estimation Process The Results of a Local State Estimator Are “Globally” Valid if There is at Least One Valid GPS-Synchronized Datum 15
The SuperCalibrator Concept PS ERC IED Vendor D Measurement Layer Phase Conductor i(t) LAN Processing Current Relay v(t) Transformer Vendor C Data Transformer Attenuator Instrumentation Potential PMU i 1 (t) i 2 (t) Burden Vendor A Super- Cables Calibrator Attenuator Anti-Aliasing Filters LAN v 2 (t) v 1 (t) PMU Vendor C Burden • Three-Phase Power System with Explicit Instrumentation Channel Model • Use Dynamic SE to Filter Phasor Data • Maintain Streaming Data and Visualizations Parallel Important Activities: Substation Automation 16
PS ERC SuperCalibrator Demonstration Implementation 17 &
High Fidelity Power System Model PS ERC • Physically Based Power System Modeling • Explicit Representation of Phase Conductors, Neutrals, Ground Conductors and Grounding – accounts for ground potential rise • Explicit Representation of Breakers, Switches • Explicit Representation of Instrumentation and Relay Inputs Integrated with the Power System • Solver Based on the Quadratized Model (improves robustness) • Visualization and Animation 18
High Fidelity Power System Simulator PS ERC Physically Based Models Example: Three Phase Power Line – MSU1 Sequence Parameter Model Physically Based Model Not Used – for Info Only 19
High Fidelity Power System Simulator PS ERC Instrumentation Channel Model BUS115A BUS115A A/D Converter A/D A/D PTOUT Control Cable, RG-8 VCHINPUT VADOUT CTBUS CCHINPUT CADOUT T, 66.4kV:115V IC Animator V V Voltage Meter Voltage Meter V V Current Voltage ( ) ( ) ~ ~ ( ) I f ( ) V f = = out g f out g f ( ) ~ ( ) ~ j , i j , v I f V f in in 20
~ ~ PS ERC V 1e V 2e ~ ~ State Definition V 1s V 2s Substation ~ ~ Definition of State for a Substation V 4e V 3e ~ ~ ~ ~ ~ V 1 V , V , V , V Vector of dimension 4: 1 , 1 , 1 , 1 , s a s b s c s n s ~ ~ ~ ~ ~ V 2 V , V , V , V Vector of dimension 4: 2 , 2 , 2 , 2 , s a s b s c s n s ~ ~ ~ ~ ~ V 1 V , V , V , V Vector of dimension 4: 2 , 2 , 2 , 2 , e a e b e c e n e … … … ~ ~ ~ ~ ~ V 4 V , V , V , V Vector of dimension 4: 4 , 4 , 4 , 4 , e a e b e c e n e 21
~ V R PS ERC Pseudomeasurements for ~ Voltages at Next Substation I R ~ i e ~ I S n i Given L V S Measurements if V S and I S of Line I at Substation k Substation k Given Line i 3-Phase Model ~ ~ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤ Y Y I V = 11 12 ⎢ S ⎥ ⎢ S ⎥ ⎢ ⎥ ~ ~ ⎣ ⎦ Y Y ⎣ ⎦ ⎣ ⎦ I V 21 22 R R ~ V Compute Pseudomeasurement R ( ) ( ) ~ ~ ~ − − = − + − 1 1 pseudo , m V I Z Y Z I I Z Y Z Y V 22 22 21 S 22 22 22 21 S R − 1 ⎡ ⎤ ⎡ ⎤ Z Z Y Y = 11 12 11 12 ⎢ ⎥ ⎢ ⎥ Where: ⎣ ⎦ ⎣ ⎦ Z Z Y Y 21 22 21 22 22
PS ERC ~ ~ I 4 I 1 ~ ~ I 5 I 6 Pseudomeasurements from Kirchoff’s Current Law Substation ~ ~ I 3 I 2 ∑ ~ = General k I 0 , k : kV level ~ ~ ~ + + = Three equations, one for each phase I I I 0 For the above example: 1 2 6 ~ ~ ~ + + = I I I 0 Three equations, one for each phase 3 4 5 ( ) ( ) ~ ~ ~ ~ + + + = k I I k I I 0 Three equations, one for each phase 1 3 4 2 1 2 23
Pseudomeasurements for Shield/Neutral Wires PS ERC s/n a b c Given Line Model, compute ratio of s/n current over return current: ~ I α = ( ) s / n ~ ~ ~ − + + I I I a b c Then introduce pseudomeasurement: ( ) ~ ~ ~ ~ = α − + + pseudo , m I I I I a b c s / n 24
Phase Pseudomeasurements PS ERC (if measurement of a phase is missing) By Example: • Assume phase A voltage measurement exists • Assume phase C voltage measurement does not exist ~ ~ − = 0 , 240 pseudo m j V V e a s / n 25
Non-GPS-Synchronized Measurements PS ERC By Example: ~ ~ ~ m m m V , V , V Given : a b c ~ ~ ~ α α α j j j V e , V e , V e Replace by: a b c ~ ~ ~ m m m I , I , I Given : a b c ~ ~ ~ β β β j j j I e , I e , I e Replace by: a b c If V and I measurements from same IED: ⇒ α = β 26
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