I NTEGRATION OF S YNCHRO -P HASOR M EASUREMENTS IN P OWER S YSTEMS S TATE E STIMATION FOR E NHANCED...

INTEGRATION OF SYNCHRO-PHASOR MEASUREMENTS IN POWER SYSTEMS STATE ESTIMATION FOR ENHANCED POWER SYSTEM RELIABILITY

Hassan Ghoudjehbaklou, Ph.D.– Open Systems International, Inc.

Gary Roskos – Open Systems International, Inc.

AGENDA

• PMUs and the Smart Grid

• PMUs and the State Estimation (SE)

• Effect of PMU in Observability

• Enhancing Solutions for Unobservable Islands

• Certification Tests for SE PMU

• Conclusions – How PMUs Can Help?

APPLICATIONS OF PMUS (WIKIPEDIA)

• Power system automation, as in smart grids

• Load shedding and other load control techniques such as demand response mechanisms to manage a power system. (i.e. Directing power where it is needed in real-time)

• Increase the reliability of the power grid by detecting faults early, allowing for isolation of operative system, and the prevention of power outages.

• Increase power quality by precise analysis and automated correction of sources of system degradation.

• Wide Area measurement and control, in very wide area super grids, regional transmission networks, and local distribution grids.

PMUS AND THE SMART GRID

Phasor Measurement Units (PMUs) Provide Synchronized, Wide-Area Power Measurements

• PMUs provide the Magnitude and Angle of all power measurements at all grid locations simultaneously

• Measurements are available as frequentlyas 30 times each second

PMUS AND THE SMART GRID

Thoughtful PMU deployment is a key element to Smart Grid development at the transmission level, accomplishing these Smart Grid goals:

Increased System Reliability

• High Quality, Real-time Data• Advanced Analysis, Optimization and Controls

• Aggregate transmission operations and planning• Enhance grid security and stability (reliability)• Manage losses and congestion

• Enhanced Communications Infrastructure and Data Security

, Efficiency and Security

CURRENT EVENTS AND CHALLENGES

PMU Technology is Now Widely Available:

• PMU Devices are Readily Available From Multiple Vendors

• Open Connectivity/Interoperability via IEEE Standards

• GPS and Communications Equipment is Affordable and Hardened for Substation Use

• Utility Communications Infrastructure is Improving Daily


Multiple Active Pilot Projects and Research Programs are in Place

• Basic Research in Massive-Volume, Real-Time Data Processing and Dynamic Applications

• Basic Research in New Approaches to Grid Stability

• Strategic Deployment • Post-event analysis

• Model verification

• Data integrity and visualization


Implementation Hurdles• Device Deployment ( )

• Communications Infrastructure Deployment ( )

• Application Development - “Chicken and Egg” Problem

• Can’t Justify Applications without Data

• Can’t Justify Data Collection without Applications

SEL3306 PDC

PMU PROJECT LAB

OSI monarch EMS System

SEL 5076Sychrowave SW

OpenPMU:• Brings PMU Data Directly to

EMS• Initially, Utilize EMS

Development/QA System for Testing and Comparisons

OSI PMU IMPLEMENTATION

Visualization Tools


Early Lessons Learned (Learning)

• IEEE Standards Revisions

• Communications: Security/Redundancy/Failover

• Visualization Tool Improvements

• Troubleshooting

SRP Research with Arizona State University

• Optimal PMU positioning in electric power system – based on achieving maximum State Estimation improvement (Prof. Heydt, Vittal)

• Synchrophasor technology in validation of T-line impedance parameters (Prof. Tylavsky)

• Decision tree assisted online Security Assessment using PMU measurements (Prof. Vittal)

• Generator dynamic parameters validation (Prof. Heydt)


Current and Future SRP PMU Uses• Instantaneous State of the Electric System View

• Enhanced State Estimation (Measurement)

• Operator Visualization

• Black Start Visibility

• Line Impedance Derivation

• Disturbance Post-analysis

• Island Phase Angle Studies

PMU IMPLEMENTATION

PMU IMPLEMENTATION

PMU Observations• Will be the Most Important Measuring Device in Transmission

System Monitoring and Control

• Will Revolutionize Power Systems Monitoring and Control

• Gradual Migration Towards Full PMU Implementation for the Transmission Grid

• For Full Potential, a PMU System Must Have Communication Infrastructure Support Including Coverage and Speed to Match Streaming PMU Measurements

• WECC Synchronized Phasor Network (DMWG & WAMTF)

• NASPInet

OSI APPLICATION DEVELOPMENT

OSI is Working to Bring PMU Data into theEMS Environment to Meet Several Goals,Including:

Ease of ImplementationSolution Accuracy

Input DataSystem Models

Solution SpeedIncreased Observability

Development of Enhanced Visualization ToolsSituational Awareness

Development of Enhanced Dynamic Analysis ToolsTake advantage of a reduced solution cycle

OSI APPLICATION DEVELOPMENT

Short-term Enhancements:• Enhanced Communications Security• Enhanced Fail-over Capabilities• Enhanced Visualization Tools

Current OSI PMU-Specific Development:• Enhanced Data Access• Optimized Hybrid State Estimation• Advanced Data Archive/Historian Capabilities• Enhanced Dynamic Stability Analysis and Control• More Real-time and Historical Visualization Tools• Next-generation Data Security Tools

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PMU DEPLOYMENT STRATEGIES

Limited Deployment• Measurement and Model Improvement

• Both sides of a variable device (Phase-Shifter, LTC, DC Line, etc.)• Measurement or Visibility Problem Areas

• Interconnections

Large-Scale Deployments• Start at Highest Voltages

• Cover 500kV, then 345kV, etc.

• Grow Contiguous PMU Measurement Areas• Start at one end and work toward the other

PMU DEPLOYMENT STRATEGIES

Long-Term Goals• High-Quality, Sub-second State and

Model Measurement• System state measured, not estimated• System parameters measured, not calculated• Dynamic events detectable

• Add Applications to Capitalize on New Paradigm

PMUS AND THE STATE ESTIMATION (SE)

Effects on:• Observability• Solution accuracy for observable islands and

boundaries• Bad data detection• Solution accuracy for the unobservable

islands

TOPOLOGICAL OBSERVABILITY

Step 1: Determine the measurement islands. All islands with PMUs will have the same group/island number

Step 2: Reduce the effect of bad angle measurements (Use Median of the angles)

Step 3: All Branches within a measurement islands will have observable flows

Step 4: Enlarge the observable islands using n-1 rule recursively

Step 5: If voltage/angle of both sides of a branch are measured, add its calculated flows as pseudo measurement, for added stability and accuracy

Step 6: Change unobservable islands to observables, if all injections are measured or at most one injection is not measured

TOPOLOGICAL OBSERVABILITY

PMU Voltage/Angle Measurements

Injection Measurement

Flow Measurement

PMU measurements added to model studied by P. Katsilas, et. al. (2003)

Actual Flows

SE FLOWS (NO PMU)

SE Flows (W/ PMU)

SELECTION OF REFERENCE ANGLES FOR SE (NO PMUS)

U2

U3

U4

U1U1

U2

O1

O2

O3

O1

O2

Electric Island 1 Electric Island 2

Main ObservableIsland

Main Observable Island

ActionIn Flat start, initial angles are set to zero

ConvergenceGood convergence of SE for Observable islandsPoor convergence for unobservable islands

Accuracy of the SE solutionGood for inner observable islandPoor for close to boundariesWorst for unobservable islands

SELECTION OF REFERENCE ANGLES FOR SE (NO PMUS)

SELECTION OF REFERENCE ANGLES FOR SE WITH PMUS

U2

U3

U4

U1U1

U2

O1

O2

O3

O1

O2




SELECTION OF REFERENCE ANGLES FOR SE WITH PMUS Action

In Flat start, initial angles of the observable islands are set to the Median angles of all PMUs of that island. Initial angles of unobservable islands are set to zero.

ConvergenceGood convergence of SE for Observable islandsPoor convergence for unobservable islands

Accuracy of the SE solutionGood for inner observable islandPoor for close to boundariesWorst for unobservable islands

HEURISTIC SELECTION OF REFERENCE ANGLES FOR SE WITH PMUS

U2

U3

U4

U1U1

U2

O1

O2

O3

O1

O2




Selection of PMU Based Reference Angle for SE

HEURISTIC SELECTION OF REFERENCE ANGLES FOR SE WITH PMUS

ActionIn Flat start, initial angles of the observable islands are set to the Median angles of all PMUs of that island. Initial angles of unobservable islands are set to angle reference of the electrical island.

ConvergenceGood convergence of SE for Observable islandsBetter chance of convergence for unobservable islands

Accuracy of the SE solutionGood for observable islandGood for close to boundariesGood for unobservable islands (depends on schedules)

PMU SE CERTIFICATION DATABASES

Following slides present results for series of tests for Phasor Measurement Units (PMU) implementation in State Estimation (SE). Four different databases are considered for this study:

IEEE-14 (Power Flow solution as PMU Measurements) Large Customer no. 1 (With actual PMU

measurements) Larger Customer no. 2 (No PMU Measurements)

PMU SE CERTIFICATION TEST 1

Test 1 – Verify Observability and solvability of the PMU SE with only Phase angle and Voltage Magnitude Measurements at all buses with no other measurements. Compare the results with only bus injection measurements or only branch flow measurements.

Action Summary – All tests completed with solution matching within the tolerances

Conclusion – When all measurements are good, phase angles and voltage magnitudes provide good observability and accurate solution (This fact has been reported by other researchers as well.)


Test2 – Introduce some bad angle measurements to the cases with all phase angle and voltage magnitude measurements. Note the effect on the solution quality and convergence.

Action Summary – Initially some tests completed and bad angles detected. Later Median angle enhancement was employed for the reference angle of the measurement islands. That made all cases converge, when only few angles were bad.

Conclusion – SE solution is very susceptible to bad angle measurements (As reported by other researchers) and some heuristics should be deployed.


Test3 – Use databases with PMU measurements for the existing large customers (if the large customer does not have PMU, introduce some PMUs in the model and use phase angles from a Power Flow solution as measurement.) Verify Convergence of PMU SE.

Action Summary – Initially some tests completed when phase angles where small. Later with enhancement for large angles, all cases converged, when all angles where good. Using the enhancement of Power Flow for PMU, all cases converged and good results were obtained for the unobservable as well as observable islands.

Conclusion – Classical SE and PF need to be enhanced to handle both large and bad angle measurements..


Test4 – Verify that adding phase angle and voltage magnitude measurements actually changes observable islands.

Action Summary – To observe any change in the observable island the PMU measurements need to be close to the boundaries in the unobservable islands.

Conclusion – Not all PMUs directly impact the quality of the solution of the network. Some have more effect than the others.

CONCLUSIONS

How PMUs can help SE. Provides redundant measurement that could enhance

observability and improve quality of the solution for the observable island.

Provides angle reference for measurement islands that enhances stability and accuracy of the solution for the unobservable island.

CONCLUSIONS What Enhancements are needed for

PMU SE? Enhancing Observability algorithm for PMU

measurements. Good selection of PMU phase angles for

measurements islands. Improved heuristics for handling unobservable islands.

What Other improvements are possible for PMU SE?

Model verification (parameter estimation). Real-time State Estimation of a critical sub-network. Enhanced Visualizations.

QUESTIONS?

I NTEGRATION OF S YNCHRO -P HASOR M EASUREMENTS IN P OWER S YSTEMS S TATE E STIMATION FOR E NHANCED...

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