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Power System Voltage Control and

StabilityV. Ajjarapu ([email protected])Iowa State University

Ames, USA

Third NSF Workshop on US-Africa

Research and Education Collaboration

Abuja, Nigeria, December 13-15, 2004

TECHNOLOGY &

ENVIRONMENT

ENERGY &

EDUCATION

TECHNOLOGY &

ENVIRONMENT

ENERGY &

EDUCATION


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Outline Introduction

Aim

Educators Involved

Area of Research POWER SYSTEM SECURITY AND CONTROL An Overview

Medium of Interaction Web based

Travel

Activities Planned


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Our Department

48 faculty

Power: 4 + 2

Over 30 power graduate students Typical undergraduate power class: 50

Mainly power systems: Security and

dynamics , risk analysis, economics andmarkets

State of the art power electronics lab


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Aim

Building African collaboration with ISU

researchers to build further understanding

of different power system case studies.

Developing a roadmap for future research

activities in power / energy, information

systems technology, environmental and

social dynamics, and education pedagogy


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Educators Involved

Prof. George O. Anderson, Univ. of

Botswana

Dr. Tanimu Abubakar, Ahmadu Bello

University, Zaria, Nigeria

Dr. Venkataramana Ajjarapu (with

support from EPNES ISU faculty)

Graduate/Undergraduate Students from

these Universities


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Research : POWER SYSTEM SECURITY AND

CONTROL:

Main Area of Expertise : Voltage Stability , Oscillatory

Stability, VAR Planning and dispatch , ATC :

Sub Area: Power Electronics and Real Time Control

The group is developing a comprehensive approach for voltage

and oscillatory stability analysis and control. This group is also

actively involved in the Available Transfer Capability(ATC)

evaluation as limited by voltage as well as oscillatory stability.Reactive power requirements and pricing required for deregulated

environment. These techniques will be applied to realistic

practical power networks.


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Our Groups Research

Overview Developing techniques that are very

effective for stressed power systems

A single tool can be adapted for cost

based security with timing of controlinformation

Available Transfer Capability (ATC) is part

of this research Web Based Security Tools for Distance

Education


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Power Flow, CPF and EQTP

Conventional power flow program calculates

steady state solution for a given operating

condition.

Continuation power flow (CPF) traces a series ofpower flow solutions for a given scenario. You

can also trace the bottom of the PV curve.

Equilibrium Tracing Program (EQTP) is an

extension of CPF. DAE instead of pure powerflow equation is used to represent the power

system. It has the capability of detecting both

voltage and oscillatory instabilities.


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Security Margin Tracing

Illustration of voltage stability, oscillatory stability and damping ratio boundary

tracing

Damping ratio boundary for D= D0

Voltage stability margin boundary

Oscillatory stability margin boundary

A1A2

Predictor

Corrector

Parameter

Voltage


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Numerical results for Identification: CPF


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Example For Voltage Stability Boundary: Reactive

Power Variation

0 2 4 6 8 10 121200

1300

1400

1500

1600

1700

1800

shunt capacitance added at bus 8 (p.u.)

totalsystemloadmargin(MW)


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Optimal Margin Boundary

Tracing


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Basic Formulation

For a sequence of specified margin levels:

Minimize a cost function : f(U)

Subject to : Equality Conditions : F, G

Inequality constraints : IOptimality conditions :

Margin boundary conditions : Cobt

Results in a set of nonlinear equations of the form:

0

,...),,(

),,,,,(

),,,(

),,,(

xu

obt

hl

FfC

ssUYXI

UYXG

UYXF


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Formulation (Cont.)

The formulation could automatically generate

a whole set of cost based optimal control

configurations with each optimal control

configuration corresponding to specific

margin level that can be realized.


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Sample Result for OMBT


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Continuation Based Time

Domain Simulation


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Key Points

No divergence due to singularity of

Time step size is adjusted according to the

variation of dS/dt

Small time steps for fast dynamics and

large time steps for slow dynamics


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Trajectory Before and After a Line

Outage (with load variation)

0 20 40 60 80 100 120

0.94

0.945

0.95

0.955

0.96

0.965

0.97

0.975

0.98

0.985

time (sec)

volta

ge

ofBUS4

(p.u.)

Voltage Time Domain Trajectory


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QSS Simulation

0 50 100 150 200 2500.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

time (sec)

voltage

ofBUS4

(p.u.)

Voltage Time Domain Trajectory


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Overall Strategy

t

0 1 2 i

Scenario CredibleContingency Set

Cj{C1,C2, ,Cm}

No

No

Yes Yes

Trace Eigenvalue

for Hopf and

Damping Margin

Preventive

Control

Strategies

All Credible

Contingencies

Tested ?

Sufficient

Margin ?

j =j +1

i =i +1

Check for (A+AT)

singularity

Voltage stability margin

Oscillatory stability margin

Damping ration margin

(A+AT) singular

before SNB?

No

Yes


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Research Needs

On line monitoring :Fast calculations

Accuracy vs Speed

Timing Information: Fastvs Slow Collapse

Integration of Cost ofVoltage and OscillatoryStability Control inOverall Security

Assessment


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Optimal Strategies for Load Shedding :when, where and how much


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Capabilities at ISU

A method to quickly identifies voltage andoscillatory instability points.

The change in the instability margin

boundaries can be further obtained for any

large change in system parameters. Optimization and Time Domain Simulations

are part of Continuation Based Approach

An efficient eigenvalue tracking method isintroduced. Provides damping information

Provides eigenvalue and eigenvector sensitivity

information as a by product


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CapabilitiesCont..

Automatic PV Curve Tracing.

Field current and armature current limits are

included.

Provides true maximum power point byconsidering relevant dynamic factors.

There is no need for slack bus

Can solve unsolvable cases created by a lineor generator outages


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Capabilities Cont

Sensitivity Analysis (qualitative)

Screens the contingencies that may lead to

voltage collapse

Locates the weak areas , identifies the criticalgenerators

Provides voltage stability margin estimation


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Capabilities Cont..

Available Transfer Capability as Limited

by Voltage and Oscillatory Stability

Simulates simultaneous multi-area

transactions

Provides Transaction Sensitivity: Identifies

and ranks the transactions that are

detrimental to voltage stability Reactive power pricing /amount /location/ to

maintain voltage security


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Capabilities Cont..

Preventive and Corrective Strategies

Against the Voltage Collapse

Strategies for minimum load shedding

Strategies for under-voltage load shedding

Strategies to maintain a certain voltage

stability margin


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Capabilities Cont..

Development of Advanced Algorithms for

steady state, dynamic and time domain

simulations

A simulation engine that can allow transient

and quasi- steady state analysis

to obtain a comprehensive analysis to predict

and control instabilities When , where and how much control


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Capabilities Cont..

On Line Voltage Stability Monitoring and

Control:

Developing methodologies to utilize off line

studies for on line implementation


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Application to Botswana 32 Bus

Test System


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Botswana System (Cont..)

Demand : 243 MW

Supply

Local (coal): 128MW

ESKOM and SAPP : 115MWSimulation :

Software : Aristo (Advanced Real Time Interactive

Simulator for Training and Operation ) by ABB

Dr. Anderson applied this software for Power flow andFault analysis for 32 bus equivalent system


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Activities Planned wrt EPNES

Project (research)

Task 1: Setting up a test case for Botswana System

Task 2: Study the maximum loadability with respect

various contingencies and scenarios

Task 3: Apply margin sensitivity to find the

locations for shunt capacitors and series

capacitors

Task 4: Develop Automaton for backward algorithm


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Activities Planned (education)

Botswana group will participate in EE458

course

Develop I hour lecture material for this course


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1. Evolutionary history of the power industry; present industry structure;

2. Discrete optimization;

3. Power system operation;

4. Electricity markets;

5. Power system planning and cost-effective solutions;

6. Cost recovery for transmission investment; basics of public goodeconomics;

7. Cost-recovery models:

Tariff-based model; Performance-based model;

Market-driven model;

8. Tax treatment of transmission investments.

EE/Econ 458: Economic systems for planning in electric power

Students completing this course will be able to conduct studies in policy,

economics, & engineering associated with transmission expansion; they willenhance their skills using optimization methods for engineering & economic

problem-solving.

Will offer Fall 2004 on-campus, and via distance-education.


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Web Based

Interaction


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Characteristics

Platform (OS) Independent

Standardized System Input Files

Graphic PV Curves Output

Detailed Simulation Process Output

Margin Sensitivity


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Simulation Website

http://design-2.ece.iastate.edu/newsim/index.php
http://design-2.ece.iastate.edu/newsim/index.phphttp://design-2.ece.iastate.edu/newsim/index.phphttp://design-2.ece.iastate.edu/newsim/index.phphttp://design-2.ece.iastate.edu/newsim/index.php


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Simulation Website Cont..

Input Files IEEE Common Data Format is adopted as the

input file for power system topology andparameters

Another standardized control file is used to

specify load and generation increase scenario

Sample Test System input files are provided


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Upload Input Files


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Download Sample Systems


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Multiple Simulation Outputs

Tabular Output


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Outputs Cont..

Graphic PV Curve


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Outputs Cont..

Generator Reactive Power Output

Documents

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