FAST VOLTAGE STABILITY INDEX FOR VOLTAGE STABILITY ...

FAST VOLTAGE STABILITY INDEX FOR VOLTAGE STABILITY ASSESSMENT

IN POWER NETWORK

REETHA SHAMINI A/P PACHYMUTHU

A project report submitted in partial fulfilment of

the requirements for the award of the degree of

Master of Engineering (Electrical Power)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2016

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To my beloved father, mother and sister.

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ACKNOWLEDGEMENT

In preparing this project report, I was in contact with many people, academicians,

and practitioners. They have contributed towards my understanding and thoughts. In

particular, I wish to express my sincere appreciation to my main project supervisor,

Dr. Saiful Nizam, for encouragement, guidance, critics and friendship.

I am also indebted to Universiti Teknologi Malaysia (UTM) for providing a good

platform to retrieve online journals and conference papers. Librarians at UTM also

deserve special thanks for their assistance in supplying the relevant literatures.

My fellow postgraduate students should also be recognised for their support. My

sincere appreciation also extends to all my colleagues and others who have provided

assistance at various occasions. Their views and tips are useful indeed. Unfortunately,

it is not possible to list all of them in this limited space. I am grateful to all my family

members.

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ABSTRACT

This project is conducted to assess the method which can monitor and provide an

early detection of voltage instability of the power system network. Voltage stability

assessment carried out for different operating scenarios and the status of the network

stability were monitored using FVSI index. A modified IEEE 6 bus feeder was used in

this assessment with seven different scenarios were tested in Power World software. This

scenarios includes the normal operation, contingencies and load shedding. The FVSI for

all the scenarios were compared and effectiveness of the load shedding conducted were

also assessed. A range of index threshold were determined in order to group the stability

of the network and it is a determining factor for load shedding. This FVSI index

assessment is able to monitor the status of the network pre and post load shedding.

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ABSTRAK

Projek ini dijalankan untuk menilai kaedah yang boleh memantau dan

menyediakan pengesanan awal ketidakstabilan voltan rangkaian sistem kuasa. Penilaian

kestabilan voltan dijalankan untuk senario operasi yang berbeza dan status kestabilan

rangkaian dipantau menggunakan indeks FVSI . Bas IEEE 6 yang telah diubahsuai

digunakan dalam penilaian ini dengan tujuh senario yang berbeza yang telah diuji dalam

perisian Power World. Senario-senario ini termasuk operasi biasa , luar jangkaan dan

penyisihan beban. Indeks FVSI untuk semua senario dibandingkan dan keberkesanan

penyisihan beban yang dijalankan juga dinilai. Pelbagai ambang indeks ditentukan untuk

penentuan kumpulan kestabilan rangkaian dan ia adalah faktor penentu untuk penyisihan

beban. Penilaian indeks FVSI ini dapat memantau status pra rangkaian dan pasca

penyisihan beban.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

LIST OF SYMBOLS xiv

LIST OF APPENDICES xv

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Problem Statement 3

1.3 Scope of Work 3

1.4 Objectives 3

2 LITERATURE REVIEW 5

2.1 Load Shedding 5

2.2 Types of Power Distribution Systems Design 6

2.2.1 Radial Distribution System 6

2.2.2 Ring Distribution System 7

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2.2.3 Interconnected System 8

2.3 Voltage Stability 9

2.3.1 Voltage Stability Index 10

2.3.1.1 The L- index 10

2.3.1.2 VSI index 11

2.3.1.3 SVSI index 13

2.3.1.4 FVSI index 16

2.4 Voltage stability for Radial Distribution Network 17

2.5 Voltage stability threshold value 18

2.6 Summary 19

3 METHODOLOGY 20

3.1 Introduction 20

3.2 Simulation of Scenarios 20

3.2.1 Simulation of Normal Operation Scenario 20

3.2.2 Simulation of Case Study 1 22



3.3 Implementation of Load Shedding Scenarios 27

3.3.1 Simulation of Case Study 4, Case Study 5

And Case Study 6 27

3.4 Calculation of FVSI index 30

3.5 Project Flowchart 30

3.6 Summary 32

4 RESULTS AND DISCUSSION 28

4.1 Results of the Power World Simulation 33

4.1.1 Classification of FVSI 34

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4.2 FVSI index for Scenarios 35

4.2.1 FVSI index for Normal Operation Scenario 36

4.2.2 FVSI index for Case Study 1 36



4.3 FVSI index for Scenarios Post Load Shedding 40




4.4 Comparison of Case Studies with Normal Operation

Scenario 44

4.5 Summary 46

5 CONCLUSION AND FUTURE WORKS 47

5.1 Conclusion 47

5.2 Future Work 47

REFERENCES 48

Appendix A 49

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LIST OF TABLE

TABLE NO. TITLE PAGE

3.1 Parameters for Normal Operation Scenario 22

3.2 Parameters for Case Study 1 23






4.1 Summary of FVSI index result for all scenarios 34

4.2 Grouping of branches according to FVSI threshold. 35

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Simple radial system 7

2.2 Ring distribution system 8

2.3 Interconnected system 9

2.4 Thevenin equivalent representation of load bus

connected to a power system 11

2.5 Two-bus power system model 16

3.1 Normal operation scenario in Power World 21

3.2 Case study 1 – load increase in Power World 23

3.3 Case study 2 – supply decrease & demand

increase in Power World 24

3.4 Case study 3 – supply decrease & demand

increase & line outage in Power World 26

3.5 Case study 4 – load shed of Case study 1 27

3.6 Case Study 5 – load shed of Case study 2 28

3.7 Case Study 6 – load shed of Case study 3 29

3.8 Flowchart of Scenarios Simulation and FVSI calculation 31

4.1 Graphical representation for normal operation scenario 36

4.2 Graphical representation for Case Study 1 38






4.8 Graphical representation for comparison between

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Case Study 1, Case Study 4 and Normal operation 45

4.9 Graphical Representation for Comparison between


4.10 Graphical Representation for Comparison between


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LIST OF ABBREVIATIONS

FLS - Fast Load Shed

FVSI - Fast Voltage Stability Index

IEEE - Institute of Electrical and Electronics Engineers

RED - Relative Electrical Distance

SVSI - Simplified Voltage Stability Index

UFLS - Under Frequency Load Shedding

UTM - Universiti Teknologi Malaysia

UVLS - Under Voltage Load Shedding

VSI - Voltage Stability Index

VSM - Voltage Stability Margin

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LIST OF SYMBOLS

Fji - element in row j and column i of matrix F (taken from Y bus matrix)

g - number of generator buses

n - total number of buses of the network

Qj - reactive power at receiving end

Vi - voltage at bus i or sending end voltage

Vj - voltage at bus j

Vg - voltage phasors at the nearest generator

Vl - voltage phasors at the analysed load bus

X - line reactance

Z - line impedance

[A] - matrix with size (n – g) x g

α1 - set of load buses

αG - set of generator buses

xv

LIST OF APPPENDICES

APPENDIX TITLE PAGE

A Example of FVSI calculation 41

CHAPTER 1

INTRODUCTION

1.1 Introduction

Power shortage in an electrical network is noted to be a very complex and an

undesired event. This is due to the extensive effect it brings to various parties such as the

utility companies, industrial consumers, oil and gas production, hospitals, country’s safety

and etc. The major effect of voltage collapse causing the entire system to breakdown or

also known as blackout is in terms of cost and safety, whereby it would be a humongous

loss of production to the consumers.

However, to minimize these vital effects, load shedding system is applied to ensure

the availability of electrical power to all essential and most critical loads in the network.

The load shedding scheme shall fulfill the following objectives which are to prevent

collapse of the electrical power system during insufficient power source available at the

national grid or smart grid; and it shall act fast and reduce loads according to the

availability of power source, before the electrical upset leads to overloading and protective

tripping of the remaining sources and eventually the total radial distribution network

blackout. Load shedding scheme is also prominent to minimize disturbance to the process

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of production in industries, hence, it shall shed only the amount of loads that are necessary

to compensate the power deficiency according to a pre-defined priority order quickly.

Eventually, these has raised an alarming concern on load shedding scheme which

has to be precise and rapid to respond to the unplanned events of power supply shortage

to protect the electricity power system from a total blackout. As swift respond is expected,

a real time on - line monitoring of power system stability has become an important factor

for electric power utilities. Numerous analysis method were developed and implemented

throughout the years in order to produce an effective and immediate load shed practice as

the last resort to prevent from causing further damages. An early detection indicating

unusual activities of the system’s stability is required in order for a prompt activation of

load shedding scheme. Referring to previous works, system stability detection methods

were clearly explained. There are also many studies on monitoring the system stability

which is capable to assist in load shedding scheme activation. These monitoring and

optimization methods to activate load shedding and estimate the minimum amount of

loads to be shed are for instance, Fast Load Shed (FLS), Voltage Stability Margin (VSM)

and Gravity Search Algorithm and so on. This project will analyze another real time online

monitoring method by utilizing a suitable voltage stability index such as Fast Voltage

Stability Index (FVSI). The effectiveness of this index to monitor the system’s stability

pre and post load shedding can be tested for a power system network using simulation

software Power World and Microsoft Excel. Hence, the FVSI figured from the

computational method used, it is expected to enhance the reliability and speed of load

shedding scheme.

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1.2 Problem Statement

The load shedding scheme shall act fast and reduce loads according to the

availability of power source, before the electrical upset leads to overloading and

eventually the total network blackout. A rapid respond is expected and a real time on -

line monitoring of power system stability is required to promptly detect and execute load

shedding. Thus, continuous monitoring and quick indicator of a possible system voltage

instability event is needed to kick start load shedding.

1.3 Scope of Work

The scope of work for this project involves selecting a suitable IEEE test feeder

which can be modified and allows to manipulate the reactive load demand. Computing the

FVSI index formula for the respective system is also part of this project. Besides that, the

manipulation of the reactive power demand is required in addition to the observation of

changes in FVSI index. The comparison of the outcome of FVSI method with different

operating scenarios is one of the scope of work. In addition to these, a thorough analyses

of the results and grouping of the branches according to the threshold value is required.

Finally, a conclusion of the stability status of the branches also is involved in this project.

1.4 Objectives

The first objective of this projects is to estimate the proximity to stability problems

in a power system network using voltage stability schemes. The second objective is to

locate voltage sensitive branches which would have the highest contribution towards

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voltage instability for a power system network. The third objective is to analyse variation

of FVSI index for pre and post load shedding for different operating scenarios.

1.5 Project Outline

This project report consists of five main chapters which are the introduction,

literature review, methodology, results and discussion and finally, the conclusion.

Chapter 1 of this report will concentrate on the general overview of the system

which undergoes voltage instability. This covers the problem of the system faced and the

objective of this project report which can assist it mitigation process of the problem to

occur.

Chapter 2 of this report will discuss on the literature review of the power system

network, voltage stability indices and also the load shedding system. It gives a brief

overview of each system and methods.

Chapter 3 is the methodology which gives the step by step explanation of the

modeling and simulation done in this project. It also shows the index calculation for each

scenarios.

CHAPTER 5

CONCLUSION AND FUTURE WORKS

5.1 Conclusion

In conclusion, this project is able to estimate the proximity to stability problems in

a power system network using voltage stability scheme, FVSI. Besides that, the voltage

sensitive branches which would have the highest contribution towards voltage instability

in a network was also located by following the threshold values set. This project also

analysed the effect of reactive power of the load and voltage of the source on the stability

of the network. The efficiency of FVSI to monitor and indicate the status of the system

was verified by the load shedding scenario.

5.2 Future Work

As a future recommendation, this stability assessment can be developed together

with other system such as Electrical Network Monitoring System (ENMCS), power

management scheme and others. It can also be implemented in a micro grid or smart

electrical energy network. This method can become a monitoring device of the stability

for a standalone network in a green building, home or remote area.

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1. C.Mozina, Undervoltage Load Shedding, Consultant, Beckwith Electric Co. Inc,

2. Eaton, Power Distribution Systems, retrieved from www.eaton.com/consultants,

CA08104001E, 2013.

3. A.Hamzah, Distribution System Design, Academia, retrieved from

https://www.academia.edu/9245951/Distribution_System_Design, 2015.

4. S.Perez-Londono, L.F. Rodriguez, G. Olivar, A Simplified Voltage Stability

Index (SVSI), Electrical Power and Energy Systems 63 , Page 806- 813,

Universidad Tecnológica de Pereira, Pereira, Colombia, 2014.

5. A.Ramasamy, R. Verayiah, H. I. Zainal Abidin, I.Musirin, A Study On FVSI

Index As An Indicator For Under Voltage Load Shedding (UVLS), Proceedings

of ICEE 2009 3rd International Conference on Energy and Environment,2009.

6. S.K.Nandha Kumar, Dr.P .Renuga, FVSI based Reactive Power Planning using

Evolutionary Programming, 978-1-4244-7770-8/10/$26.00 ©2010, IEEE, 2010.

7. A.J. Pujara, G.Vaidya, Voltage stabilitindex of radial disrtibution network,

Proceedings Of ICETECT , 2011.

8. M. Klaric, I. Kuzle and T. Tomisa, Simulation of Undervoltage Load Shedding to

Prevent Voltage Collapse, Faculty of Electrical Engineering and Computing,

Zagreb, Croatia.

9. I. Musirin, T.K. Abdul Rahman, New Technique for Weak Area Clustering in

Power System Network, Faculty of Electrical Engineering, Selangor, Malaysia.

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