FAST VOLTAGE STABILITY INDEX FOR VOLTAGE STABILITY ...
Transcript of 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
3.2.3 Simulation of Case Study 2 24
3.2.4 Simulation of Case Study 3 25
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
4.2.3 FVSI index for Case Study 2 38
4.2.4 FVSI index for Case Study 3 39
4.3 FVSI index for Scenarios Post Load Shedding 40
4.3.1 FVSI index for Case Study 4 41
4.3.2 FVSI index for Case Study 5 42
4.3.3 FVSI index for Case Study 6 43
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
3.3 Parameters for Case Study 2 25
3.4 Parameters for Case Study 3 26
3.5 Parameters for Case Study 4 28
3.6 Parameters for Case Study 5 29
3.7 Parameters for Case Study 6 30
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
4.3 Graphical representation for Case Study 2 39
4.4 Graphical representation for Case Study 3 40
4.5 Graphical representation for Case Study 4 42
4.6 Graphical representation for Case Study 5 43
4.7 Graphical representation for Case Study 6 44
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
Case Study 2, Case Study 5 and Normal operation 45
4.10 Graphical Representation for Comparison between
Case Study 3, Case Study 6 and Normal operation 46
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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
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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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Index As An Indicator For Under Voltage Load Shedding (UVLS), Proceedings
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