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HIERARCHICAL VOLTAGE CONTROL STRATEGY IN
INTERCONNECTED POWER SYSTEMS
MOHD FHIRDAUS BIN ZAINAL ABIDIN
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
JANUARY 2013
iii
To my beloved father and mother
iv
ACKNOWLEDGEMENT
Throughout the entire process of development and implementation of the project,
I was very fortunate to have a number of wonderful and experienced people who have
been giving me assistance and direction towards completing this project. First and
foremost, I would like to thanks to Allah SWT who gave me the opportunity to do my
Master studies while others still don’t get this chance. Then I would like to express
deepest gratitude to my project supervisor, Dr. Mohamed Shaaban for his advice, aid
and guidance and may Allah SWT give him rewards in Jannah.
Last but not least, I am also thankful to my family and friends who have been
praying to Allah SWT for my success and support me.
v
ABSTRACT
In interconnected power systems, voltage variation is controlled in a centralized
way which can only be done at the control centre to monitor and restore the voltage
profile in the system within the permissible value. A large power system can have a
complicated network which makes coordination a difficult task to come up with an
efficient way to maintain system voltage profile. A decentralized area control will be
developed based on the electrical distance concept with reference to the pilot bus using
the sensitivity of the reactive power and voltage in the network. A voltage control
scheme will be produced to maintain voltage profile in the decentralized control area by
using a local element; which is the transformer by optimizing the tap setting to improve
voltage profile in the system. This voltage control system will enable a better use of
existing reactive power resources. A network of 118 bus system is used as a test case.
The comparison with different implementation of the voltage control with generators
only will be analyzed. A Matlab program will simulate the voltage profile by using
Newton Raphson load flow. The impact of LTCs transformer appears by manipulating
the admittance matrix and results on improving the system voltage profile to overcome
bus voltage fluctuations.
vi
ABSTRAK
Di dalam sistem kuasa elektrik, perubahan voltan di kawal dan diawasi melalui
satu pusat kawalan sahaja. Satu pusat kawalan itu digunakan untuk memastikan nilai
perubahan voltan dapat di kembalikan kepada jumlah asal. Apabila semakin bertambah
bilangan beban di dalam sistem, penstrukturan kawalan voltan sukar mengenal pasti
kaedah terbaik untuk mengawal sistem voltan. Dengan mengunakan konsep pengagihan
pusat kawalan, iaitu berdasarkan sensitif di antara voltan dan kuasa tidak aktif. Kawalan
voltan akan mengunakan pengubahalih dengan mengubah kedudukan tempat lilitan
bertemu. Penggunaan pungubahalih dapat memaksimakan penggunaan bekalan kuasa
tidak aktif yang mana kedudukannya hamper dengan beban. Projek ini menggunakan
IEEE 118 kes data untuk melihat impak pengubahalih terhadap kawalan voltan didalam
rangka kawasan yang luas dan kompleks.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE PAGE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF FIGURES x
LIST OF TABLE xii
LIST OF ABBREVIATIONS xiii
1 INTRODUCTION 1
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Objectives 3
1.4 Scope of the Project 4
1.5 Structure of project report 4
2 LITERATURE REVIEW 6
viii
2.1 Introduction 6
2.2 Reactive power source 6
2.2.1 Generators 7
2.2.2 Transformer 8
2.2.3 Transmission Line 10
2.2.4 Loads 10
2.2.5 Reactive Power compensation devices 11
2.2.5.1 Synchronous condenser 11
2.2.5.2 Static Var Compensator 11
2.2.5.3 Static Syncronous Compensator 12
2.2.5.4 Shunt reactor and capacitor 12
2.3 Hierarchical voltage control scheme 13
2.4 Voltage control technique 15
2.4.1 Italy 16
2.4.2 Spain 17
2.4.3 Belgium 18
2.4.4 China 19
2.5 Conclusion 20
3 METHODOLOGY 22
3.1 Introduction 23
3.2 Research Flow Chart 22
3.3 Characteristic of hierarchical voltage control 23
3.3.1 Electrical distance 23
3.3.2 Zone partitioning 25
3.3.3 Pilot bus determination 27
3.3.4 Application of LTCs transformer 28
3.4 Development of voltage control scheme 29
4 RESULTS AND ANALYSIS 33
4.1 Introduction 33
ix
4.2 Case 1: Load increase at bus 67 35
4.3 Case 2: Load increase at bus 11 39
4.4 Case 3: Load increase at bus 23 and addition load bus 9 43
4.5 Case 4: Load addition at bus 38 47
4.6 Summary of results 51
5 CONCLUSIONS 53
5.1 Conclusions 53
5.2 Future work 54
REFERENCES 55
x
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Reactive power capability dependence on real power
production for a synchronous generator 7
2.2 Off-load Tap changing transformer. 9
2.3 Flow chart of voltage control system 14
2.4 Organization of Decentralized secondary voltage control 16
2.5 Hierarchical structure for transmission network voltage
control in Italy 17
2.6 Proposed reactive power management and voltage control
in Spanish electric system 18
2.7 General Diagram of the proposed hierarchical voltage control
for the network of Belgium 19
2.8 Physical structure of china hierarchy voltage control 20
3.1 Transformer Equivalent circuit 28
3.2 Flow chart of voltage control scheme development 29
4.1 Adjustment of load bus 67 35
4.2 Tap changer unit 4, 5 and 6 adjustments 36
4.3 Comparison of system voltage profile before control and
xi
after control 37
4.4 Comparison of LTCs transformer and generator application in
voltage control scheme 38
4.5 Adjustment of load bus 11 40
4.6 Tap changer unit 1, 2 and 3 adjustment 40
4.7 Comparison of system voltage profile before control
and after control 41
4.8 Comparison of LTCs transformer and generator application in
voltage control scheme 42
4.9 Adjustment of load bus 23 and bus 9 43
4.10 Tap changer unit 9 adjustment 44
4.11 Comparison of system voltage profile before control
and after control 45
4.12 Comparison of LTCs transformer and generator application in
voltage control scheme 46
4.13 Adjustment of load bus 38 47
4.14 Tap changer unit 2, 3 and 4 adjustments 48
4.15 Comparison of system voltage profile before control
and after control 49
4.16 Comparison of LTCs transformer and generator application in
voltage control scheme 50
xii
LIST OF TABLE
TABLE NO. TITLE PAGE
4.1 Information of Transformers 33
4.2 Partition of 118 bus system 34
4.3 Reactive power allocation 35
4.4 Zone and bus affected 36
4.5 LTCs engagement to restore voltage profile 37
4.6 Comparison between system voltage before and after control 38
4.7 Comparison between generator and LTCs transformer
application results 39
4.8 Zone and bus affected 40
4.9 LTCs engagement to restore voltage profile 41
4.10 Comparison between system voltage before and after control 42
4.11 Comparison between generator and LTCs transformer
application result 43
4.12 Zone and bus affected 44
4.13 LTCs engagement to restore voltage profile 45
xiii
4.14 Comparison between system voltage before and after control 46
4.15 Comparison between generator and LTCs transformer
application result 47
4.16 Zone and bus affected 47
4.17 LTCs engagement to restore voltage profile 48
4.18 Comparison between system voltage before and after control 49
4.19 Comparison between generator and LTCs transformer
application result 51
xiv
LIST OF ABBREVIATIONS
SVC - Secondary Voltage Control
PVR - Primary Voltage Regulator
LTCs - Load Tap Changers
TVC - Tertiary Voltage Control
STATCOM - Static Syncronous Compensator
DC - Direct Current
TCR - Thyristor Control Reactor
TSC - Thyristor Switch Capacitor
CSVC - Coordinated Secondary Voltage Control
DSVC - Decentralized Secondary Voltage Control
AVR - Automatic Voltage Regulator
TSO - Transmission System Operator
SVR - Secondary Voltage Regulator
CHAPTER 1
INTRODUCTION
1.1 Introduction
In interconnected power system, the large system give the coordinator in the
control system, difficulty to implement voltage control in the system because of the
complexity of the system [1]. All equipment used in power systems are rated for a
certain voltage with a permissible band of voltage variations. Voltage at various buses
must be controlled within specified regulation figure [2]. The real power demanded by
the load must be equal to the real power produced. Practical loads are consume reactive
power and the reactive power demand may exceed the fixed value which will causes the
receiving end voltage to varied to meet the reactive power demand. Thus a reactive
power was related to the receiving end voltage. To maintain the receiving end voltage
within its tolerance value, a fixed amount of reactive power must be produced from the
line.
Voltage control is intended to compensate for voltage and reactive power
demand disturbances in order to maintain a proper voltage profile along the network. A
decentralized area will be developed based on the electrical distance with reference of
pilot bus using the sensitivity of the reactive power and voltage in the network [3].
Currently, there are three level model of voltage control in interconnected power system,
first the primary voltage control in which the controller will get the voltage profile of the
2
network and will provide an automatic control with the closed loop design. Normally,
the generating will become the primary source of controlling voltage by adjustment
excitation of the generator. Then, secondary voltage control which gets the voltage
profiles of the network in the small scale of area by finding the voltage in the pilot bus.
The controlling method will be developed by the sources of reactive inside the control
area or local area.
The network is divided into control areas that are semi-independent or at least
have no effect on the adjoining areas and the voltage plan of each of them is fixed and
controlled by acting in a coordinated way on control equipment available and on the set
point voltage of the generators in operation. This action is performed on a "pilot" point
of the area which should be representative of the change in voltages throughout the area
[4]. Lastly is tertiary optimization in which the operator of the system tries to optimize
the voltage profile and provides for the reference value of secondary voltage control [5-
7]. This project will focus on the secondary voltage control; whereby the controlling
will be at the local area. Secondary voltage control practices in many power utilities
aims to maintained voltage magnitude within the required band [8]. The monitoring and
optimizing of the voltage stability margin has not commonly been associated with the
routine secondary voltage controls [9]. The secondary voltage control applications rely
on the automatic/manual control of individual secondary voltage control devices.
The automatic operation of LTCs, an important secondary voltage control
device, has been known as a potential source of deterioration of the voltage stability
margin [10]. The conventional manual control operations of reactive sources are
performed based on the operator’s past experience or rigid operation manual. When a
system encounters disturbances under stressful conditions, fast and regionally
coordinated control decisions need to be made within limited time frame. The design of
a hierarchical voltage control system strategy is important to mitigate the impact of
disturbances on power system stability.
3
1.2 Problem Statement
To control the voltage variation in interconnected power system, there were three
stages of monitoring and control which is primary voltage control whereby the voltage
control is set by the generation in the system but the problem was when there was a
remote bus that far from the generating resource, there will be reactive power losses
during transmission of energy. By conducting the hierarchical voltage control strategy
to include the secondary voltage control which is to coordinate the reactive power
sources within the area in interconnected power system.
A number of load tap changers (LTCs) are available to regulate distribution
network voltages. LTCs operations cause transients and wear on the LTCs themselves.
Therefore, it is desirable to minimize the number of tap operations. Traditionally, LTCs
control is based entirely on local measurements with no coordination between different
voltage levels or branches of the network. Since there are many cascaded tap changers,
this gives rise to unwanted effects. For example, tap operations in different levels or
branches of the networks might counteract one another and the short spikes will occur
due to counteracting tap operations.
1.3 Objectives
The objectives of this project have been classified as follows:
i. To identify the impact of LTCs Transformer on voltage variation and control
in the transmission line.
ii. Comparison of LTCs Transformer and Generator in term of efficiency of
controlling voltage in interconnected power system.
4
iii. Simulate the voltage control during overload by adding load and increasing
the load
1.4 Scope of Projects
Before doing any analysis and simulation setup, literature review is needed to
provide a good theory and understanding. The input knowledge can be obtained from
various resources such as books, journals, internet, and papers. This project is primarily
focused on developed decentralize voltage control by partition it into several area in
interconnected power system.
After the mathematical model of voltage control has been developed, the system
will be tested on the IEEE 118 bus interconnected power system, the simulation will be
conducted by using MATLAB and the data will be collected. The data approximately
will show the bus that will be affected for the voltage variation and the reactive
compensation coordination strategy will be implementing to the voltage control system.
1.5 Structure of project report
Chapter 1: This chapter described the introduction of voltage control in
interconnected power systems and importance of voltage control. In addition to that, it
provides introductory explanations about problem statement, project objectives and
scope of project.
Chapter 2: A review of the literature in the previous research is presented in this
chapter, which includes the reactive power resources and the implementation technique
in voltage control from several utilities.
5
Chapter 3: This chapter describes the methodology of this project. The steps and
procedure to develop the voltage control scheme and its characteristics will be discussed.
Chapter 4: This chapter discusses and analyzes the result of voltage control scheme
implementation on the test system.
Chapter 5: The project is concluded in this chapter. Recommendations for future
works were also discussed in this chapter.
55
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control objectives," Doctorate of Philosophy, Electrical and Computer
Engineering, Georgia institute of technology, Georgia, 2009.
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ETH Zürich, 2006.
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System Under Coordinated Secondary Voltage Control," in 14th PSCC-Power
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56
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