HIERARCHICAL VOLTAGE CONTROL STRATEGY IN...

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

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To my beloved father and mother

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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.

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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.

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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.

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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

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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

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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

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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

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after control 37

4.4 Comparison of LTCs transformer and generator application in

voltage control scheme 38


4.6 Tap changer unit 1, 2 and 3 adjustment 40

4.7 Comparison of system voltage profile before control

and after control 41



4.9 Adjustment of load bus 23 and bus 9 43

4.10 Tap changer unit 9 adjustment 44






4.14 Tap changer unit 2, 3 and 4 adjustments 48





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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





application result 43



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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

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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.

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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.

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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.

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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.

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[2] Y. Song, "Design of secondary voltage and stability controls with multiple

control objectives," Doctorate of Philosophy, Electrical and Computer

Engineering, Georgia institute of technology, Georgia, 2009.

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ETH Zürich, 2006.

[4] F. A. B. Lemos, et al., "Assessment of a Sub-Transmission and Distribution

System Under Coordinated Secondary Voltage Control," in 14th PSCC-Power

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[5] M. Shahidehpour and Y. Wang, Communication and control in electric power

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[20] O. A. Mousavi and R. Cherkaoui, "Literature Survey on Fundamental Issues of

Voltage and Reactive Power Control," power, swiss federal institute of

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Automatic Zone Partitioning," International review of electrical engineering,

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