ABSTRACT
Power system network is designed to operate in a prescribed voltage and frequency for stability
and for better power quality. Unexpected contingencies leads to instability related problems in
the system. This research develops a sensitivity index based technique with contingency
analysis for Unified Power Flow Controller (UPFC) placement for Nigeria 330kV power
transmission system. The research employed Newton Raphson power flow method considering
multiple contingency analyses which include double line outages, line and load outages, double
load outages and load increments. The identification of the severity of the violated bus voltages
was achieved through the use of Active Power Performance Index (APPI) and Reactive Power
Performance Index (RPPI). The contingency cases were addressed through the sizing and
placement of UPFC on the network and simulated in Matlab R2013a environment. The analyses
shows that the predominately violated buses and the sizes of the UPFC placed are Maiduguri
bus (-183 MVar), Birni Kebbi bus (99 MVar) Oshogbo bus (-84MVar), Jos bus (-28 MVar),
Gombe bus (-13 MVar) and Kano bus (21 MVar). The result shows 1.3% (694.6233MVar)
reduction in the total reactive power loss as compared with base case of (703.7499MVar) after
the placement of UPFC and a total voltage improvement of 3.11% (31.9298pu) as compared to
the base case voltage deviation of (32.9541pu). The developed approach was analyzed on IEEE
30 bus network with a transmission line power loss reduction of (0.00166pu) and a voltage
improvement of 0.83% (30.6753pu) as compared to the work of Reddy et al., (2014) with power
loss of (0.02116pu) and a voltage of (30.4214pu).
TABLE OF CONTENTS
DECLARATION i
CERTIFICATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
TABLE OF CONTENTS vi
LIST OF FIGURES xi
LIST OF TABLES xii
LIST OF ACRONYM xiii
TABLE OF CONTENTS
CHAPTER ONE: INTRODUCTION
1.1 Background of the Study 1
1.2 Significance of Research 3
1.3 Statement of Problem 4
1.4 Aim and Objectives 5
1.5 Methodology 5
1.6 Scope of the Research 6
1.7 Research Outline 7
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction 8
viii
2.2 Review of Fundamental Concept 8
2.2.1 Electrical Power System 8
2.2.2 Transmission line network 9
2.2.3 Power System Stability 13
2.2.3 Power System Operating States 14
2.3 Power System Buses 15
2.4 Power Flow Studies 16
2.4.1 Power Flow Methods 16
2.4.2 Newton-Raphson iterative method 17
2.4.3 Algorithm for Newton Raphson Method 22
2.5.1 Contingency Selection 24
2.5.2 Performance Index 24
2.6 Conventional Methods to Regulate Voltage 28
2.6.1 Flexible AC Transmission Systems (FACTS) devices 29
2.6.2 Types of FACTS Controllers 20
2.6.2 The role of FACTS controllers in power system operation 33
2.6.3 FACTS Controllers 34
2.7 Line Loadability 37
2.7.1 Maximum Loadability Formulation 38
2.8 Nigeria Network Description 39
ix
2.8.1 Nigeria 330kV 30 Bus Transmission Network 40
2.3 Review of Related Works 42
CHAPTER THREE: MATERIALS AND METHOD
3.1 Introduction 49
3.2 Materials 49
3.2.1 Simulation platform 49
3.3 Methodology 50
3.3.1 Power Flow Analysis 49
3.3.2 Contingency Analysis 51
3.2.3 Contingency Selection 51
3.2.4 Sensitivity Index 53
3.2.5 Analysis of the proposed method 53
3.2.6 Performance Evaluation 53
CHAPTER FOUR: RESULT AND DISCUSSION
4.1 Introduction 55
4.2 Nigerian Transmission Network 55
4.2.1 Pre-contingency Analysis (Base Case) 55
4.2.2. Contingency Analysis 55
4.2.2.1 Case 1: Line Outage Contingency Analysis 56
4.2.2.2 Case 2: Line and Load Outages Contingency Analysis 60
x
4.2.2.3 Case 3: Load Increment Contingency Analysis 64
4.2.2.4 Case 4: Load Outage Contingency Analysis 68
4.2.3 Priority Load 72
4.3 Validation 72
4.3.1 Validating with the Base Case Voltage 72
4.3.2 Validating with the work of Reddy et al., (2014) 74
CHAPTER FIVE: SUMMARY, CONCLUSION AND RECOMMENDATION
5.1 Introduction 77
5.2 Conclusion 77
5.3 Significant Contributions 78
5.4 Recommendations 78
References 79
Appendix 82
CHAPTER ONE
INTRODUCTION
1.1 Background To The Study
An electric power system is a network of electrical components deployed to supply, transfer, and
use electric power (Pai, 2012). Electric power system is design for efficiency, reliability, ease of
operation, and to meet consumer needs at minimum cost. Power system stability refers to that
property of the power system which enables the system to maintain an equilibrium operating point
under normal conditions and to attain a state of equilibrium after being subjected to a disturbance
(Aman et al., 2014).
Power systems are subjected to a wide range of small or larger disturbances during operation.
Small disturbances are changes in loading conditions which occur continually. Small or larger
disturbances could be faults, load changes, generator outages, line outages, voltage collapse or
some combination of these. The power system must adjust to these changing conditions and
continue to operate satisfactorily and within the desired bounds of voltage and frequency. The
power system should be designed to survive both small and large types of disturbances (Tziouvaras
& Hou, 2004).
One of the key concerns in transmission of electricity is power loss in transmission lines often
referred to as line loss or transmission loss which is dissipated as heat due to the resistance of the
conductors. The smaller the surface area of the conductors, the smaller the loss due to heat
dissipation, hence, high voltages require less surface area, resulting in reduced line loss. With highvoltage
lines, the voltage can be stepped up at the generating station, transmitted through the
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transmission grid to a load center, and there stepped down to the lower voltages required by
distribution lines (Bergen, 2009).
Secure operation of power systems have become a critical issue nowadays, as they are heavily
loaded and are being operated in ways not been originally designed (Kavitha & Neela, 2016).
Security is a term used to reflect a power system’s ability to meet its load without unduly stressing
its apparatus or allowing variables to stray from prescribed range under certain contingencies
(Rohini et al., 2015). Moreover any of the unexpected contingencies may collapse the system
suddenly. To overcome this situation it is essential to have the study of contingency analysis and
to trace the critical contingencies in advance; so that necessary supporting FACTS devices can be
installed (Kavitha & Neela, 2016). In order to provide proper security in power system during
contingencies FACTS devices is widely used.
Since, power system operation is affected by stability related problems, leading to unpredictable
system behavior, FACTS technology opens up new opportunities for controlling power and hence,
enhancing the usable capacity of transmission lines. The possibility that current through a line can
be controlled enables a large potential of increasing the capacity of existing lines with larger
conductors, and use of one of the FACTS Controllers to enable corresponding power to flow
through such lines under normal and contingency conditions (Zhang et al., 2012). UPFC is a
versatile FACTS device. The choice of this FACTS device in this research is due to its capability
of providing active, reactive and bus voltage control under normal and network contingencies
conditions without violating the operating limits. Since UPFC can be installed in different
locations, its effectiveness will be different; hence, it is highly important to determine the optimal
location of this device in the power system for voltage stability margin improvement, increase in
power transmission capacity and for power blackout prevention (Shaheen et al., 2011).
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Power flow analysis which is the backbone of power system analysis and design is necessary for
planning, operation, economic scheduling and exchange of power between utilities (Wane &
Verma, 2013). The principle of power flow analysis is to find the magnitude and phase angle of
voltage at each bus and the real and reactive power flowing in each transmission lines. The
conventional techniques used for solving the load flow problems are iterative. These techniques
are Newton-Raphson (NR), Gauss-Seidel (GS) and Fast Decouple Newton-Raphson (FDNR)
methods. These techniques are difficult and take a lot of time to perform hence, MATLAB R2013
programming software is used for solving problem speedily.
Contingency analysis and selection for the placement of this FACTS device is performed using
Newton-Raphson and two kinds of performance indices namely, active power performance index
and reactive power performance index respectively. Hence, the impacts of this FACTS placement
to mitigate power losses and to increase loadability during these contingencies are investigated on
Nigerian 330kV transmission network.
1.2 Motivation
Electrical power system is expected to be stable and reliable at all times. Violations of bus voltages
arising as a result of equipments straying from its operating limit due to disturbance in form of
outage of lines, outage of generators and load variations is a major concern in power system. The
reason of incorporating FACTS devices (UPFC) into power system network with contingencies is
for voltage stability and a mean to increase the line loadability thereby making the system stable
and reliable. APPI and RPPI are sensitivity indices used in the selection and ranking of the
violated voltage buses. The impact of the UPFC creates voltage stability and increase in the line
loadability of the network.
1.3 Statement Of Problem
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Multiple contingencies describe a set of single contingencies which occur one at a time that is; the
outage of equipment could spur to the outage of another on the same network. Multiple
contingencies related problems on power system such as sudden drop or addition of heavy load or
line outages can violate the power quality constraint of the network. In cases of sudden load
variations, the system is considered insecure and the loadability of the network is severely affected.
Several literatures have been reviewed to shows different techniques carried out for solving and
analyzing contingency on power system network through the placements of FACTS devices. Due
to the limitations attached to some of these methods is the reason for the choice of sensitivity
indices used in this research. APPI and RPPI used in this research help to quantify and rank the
contingency identified according to the level of their severity. The ranking from the indices was
used for the placement of the UPFC to mitigate the effects of the contingencies hence, reducing
the degree of the line overload and stabilizing the bus voltages of the network.
1.4 Aim And Objectives
The aim of this research is to develop a sensitivity index based technique for the placement of
UPFC with contingency analysis on Nigerian 330kV transmission network.
The objectives of the research are to:
i. Adopt Newton Raphson power flow algorithm for power flow analysis on Nigerian
330kV transmission network.
ii. Implement sensitivity index based technique for UPFC placement with contingency
analysis on the Nigerian 330kV transmission network.
iii. Make a comparative assessment of the result of the proposed method with that of the
work of Reddy et al., (2014) in term of voltage profile.
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1.5 Methodology
The methodology used to carry out this research work is as follows:
i. The adoption of Newton Raphson method for power flow analysis.
ii. Implementation of a sensitivity index based technique for contingency ranking and
for determination of UPFC device placement using APPI and RPPI.
iii. Implementation analysis of the proposed method is performed on Nigerian 330kV
transmission network to improve the network voltage profile and the lines transfer
capabilities.
iv. Comparison of the result of the proposed method with that of the work of Reddy et
al., (2014) using charts of voltage profile.
1.6 Significance Of Research
The significance of this research is to analyze a sensitivity index based technique for the placement
of UPFC with contingency analysis on Nigerian transmission network. The placement of the UPFC
will help in the improvement of the performance of the power system by mitigating voltage
instability arising from various forms of disturbances and in the increment of the network line
transfer capability. Although, most of the placements of these FACTS has been majorly considered
by researchers in networks under single line contingency to improve the power quality of the
network, hence, most of these research works considered the uniformly distribution of load
ignoring the presence and location of priority load in the network which this research seeks to
considered.
1.7 Scope And Limitation Of The Research
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This research covers the development of sensitivity index for the placement of UPFC with
contingency analysis on Nigerian 330kV transmission network. The various contingency
considered in this research includes the line outages, load outages, line and load outages and load
increment. The placement of UPFC on the network helps to mitigate the effect of the contingency
on the bus voltages. Hence, the voltage profile improvement results to an increase in the line
loadability of the network. However, the contingency analysis performed in this research did not
investigate the extreme of contingency which could involve the outage of generators leading to
blackout in the network.
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