ABSTRACT
In this thesis, the objective is to determine the steady state operating condition of thirteen bus Ogui-
Enugu Radial power distribution network. The steady-state was determined by finding out, for a
given set of loading conditions, the flow of active and reactive powers throughout the network, the
voltage magnitudes and phase angles at all buses of the network. This was achieved using Newton-
Raphson power flow algorithm written in MATLAB environment. A critical analysis of the
network results revealed that buses 11, 12 and 13 far away from the slack generator have voltage
magnitudes not within the acceptable voltage limits of ±6% of the declared voltage. Against this
background, a power electronic FACTS-Device currently used in the electricity supply industry for
the purpose of voltage regulation, active and reactive power flow control was installed at bus 13 to
determine how FACTS controller narrows the gap between the electromechanically controlled and
the power electronic controlled power system mode of operation. The result of the STATCOM
Newton-Raphson power flow algorithm written in MATLAB environment shows that voltage
magnitudes at buses 11, 12 and 13 fell back within the acceptable limit of ±6% of declared voltage
and eminently increased real power flow in those buses but conversely reduced the reactive power
flow in those buses specified. The result of the study gives an insight into the new opportunities
available in power semi-conductor control of power system parameters and enhancement of power
quality using FACTS- DEVICES.
TABLE OF CONTENTS
Cover page ——————————————————————————————— i
Declaration page ————————————————————————————– ii
Certification page ————————————————————————————– iii
Title Page ——————————————————————————————– iv
Dedication ———————————————————————————————- v
Acknowledgement ————————————————————————————- vi
Abstract ————————————————————————————————- vii
List of Figures —————————————————————————————– viii
List of Tables —————————————————————————————— ix
List of Abbreviations ———————————————————————————- x
Table of Contents ————————————————————————————– xi
CHAPTER ONE: INTRODUCTION
1.1 Background of the research ——————————————————————– 1
1.2 Statement of the problem ———————————————————————– 3
1.3 Objectives / Purpose of the study————————————————————– 4
1.4 Scope of the study ——————————————————————————- 5
1.5 Significance of the study ———————————————————————- 6
CHAPTER TWO: LITERATURE REVIEW
2.1 Generalities on Facts Devices —————————————————————– 7
2.2 Opportunities for FACTS DEVICES ——————————————————- 8
2.3 Basic types of FACTS DEVICES ———————————————————- 10
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2.4 Modeling of FACTS DEVICES ————————————————————- 11
2.5 FACTS Controllers Based on Conventional thyristors ———————————- 11
2.5.1 Thyristor-controlled Reactor (TCR) ——————————————————– 12
2.5.2 Static Var Compensator (SVC) ————————————————————– 14
2.5.3 Thyristor-Controlled Series Compensator (TCSC) ————————————— 15
2.6 Facts Controller Based on fully controlled Semi-conductor Devices. —————– 16
2.6.1 Voltage Source Converter. ——————————————————————- 17
2.6.2 Pulse Width Modulation Control. ———————————————————– 19
2.6.3 Principles of Voltage Source Converter Operation. ————————————– 22
2.6.4 Static Compensator (STATCOM) ———————————————————- 23
2.6.5 Solid State Series Compensator (SSSC) ————————————————— 25
2.6.6 Unified Power Flow Controller (UPFC) ————————————————— 27
2.6.7 High Voltage Direct-Current Based on Voltage Source Converter (HVDC-VSC) – 29
2.7 Choice of FACTS DEVICES —————————————————————- 31
2.8 Application of STATCOM Controller to power System Studies. ———————- 33
CHAPTER THREE: MATHEMATICAL MODELS OF CONVENTIONAL POWER
FLOW AND POWER FLOW INCLUDING FACTS CONTROLLER (STATCOM).
3.1 Methodology. ————————————————————————————- 39
3.2 General Power Flow Concepts. —————————————————————- 40
3.2.1 Basic Formulation —————————————————————————– 41
3.2.2 Variables and Bus Classification ———————————————————— 45
3.3 Power Flow Solution Methods.————————————————————– 46
3.3.1 Early Power Flow Algorithms —————————————————————- 46
3.3.2 Newton-Raphson Algorithm —————————————————————— 47
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3.3.3 State Variable Initialization —————————————————————— 51
3.3.4 Generator Reactive Limits. ——————————————————————- 51
3.4 Power Flow Model for the FACTS DEVICES (Static Synchronous Compensator) – 52
3.5 Per-Unit System. ——————————————————————————- 57
CHAPTER FOUR: ANALYSIS OF OGUI-ENUGU POWER DISTRIBUTION
NETWORK PARAMETER.
4.1 Simulation ————————————————————————————— 59
4.2 Case Study. ————————————————————————————- 60
4.3 Results and Discussions. ——————————————————————— 63
CHAPTER FIVE: CONCLUSION
5.1 Thesis Contribution——————————————————————————70
5.2 Suggestion for Further Research—————————————————————71
References ———————————————————————————————–73
Appendix1————————————————————————————————-78
Appendix2————————————————————————————————-85
Appendix3————————————————————————————————-95
Appendix4————————————————————————————————-96
Appendix5————————————————————————————————-97
Appendix6————————————————————————————————-98
Appendix7————————————————————————————————-99
Appendix8————————————————————————————————-100
Appendix9————————————————————————————————-101
Appendix10————————————————————————————————102
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Appendix11————————————————————————————————103
Appendix12————————————————————————————————-104
Appendix13————————————————————————————————-105
Appendix14————————————————————————————————-106
Appendix15————————————————————————————————-
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE RESEARCH.
Energy efficiency is an important issue in power system engineering. In fact, energy
consumption reduction and energy efficiency improvement play a key role in the world energy
policies. The main goal is to fulfill the Kyoto protocol and in order to achieve these objectives,
many regional bodies have adopted the “20/20” policy; cut the annual consumption of primary
energy by 20% by the year 2020 [1]. In Nigeria, manufacturers spend 60% of their running cost
on power [2] and this has caused the demise of many companies and relocation of hitherto
Nigerian companies like the Michelin and Lever brothers to Ghana since made in Nigeria goods
cannot compete favourably in the open market. Again, this ugly trend poses a serious threat to
Nigeria’s industrialization and her target of getting into the top 20 economies of the world by
the year 2020 would be a mirage.
Recently, many countries of the world have started to open up their electricity markets.
The deregulation of the electric power business has created many changes and challenges in the
energy sector. An industry with nearly a century record of having a completely stable price
structure imposed upon by restricted and regulated policy is now faced with a totally opposite
situation of electricity market dynamics.
Now, the industry is suddenly faced with the responsibility for many pricing decisions in an
environment that can be highly volatile. The deregulation of electric power pricing has created a
stimulus for some high quality scientific and economic research and several of these researches
focus on power quality improvement, cost, and efficiency to reflect contemporary electricity
market dynamics [3-7]. This deregulation translated into separation of generation, transmission
and distribution. Each country has its own liberalization model. The Federal Government of
Nigeria has adopted the public-private partnership (PPP) model to privatize the Power Holding
Company of Nigeria’s (PHCN’s) eleven successor distribution companies [8]. At the ultimate
phase, every sector is independent of one another and this would result in improved power
system efficiency and price decrease of the kilowatts hour (KWH), particularly for large
customers.
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The National Council on Privatization (NCP) of the Federal Government at its meeting
headed by the Vice-president Arc Mohammed Namadi Sambo on the 19th August 2010,
approved Power System efficiency improvement programs as the primary basis for the core
investor privatization of the eleven successor distribution companies of PHCN because the
present Aggregate Technical, Commercial and Collection (ATCC) losses sustained by the
various distribution companies are estimated at between 40 and 50 percent of the power
wheeled to them [9] .
Presently, the PHCN generates meager 4,000MW of electricity for a population of over 160
million people and this has plunged the country into its current abysmal socio-economic
quagmire, such that per capita electricity consumption is at its lowest of 25.00Watts compared
with South Africa’s 890Watts [10]. Now all over the world, there is a relationship between the
capacity of power and the Gross Domestic Product (GDP) of any country, it has been proven
that the nations that have higher capacity of power like the US, China and France, Germany and
Japan one can trace a very close colouration between their GDP growth and power consumption
growth.
Despite the insufficient PHCN’s 400MW generation of electricity, the distribution companies
are experiencing (40-50%) ATCC losses of the power wheeled to them and this calls for urgent
attention, thus this research work.
As a result of this undesirable inefficiency in our power sector, the electricity supply
industries are presently undergoing a profound transformation. Market forces, scarce natural
resources and an ever increasing demand for electricity are some of the drivers responsible for
such an unprecedented change. Against this background of rapid evolution, the expansion
programs of many utilities are being thwarted by a variety of well-founded, environmental,
Land use and regulatory pressures that prevent the licensing and building of new transmission,
distribution lines and electricity generating plants. An in-depth analysis of the options available
for maximizing existing transmission and distribution assets, with high levels of reliability and
stability has pointed in the direction of power electronics. Power electronic equipment and
methods have indeed formed a new technological thinking that comes under the generic title of
FACTS an acronym for Flexible Alternating Current Transmission System. There is general
agreement that novel power electronic equipment and techniques are potential complements for
conventional solution which are normally based on electromechanical technologies that have
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slow response times and high maintenance costs [11-12]. From the operational point of view,
FACTS Technology is concerned with the ability to control, in an adaptive fashion, the path of
the power flows throughout the network, where before the advent of FACTS, high-speed
control was very restricted. The ability to control the line impedance and the nodal voltage
magnitude and phase angles at both the sending and receiving ends of key
transmission/distribution lines, with almost no delay, has significantly increased the
transmission capabilities of the network while considerably enhancing the security of the
system. In this research, power flow Matlab program of Ogui-Enugu Power System Distribution
network incorporating FACTS controller model is critically analyzed to evaluate the technical
and economical benefits of a wide range of alternative solutions offered by the FACTS
technology.
In addition, suggestions will be made for further research in the field of energy efficiency
improvement.
1.2 STATEMENT OF THE PROBLEM.
In power distribution systems, unbalanced feeder structures and unbalanced loading are
normal phenomenon. Unbalanced feeders not only increase energy losses and the risk of
overloading situation, but also affect power system quality and electricity price. Unbalanced
loading causes unbalance voltages even when the voltage at source is balanced. Lower, Higher
or unbalanced voltage can cause over temperature increase on motor and that phenomenon will
decrease the life time of the motor. As a result, operating and maintenance cost for distribution
system will be increased. Relative to equipment utilization, phase balancing can extend the
useful life of a substation transformer, which is generally one of the most expensive pieces of
equipment in the circuit. The phase voltage and current unbalances are major factors leading to
extra losses, equipment overloading and mal-function of the protective relay. Consequently, the
service quality and operational efficiency of a distribution system is reduced [13-15].
Furthermore, the characteristics of a given power system evolve with time, as load grows and
generation is added. If the distribution facilities are not upgraded sufficiently, the power system
becomes vulnerable to steady-state and transient stability problems, as stability margins become
narrower.
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The ability of the distribution system to transmit power becomes impaired by one or more of
the following steady-state and dynamic limitation viz [16-18].
Angular Stability
Voltage Magnitude
Thermal Limits
Transient Stability/Dynamic Stability.
These limits define the maximum electrical power to be transmitted without causing damage to
distribution lines and electric equipment.
In a power system like the Ogui-Enugu power distribution network, electrical energy is
delivered to the ultimate consumers through a network of distribution lines. For satisfactory
operation of consumer loads, it is desirable that consumers are supplied with substantial
constant voltage because too wide variations of voltage cause erratic and malfunctioning of
power appliances and extra power losses.
1.3 OBJECTIVES/PURPOSE OF THE STUDY.
Electricity is modern society’s most convenient and useful form of energy. Without it, the
present social and physical infrastructure would not all be feasible. The increasing per capita
consumption of electricity throughout the world reflects a growing standard of living of the
people [19]. The greater the per capita consumption of electrical energy in a country, the higher
is the standard of living of its people. To reflect this global trend, the Electric Power Research
Institute (EPRI) in the US launched the Flexible Alternating Current Transmission System
(FACTS) initiative in the later 1980’s with two main objectives: To increase the power transfer
capability of electric power system and to conveniently keep voltage constant over designated
routes [20].
Without any doubt, the application of FACTS-DEVICE to Ogui-Enugu Power Distribution
Network intends to achieve the following objectives:
To determine if the voltage variations are undesirable and not within the prescribed
regulatory limit of ±6% of declared voltage.
To increase the power transfer capability of the power distribution network by
controlling the flows in heavily loaded lines resulting in an increased loadability.
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To improve the stability of the network by using power electronic FACTS-DEVICE to
keep the voltage magnitude constant at the consumers terminal. This would help to
fulfill government policy of supplying consumers with ±6% of declared voltage.
1.4 SCOPE OF THE STUDY
In its most general expression, the FACTS concept is based on the substantial incorporation
of power electronic devices and methods into the high-voltage side of the network, to make it
electronically controllable during steady-state and transient conditions [21].
Several kinds of FACTS controllers have been commissioned in various parts of the world.
The most popular are the Thyristor-Controlled Phase Shifter (PS), Load Tap Changer (LTC),
Thyristor-Controlled reactor (TCR), Thyristor-Controlled Series Compensator (TCSC),
Interphase Power Controller (IPC), Static Synchronous Compensator (STATCOM), Solid-State
Series Controllers (SSSC), Unified Power Flow Controller (UPFC), StaticVar Compensators
(SVC), High-Voltage Direct Current link (HVDC). And Hingorani’s sub synchronous
resonance (SSR) damper.
In high-voltage transmission, the most popular FACTS equipment is the UPFC and the
HVDC-VSC. At the low voltage distribution level, the SVC provides the core of the following
custom power equipment: the distribution STATCOM, the dynamic voltage restorer and active
filters. Again in distribution system, FACTS controllers based on conventional Thyristors like
TCR, SVC, and the TCSC are fast giving way for Solid-State transfer switch-controlled
thyristors like STATCOM. The STATCOM provides all the functions that the SVC can provide
but at a higher speed. It is more compact and requires only a fraction of the land for its
installation. The STATCOM is essentially a voltage source converter (VSC) using insulated
gate bipolar transistor (IGBT) interfaced to the AC system through a shunt connected
transformer. The voltage source converter (VSC) is the basic building block of the new
generation of power electronic converters that have emerged from the FACTS initiative.
It is pertinent to state that the remit/crux of this research is the study of FACTS Controller
models and procedures with which to use the most suitable FACTS controller to assess the
steady-state operation of electrical power system distribution network at the fundamental
frequency. The models of the aforementioned FACTS controllers are developed from first
principle with strong reference to the physical structure of the FACTS controller.
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Furthermore, the power system distribution network application tool is termed “Power Flow”.
And the most popular variant of the tool namely positive sequence power flow [22] is applied
since we are involved with only balanced operation.
Sequel to the above, Newton-Raphson Power flow algorithm is applied to 13 bus injection
sub-stations of Ogui-Enugu power distribution network (Conventional Power Flow) written in
MATLAB environment to determine steady-state complex voltages at all buses of the network,
from which the active and reactive power flows in every transmission/distribution line and
transformers are calculated. Again, the FACTS model is reapplied as power electronic
controller to the same Ogui-Enugu power distribution network to determine how FACTS
controller narrows the gap between the electromechanical controlled and the power electronic
controlled power system mode of operation. The result of the study gives an insight into the
new opportunities available in power semi-conductor control of power system parameters and
enhancement of power quality using FACTS devices.
1.5 SIGNIFICANCE OF THE STUDY:
In a modern powers system, there are several elements between the generating station and the
consumers. Several voltage control equipment are used at various points in the system for the
following reasons [23-24]:
The power network is extensive and there is considerable voltage drop in transmission
and distribution system
The various circuits of the power system have dissimilar load characteristics. For these
reasons, it is necessary to provide individual means of voltage control for each circuit or
groups of circuit.
In view of the above analysis, the significance of this technical research work includes:
Helping government agencies like the Nigerian Electricity Regulatory Commission
(NERC) to postulate and implement power policies like statutory limit of voltage
variation, optimization and improved power quality.
This technical research work has equally shown that power electronic high speed control
FACTS-DEVICE is a more efficient method of voltage control than the
electromechanically controlled synchronous condenser presently in use at ogui power
distribution network.
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