As the demand of electricity from an already congested network increases, ensuring voltage stability across the network becomes challenging. One approach in ensuring system stability is to attain system redundancy but their economic and ecological limitations to this. A more cost effective means would involve the use of existing network component and incorporate less expensive scheme and policies to maintain reliable system operation. Flexible alternating Current Transmission System (FACTS) such as the Unified Power Flow Controller (UPFC) are devices incorporated to achieve improvement in overall system performance such s increasing transmission line flows, minimizing losses, and improving voltage profile across the network buses.
Table Of Contents
Approval Page Vi
Table of Contents Xi
List of Figures Xiii
List of Tables Xiv
1.1. Background 1
1.2. Statement of Problem 2
1.3. Aim and Objective 2
1.4. Project Outline 3
CHAPTER TWO 4
2.1.1 Concept of FACT 4
2.1.1. Voltage Stability 5
2.1.2. Voltage Collapse 5
2.1. CONVENTIONAL METHODS OF REACTIVE POWER
2.1.1. Shunt Reactors 7
2.1.2. Shunt Capacitors 8
2.1.3. Synchronous Condensers 9
2.1.4. Load shedding 10
2.1.5. Tap Changing of Transformers 10
2.2. FLEXIBLE ALTERNATING CURRENT TRANSMISSION SYSTEMS (FACTS) 11
2.2.1. Static Synchronous Compensator (STATCOM) 12
2.2.2. Thyristor-Switched Series Capacitor (TSSC) 13
2.2.3. Static Synchronous Series Compensator (SSSC) 14
2.2.4. Thyristor-Controlled Series Capacitor (TCSC) 16
2.2.5. Unified Power Flow Controller (UPFC) 17
CHAPTER THREE 20
3.1. LOCATION OF UPLC 20
3.2. Newton Raphson Load Flow Method 21
3.2.1. Formation of the Y-bus 24
3.2.2. Forming the Jacobian matrix 25
3.3. Incorporating the UPLC in Newton Raphson Load Flow 26
CHAPTER FOUR 30
SIMULATION AND RESULTS ANALYSIS 30
CHAPTER FIVE 35
CONCLUSION AND RECOMMENDATIONS 35
APPENDIX A 38
LIST OF FIGURES
Figure2. 1 A reactor located at 330/132KV transmission station in
Alaoji, Aba, Abia State 8
Figure2. 2 A typical capacitor bank 9
Figure2. 3 A static synchronous compensator 13
Figure2. 4.(a) circuit diagram of a TSSC, (b) course of capacitor voltage for
the basic element in a TSSC 13
Figure2. 5:: (a) A two machine system with a series capacitor compensated line, (b) its associated phasor diagram 15
Figure2. 6:Thyristor-Controlled Series Capacitor (TCSC) 17
Figure2. 7: Concept of the UPFC in a two-machine power system 18
Figure2. 8: Implementation of UPLC 19
Figure3. 1: One line diagram of the power system model 20
Figure3. 2: A two bus system for illustrating Newton Raphson Power flows 24
Figure3. 3:Unified power flow controller equivalent circuit 26
Figure 4. 1:voltages of the buses without the UPFC between buses 3 and 4 31
Figure 4. 2: voltages of the buses with the UPFC between buses 3 and 4 32
LIST OF TABLES
Table 4. 1:Bus voltages without the UPFC 30
Table 4. 2.Line Flows and Losses without UPFC 31
Table 4. 3. Bus voltages with UPFC 32
Table 4. 4. Line Flows and Losses with UPFC 33
Table 4. 5: voltages of the buses with and without the UPFC between buses
3 and 4 34
The control of voltage and power flows is a major issue in power system operation. This is because, due to the topological differences between distribution and transmission systems, different strategies have evolved.
This project contains contributions for power flows control and voltage stability schemes for distribution and transmission systems. A particular interest is taken to the development of control schemes to avoid so-called voltage collapse, which can result in widespread outages. In order to achieve efficient and reliable operation of power system, the control of voltage and reactive power should satisfy the following objectives:
- Voltages at all terminals of all equipment in the system are within acceptable limits
- System stability is enhanced to maximize utilization of the transmission system
- The reactive power flow is minimized so as to reduce RI2 and XI2
This ensures that the transmission system operates mainly for active power. Since the power system supplies power to a vast number of loads and is feeding from many generating units, there is a problem of maintaining voltages within required limits. As load varies, the reactive power requirements of the transmission system vary. Since there is no cost free means of conveying reactive power over long distances, voltage control has to be effected by using special devices located through the system which possess difficulties in keeping sufficient levels of voltage in the power system network.
In recent decades, there has been significant progress in terms of equipment designed to improve the stability of voltage in power systems. This is mainly due to the development of power supply systems in the world, which requires seeking better ways of adjusting and controlling power flows and voltage levels
The proper selection and coordination of equipment for controlling reactive power and voltage stability are among the major challenges of power system engineering. These challenges necessitated the evolution of certain to achieve control or compensation of reactive power. In order to cover the additional demand for reactive power and retain the ability to control voltage stability acceptable range, various sources of reactive power, particularly of the FACTS family has been employed.
The characteristics of a given power system evolve with time, as load grows and generation is added. If the transmission facilities are not upgraded sufficiently the power system becomes vulnerable to steady-state and transient stability problems, as stability margins become narrower, posing a limit on the ability of these lines to transmit power. In principle, limitations on power transfer can always be relieved by the addition of new transmission and generation facilities. Conversely, these are not easy to come by, coupled with the high cost of executing such projects. Alternatively, UPFC can enable the same objectives to be met with no major alterations to system layout. How UPFC can be used to attain a great degree of power flow and voltage profile controllability in power system network is the challenge of this project.
To implement unified power flow controller (UPFC) for improvement of voltage stability in a congested electric network
To develop mathematical models for transmission systems and UPFC, which can to be blended together, coded, and used extensively.
To illustrate the controllable features of UPFC in active and reactive power flows in a transmission line.
To maintain the nodal voltage magnitudes in a power system in the limit for system security
Chapter 1 introduces the work carried out in this project and lists its objectives and
Chapter 2 focuses on the literature review.
Chapter 3 presents the methodology adopted in completing the project, the modeling equations and mathematical solutions backing up the work.
Chapter 4 presents the simulation work done in MATLAB and discuss the results.
Chapter 5 presents the conclusion, recommendations and future areas of research.
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