POWER SYSTEM PERFORMANCE ENHANCEMENT USING FLEXIBLE AC TRANSMISSION SYSTEM DEVICES by © SARAVANA KUMAR RAJENDRAN, B. E. A Thesis submitted to the School of Graduate Studies in partial fulfillment of the requirements for the degree of Master of Engineering Faculty of Engineering and Applied Science Memorial University of Newfoundland May 2015 St. John’s Newfoundland and Labrador Canada Abstract The objective of this research is to investigate the performance enhancement of a power system using Flexible AC Transmission System (FACTS) devices. It is intended to show how the reliability and performance of the power system is improved. The focus is to enhance the understanding of the system operating with and without these devices. Power transmission can always be improved by upgrading or adding new transmission circuits. But this is not a practical solution. FACTS devices are feasible alternatives for optimizing the transmission systems. Providing reactive shunt compensation with shunt- connected capacitors and reactors is a well-established technique to get a better voltage profile in a power system. Shunt capacitors lack dynamic capabilities, and so dynamically controlled reactive power compensation is essential. This feature is provided by FACTS devices. Implementation of new equipment consisting high power electronics based technologies such as FACTS becomes essential for improvement of operation and control of power systems. FACTS promote the use of static controllers to enhance the controllability and increase the power transfer capability. Three software tools were used in this thesis, such as, MATLAB, PSCAD and PowerWorld. Thyristor Controlled Reactors (TCR), Thyristor Controlled Series Capacitors (TCSC), Static Var Compensators (SVC) are used as FACTS devices for consideration in the power system study. This thesis aims at examining the ability of FACTS devices and distributed FACTS devices for power flow control and reactive power compensation in a power system. ii Acknowledgements Dedicated to my parents Mr. Rajendran & Ms. Rajamani First and foremost, I would like to thank my supervisor Dr. Benjamin Jeyasurya for his advice, guidance and support towards my research. I would like to extend my gratitude to Dr. John Quaicoe for helping me with the thesis. I thank all the professors throughout my life for teaching me whatever little things I know. My sincere thanks to Natural Sciences and Engineering Research Council of Canada (NSERC), Memorial University of Newfoundland School of Graduate Studies for their generous funding and the Faculty of Engineering and applied science for providing the opportunity and resources for this research. I extend my sincere thanks to the associate dean Dr. Leonard Lye, Ms. Moya Crocker and Ms. Colleen Mahoney. I am thankful to my sister Selva Kalyani & my brother Siva Kumar, for showering unconditional love and affection, and also to my brother Dr. Sridhar for being a constant source of inspiration and encouragement. Last but not the least, my heartfelt thanks to my friends and colleagues who supported me during my master’s program iii Table of Contents Page Abstract ...................................................................................................... ii Acknowledgements ..................................................................................... iii Table of Contents ....................................................................................... iv List of Tables ............................................................................................. viii List of Figures ............................................................................................ ix List of Symbols and Abbreviations ............................................................ xii 1. Introduction .......................................................................................... 1 1.1. Background of the research ............................................................................... 1 1.2. Objectives of the research ................................................................................. 1 1.3. Organization of the thesis ................................................................................. 2 2. Overview of Flexible AC Transmission Systems (FACTS) .......................... 4 2.1. Introduction ....................................................................................................... 4 2.2. Motivation for the development of FACTS technology ................................... 5 2.3. Classification of FACTS controllers ................................................................. 6 2.4. Series FACTS controllers ................................................................................. 8 2.4.1 Thyristor-Controlled Series Compensator (TCSC) ................................. 8 2.4.1.1 Principle of operation, configuration and control of TCSC ........ 9 2.4.1.2 Applications and installations of TCSC ...................................... 10 iv 2.4.2 Static Synchronous Series Compensator (SSSC) .................................. 11 2.4.2.1 Principle of operation, configuration and control of SSSC ......... 12 2.4.2.2 Applications and installations ...................................................... 13 2.5 Shunt FACTS controllers .................................................................................. 13 2.5.1 Static VAR Compensator (SVC) ........................................................... 13 2.5.1.1 FACTS devices in SVC ............................................................... 14 2.5.1.1.1 Thyristor-Controlled Reactor (TCR) .............................. 14 2.5.1.1.2 Thyristor-Switched Capacitor (TSC) .............................. 15 2.5.1.2 Principle of operation, configuration and control of SVC ........... 16 2.5.1.3 Applications and installations of SVC ......................................... 17 2.5.2 Static synchronous Compensator (STATCOM) .................................... 18 2.5.2.1 Principle of operation, configuration and control of STATCOM 19 2.5.2.2 Applications and installations of STATCOM ............................. 20 2.6 Combined Series-Shunt FACTS controllers ..................................................... 21 2.6.1 Unified Power Flow Controller (UPFC) ............................................... 21 2.6.1.1 Principle of operation, configuration and control of UPFC ........ 22 2.6.1.2 Applications and installations of UPFC ...................................... 24 2.7 Advantages of FACTS devices ......................................................................... 25 2.8 Summary ........................................................................................................... 26 3. Midpoint Reactive Power Compensation .............................................. 27 3.1. Introduction ....................................................................................................... 27 3.2. Reactive power in power system ...................................................................... 28 3.3. Basics of power transmission .......................................................................... 29 v 3.3.1 Case study: Simple 2-bus system .......................................................... 30 3.4. Compensation of reactive power in the power system ..................................... 33 3.4.1 Case study: Shunt reactive power compensation in 2-bus system ........ 34 3.5. Midpoint Compensation .................................................................................... 38 3.5.1 Case study: Reactive power compensation of Hydro-Quebec system .. 40 3.5.1.1 Reactive Power Support using VAR Compensator ...................... 44 3.5.1.2 Mid-point Voltage Magnitude ....................................................... 48 3.5.1.3 Mid-point VAR Compensator Design .......................................... 55 3.6. Summary ........................................................................................................... 58 4. Application of Thyristor Controlled Reactor (TCR) and Thyristor Controlled Series Capacitor (TCSC) in Reactive Power Compensation ........................ 59 4.1. Introduction ....................................................................................................... 59 4.2. Thyristor controlled reactor (TCR) ................................................................... 60 4.2.1 The Single phase TCR .......................................................................... 60 4.2.2 TCR circuit modeled in PSCAD ........................................................... 64 4.2.3 Simulation ............................................................................................. 66 4.3. Thyristor Controlled Series Capacitor (TCSC) ................................................. 69 4.3.1 Principle of operation of the TCSC ....................................................... 71 4.3.2 TCSC circuit modeled in PSCAD .......................................................... 74 4.3.3 Case study: 2-bus system ...................................................................... 77 4.4. Summary ........................................................................................................... 80 5. Power Flow Control using Distributed Flexible AC Transmission Systems (D-FACTS) Devices ................................................................................ 81 vi 5.1. Introduction .................................................................................................................. 81 5.2. Distributed FACTS devices .............................................................................. 81 5.3. D-FACTS case study: 7-bus system ................................................................. 86 5.4. D-FACTS case study 2: 5-bus system .............................................................. 91 5.5. Improving the D-FACTS through positioning .................................................. 93 5.6. Summary ........................................................................................................... 96 6. Conclusion and Future Work ............................................................... 97 6.1. Overview of the thesis ....................................................................................... 97 6.2. Summary of the research and contribution of the thesis ................................... 98 6.3. Recommendations for future work ................................................................... 98 References .................................................................................................. 99 vii List of Tables Table 2.1 Application of FACTS devices ........................................................................ 25 Table 3.1 Load vs. Load voltage ...................................................................................... 32 Table 3.2 Compensated reactive power and change in phase angle ................................ 36 Table 3.3 Power transfer vs receiving end voltage .......................................................... 41 Table 3.4 Load demand increase vs Reactive power compensation ................................ 45 Table 3.5 Midpoint voltage variation ............................................................................... 49 Table 3.6 Reactive power demand vs supply ................................................................... 51 Table 4.1 TCR parameters ............................................................................................... 66 Table 4.2 TCSC parameters ............................................................................................. 74 Table 4.3 Power values for various series capacitor ........................................................ 79 Table 5.1 Details for the 7-bus system ............................................................................. 86 Table 5.2 Increase in the Line current magnitude vs. Load demand ............................... 90 Table 5.3 Details for the 5-bus test system ...................................................................... 92 Table 5.4 Details for the 4-bus test system ...................................................................... 94 Table 5.5 Line details for the 4-bus test system ............................................................... 94 Table 5.6 Power flow in the lines due to D-FACTS application in other lines ............... 95 viii List of Figures Figure 2.1 Single line diagram of a TCSC ....................................................................... 9 Figure 2.2 Single line diagram of a SSSC ....................................................................... 11 Figure 2.3a Single line diagram of a TCR ....................................................................... 15 Figure 2.3b Single line diagram of a TSC ....................................................................... 15 Figure 2.4 Single line diagram of a SVC ......................................................................... 16 Figure 2.5 Single line diagram of a STATCOM .............................................................. 18 Figure 2.6 Single line diagram of a UPFC ....................................................................... 22 Figure 3.1 Model of a simple transmission system .......................................................... 29 Figure 3.2 PI model of a transmission line ...................................................................... 31 Figure 3.3 one line diagram of a simple 2-bus power system ......................................... 31 Figure 3.4 Load real power vs. Receiving end load voltage ............................................ 33 Figure 3.5 One line diagram of simple power system with VAR compensation ............. 35 Figure 3.6 Load increase vs. compensation needed ......................................................... 37 Figure 3.7 Hydro-Quebec model transmission system .................................................... 40 Figure 3.8 Power transferred vs. receiving end voltage ................................................... 42 Figure 3.9 Lack of generated reactive power ................................................................... 43 Figure 3.10 Synchronous generator as 'var' compensator ................................................ 44 Figure 3.11 Load demand vs. Compensated reactive power ........................................... 46 ix Figure 3.12 Phase angle vs. Load real power .................................................................. 47 Figure 3.13 Variation of midpoint voltage ...................................................................... 50 Figure 3.14 Reactive power flows at the receiving end ................................................... 52 Figure 3.15 Midpoint voltage and load angle as functions of P/Po ................................. 53 Figure 3.16 Midpoint control ........................................................................................... 54 Figure 3.17 Relationship between active power, reactive power and load angle ............ 56 Figure 4.1 The basic TCR model ..................................................................................... 61 Figure 4.2 Control characteristics of TCR susceptance ................................................... 63 Figure 4.3 Thyristor controlled reactor ............................................................................ 65 Figure 4.4 Circuit to generate thyristor pulses ................................................................. 66 Figure 4.5 Current waveforms for various firing angles .................................................. 67 Figure 4.6 Susceptance of TCR as a function of firing angle .......................................... 68 Figure 4.7 Reactive power as a function of firing angle .................................................. 69 Figure 4.8 Schematic representation of TCSC ................................................................. 70 Figure 4.9 Equivalent circuit of TCSC ............................................................................ 70 Figure 4.10 Variation of TCSC reactance with firing angle ............................................ 72 Figure 4.11 Single-phase TCSC - PSCAD model ........................................................... 74 Figure 4.12 TCSC waveforms in capacitive mode of operation (α = 150°) .................... 75 Figure 4.13 TCSC waveforms in inductive mode of operation (α = 120°) ..................... 75 x