Power System Analysis and Design 5th Edition SI PDF

This page intentionally left blank This is an electronic version of the print textbook. Due to electronic rights restrictions, some third party content may be suppressed. Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. The publisher reserves the right to remove content from this title at any time if subsequent rights restrictions require it. For valuable information on pricing, previous editions, changes to current editions, and alternate formats, please visit www.cengage.com/highered to search by ISBN#, author, title, or keyword for materials in your areas of interest. POWER SYSTEM ANALYSIS AND DESIGN FIFTH EDITION, SI J. DUNCAN GLOVER FAILURE ELECTRICAL, LLC MULUKUTLA S. SARMA NORTHEASTERN UNIVERSITY THOMAS J. OVERBYE UNIVERSITY OF ILLINOIS Australia Brazil Japan Korea Mexico Singapore Spain United Kingdom United States Power System Analysis and Design, c 2012, 2008 Cengage Learning Fifth Edition, SI ALL RIGHTS RESERVED. No part of this work covered by the copyright J. Duncan Glover, Mulukutla S. Sarma, herein may be reproduced, transmitted, stored, or used in any form or and Thomas J. Overbye by any means graphic, electronic, or mechanical, including but not limited Publisher, Global Engineering: to photocopying, recording, scanning, digitizing, taping, Web distribution, Christopher M. Shortt information networks, or information storage and retrieval systems, except as permitted under Section 107 or 108 of the 1976 United States Acquisitions Editor: Swati Meherishi Copyright Act, without the prior written permission of the publisher. 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James Whitcomb Riley This page intentionally left blank CONTENTS Preface to the SI Edition xii Preface xiii List of Symbols, Units, and Notation xix CHAPTER 1 Introduction 1 Case Study: The Future Beckons: Will the Electric Power Industry Heed the Call? 2 1.1 History of Electric Power Systems 10 1.2 Present and Future Trends 17 1.3 Electric Utility Industry Structure 21 1.4 Computers in Power System Engineering 22 1.5 PowerWorld Simulator 24 CHAPTER 2 Fundamentals 31 Case Study: Making Microgrids Work 32 2.1 Phasors 46 2.2 Instantaneous Power in Single-Phase AC Circuits 47 2.3 Complex Power 53 2.4 Network Equations 58 2.5 Balanced Three-Phase Circuits 60 2.6 Power in Balanced Three-Phase Circuits 68 2.7 Advantages of Balanced Three-Phase Versus Single-Phase Systems 74 CHAPTER 3 Power Transformers 90 Case Study: PJM Manages Aging Transformer Fleet 91 3.1 The Ideal Transformer 96 3.2 Equivalent Circuits for Practical Transformers 102 3.3 The Per-Unit System 108 3.4 Three-Phase Transformer Connections and Phase Shift 116 3.5 Per-Unit Equivalent Circuits of Balanced Three-Phase Two-Winding Transformers 121 3.6 Three-Winding Transformers 126 3.7 Autotransformers 130 3.8 Transformers with O¤-Nominal Turns Ratios 131 vii viii CONTENTS CHAPTER 4 Transmission Line Parameters 159 Case Study: Transmission Line Conductor Design Comes of Age 160 Case Study: Six Utilities Share Their Perspectives on Insulators 164 4.1 Transmission Line Design Considerations 169 4.2 Resistance 174 4.3 Conductance 177 4.4 Inductance: Solid Cylindrical Conductor 178 4.5 Inductance: Single-Phase Two-Wire Line and Three-Phase Three-Wire Line with Equal Phase Spacing 183 4.6 Inductance: Composite Conductors, Unequal Phase Spacing, Bundled Conductors 185 4.7 Series Impedances: Three-Phase Line with Neutral Conductors and Earth Return 193 4.8 Electric Field and Voltage: Solid Cylindrical Conductor 199 4.9 Capacitance: Single-Phase Two-Wire Line and Three-Phase Three-Wire Line with Equal Phase Spacing 201 4.10 Capacitance: Stranded Conductors, Unequal Phase Spacing, Bundled Conductors 204 4.11 Shunt Admittances: Lines with Neutral Conductors and Earth Return 207 4.12 Electric Field Strength at Conductor Surfaces and at Ground Level 212 4.13 Parallel Circuit Three-Phase Lines 215 CHAPTER 5 Transmission Lines: Steady-State Operation 233 Case Study: The ABCs of HVDC Transmission Technologies 234 5.1 Medium and Short Line Approximations 248 5.2 Transmission-Line Di¤erential Equations 254 5.3 Equivalent p Circuit 260 5.4 Lossless Lines 262 5.5 Maximum Power Flow 271 5.6 Line Loadability 273 5.7 Reactive Compensation Techniques 277 CHAPTER 6 Power Flows 294 Case Study: Future Vision 295 Case Study: Characteristics of Wind Turbine Generators for Wind Power Plants 305 6.1 Direct Solutions to Linear Algebraic Equations: Gauss Elimination 311 6.2 Iterative Solutions to Linear Algebraic Equations: Jacobi and Gauss–Seidel 315 6.3 Iterative Solutions to Nonlinear Algebraic Equations: Newton–Raphson 321 CONTENTS ix 6.4 The Power-Flow Problem 325 6.5 Power-Flow Solution by Gauss–Seidel 331 6.6 Power-Flow Solution by Newton–Raphson 334 6.7 Control of Power Flow 343 6.8 Sparsity Techniques 349 6.9 Fast Decoupled Power Flow 352 6.10 The ‘‘DC’’ Power Flow 353 6.11 Power-Flow Modeling of Wind Generation 354 Design Projects 1–5 366 CHAPTER 7 Symmetrical Faults 379 Case Study: The Problem of Arcing Faults in Low-Voltage Power Distribution Systems 380 7.1 Series R–L Circuit Transients 382 7.2 Three-Phase Short Circuit—Unloaded Synchronous Machine 385 7.3 Power System Three-Phase Short Circuits 389 7.4 Bus Impedance Matrix 392 7.5 Circuit Breaker and Fuse Selection 400 Design Project 4 (continued ) 417 CHAPTER 8 Symmetrical Components 419 Case Study: Circuit Breakers Go High Voltage 421 8.1 Deﬁnition of Symmetrical Components 428 8.2 Sequence Networks of Impedance Loads 433 8.3 Sequence Networks of Series Impedances 441 8.4 Sequence Networks of Three-Phase Lines 443 8.5 Sequence Networks of Rotating Machines 445 8.6 Per-Unit Sequence Models of Three-Phase Two-Winding Transformers 451 8.7 Per-Unit Sequence Models of Three-Phase Three-Winding Transformers 456 8.8 Power in Sequence Networks 459 CHAPTER 9 Unsymmetrical Faults 471 Case Study: Fires at U.S. Utilities 472 9.1 System Representation 473 9.2 Single Line-to-Ground Fault 478 9.3 Line-to-Line Fault 483 9.4 Double Line-to-Ground Fault 485 9.5 Sequence Bus Impedance Matrices 492 Design Project 4 (continued ) 512 Design Project 6 513 x CONTENTS CHAPTER 10 System Protection 516 Case Study: The Future of Power Transmission 518 10.1 System Protection Components 525 10.2 Instrument Transformers 526 10.3 Overcurrent Relays 533 10.4 Radial System Protection 537 10.5 Reclosers and Fuses 541 10.6 Directional Relays 545 10.7 Protection of Two-Source System with Directional Relays 546 10.8 Zones of Protection 547 10.9 Line Protection with Impedance (Distance) Relays 551 10.10 Di¤erential Relays 557 10.11 Bus Protection with Di¤erential Relays 559 10.12 Transformer Protection with Di¤erential Relays 560 10.13 Pilot Relaying 565 10.14 Digital Relaying 566 CHAPTER 11 Transient Stability 579 Case Study: Real-Time Dynamic Security Assessment 581 11.1 The Swing Equation 590 11.2 Simpliﬁed Synchronous Machine Model and System Equivalents 596 11.3 The Equal-Area Criterion 598 11.4 Numerical Integration of the Swing Equation 608 11.5 Multimachine Stability 613 11.6 A Two-Axis Synchronous Machine Model 621 11.7 Wind Turbine Machine Models 625 11.8 Design Methods for Improving Transient Stability 632 CHAPTER 12 Power System Controls 639 Case Study: Overcoming Restoration Challenges Associated with Major Power System Disturbances 642 12.1 Generator-Voltage Control 652 12.2 Turbine-Governor Control 657 12.3 Load-Frequency Control 663 12.4 Economic Dispatch 667 12.5 Optimal Power Flow 680 CHAPTER 13 Transmission Lines: Transient Operation 690 Case Study: VariSTAR8 Type AZE Surge Arresters 691 Case Study: Change in the Air 695 13.1 Traveling Waves on Single-Phase Lossless Lines 707 13.2 Boundary Conditions for Single-Phase Lossless Lines 710 CONTENTS xi 13.3 Bewley Lattice Diagram 719 13.4 Discrete-Time Models of Single-Phase Lossless Lines and Lumped RLC Elements 724 13.5 Lossy Lines 731 13.6 Multiconductor Lines 735 13.7 Power System Overvoltages 738 13.8 Insulation Coordination 745 CHAPTER 14 POWER DISTRIBUTION 757 Case Study: The Path of the Smart Grid 759 14.1 Introduction to Distribution 770 14.2 Primary Distribution 772 14.3 Secondary Distribution 780 14.4 Transformers in Distribution Systems 785 14.5 Shunt Capacitors in Distribution Systems 795 14.6 Distribution Software 800 14.7 Distribution Reliability 801 14.8 Distribution Automation 804 14.9 Smart Grids 807 Appendix 814 Index 818 P R E FA C E TO T H E S I E D I T I O N This edition of Power System Analysis and Design has been adapted to incor- porate the International System of Units (Le Système International d’Unités or SI) throughout the book. LE SYSTÈME INTERNATIONAL D’UNITÉS The United States Customary System (USCS) of units uses FPS (foot– pound–second) units (also called English or Imperial units). SI units are pri- marily the units of the MKS (meter–kilogram–second) system. However, CGS (centimeter–gram–second) units are often accepted as SI units, espe- cially in textbooks. USING SI UNITS IN THIS BOOK In this book, we have used both MKS and CGS units. USCS units or FPS units used in the US Edition of the book have been converted to SI units throughout the text and problems. However, in case of data sourced from handbooks, government standards, and product manuals, it is not only ex- tremely di‰cult to convert all values to SI, it also encroaches upon the intel- lectual property of the source. Also, some quantities such as the ASTM grain size number and Jominy distances are generally computed in FPS units and would lose their relevance if converted to SI. Some data in ﬁgures, tables, ex- amples, and references, therefore, remains in FPS units. For readers unfamil- iar with the relationship between the FPS and the SI systems, conversion ta- bles have been provided inside the front and back covers of the book. To solve problems that require the use of sourced data, the sourced values can be converted from FPS units to SI units just before they are to be used in a calculation. To obtain standardized quantities and manufacturers’ data in SI units, the readers may contact the appropriate government agencies or authorities in their countries/regions. INSTRUCTOR RESOURCES A Printed Instructor’s Solution Manual in SI units is available on request. An electronic version of the Instructor’s Solutions Manual, and PowerPoint slides of the ﬁgures from the SI text are available through http://login. cengage.com. The readers’ feedback on this SI Edition will be highly appreciated and will help us improve subsequent editions. The Publishers xii P R E F A C E The objective of this book is to present methods of power system analysis and design, particularly with the aid of a personal computer, in su‰cient depth to give the student the basic theory at the undergraduate level. The approach is designed to develop students’ thinking processes, enabling them to reach a sound understanding of a broad range of topics related to power system engineering, while motivating their interest in the electrical power industry. Because we believe that fundamental physical concepts underlie creative engineering and form the most valuable and permanent part of an engineering education, we highlight physical concepts while giving due attention to math- ematical techniques. Both theory and modeling are developed from simple be- ginnings so that they can be readily extended to new and complex situations. This edition of the text features new Chapter 14 entitled, Power Distribu- tion. During the last decade, major improvements in distribution reliability have come through automated distribution and more recently through the introduction of ‘‘smart grids.’’ Chapter 14 introduces the basic features of pri- mary and secondary distribution systems as well as basic distribution compo- nents including distribution substation transformers, distribution transformers, and shunt capacitors. We list some of the major distribution software vendors followed by an introduction to distribution reliability, distribution automation, and smart grids. This edition also features the following: (1) wind-energy systems model- ing in the chapter on transient stability; (2) discussion of reactive/pitch control of wind generation in the chapter on powers system controls; (3) updated case studies for nine chapters along with four case studies from the previous edition describing present-day, practical applications and new technologies; (4) an updated PowerWorld Simulator package; and (5) updated problems at the end of chapters. One of the most challenging aspects of engineering education is giving students an intuitive feel for the systems they are studying. Engineering sys- tems are, for the most part, complex. While paper-and-pencil exercises can be quite useful for highlighting the fundamentals, they often fall short in imparting the desired intuitive insight. To help provide this insight, the book uses PowerWorld Simulator to integrate computer-based examples, problems, and design projects throughout the text. PowerWorld Simulator was originally developed at the University of Illinois at Urbana–Champaign to teach the basics of power systems to nontechnical people involved in the electricity industry, with version 1.0 in- troduced in June 1994. The program’s interactive and graphical design made xiii xiv PREFACE it an immediate hit as an educational tool, but a funny thing happened—its interactive and graphical design also appealed to engineers doing analysis of real power systems. To meet the needs of a growing group of users, PowerWorld Simulator was commercialized in 1996 by the formation of PowerWorld Corporation. Thus while retaining its appeal for education, over the years PowerWorld Simulator has evolved into a top-notch analysis pack- age, able to handle power systems of any size. PowerWorld Simulator is now used throughout the power industry, with a range of users encompassing uni- versities, utilities of all sizes, government regulators, power marketers, and consulting ﬁrms. In integrating PowerWorld Simulator with the text, our design philoso- phy has been to use the software to extend, rather than replace, the fully worked examples provided in previous editions. Therefore, except when the problem size makes it impractical, each PowerWorld Simulator example in- cludes a fully worked hand solution of the problem along with a PowerWorld Simulator case. This format allows students to simultaneously see the details of how a problem is solved and a computer implementation of the solution. The added beneﬁt from PowerWorld Simulator is its ability to easily extend the example. Through its interactive design, students can quickly vary example parameters and immediately see the impact such changes have on the solution. By reworking the examples with the new parameters, students get im- mediate feedback on whether they understand the solution process. The inter- active and visual design of PowerWorld Simulator also makes it an excellent tool for instructors to use for in-class demonstrations. With numerous exam- ples utilizing PowerWorld Simulator instructors can easily demonstrate many of the text topics. Additional PowerWorld Simulator functionality is in- troduced in the text problems and design projects. The text is intended to be fully covered in a two-semester or three- quarter course o¤ered to seniors and ﬁrst-year graduate students. The orga- nization of chapters and individual sections is ﬂexible enough to give the instructor su‰cient latitude in choosing topics to cover, especially in a one- semester course. The text is supported by an ample number of worked exam- ples covering most of the theoretical points raised. The many problems to be worked with a calculator as well as problems to be worked using a personal computer have been expanded in this edition. As background for this course, it is assumed that students have had courses in electric network theory (including transient analysis) and ordinary di¤erential equations and have been exposed to linear systems, matrix algebra, and computer programming. In addition, it would be helpful, but not neces- sary, to have had an electric machines course. After an introduction to the history of electric power systems along with present and future trends, Chapter 2 on fundamentals orients the students to the terminology and serves as a brief review. The chapter reviews phasor concepts, power, and single-phase as well as three-phase circuits. Chapters 3 through 6 examine power transformers, transmission-line parameters, steady-state operation of transmission lines, and power ﬂows PREFACE xv including the Newton–Raphson method. These chapters provide a basic understanding of power systems under balanced three-phase, steady-state, normal operating conditions. Chapters 7 through 10, which cover symmetrical faults, symmetrical components, unsymmetrical faults, and system protection, come under the general heading of power system short-circuit protection. Chapter 11 (pre- viously Chapter 13) examines transient stability, which includes the swing equation, the equal-area criterion, and multi-machine stability with modeling of wind-energy systems as a new feature. Chapter 12 (previously Chapter 11) covers power system controls, including turbine-generator controls, load- frequency control, economic dispatch, and optimal power ﬂow, with reactive/ pitch control of wind generation as a new feature. Chapter 13 (previously Chapter 12) examines transient operation of transmission lines including power system overvoltages and surge protection. The ﬁnal and new Chapter 14 introduces power distribution. ADDITIONAL RESOURCES Companion websites for this book are available for both students and in- structors. These websites provide useful links, ﬁgures, and other support ma- terial. The Student Companion Site includes a link to download the free stu- dent version of PowerWorld. The Instructor Companion Site includes access to the solutions manual and PowerPoint slides. Through the Instructor Com- panion Site, instructors can also request access to additional support mate- rial, including a printed solutions manual. To access the support material described here along with all additional course materials, please visit www.cengagebrain.com. At the cengage- brain.com home page, search for the ISBN of your title (from the back cover of your book) using the search box at the top of the page. This will take you to the product page where these resources can be found. ACKNOWLEDGMENTS The material in this text was gradually developed to meet the needs of classes taught at universities in the United States and abroad over the past 30 years. The original 13 chapters were written by the ﬁrst author, J. Duncan Glover, Failure Electrical LLC, who is indebted to many people who helped during the planning and writing of this book. The profound inﬂuence of earlier texts written on power systems, particularly by W. D. Stevenson, Jr., and the de- velopments made by various outstanding engineers are gratefully acknowl- edged. Details of sources can only be made through references at the end of each chapter, as they are otherwise too numerous to mention. Chapter 14 (Power Distribution) was a collaborative e¤ort between Dr. Glover (Sections 14.1–14.7) and Co-author Thomas J. Overbye (Sections 14.8 & 14.9). Professor Overbye, University of Illinois at Urbana-Champaign, xvi PREFACE updated Chapter 6 (Power Flows), Chapter 11 (Transient Stability), and Chapter 12 (Power System Controls) for this edition of the text. He also pro- vided the examples and problems using PowerWorld Simulator as well as three design projects. Co-author Mulukutla Sarma, Northeastern University, contributed to end-of-chapter multiple-choice questions and problems. We commend the following Cengage Learning professionals: Chris Shortt, Publisher, Global Engineering; Hilda Gowans, Senior Developmental Editor; Swati Meherishi, Acquisitions Editor; and Kristiina Paul, Permissions Researcher; as well as Rose Kernan of RPK Editorial Services, lnc., for their broad knowledge, skills, and ingenuity in publishing this edition. The reviewers for the ﬁfth edition are as follows: Thomas L. Baldwin, Florida State University; Ali Emadi, Illinois Institute of Technology; Reza Iravani, University of Toronto; Surya Santoso, University of Texas at Austin; Ali Shaban, California Polytechnic State University, San Luis Obispo; and Dennis O. Wiitanen, Michigan Technological University, and Hamid Ja¤ari, Danvers Electric. Substantial contributions to prior editions of this text were made by a number of invaluable reviewers, as follows: Fourth Edition: Robert C. Degene¤, Rensselaer Polytechnic Institute; Venkata Dina- vahi, University of Alberta; Richard G. Farmer, Arizona State University; Steven M. Hietpas, South Dakota State University; M. Hashem Nehrir, Montana State University; Anil Pahwa, Kansas State University; and Ghadir Radman, Tennessee Technical University. Third Edition: Sohrab Asgarpoor, University of Nebraska–Lincoln; Mariesa L. Crow, University of Missouri–Rolla; Ilya Y. Grinberg, State University of New York, College at Bu¤alo; Iqbal Husain, The University of Akron; W. H. Kersting, New Mexico State University; John A. Palmer, Colorado School of Mines; Satish J. Ranada, New Mexico State University; and Shyama C. Tandon, California Polytechnic State University. Second Edition: Max D. Anderson, University of Missouri–Rolla; Sohrab Asgarpoor, University of Nebraska–Lincoln; Kaveh Ashenayi, University of Tulsa; Richard D. Christie, Jr., University of Washington; Mariesa L. Crow, Univer- sity of Missouri–Rolla; Richard G. Farmer, Arizona State University; Saul Goldberg, California Polytechnic University; Cli¤ord H. Grigg, Rose-Hulman Institute of Technology; Howard B. Hamilton, University of Pittsburgh; Leo Holzenthal, Jr., University of New Orleans; Walid Hubbi, New Jersey Institute of Technology; Charles W. Isherwood, University of Massachusetts– Dartmouth; W. H. Kersting, New Mexico State University; Wayne E. Knabach, South Dakota State University; Pierre-Jean Lagace, IREQ Institut de Reserche d’Hydro–Quebec; James T. Lancaster, Alfred University; Kwang Y. Lee, Pennsylvania State University; Mohsen Lotfalian, University of Ev- ansville; Rene B. Marxheimer, San Francisco State University, Lamine Mili, Virginia Polytechnic Institute and State University; Osama A. Mohammed, Florida International University; Cli¤ord C. Mosher, Washington State Uni- versity, Anil Pahwa, Kansas State University; M. A. Pai, University of Illinois PREFACE xvii at Urbana–Champaign; R. Ramakumar, Oklahoma State University; Teodoro C. Robles, Milwaukee School of Engineering, Ronald G. Schultz, Cleveland State University; Stephen A. Sebo, Ohio State University; Raymond Shoults, University of Texas at Arlington, Richard D. Shultz, University of Wisconsin at Platteville; Charles Slivinsky, University of Missouri–Columbia; John P. Stahl, Ohio Northern University; E. K. Stanek, University of Missouri–Rolla; Robert D. Strattan, University of Tulsa; Tian-Shen Tang, Texas A&M University–Kingsville; S. S. Venkata, University of Washington; Francis M. Wells, Vanderbilt University; Bill Wieserman, University of Pennsylvania– Johnstown; Stephen Williams, U.S. Naval Postgraduate School; and Salah M. Yousif, California State University–Sacramento. First Edition: Frederick C. Brockhurst, Rose-Hulman Institute of Technology; Bell A. Cogbill. Northeastern University; Saul Goldberg, California Polytechnic State University; Mack Grady, University of Texas at Austin; Leonard F. Grigsby, Auburn University; Howard Hamilton, University of Pittsburgh; William F. Horton, California Polytechnic State University; W. H. Kersting, New Mexico State University; John Pavlat, Iowa State University; R. Ramakumar, Oklahoma State University; B. Don Russell, Texas A&M; Sheppard Salon, Rensselaer Polytechnic Institute; Stephen A. Sebo, Ohio State University; and Dennis O. Wiitanen, Michigan Technological University. In conclusion, the objective in writing this text and the accompanying software package will have been fulﬁlled if the book is considered to be student-oriented, comprehensive, and up to date, with consistent notation and necessary detailed explanation at the level for which it is intended. J. Duncan Glover Mulukutla S. Sarma Thomas J. Overbye This page intentionally left blank L I S T O F S Y M B O L S , U N I T S , A N D N OTAT I O N Symbol Description Symbol Description a operator 1 120 P real power at transformer turns ratio q charge A area Q reactive power A transmission line parameter r radius A symmetrical components R resistance transformation matrix R turbine-governor regulation B loss coe‰cient constant B frequency bias constant R resistance matrix B phasor magnetic ﬂux density s Laplace operator B transmission line parameter S apparent power C capacitance S complex power C transmission line parameter t time D distance T period D transmission line parameter T temperature E phasor source voltage T torque E phasor electric ﬁeld strength vðtÞ instantaneous voltage f frequency V voltage magnitude (rms unless G conductance otherwise indicated) G conductance matrix V phasor voltage H normalized inertia constant V vector of phasor voltages H phasor magnetic ﬁeld intensity X reactance iðtÞ instantaneous current X reactance matrix I current magnitude (rms unless Y phasor admittance otherwise indicated) Y admittance matrix I phasor current Z phasor impedance I vector of phasor currents Z impedance matrix j operator 1 90 a angular acceleration J moment of inertia a transformer phase shift angle l length b current angle l length b area frequency response L inductance characteristic L inductance matrix d voltage angle N number (of buses, lines, turns, etc.) d torque angle p.f. power factor e permittivity pðtÞ instantaneous power G reﬂection or refraction coe‰cient xix xx LIST OF SYMBOLS, UNITS, AND NOTATION Symbol Description Symbol Description l magnetic ﬂux linkage y impedance angle l penalty factor y angular position F magnetic ﬂux m permeability r resistivity n velocity of propagation t time in cycles o radian frequency t transmission line transit time SI Units English Units A ampere BTU British thermal unit C coulomb cmil circular mil F farad ft foot H henry hp horsepower Hz hertz in inch J joule mi mile kg kilogram m meter N newton rad radian s second S siemen VA voltampere var voltampere reactive W watt Wb weber W ohm Notation Lowercase letters such as v(t) and i(t) indicate instantaneous values. Uppercase letters such as V and I indicate rms values. Uppercase letters in italic such as V and I indicate rms phasors. Matrices and vectors with real components such as R and I are indicated by boldface type. Matrices and vectors with complex components such as Z and I are indicated by boldface italic type. Superscript T denotes vector or matrix transpose. Asterisk (*) denotes complex conjugate. 9 indicates the end of an example and continuation of text. PW highlights problems that utilize PowerWorld Simulator. 1300 MW coal-ﬁred power plant (Courtesy of American Electric Power Company) 1 INTRODUCTION E lectrical engineers are concerned with every step in the process of genera- tion, transmission, distribution, and utilization of electrical energy. The elec- tric utility industry is probably the largest and most complex industry in the world. The electrical engineer who works in that industry will encounter challenging problems in designing future power systems to deliver increasing amounts of electrical energy in a safe, clean, and economical manner. The objectives of this chapter are to review brieﬂy the history of the electric utility industry, to discuss present and future trends in electric power systems, to describe the restructuring of the electric utility industry, and to introduce PowerWorld Simulator—a power system analysis and simulation software package. 1 2 CHAPTER 1 INTRODUCTION CASE S T U DY The following article describes the restructuring of the electric utility industry that has been taking place in the United States and the impacts on an aging transmission infrastructure. Independent power producers, increased competition in the generation sector, and open access for generators to the U.S. transmission system have changed the way the transmission system is utilized. The need for investment in new transmission and transmission technologies, for further refinements in restructuring, and for training and education systems to replenish the workforce are discussed. The Future Beckons: Will the Electric Power Industry Heed the Call? CHRISTOPHER E. ROOT Over the last four decades, the U.S. electric power the nation’s transmission system. And while prices industry has undergone unprecedented change. In for distribution and transmission of electricity re- the 1960s, regulated utilities generated and deliv- mained regulated, unregulated energy commodity ered power within a localized service area. The markets have developed in several regions. FERC decade was marked by high load growth and mod- has supported these changes with rulings leading est price stability. This stood in sharp contrast to to the formation of independent system oper- the wild increases in the price of fuel oil, focus on ators (ISOs) and regional transmission organ- energy conservation, and slow growth of the 1970s. izations (RTOs) to administer the electricity mar- Utilities quickly put the brakes on generation ex- kets in several regions of the United States, pansion projects, switched to coal or other nonoil including New England, New York, the Mid-Atlantic, fuel sources, and significantly cut back on the ex- the Midwest, and California. pansion of their networks as load growth slowed to The transmission system originally was built to a crawl. During the 1980s, the economy in many deliver power from a utility’s generator across town regions of the country began to rebound. The to its distribution company. Today, the transmission 1980s also brought the emergence of independent system is being used to deliver power across states power producers and the deregulation of the natu- or entire regions. As market forces increasingly ral gas wholesale markets and pipelines. These de- determine the location of generation sources, the velopments resulted in a significant increase in nat- transmission grid is being asked to play an even ural gas transmission into the northeastern United more important role in markets and the reliability States and in the use of natural gas as the preferred of the system. In areas where markets have been fuel for new generating plants. restructured, customers have begun to see signifi- During the last ten years, the industry in many cant benefits. But full delivery of restructuring’s areas of the United States has seen increased com- benefits is being impeded by an inadequate, under- petition in the generation sector and a fundamental invested transmission system. shift in the role of the nation’s electric transmission If the last 30 years are any indication, the struc- system, with the 1996 enactment of the Federal ture of the industry and the increasing demands Energy Regulatory Commission (FERC) Order No. placed on the nation’s transmission infrastructure 888, which mandated open access for generators to and the people who operate and manage it are likely to continue unabated. In order to meet (‘‘The Future Beckons,’’ Christopher E. Root. > 2006 IEEE. the challenges of the future, to continue to maintain Reprinted, with permission, from Supplement to IEEE Power the stable, reliable, and efficient system we have & Energy (May/June 2006) pg. 58–65) known for more than a century and to support the CASE STUDY 3 continued development of efficient competitive in the form of lower prices, greater supplier choice, markets, U.S. industry leaders must address three and environmental benefits, largely due to the de- significant issues: velopment and operation of new, cleaner genera-. an aging transmission system suffering from tion. There is, however, a growing recognition that the delivery of the full value of restructuring to cus- substantial underinvestment, which is exacer- tomers has been stalled by an inadequate transmis- bated by an out-of-date industry structure. the need for a regulatory framework that will sion system that was not designed for the new de- mands being placed on it. In fact, investment in the spur independent investment, ownership, and nation’s electricity infrastructure has been declining management of the nation’s grid. an aging workforce and the need for a suc- for decades. Transmission investment has been falling for a quarter century at an average rate of almost cession plan to ensure the existence of the US$50 million a year (in constant 2003 U.S. dollars), next generation of technical expertise in the though there has been a small upturn in the last few industry. years. Transmission investment has not kept up with load growth or generation investment in recent ARE WE SPENDING ENOUGH? years, nor has it been sufficiently expanded to ac- In areas that have restructured power markets, commodate the advent of regional power markets substantial benefits have been delivered to customers (see Figure 1). Figure 1 Annual transmission investments by investor-owned utilities, 1975–2003 (Source: Eric Hirst, ‘‘U.S. Transmission Capacity: Present Status and Future Prospects,’’ 2004. Graph used with permission from the Edison Electric Institute, 2004. All rights reserved) 4 CHAPTER 1 INTRODUCTION TABLE 1 Transmission investment in the United continued to increase, even when adjusted to reflect States and in international competitive markets PJM’s expanding footprint into western and southern Country Investment Number of regions. in High Voltage Transmission- Because regions do not currently quantify the Transmission Owning costs of constraints in the same way, it is difficult to (>230 kV) Entities make direct comparisons from congestion data be- Normalized tween regions. However, the magnitude and up- by Load for 2004–2008 (in ward trend of available congestion cost data in- US$M/GW/year) dicates a significant and growing problem that is increasing costs to customers. New Zealand 22.0 1 England & Wales 16.5 1 (NGT) THE SYSTEM IS AGING Denmark 12.5 2 Spain 12.3 1 While we are pushing the transmission system The Netherlands 12.0 1 harder, it is not getting any younger. In the north- Norway 9.2 1 eastern United States, the bulk transmission system Poland 8.6 1 Finland 7.2 1 operates primarily at 345 kV. The majority of this United States 4.6 450 system originally was constructed during the 1960s (based on (69 in EEI) and into the early 1970s, and its substations, wires, representative towers, and poles are, on average, more than 40 data from EEI) years old. (Figure 2 shows the age of National Grid’s U.S. transmission structures.) While all util- ities have maintenance plans in place for these sys- Outlooks for future transmission development tems, ever-increasing congestion levels in many vary, with Edison Electric Institute (EEI) data sug- areas are making it increasingly difficult to schedule gesting a modest increase in expected transmission circuit outages for routine upgrades. investment and other sources forecasting a con- The combination of aging infrastructure, in- tinued decline. Even assuming EEI’s projections are creased congestion, and the lack of significant ex- realized, this level of transmission investment in the pansion in transmission capacity has led to the need United States is dwarfed by that of other inter- to carefully prioritize maintenance and construc- national competitive electricity markets, as shown tion, which in turn led to the evolution of the in Table 1, and is expected to lag behind what is science of asset management, which many utilities needed. have adopted. Asset management entails quantifying The lack of transmission investment has led to the risks of not doing work as a means to ensure a high (and increasing in some areas) level of that the highest priority work is performed. It has congestion-related costs in many regions. For in- significantly helped the industry in maintaining reli- stance, total uplift for New England is in the range of ability. As the assets continue to age, this combina- US$169 million per year, while locational installed tion of engineering, experience, and business risk capacity prices and reliability must-run charges are will grow in importance to the industry. If this is not on the rise. In New York, congestion costs have in- done well, the impact on utilities in terms of reli- creased substantially, from US$310 million in 2001 to ability and asset replacement will be significant. US$525 million in 2002, US$688 million in 2003, and And while asset management techniques will US$629 million in 2004. In PJM Interconnection help in managing investment, the age issue un- (PJM), an RTO that administers electricity markets doubtedly will require substantial reinvestment at for all or parts of 14 states in the Northeast, some point to replace the installed equipment at Midwest, and Mid-Atlantic, congestion costs have the end of its lifetime. CASE STUDY 5 Figure 2 Age of National Grid towers and poles TECHNOLOGY WILL HAVE A ROLE reasonable to expect this solution to become more prevalent, it is important to recognize that it is not The expansion of the transmission network in the inexpensive. United States will be very difficult, if not impossi- Technology has an important role to play in ble, if the traditional approach of adding new utilizing existing lines and transmission corridors overhead lines continues. Issues of land availability, to increase capacity. Lightweight, high-temperature concerns about property values, aesthetics, and overhead conductors are now becoming available other licensing concerns make siting new lines a for line upgrades without significant tower mod- difficult proposition in many areas of the United ifications. Monitoring systems for real-time ratings States. New approaches to expansion will be re- and better computer control schemes are providing quired to improve the transmission networks of improved information to control room operators the future. to run the system at higher load levels. The devel- Where new lines are the only answer, more opment and common use of static var compensa- underground solutions will be chosen. In some tors for voltage and reactive control, and the gen- circumstances, superconducting cable will become a eral use of new solid-state equipment to solve real viable option. There are several companies, includ- problems are just around the corner and should ing National Grid, installing short superconducting add a new dimension to the traditional wires and lines to gain experience with this newly available transformers approach to addressing stability and technology and solve real problems. While it is short-term energy storage issues. 6 CHAPTER 1 INTRODUCTION These are just a few examples of some of the ex- (and perhaps ultimate removal) of administrative citing new technologies that will be tools for the fu- mechanisms to mitigate market power. This would ture. It is encouraging that the development of new also allow for common asset management ap- and innovative solutions to existing problems con- proaches to the transmission system. The creation tinues. In the future, innovation must take a leading of independent transmission companies (ITCs), i.e., role in developing solutions to transmission prob- companies that focus on the investment in and op- lems, and it will be important for the regulators to eration of transmission independent of generation encourage the use of new techniques and tech- interests, would be a key institutional step toward nologies. Most of these new technologies have an industry structure that appropriately views a higher cost than traditional solutions, which will transmission as a facilitator of robust competitive place increasing pressure on capital investment. It will electricity markets. ITCs recognize transmission as be important to ensure that appropriate cost recov- an enabler of competitive electricity markets. Poli- ery mechanisms are developed to address this issue. cies that provide a more prominent role for such companies would align the interests of transmission owners/operators with those of customers, permit- INDUSTRY STRUCTURE ting the development of well-designed and enduring Another factor contributing to underinvestment power markets that perform the function of any in the transmission system is the tremendous frag- market, namely, to drive the efficient allocation of mentation that exists in the U.S. electricity industry. resources for the benefit of customers. In its policy There are literally hundreds of entities that own statement released in June 2005, FERC reiterated its and operate transmission. The United States has commitment to ITC formation to support improving more than 100 separate control areas and more the performance and efficiency of the grid. than 50 regulators that oversee the nation’s grid. Having no interest in financial outcomes within The patchwork of ownership and operation lies in a power market, the ITC’s goal is to deliver maxi- stark contrast to the interregional delivery de- mum value to customers through transmission mands that are being placed on the nation’s trans- operation and investment. With appropriate in- mission infrastructure. centives, ITCs will pursue opportunities to leverage Federal policymakers continue to encourage relatively small expenditures on transmission con- transmission owners across the nation to struction and management to create a healthy mar- join RTOs. Indeed, RTO/ISO formation was in- ket and provide larger savings in the supply portion tended to occupy a central role in carrying forward of customer’s bills. They also offer benefits over FERC’s vision of restructuring, and an extraordinary nonprofit RTO/ISO models, where the incentives amount of effort has been expended in making this for efficient operation and investment may be less model work. While RTOs/ISOs take a step toward focused. an independent, coordinated transmission system, it An ideal industry structure would permit ITCs remains unclear whether they are the best long- to own, operate, and manage transmission assets term solution to deliver efficient transmission sys- over a wide area. This would allow ITCs to access tem operation while ensuring reliability and deliver- economies of scale in asset investment, planning, and ing value to customers. operations to increase throughout and enhance reli- Broad regional markets require policies that fa- ability in the most cost-effective manner. This struc- cilitate and encourage active grid planning, manage- ture would also avoid ownership fragmentation ment, and the construction of transmission up- within a single market, which is a key obstacle to grades both for reliability and economic needs. A the introduction of performance-based rates that strong transmission infrastructure or network plat- benefit customers by aligning the interests of trans- form would allow greater fuel diversity, more stable mission companies and customers in reducing con- and competitive energy prices, and the relaxation gestion. This approach to ‘‘horizontal integration’’ of CASE STUDY 7 the transmission sector under a single regulated regional needs and do so in a way that is cost for-profit entity is key to establishing an industry effective for customers. structure that recognizes the transmission system. Cost recovery and allocation: Comprehensive re- as a market enabler and provider of infrastructure gional planning processes that identify needed to support effective competitive markets. Market transmission projects must be accompanied by administration would be contracted out to another cost recovery and allocation mechanisms that (potentially nonprofit) entity while generators, other recognize the broad benefits of transmission suppliers, demand response providers, and load and its role in supporting and enabling regional serving entities (LSEs) would all compete and in- electricity markets. Mechanisms that allocate novate in fully functioning markets, delivering still- the costs of transmission investment broadly increased efficiency and more choices for customers. view transmission as the regional market en- abler it is and should be, provide greater cer- REGULATORY ISSUES tainty and reduce delays in cost recovery, and, thus, remove obstacles to provide further The industry clearly shoulders much of the respon- incentives for the owners and operators of sibility for determining its own future and for taking transmission to make such investment. the steps necessary to ensure the robustness of the. Certainty of rate recovery and state cooperation: It nation’s transmission system. However, the industry is critical that transmission owners are assured also operates within an environment governed by certain and adequate rate recovery under a substantial regulatory controls. Therefore, policy- regional planning process. Independent admin- makers also will have a significant role in helping istration of the planning processes will assure to remove the obstacles to the delivery of the full that transmission enhancements required for benefits of industry restructuring to customers. In reliability and market efficiency do not unduly order to ensure adequate transmission investment burden retail customers with additional costs. and the expansion of the system as appropriate, the FERC and the states must work together to following policy issues must be addressed: provide for certainty in rate recovery from. Regional planning: Because the transmission sys- ultimate customers through federal and state tem is an integrated network, planning for sys- jurisdictional rates. tem needs should occur on a regional basis.. Incentives to encourage transmission investment, Regional planning recognizes that transmission independence, and consolidation: At a time when investment and the benefits transmission can a significant increase in transmission investment deliver to customers are regional in nature is needed to ensure reliability, produce an ade- rather than bounded by state or service area quate platform for competitive power markets lines. Meaningful regional planning processes and regional electricity commerce, and to pro- also take into account the fact that transmission mote fuel diversity and renewable sources of provides both reliability and economic benefits. supply, incentives not only for investment but Comprehensive planning processes provide for also for independence and consolidation of mechanisms to pursue regulated transmission transmission are needed and warranted. In- solutions for reliability and economic needs in centives should be designed to promote trans- the event that the market fails to respond or is mission organizations that acknowledge the identified as unlikely to respond to these needs benefits to customers of varying degrees of in a timely manner. In areas where regional transmission independence and reward that in- system planning processes have been im- dependence accordingly. These incentives may plemented, such as New England and PJM, take the form of enhanced rates of return or progress is being made towards identifying and other financial incentives for assets managed, building transmission projects that will address operated, and/or owned by an ITC. 8 CHAPTER 1 INTRODUCTION The debate about transmission regulation will to 500 today. Overall, the number of engineering continue. Ultimately, having the correct mixture of graduates has dropped 50% in the last 15 years. incentives and reliability standards will be a critical Turning this situation around will require a long- factor that will determine whether or not the na- term effort by many groups working together, tion’s grid can successfully tie markets together and including utilities, consultants, manufacturers, uni- improve the overall reliability of the bulk transmis- versities, and groups such as the IEEE Power En- sion system in the United States. The future trans- gineering Society (PES). mission system must be able to meet the needs of Part of the challenge is that utilities are compet- customers reliably and support competitive markets ing for engineering students against other in- that provide them with electricity efficiently. Failure dustries, such as telecommunications or computer to invest in the transmission system now will mean software development, that are perceived as being an increased likelihood of reduced reliability and more glamorous or more hip than the power in- higher costs to customers in the future. dustry and have no problem attracting large num- bers of new engineers. For the most part, the power industry has not WORKFORCE OF THE FUTURE done a great job of selling itself. Too often, headlines Clearly, the nation’s transmission system will need focus on negatives such as rate increases, power considerable investment and physical work due to outages, and community relations issues related to a age, growth of the use of electricity, changing mar- proposed new generation plant or transmission line. kets, and how the networks are used. As previously To a large extent, the industry also has become a noted, this will lead to a required significant in- victim of its own success by delivering electricity so crease in capital spending. But another critical re- reliably that the public generally takes it for granted, source is beginning to become a concern to many in which makes the good news more difficult to tell. It the industry, specifically the continued availability of is incumbent upon the industry to take a much more qualified power system engineers. proactive role in helping its public—including tal- Utility executives polled by the Electric Power ented engineering students—understand the ded- Research Institute in 2003 estimated that 50% of ication, commitment, ingenuity, and innovation that is the technical workforce will reach retirement in the required to keep the nation’s electricity system next 5–10 years. This puts the average age near 50, humming. PES can play an important role in this. with many utilities still hiring just a few college On a related note, as the industry continues to graduates each year. Looking a few years ahead, at develop new, innovative technologies, they should the same time when a significant number of power be documented and showcased to help generate engineers will be considering retirement, the need excitement about the industry among college-age for them will be significantly increasing. The supply engineers and help attract them to power system of power engineers will have to be great enough to engineering. replace the large numbers of those retiring in addi- The utilities, consultants, and manufacturers must tion to the number required to respond to the an- strengthen their relationships with strong technical ticipated increase in transmission capital spending. institutions to continue increasing support for elec- Today, the number of universities offering power trical engineering departments to offer power sys- engineering programs has decreased. Some uni- tems classes at the undergraduate level. In some versities, such as Rensselaer Polytechnic Institute, cases, this may even require underwriting a class. no longer have separate power system engineering Experience at National Grid has shown that when departments. According to the IEEE, the number of support for a class is guaranteed, the number of power system engineering graduates has dropped students who sign up typically is greater than ex- from approximately 2,000 per year in the 1980s pected. The industry needs to further support these CASE STUDY 9 efforts by offering presentations to students on the electrical demand—and new overhead transmission complexity of the power system, real problems that lines will be only one of the solutions considered. need to be solved, and the impact that a reliable, The second is that it will be important for fur- cost-efficient power system has on society. Sponsor- ther refinement in the restructuring of the industry ing more student internships and research projects to occur. The changes made since the late 1990s will introduce additional students and faculty to the have delivered benefits to customers in the North- unique challenges of the industry. In the future, the east in the form of lower energy costs and access industry will have to hire more nonpower engineers to greater competitive electric markets. Regulators and train them in the specifics of power system en- and policymakers should recognize that in- gineering or rely on hiring from overseas. dependently owned, operated, managed, and widely Finally, the industry needs to cultivate relation- planned networks are important to solving future ships with universities to assist in developing pro- problems most efficiently. Having a reliable, re- fessors who are knowledgeable about the industry. gional, uncongested transmission system will enable This can take the form of research work, consult- a healthy competitive marketplace. ing, and teaching custom programs for the industry. The last, but certainly not least, concern is with National Grid has developed relationships with the industry’s future workforce. Over the last year, several northeastern U.S. institutions that are of- there has been significant discussion of the issue, fering courses for graduate engineers who may not but it will take a considerable effort by many to have power backgrounds. The courses can be of- guide the future workforce into a position of ap- fered online, at the university, or on site at the utility. preciating the electricity industry and desiring to This problem will only get worse if industry enter it and to ensure that the training and educa- leaders do not work together to resolve it. The in- tion systems are in place to develop the new en- dustry’s future depends on its ability to anticipate gineers who will be required to upgrade and main- what lies ahead and the development of the neces- tain the electric power system. sary human resources to meet the challenges. The industry has many challenges, but it also has great resources and a good reputation. Through the efforts of many and by working together through CONCLUSIONS organizations such as PES, the industry can move The electric transmission system plays a critical role forward to the benefit of the public and the United in the lives of the people of the United States. It is States as a whole. an ever-changing system both in physical terms and how it is operated and regulated. These changes ACKNOWLEDGMENTS must be recognized and actions developed accord- ingly. Since the industry is made up of many orga- The following National Grid staff members con- nizations that share the system, it can be difficult to tributed to this article: Jackie Barry, manager, agree on action plans. transmission communications; Janet Gail Besser, There are a few points on which all can agree. vice president, regulatory affairs, U.S. Transmission; The first is that the transmission assets continue to Mary Ellen Paravalos, director, regulatory policy, get older and investment is not keeping up with U.S. Transmission; Joseph Rossignoli, principal ana- needs when looking over a future horizon. The is- lyst, regulatory policy, U.S. Transmission. sue will only get worse as more lines and sub- stations exceed the 50-year age mark. Technology FOR FURTHER READING development and application undoubtedly will in- crease as engineers look for new and creative ways National Grid, ‘‘Transmission: The critical link. De- to combat the congestion issues and increased livering the promise of industry restructuring to 10 CHAPTER 1 INTRODUCTION customers,’’ June 2005 [Online]. Available: http:// BIOGRAPHY www.nationalgridus.com/transmission_the_critical_ Christopher E. Root is senior vice president of link/ Transmission and Distribution (T&D) Technical Ser- E. Hirst, ‘‘U.S. transmission capacity: Present vices of National Grid’s U.S. business. He oversees status and future prospects,’’ Edison Electric Inst. the T&D technical services organization in New and U.S. Dept. Energy, Aug. 2004. England and New York. He received a B.S. in elec- Consumer Energy Council of America, ‘‘Keep- trical engineering from Northeastern University, ing the power flowing: Ensuring a strong trans- Massachusetts, and a master’s in engineering from mission system to support consumer needs for Rensselaer Polytechnic Institute, New York. In cost-effectiveness, security and reliability,’’ Jan. 2005 1997, he completed the Program for Management [Online]. Available: http://www.cecarf.org Development from the Harvard University Gradu- ‘‘Electricity sector framework for the future,’’ ate School of Business. He is a registered Profes- Electric Power Res. Inst., Aug. 2003. sional Engineer in the states of Massachusetts and J. R. Borland, ‘‘A shortage of talent,’’ Transmission Rhode Island and is a Senior Member of the IEEE. Distribution World, Sep. 1, 2002. 1.1 HISTORY OF ELECTRIC POWER SYSTEMS In 1878, Thomas A. Edison began work on the electric light and formulated the concept of a centrally located power station with distributed lighting serving a surrounding area. He perfected his light by October 1879, and the opening of his historic Pearl Street Station in New York City on September 4, 1882, marked the beginning of the electric utility industry (see Figure 1.1). At Pearl Street, dc generators, then called dynamos, were driven by steam engines to supply an initial load of 30 kW for 110-V incandescent lighting to 59 customers in a one-square-mile (2.5-square-km) area. From this beginning in 1882 through 1972, the electric utility industry grew at a remarkable pace—a growth based on continuous reductions in the price of electricity due primarily to technological acomplishment and creative engineering. The introduction of the practical dc motor by Sprague Electric, as well as the growth of incandescent lighting, promoted the expansion of Edison’s dc systems. The development of three-wire 220-V dc systems al- lowed load to increase somewhat, but as transmission distances and loads continued to increase, voltage problems were encountered. These limi- tations of maximum distance and load were overcome in 1885 by William Stanley’s development of a commercially practical transformer. Stanley installed an ac distribution system in Great Barrington, Massachusetts, to supply 150 lamps. With the transformer, the ability to transmit power at high voltage with corresponding lower current and lower line-voltage drops made ac more attractive than dc. The ﬁrst single-phase ac line in the United States operated in 1889 in Oregon, between Oregon City and Portland—21 km at 4 kV. SECTION 1.1 HISTORY OF ELECTRIC POWER SYSTEMS 11 FIGURE 1.1 Milestones of the early electric utility industry (H.M. Rustebakke et al., Electric Utility Systems Practice, 4th Ed. (New York: Wiley, 1983). Reprinted with permission of John Wiley & Sons, Inc. Photos courtesy of Westinghouse Historical Collection) The growth of ac systems was further encouraged in 1888 when Nikola Te- sla presented a paper at a meeting of the American Institute of Electrical En- gineers describing two-phase induction and synchronous motors, which made ev- ident the advantages of polyphase versus single-phase systems. The ﬁrst three- phase line in Germany became operational in 1891, transmitting power 179 km at 12 kV. The ﬁrst three-phase line in the United States (in California) became operational in 1893, transmitting power 12 km at 2.3 kV. The three-phase induc- tion motor conceived by Tesla went on to become the workhorse of the industry. In the same year that Edison’s steam-driven generators were inaugurated, a waterwheel-driven generator was installed in Appleton, Wisconsin. Since then, most electric energy has been generated in steam-powered and in water- powered (called hydro) turbine plants. Today, steam turbines account for more than 85% of U.S. electric energy generation, whereas hydro turbines account for about 6%. Gas turbines are used in some cases to meet peak loads. Also, the addition of wind turbines into the bulk power system is expected to grow considerably in the near future. 12 CHAPTER 1 INTRODUCTION Steam plants are fueled primarily by coal, gas, oil, and uranium. Of these, coal is the most widely used fuel in the United States due to its abun- dance in the country. Although many of these coal-fueled power plants were converted to oil during the early 1970s, that trend has been reversed back to coal since the 1973–74 oil embargo, which caused an oil shortage and created a national desire to reduce dependency on foreign oil. In 2008, approximately 48% of electricity in the United States was generated from coal. In 1957, nuclear units with 90-MW steam-turbine capacity, fueled by uranium, were installed, and today nuclear units with 1312-MW steam- turbine capacity are in service. In 2008, approximately 20% of electricity in the United States was generated from uranium from 104 nuclear power plants. However, the growth of nuclear capacity in the United States has been halted by rising construction costs, licensing delays, and public opinion. Although there are no emissions associated with nuclear power generation, there are safety issues and environmental issues, such as the disposal of used nuclear fuel and the impact of heated cooling-tower water on aquatic hab- itats. Future technologies for nuclear power are concentrated on safety and environmental issues [2, 3]. Starting in the 1990s, the choice of fuel for new power plants in the United States has been natural gas due to its availability and low cost as well as the higher e‰ciency, lower emissions, shorter construction-lead times, safety, and lack of controversy associated with power plants that use natural gas. Natural gas is used to generate electricity by the following processes: (1) gas combustion turbines use natural gas directly to ﬁre the turbine; (2) steam turbines burn natural gas to create steam in a boiler, which is then run through the steam turbine; (3) combined cycle units use a gas combustion turbine by burning natural gas, and the hot exhaust gases from the combus- tion turbine are used to boil water that operates a steam turbine; and (4) fuel cells powered by natural gas generate electricity using electrochemical re- actions by passing streams of natural gas and oxidants over electrodes that are separated by an electrolyte. In 2008, approximately 21% of electricity in the United States was generated from natural gas [2, 3]. In 2008, in the United States, approximately 9% of electricity was gen- erated by renewable sources and 1% by oil [2, 3]. Renewable sources include conventional hydroelectric (water power), geothermal, wood, wood waste, all municipal waste, landﬁll gas, other biomass, solar, and wind power. Renew- able sources of energy cannot be ignored, but they are not expected to supply a large percentage of the world’s future energy needs. On the other hand, nu- clear fusion energy just may. Substantial research e¤orts have shown nuclear fusion energy to be a promising technology for producing safe, pollution-free, and economical electric energy later in the 21st century and beyond. The fuel consumed in a nuclear fusion reaction is deuterium, of which a virtually in- exhaustible supply is present in seawater. The early ac systems operated at various frequencies including 25, 50, 60, and 133 Hz. In 1891, it was proposed that 60 Hz be the standard fre- quency in the United States. In 1893, 25-Hz systems were introduced with the SECTION 1.1 HISTORY OF ELECTRIC POWER SYSTEMS 13 FIGURE 1.2 Growth of U.S. electric energy consumption [1, 2, 3, 5] (H. M. Rustebakke et al., Electric Utility Systems Practice, 4th ed. (New York: Wiley, 1983); U.S. Energy Information Administration, Existing Capacity by Energy Source—2008, www.eia.gov; U.S. Energy Information Administration, Annual Energy Outlook 2010 Early Release Overview, www.eia.gov; M.P. Bahrman and B.K. Johnson, ‘‘The ABCs of HVDC Transmission synchronous converter. However, these systems were used primarily for rail- Technologies,’’ IEEE road electriﬁcation (and many are now retired) because they had the dis- Power & Energy advantage of causing incandescent lights to ﬂicker. In California, the Los Magazine, 5, 2 (March/ Angeles Department of Power and Water operated at 50 Hz, but converted April 2007), pp. 33–44) to 60 Hz when power from the Hoover Dam became operational in 1937. In 1949, Southern California Edison also converted from 50 to 60 Hz. Today, the two standard frequencies for generation, transmission, and distribution of electric power in the world are 60 Hz (in the United States, Canada, Japan, Brazil) and 50 Hz (in Europe, the former Soviet republics, South America except Brazil, and India). The advantage of 60-Hz systems is that generators, motors, and transformers in these systems are generally smaller than 50-Hz equipment with the same ratings. The advantage of 50-Hz systems is that transmission lines and transformers have smaller reactances at 50 Hz than at 60 Hz. As shown in Figure 1.2, the rate of growth of electric energy in the United States was approximately 7% per year from 1902 to 1972. This corre- sponds to a doubling of electric energy consumption every 10 years over the 70-year period. In other words, every 10 years the industry installed a new electric system equal in energy-producing capacity to the total of what it had built since the industry began. The annual growth rate slowed after the oil embargo of 1973–74. Kilowatt-hour consumption in the United States in- creased by 3.4% per year from 1972 to 1980, and by 2.1% per year from 1980 to 2008. Along with increases in load growth, there have been continuing in- creases in the size of generating units (Table 1.1). The principal incentive to build larger units has been economy of scale—that is, a reduction in installed cost per kilowatt of capacity for larger units. However, there have also been steady improvements in generation e‰ciency. For example, in 1934 the average heat rate for steam generation in the U.S. electric industry was 14 CHAPTER 1 INTRODUCTION TABLE 1.1 Generators Driven by Single-Shaft, Growth of generator Hydroelectric Generators 3600 r/min Fossil-Fueled Steam Turbines sizes in the United States (H. M. Size Year of Size Year of Rustebakke et al., (MVA) Installation (MVA) Installation Electric Utility Systems 4 1895 5 1914 Practice, 4th Ed. (New 108 1941 50 1937 York: Wiley, 1983). 158 1966 216 1953 Reprinted with 232 1973 506 1963 permission of John 615 1975 907 1969 Wiley & Sons, Inc.) 718 1978 1120 1974 18,938 kJ/kWh, which corresponds to 19% e‰ciency. By 1991, the average heat rate was 10,938 kJ/kWh, which corresponds to 33% e‰ciency. These improvements in thermal e‰ciency due to increases in unit size and in steam temperature and pressure, as well as to the use of steam reheat, have resulted in savings in fuel costs and overall operating costs. There have been continuing increases, too, in transmission voltages (Table 1.2). From Edison’s 220-V three-wire dc grid to 4-kV single-phase and 2.3-kV three-phase transmission, ac transmission voltages in the United States have risen progressively to 150, 230, 345, 500, and now 765 kV. And ultra-high voltages (UHV) above 1000 kV are now being studied. The in- centives for increasing transmission voltages have been: (1) increases in TABLE 1.2 transmission distance and transmission capacity, (2) smaller line-voltage drops, (3) reduced line losses, (4) reduced right-of-way requirements per MW History of increases in transfer, and (5) lower capital and operating costs of transmission. Today, three-phase transmission voltages in the United one 765-kV three-phase line can transmit thousands of megawatts over hun- States (H. M. dreds of kilometers. Rustebakke et al., The technological developments that have occurred in conjunction with Electric Utility Systems ac transmission, including developments in insulation, protection, and con- Practice, 4th Ed. (New trol, are in themselves important. The following examples are noteworthy: York: Wiley, 1983). Reprinted with permission of John 1. The suspension insulator Wiley & Sons, Inc.) 2. The high-speed relay system, currently capable of detecting short- Voltage Year of circuit currents within one cycle (0.017 s) (kV) Installation 3. High-speed, extra-high-voltage (EHV) circuit breakers, capable of 2.3 1893 interrupting up to 63-kA three-phase short-circuit currents within 44 1897 two cycles (0.033 s) 150 1913 165 1922 4. High-speed reclosure of EHV lines, which enables automatic re- 230 1923 turn to service within a fraction of a second after a fault has been 287 1935 345 1953 cleared 500 1965 5. The EHV surge arrester, which provides protection against transient 765 1969 overvoltages due to lightning strikes and line-switching operations SECTION 1.1 HISTORY OF ELECTRIC POWER SYSTEMS 15 6. Power-line carrier, microwave, and ﬁber optics as communication mechanisms for protecting, controlling, and metering transmission lines 7. The principle of insulation coordination applied to the design of an entire transmission system 8. Energy control centers with supervisory control and data acquisi- tion (SCADA) and with automatic generation control (AGC) for centralized computer monitoring and control of generation, trans- mission, and distribution 9. Automated distribution features, including advanced metering in- frastructure (AMI), reclosers and remotely controlled sectionalizing switches with fault-indicating capability, along with automated mapping/facilities management (AM/FM) and geographic informa- tion systems (GIS) for quick isolation and identiﬁcation of outages and for rapid restoration of customer services 10. Digital relays capable of circuit breaker control, data logging, fault locating, self-checking, fault analysis, remote query, and relay event monitoring/recording. In 1954, the ﬁrst modern high-voltage dc (HVDC) transmission line was put into operation in Sweden between Vastervik and the island of Gotland in the Baltic sea; it operated at 100 kV for a distance of 100 km. The ﬁrst HVDC line in the United States was the G400-kV (now G500 kV), 1360-km Paciﬁc Intertie line installed between Oregon and California in 1970. As of 2008, seven other HVDC lines up to 500 kV and eleven back-to-back ac-dc links had been installed in the United States, and a total of 57 HVDC lines up to 600 kV had been installed worldwide. For an HVDC line embedded in an ac system, solid-state converters at both ends of the dc line operate as rectiﬁers and inverters. Since the cost of an HVDC transmission line is less than that of an ac line with the same capac- ity, the additional cost of converters for dc transmission is o¤set when the line is long enough. Studies have shown that overhead HVDC transmission is economical in the United States for transmission distances longer than about 600 km. However, HVDC also has the advantage that it may be the only feasible method to: 1. interconnect two asynchronous networks; 2. utilize long underground or underwater cable circuits; 3. bypass network congestion; 4. reduce fault currents; 5. share utility rights-of-way without degrading reliability; and 6. mitigate environmental concerns. In the United States, electric utilities grew ﬁrst as isolated systems, with new ones continuously starting up throughout the country. Gradually, however, FIGURE 1.3 Major transmission in the United States—2000 (( North American Electric Reliability Council. Reprinted with permission) SECTION 1.2 PRESENT AND FUTURE TRENDS 17 neighboring electric utilities began to interconnect, to operate in parallel. This improved both reliability and economy. Figure 1.3 shows major 230-kV and higher-voltage, interconnected transmission in the United States in 2000. An in- terconnected system has many advantages. An interconnected utility can draw upon another’s rotating generator reserves during a time of need (such as a sudden generator outage or load increase), thereby maintaining continuity of service, increasing reliability, and reducing the total number of generators that need to be kept running under no-load conditions. Also, interconnected utilities can schedule power transfers during normal periods to take advantage of energy-cost di¤erences in respective areas, load diversity, time zone di¤erences, and seasonal conditions. For example, utilities whose generation is primarily hydro can supply low-cost power during high-water periods in spring/summer, and can receive power from the interconnection during low-water periods in fall/winter. Interconnections also allow shared ownership of larger, more e‰- cient generating units. While sharing the beneﬁts of interconnected operation, each utility is obligated to help neighbors who are in trouble, to maintain scheduled in- tertie transfers during normal periods, and to participate in system frequency regulation. In addition to the beneﬁts/obligations of interconnected operation, there are disadvantages. Interconnections, for example, have increased fault currents that occur during short circuits, thus requiring the use of circuit breakers with higher interrupting capability. Furthermore, although overall system reliability and economy have improved dramatically through inter- connection, there is a remote possibility that an initial disturbance may lead to a regional

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