electric energy systems. analysis and operation

ElectricEnergy Systems

Analysis and Operation

2009 by Taylor & Francis Group, LLC

The ELECTRIC POWER ENGINEERING SeriesSeries Editor Leo L. Grigsby

Published Titles

Electric DrivesIon Boldea and Syed Nasar

Linear Synchronous Motors: Transportation and Automation SystemsJacek Gieras and Jerry Piech

Electromechanical Systems, Electric Machines,and Applied MechatronicsSergey E. Lyshevski

Electrical Energy Systems, Second EditionMohamed E. El-Hawary

The Induction Machine HandbookIon Boldea and Syed Nasar

Power QualityC. Sankaran

Power System Operations and Electricity MarketsFred I. Denny and David E. Dismukes

Computational Methods for Electric Power SystemsMariesa Crow

Electric Power Substations EngineeringJohn D. McDonald

Electric Power Transformer EngineeringJames H. I

Electric Power Distribution HandbookTom Short

Synchronous GeneratorsIon Boldea

Variable Speed GeneratorsIon Boldea

Harmonics and Power SystemsFrancisco C, De La Rosa

Electric MachinesCharles A. Gross

Distribution System Modeling and Analysis, Second EditionWilliam H. Kersting

Electric Energy Systems: Analysis and OperationAntonio Gomez-Exposito, Antonio J. Conejo, and Claudio Canizares


ElectricEnergy Systems

Analysis and Operation

EDITED BY

ANTONIO GOMEZ-EXPOSITOUniversity of Sevilla

Spain

ANTONIO J. CONEJOUnversity of Castilla-La Mancha

Ciudad-Real, Spain

CLAUDIO CANIZARESUniversity ofWaterloo

Ontario, Canada

CRC PressTaylor &. Francis Group

Boca Raton London New York

CRC Press is an imprint of the

Taylor & Francis Group, an informa business


Cover: 34-MW Wind Farm at Arlanzon (Burgos province, in Spain). Courtesy of Neo Energfa.

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2009 by Taylor & Francis Group, LLCCRC Press is an imprint of Taylor & Francis Group, an Informa business

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Library of Congress Cataloging-in-Publication Data

Electric energy systems : analysis and operation / editors, Antonio Gomez-Exposito, Antonio J.Conejo, Claudio Canizares.

p. cm. (The electric power engineering series)Includes bibliographical references and index.ISBN 978-0-8493-7365-7 (hardback : alk. paper)1. Electric power systems. I. Gomez Exposito, Antonio. II. Conejo, Antonio J. III. Canizares,

Claudio.

TK1001.E347 2008621.319-dc22 2008013036

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Experience is not always the kindest of teachers,but it is surely the best

Spanish Proverb


Contents

Foreword ................................................................................................................................ ixEditors .................................................................................................................................. xiiiContributors ........................................................................................................................... xv

Chapter 1 Electric Energy SystemsAn Overview ............................................................. 1

Ignacio J. Prez-Arriaga, Hugh Rudnick, and Michel Rivier Abbad

Chapter 2 Steady-State Single-Phase Models of Power System Components ..................... 51

Edmund Handschin, Antonio F. Otero, and Jos Cidrs

Chapter 3 Load Flow ....................................................................................................... 95

Antonio Gmez-Expsito and Fernando L. Alvarado

Chapter 4 State Estimation ............................................................................................. 127

Antonio Gmez-Expsito and Ali Abur

Chapter 5 Economics of Electricity Generation .............................................................. 165

Francisco D. Galiana and Antonio J. Conejo

Chapter 6 Optimal and Secure Operation of Transmission Systems ................................. 211

Jos Luis Martnez Ramos and Vctor Hugo Quintana

Chapter 7 Three-Phase Linear and Nonlinear Models of Power System Components ....... 265

Enrique Acha and Julio Usaola

Chapter 8 Fault Analysis and Protection Systems ........................................................... 303

Jos Cidrs, Jos F. Miambres, and Fernando L. Alvarado

Chapter 9 Frequency and Voltage Control ....................................................................... 355

Gran Andersson, Carlos lvarez Bel, and Claudio Caizares

Chapter 10 Angle, Voltage, and Frequency Stability ......................................................... 401

Claudio Caizares, Luis Rouco, and Gran Andersson

vii


viii Contents

Chapter 11 Three-Phase Power Flow and Harmonic Analysis ........................................... 461

Wilsun Xu and Julio Garca-Mayordomo

Chapter 12 Electromagnetic Transients Analysis .............................................................. 509

Juan A. Martnez-Velasco and Jos R. Mart

Appendix A Solution of Linear Equation Systems ............................................................. 583

Fernando L. Alvarado and Antonio Gmez-Expsito

Appendix B Mathematical Programming .......................................................................... 601

Antonio J. Conejo

Appendix C Dynamic Models of Electric Machines .......................................................... 627

Luis Rouco


Foreword

The purpose of this book is to merge, update, and extend the material in both classical power systemanalysis books and power economics books, within the framework of currently restructured electricenergy systems. This effort is clearly needed to address the operations and planning problems innowadays unbundled generation, transmission, and distribution systems.

In addressing the aforementioned issues, we realized that the challenges were significant. Firstof all, we had to provide added value to the reference books on the topic. Fortunately, achievingthis goal was facilitated by the economic and technical revolution that the electric sector has beenundergoing during the last two decades. This revolution has dramatically changed or made obsoletemany important concepts as they are considered in existing books. Another difference between thisand earlier books lies in the addition of some advanced chapters, which are usually covered inspecialized monographs, as well as in the deeper treatment of certain classical topics.

The second and perhapsmore difficult challengewas the need to avoid an encyclopedic approach,both in scope and content. A book coauthored by 24 researchers, each one writing on his own area ofexpertise, can easily degenerate into a voluminous collection of disconnected papers, which mightonly be useful for a minority of specialists. Being aware of this risk, the authors have made asignificant effort to begin with the basic principles, paying attention to the topics any power engineershould know, includingmany solved examples, and directing the reader to other chapters if necessary.Some redundant material has been intentionally left out in order not to distract the readers attentionby cross referencing. An added advantage of the approach used here is that many chapters becomeself-sufficient for those readers with a certain background in power systems who simply desire tokeep themselves updated.

Our objective was to keep the spectrum of readers to whom this book is directed fairly broad. Onthe one hand, instructors and undergraduate students of engineering schools can use it as a textbook,with the material being possibly fully covered in two terms. Depending on the particular context, theinstructor may have to pick up only a subset of chapters, discarding those that are covered in othersubjects of the curriculum. This may be the case of protections, overvoltages, synchronous machines,etc. On the other hand, considering the advanced level of certain chapters, and the inclusion, for thefirst time in a textbook of this breadth and depth, of the regulatory issues, which are changingthe electric sector, this volume can also serve as a handbook for graduate students and practicingprofessionals who lack the time to search for original sources (papers and technical reports). Thesereaders will surely welcome the large number of references at the end of each chapter, which willallow them to acquire a deeper knowledge on the topics of their own interest.

It is assumed here that the reader has a minimum background in algebra (matrices, complexnumbers, etc.), calculus (linear differential equations, Laplace and Fourier transform, etc.), physics(electromagnetic fields, rotating mass dynamics, etc.), circuits (nodal equations, three-phase circuits,etc.) and, if possible, electric machines and microeconomics. This is usually the case of thoseundergraduate students who enroll for the first time in a course on power system analysis.

Owing to space limitations, the book is mainly focused on the operation of generation andtransmission systems, although part of the material (e.g., certain component models, three-phaseand harmonic load flows, reliability indices and protections) is of application also in the analysis ofdistribution networks. For the same reason, the long-term planning problem has not been explicitlydealt with; nevertheless, several chapters and parts of others (e.g., load flow, generation scheduling,security, reliability, and stability) present essential tools for network expansion studies, design andcomparison of alternatives, etc., which are directly linked with the short-term planning problem.

ix


x Foreword

The book has been organized in 12 chapters and 3 appendices, which could have been arrangedin several ways. A possibility could have been to begin with the most classical chapters (load flow,frequency regulation, economic dispatch, short circuits, and transient stability), and then continuewith what could be labeled advanced topics (market issues, state estimation, electromagnetic tran-sients, harmonics, etc.). However, it is difficult in many cases to place the division between basicand advanced material properly speaking, particularly in those chapters specifically dealing with theoperation of generation and transmission systems. The scheme adopted in this book is based insteadon the different working regimes of the power system, which are crucial to determine the techniquesand tools needed to study the time scales involved.

The five chapters following the introductory one cover what is essentially the balanced sinusoidalsteady-state regime, which, rigorously speaking, should be called quasi-steady-state because of theslow but continuous variation of the loads. In this context, mainly related to the real-time operationof power systems, phasors and complex power constitute the basic tools on which the differentanalytical and computational methods are built. On the other hand, the last six chapters are devotedto the transient and nonsinusoidal states of a power system, including both balanced and unbalancedconditions. The system under transients originated by faults is first dealt with, followed by the slowerelectromechanical oscillations, to end with the faster electromagnetic transients.

Chapter 1 makes an original presentation of what power systems have been in the past and whatthey have become nowadays, from the technical, economical and regulatory points of view. It consti-tutes by itself very valuablematerial to be disseminated among those young students who erroneouslybelieve that professional challenges can only be found in computer engineering and communications.

Besides conventional components, Chapter 2 briefly deals with cables and asynchronousmachinemodeling, of renewed interest in view of the growth of distributed generation. An introduction toload forecasting techniques is also presented.

In Chapter 3, which is devoted to the classic power flow or load flow problem, the section onlarge-scale systems, complemented by Appendix A, stands out. The reader may find interesting thediscussion about the simplifications behind the fast decoupled load flow. Power flow and voltageregulating devices are presented, starting from a common framework, in an original manner.

Chapter 4 provides many more details than it is usual in textbooks about advanced topics relatedto state estimation, like nonquadratic estimators and topology error identification.

Chapter 5 starts with a rigorous and general treatment of the economic dispatch problem, payingspecial attention to transmission loss coefficients, and finishes with the formulation of the optimiza-tion problems currently faced by producers, consumers, and other agents of electricity markets.

The presence of Chapter 6, entirely devoted to the operation of the transmission subsystem, isnew in textbooks of this nature, but we believe it is fundamental to provide a comprehensive viewof all the problems and tasks involved at this level. The new paradigm under which transmissionnetworks are operated, based on open and nondiscriminatory access, and the resulting challenges arepresented and discussed in this chapter.

The second part of the book starts with Chapter 7, which is devoted to a general treatment ofthree-phase linear and nonlinear models of power system components, including power electronicscomponents, such as filters, voltage-source converters, etc. Several of the models described here areused in the following chapters.

Chapter 8 comprises two closely related subjects, namely fault analysis, including a brief refer-ence to grounding systems, and protections. More attention than usual is paid to the matrix-basedsystematic analysis of short circuits in large-scale systems.

Automatic regulation and control of voltages and frequency is dealt with in Chapter 9 from abroader perspective, beginning with local or primary control strategies and ending with the region-wide secondary and tertiary control schemes. These controls and associated concepts, such ashierarchical and wide-area control, are presented and discussed within the context of practical gridrequirements in Europe and North America, and in view of their role in competitive electricitymarkets, particularly in relation to ancillary services.


Foreword xi

Power system stability analysis is discussed in Chapter 10 in a novel and up-to-date manner.This chapter assumes that the reader is familiar with basic system element models and controls,particularly those associated with the synchronous machine, as discussed in Chapters 7 and 9 andAppendix C. Each stability subtopic, that is, angle, voltage, and frequency stability, is first definedand the main concepts and analysis techniques are then explained using basic and simple systemmodels. This is followed by a discussion of practical applications, analysis tools and measures forstability improvement, closing with a brief description of a real instability event, which is a uniquefeature of this book with respect to other textbooks in the topic.

Chapters 11 addresses again the power flow problem but under nonsinusoidal and unbalancedconditions. This chapter presents advanced topics whose relevance is steadily increasing, given thegrowing portion and size of electronic converters connected to power systems.

Ignored or superficially covered in most textbooks, in Chapter 12 analytical and computationaltechniques for the study of electromagnetic transients are explained in detail, as well as some relatedapplications, like propagation and limitation of overvoltages.

The book closes with three appendices covering the solution of large-scale sparse systems oflinear equations (Appendix A), the fundamentals of optimization (Appendix B), and the modelingof induction and synchronous machines (Appendix C).

The analytical and computational techniques covered in this book have been selected taking intoaccount that the speed of response in the analysis of very large nonlinear systems is often crucialfor the results to be of practical use. In this sense, electric energy systems constitute a unique case,because of their size, complexity, and strict control requirements.

We are thankful to all the colleagues, students, and institutions who have helped us in the complexendeavor of editing andpartlywriting this book.Wehope that this bookwill be helpful for the newgen-erations of power engineering students and professionals, which is the solemotivation for this project.

A. Gmez ExpsitoSevilla, Spain

A. J. ConejoCiudad Real, Spain

C. CaizaresWaterloo, Canada


Editors

Antonio Gmez-Expsito received a six-year Industrial Engineering degree, major in ElectricalEngineering, with honors, in 1982, and a Doctor of Engineering degree in 1985, both from theUniversity of Seville, Spain. He is currently a full professor at the University of Seville, where he ischairing the Department of Electrical Engineering, the Post-Graduate Program on Electrical EnergySystems and the recently created Endesa Cathedra. In the late eighties, he created and is leading aresearch group with over twenty researchers, including fourteen doctors. Previously he was also avisiting professor in California and Canada.

Prof. Gmez-Expsito has coauthored several textbooks and monographs about Circuit Theoryand Power System Analysis, of which the one published by Marcel Dekker, Power System StateEstimation: Theory and Implementation, stands out. He is also coauthor of nearly 200 technicalpublications, many of them in IEEE Transactions. In addition to his regular consulting activity, hehas been principal investigator of over forty research projects, funded by public institutions and allmajor Spanish utilities. Practical results of those projects are power system state estimators, expertsystems, digital relays, fault locators, training simulators, etc.

Prof. Gmez-Expsito is amember of theEditorial Board of the IEEELatinAmericaTransactionsand has been involved in the organizing and technical committees of nearly twenty internationalconferences. Among other recognitions, he received in 2005 the City of Seville Award for hisresearch activities in electric energy efficiency, as well as the Novare Award in 2007, granted byEndesa to fund a 0.5 Meuros research project. He is a Fellow of the IEEE.

Antonio J. Conejo received an MS degree from MIT, Cambridge, Massachusetts and a PhD degreefrom the Royal Institute of Technology, Stockholm, Sweden. He is currently a full professor ofElectrical Engineering at the Universidad de Castilla-La Mancha, Ciudad Real, Spain. A coauthor ofDecomposition Techniques in Mathematical Programming: Engineering and Science Applications,professor Conejo has authored or coauthored over ninety papers in refereed journals, and has been theprincipal investigator of many research projects. His research interests include control, operations,planning and economics of electric energy systems, as well as statistics and optimization theory andits applications. Professor Conejo is a member of the editorial board of the IEEE Transactions onPower Systems and an IEEE Fellow.

Claudio A. Caizares received an Electrical Engineering degree in April 1984 from the EscuelaPolitcnica Nacional (EPN), Quito-Ecuador, where he held various teaching and administrative posi-tions from 1983 to 1993. His MSc (1988) and PhD (1991) degrees in Electrical Engineering arefrom the University of Wisconsin-Madison. He is currently a full professor at the University ofWaterloo, Department of Electrical and Computer Engineering, and was the associate chairman ofGraduate Studies (20002003), deputy chair (20032004), and acting chair (JulyAugust 2004) ofthe Department. In the 19992000 academic year, he was a Visiting Professor at the Dipartimento diElettrotecnica of the Politecnico di Milano, and worked as a research consultant for ENEL-Ricercaand CESI in Milan. During his 20062007 sabbatical leave, he was an invited professor at eachof the following institutions: ETH, Zurich, Switzerland (SeptemberOctober 2006); University ofCastilla-La Mancha, Ciudad Real, Spain (NovemberDecember 2006); and University of Seville,Seville, Spain (JanuaryFebruary 2007). His research activities concentrate mostly on the study ofnonlinear systems stability, modeling and computational issues in ac/HVDC/FACTS power systems,and more recently in the areas of price forecasting, demand side management/demand response and

xiii


xiv Editors

multicarrier energy systems, all within the context of competitive electricity markets. In these areas,he is continuously collaborating with industry and university researchers in Canada and abroad,supervising multiple research fellows and graduate students, some of whom have received awards atimportant international conferences, and several hold leadership positions in industry and academia.Of his multiple teaching activities, in 2003, his leadership role in the proposal and development ofa very successful Power Engineering online program for industry professionals, with strong supportand significant funding from Hydro One Networks Inc., should be highlighted.

Dr. Caizares has authored and coauthored over 170 journal and conference papers, as well asvarious technical reports, book chapters and a popular computer program for bifurcation analysis ofpower systems. He has been invited to make keynote presentations at various seminars and confer-ences throughout the world, as well as participate in several technical IEEE and CIGRE committeesand special publications. He is an active member of various IEEE and CIGRE committees, workinggroups and task forces, and currently holds, and has held in the past, several leadership appointmentsin some of these committees, which have led to IEEE-PES Working Group Recognition awards. InJanuary 2007, he was granted the IEEE Fellow rank for contributions to voltage stability of powersystems. He is also a registered professional engineer in the province of Ontario, Canada.


Contributors

Michel Rivier AbbadUniversidad Pontificia Comillas de MadridMadrid, Spain

Ali AburNortheastern UniversityBoston, Massachusetts, USA

Enrique AchaUniversity of GlasgowGlasgow, Scotland, United Kingdom

Fernando L. AlvaradoUniversity of WisconsinMadison, Wisconsin, USA

Gran AnderssonETHZurich, Switzerland

Carlos lvarez BelPolytechnic University of ValenciaValencia, Spain

Claudio CaizaresUniversity of WaterlooWaterloo, Ontario, Canada

Jos CidrsUniversity of VigoVigo, Spain

Antonio J. ConejoUniversidad de Castilla La ManchaCiudad Real, Spain

Francisco D. GalianaMcGill UniversityMontral, Qubec, Canada

Julio Garca-MayordomoUniversidad Politcnica de MadridMadrid, Spain

Antonio Gmez-ExpsitoUniversity of SevilleSeville, Spain

Edmund HandschinTechnische Universitt DortmundDortmund, Germany

Jos R. MartThe University of British ColumbiaVancouver, Canada

Jos Luis Martnez RamosUniversity of SevilleSeville, Spain

Juan A. Martnez-VelascoUniversitat Politcnica de CatalunyaBarcelona, Spain

Jos F. MiambresUniversity of Basque CountryBilbao, Spain

Antonio F. OteroUniversity of VigoVigo, Spain

Ignacio J. Prez-ArriagaUniversidad Pontificia Comillas de MadridMadrid, Spain

Vctor Hugo QuintanaUniversity of WaterlooWaterloo, Ontario, Canada

xv


xvi Contributors

Luis RoucoUniversidad Pontificia Comillas de MadridMadrid, Spain

Hugh RudnickPontificia Universidad Catolica de ChileSantiago, Chile

Julio UsaolaUniversidad Carlos III de MadridMadrid, Spain

Wilsun XuUniversity of AlbertaEdmonton, Alberta, Canada


1 Electric Energy SystemsAnOverview

Ignacio J. Prez-Arriaga, Hugh Rudnick,and Michel Rivier Abbad

CONTENTS

1.1 A First Vision..................................................................................................................... 21.1.1 The Energy Challenges in Modern Times ................................................................ 21.1.2 Characteristics of Electricity.................................................................................... 31.1.3 Electrical Energy Systems: The Biggest Industrial System

Created by Humankind ........................................................................................... 31.1.4 History ................................................................................................................... 4

1.1.4.1 Technological Aspects .............................................................................. 41.1.4.2 Organizational Aspects ............................................................................. 6

1.1.5 Environmental Impact ............................................................................................. 71.2 The Technological Environment ......................................................................................... 9

1.2.1 Electric Power System Structure.............................................................................. 91.2.2 Consumption ........................................................................................................ 10

1.2.2.1 Demand Growth ..................................................................................... 101.2.2.2 Demand Profiles ..................................................................................... 131.2.2.3 Service Quality ....................................................................................... 15

1.2.3 Generation ............................................................................................................ 161.2.3.1 Different Generation Technologies .......................................................... 161.2.3.2 The Whys and Wherefores of a Generation Mix .................................... 20

1.2.4 Transmission ........................................................................................................ 211.2.4.1 Power Lines............................................................................................ 221.2.4.2 Substations ............................................................................................. 23

1.2.5 Distribution........................................................................................................... 251.2.6 Control and Protection .......................................................................................... 25

1.3 The Economic Environment ............................................................................................. 271.3.1 The Electric Sector and Economic Activity............................................................ 271.3.2 Expansion and Operation in the Traditional Context .............................................. 27

1.3.2.1 Long Term.............................................................................................. 281.3.2.2 Medium Term......................................................................................... 291.3.2.3 Short Term.............................................................................................. 301.3.2.4 Real Time............................................................................................... 31

1.3.3 Expansion and Operation in the New Regulatory Context ...................................... 311.3.3.1 Long Term.............................................................................................. 321.3.3.2 Medium Term......................................................................................... 321.3.3.3 Short Term.............................................................................................. 331.3.3.4 Real Time............................................................................................... 33

1


2 Electric Energy Systems: Analysis and Operation

1.4 The Regulatory Environment ............................................................................................ 331.4.1 Traditional Regulation and Regulation of Competitive Markets .............................. 331.4.2 New Regulatory Environment................................................................................ 34

1.4.2.1 Motivation .............................................................................................. 341.4.2.2 Fundamentals ......................................................................................... 341.4.2.3 Requirements.......................................................................................... 35

1.4.3 Nature of Electric Activities .................................................................................. 351.4.3.1 Unbundling of Activities ......................................................................... 361.4.3.2 Generation Activities .............................................................................. 361.4.3.3 Network Activities .................................................................................. 371.4.3.4 Transmission .......................................................................................... 381.4.3.5 Distribution ............................................................................................ 391.4.3.6 Transaction Activities ............................................................................. 411.4.3.7 Ancillary Activities................................................................................. 431.4.3.8 Coordination Activities ........................................................................... 43

1.4.4 Practical Aspects of Regulation ............................................................................. 441.4.4.1 Transition to Competition ....................................................................... 441.4.4.2 Stranded Benefits.................................................................................... 451.4.4.3 Environmental Costs ............................................................................... 451.4.4.4 Structural Aspects................................................................................... 451.4.4.5 Security of Supply in Generation............................................................. 451.4.4.6 Independent Regulatory Body ................................................................. 46

1.4.5 The Trends in Regulation: International Experiences.............................................. 461.5 Modeling Requirements of Modern Electric Energy Systems ............................................ 471.6 Future Challenges and Prospects....................................................................................... 49References and Further Reading................................................................................................ 50

1.1 A FIRST VISION

1.1.1 THE ENERGY CHALLENGES IN MODERN TIMES

Energy is a fundamental ingredient ofmodern society and its supply impacts directly on the social andeconomic development of nations. Economic growth and energy consumption go hand-in-hand. Thedevelopment and quality of our lives and our work are totally dependent on a continuous, abundant,and economic energy supply. This reality is being faced worldwide as basic energy resources havebecome scarce and increasingly costly. While coal remains an abundant resource, oil and natural gassupply face restrictions, concerns arising on declining volumes in the long term. This reliance onenergy for economic growth has historically implied dependence on third parties for energy supply,with geopolitical connotations, as energy resources have not been generally in places where highconsumption has developed. Energy has transformed itself into a new form of international politicalpower, utilized by owners of energy resources (mainly oil and natural gas).

Within that framework, electricity has become a favorite form of energy usage at the consumerend, with coal, oil, gas, uranium, and other basic resources used to generate electricity. With its ver-satility and controllability, instant availability and consumer-end cleanliness, electricity has becomean indispensable, multipurpose form of energy. Its domestic use now extends far beyond the initialpurpose, to which it owes its colloquial name (light or lights), and has become virtually irre-placeable in kitchensfor refrigerators, ovens, and cookers or ranges, and any number of otherappliancesand in the rest of the house as well, for air conditioner, radio, television, computers, and


Electric Energy SystemsAn Overview 3

the like. But electricity usage is even broader in the commercial and industrial domains: in additionto providing power for lighting and air conditioning, it drives motors with a host of applications: lifts,cranes, mills, pumps, compressors, lathes, or other machine tools, and so on and so forth: it is nearlyimpossible to imagine an industrial activity that does not use electricity. Thus, modern societies havebecome totally dependent on an abundant electricity supply.

1.1.2 CHARACTERISTICS OF ELECTRICITY

At first glance, electricity must appear to be a commodity much like any other on consumers list ofroutine expenses. In fact, this may be the point of view that prompted the revolution that has rockedelectric energy systems worldwide, as they have been engulfed in the wave of liberalization andderegulation that has changed so many other sectors of the economy. And yet electricity is defined bya series of properties that distinguish it from other products, an argument often wielded in an attemptto prevent or at least limit the implementation of such changes in the electricity industry. The chiefcharacteristic of electricity as a product that differentiates it from all others is that it is not susceptible,in practice, to being stored or inventoried. Electricity can, of course, be stored in batteries, but price,performance, and inconvenience make this impractical for handling the amounts of energy usuallyneeded in the developed world. Therefore, electricity must be generated and transmitted as it isconsumed, which means that electric systems are dynamic and highly complex, as well as immense.At any given time, these vast dynamic systems must strike a balance between generation and demandand the disturbance caused by the failure of a single component may be transmitted across the entiresystem almost instantaneously. This sobering fact plays a decisive role in the structure, operation,and planning of electric energy systems, as discussed below.

Another peculiarity of electricity is its transmission: this is not a product that can be shipped inpackages from its origin to destination by the most suitable medium at any given time. Electricpower is transmitted over grids in which the pathway cannot be chosen at will, but is determined byKirchhoffs laws, whereby current distribution depends on impedance in the lines and other elementsthrough which electricity flows. Except in very simple cases, all that can be said is that electricpower flows into the system at one point and out of it at another, because ascribing the flow to anygiven path is extraordinarily complex and somewhat arbitrary. Moreover, according to these laws ofphysics, the alternative routes that form the grid are highly interdependent, so that any variation in atransmission facility may cause the instantaneous reconfiguration of power flows and that, in turn,may have a substantial effect on other facilities. All this renders the dynamic balance referred to inthe preceding paragraph even more complex.

1.1.3 ELECTRICAL ENERGY SYSTEMS: THE BIGGEST INDUSTRIAL SYSTEMCREATED BY HUMANKIND

Indeed, for all its apparent grandiloquence, the introductory sentence to this unit may be no exagger-ation. The combination of the extreme convenience of utility and countless applications of electricityon the one hand and its particularities on the other hand has engendered these immense and sophisti-cated industrial systems. Their size has to do with their scope, as they are designed to carry electricityto practically any place inhabited by human beings from electric power stations located wherever asupply of primary energyin the form of potential energy inmovingwater or any of several fuelsismost readily available. Carrying electric power from place of origin to place of consumption callsfor transmission grids and distribution grids or networks that interconnect the entire system andenable it to work as an integrated whole. Their sophistication is a result of the complexity of theproblem, determined by the characteristics discussed above: the apparently fragile dynamic equi-librium between generation and demand that must be permanently maintained is depicted in thehighly regular patterns followed by the characteristic magnitudes involvedthe value and frequency



of voltage and currents as well as the waveform of these signals. Such regularity is achieved withcomplicated control systems that, based on the innumerable measurements that continuously monitorsystem performance, adapt its response to constantly changing conditions. A major share of thesecontrol tasks is performed by powerful computers in energy management centers running a hostof management applications: some estimate demand at different grid buses several minutes, hours,days, or months in advance; other models determine the generation needed to meet this demand;yet other programs compute the flow in system lines and transformers and the voltage at grid busesunder a number of assumptions on operating conditions or component failure, and determine themostsuitable action to take in each case. Others study the dynamic behavior of the electric power systemunder various types of disturbance. Some models not only attempt to determine the most suitablecontrol measures to take when a problem arises, but also to anticipate their possible occurrence,modifying system operating conditions to reduce or eliminate its vulnerability to the most likelycontingencies.

This, however, is not all: the economic aspect of the problem must also be borne in mind. Theactors that make the system work may be private companies that logically attempt to maximizetheir earnings or public institutions that aim to minimize the cost of the service provided. In eithercase, the economic implications of the decisions made cannot be ignored, except, of course, wheresystem safety is at stake. The system operates under normal conditions practically always, so there issufficient time to make decisions that are not only safe, but also economically sound. Hence, whendemand rises foreseeably during the day, power should be drawn from the facilities with unusedcapacity that can generate power most efficiently. The objective is to meet daily load curve needswith power generated at the lowest and least variable cost. This new dimension in the operation ofelectric energy systems is present in all timescales: from the hourly dispatch of generating plantto the choice of which units should start-up and stop and when, including decisions on the use ofhydroelectric reserve capacity, maintenance programing and investment in new facilities. It shouldmoreover be stressed that all these decisions are made in a context of uncertainty: about the futuredemand to be met, plant availability, the prices of the various parameters involved in the productionprocess, in particular, fuel, and even the regulatory legislation in effect when long-term decisions areto be implemented.

1.1.4 HISTORY

1.1.4.1 Technological Aspects

The first electric light systems, installed around 1870, consisted of individual dynamos that fedthe electrical systemarc lampsin place in a single residence. Thomas Edison discovered theincandescent light bulb around 1880 and authored the idea of increasing the scale of the processby using a single generator to feed many more bulbs. In 1882, Edisons first generator, driven bya steam turbine located on Pearl Street in lower Manhattan, successfully fed a direct current at avoltage of 100V to around four hundred 80W bulbs in office and residential buildings on the WallStreet. Shortly, thereafter Londons 60 kW Holborn Viaduct station was commissioned, which alsogenerated 100V direct current. This local generation and distribution scheme was quickly adopted,exclusively for lighting, in many urban and rural communities worldwide.

The invention of the transformer in France in 18831884 revealed, in a process not exempt fromcontroversy, the advantages of alternating current, which made it possible to conveniently raise thevoltage to reduce line losses and voltage drops over long transmission distances. Alternating, single-phase electric current was first transmitted in 1884 at a voltage of 18 kV. On August 24, 1891, three-phase current was first transmitted from the hydroelectric power station at Lauffen to the InternationalExposition at Frankfurt, 175 km away. Swiss engineer Charles Brown, who with his colleague andfellow countryman Walter Boveri founded the Brown-Boveri Company that very year, designed thethree-phase AC generator and the oil-immersed transformer used in the station. In 1990, the Institute



200

400

1600

1400

1200

1000

800

600

kV

(Phase-to-phase voltage)

DC

AC

1900 1920 1940 1960 20001980

Year

USA

Sweden

USSR

Canada

USA

Canada

Mozambique

Brazil

Russia

Sweden

EnglandFrance

New Zealand

USA

USSR

USA

FIGURE 1.1 Maximum AC and DC rated voltages. (From Tor, J. L., Transporte de la energa elctrica.Universidad Pontificia Comillas (ICAI-ICADE), Madrid, 1997.)

of Electrical and Electronic Engineers (IEEE) agreed to take August 24, 1891 as the date markingthe beginning of the industrial use and transmission of alternating current.

The transmission capacity of alternating current lines increases in proportion to the square of thevoltage, whereas the cost per unit of power transmitted declines in the same proportion. There wasthen an obvious motivation to surmount the technological barriers limiting the use of higher voltages.Voltages of up to 150 kV were in place by 1910 and the first 245 kV line was commissioned in1922. The maximum voltage for alternating current has continued to climb ever since, as Figure 1.1shows. And yet direct current has also always been used, since it has advantages over alternatingcurrent in certain applications, such as electrical traction and especially electricity transmission inoverhead, underground, or submarine lines when the distances are too long for alternating current.The upward trend inmaximumdirect current voltage throughout the twentieth century is also depictedin Figure 1.1.

The alternating voltage frequency to be used in these systems was another of the basic designparameters that had to be determined. Higher frequencies can accommodatemore compact generatingand consumption units, an advantage offset, however, by the steeper voltage drops in transmission anddistribution lines that their use involves. Some countries such as the United States, the Canada, theCentral American countries, and the northernmost South American countries adopted a frequency of60Hz, while countries in the rest of South America, Europe, Asia, and Africa adopted a frequency of50Hz. The International Electrotechnical Commission was created in 1906 to standardize electricalfacilities everywhere as far as possible. It was, however, unable to standardize frequency, whichcontinues to divide countries around the world into two different groups.

The advantages of interconnecting small electric energy systems soon became obvious. Thereliability of each system was enhanced by the support received from the others in the event ofemergencies. Reserve capacity could also be reduced, since each system would be able to draw from



the total grid reserve capacity. With such interconnections, it was possible to deploy the generatorunits to be able to meet demand most economically at any given time; the advantage this affordsis particularly relevant when peak demand time frames vary from one system to another and whenthe generation technology mix, hydroelectric and steam, for instance, likewise differs. In 1926, theEnglish Parliament created the Central Electricity Board and commissioned it to build a high-voltagegrid that would interconnect the 500 largest generation stations then in operation.

1.1.4.2 Organizational Aspects

What sort of organizational structure is in place in the sector responsible for planning, operating, andmaintaining electric energy systems? Who makes the decisions in each case and under what criteria?The answers to these questions have evolved over time, largely to adapt to the conditioning factorsimposed by technological development, but also depending on prevailing economic theory. As men-tioned above, the first industrial applications of electricity were strictly local, with a generator feedinga series of light bulbs in the surrounding area. Whole hosts of individual systems sprang up under pri-vate or public, usually municipal, initiative, primarily to provide urban lighting and, somewhat later,to drive electric motors for many different purposes. The vertically integrated electric utility, whichgenerates, transmits, distributes, and supplies electricity, evolved naturally and was the predominantmodel in most countries until very recently. The enormous growth of electricity consumption, thehuge economies of scale in electricity generation, and the increase in the transmission capacity ofhigh-voltage lines drove the development of transmission grids, often under state protection, to inter-connect individual systems, giving rise to literally nationwide systems. Technical specialization andthe huge volume of resources required to build large power stations led to the coexistence of localdistribution companies, with scant or nil production capacity, and large vertically integrated utilities,which also sold wholesale electric power to small distributors.

Because of its special characteristics, electricity, or more appropriately its supply, has long beenregarded to be a public service in most countries, an approach that justified state intervention toguarantee reasonable quality and price. In some cases, intervention consisted of nationalizing theelectricity industry, such as in nearly all European countries until the 1990s. In others, electricutilities were subject to the legal provisions typically applied to monopolies, namely the requirementto meet certain minimum quality standards and the imposition of regulated prices to cover the costsincurred, including a reasonable return on the investment made. Until recently, this was the generallyaccepted model for industry regulation, in which the vertical integration of electric utilities was neverquestioned.

In the early 1990s, however, a radically different view of the electricity business began to takehold the world over. This approach challenged the vertically integrated structure of electric powersuppliers. Densely interconnected transmission grids in most countries and even between countriesnow enable a generator located at any bus on the grid to compete with other operators to supplyelectricity virtually anywhere on the grid. It is therefore possible to separate strictly monopolisticgrid activities from the generation and supply businesses, which can be conducted on a competitivemarket.

Under this new approach of the electricity business, electric power system operation and planningacquire a whole new dimension. Each generator decides individually when and howmuch to produce,how to manage the water in their dams, and how to plan and implement their plant maintenanceprograms. Decisions on investment in new power plants are not made centrally by anybody orcompany responsible for guaranteeing supply, but by private investors seeking a return on theirinvestment, who are not responsible for overall security of supply. The distribution business has notbeen significantly impacted by this new regulatory framework, except that it must be unbundledfrom supply, which is now competitive. Transmission, on the contrary, has been the object of a majoroverhaul, for its crucial importance in determining the competitive conditions under which wholesalemarket actors must operate.



Although technological and economic factors are ever present, the role played by regulation growsin importance with the geographic and political scope of electrical systems, particularly under com-petitive market conditions. In regional or supranational electric energy systems, for instance, ruleshave had to be established in the virtual absence of regulatory provisions for the operation of inter-national markets. The European Unions Internal Electricity Market is paradigmatic in this regard:it covers 27 countries, 25 in the European Union including Norway and Switzerland. Other regionalmarkets, in different stages of implementation, include the Australian national market, which encom-passes several states in that country; Mercosur, servicing Argentina, Brazil, Paraguay, and Uruguay;the Central American Electricity Market; and the Regional Transmission Organizations in the UnitedStates that link several different but centrally managed electric utilities.

The motivation for establishing these regional markets is essentially economic: lower costs tomaintain system safety and the advantage of mutually beneficial transactions among the differentsystems. Interconnecting whole electric energy systems poses interesting technological problemssuch as cooperation to maintain a common frequency across the entire system, abiding by tradearrangements stipulated between the various countries, support in emergency situations, global anal-ysis and control of certain grid stability phenomena, or management of grid restrictions derived frominternational trade, that had been essentially solved or kept under control in the context of verticallyintegrated electric utilities through well-established rules for support in emergencies in a climate ofcooperation, scant competition, and limited trade.

These technical problems have become more acute and their complexity has grown with the needto accommodate economic and regulatory considerations in the recent context of open competition.The proliferation of international transactions conducted in a completely decentralized manner byindividual playersbuyers and sellers entitled to access the regional grid as a wholehas com-plicated matters even further. In addition to these technological problems, other issues must alsobe addressed, such as harmonizing different national regulations, organizing and designing oper-ating rules for regional markets, determining the transmission tolls to be applied in internationaltransactions, pursuing economic efficiency in the allocation of limited grid capacity, and solvingtechnical restrictions or proposing suitable regulatory mechanisms to ensure efficient transmissiongrid expansion.

1.1.5 ENVIRONMENTAL IMPACT

In addition to ongoing technological development and the winds of change blowing in the globaleconomy, a factor of increasingweight in the electricity industry, as in all other human activities, is thegrowing awareness of the importance of the natural environment. There is awidespread belief that oneof the major challenges facing humanity today is the design of a model for sustainable development,defined to be development that meets the needs of the present without compromising the abilityof future generations to meet their own needs. Besides such weighty issues as the enormous socialand economic inequalities between peoples or the existence of a growth model that can hardly beextended to the entire world population, other questions, such as the intense use of the known energyresources and their adverse impact on the environment, problems that relate directly to electric energysystems, also come under the umbrella of sustainable development. For these reasons, environmentalimpact is a factor of increasing relevance and importance that conditions the present operation anddevelopment of these systems and will indisputably have an even more intense effect on the industryin the future.

Generation is arguably the line of business in electric energy systems that produces the greatestenvironmental impact, in particular with regard to steam plant emissions and the production ofmoderately and highly radioactive waste. As far as combustion is concerned, coal- and oil-firedsteam plants vie with the transport industry for first place in the emission of both carbon dioxide(CO2), associated with greenhouse gas-induced climate change, nitrous oxides (NOx) and sulfurdioxide (SO2), the former is related to the formation of tropospheric ozone and both are responsible



for acid rain. Carbon dioxide is an inevitable by-product of the combustion of organic material, NOxcomes from the nitrogen in the air and SO2 from the sulfur in coal and oil. Other environmentaleffects of conventional steam power stations include the emission of particles and heavy metals, thegeneration of solid wastes such as fly ash and slag, the heating of river, reservoir, or sea water to coverrefrigeration needs and, indirectly, the impact of mining. With respect to nuclear power stations, inturn, even assuming that the strict safety measures in place suffice to rule out the likelihood of anaccidental catastrophe, the inevitable accumulation of radioactive waste is, irrefutably, an unsolvedproblem that conditions coming generations so severely that nuclear power as it is known todaycannot be regarded to be a sustainable source of energy.

In any event, it must be borne in mind that even generation facilities that use renewable energyand are considered to be the most environment-friendly technologies, have an adverse impact. Themost numerous, namely hydroelectric power plants, which have existed ever since electric powerwas first industrialized, change the surroundings radically. Some of its ill-effects are alteration ofhydrology, disturbance of habitats, or even transformation of the microclimate, not to mention therisk of accidents that can spell vast ecological and human disaster. Other more recent technologiesalso have adverse consequences: wind, the disturbance of natural habitats and noise; solar, landoccupancy, and the pollution inherent in the manufacture of the components required for the cells,and more specifically, the heavy metals present in their waste products; the use of biomass has thesame drawbacks as conventional steam plants, although the effect is less intense, no SO2 is emittedand, if properly managed, it is neutral with respect to CO2 emissions. In fact, all electricity generationactivities have one feature in common, namely the occupation of land and visual impact, but the areainvolved and the (not necessarily proportional) extent of social rejection vary considerably withtechnology and specific local conditions.

In a similar vein, the huge overhead lines that carry electric power across plains, mountain ranges,valleys, and coasts and circle large cities, have at least a visual impact on the environment, whichis being taken more and more seriously. Less visible but indubitably present are the electromagneticfields that go hand-in-hand with the physics of electricity, although their potential effects on people,fauna, and flora are still under examination. Such considerations have important consequences,since environmental permits and rights of way constitute strong constraints on the expansion ofthe transmission grid. As a result, the grid is operating closer and closer to its maximum capacity,occasioning new technical problems, relating to its dynamic behavior, for instance, which logicallyhave economic consequences. In some cases, alternative solutions are available, albeit at a highercost, such as running underground lines in densely populated areas.

But the question is not solely one of establishing the magnitude of the environmental impact ofthe electricity industry or of the awareness that minimizing this impact generally entails increasedsystem costs. The question, rather, is whether this impact should be considered when deciding howto best allocate societys scant resources. In a free market, the tool for resource allocation is productprice; in this case, of the various power options. Nonetheless, the general opinion, among both thepublic at large and governmental authorities at the various levels, is that energy prices do not coverall the types of impact discussed above. This is what is known as a market failure or externality,defined to be the consequences of some productive or consumption processes for other economicagents that are not fully accounted for by production or consumption costs. The existence of suchexternalities, also called external costs, therefore leads to an undue allocation of resources in theeconomy, preventing the market from properly and efficiently allocating resources on the groundsof their price. Indeed, since account is not taken of these external costs, the price of energy is lower,and therefore consumption and environmental impact are higher, than they would be if total powercosts were efficiently allocated. The existence of externalities, if not taken into consideration, alsoleads to the choice of more highly polluting power technologies than if allocation were optimum. Tocorrect this market failure and reach optimum allocation, such costs must be internalized, buildingthem into the price in a way that the economic agents can include them in their decision-making andensure an optimum outcome for society as a whole.



1.2 THE TECHNOLOGICAL ENVIRONMENT

1.2.1 ELECTRIC POWER SYSTEM STRUCTURE

Electric energy systems have developed along more or less the same lines in all countries, convergingtoward a very similar structure and configuration. This is hardly surprising when account is takenof the very specific characteristics of the product they sell. As mentioned earlier, electricity gener-ation, transmission, distribution, and supply are inevitably conditioned by the fact that generationand demand must be in instantaneous and permanent balance. The relevance of technical factors inmaintaining such large-scale systems in dynamic equilibrium cannot be overlooked. A disturbanceanywhere on the system may endanger the overall dynamic balance, with adverse consequences forthe supply of electricity across vast areas, even whole regions of a country or an entire country. It isperhaps for this reason that the existence of sophisticated real-time control, supervision and moni-toring systems, together with the protection facilities is what, from the technical standpoint, chieflydifferentiates the configuration and structure of electric energy systems from other industrial activi-ties. The functions typical of any industry, such as production, shipping, planning, and organization,are also highly specialized in the electricity industry.

The organization of the electricity industry, like any other, is divided into production centersgenerating plant; transmission (equivalent to transport or shipping in other industries); the high-voltage grid; distribution; the low-voltage grid or network; and consumption (also termed supply insome contexts), in addition to the associated protection and control systems. More formally, systemconfiguration and structure are as depicted in Figure 1.2. Production centers generate electricity atvoltages of several kilovolts, typically from 6 to 20 kV, and immediately transform this power tovoltages of hundreds of kilovolts: 132, 220, 400, 500, and 700 kV are relatively common values tooptimize long-distance transmission over electric lines to the areaswhere consumption ismost intense.Raising the voltage makes it possible to transmit large amounts of electric power, the entire outputfromanuclear powered generator for instance, over long distances using reasonably inexpensive cable

Generationplants

Distributedgeneration

Very largeconsumers

Largeconsumers

Mediumconsumers Small

consumers

HVsubstations

HVsubstations

HVtransmission

grid

Distributiongrid

Interconnections

FIGURE 1.2 Electric power system configuration and structure.



technology with minimum line losses. The transmission grid interconnects all the major productionand consumption centers, generally forming a very dense web to guarantee high reliability, withalternative pathways for the supply of electric power in the event of failure in a few of the lines.These electric power transmission highways are interconnected at communication nodes known aselectric substations; the regional grids are spun out from the stations at a somewhat lower voltage, 132,66, or 45 kV in Spain, for instance, and in turn feed local distribution networks, which bring electricpower to consumers at less hazardous voltages, adapted to consumer needs: 20,000, 15,000, 6600,380, or 220V. Successive substations step the working voltage down in several phases and centralizethe measuring and protection devices for the entire transmission grid. The configuration of thesegrids is usually radial, with tentacles stretching out to even the most remote consumption points. Asthe lines are split up at each step, the grids carry less and less power and consequently can operate atlower voltages. Consumers connect to the voltage level best suited to their power needs, in accordancewith the basic principle that the lower the voltage, the smaller the power capacity. This means thathighly energy-intensive businesses, iron and steel plants and mills, aluminium plants, railways, andthe like, connect directly to the high-voltage grid; other major consumers for example, large factoriesreceive power at a somewhat lower voltage and small consumers like households, retailers, smallfactories are connected to the low-voltage network. On the basis of amore or less reciprocal principle,generating stations with a very small output feed their electric power directly into the distributionnetwork instead of connecting to the high-voltage grid. Such generators, which usually run smallhydroelectric, photovoltaic, wind, combined heat and power, or other types ofmodular power stationsengaging in distributed generation, are sometimes grouped under a single category for regulatorypurposes; an example would be Spains Electricity Act, which deals with them collectively underthe term special regime generators. The points below focus on these chief components of electricenergy systems: consumption, production, transmission, distribution, and protection and control.

1.2.2 CONSUMPTION

1.2.2.1 Demand Growth

Electricity demand has undergone high, sustained growth since the beginning. The creation of stan-dards for the electricity product, voltage, frequency, current, paved the way for the enormous boomin electricity consumption. This in turn laid the ground for the standardization of electrically poweredfixtures and facilitiesfrom light bulbs and motors to PCsdramatically lowering manufacturingcosts and enhancing product versatility, making it possible to use a given electrically powered itemvir-tually anywhere. Electric power consumption is one of the clearest indicators of a countrys industrialdevelopment and closely parallels GDP growth. As noted earlier, there are scarcely any productionprocesses or sectors involved in creating wealth that do not require electricity. But electric powerconsumption has also been used as a measure of social development. Electricity consumption percapita and especially the degree of electrification in a country, that is, the percentage of the populationliving in electrified homes, provide a clear indication of the standard of living. This is not surprising,since such basics as lighting, supply of potable water, refrigerators, and other household appliances

consumption to other basic indicators, such as GDP, population, or energy consumption. The growthrate is obviously higher in countries with low baseline levels of electric power consumption and higheconomic growth.

Electrification rates and electricity consumption per capita varywidely from one area of theworld

no electricity.But the growth in electricity consumption is not limited to developing countries: it has definitely

steadied, but is certainly not flat in developed countries. While the industrial worlds consumermentality may partly be driving such growth, it is nonetheless true that new uses are continuously


depend on access to electricity. The curves in Figures 1.3 through 1.5 relate the growth in electricity

to another, as Table 1.1 eloquently illustrates [1]. One-third of the Earths six million inhabitants have


Worldwide

Electricity

GDP

Primary energy

Population

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

FIGURE 1.3 World growth rate referred to 1980 value. (From Energy Information Administration, U.S.Government; U.S. Department of Agriculture.)

Transition economies

Electricity

GDP

Primary energy

Population

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

1.00

2.00

0.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

FIGURE 1.4 Transition economies growth rate referred to 1980 value. (From Energy Information Adminis-tration, U.S. Government; U.S. Department of Agriculture.)

Developing countriesElectricity

GDP

Primary energy

Population

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

0.50

1.00

0.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

FIGURE 1.5 Developing countries growth rate referred to 1980 value. (From Energy Information Adminis-tration, U.S. Government; U.S. Department of Agriculture.)



Table 1.1Electricity Consumption Per Capita (kWh), 19802004

Region 1980 1983 1986 1989 1992 1995 1998 2001 2004

North America 9,792 9,863 10,677 12,035 12,115 12,716 13,258 13,392 13,715Latin America 796 860 1,005 1,048 1,090 1,209 1,331 1,356 1,495Europe 4,111 4,240 4,711 5,005 4,983 5,192 5,520 5,854 6,138Former Soviet Union 4,584 4,881 5,045 5,351 4,848 3,989 3,777 4,003 4,266Asia & Oceania 476 514 587 697 793 926 1,009 1,112 1,329Middle East 599 807 929 1,064 1,137 1,364 1,563 1,744 2,027Africa 375 392 443 457 450 467 477 496 542

World 1,663 1,698 1,827 1,980 1,986 2,062 2,150 2,242 2,421

Source: Energy Information Administration, U.S. Government.

found for electric power. The generalized use of air conditioning in these countries is an obviousexample and one that has brought a radical change in seasonal consumption curves, as explainedbelow.

In addition, sustained electricity consumption growth exists despite substantial improvement inthe efficiency of most equipment and processes using electric power, which reduces the input powerin kWh needed to attain a given result. More and more voices are being raised in defence of the needto rationalize the consumption of electricity and all other forms of energy. Aware of the environmentalimpact of such consumption and the vast amount of natural resources that are literally going up insmoke, such voices rightly call for intergenerational solidarity to be able to bequeath to cominggenerations an ecologically acceptable planet whose energy resources have not been depleted. Hencethe importance of demand sidemanagement (DSM), a term coined in the United States tomean all thetechniques and actions geared to rationalize the consumption of electric power. The aim, on the onehand, is more efficient use of existing consumption to reduce the enormous investment involved in theconstruction of new stations and the substantial cost of producing electricity and, on the other hand,adjust energy savings by cutting down certain consumptions, with the same beneficial implications.DSM should, therefore, be an active component of future electric energy systems, reflecting theattempt to internalize environmental costs, for instance, which are so often ignored. The role andsuitable regulation of this business is one of the challenges facing the new structure and regulationof a liberalized electricity industry.

It may be important in this regard for consumers, the final and key link in the electricity chain,to receive the sophisticated economic signals that deregulation is sending out to the various otherplayers involvedproducers, transmitters, distributors, and suppliers. Pricing should be designed tomake consumers aware of the real (economic and environmental) cost of meeting their power needs,taking account of their consumption patterns in terms of hourly profile and total load. In the mediumterm, this should accustom domestic, commercial, and industrial users to monitor and activelycontrol electric consumption, in much the same way that discriminatory hourly telephone ratesencourage customers to make nonurgent long-distance calls at off-peak times. Similarly, customerswill voluntarily reduce electricity consumption by foregoing the most superfluous applications attimes when higher prices signal that expensive resources are being deployed or that the marginbetween the demand and the supply of electric power is narrow. The capacity of demand to respondto pricing is generally characterized by a parameter termed price elasticity of demand. This isdefined to be the percentage variation in consumption of electricity or any other product in responseto a unit variation in the price. Electricity demand is characterized, generally speaking, by scant short-term elasticity; in other words, the reaction to changes in price are small, although this assertion is



more accurate for some types of consumer than others. Such limited elasticity is arguably due tothe mentality prevailing until very recently in the electricity industry: continuity of supply wasregarded to be a nearly sacred duty, to be fulfilled at any price. Consumers, who were identified,indeed, as subscribers rather than customers, were merely passive recipients of the service provided.Advances in communications technology, in conjunction with the liberalization of the electric andenergy industries in much of the world, are going to change consumers role radically. Demand sidementality overall will not change readily or quickly. Nonetheless, the years to come will very likelywitness the maturing and accentuation of the role played by demand in the electricity industry, whichwill become as relevant as other areas, such as generation. Elasticity will grow although much of thedemand will foreseeably remain impervious to price.

1.2.2.2 Demand Profiles

Consumption is characterized by a variety of items from the technical standpoint. The two mostimportant items are power and energy. Power, measured in watts (W), is the energy (Wh) requiredper unit of time. Power, therefore, is the instantaneous energy consumed. Since electric poweris not stored, electric facilities must be designed to withstand the maximum instantaneous energyconsumed, in other words, to withstand the maximum power load in the system throughout theconsumption cycle. Therefore, not only the total electric capacity needed, but the demand profileover time is especially relevant to characterize consumption. Such profiles, known as load curves,represent power consumed as a function of time. It may be readily deduced that a given value ofenergy consumed may have a number of related load profiles. Some may be flat, indicating veryconstant electricity consumption over time, while others may have one or several very steep valleysor peaks, denoting very variable demand. An aluminium plant working around the clock 365 daysa year and a factory operating at full capacity only during the daytime on weekdays would exemplifythese two types of profiles. Load profiles commonly generate repetitive patterns over time. Thus, forinstance, weekday demand is normally very uniform, as is the weekly load during a given season.Therefore, depending on the timescale considered, the load profile to be used may be daily, weekly,monthly, seasonal, yearly, or even multiyearly. Load profiles also have economic relevance, as will

a spiked load profile. For this reason, load curves constitute one of the most relevant parametersconsidered in the methods used to set tariffs.

Summing all the individual consumption curves for an electric power system yields the total daily,weekly, monthly, seasonal, yearly, and multiyearly load curves, each with a characteristic and highly

Hours28/09/20061 2 3 4 5 6 7 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

100

0

200

300

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500

600

700

MW

h

Thermal

PassDam

8

FIGURE 1.6 Hourly power load for a South American system.


be seen in the discussion below: for any given demand level, it is less expensive to cover a flat than

significant power profile. Figures 1.6 through 1.8 show load curves for a South American electric


DaysSeptember 2006

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

20,000

0

40,000

60,000

80,000

100,000

120,000

140,000

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h

25 26 27 28 29 30

ThermalDamPass

FIGURE 1.7 Monthly power load for a South American system.

Months

5,00,000

0

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

MW

h

4,000,000

Sep-

05

Oct-0

5

Nov-

05

Dec-

05

Jan-

06

Feb-

06

Mar

-06

Apr-0

6

May

-06

Jun-

06

Jul-0

6

Aug-

06

ThermalDamPass

FIGURE 1.8 Yearly power load for a South American system.

run of river hydro (pass), reservoir hydro (dam), and thermal generation. There are very clear peaksand valleys in each, denoting cyclical, maximum and minimum demands. Demand forecasting isan essential problem to solve in foreseeing the conditions under which the system will be operatingin the short, medium, and long term. Normal procedure is to base the prediction on historical dataadjusted to take account of factors affecting the expected load. The most important of these factorsinclude temperature, since many electrical devices are used for space heating or cooling; numberof working days, to account for the difference in consumption on business days and holidays; andeconomic growth, in view of the above-mentioned close relationship between economic activity andelectricity consumption. Therefore, consumption at any given time can be reasonably well predictedfrom time series data corrected for foreseeable variations in growth, working days, and temperature,and taking account as well of special events that may have a substantial effect on demand.

particularly useful in certain applications and studies. Such curves represent the length of time that

represent time in hours and the ordinate values demand in megawatts. Therefore, each point on thecurve indicates the total hours during the year that demand exceeded a given value. In the example,the load was in excess of 15,000 MW for a total of 1200 h in 2005. The load monotone can be plotted


demand exceeds a given load. The thick line in Figure 1.9 is the approximate monotonic load curve

energy system, specifically central Chile (www.cdec-sic.cl), with indication of energy supplied by

for a Canadian utility, which generates with hydro energy (www.gcpud.org): the abscissa values

Aggregate electricity consumption can also be represented as a monotonic load curve, which is

http://www.cdec-sic.clhttp://www.gcpud.org


5,000

10,000

15,000

20,000

25,000

MW

h

Hours

24 408

792

1176

1560

1944

2328

2712

3096

3480

3864

4248

4632

5016

5400

5784

6168

6552

6936

7320

7704

8088

8472

FIGURE 1.9

directly from the chronological load curve by ranking demand in descending order. The integral ofthe load monotone represents the energy consumed in the time frame considered. It will be noted,however, that whereas a given load curve can have only one load monotone, the opposite is nottrue. Although the chronological information contained in load curves is lost in monotonic curves,the latter are widely used for their simplicity. Probabilistic monotone curves are commonly used inprospective studies, which are based on demand forecasts subject to some degree of uncertainty;in this case the x-axis values represent the likelihood that demand will exceed a given value. As inthe case of chronological demand profiles, monotonic load curves can be plotted for daily, weekly,monthly, seasonal, yearly, or multiyearly consumption.

In addition to the power and energy properties discussed at length in the foregoing paragraphs,consumption is characterized by other technical factors. Account must be taken, for instance, ofthe fact that while real power and energy are consumed in the system, reactive power is also eithergenerated or consumed, usually the latter, since inductive motors, which consume reactive power,generally predominate. This gives rise to a power factor less than unity, which penalizes consumptionas far as the tariff charged is concerned, because it entails the circulation of unproductive currentand ohmic dissipation, and line capacity saturation with it. Moreover, consumption may depend onsupply conditions (voltage, frequency) be static or dynamic, or vary with connection time due toheating or other effects. All of this must be taken into account in load modeling.

1.2.2.3 Service Quality

Electric power consumption may be very sensitive to the technical properties of the supply of elec-tricity. Many devices malfunction or simply do not operate at all, unless the voltage wave is perfectlysinusoidal and its frequency and magnitude are constant and stable over time. The precision, quality,features, and performance of electrical devices depend on the quality of the current that powers them.Problems may also arise in almost any type of electrical device when the supply voltage is too low ortoo high (overvoltage). Computer, motor, and household appliance performance may suffer or thesedevices may even fail altogether when the supply voltage swings up or down. Most electrically pow-ered equipment, especially a particularly expensive equipment or any equipment regarded to be vitalfor the proper and safe operation of all kinds of processes, is fitted with protection systemsfuses,circuit breakers and switches, protection relaysto prevent damage caused by voltage fluctuations


Monotonic load curve for a Canadian utility. (From Grant County PUD, http://www.gcpud.org/energy.htm.)

http://www.gcpud.orghttp://www.gcpud.org


outside an acceptable range. Thus, for instance, the motors that drive the cooling pumps in nuclearpower plants are fitted with under and overvoltage protection that may even trip systems that causeplant shutdown, given the vital role of these motors in safe plant operation. Finally, outages, whethershort or long, are clearly detrimental to service quality. For example, unstored information repre-senting hours of work on a PC may be lost because of an untimely power outage. But power failurescan cause even greater harm in industries such as foundries or in chemical or mechanical processeswhose interruption may entail huge losses.

In developed countries, where the universal supply of electricity is guaranteed, attention increas-ingly focuses on quality, as in any other commercial product. Consumption and consumers havebecome more demanding in this regard and electricity industry regulation authorities assiduouslyinclude quality standards in laws and regulations. Designing the proper signals to suitably combineefficiency with high-quality service is one of the major challenges facing the new regulatory system.

The factors that basically characterize quality of electricity service are set out briefly below:

Supply outages: Supply interruptions may have serious consequences for consumers. Theduration of such interruptions may be very shortin which case they are called micro-outages, often caused by the reconnection of switches after a short circuitor long.Normally, the harm caused increases nonlinearly with the duration of the outage.

Voltage drops: Momentary dip in supply voltage caused by system short circuits or failures,lasting only until the fault is cleared, or due to the start-up of nearby motors with high inputdemand when first switched on, occasioning voltage drops in the supply network. Somedevices are particularly sensitive to these drops, particularly motors whose electromagnetictorque varies with the square of the supply voltage.

Voltage wave harmonics: Deviations from the fundamental frequency of the voltage sinewave due to the saturation of ferromagnetic materials, in system transformers or generators,for instance, or to the loads themselves; these deviations may also have adverse effects onconsumer appliances.

Flicker: Low-frequency fluctuations in voltage amplitude normally due to certain types ofloads. Arc furnaces and electronic devices with thyristors usually cause flicker, which isdetrimental to the proper operation of devices connected to the network. The solution to thisproblem is complex, since it depends not on the supplier but on system loads.

Overvoltage: Voltage increases caused by short circuits, faults, lightning, or any other event,potentially causing severe damage to consumer appliances.

Finally, it should be added that electric power consumption may vary broadly with temperatureor contingencies. What must be borne in mind in this regard is, as mentioned earlier, that this demandmust bemet instantaneously and therefore the electric power supply system, power stations, transmis-sion, distribution, must be designed to be able to detect and respond immediately to such variations.The system must be fitted with sophisticated measurement, control and supervisory equipment, andmust have reserve generating capacity ready to go into production at all times. But most users flippingswitches in their homes or workplaces to turn on the lights or start-up an appliance or tool are blithelyunaware of the host of systems, services, and processes needed to provide that service.

1.2.3 GENERATION

1.2.3.1 Different Generation Technologies

The electricity required tomeet these consumptionneeds is generated in production centers commonlycalled power plants or stations, where a source of primary energy is converted into electric powerwith clearly defined characteristics. Specifically, these facilities generate a three-phase, sinusoidalvoltage system, with a strictly standardized and controlled wave frequency and amplitude. There are




FIGURE 1.10 Hydroelectric, thermal, and nuclear plants.

many generation technologies, usually associated with the fuel used. Conventional power stationsare divided into hydroelectric, thermal, and nuclear plants, as shown in Figure 1.10.

The primary source of energy used in hydroelectric stations is water, which is expressed, ener-getically speaking, in terms of flow rate and height or head. Hydroelectric energy is converted by ahydraulic turbine into mechanical energy, characterized by the torque and speed of the shaft coupledto the electric generator. In other words, hydraulic energy is converted into electrical energy in thegenerator, producing voltage and current in the machine terminals. Because of the source of primaryenergy used, hydroelectric stations produce less atmospheric pollution than other conventional gen-eration technologies. Another advantage to this type of stations, in addition to the cost of the fueland lack of pollution, is their connection and disconnection flexibility, making them highly suitableregulating stations to adjust production to demand needs. Nonetheless, they are costly to build, andensuring a