IEEE Power & Energy Society

Book Reviews

Four Attention Grabbers

Machines, Substations, Modeling, and Analysis

Four books are reviewed in this issue. We start with Electrical Machines with MATLAB, which the reviewer says is “an excellent text for a five-credit hour course at an engineering school.” The second book, Electric Power Substations Engineering, the reviewer calls “a valuable asset for every substation engineer.” The third reviewed book, Principles of Power Engineering Analysis, “provides valuable information that should be used for a three-credit graduate course in power engineering.” The last book, Distribution System Modeling and Analysis, is called an “authoritative textbook on the subject of distribution system modeling and analysis” by the reviewer.

Electrical Machines with MATLAB

By Turan Gönen, ISBN 9781439877999

I was not familiar with the first edition of this book. The second edition contains five new chapters introducing renewable energy, wind, solar, energy storage, and the smart grid. In addition, the second edition uses MATLAB to recalculate and check the accuracy of the valuable and informative examples provided throughout.

Electrical Machines with MATLABMy career in the electric utility industry has lasted for over 40 years, and the vast majority of the time has been spent with an investor-owned electric utility working with electrical machinery. I am pleased to say that reviewing this book has been an entertaining treat. The original target of the first edition was junior-level undergraduate students and the practicing engineer, both electrical and nonelectrical. I feel that this text hit the intended target on the bull’s eye. Where was it when I started college in 1967?

Chapter 1 is a comprehensive introduction to the basic electric utility system, an overview of rotating machines, and a review of single-phase ac circuits. Chapter 2 gets right into three-phase circuits. This is a clear and concise presentation of the concepts of three-phase power including a balanced system, the effects of an unbalanced system, and a good discussion on the topic of power factor. Chapter 3 is a presentation of magnetism and magnetic circuits. Dr. Gönen does an outstanding job of describing how magnetism and flux relate to the design of generators, motors, transformers, instrumentation, television, radios, computers, power tools, and a variety of other devices. This chapter has a clear explanation of EMF and MMF. Also included is an introduction to the common types of magnets used in permanent magnet motors. After reading Chapter 4, you will know transformer fundamentals. Everything is explained: construction, core type, shell type, theory, equivalent circuits, performance, three phase, and auto transformers.

Chapter 4 is a true mini course in transformers. Chapter 5 on electromechanical energy conversion reminds us that “energy is neither created nor destroyed; it is simply changed in form.” Here Dr. Gönen explains the fundamentals of electromechanical energy converters, which we know as motors and generators. The “work horse of industry,” the three-phase induction motor, is covered in Chapter 6. This chapter explains the basics of the magnetic field, induced voltages, the concept of slip, equivalent circuits, and induction motor performance characteristics. There is a very understandable section on rotor design as it relates to starting speed-torque capability. A motor designer once told me that for a large motor we only pay him to get it started; running is free.

Chapter 7 explains the principles of the synchronous motor and generator. I liked a statement used early in this chapter: “The synchronous machine rotors are simply rotating electromagnets, which have the same number of poles as the stator winding.” A very understandable discussion of excitation issues is also presented. I do take exception to Dr. Gönen’s comment that solid-steel forgings used on synchronous generators do not require damper windings; they most certainly do. The rotor’s damper winding configuration determines its capability to handle negative sequence currents. The versatile direct current motor is covered in Chapter 8, along with a good description of commutation. Single-phase motors, which constitute 90% of all motors in service, are thoroughly reviewed in Chapter 9. This is a comprehensive chapter on the various classifications of single-phase motors. The universal motor, the single-phase synchronous motor, and permanent magnet motors are also explained. Chapter 10 discusses electric machine behavior associated with transients and dynamics.

The text then moves into the new chapters added in the second edition of this excellent book. Chapter 11 is a brief introduction to the topic of renewable energy. I found Chapter 12, covering wind energy, to be especially informative. The categories of wind turbines and the associated illustrations of wind turbine designs will make a drive through the countryside more enjoyable. I was disappointed to learn that the typical wind energy conversion system captures only 20–30% of the available energy. Furthermore, I was surprised to learn of the significant number of variables involved. Similar to the chapter on wind, Chapter 13 is an excellent overview of issues associated with solar energy, including a wealth of information on the solar cell. Did you know that the power density of sunlight is defined with a unit called SUN; how about that! With the sun directly overhead on a very clear day, the power density of sunlight is equal to 1 kW/m².

After reading the chapters on wind and solar energy, it seems obvious to have Chapter 14 on energy storage systems. This chapter offers a brief discussion of storage methods such as pumped hydro, compressed air, capacitors, and superconducting magnetic energy storage. There is an informative section on issues associated with battery types.

The body of this text ends with Chapter 15, covering the smart grid. The smart grid may be very smart, but it is equally very complex. Dr. Gönen does a fine job of presenting the complexity of this concept. There are many diagrams, sketches, graphs, and flow charts attempting to explain the smart grid. As you read about the smart grid, pay attention to the TLAs; there are a plethora of them in this chapter. Oh, a TLA is a three-letter acronym.

Don’t ignore the seven appendices in this book. Each one offers very useful information. The glossary for electrical machines terminology is a valuable resource.

Electrical Machines with MATLAB is an excellent text for a five-credit hour course at an engineering school. Additionally, the typical utility/industrial engineer would benefit from consulting this book. Dr. Gönen’s use of step-by-step examples throughout the text is beneficial to understanding the material.

However, I do not see a strong connection between the second edition of Electrical Machines and MATLAB as highlighted in the book’s title. The preface states that the end-of-chapter problems have been recalculated “using MATLAB.” I trust that the calculations were not wrong in the first edition. Additionally, the method of calculation is not as important as the correct results. For those interested in MATLAB, the MATLAB script is provided for several of the example problems.

Finally, I thoroughly enjoyed Dr. Gönen’s “words of wisdom” that graced the beginning of each chapter. It is a pleasure to have these philosophical vignettes in an engineering work of this caliber.

— James R. Michalec

Electric Power Substations Engineering

By John D. McDonald, editor, third edition, 2012, ISBN 9781439856383

Having enjoyed the past 30 years designing and managing electric power substations, it was a pleasure to hold in my hands and review a technical publication solely dedicated to substations!

Electric Power Substations EngineeringThis third edition has updated 15 of the 20 chapters from the previous edition and added two new chapters on recent technology: Energy Storage and the Role of Substations in Smart Grids.

In addition to the technical information presented in each chapter, I appreciate that most include references to the latest IEEE and IEC standards, CIGRE publications, and other papers. This aids the reader with where to go for further research and information. Plus the authors are all well experienced in their fields, with many of them being current and recent colleagues within the IEEE/PES Substations Committee. Many of the chapters are fewer than 20 pages, so the information is provided in an efficient manner, along with interesting photos and graphics.

The first chapter provides an effectively brief synopsis on how a substation “happens,” including determining the need, budgeting and financing, site selection, and commissioning. A broad flowchart is provided that quickly steps you through the design and construction process, along with a listing of design elements.

With your appetite whetted, the next three chapters walk you through basic layout and types of substation switching equipment and schemes, whether gas insulated (GIS) or air insulated. Chapter 3 addresses the common bus switching arrangements and provides a handy comparison table of the reliability and cost advantages and disadvantages. One aspect I’d like to see added to future editions is a discussion of space allocation for future capacity needs and/or mobile emergency equipment. And the circuit breaker section should include the latest application of vacuum technology at 72 kV.

Chapter 5 provides a comprehensive description of high-voltage power electronics, to improve transmission of both dc (HVdc) and ac (FACTS). Example projects are described for the United States, Europe, and the recent ±800 kV UHV dc projects in China. FACTS controllers are discussed in varying configurations, including static var compensators, thyristor-controlled series compensation, static synchronous compensator, and the recent voltage-sourced converter application.

Chapter 6 addresses the many necessary interfaces between automation and substation devices, particularly for control with microprocessor-based components. The choices for physical location are outlined, as well as environmental factors of temperature, contamination, and electrical noise and transients. Then the measuring performance requirements are described for analog inputs, along with explaining the characteristics of digitized measurements and new technologies on the horizon that are replacing traditional iron core transformers. Status monitoring includes topics of contact bouncing performance and wetting sources. Control functions address the need for interposing relays, latching devices, and integrity concerns for communication channels. Then the different communication network topologies are described, and the varying aspects of a good test plan.

Chapter 7 continues into much more detail about integration issues of protocol consideration, system architecture and documentation, and network topology. It includes more detailed descriptions of the system components, for example, data concentrators, gateways, protocol convertors, and Ethernet switches. The IEC 61850 standard protocol is described along with GOOSE messaging and station and process bus. The chapter includes a discussion on synchrophasors. There is some duplication of basic information between Chapters 6 and 7, and I’d recommend both chapters be combined in the next edition and relocated further back in the book to adjoin with communication and cyber security topics.

The next seven chapters (8–14) address varying environmental and safety aspects of substation design. Chapter 8 describes the concerns of oil containment, discharge control systems, and oil spill prevention techniques. Many other issues important to community acceptance are then addressed in Chapter 9, such as aesthetics, noise, landscaping, electric and magnetic fields, and fencing/wall security. There’s short mention of fire protection, grounding, and physical security, yet these topics are addressed in more detail in later chapters. Mitigating the adverse affects of animal intrusion is discussed in Chapter 10, starting with a table recommending clearance requirements for certain animal types and then describing differing barrier methods, deterrent and isolation devices, and insulation systems.

Chapter 11 begins with the reasons for the substation grounding system and the dangerous ground circuit conditions of intolerable step and touch potentials. It then describes the design criteria that limit these conditions to tolerable levels, including soil resistivity, grid resistance, grid current division, and conductor and connector material selection. I’d like to see a discussion of nonconductive fencing, surface rock layer, temporary personal grounds, and maintaining ground grid integrity also included in this chapter. Aside from electrical faults, another contributor to substation ground grid current is direct lightning stroke, which leads to lightning shielding covered next in Chapter 12. Starting with the phenomena and parameters of lightning, this chapter then describes the numerous design methods and electromagnetic models available that support design methods of lightning rods, masts, and shield wires. Of course the need for lightning shielding design depends upon the keraunic level of that substation location.

Transitioning from keraunic levels to seismic levels, Chapter 13 outlines the seismic design process and the differing qualification levels and methods for design earthquake. It then describes selecting desired performance levels, the importance of installation practices, and flexibility of interconnecting buswork. Chapter 14 initially addresses the objectives of fire protection and also the philosophies. Fire hazards are described, followed by the numerous mitigation measures, fire incident management, and an assessment checklist.

Chapter 15 on communications includes an extensive reference section, provides a historical perspective of SCADA and protocols, and details the numerous communication media, including power line carrier, phone, microwave, satellite and spread-spectrum radio. Physical security is covered next in Chapter 16 and outlines a comprehensive security plan, starting with threat assessment, then vulnerability and risk assessment, and ending in describing implementation methods, such as locks, barriers, lighting, detection systems, and management of sensitive records. The NERC security guidelines are mentioned, but need to be updated to the latest NERC requirements in CIP-006. The next chapter on cybersecurity immediately points to NERC’s critical infrastructure protection (CIP) requirements and discusses the security threats to an automated substation system. Issues like open protocols and lack of authentification are mentioned, leading to the effective measures to enhance cybersecurity. An effective security program is described, along with detecting and responding to cyber intrusion, and future measures are mentioned as well.

The remaining five chapters in the book cover a variety of interesting topics: gas-insulated transmission line (GIL), substation asset management, project commissioning and close-out, energy storage and smart grids. GIL often accompanies GIS installation, particularly when current levels require multiple cables and yet also can be utilized for effective routing as substation layouts becomes more cramped. In addition to cramped layouts as the substation expands over time, the age of the installed assets is increasing. So the asset management chapter provides useful life-cycle management and maintenance approaches. Effective asset management requires good records, and the commissioning chapter describes numerous areas: proper testing, inspections, “as-built” construction drawings, and equipment manuals. It discusses project punch lists, notifying stakeholders, and developing lessons learned for future leverage. It also addresses the financial aspect of completing invoices, canceling charge orders, and developing unit costs. When new transmission facilities are commissioned, I’d like to see the NERC requirements emphasized here, whether for protective relay coordination, facility ratings, or operations.

Chapter 21 focuses on the emerging technology and industry drivers for energy storage. Several types of battery storage are discussed, in addition to flywheels and compressed air, culminating in a comparison of these and other developing technologies. The final chapter addresses the role of substations in smart grids. As our electric grid transforms, it’s crucial to understand the key role substations play in this today and into the future. The substation design itself will likely need to evolve in support of an advanced, centralized communication hub, smart feeder applications, 61850 fiber-optic connections to equipment, local energy storage and voltage control, or bidirectional power flow from increased distributed generation.

In summary, this handbook is a valuable asset for every substation engineer. It provides an expert presentation of the many facets of proper substation engineering. It also addresses the changing technology and innovative approaches in meeting new industry challenges, particularly cybersecurity, communications, 61850 protocols, energy storage, and voltage-sourced converters.In summary, this handbook is a valuable asset for every substation engineer. It provides an expert presentation of the many facets of proper substation engineering. It also addresses the changing technology and innovative approaches in meeting new industry challenges, particularly cybersecurity, communications, 61850 protocols, energy storage, and voltage-sourced converters.

— John Randolph

Principles of Power Engineering Analysis

By Robert C. Degeneff and M. Harry Hesse, ISBN 978-1-4398-9231-2

Principles of Power Engineering AnalysisPrinciples of Power Engi­neering Analysis presents concepts of three-phase electric transmission from a physical perspective. The text provides valuable information that should be used for a three-credit graduate course in power engineering, while also providing a succinct review of undergraduate background information in extensive appendices. Detailed transmission line characteristics and transformer parameters are comprehensively derived and analyzed under both balanced and unbalanced conditions. The appendices provide a review of basics, such as electric and magnetic fields and matrix algebra, but also include material that may be new to graduate students, such as Carson’s earth-return correction factors.

Reading this book brought back fond memories of Prof. Harry Hesse discussing “basic fundamentals” and then building on them to solve complex problems. Dr. Hesse was a much beloved professor at Rensselaer Polytechnic Institute (RPI), where he brought vectors to life. He presented new material to students in a theoretically rigorous way and then related it to real problems, many of which he had solved for many years as an employee of General Electric (GE). Dr. Hesse passed away on 24 August 1995.

Dr. Degeneff remains true to the RPI motto of “knowledge and thoroughness.” After many years of experience at GE, he joined the faculty at RPI where he taught power engineering analysis and electrical power transients and was active in undergraduate education. Dr. Degeneff has extensive research experience in the design and performance of power apparatus. He was named professor emeritus in 2008 and is currently president of Utility Systems Technologies, which builds electronic voltage regulators and power quality mitigation equipment and provides consulting services.

Principles of Power Engineering Analysis provides a unique approach and content. It is refreshing to see a text focus solely on a physical approach to power engineering at a time when most books use more of a system perspective. Students wishing to understand detailed transmission line and transformer models would be well served by the text. Students who are new to applications of electromagnetic fields and waves, however, would require extensive review of the appendices prior to delving into the main chapters. The book recognizes many issues that are not fully developed in the text, such as radio interference, but it does provide sound references for interested readers.

Section 1 discusses transmission line characteristics. Starting with the basic magnetic field and electric field equations, the book examines single conductors in space and then derives series and shunt parameters for three-phase circuits. The section discusses the effect of ground for both untransposed as well as transposed circuits.

Section 2 starts with ideal single-phase two-winding transformers and builds on that analysis to address the analysis of three-phase transformers, autotransformers, and multiwinding transformers. Similar to other books, Principles of Power Engineering Analysis discusses three-winding transformers, but the text then uniquely extends the discussion up to five windings.

Section 3 is a brief review of the analysis of balanced three-phase systems. The section builds to discussions of magnetizing currents in three-phase transformers and interestingly shows the steady-state power transfer limit with intermediate voltage regulation. Several system applications, such as the use of shunt compensation and voltage-regulating and phase-shifting transformers, are only briefly mentioned but are more extensively discussed later in the text.

Section 4 discusses some examples of unbalanced system conditions. It first discusses loads and then introduces symmetrical components. This section emphasizes a basic understanding of sequence networks and does not summarize zero sequence representations of transformers. The student needs to demonstrate that basic understanding in an exercise analyzing an unbalanced load, which appears at the end of the chapter.

Section 4 discusses some examples of unbalanced system conditions. It first discusses loads and then introduces symmetrical components. This section emphasizes a basic understanding of sequence networks and does not summarize zero sequence representations of transformers. The student needs to demonstrate that basic understanding in an exercise analyzing an unbalanced load, which appears at the end of the chapter.

Section 5 details the symmetrical component representation of transmission lines through detailed numerical examples of both single and double circuits. Electromagnetic and electrostatic unbalanced conditions are discussed for unbalanced lines.

Section 6 shows the symmetrical component representation of transformers. The section begins with a Y-Δ transformer, but it extensively explains a 90° positive sequence phase shift instead of the expected 30° one that is in common use. The section continues with zero sequence representations of various transformer connections, including grounding transformers and zig-zag transformers.

Section 7 demonstrates the sequence connections for various types of unbalanced faults. Because results are only briefly summarized, the interested student should review the basic transformation equations discussed in Section 4 to have a better understanding of their derivation.

Section 8 discusses the design of untransposed transmission lines and their representation with symmetrical components. Conversion of the “unsymmetrical” symmetrical component matrix to a “symmetrical” matrix using a transposition matrix is discussed.

Finally, Section 9 reviews Clarke components. It was refreshing to see these components explained in a text, but I would have like to see more examples and exercises.

A strong background in fields and waves and some basics of power engineering is required to fully understand this graduate-level book. Readers would be well served by fully understanding the material covered in the appendices prior to reading the main sections of the textbook. The appendices comprise approximately 1/3 of the book and cover the following:

  • Principles of electricity and magnetism: reviews the basic electromagnetic concepts underlying the physical discussions presented in the book.
  • Concept of flux-linkage and inductance: explains Faraday’s law and inductance.
  • Electromagnetic field above a perfectly conducting plane: examines the charge distribution on a perfectly conducting plane resulting from a perfectly charged line above it.
  • Carson’s earth-return correction factors: discusses wave propagation along a transmission line over a simplified model of the earth and formulas for calculating the inductive disturbances in neighboring transmission systems.
  • Matrix algebra: concisely reviews concepts of matrix algebra.
  • Magnetic energy in transformers: shows the total magnetic energy stored in power transformers on common closed magnetic cores.
  • Exciting current in three-legged core-type transformer: discusses the fundamental frequency as well as the third- and fifth-harmonic magnetizing current.
  • Hyperbolic functions: defines these functions, which are useful for the study of long transmission lines.
  • Equivalent networks: discusses two-port, gamma and reverse gamma, and delta and wye networks; additional forms, operations, and theorems are reviewed.
  • Y-Δ relationships: uses a matrix approach.
  • Analysis of electromagnetic circuits: briefly reviews material that should have been covered in undergraduate courses.

The list of symbols and contexts at the end of the appendices is particularly helpful to all readers.

The writing style is clear but very heavily mathematical and sometimes without references to equations covered in previous sections. A more complete explanation of the equations would facilitate learning by students new to the subject. The exercises were relevant and facilitate understanding. Solutions to some of the exercises included with several of the sections would be beneficial to all students. Several sections mention topics of interest and then provide references without further explanation. It is my hope that future editions of the text more fully address these topics and expand discussions of other fundamentals, such as phase angle transformers and load tap changers. The figures were clear and helpful.

Principles of Power Engineering Analysis successfully presents graduate-level material on both transmission lines and transformer characteristics and a detailed treatment of symmetrical components. The book fills the need for a text with a physical approach to electric power engineering and is timely given the growth of electric transmission expansion and the crying need for personnel who understand both basics and some advanced concepts. As one of “Dr. Greenwood’s boys” at RPI, I wish this text had been available to me then and am glad that I now have it as a reference. The book, however, is not for those who are new to the topics discussed.

— Michael I. Henderson

Distribution System Modeling and Analysis

By William H. Kersting, third edition, 2012, ISBN 13: 978-0849358067

This new edition is very timely given the international attention on smart grids, including increased demand for better modeling and analysis methods to support planning and operations of smart distribution systems. The book is an authoritative textbook on the subject of distribution system modeling and analysis. It develops models for each component in a distribution feeder using generalized matrices and develops the modified ladder technique to perform load flow analysis and a method in the phase domain to perform short-circuit analysis.

Distribution System Modeling and AnalysisThe book begins with an introductory chapter about the basic components of a distribution system and a practical overview of radial feeders. Then it leads into the second chapter with a thorough and real-world discussion about the nature of loads including the terminology for describing the changing load in a distribution system and an overview of how load is defined for individual customers as well as how the demand of the aggregated customer loads of a distribution transformer is computed. In Chapter 3, approximate methods are given for computing the voltage drop and power loss of line segments with uniformly distributed loads and for geometric areas with constant load densities. Chapters 4 and 5 present methods for computing the phase and sequence impedances and shunt admittances of overhead lines and underground cables using modified Carson’s equations.

In Chapters 6–8, the phase frame models for the series components (distribution line segments, step-voltage regulators, and transformer banks) are developed. In Chapter 9, phase frame models for the shunt components (static loads, induction machines, and capacitor banks) are presented. Models for constant impedance (Z), constant current (I), and constant real and reactive power (P) loads are developed for wye connected or delta connected, three-phase, two-phase, or single-phase loads with any degree of unbalance. In addition, an extended model is developed for a three-phase induction machine operating as a motor or generator.

In Chapter 10, the modified ladder technique is derived and demonstrated through the analysis of a general radial distribution feeder under normal steady-state operating conditions (power-flow analysis) and under short-circuit conditions (short-circuit analysis). The phase frame models of the series and shunt components are used in the power flow analysis. Further an unbalanced feeder is modeled for short-circuit calculations, and models for each type of short circuit are developed. In Chapter 11, models for the single-phase, center-tapped transformer and the three-phase transformer banks using the center-tapped transformer are developed and demonstrated.

I have used the earlier editions of this book multiple times over the last decade to teach a distribution systems analysis graduate course. The book is well written for use by professors teaching a senior-level or introductory graduate course in distribution systems analysis, as well as for students and practicing engineers looking for a reference textbook with theory and detailed examples on distribution component models and system analysis techniques. A detailed example follows the development of each new component model and analysis technique, which includes step-by-step explanations of the derivations and intermediate calculations. Further problems are included at the end of each chapter to study the component and feeder models and analysis techniques for various phasing and types of connections.

The new material in the third edition enhances the earlier editions by putting a greater emphasis on the implementation of the component models in a computer program for purposes of planning and for real-time analysis. According to the author, a major effort was made to demonstrate, through the use of several examples, computer programs that can be developed to assist the engineer in the planning and operation of present and future systems. The major additions are as follows:

  • As new component models are introduced in the textbook, an example is included to demonstrate how a Mathcad program can simplify the analysis. Further, some homework assignments are recommended to be solved by writing a computer program in Mathcad or some other programming language. The inclusion of the Mathcad examples and problems in this new edition will provide many opportunities for students/engineers to develop skills in the implementation of the computer calculations for a simple feeder, which is critically important today. Practicing engineers are now expected to be able to write short programs to perform quick calculations to assist in making engineering decisions. MATLAB may have been a better choice for use in this textbook because it is a more commonly used computational tool of college students. However, students should be able to easily transfer the Mathcad examples into MATLAB code, if desired.
  • Another major addition is the use of Milsoft Utility Solutions Inc.’s distribution analysis program Windmil. Milsoft has made available a student version of Windmil along with a user manual that can be downloaded from the company’s Web site. Many of the examples in this textbook are included in the user manual. The new edition revised the problems from the earlier editions, which were to be solved using the Radial Distribution Analysis Package (RDAP), to be solved using Windmil. Also starting in Chapter 4, there is a Windmil assignment at the end of each chapter. Each assignment in Chapters 4–9 builds on the system studied in the previous chapter with the addition of the type of component model studied in that chapter. The Windmil assignments in Chapter 10 encompass the implementation of a 13-node feeder using given system data and the determination of settings of voltage regulators and capacitor bank. The Chapter 11 assignments expand the system developed in Chapter 10 with transformers and secondary loads. The inclusion of Windmil assignments demonstrates how a commercial program such as Windmil can be used for studying complex systems.
  • In the earlier editions, the modified ladder technique was not introduced until Chapter 10. In this new edition, the modified iterative ladder technique is introduced in Chapter 6 to demonstrate the computation of load voltages and currents for a nonlinear system with distribution lines serving constant PQ loads. The modified ladder technique is demonstrated for the voltage regulators in Chapter 7, the various transformer connections in Chapter 8, and the load models in Chapter 9. The technique is fully developed in Chapter 10. When teaching my distribution analysis course with the earlier editions, after completing Chapter 6, I would skip to Chapter 10 and present the modified ladder technique. Then I would use the technique to present examples for each component model in Chapters 6–9. It is exciting to see that the author has now introduced the modified ladder technique in Chapter 6 and included examples and homework assignments in Chapters 6-9 that use the technique with each component model in a simple system. This change will greatly benefit students/engineers as it allows for more detailed discussion of the component models and their parameters in the chapter where the individual component model is introduced.

Overall this new edition includes additions that will make this textbook even more attractive for a distribution course or for students/engineers wishing to learn about the subject on their own. In addition to the detailed examples and problems, the Windmil assignments provide case studies for students/engineers to gain a more practical understanding of distribution system modeling and analysis.

— Karen Butler-Purry

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