Electric Power Distribution Reliability By Richard E. Brown
Series Introduction
Power engineering is the oldest and most traditional of the various areas within electrical engineering, yet no other facet of modern technology is currently undergoing a more dramatic revolution in technology or business structure. Perhaps the most fundamental change taking place in the electric utility industry is the move toward a quantitative basis for the management of service reliability. Traditionally, electric utilities achieved satisfactory customer service quality through the use of more or less "one size fits all situations" standards and criteria that experience had shown would lead to no more than an acceptable level of trouble on their system. Tried and true, these methods succeeded in achieving acceptable service quality.
But evolving industry requirements changed the relevance of these methods in two ways. First, the needs of modern electric energy consumers changed. Even into the early 1980s, very short (less than 10 second) interruptions of power had minimal impact on most consumers. Then, utilities routinely performed field switching of feeders in the early morning hours, creating 10-second interruptions of power flow that most consumers would not even notice. But where the synchronous-motor alarm clocks of the 1960s and 1970s would just fall a few seconds behind during such interruptions, modern digital clocks, microelectronic equipment and computers cease working altogether. Homeowners of the 1970s woke up the next morning—not even knowing or caring—that their alarm clocks were a few seconds behind. Homeowners today wake up minutes or hours late, to blinking digital displays throughout their home. In this and many other ways, the widespread use of digital equipment and automated processes has redefined the term "acceptable service quality" and has particularly increased the importance of interruption frequency as a measure of utility performance.
Second, while the traditional standards-driven paradigm did achieve satisfactory service quality in most cases, it did not do so at the lowest possible cost. In addition, it had no mechanism for achieving reliability targets in a demonstrated least-cost manner. As a result, in the late 20th century, electric utility management, public utility regulators, and energy consumers alike realized there had to be a more economically effective way to achieve satisfactory reliability levels of electric service. This was to engineer the system to provide the type of reliability needed at the lowest possible cost, creating a need for rigorous, quantitative reliability analysis and engineering methods—techniques capable of "engineering reliability into a system" in the same way that capacity or voltage regulation targets had traditionally been targeted and designed to.
Many people throughout the industry contributed to the development of what are today the accepted methods of reliability analysis and predictive design. But none contributed as much to either theory, or practice, as Richard Brown. His work is the foundation of modern power distribution reliability engineering. It is therefore with great pride that I welcome Electric Power Distribution Reliability as the newest addition to the Marcel Dekker series on Power Engineering. This is all the more rewarding to me because for the past six years Richard Brown has been one of my most trusted co-workers and research collaborators at ABB, and a good friend.
Dr. Brown's book lays out the rules and structure for modern power distribution reliability engineering in a rigorous yet accessible manner. While scrupulously correct in theory and mathematics, his book provides a wealth of practical experience and useful knowledge that can be applied by any electric power engineer to improve power distribution reliability performance. Thus, Electric Power Distribution Reliability fits particularly well into the theme of Marcel Dekker's Power Engineering Series, which focuses on providing modern power technology in a context of proven, practical application—books useful as references as well as for self-study and classroom use. I have no doubt that this book will be the reference in power delivery reliability engineering for years to come. Good work, Richard.
Preface
Distribution reliability is one of the most important topics in the electric power industry due to its high impact on the cost of electricity and its high correlation with customer satisfaction. The breadth and depth of issues relating to this subject span nearly every distribution company department including procurement, operations, engineering, planning, rate making, customer relations and regulatory. Due in large part to its all-encompassing nature, distribution reliability has been difficult for utilities to address in a holistic manner. Most departments, if they address reliability at all, do so in isolation without considering how their actions may relate to those in different parts of the company—an understandable situation since there has been no single reference that covers all related issues and explains their interrelationships. This book is an attempt to fill this void by serving as a comprehensive tutorial and reference book covering all major topics related to distribution reliability. Each subject has been extensively researched and referenced with the intent of presenting a balance of theory, practical knowledge and practical applications. After reading this book, readers will have a basic understanding of distribution reliability issues and will know how these issues have affected typical utilities in the past. Further, readers will be knowledgeable about techniques capable of addressing reliability issues and will have a basic feel for the results that can be expected from their proper application.
Electric Power Distribution Reliability is intended for engineering professionals interested in the topic described by its title. Utility distribution planners will find it of greatest use, but it also contains valuable information for engineers, dispatchers, operations personnel and maintenance personnel. Because of its breadth, this book may also find use with distribution company directors and executives, as well as with state regulatory authorities. It is intended to be a scholarly work and is suitable for use with senior or graduate level instruction as well as for self-instruction.
This book is divided into seven chapters. Although each is a self-contained topic, the book is written so that each chapter builds upon the knowledge of prior chapters. As such, this book should be read through sequentially upon first encounter. Terminology and context introduced in prior chapters are required knowledge to fully comprehend and assimilate subsequent topics. After an initial reading, this book will serve well as a refresher and reference volume and has a detailed index to facilitate the quick location of specific material.
The first chapter, "Distribution Systems," presents fundamental concepts, terminology and symbology that serve as a foundation of knowledge for reliability-specific topics. It begins by describing the function of distribution systems in the overall electric power system. It continues by describing the component and system characteristics of substations, feeders and secondary systems. The chapter concludes by discussing issues associated with load characteristics and distribution operations.
The second chapter, "Reliability Metrics and Indices," discusses the various aspects of distribution reliability and defines terms that are frequently used later in the book. It begins at a high level by discussing power quality and its relationship to reliability. Standard reliability indices are then presented along with benchmark data and a discussion of their benefits and drawbacks. The chapter continues by discussing reliability from the customer perspective including the customer cost of interrupted electrical service and the customer surveys used to obtain this information. The chapter ends with a discussion of reliability targets and the industry trend towards performance-based rates, reliability guarantees and customer choice.
Remembering that reliability problems are caused by real events, Chapter 3 provides a comprehensive discussion of all major causes of customer interruptions. It begins by describing the most common types of equipment failures and their associated failure modes, incipient failure detection possibilities and failure prevention strategies. It then discusses reliability issues associated with animals, presents animal data associated with reliability and offers recommendations to mitigate and prevent animal problems. The chapter continues by discussing severe weather including wind, lightning, ice storms, heat storms, earthquakes and fires. Human causes are the last interruption category addressed, including operating errors, vehicular accidents, dig-ins and vandalism. To place all of this information in perspective, the chapter concludes by discussing the most common interruption causes experienced by typical utilities.
The analytical section of this book begins in Chapter 4, "Component Modeling." The chapter starts by defining the component reliability parameters that form the basis of all reliability models. It then discusses basic modeling concepts such as hazard functions, probability distribution functions and statistics. It ends by providing component reliability data for a wide variety of distribution equipment, which can be used both as a benchmark for custom data or as generic data in lieu of custom data.
The topic of component reliability modeling leads naturally into the next chapter, "System Modeling." This chapter begins with a tutorial on basic system analysis concepts such as states, Venn diagrams, network modeling and Markov modeling. The bulk of the chapter focuses on analytical and Monte Carlo simulation methods, which are the recommended approaches for most distribution system reliability assessment needs. Algorithms are presented with detail sufficient for the reader to implement models in computer software, and reflect all of the major system issues associated with distribution reliability. For completeness, the chapter concludes by presenting reliability analysis techniques commonly used in other fields and discusses their applicability to distribution systems.
The sixth chapter, "System Analysis," focuses on how to use the modeling concepts developed in the previous two chapters to improve system reliability. It begins with the practical issues of actually creating a system model, populating it with default data and calibrating it to historical data. It then presents techniques to analyze the system model including visualization, risk analysis, sensitivity analyses, root-cause analysis and loading analysis. One of the most important topics of the book comes next: strategies to improve reliability and how to quantify their impact by incorporating them into component and system models. The chapter then discusses how to view reliability improvement projects from a value perspective by presenting the basics of economic analysis and the prioritization method of marginal benefit-to-cost analysis. The chapter concludes with a comprehensive example that shows how system analysis techniques can be applied to improve the reliability of an actual distribution system.
Since most distribution companies would like to optimize the reliability of their distribution system, this book concludes with a chapter on system optimization. It begins by discussing common misconceptions about optimization and continues by showing how to properly formulate an optimization problem. It then presents several optimization methods that are particularly suitable for distribution system reliability. Finally, the book presents several practical applications of reliability optimization and discusses potential barriers that might be encountered when attempting to implement a reliability optimization initiative that spans many distribution company departments and budgets.
Electric Power Distribution Reliability is the product of approximately ten years of effort in various aspects of electric power distribution reliability. I would like to thank the following people for teaching, collaborating and supporting me during this time. In the academic world, I would like to thank Dr. Mani Venkata, Dr. Richard Christie and Dr. Anil Pahwa for their insight, guidance and support. In industry, I would like to acknowledge the contributions and suggestions of my co-workers at ABB with special thanks to Mr. Lee Willis, Dr. Andrew Hanson, Mr. Jim Burke, Mr. Mike Marshall, Mr. Tim Taylor, Mr. Greg Welch, Mr. Lavelle Freeman and Dr. Fangxing Li. I would also like to thank Rita Lazazzaro and Lila Harris at Marcel Dekker, Inc., for their involvement and efforts to make this book a quality effort. Last, I would like to offer special thanks to my wife Christelle and to my daughter Ashlyn for providing the inspiration and support without which this book would not be possible.
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