HANDBOOK OF LARGE TURBO-GENERATOR OPERATION AND MAINTENANCE

Transcription

1 HANDBOOK OF LARGE TURBO-GENERATOR OPERATION AND MAINTENANCE

2 Books in the IEEE Press Series on Power Engineering Principles of Electric Machines with Power Electronic Applications, Second Edition M.E. El-Hawary Pulse Width Modulation for Power Converters: Principles and Practice D. Grahame Holmes and Thomas Lipo Analysis of Electric Machinery and Drive Systems, Second Edition Paul C. Krause, Oleg Wasynczuk, and Scott D. Sudhoff Risk Assessment for Power Systems: Models, Methods, and Applications Wenyuan Li Optimization Principles: Practical Applications to the Operations of Markets of the Electric Power Industry Narayan S. Rau Electric Economics: Regulation and Deregulation Geoffrey Rothwell and Tomas Gomez Electric Power Systems: Analysis and Control Fabio Saccomanno Electrical Insulation for Rotating Machines: Design, Evaluation, Aging, Testing, and Repair Greg Stone, Edward A. Boulter, Ian Culbert, and Hussein Dhirani Signal Processing of Power Quality Disturbances Math H. J. Bollen and Irene Y. H. Gu Instantaneous Power Theory and Applications to Power Conditioning Hirofumi Akagi, Edson H. Watanabe and Mauricio Aredes Maintaining Mission Critical Systems in a 24/7 Environment Peter M. Curtis Elements of Tidal-Electric Engineering Robert H. Clark Handbook of Large Turbo-Generator Operation and Maintenance, Second Edition Geoff Klempner and Isidor Kerszenbaum

3 HANDBOOK OF LARGE TURBO-GENERATOR OPERATION AND MAINTENANCE Geoff Klempner Isidor Kerszenbaum Mohamed E. El-Hawary, Series Editor IEEE Press A JOHN WILEY & SONS, INC., PUBLICATION

4 IEEE Press 445 Hoes Lane Piscataway, NJ IEEE Press Editorial Board Lajos Hanzo, Editor in Chief R. Abari T. Chen O. Malik J. Anderson T. G. Croda S. Nahavandi S. Basu S. Farshchi M. S. Newman A. Chatterjee B. M. Hammerli W. Reeve Kenneth Moore, Director of IEEE Book and Information Services (BIS) Steve Welch, IEEE Press Manager Jeanne Audino, Project Editor Technical Reviewers Robert Hindmarsh, Siemens Nils Nilsson, Cboss, Inc. Copyright 2008 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) , fax (978) , or on the web at Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) , fax (201) , or online at Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representation or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the United States at (800) , outside the United States at (317) or fax (317) Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic formats. For more information about Wiley products, visit our web site at Library of Congress Cataloging-in-Publication Data is available. ISBN Printed in the United States of America

5 To our families: Susan Klempner, Jackie, Livi, and Yigal Kerszenbaum

6 Preface Acknowledgments xix xxiii I THEORY, CONSTRUCTION, AND OPERATION 1 Principles of Operation of Synchronous Machines Introduction to Basic Notions on Electric Power Magnetism and Electromagnetism Electricity Electrical Mechanical Equivalence Alternating Current (ac) Three-Phase Circuits Basic Principles of Machine Operation Faraday s Law of Electromagnetic Induction Ampere Biot Savart s Law of Electromagnetic 18 Induced Forces Lenz s Law of Action and Reaction Electromechanical Energy Conversion The Synchronous Machine Background Principles of Construction Rotor Windings Stator Windings Basic Operation of the Synchronous Machine No-Load Operation Motor Operation Generator Operation Equivalent Circuit Machine Losses 36 Additional Reading 38 vii

7 viii 2 Generator Design and Construction Stator Core Stator Frame Flux and Armature Reaction Electromagnetics End-Region Effects and Flux Shielding Stator Core and Frame Forces Stator Windings Stator Winding Wedges End-Winding Support Systems Stator Winding Configurations Stator Terminal Connections Rotor Forging Rotor Winding Rotor Winding Slot Wedges Amortisseur Winding Retaining Rings Bore Copper and Terminal Connectors Slip-Collector Rings and Brush Gear Rotor Shrink Coupling Rotor Turning Gear Bearings Air and Hydrogen Cooling Rotor Fans Hydrogen Containment Hydrogen Coolers 118 References Generator Auxiliary Systems Lube-Oil System Hydrogen Cooling System Seal-Oil System Stator Cooling Water System System Components Stator Cooling Water Chemistry Stator Cooling Water System Conditions Exciter Systems Types of Excitation Systems Excitation System Performance Characteristics Voltage Regulators Operation and Control Basic Operating Parameters Machine Rating Apparent Power 145

8 ix Power Factor Real Power Terminal Voltage Stator Current Field Voltage Field Current Speed Hydrogen Pressure Hydrogen Temperature Short-Circuit Ratio Volts per Hertz and Overfluxing Events Operating Modes Shutdown Turning Gear Run-up and Run-Down Field Applied Offline (Open Circuit) Synchronized and Loaded (Online) Start-up Operation Online Operation Shutdown Operation Machine Curves Open-Circuit Saturation Characteristic Short-Circuit Characteristic Capability Curves V-Curves Special Operating Conditions Unexcited Operation ( Loss-of-Field Condition) Negative-Sequence Currents Off-Frequency Currents Load Cycling and Repetitive Starts Overloading Extended Turning-Gear Operation Loss of Cooling Overfluxing Overspeed Loss of Lubrication Oil Out-of-Step Synchronization and Near Short Circuits Ingression of Cooling Water and Lubricating Oil Under- and Overfrequency Operation (U/F and O/F) Basic Operation Concepts Steady-State Operation Equivalent Circuit and Vector Diagram Power Transfer Equation between Alternator and 196 Connected System Working with the Fundamental Circuit Equation 198

9 x Parallel Operation of Generators Stability Sudden Short Circuits System Considerations Voltage and Frequency Variation Negative-Sequence Current Overcurrent Current Transients Overspeed Grid-Induced Torsional Vibrations Basic Principles of Shaft Torsional Vibration Spring Model of a Turbo-Generator Shaft Train Determination of Shaft Torque and Shaft Torsional Stress Material Changes due to Torsional Vibrations Types of Grid-Induced Events Monitoring of Torsional Vibration Events Industry Experience and Alleviation Techniques Excitation and Voltage Regulation The Exciter Excitation Control Performance Curves Losses Curves Efficiency Curve Sample of Generator Operating Instructions 239 References Monitoring and Diagnostics Generator Monitoring Philosophies Simple Monitoring with Static High-Level Alarm Limits Dynamic Monitoring with Load-Varying Alarm Limits Artificial Intelligence Diagnostic Systems Monitored Parameters Generator Electrical Parameters Stator Core and Frame Stator Winding Rotor Excitation System Hydrogen Cooling System Lube-Oil System Seal-Oil System Stator Cooling Water System 324 References Generator Protection Basic Protection Philosophy Generator Protective Functions 334

10 xi 6.3 Brief Description of Protective Functions Synchronizer and Sync-Check Relays (Functions and 25) Short-Circuit Protection (Functions 21, 50, 51,51V, 339 and 87) Volts/Hertz Protection (Function 24) Over- and Undervoltage Protection (Functions and 27) Reverse Power Protection (Function32) Loss-of-Field Protection (Function 40) Stator Unbalanced Current Protection (Function 46) Stator and Rotor Thermal Protection (Function 49) Voltage Balance Protection (Function 60) Time Overcurrent Protection for Detection of 349 Turn-to-Turn Faults (Function 61) Breaker Failure Protection (Function 62B) Rotor Ground-Fault Protection (Function 64F) Over-/Underfrequency Protection (Function 81) Out-of-Step Operation (Loss of Synchronism) 353 (Function 78) 6.4 Specialized Protection Schemes Protection Against Accidental Energization dc Field Ground Discrimination Vibration Considerations Operation of the Isolated-Phase Bus (IPB) at Reduced 362 Cooling and Risks from H 2 Leaks into the IPB Calculation of the H 2 Mix in the IPB for a Given H Leak from the Generator into the IPB 6.5 Tripping and Alarming Methods 367 References 372 II INSPECTION, MAINTENANCE, AND TESTING 7 Inspection Practices and Methodology Site Preparation Foreign Material Exclusion Foreign Material Exclusion - Procedures Experience and Training Safety Procedures Electrical Clearances Inspection Frequency Generator Accessibility Inspection Tools Inspection Forms 394 References 409

11 xii 8 Stator Inspection Stator Frame and Casing External Components Internal Components Caged Stator Cores Inspection and Removal Stator Core Stator Bore Contamination Blocked Cooling Vent Ducts Iron Oxide Deposits Loose Core Iron/Fretting and Interlaminar Failures Bent/Broken Laminations in the Bore Space Block Support and Migration Migration of Broken Core Plate and Space Block 461 Thick Plates Laminations Bulging into Air Vents Greasing/Oxide Deposits on Core Bolts Core-Compression Plates Core-End Flux Screens and Flux Shunts Frame-to-Core Compression (Belly) Bands Back-of-Core Burning Core-End Overheating Stator Windings Stator Bar/Coil Contamination (Cleanliness) End-Winding Blocking and Roving Surge-Rings Surge-Ring Insulation Condition End-Winding Support Structures Ancillary End-Winding Support Hardware Asphalt Bleeding/Soft Spots Tape Separation/Girth Cracking Insulation Galling/Necking beyond the Slot Insulation Bulging into Air Ducts Insulation Condition, Overheating, and Electrical Aging Corona Activity Stator Wedges End-Wedge Migration Out of Slot Side-Packing Fillers Leaks in Water-Cooled Stator Windings Magnetic Termites Flow Restriction in Water-Cooled Stator Windings Hoses, Gaskets, and O-Rings in Water-Cooled 518 Stator Windings 8.4 Phase Connectors and Terminals Circumferential Bus Insulation Phase Droppers 523

12 xiii High-Voltage Bushings Standoff Insulators Bushing Vents Bushing-Well lnsulators and Hydrogen Sealant Condition Generator Current Transformers (CTs) Hydrogen Coolers 532 References 534 Additional Reading Rotor Inspection Rotor Cleanliness Retaining Rings Nonmagnetic 18 5 and Retaining Rings Removal of Retaining Rings Fretting/Movement at Interference Fit Surfaces of Wedges and Rings Tooth Cracking Centering (Balance) Rings Fan Rings or Hubs Fan Blades Bearings and Journals Balance Weights and Bolts End Wedges and Damper Windings Other Wedges Windings General Conductor Material Rotor Windings Slot Region Slot Liner Turn Insulation Creepage Block and Top Channel C-Channel Subslot End Windings and Main Leads Retaining Ring Liners End Turns and Blocking Shorted Turns Top-Tooth Cracking dc Main Leads Coil and Pole Connections Collector Rings Collector Ring Insulation Bore Copper and Radial (Vertical) Terminal Stud Connectors Brush-Spring Pressure and General Condition Brush Rigging Shaft Voltage Discharge (Grounding) Brushes Rotor Winding Main Lead Hydrogen Sealing Inner and Outer Circumferential Pole Slots (Body Flex Slots) 633

13 xiv 9.22 Blocked Rotor Radial Vent Holes Shifting of Winding and/or 635 Insulation 9.23 Couplings and Coupling Bolts Bearing Insulation Hydrogen Seals Journal Seals Thrust-Collar Seals Carbon Seals Rotor-Body Zone Rings Rotor Removal 648 References Auxiliaries Inspection Lube-Oil System Hydrogen Cooling System Hydrogen Desiccant/Dryer Seal-Oil System Stator Cooling Water System Exciters Rotating Systems Inspection Static Systems Inspection Brushless Systems Inspection Specific Inspection Items Generator Maintenance Testing Stator Core Mechanical Tests Core Tightness Core and Frame Vibration Testing Stator Core Electrical Tests EL CID Testing Rated Flux Test with Infrared Scan Core Loss Test Through-Bolt Insulation Resistance Insulation Resistance of Flux Screens Stator Winding Mechanical Tests Wedge Tightness Stator End-Winding Vibration Water-Cooled Stator Winding Tests Air Pressure Decay Tracer Gases Vacuum Decay Pressure Drop Flow Testing Capacitance Mapping Stator Winding Electrical Tests 702

14 xv Pretesting Requirements Series Winding Resistance Insulation Resistance (IR) Polarization Index (PI) Dielectric Absorption during dc Voltage Application dc Leakage or Ramped Voltage dc Hi-Pot ac Hi-Pot Partial Discharge (PD) Off-line Testing Capacitance Measurements Dissipation/Power Factor Testing Dissipation/Power Factor Tip-up Test Rotor Mechanical Testing Rotor Vibration Rotor Nondestructive Examination Inspection 719 Techniques Some Additional Rotor NDE Specifics Air Pressure Test of Rotor Bore Rotor Electrical Testing Winding Resistance Insulation Resistance (IR) Polarization Index (PI) dc Hi-Pot ac Hi-Pot Shorted Turns Detection General Shorted Turns Detection by Recurrent Surge Oscillation 736 (RSO) Shorted Turns Detection by Open-Circuit Test Shorted Turns Detection by Winding Impedance Shorted Turns Detection by Low-Voltage dc or Volt 742 Drop Shorted Turns Detection by Low-Voltage ac or C 743 Core Test Shorted Turns Detection by Shorted Turns Detector 744 (Flux Probe) Field-Winding Ground Detection by the Split-Voltage 762 Test Field Ground Detection by the Current-through-Forging 762 Test Shaft Voltage and Grounding Hydrogen Seals NDE Insulation Resistance Bearings NDE 766

15 xvi Insulation Resistance Thermal Sensitivity Testing and Analysis Background Typical Thermal Sensitivity Test Heat-Run Testing Test Procedure Acceptance Parameters Hydrogen Leak Detection Pressure Drop SF Helium Snoop Ultrasonic 777 References Maintenance General Maintenance Philosophies Breakdown Maintenance Planned Maintenance Predictive Maintenance Condition-Based Maintenance (CBM) Operational and Maintenance History Maintenance Intervals/Frequency Type of Maintenance Extent of Maintenance Repair or Replacement Rehabilitation/Upgrading/Uprating Obsolescence Work Site Location Transportation Workforce Spare Parts Uprating Drivers for Uprating Uprating Considerations Component Evaluations Reliability and Effect of Uprating on Generator Life Required Inspection and Tests Prior to Uprating Required Maintenance Prior to Uprating Heat-Run Testing After Uprating Maintenance Schedule After Uprating Long-Term Storage and Mothballing Reasons for Storage of Generator Equipment General Requirements Storage Requirements 812

16 xvii Monitoring and Maintenance During Storage Restoration from Storage Long Term Storage Maintenance Procedures and 822 Testing Life Cycle Management (LCM) Single Point Vulnerability (SPV) Analysis 827 References 828 Index 829

17 PREFACE It is not uncommon for a large utility to have units of disparate size, origin, and vintage in its fleet of generators. Among its dozens of generators, there might be some from the 1950s or 1960s and some with their original asphalt or thermoplastic windings. These, and later units, may be running with and without magnetic retaining rings. Some might have thermoelastic windings of all sorts, with or without asbestos; they might be hydrogen-cooled or air-cooled, have split-stator windings, be self-excited or different types of externally excited, steam-driven or combustion-driven, and the list goes on and on. Now, take that diversity and include units operating in 50 and 60 Hz grids, built by Western, Asian, and Eastern European manufacturers to different standards. This is what you may find in some of the new independent, deregulated power producers that, in addition to building new plants, have purchased entire fleets of older units in several countries around the globe. The reasons why one may find so many old units still in operation are not difficult to discern. First of all, a typical generator is made with an intent to last no less than 30 years or so. Second, replacing an operating unit is very capital intensive and, thus, done only when a catastrophic failure has occurred or some other major failure of the machine that renders continuous operation not economically viable. Third, although expected to last 30 years, large turbogenerators are known to have their lives extended far beyond that, if well maintained and operated. Sometimes that also requires replacing a major component, such as the armature winding and/or a rotor winding (or the entire rotor!). Significant changes in design tend to occur every few years, for different components. For instance, a history of the insulation systems encountered in generators shows that every few years there is some big change resulting in increased ratings. These changes typically derive from the adoption of a new materials such as the change from magnetic to nonmagnetic material for retaining rings. Not all changes are always positive. Some new designs end up being reversed or revised after experience unmasks significant defects in them. There are countless scraps of information about the operation, maintenance, and troubleshooting of large turbogenerators in many publications. All vendors at one stage or another have produced and published interesting literature about the operation of their generators. In particular, the technical information letters put out by some manufacturers (called different names by different vendors) offer a wealth of detailed xix

18 xx PREFACE O&M topics. Institutions such as EPRI in the United States, CIGRE, IEC, ANSI, IEEE, and other national standards cover various aspects of the operation and maintenance of generators in general, but offer no specifics that may help troubleshoot a particular unit. It is difficult to obtain from those sources a condensed and operational set of insights useful to the solution of a given problem with a specific machine. It is no wonder then that with so many dissimilar units in operation and such a variegated experience, we are often forced to call the experts, who tend to be folks almost as old as the oldest units in operation. These are individuals who have crawled, inspected, tested, and maintained many diverse generators over the years. In doing so, they have retained knowledge about the different design, material, and manufacturing characteristics, typical problems, and most effective solutions. This type of expertise cannot be learned in a classroom. Unfortunately, not every company retains an individual with the breadth and depth of expertise required for troubleshooting all its units. In fact, with the advent of deregulation, many small nonutility (third-party) power producers operate small fleets of generators without the benefit of in-house expertise. In lieu of that, they depend heavily on OEMs and independent consultants. Large utilities in many places have also seen their expertise dissipate, not to a small extent because of a refocus of management priorities. All these developments are occurring at the same time that these units are called to operate in a more onerous environment. Economic dispatch in a deregulated or semideregulated world results in an increased use of double-shifting and loadcycling. Some effort has been made over the years to capture the experts knowledge and make it readily available to any operator. This effort took the shape of expert systems. However, adaptation of these computer programs to the many different types of generators and associated equipment in existence has proved to be the Achilles heel of this technology. This book is designed to partially fill the gap by offering a comprehensive view of the many issues related to the operation, inspection, maintenance, and troubleshooting of large turbine generators. The contents of this second edition have been significantly enhanced and many new additional topics included. All of the information in the book is the result of many years of combined hands-on experience of the authors. It was written with the machine s operator and inspector in mind, as well as providing a guide to uprating and life enhancement of large generators. Although not designed to provide a step-by-step guide for the troubleshooting of large generators, it serves as a valuable source of information that may prove to be useful during troubleshooting activities. The topics covered are also cross-referenced to other sources. Many such references are included to facilitate those readers interested in enlarging their knowledge of a specific issue under discussion. For the most part, theoretical equations have been left out, as there are several exceptionally good books on the theory of operation of synchronous machines. Those readers who so desire can readily access those books. Several references are cited. This book, however, is about the practical aspects that characterize the design, operation, and maintenance of large turbine-driven generators, and a significant number of practical calculations used commonly in maintenance and testing situations have been added.

19 PREFACE xxi Chapter 1 ( Principles of Synchronous Machines ) provides a basis of theory for electricity and electromagnetism upon which the machines covered in this book are based. As well, the fundamentals of synchronous machine construction and operation are also discussed. This is for the benefit of generator operators who have a mechanics background and are inclined to attain a modicum of proficiency in understanding the basic principles of operation of the generator. It also comes in handy for those professors who would like to adopt this book as a reference for a course on large rotating electric machinery. Chapters 2 and 3 ( Generator Design and Construction and Generator Auxiliary Systems ) contain a very detailed and informative description of all the components found in a typical generator and its associated auxiliary systems. Described therein are the functions that the components perform, as well as all relevant design and operational constrains. Some additional insight into design methods and calculations are also provided. Chapter 4 ( Operation and Control ) introduces the layperson to the many operational variables that describe a generator. Most generator grid interaction issues and their affect on the machine components and operation are covered in great detail. Chapter 5 ( Monitoring and Diagnostics ) and Chapter 6 ( Generator Protection ) serve to introduce all aspects related to the on-line and off-line monitoring and protection of a large turbogenerator. Although not intended to serve as a guideline for designing and setting up the protection systems of a generator, they provide a wealth of background information and pointers to additional literature. Chapters 7 ( Inspection Practices and Methodology ), leads off the second part of the book with a look at preparing for a hands-on inspection of large generators. The chapter discusses the issues of concern for both safety of personnel and the equipment as well as the types of tools and approaches used in inspecting large generators. This chapter also contains a collection of most inspection forms typically used for inspecting turbogenerators. These forms are very useful and can be readily adapted to any machine and plant. Chapter 8 ( Stator Inspection ), Chapter 9 ( Rotor Inspection ), and Chapter 10 ( Auxiliaries Inspection ) constitute the core of this book. They describe all components presented in Chapters 2 and 3, but within the context of their behavior under real operational constraints, modes of failure, and typical troubleshooting activities. These chapters provide detailed information on what to look for, and how to recognize problems in the machine during inspection. Chapters 8 and 9 also contain some basic formulas and procedures for some of the various activities that occur during inspection, maintenance, and testing of large generators. Chapter 11 ( Generator Maintenance Testing ) contains a comprehensive summary of the many techniques used to test the many components and systems comprising a generator. The purpose of the descriptions is not to serve as a guide to performing the tests-there are well-established guides and standards for that rather, they are intended to illustrate the palette of possible tests to choose from. Provided as well is a succinct explanation of the character of each test and explanations of how they are carried out. Chapter 12 ( Maintenance Philosophies ) is included to provide some perspective to the reader on the many choices and approaches that can be taken in generator and

20 xxii PREFACE auxiliary systems maintenance. Often, there are difficult decisions on how far to take maintenance. In some cases, only basic maintenance may be required, and on other occasions it may be appropriate to carry out extensive rehabilitation of existing equipment or even replacement of components. This chapter discusses some of the issues that need to be considered when deciding on what, how much, and where to do it. Along with the regular maintenance aspects, other important issues like uprating and long-term storage are also addressed. We hope that this book will be not only useful to the operator in the power plant but also to the design engineer and the systems operations engineer. We have provided a wealth of information obtained in the field about the behavior of such machines, including typical problems and conditions of operation. The book should also be useful to the student of electrical rotating machines as a complementary reference to the books on machine theory. Although we have tried our best to cover each topic as comprehensively as possible, the book should not be seen as a guide to troubleshooting. In each case in which a real problem is approached, a whole number of very specific issues only relevant to that very unique machine come into play. These can never be anticipated or known and thus described in a book. Thus, we recommend the use of this book as a general reference source, but that the reader should always obtain adequate on-the-spot expertise when approaching a particular problem. We remain intent on updating the contents of this book from time to time, from our own experience as well as from that of others. Therefore, we would welcome from the readers their comments, which they can submit to the publisher, for incorporation in future editions. Toronto, Ontario, Canada Irvine, California August 2008 GEOFF KLEMPNER ISIDOR KERSZENBAUM

21 ACKNOWLEDGMENTS The contents of this book are impossible to learn in a class. They are the result of personal experience accumulated over years of working with large turbine-driven generators. Most of all, they are the result of the invaluable long-term contribution of coworkers and associates. Each author was motivated by an important individual at an early stage of his career, and by many outstanding individuals in the profession over subsequent years. Attempting to mention all these people would lead to the unintended omission of some. The authors are most indebted to the IEEE Press for reviewing the second edition proposal and supporting its publication. They also wish to express their sincere gratitude to the technical reviewers, Robert Hindmarsh and Nils Nilsson, for painstakingly reviewing the final manuscript and making numerous useful remarks. The authors also would like to thank the members of the editorial departments of the IEEE Press and John Wiley & Sons, the reviewers, and all others involved in the publication of this book for their support in making its publication possible. Finally, but certainly most intensely, the authors wish to thank their immediate families for their continuous support and encouragement. G.K. I.K. xxiii