CONTENTS

Preface

Acknowledgments

I THEORY, CONSTRUCTION, AND OPERATION

1 Principles of Operation of Synchronous Machines

1.1 Introduction to Basic Notions on Electric Power

1.2 Electrical-Mechanical Equivalence

1.3 Alternating Current (ac)

1.4 Three-Phase Circuits

1.5 Basic Principles of Machine Operation

1.6 The Synchronous Machine

1.7 Basic Operation of the Synchronous Machine

Additional Reading

2 Generator Design and Construction

2.1 Stator Core

2.2 Stator Frame

2.3 Flux and Armature Reaction

2.4 Electromagnetics

2.5 End-Region Effects and Flux Shielding

2.6 Stator Core and Frame Forces

2.7 Stator Windings

2.8 Stator Winding Wedges

2.9 End-Winding Support Systems

2.10 Stator Winding Configurations

2.11 Stator Terminal Connections

2.12 Rotor Forging

2.13 Rotor Winding

2.14 Rotor Winding Slot Wedges

2.15 Amortisseur Winding

2.16 Retaining Rings

2.17 Bore Copper and Terminal Connectors

2.18 Slip/Collector Rings and Brush Gear

2.19 Rotor Shrink Coupling

2.20 Rotor Turning Gear

2.21 Bearings

2.22 Air and Hydrogen Cooling

2.23 Rotor Fans

2.24 Hydrogen Containment

2.25 Hydrogen Coolers

References

3 Generator Auxiliary Systems

3.1 Lube-Oil System

3.2 Hydrogen Cooling System

3.3 Seal-Oil System

3.4 Stator Cooling Water System

3.5 Exciter Systems

4 Operation and Control

4.1 Basic Operating Parameters

4.2 Operating Modes

4.3 Machine Curves

4.4 Special Operating Conditions

4.5 Basic Operation Concepts

4.6 System Considerations

4.7 Grid-Induced Torsional Vibrations

4.8 Excitation and Voltage Regulation

4.9 Performance Curves

4.10 Sample of Generator Operating Instructions

References

5 Monitoring and Diagnostics

5.1 Generator Monitoring Philosophies

5.2 Simple Monitoring with Static High-Level Alarm Limits

5.3 Dynamic Monitoring with Load-Varying Alarm Limits

5.4 Artificial Intelligence Diagnostic Systems

5.5 Monitored Parameters

References

6 Generator Protection

6.1 Basic Protection Philosophy

6.2 Generator Protective Functions

6.3 Brief Description of Protective Functions

6.4 Specialized Protection Schemes

6.5 Tripping and Alarming Methods

References

II INSPECTION, MAINTENANCE, AND TESTING

7 Inspection Practices and Methodology

7.1 Site Preparation

7.2 Experience and Training

7.3 Safety Procedures—Electrical Clearances

7.4 Inspection Frequency

7.5 Generator Accessibility

7.6 Inspection Tools

7.7 Inspection Forms

References

8 Stator Inspection

8.1 Stator Frame and Casing

8.2 Stator Core

8.3 Stator Windings

8.4 Phase Connectors and Terminals

8.5 Hydrogen Coolers

References

9 Rotor Inspection

9.1 Rotor Cleanliness

9.2 Retaining Rings

9.3 Fretting/Movement at Interference Fit Surfaces of Wedges and Rings

9.4 Centering (Balance) Rings

9.5 Fan Rings or Hubs

9.6 Fan Blades

9.7 Bearings and Journals

9.8 Balance Weights and Bolts

9.9 End Wedges and Damper Windings

9.10 Other Wedges

9.11 Windings—General

9.12 Windings—Slot Region

9.13 End Windings and Main Leads

9.14 Collector Rings

9.15 Collector Ring Insulation

9.16 Bore Copper and Radial (Vertical) Terminal Stud Connectors

9.17 Brush-Spring Pressure and General Condition

9.18 Brush Rigging

9.19 Shaft Voltage Discharge (Grounding) Brushes

9.20 Rotor Winding Main Lead Hydrogen Sealing—Inner and Outer

9.21 Circumferential Pole Slots (Body Flex Slots)

9.22 Blocked Rotor Radial Vent Holes—Shifting of Winding and/or Insulation

9.23 Couplings and Coupling Bolts

9.24 Bearing Insulation

9.25 Hydrogen Seals

9.26 Rotor-Body Zone Rings

9.27 Rotor Removal

References

10 Auxiliaries Inspection

10.1 Lube-Oil System

10.2 Hydrogen Cooling System

10.3 Seal-Oil System

10.4 Stator Cooling Water System

10.5 Exciters

11 Generator Maintenance Testing

11.1 Stator Core Mechanical Tests

11.2 Stator Core Electrical Tests

11.3 Stator Winding Mechanical Tests

11.4 Water-Cooled Stator Winding Tests

11.5 Stator Winding Electrical Tests

11.6 Rotor Mechanical Testing

11.7 Rotor Electrical Testing

11.8 Hydrogen Seals

11.9 Bearings

11.10 Thermal Sensitivity Testing and Analysis

11.11 Heat-Run Testing

11.12 Hydrogen Leak Detection

References

12 Maintenance

12.1 General Maintenanc e Philo sophie s

12.2 Operational and Maintenance History

12.3 Maintenance Intervals/Frequency

12.4 Type of Maintenance

12.5 Work Site Location

12.6 Workforce

12.7 Spare Parts

12.8 Uprating

12.9 Long-Term Storage and Mothballing

12.10 Life Cycle Management (LCM)

12.11 Single Point Vulnerability (SPV) Analysis

References

Color Plates

Index

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

IEEE Press
445 Hoes Lane
Piscataway, NJ 08855

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.

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

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 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 load-cycling.

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.

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 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.

GEOFF KLEMPNER
ISIDOR KERSZENBAUM

Toronto, Ontario, Canada
Irvine, California
August 2008

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.

I

THEORY, CONSTRUCTION, AND OPERATION

1

PRINCIPLES OF OPERATION OF SYNCHRONOUS MACHINES

The synchronous electrical generator (also called alternator) belongs to the family of electric rotating machines. Other members of the family are the direct-current (dc) motor or generator, the induction motor or generator, and a number of derivatives of all these three. What is common to all the members of this family is that the basic physical process involved in their operation is the conversion of electromagnetic energy to mechanical energy, and vice versa. Therefore, to comprehend the physical principles governing the operation of electric rotating machines, one has to understand some rudiments of electrical and mechanical engineering.

Chapter 1 is written for those who are involved in operating, maintaining, and trou- ble-shooting electrical generators, and who want to acquire a better understanding of the principles governing the machines’ design and operation, but who do not have an electrical engineering background. The chapter starts by introducing the rudiments of electricity and magnetism, quickly building up to a description of the basic laws of physics governing the operation of the synchronous electric machine, which is the type of machine to which all turbogenerators belong.

1.1 INTRODUCTION TO BASIC NOTIONS ON ELECTRIC POWER

1.1.1 Magnetism and Electromagnetism

Certain materials found in nature exhibit a tendency to attract or repel each other. These materials, called magnets, are also called ferromagnetic because they include the element iron as one of their constituent elements.

Magnets always have two poles: one called north, the other called south. Two north poles always repel each other, as do two south poles. However, north and south poles always attract each other. A magnetic field is defined as a physical field established between two poles. Its intensity and direction determine the forces of attraction or repulsion existing between the two magnets.

Figures 1.1 and 1.2 are typical representations of two interacting magnetic poles and the magnetic field established between them.

Magnets are found in nature in all sorts of shapes and chemical constitution. Magnets used in industry are artificially made. Magnets that sustain their magnetism for long periods of time are denominated “permanent magnets.” The magnetic field produced by the north and the south pole of a permanent magnet is directional from north to south (see Fig. 1.3). These are widely used in several types of electric rotating machines, including synchronous machines. However, due to mechanical as well as operational reasons, permanent magnets in synchronous machines are restricted to those with ratings much lower than large turbine-driven generators, which is the subject of this book. Turbine-driven generators (for short: turbogenerators) take advantage of the fact that magnetic fields can be created by the flow of electric currents in conductors. See Fig. 1.4.

Fig. 1.1 Schematic representation of two magnetic poles of opposite polarity, with the magnetic field between them shown as “lines of force.”

Fig. 1.2 Schematic representation of two north poles and the magnetic field between them. South poles will create similar field patterns, but the lines of force will point toward the poles.

Fig. 1.3 Schematic representation of a “permanent magnet” showing the north and south poles and the magnetic field between them. Note that the magnetic field flows from north to south (outside the magnet).

A very useful phenomenon is that forming the conductor into the shape of a coil can augment the intensity of the magnetic field created by the flow of current through the conductor. In this manner, as more turns are added to the coil, the same current produces larger and larger magnetic fields. For practical reasons, all magnetic fields created by current in a machine are generated in coils. See Fig. 1.5.

Fiq. 1.4 Schematic representation of a magnetic field created by the flow of current in a conductor. The direction of the lines of force is given by the “law of the screwdriver”: mentally follow the movement of a screw as it is screwed in the same direction as that of the current; the lines of force will then follow the circular direction of the head of the screw. The magnetic lines of force are perpendicular to the direction of current.

Fig. 1.5 Schematic representation of a magnetic field produced by the flow of electric current in a coil-shaped conductor.

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