Disturbance Analysis for Power Systems E-Book

Mohamed A. Ibrahim

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Serie: Wiley - IEEE
• Sprache: Englisch

Seitenzahl: 887

Veröffentlichungsjahr: 2011

Beschreibung

More than ninety case studies shed new light on power system phenomena and power system disturbances

Based on the author's four decades of experience, this book enables readers to implement systems in order to monitor and perform comprehensive analyses of power system disturbances. Most importantly, readers will discover the latest strategies and techniques needed to detect and resolve problems that could lead to blackouts to ensure the smooth operation and reliability of any power system.

Logically organized, Disturbance Analysis for Power Systems begins with an introduction to the power system disturbance analysis function and its implementation. The book then guides readers through the causes and modes of clearing of phase and ground faults occurring within power systems as well as power system phenomena and their impact on relay system performance. The next series of chapters presents more than ninety actual case studies that demonstrate how protection systems have performed in detecting and isolating power system disturbances in:

• Generators

• Transformers

• Overhead transmission lines

• Cable transmission line feeders

• Circuit breaker failures

Throughout these case studies, actual digital fault recording (DFR) records, oscillograms, and numerical relay fault records are presented and analyzed to demonstrate why power system disturbances happen and how the sequence of events are deduced. The final chapter of the book is dedicated to practice problems, encouraging readers to apply what they've learned to perform their own system disturbance analyses.

This book makes it possible for engineers, technicians, and power system operators to perform expert power system disturbance analyses using the latest tested and proven methods. Moreover, the book's many cases studies and practice problems make it ideal for students studying power systems.

Leseprobe

Contents

Cover

Title Page

Copyright

Dedication

Preface

Chapter 1: Power System Disturbance Analysis Function

1.1 Analysis Function of Power System Disturbances

1.2 Objective of DFR Disturbance Analysis

1.3 Determination of Power System Equipment Health Through System Disturbance Analysis

1.4 Description of DFR Equipment

1.5 Information Required for the Analysis of System Disturbances

1.6 Signals to be Monitored by a Fault Recorder

1.7 DFR Trigger Settings of Monitored Voltages and Currents

1.8 DFR and Numerical Relay Sampling Rate and Frequency Response

1.9 Oscillography Fault Records Generated by Numerical Relaying

1.10 Integration and Coordination of Data Collected from Intelligent Electronic Devices

1.11 DFR Software Analysis Packages

1.12 Verification of DFR Accuracy in Monitoring Substation Ground Currents

1.13 Using DFR Records to Validate Power System Short-Circuit Study Models

1.14 COMTRADE Standard

References

Chapter 2: Phenomena Related to System Faults and the Process of Clearing Faults from a Power System

2.1 Shunt Fault Types Occurring in a Power System

2.2 Classification of Shunt Faults

2.3 Types of Series UNBALANCE in a Power System

2.4 Causes of Disturbance in a Power System

2.5 Fault Incident Point

2.6 Symmetric and Asymmetric Fault Currents

2.7 Arc-Over or Flashover at the Voltage Peak

2.8 Evolving Faults

2.9 Simultaneous Faults

2. 10 Solid or Bolted (RF = 0) Close-in Phase-to-Ground Faults

2.11 Sequential Clearing Leading to a Stub Fault that Shows a Solid (RF = 0) Remote Line-to-Ground Fault

2.12 Sequential Clearing Leading to a Stub Fault that Shows a Resistive Remote Line-to-Ground Fault

2.13 High-Resistance Tree Line-to-Ground Faults

2.14 High-Resistance Line-to-Ground Fault Confirming the Resistive Nature of the Fault Impedance When Fed from One Side Only (Stub)

2.15 Phase-to-Ground Faults on an Ungrounded System

2.16 Current in Unfaulted Phases During Line-to-Ground Faults

2.17 Line-to-Ground Fault on the Grounded-Wye (GY) Side of a Delta/GY Transformer

2.18 Line-to-Line Fault on the Grounded-Wye Side of a Delta/GY Transformer

2.19 Line-to-Line Fault on the Delta Side of a Delta/GY Transformer with no Source Connected to the Delta Winding

2.20 Subcycle Relay Operating Time During an EHV Double-Phase-to-Ground Fault

2.21 Self-Clearing of a C-g Fault Inside an Oil Circuit Breaker Tank

2.22 Self-Clearing of a B-g Fault Caused by a Line Insulator Flashover

2.23 Delayed Clearing of a Pilot Scheme Due to a Delayed Communication Signal

2.24 Sequential Clearing of a Line-to-Ground Fault

2.25 Step-Distance Clearing of an L-g Fault

2.26 Ground Fault Clearing in Steps by an Instantaneous Ground Element at one end and a Ground Time Overcurrent Element at the other end

2.27 Ground fault Clearing by Remote Backup Following the Failures of both Primary and Local Backup (Breaker Failure) Protection Systems

2.28 Breaker Failure Clearing of a Line-to-Ground Fault

2.29 Determination of the Fault Incident Point and Classification of Faults Using a Comparison Method

References

Chapter 3: Power System Phenomena and Their Impact on Relay System Performance

3.1 Power System Oscillations Leading to Simultaneous Tripping of both ends of a Transmission Line and the Tripping of one end Only on an Adjacent Line

3.2 Generator Oscillations Triggered by a Combination of L-g Fault, Loss of Generation, and Undesired Tripping of three 138-kV Lines

3.3 Stable Power Swing Generated During Successful Synchronization of a 200-MW Unit

3.4 Major System Disturbance Leading to Different Oscillations for Different Transmission Lines Emanating from the same Substation

3.5 Appearance of 120-Hz Current at a Generator Rotor During a High-Side Phase-to-Ground Fault

3.6 Generator Negative-Sequence Current Flow During Unbalanced Faults

3.7 Inadvertent (Accidental) Energization of a 170-MW Hydro Generating Unit

3.8 Appearance of Third-Harmonic Voltage at Generator Neutral

3.9 Variations of Generator Neutral Third-Harmonic Voltage Magnitude During System Faults

3.10 Generator Active and Reactive Power Outputs During a GSU High-Side L-g Fault

3.11 Loss of Excitation of a 200-MW Unit

3.12 Generator Trapped (Decayed) Energy

3.13 Nonzero Current Crossing During Faults and Mis-Synchronization Events

3.14 Generator Neutral Zero-Sequence Voltage Coupling Through Step-Up Transformer Interwinding Capacitance During a High-Side Ground Fault

3.15 Energizing a Transformer with a Fault on the High Side within the Differential Zone

3.16 Transformer Inrush Currents

3.17 Inrush Currents During Energization of the Grounded-Wye Side of a YG/Delta Transformer

3.18 Inrush Currents During Energization of a Transformer Delta Side

3.19 Two-Phase Energization of an Autotransformer with a Delta Winding Tertiary During a Simultaneous L-g Fault and an Open Phase

3.20 Phase Shift of 30° Across the Delta/Wye Transformer Banks

3.21 Zero-Sequence Current Contribution from a Remote Two-Winding delta/YG Transformer

3.22 Conventional Power-Regulating Transformer Core type Acting as a Zero-Sequence Source

3.23 Circuit Breaker Re-Strikes

3.24 Circuit Breaker Pole Disagreement During a Closing Operation

3.25 Circuit Breaker Opening Resistors

3.26 Secondary Current Backfeeding to Breaker Failure Fault Detectors

3.27 Magnetic Flux Cancellation

3.28 Current Transformer Saturation

3.29 Current Transformer Saturation During an Out-of-Step System Condition Initiated by Mis-Synchronization of a Generator Breaker

3.30 Capacitive Voltage Transformer Transient

3.31 Bushing Potential Device Transient During Deenergization of an EHV Line

3.32 Capacitor Bank Breaker Re-Strike Following Interruption of a Capacitor Normal Current

3.33 Capacitor Bank Closing Transient

3.34 Shunt Capacitor Bank Outrush into Close-in System Faults

3.35 SCADA Closing into a Three-Phase Fault

3.36 Automatic Reclosing into a Permanent Line-to-Ground Fault

3.37 Successful High-Speed Reclosing Following a Line-to-Ground Fault

3.38 Zero-Sequence Mutual Coupling–Induced Voltage

3.39 Mutual Coupling Phenomenon Causing False Tripping of a High-Impedance Bus Differential Relay During a Line Phase-to-Ground Fault

3.40 Appearance of Nonsinusoidal Neutral Current During the Clearing of Three-Phase Faults

3.41 Current Reversal on Parallel Lines During Faults

3.42 Ferranti Voltage Rise

3.43 Voltage Oscillation on EHV Lines Having Shunt Reactors at their Ends

3.44 Lightning Strike on an Adjacent Line Followed by a C-g Fault Caused by a Separate Lightning Strike on the Monitored Line

3.45 Spill Over of a 345-kV Surge Arrester Used to Protect a Cable Connection, Prior to its Failure

3.46 Scale Saturation of an A/D Converter Caused by a Calibration Setting Error

3.47 Appearance of Subsidence Current at the Instant of Fault Interruption

3.48 Energizing of a Medium Voltage Motor that has an Incorrect Formation of the Stator Wining neutral

3.49 Phase Angle Change from Loading Condition to Fault Condition

References

Chapter 4: Case Studies Related to Generator System Disturbances

4.1 Generator Protection Basics

Case Studies

References

Chapter 5: Case Studies Related to Transformer System Disturbances

5.1 Transformer Basics

5.2 Transformer Differential Protection Basics

5.3 Case Studies

References

Chapter 6: Case Studies Related to Overhead Transmission-Line System Disturbances

6.1 Line Protection Basics

6.2 Case Studies

References

Chapter 7: Case Studies Related to Cable Transmission Feeder System Disturbances

Case Studies

References

Chapter 8: Case Studies Related to Breaker Failure Protection System Disturbances

8.1 Breaker Failure Protection Basics

Case Studies

References

Chapter 9: Problems

Index

Copyright © 2012 by Mohamed A. Ibrahim. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Ibrahim, Mohamed A., 1943-

Disturbance analysis for power systems / Mohamed A. Ibrahim.

p. cm.

Includes index.

ISBN 978-0-470-91681-0 (cloth)

1. Electric power system stability. 2. Transients (Electricity) 3. Electric power failures.

4. Electric network analysis. I. Title.

TK1010.I27 2011

621.319–dc22

2010048274

ePDF ISBN: 978-1-118-17211-7

oBook ISBN: 978-1-118-17209-4

ePub ISBN: 978-1-118-17210-0

10 9 8 7 6 5 4 3 2 1

To my mother, who taught me without knowing how to read or write;

my father; my wife; and my family

Preface

The fault recording equipment used in monitoring power systems evolved from a wet trace and light beams writing on special photo-sensitive paper or film oscillograms to digital, microprocessor-based technology. Some of the old records took days to develop, as in the case of the wet trace and recurring problems with sensitive papers. As a result, some key records were lost, making the analysis of power system disturbances extremely difficult. In addition, starting recording equipment was a hassle, causing unreliable oscillograph operations. A digital fault recorder (DFR) is considered an intelligent electronic device that can be accessed via communication links to send fault records automatically to remote operating centers and engineering offices immediately following a disturbance. This allowed a rapid analysis to make it possible to restore the system. Accurate root-mean-square measurements as well as a host of software packages can be executed to verify the system model and to assess the impact of disturbances on power system equipment.

Analysis of power system disturbances is an important function that monitors the performance of a protection system. It can also provide a wealth of valuable information regarding correct behavior of the system. Understanding power system phenomena can be simplified, and adoption of safe operating limits and protective relaying practices can be enhanced. Review of DFR and numerical relay fault records for system operations can help to isolate incipient problems so that corrections can be implemented before the problems become serious. Understanding power system oscillations and system relaying response during a power swing condition can be enhanced, thus avoiding system blackouts. In addition, understanding power system engineering concepts and the use of symmetrical components in the analysis of power system faults can be enforced and enhanced through DFR analysis.

A bulk power system is normally protected by two redundant relaying systems. The performance of these systems can be monitored through an analysis of system disturbances. Restoration of a power system requires correct analysis of the disturbance that caused the outage to confirm that it is safe to reenergize the system. Correct analysis can contribute to safe restoration without the fear of energizing faulty power system equipment. In addition, through proper system disturbance analysis confidence can be gained in the philosophy behind relaying application.

To facilitate the reader's review process, the DFR records are accompanied by unique functional system diagrams that show the voltages and currents monitored, using designation labels that match the records. A section is devoted to documenting power system phenomena as they appear in actual case studies. This will provide engineers who have limited experience with such problems the necessary background to perform their own analyses of their systems.

The book serves as a forum to document and present my 40+ years of experience in the area of power system disturbance analysis. Many colleagues from the American Electric Power Service Corp., the New York Power Authority, and several utilities have contributed to the book directly or indirectly, and I am grateful for their input. It has been my intention to simplify the topics presented and provide clear guidance as well as basic education to relay engineers. In this new format, the theory and basic fundamentals of relay applications are first briefly explained. This is then followed by real case studies involving system disturbances, to enforce these basics. The studies are based on actual occurrences collected through my years of involvement in the protection of utility systems. The real names of utility plants, substations, and lines have been replaced by generic labels.

In the old vertical integration environment, training and education were essential to most utilities. In the highly competitive new environment, exchange of experience and technical information is hampered, as is passing useful experience to young engineers. At this point in the history of protective relaying, the fundamentals that have been handed down from generation to generation are in danger of becoming lost. This has given me the impetus to document my experience in a useful format that can benefit engineers, since little training is now available for engineers entering the protection and control field in the area of system disturbance analysis.

In the book I present in detail how power system disturbance analysis is used as an important tool to judge the performance of protection systems. Actual DFR records, oscillograms, and numerical relay fault records are analyzed to demonstrate how to deduce the sequence of events. Topics such as the information needed for analysis, fault incident angle, and power system phenomena and their impact on relay system performance are covered. Power system phenomena derived from an analysis of system disturbances are described. In addition, case studies of actual system disturbances involving the performance of protection systems for generators, transformers, overhead transmission lines, cable feeders, and breaker failures are included. Several chapters are devoted to system disturbance analysis as a tool for optimizing the performance of relaying schemes. In addition, the book can serve as a tool for validating power system models and provides a wealth of technical information about the behavior of power systems.

The book is intended primarily for engineers and technicians working in the areas of protection and control, power system operation, and electrical power system equipment. It is also intended for operators and support staff at energy control centers to enhance their technical background in the safe restoration of a power system following a disturbance. The book will provide engineers with a basic background in most power system phenomena and their impact on the behavior of protection systems. The book can also be used as a textbook for undergraduate and graduate students seeking to enhance their power backgrounds. A chapter is devoted to problems, to enhance understanding of the system disturbance analysis function. The book can thus provide an incentive to colleges to offer the system disturbance analysis topic in either an undergraduate or graduate course.

Mohamed A. Ibrahim

Chapter 1

Power System Disturbance Analysis Function

An analysis of system disturbances provides a wealth of valuable information regarding power system phenomena and the behavior of protection systems. Experience can be enhanced and knowledge can be gained from the analysis function. This book is organized, first, to cover the analysis function and how it can be implemented. Then, in the following sections, phenomena related to system faults and the clearing process of faults from the power system are described. Power system phenomena derived from an analysis of system disturbances are stated. In addition, case studies of actual system disturbances involving the performance of protection systems for generators, transformers, overhead transmission lines, cable feeders, and breaker failures are provided. A section is devoted to problems that enhance an understanding of the system disturbance analysis function.

Analysis of system disturbance is based on 60-Hz phenomena associated with power system faults. Therefore, sampling rates of digital fault recorders (DFRs) are designed to fulfill this requirement. High-frequency power system transient analysis requires special devices other than conventional DFRs and numerical relays, with unique requirements different from those of a traditional power system disturbance analysis function.

To analyze the performance of protective relaying systems, high-speed digital fault and disturbance recording devices need to be employed properly. Equipment can be used for continuous monitoring of the behavior of relaying installed on a power system during the occurrence of either faults or power swing or switching operations. The equipment can be used to explain undesired operations and to assess system performance during correct operation. Analysis of fault records will help in adapting operating and protection practices and in assuring the reliability of a bulk power system. The analysis will also help to isolate problems and incipient failures. In addition, the strategic placement of DFR equipment should provide adequate coverage of the overall system response to any type of system fault or wide-area system disturbance. For this reason, DFR applications and implementation on a bulk power system are mandated by industry standards and regulations.

A review of DFR records for every operation in a system will help to isolate incipient difficulties so that corrections can be provided before a serious problem develops and to provide basic useful information about the performance of the relaying system. A review of all fault records for disturbances on a system can enhance the reliability of a relay system. Systematic analysis of disturbances can play an important role in system blackout avoidance. When they occur during the early stage of analysis, flagging relay and system problems should be addressed before they precipitate into wider-area interruption and system blackouts. This can be accomplished by analyzing correct operations and finding the causes of incorrect operations. In addition, it can provide a better assessment of the validity of relay setting calculations, correct current transformer (CT) and voltage transformer (PT) ratios, and correct breaker operations. It can also enhance the system restoration process by providing fault types and locations and a better measure of power quality.

The proposed NERC Reliability Standard PRC-002-02, “Disturbance Monitoring and Reporting Requirements,” is noted here as a document which ensures that regional reliability organizations establish requirements for the installation of disturbance-monitoring equipment and reporting of disturbance data to facilitate analyses of system events and verification of system models.

1.1 Analysis Function of Power System Disturbances

Analysis of power system disturbances can be summarized on the basis of the following primary functions:

1. The need to view fault data as soon as possible after a fault or disturbance occurs so as to restore the system safely.

2. The need to design the DFR with a reasonable pre-fault time (5 to 10 cycles) to capture incipient initiating conditions (e.g., surge arrester spillover).

3. The need to design the DFR with a long post-fault time, adjustable from 0 to 5 s, to be able to analyze backup protection clearing times (60 cycles or more) and limited power system swings (several seconds) following the occurrence of system disturbances.

4. The need to manipulate the data time base on the DFR record to analyze the effect of faults.

5. The need, finally, to manipulate the DFR data channels and view only those selected.

Ideally, the analysis function should be carried out for all relay operations in a system. The normally cleared events can lead to the discovery of equipment problems and can also be used as a teaching example for power system behavior and phenomena. From the analysis function, monthly disturbance analysis reports can be prepared. In addition, other reports can be generated. The analysis function will focus primarily on providing answers to the following basic questions:

1. What happened?

2. Why did it happen?

3. What is going to be done about it?

In essence, a sequence-of-events report, or time line, needs to be developed. Traditionally, a DFR monitors power system voltages and currents, whereas a sequence-of-events recorder (SER) monitors relay outputs, breaker and disconnect switch positions, alarms, relay targets, and relay communication channels. A DFR can integrate both functions by monitoring events and analog quantities. The following are some of the functions that analysis of DFR records, in conjunction with SER records, can provide: