[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

Leo J. Savio
ADAPT Corporation
Ted Haupert
TJ/H2b Analytical Services
Loren B. Wagenaar
America Electric Power
Dieter Dohnal
Maschinenfabrik Reinhausen GmbH
Robert F. Tillman, Jr.
Alabama Power Company
Dan D. Perco
Perco Transformer Engineering
Shirish P. Mehta
William R. Henning
Waukesha Electric Systems
James H. Harlow
Harlow Engineering Associates
Armando Guzmán
Hector J. Altuve
Gabriel Benmouyal
Schweitzer Engineering Laboratories
Jeewan Puri
Transformer Solutions
Robert C. Degeneff
Rensselaer Polytechnic Institute
Alan Oswalt
Consultant
Wallace Binder
Consultant
Harold Moore
H. Moore & Associates
Andre Lux
KEMA T&D Consulting
Philip J. Hopkinson
HVOLT, Inc.
3
Ancillary Topics
3.1 Insulating Media
Solid Insulation — Paper • Liquid Insulation — Oil • Sources
of Contamination
3.2 Electrical Bushings
Purpose of Electrical Bushings • Types of Bushings • Bushing
Standards • Important Design Parameters • Other Features of
Bushings • Bushings for Special Applications • Accessories
Commonly Used with Bushings • Tests on Bushings •
Maintenance and Troubleshooting
3.3 Load Tap Changers
Design Principle • Applications of Load Tap Changers • Phase-
Shifting Transformers (PST) • Rated Characteristics and
Requirements for Load Tap Changers • Selection of Load Tap
Changers • Protective Devices for Load Tap Changers •
Maintenance of Load Tap Changers • Refurbishment/
Replacement of Old LTC Types • Future Aspects
3.4 Loading and Thermal Performance
Design Criteria • Nameplate Ratings • Other Thermal
Characteristics • Thermal Profiles • Temperature Measurements
• Predicting Thermal Response • Load Cyclicality • Science of
Transformer Loading • Water in Transformers under Load •
Loading Recommendations
3.5 Transformer Connections
Introduction • Polarity of Single-Phase Transformers • Angular
Displacement of Three-Phase Transformers • Three-Phase
Transformer Connections • Three-Phase to Six-Phase
Connections • Paralleling of Transformers
3.6 Transformer Testing
Introduction • Voltage Ratio and Proper Connections •
Insulation Condition • Control Devices and Control Wiring •
Dielectric Withstand • Performance Characteristics • Other
Tests
3.7 Load-Tap-Change Control and Transformer
Paralleling
Introduction • System Perspective, Single Transformer •
Control Inputs • The Need for Voltage Regulation • LTC Control
with Power-Factor-Correction Capacitors • Extended Control
of LTC Transformers and Step-Voltage Regulators •
Introduction to Control for Parallel Operation of LTC
Transformers and Step-Voltage Regulators • Defined Paralleling
Procedures • Characteristics Important for LTC Transformer
Paralleling • Paralleling Transformers with Mismatched
Impedance
3.1 Insulating Media
3.8 Power Transformer Protection
Introduction • Transformer Differential Protection •
Magnetizing Inrush, Overexcitation, and CT Saturation •
Methods for Discriminating Internal Faults from Inrush and
Overexcitation Conditions • An Improved Approach for
Transformer Protection • Current Differential Relay •
Differential-Element Performance during Inrush Conditions •
Conclusions
3.9 Causes and Effects of Transformer Sound Levels
Transformer Sound Levels • Sound-Energy Measurement
Techniques • Sources of Sound in Transformers • Sound Level
and Measurement Standards for Transformers • Factors
Affecting Sound Levels in Field Installations
3.10 Transient-Voltage Response
Transient-Voltage Concerns • Surges in Windings •
Determining Transient Response • Resonant Frequency
Characteristic • Inductance Model • Capacitance Model • Loss
Model • Winding Construction Strategies • Models for System
Studies
3.11 Transformer Installation and Maintenance
Transformer Installation • Transformer Maintenance
3.12 Problem and Failure Investigation
Introduction • Background Investigation • Problem Analysis
where No Failure Is Involved • Failure Investigations • Analysis
of Information • Special Considerations
3.13 On-Line Monitoring of Liquid-Immersed
Transformers
Benefits • On-Line Monitoring Systems • On-Line Monitoring
Applications
3.14 U.S. Power Transformer Equipment Standards
and Processes
Processes for Acceptance of American National Standards • The
International Electrotechnical Commission (IEC) • Relevant
Power Transformer Standards Documents
Leo J. Savio and Ted Haupert
Insulating media in high voltage transformers consists of paper wrapped around the conductors in the
transformer coils plus mineral oil and pressboard to insulate the coils from ground. From the moment
a transformer is placed in service, both the solid and liquid insulation begin a slow but irreversible process
of degradation.
3.1.1 Solid Insulation — Paper
3.1.1.1 Composition of Paper — Cellulose
Paper and pressboard are composed primarily of cellulose, which is a naturally occurring polymer of
plant origin. From a chemical perspective, cellulose is a naturally occurring polymer. Each cellulose
molecule is initially composed of approximately 1000 repeating units of a monomer that is very similar
to glucose. As the cellulose molecule degrades, the polymer chain ruptures and the average number of
repeating units in each cellulose molecule decreases. With this reduction in the degree of polymerization
of cellulose, there is a decrease in the mechanical strength of the cellulose as well as a change in brittleness
and color. As a consequence of this degradation, cellulose will reach a point at which it will no longer
© 2004 by CRC Press LLC
© 2004 by CRC Press LLC