Power Transformer Design Practices

✍ Scribed by Fang Zhu, Baitun Yang

• Publisher: CRC Press
• Year: 2021
• Tongue: English
• Leaves: 283
• Edition: 1
• Category: Library

✦ Synopsis

The book presents basic theories of transformer operation, design principles and methods used in power transformer designing work, and includes limitation criteria, effective utilization of material, and calculation examples to enhance readers’ techniques of transformer design and testing.

It includes:

• Core and winding commonly used, and their performances
• Insulation structures and materials, methods for improvements on dielectric strengths on partial discharge, breakdown and electrical creepage
• Losses and impedance calculations, major influential factors, and methods to minimize load loss
• Cooling design and the method to obtain effective cooling
• Short-circuit forces calculations, the ways to reduce the short-circuit forces, and measures to raise withstand abilities
• No-load and load-sound levels, the influential factors and trends, and abatement techniques
• In-depth discussion of an autotransformer’s special features, its stabilizing winding function, and its adequate size
• Tests and diagnostics

The ways to optimize design are also discussed throughout the book as a goal to achieve best performances on economic design.

The book contains great reference material for engineers, students, teachers, researchers and anyone in the field associated with power transformer design, manufacture, testing, application and service maintenance. It also provides a high level of detail to help future research and development maintain electrical power as a reliable and economical energy resource.

✦ Table of Contents

Cover
Half Title
Title Page
Copyright Page
Dedication
Table of Contents
Preface
Authors
Chapter 1: Introduction
1.1 Basic Theory
1.1.1 Voltage and Current of Windings
1.1.2 Losses
1.1.3 Maximum Leakage Flux Density
1.1.4 Impedance
1.1.5 Efficiency and Voltage Regulation
1.1.6 Winding Disposition
1.1.6.1 Winding Space Factor
1.1.7 Winding Connections
1.1.7.1 Delta–Delta Connection
1.1.7.2 Wye–Wye Connection
1.1.7.3 Delta–Wye and Wye–Delta Connections
1.2 Practical Considerations in Design
1.2.1 Minimum I 2 R Loss
1.2.2 The Most Economic Utilization of Active Materials
1.3 Active Part Material Cost
1.3.1 Loss and Mass Ratio for Maximum Efficiency
1.3.2 Mass Ratio for Minimum Cost of Material
References
Chapter 2: Core
2.1 Core materials
2.2 Core Types
2.2.1 Three-Leg Core
2.2.2 Five-Leg Core
2.3 No-Load Loss
2.3.1 Components of No-Load Loss
2.3.1.1 Hysteresis Loss
2.3.1.2 Eddy Current Loss
2.3.1.3 Additional Losses [ 6, 7, 8 ]
2.3.1.4 Interlaminar Loss
2.3.2 Calculation of No-Load Loss
2.3.2.1 Interlaminar Losses
2.4 Exciting Characteristics[ 4, 5, 9, 10 ]
2.4.1 Core Exciting Current
2.4.2 Influence of Winding Connections on Third Harmonic Voltages and Currents
2.4.2.1 Y–Y Connection with Both Isolated Neutrals
2.4.2.2 Y–Y Connection with Both Grounded Neutrals
2.4.2.3 Y–Y Connection with Isolated Primary Neutral and Grounded Secondary Neutral
2.4.2.4 Y–D or D–Y Connection
2.4.3 Undesirable Features of Third Harmonics
2.4.4 Calculation of Exciting Current
2.5 Inrush Current
2.6 Test Failures of No-Load Loss
2.7 Core Insulation and Ground
2.8 Flux Density Generated by Quasi-DC Current
2.9 Gapped Core
References
Chapter 3: Windings
3.1 Types of Winding
3.1.1 Layer Winding
3.1.2 Multi-Start Winding [ 2, 3 ]
3.1.3 Helical Winding
3.1.4 Disc Winding
3.2 Transpositions
3.2.1 Helical Winding
3.2.2 Disc Winding
3.3 Half-Turn Effect
3.4 Axial Split Windings
3.5 Cables Used in Winding
References
Chapter 4: Insulation
4.1 Voltages on Transformer Terminals
4.1.1 Service Voltage
4.1.2 Overvoltages
4.1.2.1 Upset of Symmetry of Voltage
4.1.2.2 Lightning Impulse
4.1.2.3 Switching Impulse
4.2 Voltage Inside Transformer
4.2.1 Analysis on Ideal Model
4.2.2 Transferred Voltage
4.2.3 Voltage across Regulating Winding
4.3 Insulation Materials
4.3.1 Mineral Oil
4.3.1.1 Electrode Shape
4.3.1.2 Electrode Spacing
4.3.1.3 Electrode Area
4.3.1.4 Duration of Applied Voltage
4.3.1.5 Temperature
4.3.1.6 Oil Volume
4.3.1.7 Velocity
4.3.1.8 Moisture
4.3.1.9 Gas in Oil [ 3, 8 ]
4.3.1.10 Oil Oxidation
4.3.2 Natural Ester Liquid [9, 10]
4.3.2.1 Fire Safety
4.3.2.2 Service Life
4.3.2.3 Thermal Performance
4.3.3 Paper Insulation
4.3.3.1 Moisture
4.3.3.2 Breakdown Stresses
4.3.4 Clamping Ring
4.4 Partial Discharge and Insulation Structure
4.4.1 Oil Duct Stress
4.4.2 Corner Stress
4.4.3 Creepage Breakdown
4.5 Major Insulation Design
4.5.1 Main Insulation Gap between Windings in Same Phase
4.5.2 Main Insulation Gap between Innermost Winding and Core
4.5.3 Main Insulation Gap between Windings in Different Phases
4.5.4 End Insulation
4.6 Minor Insulation Design
4.6.1 Turn-to-turn Insulation
4.6.2 Section-to-Section Insulation
4.6.3 Tap Gap Location
4.7 Lead Insulation
4.8 Typical Electric Field Patterns
4.8.1 Uniform Field
4.8.2 Coaxial Cylindrical Electrodes
4.8.3 Cylinder to plane
References
Chapter 5: Impedances
5.1 Positive Sequence/Negative Sequence Impedance
5.1.1 Reactance between Two Windings
5.1.2 Reactance between Series Connected Windings and Other Winding
5.1.3 Reactance of Zigzag Winding
5.1.4 Reactance of Three Windings
5.1.5 Lead Reactance
5.2 Zero Sequence Impedance [4, 5]
References
Chapter 6: Load Loss
6.1 I 2 R Loss
6.2 Winding Eddy Current Loss
6.3 Circulating Current Loss
6.3.1 Transposition of Helical Winding
6.3.2 Transposition of Disk Winding
6.4 Circulating Current Loss in Winding Leads
6.5 Losses in Metallic Structure Parts
6.5.1 Tie-Plate Loss
6.5.2 Clamping Plate Loss
6.5.3 Tank Wall Loss
6.6 Shunts
6.6.1 Shield from Winding Leakage Flux
6.6.2 Shield from High Current Leads
References
Chapter 7: Cooling
7.1 Basic Knowledge
7.1.1 Aging of Insulation Paper
7.1.2 Oil Thermal Behavior
7.1.3 Temperature Limits
7.2 Temperature Rises of Oil
7.2.1 Natural Oil Flow, Natural Air Cooling
7.2.2 Natural Oil Flow, Forced Air Cooling
7.2.3 Forced Oil Flow Cooling
7.3 Loading Capacity
7.3.1 Ultimate Temperature Rises under Different Load
7.3.2 Instant Temperature Rises
7.3.3 Winding Hot Spot Rise
7.4 Cooling of Winding
7.4.1 Losses Generated in Winding Cable
7.4.2 Winding Cooling Condition
7.4.2.1 Winding Gradient with Natural Oil Flow
7.4.2.2 Winding Gradient with Directed Forced Oil Flow
References
Chapter 8: Short-Circuit Obligation
8.1 Short-Circuit Events
8.2 Radial and Axial Electromagnetic Forces
8.2.1 Radial Force
8.2.2 Axial Force
8.3 Failure Modes
8.3.1 Failure Modes Caused by Radial Forces
8.3.1.1 Tensile Stress
8.3.1.2 Buckling
8.3.1.3 Spiraling
8.3.2 Failure Modes Caused by Axial Forces
8.3.2.1 Tilting
8.3.2.2 Axial Bending
8.3.2.3 Telescoping
8.3.2.4 Collapse of Winding End Supports
8.4 Short-Circuit Forces in Special Transformers
8.5 Short-Circuit Current Calculation
8.6 Impedance Effects on Short-Circuit Force
8.6.1 Transformer Inherent Impedance
8.6.2 External Neutral Impedance in Zero Sequence Network
8.7 Short-Circuit Forces on Leads
8.8 Thermal Capability of Withstanding Short Circuits
8.9 Measures for Robust Mechanical Structure
8.10 Compressive Stress on Radial Spacer
8.11 Axial Bending Stress on Conductor
8.12 Tilting Force
8.13 Hoop Stress
References
Chapter 9: Sound Levels
9.1 No-Load Sound
9.1.1 Magneto-Motive Force
9.1.2 Magnetostriction
9.1.3 Transmission
9.1.4 Abatement Techniques
9.2 Load Sound
9.2.1 Sound from Winding
9.2.2 Sound from Tank Wall
9.2.3 Sound from Magnetic Shunts
9.2.4 Abatement Techniques
9.3 Fan Sound
9.4 Total Sound
9.5 Sound Level Measurements
9.5.1 Sound Pressure Level
9.5.2 Sound Intensity Level
9.5.3 Sound Power Level
References
Chapter 10: Autotransformers
10.1 Basic Relations
10.2 Insulation Consideration
10.3 Tap Winding Electrical Locations
10.4 Winding Physical Disposition
10.5 Use of Auxiliary Transformers
10.6 Zero Sequence Impedance and Delta-Connected Winding
10.6.1 Stabilizing Winding Rating
10.6.2 Loaded Tertiary Winding
References
Chapter 11: Testing
11.1 Preliminary Tests
11.1.1 Ratio and Polarity
11.1.2 Winding DC Resistance
11.1.3 Power Factor and Capacitance
11.1.4 Insulation Resistance
11.2 No-Load Losses and Excitation Current
11.3 Lightning Impulse and Switching Impulse
11.3.1 Lightning Impulse Waveshape and Sweep Times
11.3.2 Test Set-Up and Procedure
11.3.3 Failure Detection
11.3.4 Switching Impulse
11.3.5 Transient Analysis
11.4 Applied Voltage
11.5 Induced Voltage and Partial Discharge Measurement
11.5.1 Induced Voltage Test
11.5.2 Partial Discharge Measurement
11.6 Load Losses and Impedance
11.6.1 Load Losses and Positive Impedance
11.6.2 Zero Sequence Impedance
11.7 Temperature Rise
11.8 Audible Sound level
11.9 Others
11.9.1 Oil
11.9.2 Dissolved Gas Analysis (DGA) [ 12 ]
11.9.3 Short-Circuit
11.9.4 Diagnostic Tests
References
Index
A
B
C
D
E
F
G
H
I
K
L
M
N
O
P
R
S
T
U
V
W
Y
Z