[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

Contents
1
Theory and Principles
Chapter 1 Theory and Principles Dennis Allan and Harold Moore
Chapter 2 Equipment Types
2.1 Power Transformers H. Jin Sim and Scott H. Digby
2.2 Distribution Transformers Dudley L. Galloway and Dan Mulkey
2.3 Phase-Shifting Transformers Gustav Preininger
2.4 Rectifier Transformers Sheldon P. Kennedy
2.5 Dry-Type Transformers Paulette A. Payne
2.6 Instrument Transformers Randy Mullikin
2.7 Step-Voltage Regulators Craig A. Colopy
2.8 Constant-Voltage Transformers Arindam Maitra, Anish Gaikwad,
Ralph Ferraro, Douglas Dorr, and Arshad Mansoor
2.9 Reactors Richard F. Dudley, Michael Sharp, Antonio Castanheira,
and Behdad Biglar
Chapter 3 Ancillary Topics
3.1 Insulating Media Leo J. Savio and Ted Haupert
3.2 Electrical Bushings Loren B. Wagenaar
3.3 Load Tap Changers Dieter Dohnal
3.4 Loading and Thermal Performance Robert F. Tillman, Jr.
3.5 Transformer Connections Dan D. Perco
3.6 Transformer Testing Shirish P. Mehta and William R. Henning
3.7 Load-Tap-Change Control and Transformer Paralleling
James H. Harlow
3.8 Power Transformer Protection Armando Guzmán, Hector J. Altuve,
and Gabriel Benmouyal
3.9 Causes and Effects of Transformer Sound Levels Jeewan Puri
3.10 Transient-Voltage Response Robert C. Degeneff
3.11 Transformer Installation and Maintenance Alan Oswalt
3.12 Problem and Failure Investigation Wallace Binder
and Harold Moore
3.13 On-Line Monitoring of Liquid-Immersed Transformers Andre Lux
3.14 U.S. Power Transformer Equipment Standards and Processes
Philip J. Hopkinson
Dennis Allan
MerlinDesign
Harold Moore
H. Moore and Associates
1.1 Air Core Transformer
1.2 Iron or Steel Core Transformer
1.3 Equivalent Circuit of an Iron-Core Transformer
1.4 The Practical Transformer
Magnetic Circuit • Leakage Reactance • Load Losses • Short-
Circuit Forces • Thermal Considerations • Voltage
Considerations
References
Transformers are devices that transfer energy from one circuit to another by means of a common magnetic
field. In all cases except autotransformers, there is no direct electrical connection from one circuit to the
other.
When an alternating current flows in a conductor, a magnetic field exists around the conductor,
as illustrated in Figure 1.1. If another conductor is placed in the field created by the first conductor such
that the flux lines link the second conductor, as shown in Figure 1.2, then a voltage is induced into the
second conductor. The use of a magnetic field from one coil to induce a voltage into a second coil is the
principle on which transformer theory and application is based.
1.1 Air Core Transformer
Some small transformers for low-power applications are constructed with air between the two coils. Such
transformers are inefficient because the percentage of the flux from the first coil that links the second
coil is small. The voltage induced in the second coil is determined as follows.
E = N d/dt 10 8 (1.1)
where N is the number of turns in the coil, d/dt is the time rate of change of flux linking the coil, and
is the flux in lines.
At a time when the applied voltage to the coil is E and the flux linking the coils is lines, the
instantaneous voltage of the supply is:
The maximum value of is given by:
e = 2 E cos t = N d/dt 10 8 (1.2)
d/dt = (2 cos t 10 8 )/N (1.3)
= (2 E 10 8 )/(2 f N) (1.4)
Using the MKS (metric) system, where is the flux in webers,
© 2004 by CRC Press LLC
© 2004 by CRC Press LLC