There have been considerable advancements in various aspects of transformer engineering since the publication of the first edition in 2004. Improvements can be clearly seen in computational capabilities and monitoring/diagnostic techniques. Such new developments and encouraging feedback received on the first edition prompted the authors to embark on the task of writing the second edition. Three new chapters have been introduced in the second edition, Electromagnetic Fields in Transformers:
Theory and Computations, Transformer–System Interactions and Modeling, and Monitoring and Diagnostics. The chapter on Recent Trends in Transformer Technology has been completely revised to reflect the latest and emerging trends in the various facets of the transformer technology. Chapter 6 on short-circuit strength aspects has been updated to bring more clarity on failure mechanisms involving buckling, tilting, and spiraling phenomena. Various factors of safety are defined along with procedures for calculating them. An appendix explaining a step-by-step procedure for designing a transformer is added, which should be beneficial to engineers in the transformer industry and the student community.
A few improvements have been incorporated in the other chapters as well. Understanding the basics of electromagnetic fields is an essential prerequisite for doing advanced computations. Chapter 12 explains the field theory relevant to transformer engineering in a simple manner. Concepts from vector algebra and vector calculus are first explained followed by corresponding examples which help understand the behavior and distribution of fields inside transformers. Properties of insulating and magnetic materials used in transformers are explained from a fundamental electromagnetic perspective. Finite element method (FEM) is widely used for analysis and optimization of transformers.
While using commercial software, the knowledge of the FEM theory helps researchers and practicing engineers solve complex problems and easily interpret field solutions. The theory of FEM is explained through the solution of one-dimensional and two-dimensional problems that represent typical electrostatic and magnetostatic fields encountered in transformers. After explaining static, time-harmonic and transient formulations, advanced coupled field computations involving electromagnetic fields and external networks/other physical fields are elaborated. Brief theory/procedures for dealing with hysteresis and magnetization/magnetostrictive forces are also given at the end.
The second new chapter covers relevant theory and explanations required for understanding the effects of transformer–system interactions. The chapter starts with the modeling aspects of transformers essential for steady-state analysis of power systems. The usefulness of magnitude-regulating and phaseshifting transformers is demonstrated through examples. The section on harmonics briefly covers their sources and effects, followed by modeling strategies for analyzing them. Ferroresonance phenomena can be detrimental to transformers; the system conditions causing ferroresonant conditions are enumerated.
Adverse effects of arc-furnace loads and geomagnetic disturbances are explained later. Internal resonances due to system transients including very fast transient overvoltages are also described. Effects of switching operations involving vacuum circuit breakers on distribution transformers are highlighted. At the end, low-, mid-, and high-frequency models of transformers used for transient studies/investigative analysis are elaborated. A considerable amount of research and development efforts by the academic community, utility engineers, and transformer specialists have led to the availability of advanced diagnostic tools. After summarizing conventional tests on oil and windings.
The chapter Monitoring and Diagnostics comprehensively covers techniques for detecting partial discharges (PD), insulation degradation, and winding displacements/deformations. Methods based on electrical, acoustic, and ultra high frequency signals are practiced for PD diagnostics. Dielectric response methods used for the condition assessment of insulation are categorized into time domain and frequency domain methods. Background theory for understanding these two types of approaches is described along with diagnostic procedures.
Finally, frequency response analysis, used widely for detection of winding irregularities, is thoroughly explained. Thus, the focus of the second edition is also on diagnostic aspects and transformer–system interactions, and therefore, it is expected to help readers comprehend operational/maintenance issues and solutions in addition to the intricacies of transformer design and the applications of advanced numerical field computations.
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