A transformer is an electrical device that changes or converts the voltage level between two circuits. In the process, the current level is also converted. However, the power transferred between the circuits remains unchanged except for the generally small losses that occur in the process.

This transfer occurs only when alternating (a.c.) or transient electrical conditions are present. The operation of the transformer is based on the principle of induction discovered by Faraday in 1831. He discovered that when a changing magnetic flux connects a circuit, a voltage or electromotive force (emf) is induced in the circuit.

The voltage induced is proportional to the number of turns connected by the changing magnetic flux. Therefore, if two circuits are connected by a common magnetic flux and the number of turns connected in the two circuits is different, the induced voltage will also be different. This situation is illustrated in Figure1.1, which shows the iron core carrying the common magnetic flux. Since the coupling windings N1and N2 are different, the induced voltages V1and V2 are different.

**About the Book**

After these books were written, transformer design changed dramatically. Newer and better materials became available for core and winding construction. Powerful computers have made it possible to create more detailed models of the electrical, mechanical, and thermal behavior of transformers than ever before. While many of these modern approaches to design and construction are scattered throughout the literature, there is a need to make this information available in a single source, both as a reference for designers and power engineers and as a starting point for students and novices.

It is hoped that this book will serve both purposes. As a text for beginners, it emphasizes the physical fundamentals of transformer operation. It also discusses the physical effects resulting from various fault conditions and their impact on design. Physical principles and mathematical techniques are presented in a reasonably self-contained manner, although there are references to additional material. For professionals such as power and transformer design engineers, detailed models are presented that focus on various aspects of transformers in normal or abnormal conditions.

Cost minimization techniques are also presented as a starting point for most designs. Although this book deals primarily with power transformers, many of the physical principles and mathematical modeling techniques described are equally applicable to other types of transformers.

The book attempts to be as general as possible so that designers and users of other transformers will have little difficulty in applying many of the book’s results to their designs. The emphasis on the fundamentals should facilitate this process and facilitate the development of new, more powerful design tools in the future.

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