Chapter 1. Introduction to Transformers

Chapter 1. Introduction to Transformers - 1. INTRODUCTION...

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1 1. INTRODUCTION TO TRANSFORMERS Summary Beginning with the principle of induction discovered by Faraday, the transformer slowly evolved to fill a need in electrical power systems. The development of 3 phase a.c. power has led to a great variety of transformer types, We discuss some of these types and their use in power systems. We also discuss and contrast some of the main construction methods. The principle components of a transformer are highlighted with special emphasis on core-form power transformers. Some of the basic considerations which determine the design of these components are presented. A look at some newer technologies is given which could impact the future development of transformers. 1.1 HISTORICAL BACKGROUND Transformers are electrical devices which change or transform voltage levels between two circuits. In the process, current values are also transformed. However, the power transferred between the circuits is unchanged, except for a typically small loss which occurs in the process. This transfer only occurs when alternating current (a.c.) or transient electrical conditions are present. Transformer operation is based on the principle of induction discovered by Faraday in 1831. He found that when a changing magnetic flux links a circuit, a voltage or electromotive force (emf) is induced in the circuit. The induced voltage is proportional to the number of turns linked by the changing flux. Thus when two circuits are linked by a common flux and there are different linked turns in the two circuits, there will be different voltages induced. This situation is shown in Fig. 1.1 where an iron core is shown carrying the common flux. The induced voltages V 1 and V 2 will differ since the linked turns N 1 and N 2 differ. © 2002 by CRC Press
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INTRODUCTION 2 Devices based on Faraday’s discovery, such as inductors, were little more than laboratory curiosities until the advent of a.c. electrical systems for power distribution which began towards the end of the nineteenth century. Actually the development of a.c. power systems and transformers occurred almost simultaneously since they are closely linked. The invention of the first practical transformer is attributed to the Hungarian engineers Karoly Zipernowsky, Otto Blathy, and Miksa Deri in 1885 [Jes97]. They worked for the Hungarian Ganz factory. Their device had a closed toroidal core made of iron wire. The primary voltage was a few kilo volts and the secondary about 100 volts. It was first used to supply electric lighting. Modern transformers differ considerably from these early models but the operating principle is still the same. In addition to transformers used in power systems which range in size from small units which are attached to the tops of telephone poles to units as large as a small house and weighing hundreds of tons, there are a myriad of transformers used in the electronics industry. These latter range in size from units weighing a few pounds and used to convert electrical outlet voltage to lower values
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Chapter 1. Introduction to Transformers - 1. INTRODUCTION...

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