CHAPTER VII 

 THE TRANSFORMER 



The static transformer is a device for transferring electrical 

 energy from one alternating-current circuit to another without a 

 change in frequency. This transference is usually, but not 

 always, accompanied by a change of voltage. A transformer 

 may receive energy at one voltage and deliver it at a higher 

 voltage, in which case it is called a step-up transformer. A trans- 

 former may receive energy at one voltage and deliver it at a 

 lower voltage, in which case it is called a step-down transformer. 

 A transformer may receive energy at one voltage and deliver it 

 at the same voltage, in which case it is called a one-to-one 

 transformer. 



A static transformer has no rotating parts, and therefore it 

 requires little attention and its maintenance is low. The cost 

 per kilowatt of transformers is low as compared with other 

 apparatus and the efficiency is much higher. As there are no 

 teeth, slots, or rotating parts, and the windings can be immersed 

 in oil, it is not difficult to insulate transformers for very high 

 voltages. 



Because of these many desirable characteristics, the trans- 

 former is a very useful piece of apparatus, and as it can transform 

 from low to high voltage, and from high to low voltage, econom- 

 ically, it is largely responsible for the extensive use of alternating 

 current. 



76. The Transformer Principle. The transformer is based 

 on the principle that energy may be efficiently transferred by 

 induction from one set of coils to another set by means of 

 a varying magnetic flux, provided both sets of coils are on a 

 common magnetic circuit. 



Electromotive forces are induced by a change in flux linkages. 

 In the generator, the flux is substantially constant in magnitude. 

 The amount of flux linking the armature coils is changed by the 

 relative mechanical motion of flux and coils. In the transformer, 



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