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f *-i- 



A COURSK IN 



ELK( TRK AL ENGINEERING 



VOLUME II 

 ALTERNATING CURRENTS 



CHAPTER I 

 ALTERNATING CURRENT AND VOLTAGE 



1. General Field of Use of Alternating Current. Over 90 



nt. of the electrical energy generated at the present time is 

 generated as alternat ing current. This is not due primarily to 

 any superioi ity of alternating over direct current in its applica- 

 bility to industrial and domestic uses. In fact, there are many 

 where direct current is absolutely necessary for indus- 

 trial purposes, but even in those cases the energy is often gener- 

 ated as alternating current. 



Some of t he reasons for generating energy as alt ernat ing current 



Alternating-current can be generated at comparatively high 

 ^es and these voltages can be readily raised and lowered 

 by mean.- of static transformers. This permits the economical 

 oission of alternating current over considerable distan. 



hi sih transmission voltages. These high voltages can 



le reduc.-d HIicienily at the receiving end of the transmission line. 



Voltagefl cannot b. : and lowered on an 



industrial scale without the uai ' ing commutators, and the 



perim ge per commutator is low. Then-fore, the 



direct-current circuits cannot be char .>micall\-. 



ing-current ucnerators can be built in larue units 

 runnr iirbine drive, and tin 



.'h alternator^ is low. The largo! >inule unit 

 1 



