N >"N '/'/; .l 



79 



be noted that the use of arrows is not necessary, the subscripts 

 denoting the directions of the vectors. 



44. Generation of a Three-phase Current. As three-phase 

 is now the most common of the polyphase systems, it will be 



(a) 

 Fio. 76. Generation of 3-phase current. 



considered first. Figure 76 (a) shows three simple coils, 120 

 apart and fastened rigidly together. These coils are mounted 

 on an axis which can be rotated. The coils are shown rotating 

 in a counter-clockwise direction in a uniform magnetic field. 

 The current can be conducted from each of these three coils by 



Eoa 



EOC 



E oc 



Boa 



(4) 



77 I hree-phaae voltage waves ami \ t<> r diagram. 



mean- of dip-ring^ U shown in I M. Tlic terminals of 



coil a arc connected to rings n' . those of l> to rings 6', etc., making 



in all. 

 re 77 / -hows as Eoa the voltage in coil a. H oa is zero 





