372 



ELECTRICAL MACHINERY 



The length of the vector AC can be found in terms of 

 the vector AB in the following manner. In Fig. 244 the 

 construction of Fig. 243 is duplicated to some extent, but 

 instead of the vector polygon we have the circumscribing 

 circle. The angle a, Fig. 244, is equal to 120 for the 



FIG. 244. Diagram for derivation of Formula Giving the Ratio of a 

 Synchronous Converter. 



three-phase taps AC, hence COD ( = /2) is equal to 60. 

 Therefore, we have 



= 2AD = 2(OA sin a/2) =AB sin a/2 = AB sin 60. 



But AB = the continuous voltage -:- A/2. 



Hence 

 AC (three-phase voltage) 



= the continuous voltage o 



\/2 

 = the continuous-voltage X. 612. 



