RECTIFYING DEVICES 



371 



voltage of a single-phase converter is equal to the continuous 

 voltageXf=. This ratio is independent of the size of the 



machine, the speed, the number of poles, or anything else; 

 for a single-phase converter this is a fixed quantity, it can- 

 not be varied. 



FIG. 243. The e.m.fs. of the Coils of the Closed Circuit Winding 

 Must Form a Closed Polygon. 



Voltage for Three-phase Taps. Now, suppose the winding 

 snown in Fig. 241 is to be tapped for a three-phase a-c. sup- 

 ply; the taps would be at A, C, and D, Fig. 243. Between 

 each of these taps, there are four coils and the vectors 

 giving the different e.m.fs. are shown in Fig. 243 by AC, 

 CD, and DA. These vectors are equal to each other 

 and are 120 apart, as they should be for a three-phase 

 winding. 



