io8 



ELEMENTS OF ELECTRICAL ENGINEERING. 



55, Electromotive force and current relations in the Y-scheme of 

 connections. 



(i) Referring to the generator, (a) Electromotive force rela- 

 tions. Let E v E 2 and E^ be the electromotive forces from main 

 I to main 2, from main 2 to main 3, and from main 3 to main i, 

 respectively, see Fig. 98. From Fig. 98 it is evident that a 

 positive electromotive force in winding A produces an electro- 

 motive force from main i to main 2 (positive), and that a positive 

 electromotive force in winding B produces an electromotive force 

 from main 2 to main I (negative). Therefore E l is equal to 

 A B (vector difference). Similarly, E 2 is equal to B C, 



Fig. 103. 



and E B is equal to C ' A. These relations are shown in Fig. 

 103, and from this figure we see at once that the value of the 

 electromotive force between any pair of mains is j/j times the 

 electromotive force in each Y-connected armature winding. 



(b) Current relations. In the Y-scheme of connection the 

 currents in the mains are identical with the currents in the respec- 

 tive windings. This is evident from Fig. 98. 



