SYNCHRONOUS MACHINERY 



231 



it leads e\ in phase by 45 degrees, its maximum value is V2 E Q and 



"v/9 J? 



its effective value is EAD = 7=- = E = A/2 E. This value can 



V2; 



also be obtained by subtracting the two vectors as shown in 

 Fig. 197. 



Electrica 



FIG. 196. E.m.f. waves of a two-phase alternator. 





 FIG. 197. 



The middle points m\ and m^ of the two windings are some- 

 times connected together and a fifth terminal F used as shown 

 in Fig. 198. The common terminal F is called the neutral point 

 of the winding and may be connected to earth. The e.m.f. from 

 each of the other terminals to F is the same. 



E 



EAF = EBF = ECF = EDF = -~ ' 



FIG. 198. 



The four e.m.f .'s E A c, ECB, E B D and EDA are equal, since each is the 



Tjl 



vector difference of two e.m.f. 's of effective value -^ at right angles 



2t 



to one another, and these four e.m.f.'s are also at right angles to 

 one another and form a four-phase or quarter-phase system. 



