110 



ALTERNATING CURRENTS 



E 2 is the emf. induced in the conductors comprising the other 

 side of the coil. E\ is equal to E 2 numerically as each is induced 

 by the same number of conductors cutting the same flux. Figure 

 113 (a) gives the relation of the induced emfs. EI and E z in the 

 two coil sides respectively, when a full-pitch coil is used. When 

 one side of a coil is under a north pole the other side is in a cor- 

 responding position under a south pole. Therefore the induced 

 emfs. are 180 out of phase, but the coil connection is such that 

 these emfs. are additive as shown in Fig. 113(a). 



FIG. 114. Showing winding and end connections of an alternator armature. 



When a % pitch is used, the coil spread is equal to % X 180 

 or 150 electrical space-degrees. The emfs. E\ and E z will there- 

 fore differ in phase by 150 electrical time-degrees, as shown by 

 the angle a, Fig. 113(6). The total emf. E, which is their vector 

 sum, is slightly less than when a full-pitch coil is used. 



It will be observed that with a fractional-pitch winding only 

 two of the slots of each phase under any pole contain coil sides 

 of the same phase. In the other slots the two coil sides are of 



