124 



ALTERNATING CURRENTS 



topped wave like that of the individual coil, is well-rounded and 

 is very nearly a sine wave. This is the reason that a distributed 

 winding gives a better wave shape than a concentrated winding. 

 With a non-salient pole rotor, having a distributed winding, 

 Fig. 126, the field coils lie in the rotor slots in the manner indi- 



Ooil 1 



(6) 



FIG. 130. Resultant electromotive force wave in a 4-coil phase belt. 



cated in Fig. 131 (a). The magnetomotive force of each coil is 

 a rectangle, if the currents in the conductors be considered as 

 concentrated at their centers. This is shown in Fig. 131 (6), 

 which gives the mmf . of a single coil. The height of the rectangle 

 is equal to the mmf. of this coil, which can be expressed in am- 

 pere-turns, gilberts, or in any convenient unit. The base of each 



