THE ALTERNATOR 



123 



Ordinarily the flux distribution in a generator is not sinusoidal, 

 uilly with salient-pole machines, the wave being flat-topped, 

 U shown in Fig. 129. The electromotive force wave per con- 

 ductor has the same shape as the flux wave. If the coil is a full- 

 pitch coil, the electromotive forces in the two sides of each coil 

 will be 180 out of phase and of the same magnitude, as these 

 coil sides both lie at any instant in corresponding parts of oppo- 

 site poles. Therefore, the electromotive force wave of each coil 

 will have the same shape as the conductor electromotive force 

 wave. If but one slot per pole per phase is used, the resulting 

 electromotive force wave will have the same shape as the flux 

 which may be flat-topped as shown in Fig. 129. 



1 i 



129. Flux density in air-gap of salient-pole machine. 



ire i;jn (a) >hows a pha>e-belt, consist ing of four coils, of a 

 three-phase generator having 12 slots per pole, or four slots per 

 |H)le |M-r phase. The <hape of the elect romotive force wave for 

 each of the four full-pitch coils forming one phase of the winding 

 is the same as the shape of the llux wave. a> i< shown in Fig. \'.W 

 1 . 2, 3, and 4. As 12 slots represent L80 electrical epace- 



es, 180/12, or 1."). i- the interval in electrical space-d. 

 BO successive slots. Therefore, the four electromotive 

 !." electrical time apart, afl shown ii. 



'0. As the roil- are connected ii: the re-ultant elec- 



tromotive md by adding the ordinates of the four 



. M shoWIL The r.-siiltant u:i\e. instead of being a flat- 



