130 



ELEMENTS OF ELECTRICAL ENGINEERING. 



armature flux <' is to a certain extent in the direction of the 

 field flux <!>' in Fig. H5,and(<:) The armature flux <' neither 

 helps nor opposes the field flux < in Fig. 113. This matter is 

 discussed in Art. 65. 



(d) The distribution of <3>' is far from being harmonic (like 

 Fig. 107) and therefore the electromotive forces induced by <J>' 

 in the moving armature conductors are far from being harmonic. 

 This is the most serious obstacle to the formulation of a simple 

 method for calculating the voltage regulation of an alternator, 



Fig. 115. Fig. 1153. 



Actual and assumed distribution of 4>', leading currents. 



and indeed a simple method must be based on the assumption 

 that <>' is harmonically distributed as shown in Figs. 113^, I \^b 

 and 115^, and this means that the field magnet is assumed not 

 to have polar projections but to surround the armature uniformly 

 on all sides as indicated. 



(e) It is evident from a careful consideration of Fig. 113^ that 

 the electromotive force induced in each armature winding by the 

 flux Q' is 90 behind the electromotive force induced by the field 

 flux <I>, so that the portion of the " total induced electromotive 

 force " (due to <l>) which is used to overcome the electromotive 

 force produced by <J>' is 90 ahead of the total induced electro- 

 motive force, or 90 ahead of the current in the given armature 

 winding, since, in Fig. 113, current and voltage are supposed to 

 be in phase with each other. A careful consideration of Figs, 

 and 1 1 %b will make it evident that in every case the portion 



