138 



ELEMENTS OF ELECTRICAL ENGINEERING. 



of non-harmonic electromotive forces, and to do this would lead 

 to impractical mathematical complications. There are, however, 

 two fairly simple aspects of armature magnetizing action which, 

 although they are involved by implication in the discussion of 

 Arts. 63 and 64, should be brought out more distinctly. In 

 the first place the flux under the pole pieces is crowded to one 

 side in the direction of rotation, and in the second place the 

 armature currents oppose the field winding in forcing flux 

 through the armature when the receiving circuit is inductive and 

 they help the field winding in forcing flux through the armature 

 when the receiving circuit has negative reactance like a condenser. 



Discussion of demagnetizing action. Consider the conductors TT, Fig. 121, 

 which constitute the armature winding of a 2-pole single-phase alternator armature. 

 The electromotive force of the machine may be written 



Fig. 121. 

 <? = Esin/ (i) 



where ut is the angle shown in Fig. 121, and the current delivered by the alternator 

 may be expressed thus 



z = Isin(G>/ 6) (ii) 



where is the angle of lag of the current behind the electromotive force, which angle 

 of lag depends of course upon the character of the receiving circuit. 



Let T be the number of turns of wire on the armature (four turns are shown in 

 Fig. 121 ), then iT is the ampere-turns due to the winding at a given instant, and 

 this action is in the direction of the arrow iT, Fig. 121. The component of iT in 

 the direction of the line NS is equal to tTcosut, and this is a measure, in ampere- 



