128 ELEMENTS OF ELECTRICAL ENGINEERING. 



action of the armature current, or currents, it is convenient to 

 think of the field windings as producing a certain constant flux 

 <l>, and of the armature current or currents as producing a cer- 

 tain additional flux <&'; for brevity we will call < the "field 

 flux " and <3>' the " armature flux," although of course both <I> 

 and <' pass through the armature. 



The field flux <I> may be thought of as producing a certain 

 " total induced electromotive force" in each armature winding; 

 a portion of this total induced electromotive force is lost in bal- 

 ancing the electromotive force induced by the armature flux <3>', 

 another portion is lost in overcoming the resistance of the arma- 

 ture winding, and the remainder appears as the terminal voltage 

 of the machine. Therefore, to calculate the voltage regulation 

 of an alternator it is necessary to consider the value and phase of 

 the electromotive force induced in the armature windings by the 

 flux <'. 



In the polyphase alternator with a balanced load the armature 

 flux <3>' is constant in value (for a given value of the armature 

 currents) and fixed in space, and electromotive forces are induced 

 in the moving armature conductors as they cut this flux. In the 

 single-phase alternator, on the other hand, the armature flux <' 

 is neither constant in value nor fixed in space, and the electro- 

 motive forces induced in the armature conductors by <$>' are 

 therefore very complicated in the single phase alternator. The 

 following discussion applies primarily to the polyphase alternator 

 with a balanced load, and the discussion is made to refer explic- 

 itly to a two-pole machine for the sake of simplicity. 



When a polyphase alternator delivers current to balanced non- 

 inductive receiving circuits, the axis of the armature-magnetizing- 

 action (axis of <!>') is at right angles to the axis of the field as 

 shown in Fig. 1130, in which n and s represent the magnetic 

 poles on the armature core due to the armature magnetizing 

 action. The fine lines in Fig. 113^ represent the actual distribu- 

 tion of the armature flux <!>', and the fine lines in Fig. njb 

 represent the distribution of <!>' on the assumption that the iron 



