SYNCHRONOUS ALTERNATORS. 



[Exp. 



respectively. A magnetomotive force MT is required for a terminal 

 voltage ET, corresponding values being taken from the saturation 

 curve; at no load no other magnetomotive force is required. Under 

 load, an additional magnetomotive force BA = Mz is required to 

 overcome the magnetizing effect of the armature. In terms of mag- 

 netomotive force, Mz is equal to the ampere-turns of the armature ; 



Cos0= 1 r 



FIG. 8. Magnetomotive force method. 



in terms of its corresponding electromotive force, it is a magneto- 

 motive force which will produce an electromotive force equal to the 

 armature impedance drop, Ez. The total magnetomotive force which 

 the field must provide is the vector sum, MQ. In this sense, Mo is the 

 resultant of MT and Mz (=BA), in the same way that Eo is the 

 resultant of ET and Ez. 



Interpreting these quantities further as magnetomotive forces: 

 Mo is the magnetomotive force produced by the field; Mz (=AB, in 

 the direction of armature current, /) is the magnetomotive force 

 produced by the armature; MT is the combined magnetomotive force 

 and produces the electromotive force ET. In this sense, MT is the 

 resultant of Mo and Mz ( =AB). On open circuit the field ampere- 



