3-B] 



PREDETERMINATION. 



79 



An excitation, OG = 2.6 amperes, is required to cause normal 

 full-load current (43.4 amp.) on short circuit. The corresponding 

 impedance voltage is 2 = 234, for on short circuit the whole 

 generated voltage is used in overcoming the internal or armature 

 impedance. 



12 Synchronous Impedance. On short circuit, the whole 

 generated voltage is equal to the internal impedance drop in the 

 armature. Impedance is equal to impedance drop divided by 

 current; hence, the synchronous impedance of the armature 

 i. e., its impedance when running at synchronous speed is equal 



FIG. 2. 



40 60 80 100 120 140 



AMPERES ON SHORT CIRCUIT: I. 



Impedance, reactance, and resistance drop. (All the curves in 

 Exps. 3-A and 3-B relate to the same machine.) 



to the generated voltage o, divided by the short-circuit current 

 /s. 



For any field current, the values of EQ and 7 S are obtained 

 from curves (i) and (2), Fig. I ; the corresponding synchronous 

 impedance, Z = -^-/s, should be plotted as a curve (not 

 shown). It will be found nearly constant for a wide range, 

 diminishing, however, for high values of field current. 



13. In Fig. 2, the curve marked impedance drop is plotted by 



