294 



ELECTRICAL EQUIPMENT 



synchronous reactance is a fictitious quantity, expressing as it 

 does in a single quantity both the armature reaction and the 

 armature self-induction or reactance, it, nevertheless, represents 

 the equivalent of a true reactance and may be expressed in ohms 

 and taken just as any other reactance in determining the sus- 

 tained short-circuit current. It can also be combined in the 

 ordinary way with any external reactance. 



The per cent synchronous reactance is determined from the 



3 

 



F 6 F E 



Amperes Field 



FIG. 163A. Saturation and Synchronous Impedance Curves. 



saturation and synchronous impedance curves, Fig. 163 A, as 

 follows : 



In order to produce the normal current / a field current F e 

 is required, which would cause an open-circuit voltage e. A field 

 current Fs would produce on open circuit a normal voltage E if 

 there were no saturation. Hence, e is consumed in the syn- 

 chronous reactance with normal current flowing, and the per 

 cent synchronous reactance is 



This, combined with the per cent reactance and resistance of the 

 external circuit, will give the sustained short-circuit current I E , 



