3-B] 



PREDETERMINATION. 



77 



10 11 12 13 14 15 16 



FIELD AMPERES 



FIG. i. No-load saturation curve (i) and short-circuit current (2 and 3) 

 for different field excitations. Also full-load saturation curves (4, 5, and 6) 

 for zero power factor, current lagging. 



the short-circuit current is found for different values of field 

 current. The ammeter should have a range of about three times 

 full-load current. The speed should be normal, but special care 

 in maintaining constant speed is not necessary.* 



methods of computations used later, any drop in them is included in the 

 impedance drop of the armature. 



* ( lob). If facilities for varying the speed are provided, with constant 

 excitation vary the speed through wide range and note the practical 

 absence of change in the short-circuit current. Note, however, that the 

 open-circuit voltage is proportional to speed. How are these facts explained? 



