THE ALTERNATING CURRENT GENERATOR 253 



will not be taken up here. They were discussed and 

 analyzed in Chapter V in detail. 



External Characteristic. The external characteristic of 

 an alternator shows the relation between the terminal 

 voltage and the load current, the field current being held 

 constant at that value which gives rated voltage when 

 rated full-load current is being carried. The shape of 

 this curve resembles that of a continuous current, separately- 

 excited generator but the shape of the curve for an alternator 

 depends somewhat on the power factor of its load. Fig. 



FIG. 155. External Characteristics of an Alternator on Different 



Loads. 



155 serves to illustrate this point; the rated full-load voltage 

 is OD and the external characteristic for a non-inductive 

 load is shown by the curve BGF, for an inductive load by 

 the curve CGE, and for load of leading power factor by 

 the curve QGP. It will be noticed that the drop in terminal 

 voltage, for a given increase in load current, is greater for 

 an inductive than for a non-inductive load. 



Short-circuit Current. The value the current reaches 

 when the resistance in the load circuit is reduced to zero 

 (called the short-circuit current) may be from three to ten 

 times the rated full-load current, depending upon the 



