248 



ALTERNATORS. 



EXPERIMENT XXXIX. DETERMINATION OF RELATION 

 BETWEEN SPEED AND VOLTAGE OF AN ALTERNATOR. 



(1) At no load, 



(2) At full load, 



(3) On short-circuit. 



DIAGRAM OF CONNECTIONS. 





 F 

 R, 



V 



S 



FIG. 118. 



Source of continuous current. 

 Alternator armature. 

 Alternator field windings. 

 Non-inductive resistance in load circuit. 

 Resistance for regulating exciting current. 

 Ammeter for measuring load current. 

 Ammeter for measuring excitation. 

 Voltmeter for measuring armature voltage. 

 Switch for breaking main circuit. 



Instructions. Connect the field windings to a source of 

 direct current through a regulating resistance and ammeter. 



Connect the armature terminals to an ammeter, variable 

 load resistance, and switch in series. Connect a voltmeter 

 to the armature. 



Maintain the excitation constant throughout each set of 

 readings. 



(1) Take a series of observations of speed and voltage 

 with the switch in the main circuit open, beginning with the 

 lowest speed for which the voltmeter will give readings and 

 increasing up to full speed or slightly higher. 



(2) Take a similar series of readings with the switch in 

 the load circuit closed, and the resistance of this circuit so 

 regulated that the current is the same (as nearly as possible) 

 for each reading. 



(3) Repeat the readings at similar speeds with the arma- 

 ture terminals short-circuited through the ammeter and 



