ALTERNATORS. 



237 



more accurate representation of the relations which are indicated 

 in Fig. 108. It is, however, not quite accurate, as the losses 

 in the armature when stationary and when rotating are not 

 identical. The method shown in Figs. 108 and 110 is the one 

 usually adopted as sufficiently accurate in practice, although 

 the more complete diagram just obtained is of considerable 

 interest theoretically. 



EXPERIMENT XXXVII. DETERMINATION OF EXCITATION 

 REQUIRED TO MAINTAIN CONSTANT VOLTAGE. 



DIAGRAM OF CONNECTIONS. 

 As FOR EXPERIMENT XXXVI. 

 (See Fig. 93, page 201.) 



Instructions. Make connections as in Experiment 

 XXXVI. Run the alternator at normal speed with the 

 load circuit open, and adjust the excitation to give the full 

 v voltage. Close the main circuit switch and gradually increase 

 the load to its full value. For each value of the load current 

 adjust the field regulator so that the machine gives its normal 

 voltage. Then read the load current and exciting current. 

 The speed of the machine must be kept constant throughout 

 the experiment. 



If the machine is required to work on inductive loads, 

 the readings should be repeated with inductive loads, having 

 the minimum power-factor on which the machine will be 

 required to work. The connections for determining the 

 power-factor of the load may be made in any of the ways 

 described in Experiments VIII., XIII., or XIV. 



The results of the test should be entered in tabular form 

 as indicated below, and a curve plotted with load current 

 horizontal and exciting current measured vertically. 



DETERMINATION OF EXCITATION FOR CONSTANT VOLTAGE. 



Alternator No Type 



Normal output, . .amps., . .volts, at . .revs, per minute. 



