52 



IMPEDANCE. 



A winding concentrated into single slots, on the other hand, 

 if the air gap between armature and poles is small, will have 

 a high self-induction when opposite to a pole, and a very much 

 lower self-induction when situated between the poles. 



The self-induction will also be affected by the amount of the 

 armature current flowing, since the core will be more highly 

 saturated with heavy currents, and its permeability will be 

 lower. The main field will also affect the self-induction, 

 for the same reason. 



EXPERIMENT VII. DETERMINATION or THE IMPEDANCE 

 OF THE ARMATURE OF AN. ALTERNATOR WHILE STATIONARY. 



DIAGRAM IOF CONNECTIONS. 



Mi 



Fl<4. 23. 



M-i M z . Source of alternating current. 



m t m.,. Source of direct current. 



0. Alternator armature. 



F. Alternator field windings. 



A. Ammeter. 



V. Voltmeter. 



E. Variable resistance. 



S, 8. Switches. 



Instructions. Connect the alternator armature to a source 

 of alternating current which should give the same periodicity 

 and similar wave form to that of the alternator whose armature is 

 under test. Insert in the same circuit an ammeter, variable 

 resistance, and switch. Connect a voltmeter to the armature 

 terminals. 



Close the switch, and give the resistance R its maximum 

 value. Take readings on the ammeter and voltmeter for 

 a series of positions of the armature, which should be turned 

 through the same angle between each pair of readings, from a 

 position in which the armature coils are midway between the 



