CHAPTER VI 

 ALTERNATOR REGULATION AND OPERATION 



Alternator Regulation. It is shown in Vol. I, Chap. XI, that 

 the voltage of a shunt generator drops as load is applied. This 

 is due to three causes: the I a R a drop in the armature, arma- 

 ture reaction, and the drop in field current which results from 

 the decrease in terminal volts. As commercial alternators are 

 excited from a separate source, there is no decrease of field 

 current due to the drop in the alternator terminal voltage. How- 

 ever, both the I a R a drop in the alternator armature and armature 

 reaction ordinarily cause a drop of terminal voltage as load is 

 applied. Another factor which causes the alternator voltage to 

 drop with application of load is the reactance of the alternator 

 armature. This will be discussed later. 



The regulation of direct-current generators is inherently better 

 than the regulation of alternators. For example, shunt gen- 

 erators of commercial size regulate very closely, and it is usually 

 possible to so compound a shunt generator that its terminal 

 voltage is practically constant at all loads. In. the alternator, 

 the armature reactance drop, which is not present in the direct- 

 current generator, and the greater effect oi|ftrmature reaction, 

 result in poorer regulation. In addition, alternators cannot be 

 compounded readily. 



The regulation of the alternator depends not only on the mag- 

 nitude of the current, but on the power-factor as well. A 

 knowledge of the regulation of an alternator at various power- 

 factors is usually essential, since the arrtount by which the voltage 

 varies with the load has an important bearing on the operation 

 of the system as a whole. If the machine supplies incandescent 

 lamps, it must regulate very closely or else special regulators are 

 necessary on the lighting circuits. Moreover, alternators may 

 regulate well at unity power-factor, while at low power-factors 



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