ALTERNATOR REGULATION AND OPERATION 



159 



in the magnetomotive force method, whereas they both produce 

 errors in the same direction in the synchronous impedance 

 method. Therefore, the mmf. method usually gives results 

 closer to the actual regulation than the synchronous impedance 

 method does. The actual value of the alternator regulation 

 probably lies between the two values just determined. Were 

 t u ration curve of the machine a straight line, both methods 

 would give nearly the same result. 



71. The A. I. E. E. Method. This method, recommended by 

 tin- American Institute of Electrical Engineers, has an advantage 

 over the other two methods, in that the synchronous impedance is 



Field Current c 



(a) Vector diagram for a load of very (6) Curves used for A. I. E. E. 



low power-factor. method. 



Fio. 159. The A. I. E. E. method. 



ired when the machine is operating at full voltage, and, 

 at normal saturation. This is accomplished by apply- 

 ing a Wd of very low power-factor, usually an under-excited syn- 

 chronous motor. The vector diagram for t his condition is shown 

 in I i'_r. 1")9 (a). V is the terminal voltage under those conditions, 

 /,' the open-circuit voltage, and IX, the synchronous reactance 

 drop at rated cm-rent. As the //,' drop is small and is nearly in 

 (piadrature with I", the open-circuit volt a go is substantially equal 

 to th.- numerical sum of the terminal voltage V and IX 9 . Thcrc- 

 illv, 



i\, i: - v 



E V 



\ 



A. 



