VOLTAGE REGULATION OF THE ALTERNATOR. 135 



is equal to 1150 volts. Therefore the "total induced electromo- 

 tive force," that is the electromotive force which is induced by the 

 "fieldflux" <, is equal to i/(2O23.3) 2 -f (i I5o) 2 or 2327 volts, 

 which is of course the value to which the terminal voltage would 

 rise if the current output were reduced to zero. Therefore 

 the regulation of the machine for unity power factor is 

 (2327 2000)/2000= 0.163 or 16.3 per cent. 



(fr) For a power factor equal to 0.85. Choose the current 

 vector 01, Fig. 120, as the reference axis, lay off the full-load 



1150 volts = XI 



Fig. 120. 



terminal voltage of 2000 volts in its proper phase relation to 

 7(cos0 = o.85), and lay off RI (23.3 volts) and XI (1150 volts) 

 as shown ; the line OE will then represent the total induced 

 electromotive force, and it is, of course, the value to which the 

 terminal voltage of the machine would rise if the current output 

 were reduced to zero. The value of the zero-load voltage (corre- 

 responding to 2000 volts terminal voltage at full load and 0.85 

 power factor) is thus found to be 2800 volts, so that the regu- 

 lation is (2800 2000) /2OOO = 0.40 or 40 per cent. 



The magnetomotive force method.* If the magnetizing action 

 of the field winding and of the armature were not complicated by 



* This is called the American Institute Method, inasmuch as it is recommended by 

 the Institute Committee on Standardization. See page 255 of volume 16 of the 

 Transactions. A new report is now (1907) in preparation. 



