

TAILED STUDY OF OPERATION WITH NORMAL LOAD 67 



mve to be all the lower the greater the value of /. If it is satisfactory 

 for example, to take /=, the increase of 7 will be almost negligible. 

 The graphical determination of / and E 2 , is obtained readily from 

 the fundamental diagram (Fig. 

 26) by constructing (Fig. 36), 

 according to the scale of volts, 

 the lines Zi in the direction A iN, 

 and Zj in the perpendicular di- 

 rection, and by drawing A\A 2 

 and OA 2 . If / and / are known 

 beforehand, E 2 and i can be 



deduced inversely. [All that is 



necessary is to project the broken line A 2 A\O on the line A\N and 



on the line perpendicular thereto; the two projections are 



Ei cos;- 

 sin 



and 



The sum of their squares gives E 2 2 , from which we deduce the formula, 

 (26)]. 



This diagram also gives the algebraical expression of E 2 . thus 



V///\2 2 

 I+ (7r) +-(/ sin f-j cos 7-). 

 YM/ &1 



(26) 



From this, given the excitation-curve of the motor, the necessary 

 ampere-turns can be deduced. 



In order that the compensation may be really advantageous for 

 the line, it is necessary that the resultant currents should be notably 

 weaker than before, i.e., we must have 



In practice, compensation of this kind is especially advisable when 

 synchronous apparatus (motors or converters) is already connected on 

 the distribution- system, and serves for other purposes; because, all that 

 is then necessary is to increase slightly the excitation-current of each of 

 them, which involves no special expenditure of energy other than a 

 slight supplementary loss in the fields and in the armature. The 

 companies which operate alternating-current systems should therefore 



