182 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



If the impedance is varied by changing only the reactance, X, 

 without changing the resistance, /?, the result is less clearly seen, 

 because the direction of the reference line OY then changes at the 

 same time as the scale of amperes. This point will be discussed later 

 under the general case. 



General Case. Reactive Current Values for a Given Voltage 

 Variation as a Function of the Load. In the most frequent case the 

 voltage is raised slightly when the load increases, to compensate for 

 the line-losses. 



In Fig. 6, let =the E.M.F. corresponding to zero-load, and let 

 E', E", E'", etc., represent the successive values which E must have 

 when the load corresponds to the active currents I w ', I w ", I 



'" 



>''*'**' - ~ " ~~7!f~^ 



etc. These current-values are to be measured off on a reference-line 

 BY, starting from the point B, giving the distances BD', BD", BD'", 

 etc., and the E.M.F.'s are to be measured off, along the horizontal 

 line BO starting from B toward the left, giving the distances BO, 

 BO', BO", BO'", etc. 



From each of the " O " points thus determined, as a center, let 

 a circular arc be drawn, with the same radius, equal to the external 

 E.M.F. E, which is a constant, assumed to be known. (In Fig. 6, 

 in order to make the case more general, it is assumed that the E.M.F.'s 

 may be unequal.) The respective points of intersection of the circular 

 arcs with the lines dC, D'C', D"C", D'"C'", drawn perpendicular to 

 the reference-line BY, give the conditions corresponding to the various 

 loads. 



