THE SYNCHRONOUS MOTOR. 169 



The equation to the excitation characteristics may be derived as follows Let 7, 

 Fig. 144, represent the current and E the resultant electromotive force ; the com- 

 ponents of E are RI and XL The electromotive force E is the vector sum of 

 A and B, as shown, and the component of B parallel to 7 is 7 >// /7. From the 

 right-angled triangles of the figure we have 



/ p//\ 2 



* = x2 +(l) W 



and 



By eliminating x from these equations we have the required relation between B 

 and /; /*', A, JR and X being given. The curves, Fig. 143, were calculated 

 graphically by means of the clock diagram, Fig. 125. 



