44 



SYNCHRONOUS MOTORS 



and it indicates the corresponding value of the current, in magnitude 

 and in phase (starting from A\N). 



Knowledge of any two of the elements 2, 0, I, enables all the 

 others to be known, and also the lag <J> and the reactive and active 

 currents. 



When E\ is variable, this diagram becomes inconvenient, and 

 preference should be given to the diagram of the first kind. 



Curves of Constant Electric Power of the Motor when the 

 Generator has Constant Excitation. These curves, which indicate 



FIG. 27. 



the po-wer developed, by the motor for each position of A 2 , in the diagram, 

 are represented by Eq. (18), in polar co-ordinates referred to the 

 pole O (Fig. 27) (P 2 being supposed constant), and they now become 

 circles instead of straight lines. Let us take two rectangular axes 

 passing through O, the axis of x being directed along the line ON, 

 which makes with OA l the angle f. We can then write 



E 2 cos (f 0)=x, 



