lo-B] 



SYNCHRONOUS MOTOR. 



317 



electrical input less armature RI 2 loss; part of this mechanical 

 power is used in friction and core loss, the remainder being avail- 

 able for useful work. 



=100 



(a) under-excited. (&) under-excited. (c) over-excited. 



FIG. i. Electromotive force diagrams for a synchronous motor; three 



typical cases. 



The projection Oe of / upon E is positive and is electrical 

 power supplied by the line. The projection Of of / upon the con- 

 tinuation of E' is negative, being mechanical power developed by 

 the motor. If Of, the projection of /, should fall upon E' itself 

 and not upon its continuation, the machine would be operating 

 as a generator and not as a motor. 



The diagrams shown in Fig. I are for the three typical cases 

 in which I lags behind, falls between and precedes E and E' 

 prolonged. 



3. In normal operation, with any change of load or other 



