SYNCHRONOUS MOTORS. 293 



by the full lines, the lettering corresponding to the figures 

 already given. In this case, the current lags behind the 

 applied voltage by the angle <x . By increasing the excitation 

 of the motor the motor voltage increases from E., to the 

 dotted value E., 1 , when the angle between current and 

 applied voltage becomes again the same as before. The 

 power supplied to the motor, the resultant voltage and the 

 current in the circuit are the same as in the first case. The 

 two conditions shown in the diagram by the full and the 

 dotted lines respectively would correspond to points at the 

 same height, but on different limbs of one of the curves in 

 Fig. 130. 



In order to illustrate the statement previously made, that 

 the distance apart between the limbs of the curves depends 

 upon the self-induction of the armature, the conditions 

 shown in Fig. 139, have been repeated in Fig. 140, with 

 the only difference that the armature self-induction in the 

 latter case is assumed to be smaller, and consequently the 

 angle of lag </> is smaller. It is at once obvious from an 

 inspection of the figures that the difference in length between 

 E. 2 and E 2 l is much less in the second figure, showing 

 that the difference in excitation for the two points giving 

 equal armature currents is much less in the second case than 

 in the first. In other words, the distance between the limbs 

 of the curve will be less the lower is the armature self- 

 induction. With a non-inductive armature the two limbs 

 would coincide, and the curve showing the relation between 

 excitation and armature current would become a straight 

 line, since the value of E. 2 would be the same whether the 

 current was earlier or later than E t in phase. 



It would prove a most useful exercise for the student to 

 construct several of the " Vee " curves, like those in Fig. 130, 

 from diagrams representing several assumed conditions as to 

 armature self-induction, &c. 



