180 



ELECTRICAL MACHINERY 



being wasted as heat in the starting resistance and so the 

 equipment is operating at a fair efficiency. The motors 

 are next thrown into parallel connection and some of the 

 resistance is again put in series with them. While the 

 motors are being changed from series to parallel connection, 

 the controller handle is moving through the " transition 

 points " and the controller handle is so designed that it 



Points 



I a 



1 I 



Resistance Motor No. 1 



Motor No. 2 



FIG. 108. Connections for Series-parallel Control of Railway Motors. 



will not remain on one of these points unless held there. 

 When the transition points have been passed through 

 and the motors are connected in parallel, the resistance 

 is again cut out in two " resistance points " and, finally, 

 the two motors are each operating on the full line voltage. 

 This is the second " running point." The various connec- 

 tions used in the system of control are well shown in Fig. 108. 

 Disadvantage of the Above Scheme. The disadvantage 

 in this scheme of control is that while going through the 



