70 NIK DIKECT-CUEEENT MOTOB CH. IV 



acting as a motor, is less than that of the line ; both, however, 

 are of the same sign, since both oppose the tension of the 

 line. A, however, sends as much current into the 

 line as B takes from the line, with the result that 

 no current passes either from or into the line, but a current 

 circulates in the two dynamos. 



When there is no current passing into or out of 

 the line, the current in each motor may be written 



= - ""'. Using the value of n in Equation 26, we 



c= 



may express the value of each current thus : 



7? >> ( c )1\ 



E 



Now the torque at this point is the difference between the 

 torques on the two motors, of which one assists and one 

 resists the motion, and may therefore be written 



t,= l-4,l c (M a -M h ) ............... (28). 



Substitute for c, and we have 



t= 1-41 E ( 

 L 



In our example this torque is 60 inch-pounds; this 

 will be the torque at which no current is passing from 

 the line, and when the current generated by A is the 

 same as that passing through B. 



The current may also be found by dividing the 

 difference between the two tensions, namely, 48*4, by the 

 sum of the two resistances, 2'29, giving us a current of 

 21 '2 amperes. This may be checked by comparison with 

 the diagram. 



