CH. IV SHUNT-WOUND MOTOES 89 



If the torque load on the combined shaft is constant, 

 the current from the line will be inversely proportional to 

 the combined induction factor. Thus, in the case of 

 the motors having induction factors of 6 and 4, if the 

 current with M=4< is 100 amperes, the other currents 

 would be 80, 67, and 40 amperes. 



Hitherto we have supposed that the two motors were 

 coupled mechanically so that they were obliged to rotate 

 at the same speed. We shall now consider the case when 

 the motors are at liberty to rotate at different 

 speeds. 



To fix ideas, suppose that the two motor shafts are in 

 line, each fitted with a bevel wheel, facing the other, and 

 gearing into an intermediate wheel, the axis of which is 

 at right angles to the line of the motor shafts and free to 

 rotate in a plane at right angles to that line. Such a 

 mechanism, for instance, as is used in the Aron current 

 meter. 



The two motors are now free to rotate at different 

 speeds, and the angular speed of the intermediate shaft 

 depends on the mean of the two speeds if they rotate in the 

 same direction, and on the difference if they rotate in 

 opposite directions, and is measured by the number of 

 revolutions per second that it makes in the plane at right 

 angles to the main line of shafting, and not by the revolu- 

 tions around its own axis. If the motors rotate at equal 

 speeds in the same direction the intermediate shaft will 

 rotate at the same speed as the two motor shafts. If the 

 motors rotate at equal speeds in opposite directions, the 

 intermediate shaft will not move. 



The action of the motors may be determined graphically. 

 In Fig. 19 take ay to represent the maximum current 



