CH. VI 



EFFICIENCY 



137 



B, but when the torque is small A runs slower than B. Now 

 the load on a railway motor when once started is compara- 

 tively light, so that we may take it that motors designed 

 for this class of work will generally run slower in proportion 

 as the induction curve is higher. In other words, for equal 

 loads, wheel diameters, and velocity ratios, a motor must 



EFFICIENCY CURVES 

 25 HORSE POWER 

 RAILWAY MOTOR. 



have a low induction curve to run fast at light loads, and 

 a high induction curve to run slowly. Hence the low- 

 speed motor will have a higher efficiency than the high- 

 speed motor. We must, however, remember that the 

 terms ' high speed ' and ' low speed ' refer to the behaviour 

 of the motors at comparatively light loads ; the conditions 

 may be reversed with heavy loads. 



