CH. V SERIES-WOUND MOTORS 99 



motor is starting or when a sudden load is put on, but the 

 motor must be properly designed in order to get the full 

 benefit of this arrangement. For if the normal running 

 point is high up on the induction curve, the induction factor 

 will be only slightly increased when the heavy load is put 

 on, and the current will be nearly in proportion to thetorque. 

 If, however, the points of normal and maximum load are 

 so situated on the curve that the corresponding values of 

 the induction factor are very different, then the current 

 taken at the maximum load may be much smaller than it 

 would be if the induction factor remained constant. 



Take as an illustration the G. E. 800 railway 

 motor made by the General Electric Company, and 

 designed to exert a horizontal effort of 800 pounds on 33- 

 inch wheels, when running at 9 '4 miles an hour. 

 The torque and speed curves of this motor, as obtained 

 from actual test, are given in Fig. 21. The circles 

 indicate observations. The resistance of the magnets 

 and armature in series, when hot, was l - 245 ohms, 

 being 0'805 for the magnets, and '44 for the armature. 

 The induction curve is obtained from the speed curve by 



"Tjl __ 7~> 



using the equation M= , This curve gives the in- 



% 



duction factor for any current under normal running con 

 ditions, and takes into account all effects due to armature, 

 reaction and other losses tending to reduce the induction 

 factor. 



The curve of total torque is obtained from the equation 

 = 141cM. This curve gives the total torque for any 

 current available for all purposes, including internal torque 

 losses due to hysteresis, gear friction, &c. ; it is greater 

 than the torque actually observed by the amount of 



H 2 



