CH. VI EFFICIENCY 145 



tension 500 volts, current 35 amperes, total resistance 

 in motor circuit 1'245 ohms, resistance of motor armature 

 and magnets 0'91 ohm, generator current 23'5 amperes. 



Using Equation 62, we find at once that the torque 

 losses in the two machines amount to 5,240 watts, or 2,620 

 watts each. The C*R loss in the motor is 1,112 watts. 

 The electrical input of the motor is 17,500, leaving 

 13,360 watts as useful mechanical output. We can now 

 construct a table of energy expended in the motor. 



Watts Per cent. 



C 2 E. loss .... 1,112 6-5 



Torque loss .... 2,620 15'3 



Mechanical output . . . 13,360 78-2 



17,092 100-0 



The total efficiency of the motor is thus 78 '2 per cent. 



The results of a complete test of a G.E. 800 railway 

 motor by this method are given in Fig. 34. The losses are 

 shown in percentages of the whole input for different 

 currents. The torque losses are divided into core loss, 

 including hysteresis and eddy currents, and friction of 

 gears, by a separate experiment, in which the motor arma- 

 ture was driven by a small motor on open circuit with 

 separately excited magnets. 



