CH. XI DESIGN OF RAILWAY MOTOES 257 



Fig. 63 gives 675 x 10 4 foot-pounds, or about 3 per cent, 

 less than that estimated. These results are represented 

 below in tabular form. 



Total energy required 

 From test Calculated 



For acceleration . . 380x10* 350x10' 



For train resistance . . 174 x 10' 174 x 10' 



For torque losses . 98 x 10' 92 x 10' 



For C"R loss , 311 x 10 4 67 x 10' 



Total . . . 963 x 10* 683 x 10 4 



The difference in the energy expended is almost wholly 

 accounted for by the difference in the heat loss. The 

 existing motors require 40 per cent, more energy to 

 operate the train under the given conditions than those 

 whose induction curves have been calculated, and the 

 maximum current from the line is 28 per cent., and the 

 maximum current per motor 48 per cent, higher than 

 appears necessary. 



The force factor required to start is, by calculation, 

 257 x 72 or 18*5 kilodynes. If a hyperbola be drawn in 

 Fig. 61 having MC=lS'b kd., it will cut curve A at 

 c=257, and curve B at c=385 amperes. We thus see 

 why the existing motors have to take nearly 50 per cent, 

 more current to start than is necessary. 



We have supposed that the limit of weight fixes the 

 maximum induction factor at 72, for 257 amperes. The 

 motors in use have a maximum induction factor of 48. 

 For this value of M the best economy is obtained when 

 -y = 9'75, the induction curve is then straight. Suppose 

 that the consideration of clearance limits the val ue of v to 

 4'78, the induction curve must then be of the form in 

 Fig. 61, whose vertical ordinates bear to those of curve 



s 



