209 



CHAPTER X 



TIME CURVES 



WE shall now consider to what extent we can improve the 

 conditions of starting by a suitable choice of induction 

 factor, velocity ratio, and diameter of driving-wheel. 



The problem presents itself in two ways. 1. The 

 final speed is specified, and we have to design an equip- 

 ment that shall start up from rest and attain a certain 

 fraction of the final speed in the shortest time for a given 

 current from the line. 2. The final speed is not specified, 

 and we have to design an arrangement that shall start np 

 from rest and cover a given distance in a given time with 

 the least possible expenditure of energy. 



We may here restate the equation for the initial 

 acceleration : 



Mv c 



a=405-10~ 4 '" f.p.s. per second ...(93). 



d W 



In this equation c (l is the current available for accelera- 

 tion, and W the weight in tons per motor. If the maximum 

 current per motor is given, c a can be found by deducting 

 from it c f the current required to overcome the frictional 

 and other retarding forces. 



P 



