234 THK IIII;KIT-<TIM;KNT MOTOR CH. xi 



the actual distance covered will be very nearly equal to 

 that calculated. 



These results have been plotted in Fig. 5G. The accele- 

 ration is constant from p to a, and the speed is practically 

 constant from a to /;. The area oabc represents 500 feet. 

 The car accelerates for two-thirds of the whole time, 

 namely 20 seconds, during which time the distance 

 covered is 250 feet ; the remaining 250 feet is covered in 

 10 seconds. The error due to the assumption that the 

 acceleration is constant up to full speed does not amount 

 to one foot of distance. 



This is the form of the acceleration curve if the 

 induction factor remains constant and equal to 35'5 

 throughout the whole period ; the given distance is 

 then covered in the given time with the least possible 

 accelerating current. Any other values of v or d would 

 require a longer time or a greater accelerating current to 

 cover the distance in the given time. The current curve 

 for one motor has been plotted in the same figure. The 

 area of the curve pdefc represents the energy expended in 

 covering the given distance. 



We shall now consider the influence of series winding 

 on the acceleration and current curves. In Fig. 57 

 let values of the current be measured horizontally 

 and values of 3[ vertically. Take alt, equal to 15 

 amperes, and set up lib equal to 35'5 on the vertical 

 scale. Then b is a point on the induction curve of the 

 motor. Produce ah to cut a vertical line drawn through g 

 in the point c, where acj is 45 amperes. Then gc, equal to 

 106 of -V, is the greatest possible induction factor the 

 motor can have for 45 amperes. For the induction curve 

 of a series-wound motor cannot be convex to the current 



