CH. IX CONTROL 205 



find to what extent the motion of the car is affected by the 

 amount of current taken at this point. 



Let us take the case of a car equipped with two G. E. 

 800 motors, whose induction and torque curves are 

 given by the diagrams in Fig. 21. Suppose that the car 

 weighs 10 tons, that it runs on 33-inch wheels, with a 

 velocity ratio of 4'78. Let the tension of the line be 500 

 volts, and the resistance per motor 1 '245 ohms. Suppose, 

 also, that the frictional resistances are 325 inch-pounds of 

 torque per motor, so that the car would take 24 amperes 

 when running at full speed with the motors in parallel. 

 If the maximum current per motor is 50 amperes, we see 

 from the torque curve in Fig. 21 that the corresponding 

 torque would be 3,700 inch-pounds. Deducting the 

 frictional torque, we have 3,375 inch-pounds available 

 for acceleration, from which we find the acceleration 

 to be 2 - 8 f.p.s. per second. The results are plotted in 

 Fig. 53. 



The motors will be in series up to the point a ; after 

 this, three cases have been taken ; the first assumes 50 

 amperes per motor when in parallel, the second 35, and 

 the third 25 amperes. The corresponding current curves 

 give the total current from the line in the three cases. 

 The acceleration when in parallel ceases to be constant 

 in each case at the point /. The areas of the acceleration 

 curves have been integrated with a planimeter, and the 

 distances travelled plotted in three curves, of which the 

 vertical ordinates represent feet. From these curves 

 we can obtain the time required to cover any distance, 

 and also the corresponding energy for each of the three 

 maximum currents, 100, 70, and 50 amperes, lettered in 

 the table A, B, and C respectively. If we take distances 



