CH. V1TI THE FORCE FACTOR 171 



28'6 x 10 6 lines per pole. The induction factor is 412. 

 The force factor for 1,500 amperes is 412x1,500 = 618 

 kilodynes, and the power at 80 r.p.m. is 825 kilowatts. 

 The dynamo is a Westinghouse ten-pole railway generator. 



Example 44. The motors in use on the Liverpool 

 Overhead Railway and on the City and South London 

 Railway are rated at about the same horse-power, but on 

 actual test one of the Liverpool motors can exert a pull 

 equal to that of two of the South London motors, when 

 equal current is passing in all three. 



The motors on the Liverpool railway are designed to 

 run in parallel, two motors to each car, while those on the 

 South London Railway are designed to run permanently 

 in series, two motors also to each car. If the tension of 

 the line, the speed, the diameter of the driving wheel, and 

 the horse-power were the same in the two cases, the 

 induction factor of the Liverpool motors would have to be 

 twice that of the South London motors. Suppose the 

 values to be 120 and 60, then for 100 amperes the force 

 factors would be twelve and six kilodynes respectively. 

 Hence each of the Liverpool motors would give twice the 

 draw-bar pull of one of the South London motors for 

 the same current. The wheels on the Liverpool cars 

 have a diameter of 33 inches, while those on the South 

 London cars are 27 inches diameter, so that the respective 

 draw-bar pulls for 100 amperes would be (taking the 

 values of H as given above) for one South London motor, 

 630 pounds, and for one Liverpool motor, 1,030 pounds. 



We must not infer from what has been said that the 

 Liverpool equipment would be necessarily more efficient 

 than the South London equipment when running at full 

 speed, because, although for equal speed and draw-bar pull 



