180 THE DIKECT-CURKEXT VICTOR CH. VIII 



In Fig. 44 force factor curves are given for different 

 types of dynamos. Curve A is for a set of four-pole belt- 

 driven railway generators, and curve C for a set of six- 

 pole direct connected railway generators, made by the 

 General Electric Company. Curve li is for a set of four- 

 pole belt-driven railway generators made by the Walker 

 Manufacturing Company. The power in kilowatts is stated 

 opposite each machine. The dynamos are all for 550 volts. 

 The current can be obtained by dividing the power in each 

 case by the tension, and the induction factor can then be 

 deduced by dividing the force factor by the current. 



In Fig. 45 the weights and force factors of a complete 

 set of direct connected railway generators made by the 

 General Electric Company are given. Particulars of these 

 machines will be found in the table. The letters A, B, C 

 refer to the method of winding the armature. 



It is instructive to take different machines designed to 

 carry equal currents and see how the weight varies with 

 the induction factor. Also to take equal induction factors 

 and see how the weight varies with the current, and to take 

 equal force factors and see how the weight varies with the 

 induction factor. 



The force factor curve is really the combination of a 

 number of different force factor curves for the different 

 types, six-, eight- and ten-pole, only a certain portion of 

 each being used in practice. In the diagram the current 

 curve is assumed to be straight, and the curve of induc- 

 tion factor is obtained by dividing the force factor by the 

 current for each weight. 



Example 50. To find the lightest dynamo for 500 

 kilowatts. The current at 550 volts tension is 910 

 amperes, and the weight from the current curve is there- 



