

DETAILED' STUDY OF OPERATION WITH NORMAL LOAD 79 



To estimate the size of the motors required, we will suppose them 

 constructed for an E.M.F. equal to that which they should produce 

 when run as compensating machines. 



For the sake of economy, the manufacturers tend more and more 

 to increase the magnetic density, i.e., to ' saturate " their machines, 

 and it is scarcely prudent at present to count upon being able to increase 

 very much their counter E.M.F. by increasing the excitation. 



FIG. 37. 



From the calculations corresponding to the values of cos <f> com- 

 prised between i and 0.40, we obtain the curves given in Figs. 37 and 

 38. The curves in Fig. 37 give the saving in cost of equipment and the 

 curves in Fig. 38 give the saving in annual expense of operation. It 

 will be seen that if, from the standpoint of cost of equipment, the use 

 of motors running without load becomes rapidly advantageous as 

 cos < decreases, it is different, in any particular case, from the 

 standpoint of the annual cost of operation. 



