THE ROTARY CONVERTER. 317 



The virtual value of the alternating voltage 

 /g maximum value = - ^-sin 60 F D = sr~TtF ^ D = 



6123 F D volts. 



It may be stated generally that in a rotary converter 

 with n rings, if the electromotive force between the direct- 

 current brushes is F D , and V A the virtual alternating 

 pressure between two adjacent rings 



" A = V FD sin T ' ' (D 



The relation between the direct and alternating 

 currents is best obtained by equating D C and A C 

 powers. 



Thus, if C D and C A are the direct and virtual alternating 

 currents of a converter having n rings, i.e., arranged for 

 an w-phase alternating current, 



Direct current power = F D C^ 



The alternating current power per phase* = V A C A , and 

 the total A C power = WV A C A . 



' FfjCp = n V A C A , or substituting the value already 

 obtained for A , 



nsm 



n 



OD 



In a three-phase circuit we know the line current 

 ^A = A/ 3 x current per phase = ^/ 3 c A , 



Also n = 3. 



Thus we obtain the value of the line current by multi- 

 plying equation (2) by y'S, and substituting for n : 



_ 



3 sin 6C 

 r 



2 

 TIence the ratio of the currents for a 3-phase circuit is 



$= "943 ........ (3) 



^D 



* C A is taken to be virtual current in the armature conductors, and C\ the 

 virtual current at the slip ring. 



