CONVERSION OF ALTERNATING CURRENT. l8l 



that the RI losses of voltage in the armature windings are 

 negligible. 



Two-ring 1 converter. In the two-ring converter the two rings 

 are connected to commutator bars, one of which comes under a 

 positive direct-current brush at the instant that the other comes 

 under a negative direct-current brush ; at this instant the electro- 

 motive force between the collector rings is at its maximum value 

 and it is equal to the electromotive force between the direct- 

 current brushes. Therefore the direct electromotive force E Q 

 of a two-ring converter is equal to the maximum value, \/2 2 , 

 of the harmonic alternating electromotive force between the two 

 collector rings. Therefore 



in which E 2 is the effective value of the alternating electro- 

 motive force between the collector rings. 



Converter with n collector rings. Consider all of the armature 

 conductors which constitute one of the paths between the two rings 

 of a two-ring converter. These conductors are evenly distributed 



* 



Fig. 151. 



over one half of the armature, and the harmonic alternating elec- 

 tromotive forces which are induced in the respective conductors 

 are all equal in value but they are distributed in phase throughout 

 an angle of i8q as shown by the vectors a, Fig. 151. There- 



