314 THE ROTARY CONVERTER. 



The average amount of current flowing in a given conductor 

 will further depend upon its position relative to the 

 connections to the slip rings, since the whole of the 

 alternating current must pass to or from the external 

 circuit through the conductors situated next to these 

 connections. 



Thus, the heating of the conductors of a rotary 

 converter is not uniform, but is less than for either a 

 motor or generator rated for the same current.* For the 

 reasons above stated it will be greater in those parts 

 near to the connections to the slip rings. 



The rotary converter may also be looked upon as a 

 sort of rotating commutatiug machine through which tho 

 current passes, being changed from alternating to con- 

 tinuous, or vice versa, in the process. This point of view 

 is in some ways not so satisfactory as the one first 

 suggested, since during certain periods the current given 

 out by the armature is greater than the current supplied 

 to it, and in this case it is obviously difficult to consider 

 the input and output current as being identical. 



Losses in the Rotary Converter. As in the case of all other 

 types of transformers, there is a certain loss which is 

 independent of the output of the machine. This is, in 

 the case of the rotary converter, the power required to 

 excite and drive the converter, and may be called the 

 no-load loss. The losses which depend on the load are 

 almost entirely those due to the resistance of the arma- 

 ture conductors. These losses, except in the case of the 

 single-phase converter, are smaller than in the case of any 

 other type of generator or direct-alternating transformer 

 for a given load current. 



Hatio of Transformation. The armature voltage of a direct- 

 current machine is given by the following formula : 



' 



" 60 x 10 8 ~ 



E = Armature voltage. 

 N = Number of armature conductors. 

 n = devolutions per minute. 



Z = Number of magnetic lines passing from N poles to 

 S poles. 



* This is the case for a given a.c. current. With a single-phase converter 

 the a.c. current is almost 1J times the d.c. current, and the heating is greater 

 than for a d.c. generator of the same d.c. output. 



