CHAPTER XV 



140. Rotary converters and their uses 141. Voltage ratio in converters 142. 

 Ratio of currents 143. Relative outputs of armature when generating con- 

 tinuous, single-, two-, and three-phase currents 144. Heating of single-phase 

 converter 145. Heating of converter having N slip-rings 146. Effect of 

 number of slip-rings on output of converter 147. Six-phase converter supplied 

 from three-phase mains 148. Twelve-phase converter 149. Hunting of rotary 

 converters 150. Voltage regulation of rotary converters 151. Starting of 

 rotary converters 152. Racing of inverted rotaries 158. Converters v. motor- 

 generators. 



140. Rotary Converters and their Uses. 



A ROTARY converter is a machine by means of which may be effected 

 the transformation of alternating (single- or polyphase) currents into 

 continuous current, or the transformation of continuous into alter- 

 nating current. In most cases, the machine is employed in connection 

 with the first-mentioned purpose, and its chief practical importance 

 is due to the fact that while the transmission of power over long 

 distances is most readily and economically accomplished by means 

 of alternating currents, its actual distribution to the motors of an 

 electric railway or tramway system has hitherto been effected chiefly 

 by means of continuous current. The rotary converter supplies one 

 of the necessary links between the high- voltage alternating- current 

 transmission system, and the low-voltage (500 to 600 volts) con- 

 tinuous-current distribution system of an electric railway or tramway. 

 Were it not for its importance in electric railway work, the rotary 

 converter would probably have received much less attention than has 

 actually been bestowed on it. 



In some few cases, converters have been used for effecting the 

 opposite kind of transformation, viz. from continuous to alternating 

 current. When so used, they have sometimes been termed inverted 

 rotaries. Cases of this kind may occasionally arise in connection 

 with a large continuous-current generating station, when it is desired 

 to transmit a limited amount of power to a greater distance than 

 could economically be accomplished by the use of continuous 

 current. Continuous current is in such cases supplied to an inverted 

 rotary at the generating station, the polyphase currents from the 



