THE ROTARY CONVERTER. 



325 



and to increased hysteresis losses in the armature core. 

 In Fig. 162 the dotted line drawn just below the curve 

 indicates the theoretical ratio of current transformation. 

 The vertical distance between .this line and the curve 

 actually obtained is therefore a measure of the increased 

 current taken in driving the machine when loaded on the 

 alternating-current side. 



Referring again to Fig. 161, showing the ratio of 

 voltages, we can now separate to some extent the loss of 

 voltage into its constituents. There will be a certain loss 

 of voltage due to the direct current driving the converter, 

 equal to (no-load current x armature resistance). In the 

 present instance this was 2*5 amps, x -145 ohm = '36 

 volt. At no load this will be the only source of loss. 

 As the armature begins to supply alternating current 

 there will be an additional armature ohmic drop due to 

 this current. The value of this drop will not be simply 

 the product of either the alternating or direct current by 

 the armature resistance, since the alternating current will 

 not flow through the whole of the armature, but at certain 

 positions of the armature will largely flow from the 

 direct-current brushes to the slip rings. The value of the 

 drop may be calculated from the following figures, where 

 k is the constant by which the product (direct current 

 x armature resistance) must be multiplied to obtain the 

 true loss of voltage due to that part of the current which 

 is transformed into alternating current. 



Loss OF VOLTAGE IN KOTARY CONVERTER. 



To find the drop in the armature of a rotary converter 

 due to any load, we must use the following formula, the 

 value of k being taken from the table above : 



e = k C c R 

 Where e = drop in volts, 



C c = direct current taken or supplied, 

 R = armature resistance. 



The dotted curve in Fig. 161 is obtained by 

 adding the calculated ohmic drop at a number 



