322 



THE ROTARY CONVERTER. 



circuit open. When running at normal speed and with 

 normal excitation, read the voltage at both direct and 

 alternating terminals, and also the direct current supplied 

 to the armature. Keeping the direct-current voltage at 

 the armature terminals and also the excitation constant, 

 close the switch in the load circuit. For a series of 

 increasing values of the load current take readings on 

 both voltmeters and ammeters. The power in each 

 circuit should be calculated and the results entered in 

 tabular form as indicated below. 



From the results the following curves should be plotted 

 on a load base : (1) direct current supplied, (2) ratio of 

 transformation, (8) efficiency. 



It must be remembered that in all rotary converter 

 experiments the position of the brushes affects the voltage 

 ratio very much. The brushes should be kept fixed at the 

 neutral position. 



LOAD CHARACTERISTIC OP BOTAHY CONVERTER. 



Rotary converter No Type 



Alternating voltage Current 



Excitation Speed 



.revs, per mm. 



The efficiency is calculated by dividing the D.C. watts 

 supplied by the A.C. watts given out. It must be 

 remembered that the excitation losses should be added to 

 the input watts to give the total efficiency. Since the load 

 circuit is non-inductive, the output may be taken as the 

 product of current and voltage on the A.C. side. 



Figs. 161 and 162 show the results of such a test, 

 which was carried out on the same 2-pole machine for 

 which the magnetisation curves in Fig. 159 were drawn. 

 The full-line curve in Fig. 161 shows the ratio of voltage 

 transformation, the voltage on the direct-current side 

 being constant at 109. The curve is seen to drop fairly 

 rapidly at first, but afterwards to become practically a 

 straight line. The loss of voltage indicated by the curve 



