THE ROTARY CONVERTER. 



337 



circuit. In the present case it is apparent that with less 

 than about '6 amps, excitation the converter works with a 

 lagging current, while with more than this excitation the 

 current begins to lead. The importance of these Y-curves 

 in connection with compounding and automatic regulation 

 of converters will be mentioned later. 



In Fig. 168 is shown the ratio of voltage transfor- 

 mation at various excitations, at no-load and with a load 

 of 4 amps. 



Curve I. shows this ratio at no load, and Curve II. at 

 about quarter load consisting of 4 amps. 



The first thing that will be noticed in connection with 



~ s 



<B '7 



ff- 



5 



8 



9 



6 -7 



Amperes, excitation. 



FIG. 168. ROTARY CONVERTER DRIVEN FROM A.C. SIDE. 

 RELATION BETWEEN RATIO OF TRANSFORMATION AND EXCITATION. 



Curve II. load 4 amperes. 

 Curve I. no 1 oad. 

 Primary volts = 58. 



these curves is the wide divergence they show from the 

 true ratio of transformation, which was seen in Fig. 159 

 to be '675 for this particular machine. 



It must, however, be remembered that the volts lost in 

 the armature are not simply the product of current and 

 armature resistance, as was the case when the converter 

 was driven from the d.c. side. The volts lost are now the 

 product of current and armature impedance. Also the 

 phase of the volts thus lost will be more nearly opposed 

 to the applied voltage when the power factor of the circuit 

 is low and the current lagging. There is thus a very great 



