THE ROTARY CONVERTER. 



339 



side is considerable in that case. If a constant and not a 

 maximum ratio of voltages is required, it would be possible 

 by altering the power factor of the circuit to produce a 

 lagging current at light loads, and thus reduce the 

 secondary voltage and to make the power factor unity at 

 full load, so as to get a maximum voltage in this case 

 which might be equal to, or even higher than, the voltage 

 at no load. 



It has been shown by the results of the experiment 

 just described how the power factor of the supply circuit 



3 -4 -5 '6 -7 -8 -9 



Amperes, excitation. 



FIG. 169. ROTARY CONVERTER DRIVEN FROM A.C. SIDE. 

 Primary and secondary watts and primary current for constant load of 4 amperes. 



is altered by change of excitation an increase of excita- 

 tion produces an increase of lead in the current. 



It would consequently be possible, 'by increasing the 

 excitation of the converter in the correct proportion to 

 the load, to obtain an approximately uniform ratio of 

 conversion from no load to full load. The principle of 

 this method of regulation is to be ascribed only indirectly 

 to the change of field. The regulation is really due to 

 change of power factor in the first instance. 



