256 



ALTERNATING CURRENTS 



current remains unaltered, and the voltage across the primary 

 is maintained approximately constant, it is evident that both the 

 secondary hypothetical field and the resultant or actually existing 

 field must remain approximately constant. Hence, if the separation 

 of the phases of the two hypothetical fields is increased, the primary 

 field must necessarily increase in order to maintain the resultant 

 constant, and as a consequence the resultant will swing round so as 

 to be nearer (as regards phase) the more powerful primary component. 

 The e.m.f. induced in the secondary, whose magnitude and phase 

 depend on those of the resultant field, will thus remain approximately 



(5) 



FIG. 158. Automatic Regulation of Converter. 



unaltered in magnitude, but will be brought more nearly into coinci- 

 dence of phase with the secondary voltage of the step-down trans- 

 former, so that their vectorial resultant will be increased. The two 

 extreme positions of the induction regulator are those in which the 

 regulator secondary voltage is arithmetically subtracted from, and 

 added to, the voltage of the step-down transformer. 



In the automatic method of regulation, the field of the converter 

 is compound wound, so that with increasing load the field is auto- 

 matically strengthened. Now, a mere strengthening of the field 

 would, as already pointed out, produce no appreciable rise of voltage 

 on the continuous-current side unless there is a rise on the alternating 

 side. In order to effect this latter rise, suitable choking or reactance 

 coils are inserted in series with each phase of the converter. Let 



