ELEMENTS OF ELECTRICAL ENGINEERING. 



Lay off the line OC, Fig. 150, to represent B, describe a 

 circle about C of which the radius represents the value of A, 

 draw the line ef making with OC the angle whose tangent is 

 &LJR, and draw the line sOs' perpendicular to ef. Let us 

 suppose for the sake of simplicity that the efficiency of the con- 

 verter is 100 per cent, so that the intake of power may be con- 

 sidered equal to the output. The figure shows the phase rela- 

 tion between A and B (each phase) for a direct-current load 

 equal to 2 times OQ times Bj V R 2 -f o) 2 L 2 watts, where OQ is 

 expressed in volts (of course all lengths in Fig. 1 50 represent 



Fig. 150. 



volts). This relation is explained in Art. 69, and the factor 2 is 

 introduced because the expression given in Art. 69 gives the in- 

 take of one phase only. 



If the direct-current output is decreased, the point P 9 Fig. 1 50, 

 moves towards s causing OQ to decrease ; if the direct-current 

 output is increased the point P moves towards M, causing OQ 

 to increase ; and if the direct-current output is greatly increased 



