324 



THE ROTARY CONVERTER. 



by subtracting the constant no-load current from each 

 reading of the direct current supplied. This can most 

 simply be done on the diagram by drawing a horizontal 

 line through the point where the curve cuts the vertical 

 axis, and taking this as the horizontal axis from which to 



16 



14 



12 



10 



O 2 4 6 8 1C 12 14 16 18 2O 

 A.C. Amperes. 



FIG. 16?, CURRENT CHARACTERISTIC OF ROTARY CONVERTER 

 DRIVEN FROM D.C. SIDE. 



measure that part of the direct current which is converted 

 into alternating current. Proceeding in this way we find 

 the ratio of transformation to be 



alternating current _ IS -. .^ 



direct current 1'2 ' 4 



We can calculate from the true voltage ratios obtained 

 from the open-circuit characteristic (Fig. 159) what the 

 ratio of current transformation should be, since 



D.C. watts = A.C. watts, and ^ vo ?* s = '675 as already 



D.C. volts 



measured, hence 



D.C. amps. '675 



The difference between the ratio T45 actually observed 

 and the true ratio of 1*48 is due to the slight increase in 

 driving current required to overcome the increased iron 

 losses when the machine is loaded. These losses are 

 probably chiefly due to eddy currents in the pole faces, 



