384 ELECTRICAL MACHINERY 



the reactive component of the converter current. As the 

 overexcitation of the machine is increased, the capacity 

 of the condenser C must be imagined to increase propor- 

 tionately in order that the circuit of Fig. 251 may correctly 

 represent the conditions -in the actual synchronous con- 

 verter circuit. 



In Fig. 251 the converter is again imagined as consist- 

 ing of a resistance and a condenser in parallel, and there is 

 an inductance L in the supply line. The voltage of the line 

 is constant (with a value equal to E, irrespective of the load 

 and the excitation of the converter) and we wish to find the 

 effect on E R , the voltage impressed on the converter, as the 



FIG. 251. Inductance in the Supply Line Makes Compounding 

 Possible, because of the Condenser Action of the Converter 

 Armature. 



excitation of the machine is increased. In Fig. 251 this 

 increase of excitation is to be represented by an increase 

 in the capacity of C. 



Vector Diagram of the Circuit. The vector diagram 

 of the current and e.m.fs. is shown in Fig. 252. Suppose 

 that at first there is no superexcitation on the machine 

 so that the current and voltage E R are in phase. A circular 

 arc is constructed with E as a radius; the e.m.f. to over- 

 come the drop in the inductance L is shown at EL and hence 

 the voltage across the armature of the converter is found 

 by vectorially subtracting EL from E. The result, ER, 

 is found to be slightly less than E. 



If, now, some superexcitation is put on the converter, 



