RECTIFYING DEVICES 383 



and an alternating voltage cf 600 X. 612 = 367 volts at full 

 load. However, slightly more than this voltage would be 

 required to overcome the effect of armature impedance 

 drop which increases with the load. 



The ordinary method for compounding a converter is 

 to have an inductance inserted in the a-c. line supplying the 

 converter and to equip the converter field with a series wind- 

 ing as well as a shunt winding. By use of this series wind- 

 ing, the excitation of the machine is increased with an 

 increase of load and this increased excitation causes an 

 automatic increase in the a-c. voltage impressed on the 

 machine. 



A.C. 

 tower 

 Supply 



FIG. 250. Circuit Electrically Equivalent to the Converter Armature. 



A Converter Similar to a Synchronous Motor. Now 

 in so far as its effect on the a-c. supply line is concerned, 

 the synchronous converter acts exactly like a synchronous 

 motor and hence, if it is overexcited, it draws from the 

 line a leading reactive current, besides whatever active 

 current it may be using. The magnitude of the reactive 

 current depends upon how much the machine is over- 

 excited; the more the overexcitation the greater is the lead- 

 ing current. 



Equivalent Circuits. The armature circuit of the con- 

 verter may be represented by a condenser and resistance 

 in parallel as shown in Fig. 250. The current I r , through 

 R } represents the active current that the converter requires 

 and the current I c flowing into the condenser represents 



