386 



ELECTRICAL MACHINERY 



addition to the shunt field ; the shunt field has enough m.m.f . 

 to give the machine normal excitation and the overexcitation 

 of the converter is brought about entirely by the series field. 

 By introducing sufficient series field it is possible to com- 

 pound the converter to any degree desired. There is, 

 however, a practical limit on the amount of compounding 

 possible, for if too much inductance is introduced the 

 converter is likely to hunt badly. 



5 10 15 20 25 30 So 



Rotary load current 



FIG. 253. Curves Showing Compounding Action of an Overexcited 



Converter. 



This method of compounding is accompanied by undue 

 heating in some of the coils, as shewn in Fig. 248. 



Example of Compounding. Fig. 253 represents the effect 

 of operating a small converter, having a strong series field, 

 on a line having a correspondingly high inductance. These 

 results were obtained in the laboratory; such heavy com- 

 pounding is generally not found in practice. 



119. Compounding by the Synchronous Booster. When 

 this method of compounding is to be used, the armature 

 of a. small stationary field alternator is built up on the 



