RECTIFYING DEVICES 387 



same shaft with the armature of the synchronous con- 

 verter. The field frame for the alternator is mounted on 

 the side of the converter field frame. 



Construction of the Machine. The alternator armature 

 winding must be of the same number of phases as the 

 converter armature winding; its current capacity must be 

 equal to that of the converter armature; and its normal 

 generated voltage must be equal to the desired amount 

 of compounding. The different phases of the armature 

 winding are kept separate. The beginning of each phase 

 is connected to a slip ring and the end is connected to one 

 tap of the converter armature. 



The a-c. line supplying power to the converter is con- 

 nected (through brushes) to the alternator slip rings. 

 Hence the converter is connected to the a-c. line through 

 the armature of the alternator, which, by suitable excita- 

 tion of its field, may be made either to raise or lower the 

 voltage impressed on the a-c. taps of the converter. By 

 suitably winding the alternator field coils, and connecting 

 them in series with the continuous-current load, the com- 

 pounding may be made automatic. 



A synchronous converter fitted with a synchronous 

 booster is shown in Fig. 254. This machine was built for 

 10% compounding, therefore, the booster is somewhat 

 more than 10% of the capacity of the converter itself. 



120. Auxiliary Pole Synchronous Converter. It has 

 been stated that the ratio of voltages was fixed for a certain 

 converter and that this ratio was independent of the field 

 excitation, etc. But it has recently been shown that if 

 the field pole of a converter is made up in two or more 

 parts, the excitation of each part being under separate 

 control, a certain amount of variation of the ratio s i 

 possible. A machine having its field poles so constructed 

 is called an auxiliary pole, or split-pole converter; it has 

 been developed by one of the large manufacturers but has 

 not yet come into very general use. 



