388 



ELECTRICAL MACHINERY 



A discussion of the theory of this type of converter is 

 beyond the scope of this text; operating curves of a small 

 three-phase auxiliary pole converter are given, however, 

 in Fig. 255. In this machine it was possible to compound 

 the continuous voltage from 92 volts to 135 volts. As 

 the excitation of the auxiliary pole was varied from negative 



FIG. 254. A Synchronous Converter Fitted with a Synchronous 

 Booster. Westinghouse Electric and Mfg. Co. 



to positive, some variation in the strength of the main 

 field poles was required in order to maintain the power 

 factor of the machine high. 



121. Motor-generator Sets. One disadvantage of using 

 a synchronous converter to obtain c-c. power from an a-c. 

 supply is that the continuous voltage is fixed; in many cases 

 (notably in mine installations) c-c. power of variable voltage 



