CHAPTER XII 

 RECTIFYING DEVICES 



THE SYNCHRONOUS CONVERTER; MERCURY ARC RECTIFIER; 

 VIBRATING RECTIFIER 



111. Need of Rectifying Devices. We have mentioned 

 before the fact that it is generally best to generate electri- 

 cal power in the form of alternating-current power because 

 of the ease with which the voltage may be " stepped up " 

 for transmission and then " stepped down " again for 

 use in motors, lamps, etc. There are many installations 

 in which the power is desired as continuous-current power 

 at the place where it is used; it must generally be trans- 

 mitted from the main generating station as high voltage 

 a-c. power and then changed into c-c. power at the place 

 where it is used. This is the function of a rectifying device 

 to change a-c. power into c-c. power or vice versa. Charg- 

 ing storage batteries from a-c. lines and running c-c. rail- 

 way systems from a-c. power lines are the two cases where 

 rectifiers are mostly used to-day. For the latter purpose 

 synchronous converters (also called rotary converters) are 

 always used, while the mercury arc and vibrating rectifiers 

 are used for charging storage batteries from a-c. lines. 



112. Principle of Operation of the Synchronous Con- 

 verter. The synchronous converter is really a combined 

 synchronous motor and continuous-current generator; it 

 receives alternating-current power as a synchronous motor 

 running at synchronous speed and delivers continuous- 

 current power. In appearance and construction it is prac- 



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