io-C] 



SYNCHRONOUS CONVERTER. 



321 



EXPERIMENT io-C. Study of a Synchronous Converter. 



i. Methods for Obtaining Direct from Alternating Current. 

 Direct current is usually distributed from substations and is ob- 

 tained by means of synchronous converters which are operated by 

 alternating current transmitted from a distance. For economy 

 the transmission is usually 3-phase (54, Exp. 6-A). The con- 

 verters may be single-phase or polyphase, in practice being usually 

 either 3-phase or 6-phase (27, 27a, Exp. 6-A). The growth 

 of electric traction has been coincident with, if not indeed depen- 

 dent upon, the general use of the synchronous converter. While 

 more generally used on circuits of low frequency (25 cycles), its 

 use at 60 cycles (3, Exp. 3-A) is common. 



2. The synchronous converter is essentially a synchronous 

 motor and direct-current generator combined in one machine;* 



it has one field, which is self- 

 excited by direct current, and 

 one armature winding which is 

 provided with collector rings 

 for receiving alternating cur- 

 rent and with a commutator for 

 delivering direct current. The 

 armature connections for a 3- 

 FIG. i. Armature connections for a phase converter are shown in 



3-phase converter, 2-pole model. . 



Fig. i, which is the diagram 



for a 2-pole model. Each collector ring is tapped into the arma- 

 tu^e winding at one point in a 2-pole model, two equidistant points 

 in a 4-pole model, three equidistant points in a 6-pole model, etc. 



* (2a). Dynamotors and Motor-Generators. Provided with indepen- 

 dent armature windings, but with a common field, the machine would be a 

 dynamotor; with independent fields as well as armatures the machine would 

 be a motor-generator with motor and generator separate, a more flexible 

 arrangement in regard to control and regulation but more costly in con- 

 struction and less efficient in operation. 



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