RECTIFIERS: THE SYNCHRONOUS CONVERTER 375 



synchronous motor described on page 318, Par. 129, except that 

 the windings are now stationary in space. The armature which 

 produces the rotating field rotates at synchronous speed in one 

 direction and the rotating field itself rotates at synchronous speed 

 in the opposite direction with respect to the armature. Under 

 normal operation therefore, the field is stationary in space with 



"ct to the amortisseur windings. 



156. The Three-wire Converter. It is pointed out in Vol. I, 

 Chap. XII, that the neutral of a 3-wire system may be obtained 

 by the use of two or more slip-rings connected to the direct- 

 current armature. A reactance coil is connected across these 

 slip-rings and alternating current flows through this reactance. 

 The direct -current neutral is connected to the middle point of 

 this reactance and the direct current of the neutral divides and 



Fio. 340. D. C. neutral obtained from neutral of 4-phase, diametrically- 

 connected transformers. 



passes back into the armature through the reactance. The 

 reactance has a low resistance and has practically no effect on 

 the direct current. 



It is to be noted that a synchronous converter with the pi 



former connections provides a neutral point for just such a 

 direct-current neutral. For example, if a six-phase, douNr-Y, 

 or a six-phase star, Fig. 338, a four-phase star, Fig. 340, or a 

 three-phase Y-connection of transformer secondaries be used, 

 an excellent neutral is provided. 



In the fir-t two of these connections, the direct current flows in 

 opposite directions through the two-halves of each transformer 

 secondary, so there i- no direet-current magnet i/.in^ acti. 



In the Y -connect inn. however, this is not the case 

 and the maur n of the direct current, nctinu in cnn- 



junction with that of the alternating em-rent, produces an un- 



