352 



ALTERNATING CURRENTS 



Consider conductor a, Fig. 323, which lies midway between 

 two slip-ring taps. First consider the direct current in this 



conductor as the conductor 

 moves through successive po- 

 sitions 1, 2, 3, 4. If the load be 

 assumed constant and the width 

 of the brush be neglected, the 

 direct current will be positive, 

 and will not vary as the con- 

 ductor moves from (1) to (2) to 

 (3). At (3), the brush position, 

 the current reverses abruptly 

 and then remains constant until 

 the conductor reaches position 

 (1). This is shown in Fig. 324 (a). 

 The conductor a is midway 

 between slip-ring taps, so that it 

 is at the center of the alternating-current phase-belt which is 

 included between these slip-ring taps. The phase of the electro- 



(1) (?) (?) (4) (1) 



FIG. 323. Relative positions of con- 

 ductors and slip-ring taps. 



(a) D.C. and A.C. Currents In Conductor a. P.F.=1.0 



\ 



\ 



(6) Resultant Current 



Fio. 324. Current at unity power-factor in a conductor midway between slip- 

 ring taps. 



motive force in a is the same as that of the resultant electro- 

 motive force of the entire belt. This is evident from a study of 



