150 TREATISE ON ALTERNATING CURRENTS. 



and the phase of the induction depends, not only on the value 

 of the current, but also on the way in which the stator coils are 

 wound. 



The currents in the coils of Fig. 55 are two-phased, 

 but the induction is four-phased, for the induction 

 produced by a' differs by 180 from that produced by a. 



To obtain the resultant, we must add the curves T>\ A, B, A' 

 together. We thus obtain the dotted curves d as a graphical 

 representation of the magnitude of the induction at any time. 

 When the current A is zero, B is a maximum. Let the induction 

 then be represented by unity ; 45 later its value is 2 sin 45, or 

 \/2, and so on. 



The induction, therefore, varies between limits proportional to 

 1 and 1*414 ; that is, there is a variation of about 20'5 per cent. 



t Si,n< (pt + 4-7 



3 

 FIG. 60. 



from its mean value. This variation, however, becomes -consider- 

 ably toned down by the effect of the rotor currents. 



1O2. Tin-phase Winding's. If the stator is wound for 

 tri-phase work, as in Fig. 60, the currents in the three circuits 



may be taken to be i sin pt, i sin (pt + y\ and i sin (pt + ~\ 



respectively, and are represented graphically in Fig. 61. In order 

 to obtain the curve of induction produced by these three currents 

 flowing through the stator windings, as in Fig. 60, we must rectify 



