WAVES OF MAGNETIC FLUX 43 



Adding, we get for the resultant the rotating wave 

 V = y\ + 2/a + ya = ijB cos (pt - qx) 



Special attention may be drawn to the following points. In each 

 case, when t = 0, the induction at x = is at its maximum. This 

 means that the crest of the resultant rotating wave reaches the origin 

 at the instant when the amplitude of the first component alternating 

 wave is at its maximum. In other words, at the instant when any 

 one of the component alternating waves reaches its maximum 

 amplitude, it is coincident in position with the resultant rotating 

 wave. 



Secondly, the amplitude of the rotating wave is, in the case of 

 the two-phase system, equal to that of either component alternating 

 wave, while in the case of the three-phase system the amplitude of 

 the resultant is 1*5 times that of the component waves. 



From the above it is at once evident that, while in the case of the 

 two-phase system the e.m.f. induced in each phase by the resultant 

 rotating wave is the same as that which would be induced by the 

 alternating wave due to that phase if acting alone, the e.m.f. induced 

 in each phase of the three-phase winding is increased 50 per cent, by 

 the presence of the other two phases. This result may also be ex- 

 pressed by saying that there is no mutual inductance between the 

 two circuits of a two-phase system, but that in a three-phase system 

 the effect of mutual inductance is equivalent to a 50 per cent, increase 

 in the self-inductance. 



