FIELD STRENGTH DUE TO STATOR WINDINGS. 149 



FIELD STRENGTH DUE TO STATOR WINDINGS. 



100. It will be here assumed that the total induction at any 

 instant is proportional to the corresponding instantaneous value 

 of the ampere turns. 



101. Di-phase Winding. Two alternating-currents 

 differing by a quarter of a period, and of equal intensity, are repre- 

 sented in Fig. 58. The current represented by the curve A is a 



FIG. 58. 



quarter of a period in advance of that represented by B. 



We have now to find the curve of induction produced 

 by these currents. 



Kef erring to Figs. 55 and 57, it is seen that the currents in the 

 coils a, a' always assist those in b, b' in producing the magnetic 

 field ; that is, the effects of the currents are algebraically added. 

 Since the number of turns of wire on the stator remains constant, 

 the effect of either current in producing a magnetic field is pro- 

 portional to the current, so that we may take the current curve 

 itself to represent the induction it produces. 



Suppose this to be done for each of the four coils a, a', b, V. 

 From the way in which these coils are wound in Fig. 55, we see 

 that if the currents in a, b tend to make the induction clockwise, 

 then those in a', b' produce a counter-clockwise induction; the 

 separate inductions are, therefore, represented in Fig. 59 by the 

 curves B', A, B, A', etc., where the curves B', A are the negative 

 portions of the curves B, A in Fig. 58 rectified. 



d d, d ^ _ ..... 



FIG, 59. 



The justification for thus rectifying the curves of Fig. 58 lies 

 in the way in which the coils are wound round the Stator. 

 Fig. 59 is not a representation of the currents, but of the induction, 



