I2O 



ELEMENTS OF ELECTRICAL ENGINEERING. 



2p slots as shown in Fig. 107. In this figure the breadth of the 

 pole faces is 6 units, the distance between pole tips is 4 units, and 

 the distance from center to center of slots a and b is 2 J units. 



To determine either the average value (during half-a-cycle), or 

 the effective value of the electromotive force of an alternator from 

 a given distribution of flux and a given arrangement of the wind- 

 ings, it is in general necessary to calculate the instantaneous 

 values of the electromotive force for a series of successive posi- 

 tions of the armature, and then find the average, or the square- 

 root-of-the-average-square of these instantaneous values. 



The ordinates of the rectangular " curve" bbbb, Fig. 107, rep- 



Index 



Y//////////////////////////A 



L * I , 



Axis of time 



It one-half cycle . * 



i 



Fig. 107. 



resent the successive values of the electromotive force of the wind- 

 ings which lie in the b slots, the ordinates of the " curve " aaaa 

 represent the successive values of the electromotive force of the 

 windings which lie in the a slots, and the ordinates of the curve 

 EF represent the successive values of the electromotive force of 

 the complete winding. Knowing the successive values of the 

 electromotive force of the complete winding as represented by the 



