122 



ELEMENTS OF ELECTRICAL ENGINEERING. 



value, is equal to ?r/(2|/2). Therefore the effective value of the 

 electromotive force of an alternator having a concentrated arma- 

 ture winding, and having a harmonically distributed flux, is equal 

 to 



7r/(2i/2) x p<&Zn abvolts. 



(ft) Distributed armature winding. Consider an armature 

 winding in which the conductors are grouped in /\.p slots, that is 

 in / groups of slots each group having four slots as shown in 

 Fig. 109. Let q be the angular distance between centers of ad- 



Fig. 109. 



jacent north poles of the field magnet, and let s be the angular 

 distance from center to center of adjacent slots. 



All of the conductors in the a slots constitute a concentrated 

 winding, all of the conductors in the b slots constitute a concen- 

 trated winding, all of the conductors in the c slots constitute a 

 concentrated winding, and so on. These concentrated windings 

 are all alike, the respective electromotive forces A, B, C and D 

 which they develop are all the same in value, but they differ in 

 phase, and the phase difference A to B, B to C, and C to D 

 is sjq x 360. Therefore the four electromotive forces A, B y 



