CHAP. IV] 



INDUCED E.M.F. 



09 



metric sum of the E'a. The radius of the circle r = J/?/sinia, and 

 a. Therefore, 



E'/SE=(sm 



sin Ja). . 



(33) 



When 5=2, the formula (33) becomes identical with the expres- 

 sion given before. 



FIG. 17. A diagram illustrating the slot FIG. 18. A diagram illustrating 



factor with two slots. the slot factor with several slots. 







The angle a depends upon the number of slots and the number 

 of phases. Let there be m phases; then aSm= 180 degrees, and 



a = 180/OSm) (34) 



The values of k a in the table below are calculated by using the for- 

 mulae (33) and (34). 



VALUES OF THE SLOT FACTOR k t 



In -in-Jc --phase alternators part of the slots are of ton left empty 

 so as to reduce the breadth of the winding and th< n f<>K increase 

 the value of k,. For instance, if a punching is used with six slots 

 >le, perhaps only three or four adjacent slots are occupied. 

 In this case, it would be wrong to take the values of k t from the 

 first column of the table. If, for instance, three slots out of six 



