(HAP. IV] INDUCED E.M.F. 



(e) The mechanical arrangement and cooling of the coils is 

 somewhat simplified. 



The disadvantage of a large number of slots is that more space 

 is taken up by insulation, and the machine becomes more expen- 

 Bive, especially if it is wound for a high voltage. The electromo- 

 tive force is also somewhat reduced because the voltages induced 

 in different slots are somewhat out of phase with one another. 

 The advantages of a distributed winding generally outweigh its dis- 

 advantages, and such windings are used almost entirely. Thus, 

 it is of importance to know how to calculate the value of the 

 breadth factor kb for a given winding. 



| Phase 1 

 2 

 D ' 3 



FIG. 16. A fractional-pitch winding. 



In the winding shown in Fig. 15 each conductor is connected 

 with another conductor situated at a distance exactly equal to the 

 pole pitch. It is possible, however, to connect one armature QOH- 

 ductor to another at a distance somewhat smaller than the pole 

 pitch (Fig. 16). Such a winding is called a fractional-pilch wind- 

 ii distinction to the winding shown in Fii:. !."; the latter 

 winding is called a full-pitch or hundred-pn cent pitch winding. 

 It will lie seen from Fig. 16 that, with a two-layer fractional-pitch 

 winding, sonic slots are occupied by coils belonging to two dil: 

 phases. The advantages of the fractional -pitch winding are: 



(a) The end-connections of the winding are shortened, BO that 

 there is some saving in armature <-<>|>per. 



(6) The end -Mill,, ,t ions occupy less space in the axial <i 

 tion of the machine, so that the whole machine is shot 



