CONTINUOUS-CURRENT WINDINGS 145 



windings, and in interconnecting them, one must conform to the 

 requirements of the formula 



C 

 in which 



C = number of face conductors 

 n = poles 

 y = " winding pitch." 



If y (the mean pitch) is an odd number, it may be taken at the 

 same value at both back and front ends, i.e. y (mean) may equal 

 both yb and yf. Herein is another, although minor, point of 

 difference from multiple-circuit windings. If y is an even number, 

 yb arid yf must be respectively 1 greater and 1 less (or vice versd) 

 than the mean value of y ; or the back and front pitches may be 

 3 greater and 3 less, or 5 greater and 5 less, etc. These pitches 

 will, however, generally be taken 1 greater and 1 less. It .will be 

 shown at a later stage, under what conditions it becomes of 

 advantage to take yb and yf 3, 5, etc., greater and less than the 

 mean pitch. In Fig. 170 the mean pitch is 10 (y = 10); the back 

 pitch, yb t is equal to 9, and the front pitch, yf, to 11. The winding 

 of Fig. 170 is again shown in Fig. 171, arranged according to the 

 more usual and convenient conventions. An element of the 

 winding is heavily lined in, in order to again impress upon the 

 reader this distinguishing characteristic of a two-circuit winding. 

 It will be noticed in Fig. 171 that only two sets of brushes are 

 indicated, although the machine has six poles. For two-circuit 

 windings, two brushes suffice, independently of the number of 

 poles ; but as many sets of brushes as there are poles are generally 

 preferable. For multiple-circuit windings there must be as many 

 sets of. brushes as there are poles, the only alternative consisting 

 in cross-connecting the commutator a very undesirable practice, 

 now generally abandoned. 



Let us construct a 6-pole 2-circuit winding diagram with 58 

 conductors. We have n = 6 ; C = 58. 



As 56 is not divisible by 6, we find that the only value for the 

 mean pitch is 



6 



10 



