ALTERNATING-CURRENT WINDING 



195 



phase. The disadvantage, aud the reason why they are used very 

 infrequently, is that the pole arc must be reduced until it is only 

 about as wide as a coil, which entails a reduction in the pole area, 

 and the periphery of the armature is not so well utilised. 



SKEW-COIL WINDINGS. 



Fig. 234 will illustrate what is meant by a skew-coil wind- 

 ing. Here the coils are all of the same shape, and the winding is 

 equivalent to an ordinary long-coil, or overlapping, winding. 



The winding diagram for Fig. 234 will be the same as that shown 

 above in Fig. 223. Whereas in the latter winding the overlapping 



FIG. 234. Skew-coil Winding. 



of the ends of the coils is provided against by laying them up in 

 ranges, in the skew-coil winding the ends of the coils are skewed so 

 that they all He up in order beside one another. The skew coil is 

 probably not so easy to wind as an ordinary symmetrical coil, and 

 the insertion of the last coil on the armature after winding is not 

 an easy job. This type of winding is not used to to any great 

 extent. 



A point of considerable importance in all these winding schemes 

 is the pressure between the adjacent coils. If one inspects Figs. 

 227 and 228 and considers phase A (black), it is evident that the 

 maximum voltage exists between the points S A and T A , which is 



the machine terminal voltage. The pressure between the sides of 

 the first and last coils is practically as great as the full terminal 



