ALTERNATING-CURRENT WINDING 



219 



properties will be seen from Table XII. on page 189. Reference to 

 this table shows that the armature can be divided, and also that 

 there is one coil per phase per pole pair. Hence, for each group of 

 coils in Fig. 254 we must have a pair of poles, and these are 

 indicated at the top of the figure. The coils of one phase must be 

 connected up in the same direction as in Figs. 223 and 229. The 

 winding is a three-phase, half-coiled, double-coil, two-slot spiral 

 winding in three ranges. 



FIG. 254. Three-phase, Half-coiled, Double-coil, Two-slot Spirnl Winding 

 in three ranges (six-phase grouping). 



It is worth noting that the coils of the upper and lower ranges 

 are exactly similar in shape. If this armature had open slots which 

 permitted of form-wound coils, and if the ratio of gap diameter to 

 polar pitch is sufficiently large, there need only be two kinds of 

 formers one for the middle range coils, and another for both the 

 upper and lower range coils. The lower range coils have only to be 

 placed on the armature upside down with regard to the upper range. 



The other types of three-range winding (Fig. 230) have three 

 kinds of coils, and require a corresponding number of forms. 



