216 



ARMATURE CONSTRUCTION 



number of coils, as in Figs. 248 and 249. In connecting up a 

 winding from the diagram in Fig. 250, the coils would be pro- 

 gressively connected up around the armature in the way shown 

 in the diagram, and the terminals obtained after having connected 

 up all round. 



Fig. 248 shows the lower half of a large armature which is 

 divided horizontally. It will be seen that the coils near the 

 joints in the armature are removed, as the winding does not 

 permit of the armature being divided without disturbing these 

 coils, as will be seen from the table on p. 189. 



Fio. 251. Wound Rotor. Four-pole, Three-phase, Half -coiled, Quadruple-coil, 

 Four-slot Spiral Winding in two ranges, Y-connected. 



As this armature has open slots the coils may be form wound, 

 and those occurring at the division can be slipped into place after 

 the two halves of the machine are assembled on site. If the slots 

 are so nearly closed that form-wound coils cannot be employed, 

 it is necessary for the coils at the joints of the armature to be 

 wound on site by hand, which is undesirable. 



Fig. 251 illustrates a three-phase four-pole wound rotor for an 

 induction motor. The winding has six coils laid up in two ranges. 

 There are 48 slots, and thus 16 slots per phase. The number 



i f\ 

 of slots per pole per phase is 



4. This number will be seen 



