ALTERNATING-CURRENT WINDING 225 



made in a similar way to that in which Figs. 243 and 244 were 

 treated on pp. 205 and 206 



Before closing the subject of three-range windings, there is 

 another type given in Fig. 261, which has one coil per phase per 

 pole pair, which is equivalent to the windings already shown in 

 Figs. 228 and 239, a, 6, and c. This winding does not permit of 

 the armature being divided, and the coils must be laid up in the 

 manner of either of types e or / in Fig. 230 to permit of the 

 rotating element being withdrawable. This diagram is a de- 

 veloped diagram of the whole-coiled winding already given in 

 Fig. 228, and has the following title : three-phase, whole-coiled, 

 single-coil, two-slot spiral winding in three ranges. In Fig. 261 

 we have connected up the coils of the several phases and dis- 

 tinguished between the different ranges by three different widths 

 of coil. 



This winding possesses no superiority to any of the foregoing, 

 except, perhaps, that the windings are more distributed, and have, 

 consequently, less inductance and improved thermal emissivity. 



LAP-COIL WINDINGS. 



The difference between a lap-coil winding and a spiral-coil 

 winding has already been shown by the two diagrams, Figs. 208 and 

 215, p. 171. It is not difficult to see that any of the spiral-coil 

 windings already dealt with may be replaced by lap coils. The 

 coil element now appears as indicated in Fig. 215. 



It will be a sufficient example if we take the case of Fig. 244 

 and convert it into a lap-coil winding diagram. This has been 

 done in Fig. 262, and a comparison of this diagram with tig. 244 

 is of interest. 



This winding still retains the feature of having its twelve coils 

 distinct from one another, and it may be connected for two-phase 

 as in Fig. 243. The appearance of such a winding is shown in Fig. 

 263. This photo, however, shows part of a very large armature 

 having a much larger number of poles than Fig. 262 ; but it has 

 three slots per pole per phase, in which respect the two are identical. 



The winding diagram for Fig. 263 will be the same as Fig. 262, 

 except that it should be extended so as to have the correct number 

 of poles. A developed diagram for a portion of the winding is 

 given in fig. 264. The photograph of this winding in Fig. 263 shows 

 clearly how the elements of all the coils are of equal breadth, and 

 the manner in which the ends of the coils lie up with one another. 

 In this case we have one conductor per slot, and the slots are semi- 



15 



