198 ARMATURE CONSTRUCTION 



The other two types, C and D, shown in Fig. 236, are respectively 

 elements of a wave winding C and a retrogressive wave winding 

 D. The development of these two types of winding from the 

 elementary fundamental windings is considered in further detail 

 on pp. 229 and 232. The " coil " may have its conductors con- 

 centrated in a single slot on each side, or it may have them 

 distributed at each side in two, three, four or more slots. 



If the conductors on one side of the coil lie in only one slot 

 we designate the coil a " single coil." If they are spread over 

 two slots the coil is a " double coil" ; if over three slots, a " triple 

 coil," and so on. 



In the top row of windings, i.e. those marked a and g in Figs. 

 237, 238, and 239, the coils are " single coil," as marked at the 

 left-hand side of the row. 



In the second row, i.e. those marked b, e, h, and m, in Figs. 



237, 238, and 239, the coils are " double coil " : that is, each coil 

 consists of two parts in separate slots. 



In the third row, i.e. c, /, &, and n, they are " triple coil " ; 

 that is, in three parts, the conductors on each side of the coil 

 being distributed in three slots. 



In Fig. 237, which relates only to single-phase windings, we 

 have shown the outline of the slots, but in Figs. 238 and 239, 

 where there are twice and three times the number of slots in 

 the corresponding diagrams of Fig. 237 (as Figs. 238 and 239 are 

 for two and three phases respectively), the coils have been dis- 

 tinguished by different varieties of lines ; thus, full dotted and 

 chain lines for the different phases. 



Having now explained the terms " single-coil," " double-coil," 

 and so on, we will explain the other sub-divisions in Figs. 237, 



238, and 239. 



Fig. 237 is headed " single-phase," and is devoted exclusively 

 to single-phase windings. Under this heading there are two 

 sub-headings, viz. " whole-coiled " and " half-coiled " (as there are 

 also in Figs. 238 and 239). 



The distinction which has already been explained between these 

 two headings will be seen by an inspection of any of the windings 

 coming under them. 



By " whole-coiled " we denote that the whole system of poles is 

 subtended by coils, i.e. each pole has a coil opposite it on the 

 armature, which is the case in all the windings in Fig. 237, a, b, c, c, 

 and/. 



In the " half-coiled " windings, however, only one half of the 



