172 ARMATURE CONSTRUCTION 



Fig. 204 is in far more common use for polyphase windings than 

 that in Fig. 203, although for other reasons than the above (which 

 will be dealt with when we come to consider polyphase windings). 



Before leaving this batch of figures it is desirable to point out 

 that, in all subsequent winding diagrams, we shall adhere to the 

 style of coil in Fig. 208 in all the types of winding into which 

 this coil enters. 



This is, it will be seen, wound by commencing with the inside 

 conductor of the right-hand group and spiralling outwards, taking 

 in all the conductors successively, finishing with the outside 

 conductor of the left-hand group. 



It would have been possible to wind the coil in the reverse 

 direction, commencing with the inside conductor of the left-hand 

 group and finishing with the outside conductor of the right-hand 

 group. The previous method is, however, the most usual, and is 

 in fact easier to carry out in practice, and hence we shall adhere 

 to it throughout. 



So far, when considering single-phase windings, we have only 

 considered the number of conductors in their capacity of making 

 up a coil, and have not touched on their spacing out on the 

 armature or their distribution or concentration relative to one 

 another. Thus the conductors constituting a coil may be all 

 concentrated in a single large slot, or they may be distributed in a 

 small or large number of slots. 



The two extreme cases are represented in Figs. 209 and 210, 

 where we have taken for consideration a coil out of the winding in 

 Fig. 204, consisting of four turns. In Fig. 209 the four turns are 

 concentrated in two large slots, each one containing the conductors 

 of each side of the coil. In Fig. 210 the four turns are distributed 

 over eight small slots, resulting in one conductor per slot. The 

 conductors on each of the coils are now spread over four slots. 



We shall employ the terms " single-coil," " double-coil," 

 "triple-coil," "quadruple-coil/'' etc., to designate whether the 

 coil (as defined above) is divided into one, two, three, or four 

 parts, each part occupying a single pair of slots. Thus the coil in 

 Fig. 207 will be a " double-coil," consisting of two parts, and 

 occupying two slots on each side of the coil. Similarly, the coil in 

 Figs. 208 or 210 is a "quadruple-coil," while that in Figs. 209 and 

 211 is a "single-coil." It is desirable not to employ the terms 

 " uni-slot," " two-slot," " three-slot," etc., to define the distribution 

 of the coil, but to use these terms only to indicate the number of 

 slots per pole per phase. Thus such a terra as " four-slot " prefixed 



