ALTERNATING-CURRENT WINDING 



189 



and Fig. 223 the most common for three-phase. So far as 

 divisibility of the armature and number of ranges in the winding 

 is concerned, the following table is of interest as setting forth the 

 properties of these fundamental windings : 



TABLE XII. 



PROPERTIES OF POLYPHASE WINDINGS. 



This table brings out the point that the armature is not 

 divisible unless the winding has one coil per phase per pair of poles, 

 i.e. unless it is of the half -coiled variety. Also, both the two-phase 

 windings can be laid up in two ranges ; and, in fact, this is possible 

 with all two-phase coil windings. 



While on this matter of ranges, we shall formulate a few 

 general statements ; but first a reference to Fig. 230 is desirable. 



The sketches in Fig. 230 indicate a section through the arma- 

 ture core and the ends of the coils for various coil windings. 

 a and b show single-range windings. 



An inspection of any of the single-phase winding diagrams 

 already given will show that all single-phase windings are laid up 

 in one range, c and d show two-range windings. As has been 

 seen, both two-phase and some three-phase windings can be laid 

 up in this way. e, f, and g show three varieties of three-range 

 windings with the coils laid back to a greater or less extent. 



(1) For stationary alternator armatures, any of these varieties 

 can be employed. It is generally preferable to keep the coils well 

 back against the armature frame, and thus b } d, and e would be 

 more common. 



