CHAPTER XH 



ARMATURE WINDINGS LOSSES, AND TEMPERATURE 



RISE 



78. Types of Windings. Fundamental winding diagrams for 

 single-, two-, and three-phase, machines were illustrated and ex- 

 plained in the preceding chapter (Art. 67). Beyond this it is 

 not proposed to say much regarding the actual arrangement of 

 armature windings in alternating-current generators. Much 

 excellent matter has been published on the practice of armature 

 winding; 1 but it has little to do with the principles of electric 

 design, and, in the end, is really a study of the most convenient 

 and economical way of connecting together the active conductors 

 in the slots. There is almost no limit to the number of styles 

 of winding that can be used on alternators, or to the names that 

 may be, and are, given to these different windings; but the funda- 

 mental principles underlying the generation of an alternating 

 e.m.f. can be studied without a detailed knowledge of the many 

 practical types of armature windings. 



There is one broad distinction that can be made, and alternator 

 windings may be divided into : 



(a) Double-layer windings. 



(6) Single-layer windings. 



(a) Double-layer Winding. This is practically identical with 

 the usual D.C. winding (see Fig. 26, page 85), the coils being 

 generally of the same shape; but instead of tappings being taken 

 to a commutator, the coils are connected together in the proper 

 order, the phase windings being kept separate until finally con- 

 nected star or mesh as may be decided. With this style of 

 winding, the number of conductors per slot must be a multiple 

 of two. All coils are of the same size and shape, which is an 

 advantage; but on the other hand, the end connections are rather 

 close together, and there must also be substantial insulation be- 

 tween the two coil-sides in each slot. This type of winding is, 

 therefore, not very suitable for high pressures. One great ad- 

 vantage of the double-layer winding is that it lends itself readily 



1 MILES WALKER: "Specification and Design of Dynamo-electric Ma- 

 chines," LONGMANS & Co. 



255 



