APPENDIX C. 



ARMATURE WINDINGS. 



39, Classification of armature windings. Armatures may be 

 classified with respect to the position and arrangement of the 

 windings on the armature core, as (i) ring armatures, (2) drum 

 armatures, and (3) disk armatures. These names were origi- 

 nally applied in view of differences in the external appearance of 

 the armatures, but the distinction here intended refers to essential 

 differences of the windings of wire on the armature core. Thus, 

 in many modern dynamos of large size the armature has a 

 diameter many times as great as its length parallel to the shaft, 

 and the armature core, and to a certain extent the finished arma- 

 ture, has the appearance of a ring ; but whether the armature is 

 to be classed as a ring armature or a drum armature is determined 

 solely by the arrangement of the windings. 



1. A ring armature is one in which a ring-shaped core of 

 laminated iron has the windings placed upon it in the form of a 

 helix as shown in Fig. 17, Chapter II., and in Fig. 41, Chapter 

 II. The helical form of the winding in Fig. 41 does not show 

 clearly for the reason that the windings are grouped together in 

 coils, but these coils are connected to each other so as to con- 

 stitute a continuous helix. A ring armature may be used in 

 connection with a two-pole field magnet as shown in Fig. 17, or 

 with a multipolar field magnet as shown in Fig. 22. The simple 

 ring winding is sometimes called the helical* winding. 



2. A drum armature, as used for a bipolar field magnet, is 

 one in which a cylindrical core of laminated iron has the wire 

 wound lengthwise (parallel to the shaft) on the outside surface of 

 the core, and diametrically (nearly) across the ends. In a drum 



*The term " spiral," frequently used to designate this type of winding, is a mis- 

 nomer. 



418 



