[Illustration: FIGS. 372 and 373.--_Barrel_ and _evolute_ windings; end views showing placement of coils. When all the coils are wound on the former, the placing of them on the armature is a simple matter. After insulating the slots, the winder begins at any convenient slot, and inserts the coils as shown. Before he can fill all the slots, some of the first coils must be raised and the last ones inserted underneath. There is not much difference between barrel and evolute winding and one style may be used at one end of the armature and the other at the =opposite end=.]
=Ques. How are the inductors arranged in evolute winding?=
Ans. In fig. 373, it will be seen that the ends of the evolute connectors lie in two planes, hence the inductors must project to different distances beyond the core. Accordingly, one long and one short bar may be conveniently placed in each slot, side by side. In large machines, especially where the teeth are wide, the connectors may be straight as in fig, 370. Evolute connectors may be used for either lap or wave windings.
[Illustration: FIG. 374.--Siemens' bar armature; end view. Each inductor in the form of a bar is connected to the next by means of two evolute spiral copper strips, one bending inwardly, the other outwardly, their junction being in some cases secured to a block of wood upon the shaft. Their outer ends are attached to the bars by rivets or silver solder.]
=Barrel Winding.=--This is a form of drum winding _in which the inductors are arranged in two layers and carried out obliquely on an extension of the cylindrical surface of the drum to meet and connect with radial risers_.
[Illustration: FIGS. 375 and 376.--Single layer and double layer barrel winding. Barrel winding is a method of arranging the ends of armature coils as they pass from one pole to the next, in which, instead of using _involute_ or _butterfly_ connections, V-shaped end connections are used which lie on a cylindrical surface, which is a continuation of the armature surface. The coil _ends_ must of necessity be arranged in two layers, but the method may be used for either one or two coils per slot, the difference in arrangement for these is here illustrated.]
Barrel winding has been very widely adopted. Although it involves an increased length of armature, this gives additional cooling surface and provides for good ventilation.