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.
In barrel winding, 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 two cases being shown in figs. 375 and 376. In the single layer barrel winding, [fig. 375], each slot is occupied by but one side of one coil. In the double layer barrel winding, [fig. 376], the opposite sides of two separate coils occupy space in the same slot. The coils, on emerging from the slots bend in opposite directions, and if one side of a coil occupy the bottom portion of a slot, its other side usually occupies the top portion of a slot distant from the first slot by the polar pitch.
Fig. 377.—Westinghouse barrel wound armature. The coils are former wound from copper strap and are interchangeable. In the larger size machine they are of the single type. The illustration shows plainly the characteristic feature of barrel winding, namely the oblique end connectors carried out on the extended drum.
Bastard Winding.—In this type of winding, the end connectors project from the inductors in straight lines parallel to the shaft and then are bent inward. It has the effect of being somewhat shorter than the barrel winding. In order to secure better ventilation, it is usual to combine a bastard winding at the rear end of the armature with a barrel winding at the commutator end. This class of winding is used only with bar armatures.
Fig. 378.—Rear end of Westinghouse wave-barrel wound armature; view showing ventilation.
Former Winding.—This relates to a method of winding coils, and not to any particular type; that is, mechanical winding as distinguished from hand winding. While hand winding is necessary for ring armatures, a drum armature is wound better and more easily by the aid of machinery.
Ques. What is a "former" coil?
Ans. A former coil, as its name suggests, is one that is wound complete upon a former before being placed upon the armature.