Hawkins Electrical Guide v. 02 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

Figs. 356 to 359.—Various forms of armature teeth; fig. 356 inclined type forming a slot with parallel sides; figs. 357 and 358 projecting type which provides a support for the retaining wedges; fig. 359 enclosed type which forms "tunnels" for the inductors.

Advantages and Defects of Slotted Armatures.—The slotted armature, sometimes called the Pacinotti armature, after its inventor, has the following advantages over the smooth type:

1. The inductors are held more firmly in place to resist stresses due to electromagnetic drag and centrifugal force;

2. The inductors are protected by the teeth against mechanical injury;

3. Less reluctance of the air gap;

4. The intermittent induction due to the presence of the teeth prevents the formation of eddy currents.

5. When the teeth are saturated they oppose the shifting of the lines due to armature reaction.

Figs. 360 and 361.—Projecting and notched teeth; cross sections showing inductors and retaining wedges in place.