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

Ques. What is the period of commutation?

Ans. The time required for commutation, or the angle through which the armature must turn to commute the current in one coil.

Ques. Upon what does the period of commutation depend?

Ans. Upon the width of the brushes as shown in [fig. 300].

This fixes the angle through which the armature must revolve to commute the current in one coil. This angle is formed, as shown in the figure, by two intersecting planes, M and S, which pass through the axis of the armature and the two edges of the brush. Commutation then, begins at M and ends at S.

Ques. What is the position of the commutating plane with respect to M and S, in [fig. 300]?

Ans. It bisects the angle formed by the planes M and S.

Fig. 300.—Armature with one brush in position to illustrate the period of commutation and commutating plane. The latter is called "commutating line" by some writers. The period of commutation depends on the thickness of the brush end in contact with the commutator. Careful distinction should be made between commutating plane, neutral plane, and normal neutral plane as defined elsewhere.

Ques. What is the commutating plane?