Hawkins Electrical Guide v. 08 (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 should be the limit of the commutator speed?

Ans. The commutator speed, or tangential speed at the brushes should not exceed 3,000 feet per minute.

Fig. 2,869.—Wiring diagram for General Electric synchronous converter with series booster as illustrated in [fig. 2,868].

Ques. Name another limitation necessary for satisfactory operation.

Ans. The pressure between adjacent commutator bars should not exceed eight or ten volts.

If the commutator bars be made narrow in order to obtain the necessary number for the desired voltage with the minimum circumference and therefore low commutator speed, the brushes employed to collect the current are liable to require excessive width in order to provide the proper cross section and yet not cover more than two bars at once.

Ques. How can the commutator speed be kept within reasonable limits, other than by reducing the width of the commutator bars?

Ans. By using alternating current of comparatively low frequency.