commutator

commutator

commutator, device used in an electric generator to convert the alternating current produced in the generator into direct current before the current is sent into an external circuit; it is basically a rotary switching device synchronized with the frequency of the alternating current. Commutators are also used in electric motors to switch currents in order to maintain magnetic polarities necessary to keep the shafts of the motors turning.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Commutator

 

in electrical machinery, a mechanical frequency converter that is attached to the rotor of a machine. A commutator consists of a series of trapezoidal copper segments that are insulated from each other and from the body of the rotor. Each segment is connected to one or more turns of the armature winding. The armature winding is connected to an outside power source by carbon contact brushes. When the armature rotates, the brushes touch each of the commutator segments in turn.

The most common type of commutator is the cylindrical type, with brushes contacting the outer surface. Disk commutators, whose work (contact) surface is perpendicular to the axis of rotation of the rotor, are less frequently used. The commutator segments in low-powered machines (up to 10 kilowatts [kW]) are pressed into plastics; in machines with power ratings of 15–25 kW or more and a speed of rotation of 3,000 rpm or higher, the segments are fastened by steel tread rings. In large electric machines double or triple commutators are sometimes used to reduce mechanical stresses. The disadvantages of commutators are high consumption of electrical-grade copper, sparking, and wear caused by brush friction.

REFERENCES

Petrov, G. N. Elektricheskie mashiny, 2nd ed., part 3. Moscow, 1968.
Vazhnov, A. I. Elektricheskie mashiny. Leningrad, 1969.

V. V. BOGOMAZOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

commutator

[′käm·yə‚tād·ər]

(electromagnetism)

That part of a direct-current motor or generator which serves the dual function, in combination with brushes, of providing an electrical connection between the rotating armature winding and the stationary terminals, and of permitting reversal of the current in the armature windings.

(mathematics)

The commutator of a and b is the element c of a group such that bac = ab.

(quantum mechanics)

The commutator of a and b is [a,b ] = ab-ba.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

commutator

1. a device used to reverse the direction of flow of an electric current

2. the segmented metal cylinder or disc mounted on the armature shaft of an electric motor, generator, etc., used to make electrical contact with the rotating coils and ensure unidirectional current flow

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005