# commutator

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## commutator,

device used in an electric generatorgenerator,
in electricity, machine used to change mechanical energy into electrical energy. It operates on the principle of electromagnetic induction, discovered (1831) by Michael Faraday.
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 motorsmotor, electric,
machine that converts electrical energy into mechanical energy. When an electric current is passed through a wire loop that is in a magnetic field, the loop will rotate and the rotating motion is transmitted to a shaft, providing useful mechanical work.
to switch currents in order to maintain magnetic polarities necessary to keep the shafts of the motors turning.

## 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

## 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.

## 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
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