Commutation


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commutation

[‚käm·yə′tā·shən]
(communications)
The sampling of various quantities in a repetitive manner for transmission over a single channel in telemetering.
(electronics)
The transfer of current from one channel to another in a gas tube.
(electromagnetism)
The process of current reversal in the armature windings of a direct-current rotating machine to provide direct current at the brushes.

Commutation

 

(of electric circuits), various ways of switching the contacts of wires, cables, machines, transformers, apparatus, and instruments; used in installations that generate, distribute, and consume electric power. Changes in the direction of current flow (polarity changes) are also called commutation. Commutation is usually accompanied by transient processes that arise because of rapid redistribution of currents and voltages through the branches of an electric network.


Commutation

 

the replacement of the serfs’ labor obligations and payments in kind by a money rent; the process took place as a result of and in proportion to the penetration of commodity-money relations into the feudal village. The term “commutation” is usually used in the context of agrarian relations in Western European countries.

Commutation

The process of transferring current from one connection to another within an electric circuit. Depending on the application, commutation is achieved either by mechanical switching or by electronic switching.

Commutation was conceived over a century ago through the invention of the direct-current (dc) motor. When direct current is supplied to a winding on a rotor that is subjected to a stationary magnetic field, it experiences a rotational force and resulting output torque. As the stator north and south poles are reversed relative to the rotating winding, the rotor current is reversed by a commutator in order to maintain the unidirectional torque required for continuous motor action. See Direct-current motor, Windings in electric machinery

The principle is illustrated in Fig. 1. In its simplest form, a single rotor winding is connected between two segments of a cylindrical copper commutator which is mounted axially on the rotor. Connection to the external dc supply is through sliding carbon contacts (brushes). The segments have small insulated gaps at A and B. As A and B pass the brushes, the current in the rotor winding reverses. In the short interval where the brushes short-circuit the segments, the rotor current decays before building up in the reverse direction. The angular position of the brushes is selected to reverse the current at the appropriate rotor position.

Basic commutator for a dc motorenlarge picture
Basic commutator for a dc motor

The same principle of commutation applies to the ac commutator motor and universal ac/dc motor, which are common in variable-speed kitchen appliances and electric hand tools. See Alternating-current motor, Universal motor

The equivalent of mechanical commutation occurs in solid-state converter circuits such as those used for rectifying ac to dc or inverting dc to ac. Figure 2 shows a three-phase converter widely used in industry. For simplicity, the ac supply network is represented by equivalent phase voltages in series with the effective supply inductance. (Often this inductance is mainly the inductance per phase of a converter transformer that interfaces the converter and the three-phase supply.) Usually, supply resistance is relatively low and plays a negligible role in the converter action. As shown, thyristors 1 and 2 are conducting the dc current from phase a to phase c. A smooth dc current does not produce a voltage across the inductance L in each phase. In the cyclic conduction sequence, the dc current is commutated from phase a and thyristor 1 to phase b and thyristor 3. To achieve this, thyristor 3 is gated in a region of the ac waveform when its forward voltage is positive. Turning it on applies a reverse voltage to thyristor 1 (phase b being more positive than phase a), which ceases conduction to complete the commutation of the dc current. This is repeated in sequence for the other thyristors in each ac cycle. See Converter, Semiconductor rectifier

Three-phase converterenlarge picture
Three-phase converter
References in periodicals archive ?
The commutation payment from Maiden Bermuda to AII is the sum of the net ceded reserves in the amount of $330.7 million with respect to the Commuted Business as of December 31, 2018, less payments in the amount of $17.9 million made by the Maiden Bermuda with respect to the Commuted Business from January 1, 2019 through the effective date of the Commutation.
Commutation is a common legal process used nationwide as well as in Oklahoma to correct excessive, unjust sentences.
In the first case, Kirchhoff laws are compiled for the electrical circuit as a whole (before and after commutation), and the difference of these circuits is taken into account for by unitary discontinuous functions.
In this paper, the relationship between current, back-EMF harmonic, and torque harmonic for three-phase BLDC motor with advanced commutation control is presented.
He ultimately granted 1,715 commutations, more than any other president in U.S.
Executive clemency is a power of the President to pardon any prisoner, provided for under Article VII, Section 19 of the Constitution and pertains to reprieve, absolute or conditional pardon with or without parole conditions and commutation of sentence.
In Sections 4 and 5, we introduce spacetime noncommutativity into this framework and find all possible deformed Poincare symmetries which preserve the nontrivial commutation relations among the particle's coordinates.
* A FlexCount interpolator delivering incremental (ABZ) and latency-free commutation (UVW) signals.
The courts have recognized the president's ability to do all of the following grant a full pardon, which forgives the offense and can restore lost civil rights, such as the ability to vote or own a firearm; reduce an offender's sentence via a commutation; or issue a reprieve/respite that merely puts off full punishment until a later date (Crouch 2009, 20).
Hamilton, 49, was the first commutation to go before the eight-member elected council since 1997.
In the early days, the transaction most associated with runoff was the commutation. A commutation is an early termination of a reinsurance contract in return for a mutually agreed upon consideration.
Pointe Claire, Canada, November 07, 2014 --(PR.com)-- Future Electronics, a global leading distributor of electronic components, promotes rugged, accurate commutation encoders from CUI Inc which drastically reduce assembly time on BLDC motors.