commutation

n.

1. A substitution, exchange, or interchange.
2. 1. The substitution of one kind of payment for another.
   2. The payment substituted.
3. The travel of a commuter.
4. Electricity.
   1. Conversion of alternating to unidirectional current.
   2. Reversal of current direction.
5. Law. Reduction of a penalty to a less severe one.

[Middle English commutacioun, from Latin commūtātiō, commūtātiōn-, from commūtātus, past participle of commūtāre, to alter, exchange. See commute.]

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 also 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. See also Commutator.

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 also 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 also Converter; Semiconductor rectifier.

Three-phase converter.

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In Life Insurance the exchange of a series of installment payments, as the result of anInstallment Settlement for a Lump Sum Distribution.

noun

The act of exchanging or substituting: change, exchange, interchange, shift, substitution, switch, trade, transposition. Informal swap. See change/persist, substitute.

Commutation was the change from meeting feudal obligations in labour or in kind to cash payments. It had obvious advantages for the lord, since serf labour was often grudging and unenthusiastic, while the serf knew more precisely what his obligations were and could plan his time. A process which began in the 12th cent. accelerated in the 14th, and was almost completed by the 16th cent.

This entry contains information applicable to United States law only.

Modification, exchange, or substitution.

Commutation is the replacement of a greater amount by something lesser. To commute periodic payments means to substitute a single payment for a number of payments, or to come to a "lump sum" settlement.

In criminal law, commutation is the substitution of a lesser punishment for a greater one. Contrasted with clemency, which is an act of grace eliminating a sentence or punishment, commutation is the modification or reduction of a punishment.

The change from consecutive prison sentences to concurrent sentences is a commutation of punishment.

IN BRIEF: Reduction of a prison sentence.

The judge's commutation reduced the prisoner's sentence to five years.

Dansk (Danish)
n. - udveksling, strafnedsættelse, kommutation, ændring af strømretning

Nederlands (Dutch)
strafvermindering, afkoopsom, stroomwisseling

Français (French)
n. - (Fin) convertissement, (Jur, Ling) commutation, (US) trajet journalier

Deutsch (German)
n. - Umwandlung

Ελληνική (Greek)
n. - αντικατάσταση, υποκατάσταση, μετατροπή, μεταλλαγή, (ηλεκτρ.) μετατροπή εναλλασσόμενου ρεύματος σε συνεχές, (γραμμ.) αντιμετάθεση

Italiano (Italian)
commutazione

Português (Portuguese)
n. - comutação (f)

Русский (Russian)
замена, езда на и от работы

Español (Spanish)
n. - conmutación, cambio de dirección de la corriente

Svenska (Swedish)
n. - utbyte, ersättning, omändring, förvandling, kommutering (elektr.), pendling (trafik.)

中文（简体）(Chinese (Simplified))
交换, 减刑, 变换, 整流

中文（繁體）(Chinese (Traditional))
n. - 交換, 減刑, 變換, 整流

한국어 (Korean)
n. - 교환, 감면, 통근

日本語 (Japanese)
n. - 交換, 整流, 減刑, 二点間の反復往復, 通勤, 振替

العربيه (Arabic)
‏(الاسم) تخفيف حكم, استبدال طريقه دفع بأخرى‏

עברית (Hebrew)
n. - ‮המרה, חליפין, המתקה, המרת עונש, נסיעה בקביעות, יוממות‬

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