direct current

direct current,

abbr. DC, a movement of electric charge across an arbitrarily defined surface in one direction only. See electricityelectricity,
class of phenomena arising from the existence of charge. The basic unit of charge is that on the proton or electron—the proton's charge is designated as positive while the electron's is negative.
..... Click the link for more information. ; 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.
..... Click the link for more information. .

Direct Current

an electric current whose magnitude and direction do not change with time. It arises under the action of a direct voltage and can exist only in a closed circuit. In a nonbranching circuit the magnitude of a direct current is the same for all cross sections of the circuit. The principal laws governing direct currents are Ohm’s law, which gives the relationship between voltage and current, and Joule’s law, which defines the quantity of heat produced by a current flowing through a conductor. Calculations of networks of conductors carrying a direct current are made with the aid of Kirchhoff’s laws.

In engineering, equipment in which the current is unidirectional is regarded as DC equipment even if the magnitude of the current varies.

Rotating-machine generators are high-power sources of direct current. Direct current can also be obtained by the rectification of alternating current. Low-power sources of direct current include galvanic cells, thermocouples, and photoelectric cells; groups of such cells are called batteries—for example, solar batteries. Rotating electric machines are also used as low-power sources. Magnetohydrodynamic generators are a new, high-efficiency source of direct current. Storage batteries, which can be recharged, are a secondary source of direct current.

Low-voltage direct current finds application in many branches of industry. In electrometallurgy, for example, it is used in such processes as the melting and electrolysis of ores, primarily aluminum ores. Direct current is used in transport-vehicle traction motors and in electric drives requiring variable-speed motors with a large overload capacity where the speed can be smoothly and economically regulated within wide limits. Communication, automation, signaling, and remote-control systems often run on DC power. The use of direct current for the transmission of electric power over distances in excess of 1,000 km shows promise. Work is being done on DC power transmission with practically no losses over superconducting lines.

REFERENCES

Polivanov, K. M. Lineinye elektricheskie tsepi s sosredotochennymi postoiannymi. Moscow, 1972. (Teoreticheskie osnovy elektrotekhniki, vol. 1.)
Kasatkin, A. S. Elektrotekhnika, 3rd ed. Moscow, 1973.

A. S. KASATKIN

direct current

[də¦rekt ′kə·rənt] (electricity) Electric current which flows in one direction only, as opposed to alternating current. Abbreviated dc.

Direct current

Electric current which flows in one direction only through a circuit or equipment. The associated direct voltages, in contrast to alternating voltages, are of unchanging polarity. Direct current corresponds to a drift or displacement of electric charge in one unvarying direction around the closed loop or loops of an electric circuit. Direct currents and voltages may be of constant magnitude or may vary with time.

Direct current is used extensively to power adjustable-speed motor drives in industry and in transportation. Very large amounts of power are used in electrochemical processes for the refining and plating of metals and for the production of numerous basic chemicals.

Direct current ordinarily is not widely distributed for general use by electric utility customers. Instead, direct-current (dc) power is obtained at the site where it is needed by the rectification of commercially available alternating-current (ac) power to dc power. See Direct-current transmission, Electric power systems

direct current

In an electric circuit, a current that flows in one direction only. Also see alternating current.

direct current

a continuous electric current that flows in one direction only, without substantial variation in magnitude

direct current

current

[kur´ent] 1. something that flows.2. specifically, electricity transmitted through a circuit.alternating current a current that periodically flows in opposite directions; its amplitude fluctuates as a sine wave.convection current a current caused by movement by convection of warmer fluid into an area of cooler fluid.direct current a current that flows in one direction only; when modeled as a wave, its amplitude is constant. When used medically it is called galvanic current. This current has distinct and important polarity and marked secondary chemical effects.galvanic current a steady current" >direct current.current of injury an electric current that flows between injured myocardium and normal myocardium, because such cells have a reduced potential" >membrane potential; it may be either diastolic or systolic.current of injury, diastolic the current that flows from injured to noninjured tissue during electrical diastole.current of injury, systolic the current that flows from healthy tissue to injured tissue during electrical systole.inwardly rectifying current current that rectifies so that it passes more easily towards the interior of a cell.leakage current the electrical current that exists in the parts or metal case of electrical equipment.outwardly rectifying current current that rectifies so that it passes more easily towards the exterior of a cell.potassium rectifying c's transmembrane currents that rectify inwardly or outwardly to make adjustments in cellular functions; they are mainly responsible for the repolarization phase of the action potential. There are at least six mechanisms by which potassium ions move across cardiac cell membranes in the role of rectifier.

di·rect cur·rent (DC),

a current that flows only in one direction, for example, that is derived from a battery; sometimes referred to as galvanic current.
See also: galvanism.

direct current

A continuous electromagnetic current that flows in only one direction.

di·rect cur·rent

(DC) (di-rekt kŭrĕnt) An electrical current that flows only in one direction; e.g., that derived from a battery; sometimes referred to as galvanic current.

di·rect cur·rent

(DC) (di-rekt kŭrĕnt) An electrical current that flows only in one direction; also referred to as galvanic current.

direct current

direct current

direct current

direct′ cur′rent

di·rect current

direct current

direct current

direct current,

Direct Current

REFERENCES

direct current

Direct current

direct current

direct current

direct current

current

di·rect cur·rent (DC),

direct current

di·rect cur·rent

di·rect cur·rent

direct current

Synonyms for direct current

noun an electric current that flows in one direction steadily

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